Patent Application
20140220713
Wafer-scale arrays of imaging systems within the prior art offer the benefits of vertical (i.e., along the optical axis) integration capability and parallel assembly.
Many methods of fabrication may be employed for producing arrayed optical elements, including lithographic methods, replication methods, molding methods and embossing methods. Lithographic methods include, for example, the use of a patterned, electromagnetic energy blocking mask coupled with a photosensitive resist. Following exposure to electromagnetic energy, the unmasked regions of resist (or masked regions when a negative tone resist has been used) are washed away by chemical dissolution using a developer solution. The remaining resist structure may be left as is, transferred into the underlying common base by an etch process, or thermally melted (i.e., “reflown”) at temperatures up to 200° C. to allow the structure to form into a smooth, continuous, spherical and/or aspheric surface. The remaining resist, either before or after reflow, may be used as an etch mask for defining features that may be etched into the underlying common base. Furthermore, careful control of the etch selectivity (i.e., the ratio of the resist etch rate to the common base etch rate) may allow additional flexibility in the control of the surface form of the features, such as lenses or prisms.
Once created, wafer-scale arrays 5000 of optical elements 5002 may be aligned and bonded to additional arrays to form arrayed imaging systems 5006 as shown in
A key disadvantage of current wafer-scale imaging system integration is a lack of precision associated with parallel assembly. For example, vertical offset in optical elements due to thickness non-uniformities within a common base and systematic misalignment of optical elements relative to an optical axis may degrade the integrity of one or more imaging systems throughout the array. Also, prior art wafer-scale arrays of optical elements are generally created by the use of a partial fabrication master, including features for defining only one or a few optical elements in the array at a time, to “stamp out” or “mold” a few optical elements on the common base at a time; consequently, the fabrication precision of prior art wafer-scale arrays of optical elements is limited by the precision of the mechanical system that moves the partial fabrication master in relation to the common base. That is, while current technologies may enable alignment at mechanical tolerances of several microns, they do not provide optical tolerance (i.e., on the order of a wavelength of electromagnetic energy of interest) alignment accuracy required for precise imaging system manufacture. Another key disadvantage of current wafer-scale imaging system integration is that the optical materials used in prior art systems cannot withstand the reflow process temperatures.
Detectors such as, but not limited to, complementary metal-oxide-semiconductor (CMOS) detectors, may benefit from the use of lenslet arrays for increasing the fill factor and detection sensitivity of each detector pixel in the detector. Moreover, detectors may require additional filters for a variety of uses such as, for example, detecting different colors and blocking infrared electromagnetic energy. The aforementioned tasks require the addition of optical elements (e.g., lenslets and filters) to existing detectors, which is a disadvantage in using current technology.
Detectors are generally fabricated using a lithographic process and therefore include materials that are compatible with the lithographic process. For example, CMOS detectors are currently fabricated using CMOS processes and compatible materials such as crystalline silicon, silicon nitride and silicon dioxide. However, optical elements using prior art technology that are added to the detector are normally fabricated separately from the detector, possibly in different facilities, and may use materials that are not necessarily compatible with certain CMOS fabrication processes (e.g., while organic dyes may be used for color filters and organic polymers for lenslets, such materials are generally not considered to be compatible with CMOS fabrication processes). These extra fabrication and handling steps may consequently add to the overall cost and reduce the overall yield of the detector fabrication. Systems, methods, processes and applications disclosed herein overcome disadvantages associated with current wafer-scale imaging system integration and detector design and fabrication.
In an embodiment, arrayed imaging systems are provided. An array of detectors is formed with a common base. The arrayed imaging systems have a first array of layered optical elements, each one of the layered optical elements being optically connected with a detector in the array of detectors.
In an embodiment, a method forms a plurality of imaging systems, each of the plurality of imaging systems having a detector, including: forming arrayed imaging systems with a common base by forming, for each of the plurality of imaging systems, at least one set of layered optical elements optically connected with its detector, the step of forming including sequential application of one or more fabrication masters.
In an embodiment, a method forms arrayed imaging systems with a common base and at least one detector, including: forming an array of layered optical elements, at least one of the layered optical elements being optically connected with the detector, the step of forming including sequentially applying one or more fabrication masters such that the arrayed imaging systems are separable into a plurality of imaging systems.
In an embodiment, a method forms arrayed imaging optics with a common base, including forming an array of a plurality of layered optical elements by sequentially applying one or more fabrication masters aligned to the common base.
In an embodiment, a method is provided for manufacturing arrayed imaging systems including at least an optics subsystem and an image processor subsystem, both connected with a detector subsystem, by: (a) generating an arrayed imaging systems design, including an optics subsystem design, a detector subsystem design and an image processor subsystem design; (b) testing at least one of the subsystem designs to determine if the at least one of the subsystem designs conforms within predefined parameters; if the at least one of the subsystem designs does not conform within the predefined parameters, then: (c) modifying the arrayed imaging systems design, using a set of potential parameter modifications; (d) repeating (b) and (c) until the at least one of the subsystem designs conforms within the predefined parameters to yield a modified arrayed imaging systems design; (e) fabricating the optical, detector and image processor subsystems in accordance with the modified arrayed imaging systems design; and (f) assembling the arrayed imaging systems from the subsystems fabricated in (e).
In an embodiment, a software product has instructions stored on computer-readable media, wherein the instructions, when executed by a computer, perform steps for generating arrayed imaging systems design, including: (a) instructions for generating an arrayed imaging systems design, including an optics subsystem design, a detector subsystem design and an image processor subsystem design; (b) instructions for testing at least one of the optical, detector and image processor subsystem designs to determine if the at least one of the subsystem designs conforms within predefined parameters; if the at least one of the subsystem designs does not conform within the predefined parameters, then: (c) instructions for modifying the arrayed imaging systems design, using a set of parameter modifications; and (d) instructions for repeating (b) and (c) until the at least one of the subsystem designs conforms within the predefined parameters to yield the arrayed imaging systems design.
In an embodiment, a multi-index optical element has a monolithic optical material divided into a plurality of volumetric regions, each of the plurality of volumetric regions having a defined refractive index, at least two of the volumetric regions having different refractive indices, the plurality of volumetric regions being configured to predeterministically modify phase of electromagnetic energy transmitted through the monolithic optical material.
In an embodiment, an imaging system includes: optics for forming an optical image, the optics including a multi-index optical element having a plurality of volumetric regions, each of the plurality of volumetric regions having a defined refractive index, at least two of the volumetric regions having different refractive indices, the plurality of volumetric regions being configured to predeterministically modify phase of electromagnetic energy transmitted therethrough; a detector for converting the optical image into electronic data; and a processor for processing the electronic data to generate output.
In an embodiment, a method manufactures a multi-index optical element, by: forming a plurality of volumetric regions in a monolithic optical material such that: (i) each of the plurality of volumetric regions has a defined refractive index, and (ii) at least two of the volumetric regions have different refractive indices, wherein the plurality of volumetric regions predeterministically modify phase of electromagnetic energy transmitted therethrough.
In an embodiment, a method forms an image by: predeterministically modifying phase of electromagnetic energy that contribute to the optical image by transmitting the electromagnetic energy through a monolithic optical material having a plurality of volumetric regions, each of the plurality of volumetric regions having a defined refractive index and at least two of the volumetric regions having different refractive indices; converting the optical image into electronic data; and processing the electronic data to form the image.
In an embodiment, arrayed imaging systems have: an array of detectors formed with a common base; and an array of layered optical elements, each one of the layered optical elements being optically connected with at least one of the detectors in the array of detectors so as to form arrayed imaging systems, each imaging system including at least one layered optical element optically connected with at least one detector in the array of detectors.
In an embodiment, a method for forming a plurality of imaging systems is provided, including: forming a first array of optical elements, each one of the optical elements being optically connected with at least one detector in an array of detectors having a common base; forming a second array of optical elements optically connected with the first array of optical elements so as to collectively form an array of layered optical elements, each one of the layered optical elements being optically connected with one of the detectors in the array of detectors; and separating the array of detectors and the array of layered optical elements into the plurality of imaging systems, each one of the plurality of imaging systems including at least one layered optical element optically connected with at least one detector, wherein forming the first array of optical elements includes configuring a planar interface between the first array of optical elements and the array of detectors.
In an embodiment, arrayed imaging systems include: an array of detectors formed on a common base; a plurality of arrays of optical elements; and a plurality of bulk material layers separating the plurality of arrays of optical elements, the plurality of arrays of optical elements and the plurality of bulk material layers cooperating to form an array of optics, each one of the optics being optically connected with at least one of the detectors of the array of detectors so as to form arrayed imaging systems, each of the imaging systems including at least one optics optically connected with at least one detector in the array of detectors, each one of the plurality of bulk material layers defining a distance between adjacent arrays of optical elements.
In an embodiment, a method for machining an array of templates for optical elements is provided, by: fabricating the array of templates using at least one of a slow tool servo approach, a fast tool servo approach, a multi-axis milling approach and a multi-axis grinding approach.
In an embodiment, an improvement to a method for manufacturing a fabrication master including an array of templates for optical elements defined thereon is provided, by: directly fabricating the array of templates.
In an embodiment, a method for manufacturing an array of optical elements is provided, by: directly fabricating the array of optical elements using at least a selected one of a slow tool servo approach, a fast tool servo approach, a multi-axis milling approach and a multi-axis grinding approach.
In an embodiment, an improvement to a method for manufacturing an array of optical elements is provided, by: forming the array of optical elements by direct fabrication.
In an embodiment, a method is provided for manufacturing a fabrication master used in forming a plurality of optical elements therewith, including: determining a first surface that includes features for forming the plurality of optical elements; determining a second surface as a function of (a) the first surface and (b) material characteristics of the fabrication master; and performing a fabrication routine based on the second surface so as to form the first surface on the fabrication master.
In an embodiment, a method is provided for fabricating a fabrication master for use in forming a plurality of optical elements, including: forming a plurality of first surface features on the fabrication master using a first tool; and forming a plurality of second surface features on the fabrication master using a second tool, the second surface features being different from the first surface features, wherein a combination of the first and second surface features is configured to form the plurality of optical elements.
In an embodiment, a method is provided for manufacturing a fabrication master for use in forming a plurality of optical elements, including: forming a plurality of first features on the fabrication master, each of the plurality of first features approximating second features that form one of the plurality of optical elements; and smoothing the plurality of first features to form the second features.
In an embodiment, a method is provided for manufacturing a fabrication master for use in forming a plurality of optical elements, by: defining the plurality of optical elements to include at least two distinct types of optical elements; and directly fabricating features configured to form the plurality of optical elements on a surface of the fabrication master.
In an embodiment, a method is provided for manufacturing a fabrication master that includes a plurality of features for forming optical elements therewith, including: defining the plurality of features as including at least one type of element having an aspheric surface; and directly fabricating the features on a surface of the fabrication master.
In an embodiment, a method is provided for manufacturing a fabrication master including a plurality of features for forming optical elements therewith, by: defining a first fabrication routine for forming a first portion of the features on a surface of the fabrication master; directly fabricating at least one of the features on the surface using the first fabrication routine; measuring a surface characteristic of the at least one of the features; defining a second fabrication routine for forming a second portion of the features on the surface of the fabrication master, wherein the second fabrication routine comprises the first fabrication routine adjusted in at least one aspect in accordance with the surface characteristic so measured; and directly fabricating at least one of the features on the surface using the second fabrication routine.
In an embodiment, an improvement is provided to a machine that manufactures a fabrication master for forming a plurality of optical elements therewith, the machine including a spindle for holding the fabrication master and a tool holder for holding a machine tool that fabricates features for forming the plurality of optical elements on a surface of the fabrication master, an improvement having: a metrology system configured to cooperate with the spindle and the tool holder for measuring a characteristic of the surface.
In an embodiment, a method is provided for manufacturing a fabrication master that forms a plurality of optical elements therewith, including: directly fabricating features for forming the plurality of optical elements on a surface of the fabrication master; and directly fabricating at least one alignment feature on the surface, the alignment feature being configured to cooperate with a corresponding alignment feature on a separate object to define a separation distance between the surface and the separate object.
In an embodiment, a method of manufacturing a fabrication master for forming an array of optical elements therewith is provided, by: directly fabricating on a surface of the substrate features for forming the array of optical elements; and directly fabricating on the surface at least one alignment feature, the alignment feature being configured to cooperate with a corresponding alignment feature on a separate object to indicate at least one of a translation, a rotation and a separation between the surface and the separate object.
In an embodiment, a method is provided for modifying a substrate to form a fabrication master for an array of optical elements using a multi-axis machine tool, by: mounting the substrate to a substrate holder; performing preparatory machining operations on the substrate; directly fabricating on a surface of the substrate features for forming the array of optical elements; and directly fabricating on the surface of the substrate at least one alignment feature; wherein the substrate remains mounted to the substrate holder during the performing and directly fabricating steps.
In an embodiment, a method is provided for fabricating an array of layered optical elements, including: using a first fabrication master to form a first layer of optical elements on a common base, the first fabrication master having a first master substrate including a negative of the first layer of optical elements formed thereon; using a second fabrication master to form a second layer of optical elements adjacent to the first layer of optical elements so as to form the array of layered optical elements on the common base, the second fabrication master having a second master substrate including a negative of the second layer of optical elements formed thereon.
In an embodiment, a fabrication master has: an arrangement for molding a moldable material into a predetermined shape that defines a plurality of optical elements; and an arrangement for aligning the molding arrangement in a predetermined orientation with respect to a common base when the fabrication master is used in combination with the common base, such that the molding arrangement may be aligned with the common base for repeatability and precision with less than two wavelengths of error.
In an embodiment, arrayed imaging systems include a common base having a first side and a second side remote from the first side, and a first plurality of optical elements constructed and arranged in alignment on the first side of the common base where the alignment error is less than two wavelengths.
In an embodiment, arrayed imaging systems include: a first common base, a first plurality of optical elements constructed and arranged in precise alignment on the first common base, a spacer having a first surface affixed to the first common base, the spacer presenting a second surface remote from the first surface, the spacer forming a plurality of holes therethrough aligned with the first plurality of optical elements, for transmitting electromagnetic energy therethrough, a second common base bonded to the second surface to define respective gaps aligned with the first plurality of optical elements, movable optics positioned in at least one of the gaps, and arrangement for moving the movable optics.
In an embodiment, a method is provided for the manufacture of an array of layered optical elements on a common base, by: (a) preparing the common base for deposition of the array of layered optical elements; (b) mounting the common base and a first fabrication master such that precision alignment of at least two wavelengths exists between the first fabrication master and the common base, (c) depositing a first moldable material between the first fabrication master and the common base, (d) shaping the first moldable material by aligning and engaging the first fabrication master and the common base, (e) curing the first moldable material to form a first layer of optical elements on the common base, (f) replacing the first fabrication master with a second fabrication master, (g) depositing a second moldable material between the second fabrication master and the first layer of optical elements, (h) shaping the second moldable material by aligning and engaging the second fabrication master and the common base, and (i) curing the second moldable material to form a second layer of optical elements on the common base.
In an embodiment, an improvement is provided to a method for fabricating a detector pixel formed by a set of processes, by: forming at least one optical element within the detector pixel using at least one of the set of processes, the optical element being configured for affecting electromagnetic energy over a range of wavelengths.
In an embodiment, an electromagnetic energy detection system has: a detector including a plurality of detector pixels; and an optical element integrally formed with at least one of the plurality of detector pixels, the optical element being configured for affecting electromagnetic energy over a range of wavelengths.
In an embodiment, an electromagnetic energy detection system detects electromagnetic energy over a range of wavelengths incident thereon, and includes: a detector including a plurality of detector pixels, each one of the detector pixels including at least one electromagnetic energy detection region; and at least one optical element buried within at least one of the plurality of detector pixels, to selectively redirect the electromagnetic energy over the range of wavelengths to the electromagnetic energy detection region of said at least one detector pixel.
In an embodiment, an improvement is provided in an electromagnetic energy detector, including: a structure integrally formed with the detector and including subwavelength features for redistributing electromagnetic energy incident thereon over a range of wavelengths.
In an embodiment, an improvement is provided to an electromagnetic energy detector, including: a thin film filter integrally formed with the detector to provide at least one of bandpass filtering, edge filtering, color filtering, high-pass filtering, low-pass filtering, anti-reflection, notch filtering and blocking filtering.
In an embodiment, an improvement is provided to a method for forming an electromagnetic energy detector by a set of processes, by: forming a thin film filter within the detector using at least one of the set of processes; and configuring the thin film filter for performing at least a selected one of bandpass filtering, edge filtering, color filtering, high-pass filtering, low-pass filtering, anti-reflection, notch filtering, blocking filtering and chief ray angle correction.
In an embodiment, an improvement is provided to an electromagnetic energy detector including at least one detector pixel with a photodetection region formed therein, including: a chief ray angle corrector integrally formed with the detector pixel at an entrance pupil of the detector pixel, to redistribute at least a portion of electromagnetic energy incident thereon toward the photodetection region.
In an embodiment, an electromagnetic energy detection system has: a plurality of detector pixels, and a thin film filter integrally formed with at least one of the detector pixels and configured for at least a selected one of bandpass filtering, edge filtering, color filtering, high-pass filtering, low-pass filtering, anti-reflection, notch filtering, blocking filtering and chief ray angle correction.
In an embodiment, an electromagnetic energy detection system has: a plurality of detector pixels, each one of the plurality of detector pixels including a photodetection region and a chief ray angle corrector integrally formed with the detector pixel at an entrance pupil of the detector pixel, the chief ray angle corrector being configured for directing at least a portion of electromagnetic energy incident thereon toward the photodetection region of the detector pixel.
In an embodiment, a method simultaneously generates at least first and second filter designs, each one of the first and second filter designs defining a plurality of thin film layers, by: a) defining a first set of requirements for the first filter design and a second set of requirements for the second filter design; b) optimizing at least a selected parameter characterizing the thin film layers in each one of the first and second filter designs in accordance with the first and second sets of requirements to generate a first unconstrained design for the first filter design and a second unconstrained design for the second filter design; c) pairing one of the thin film layers in the first filter design with one of the thin film layers in the second filter design to define a first set of paired layers, the layers that are not the first set of paired layers being non-paired layers; d) setting the selected parameter of the first set of paired layers to a first common value; and e) re-optimizing the selected parameter of the non-paired layers in the first and second filter designs to generate a first partially constrained design for the first filter design and a second partially constrained design for the second filter design, wherein the first and second partially constrained designs meet at least a portion of the first and second sets of requirements, respectively.
In an embodiment, an improvement is provided to a method for forming an electromagnetic energy detector including at least first and second detector pixels, including: integrally forming a first thin film filter with the first detector pixel and a second thin film filter with the second detector pixel, such that the first and second thin film filters share at least a common layer.
In an embodiment, an improvement is provided to an electromagnetic energy detector including at least first and second detector pixels, including: first and second thin film filters integrally formed with the first and second detector pixels, respectively, wherein the first and second thin film filters are configured for modifying electromagnetic energy incident thereon, and wherein the first and second thin film filters share at least one layer in common.
In an embodiment, an improvement is provided to an electromagnetic energy detector including a plurality of detector pixels, including: an electromagnetic energy modifying element integrally formed with at least a selected one of the detector pixels, the electromagnetic energy modifying element being configured for directing at least a portion of electromagnetic energy incident thereon within the selected detector pixel, wherein the electromagnetic energy modifying element comprises a material compatible with processes used for forming the detector, and wherein the electromagnetic energy modifying element is configured to include at least one non-planar surface.
In an embodiment, an improvement is provided in a method for forming an electromagnetic energy detector by a set of processes, the electromagnetic energy detector including a plurality of detector pixels, including: integrally forming, with at least a selected one of the detector pixels and by at least one of the set of processes, at least one electromagnetic energy modifying element configured for directing at least a portion of electromagnetic energy incident thereon within the selected detector pixel, wherein integrally forming comprises: depositing a first layer; forming at least one relieved area in the first layer, the relieved area being characterized by substantially planar surfaces; depositing a first layer on top of the relieved area such that the first layer defines at least one non-planar feature; depositing a second layer on top of the first layer such that the second layer at least partially fills the non-planar feature; and planarizing the second layer so as to leave a portion of the second layer filling the non-planar features of the first layer, forming the electromagnetic energy modifying element In an embodiment, an improvement is provided in a method for forming an electromagnetic energy detector by a set of processes, the detector including a plurality of detector pixels, including: integrally forming, with at least one of the plurality of detector pixels and by at least one of the set of processes, an electromagnetic energy modifying element configured for directing at least a portion of electromagnetic energy incident thereon within the selected detector pixel, wherein integrally forming comprises depositing a first layer, forming at least one protrusion in the first layer, the protrusion being characterized by substantially planar surfaces, and depositing a first layer on top of the planar feature such that the first layer defines at least one non-planar feature as the electromagnetic energy modifying element.
In an embodiment, a method is provided for designing an electromagnetic energy detector, by: specifying a plurality of input parameters; and generating a geometry of subwavelength structures, based on the plurality of input parameters, for directing the input electromagnetic energy within the detector.
In an embodiment, a method fabricates arrayed imaging systems, by: forming an array of layered optical elements, each one of the layered optical elements being optically connected with at least one detector in an array of detectors formed with a common base so as to form arrayed imaging systems, wherein forming the array of layered optical elements includes: using a first fabrication master, forming a first layer of optical elements on the array of detectors, the first fabrication master having a first master substrate including a negative of the first layer of optical elements formed thereon, using a second fabrication master, forming a second layer of optical elements adjacent to the first layer of optical elements, the second fabrication master including a second master substrate including a negative of the second layer of optical elements formed thereon.
In an embodiment, arrayed imaging optics include: an array of layered optical elements, each one of the layered optical elements being optically connected with a detector in the array of detectors, wherein the array of layered optical elements is formed at least in part by sequential application of one or more fabrication masters including features for defining the array of layered optical elements thereon.
In an embodiment, a method is provided for fabricating an array of layered optical elements, including: providing a first fabrication master having a first master substrate including a negative of a first layer of optical elements formed thereon; using the first fabrication master, forming the first layer of optical elements on a common base; providing a second fabrication master having a second master substrate including a negative of a second layer of optical elements formed thereon; using the second fabrication master, forming the second layer of optical elements adjacent to the first layer of optical elements so as to form the array of layered optical elements on the common base; wherein providing the first fabrication master comprises directly fabricating the negative of the first layer of optical elements on the first master substrate.
In an embodiment, arrayed imaging systems include: a common base; an array of detectors having detector pixels formed on the common base by a set of processes, each one of the detector pixels including a photosensitive region; and an array of optics optically connected with the photosensitive region of a corresponding one of the detector pixels thereby forming the arrayed imaging systems, wherein at least one of the detector pixels includes at least one optical feature integrated therein and formed using at least one of the set of processes, to affect electromagnetic energy incident on the detector over a range of wavelengths.
In an embodiment, arrayed imaging systems include: a common base; an array of detectors having detector pixels formed on the common base, each one of the detector pixels including a photosensitive region; and an array of optics optically connected with the photosensitive region of a corresponding one of the detector pixels, thereby forming the arrayed imaging systems.
In an embodiment, arrayed imaging systems have: an array of detectors formed on a common base; and an array of optics, each one of the optics being optically connected with at least one of the detectors in the array of detectors so as to form arrayed imaging systems, each imaging system including optics optically connected with at least one detector in the array of detectors.
In an embodiment, a method fabricates an array of layered optical elements, by: using a first fabrication master, forming a first array of elements on a common base, the first fabrication master comprising a first master substrate including a negative of a first array of optical elements directly fabricated thereon; and using a second fabrication master, forming the second array of optical elements adjacent to the first array of optical elements on the common base so as to form the array of layered optical elements on the common base, the second fabrication master comprising a second master substrate including a negative of a second array of optical elements formed thereon, the second array of optical elements on the second master substrate corresponding in position to the first array of optical elements on the first master substrate.
In an embodiment, arrayed imaging systems include: a common base; an array of detectors having detector pixels formed on the common base, each one of the detector pixels including a photosensitive region; and an array of optics optically connected with the photosensitive region of a corresponding one of the detector pixels thereby forming arrayed imaging systems, wherein at least one of the optics is switchable between first and second states corresponding to first and second magnifications, respectively.
In an embodiment, a layered optical element has first and second layer of optical elements forming a common surface having an anti-reflection layer.
In an embodiment, a camera forms an image and has arrayed imaging systems including an array of detectors formed with a common base, and an array of layered optical elements, each one of the layered optical elements being optically connected with a detector in the array of detectors; and a signal processor for forming an image.
In an embodiment, a camera is provided for use in performing a task, and has: arrayed imaging systems including an array of detectors formed with a common base, and an array of layered optical elements, each one of the layered optical elements being optically connected with a detector in the array of detectors; and a signal processor for performing the task.
The present disclosure may be understood by reference to the following detailed description taken in conjunction with the drawings briefly described below. It is noted that, for purposes of illustrative clarity, certain elements in the drawings may not be drawn to scale.
The present disclosure discusses various aspects related to arrayed imaging systems and associated processes. In particular, design processes and related software, multi-index optical elements, wafer-scale arrangements of optics, fabrication masters for forming or molding a plurality of optics, replication and packaging of arrayed imaging systems, detector pixels having optical elements formed therein, and additional embodiments of the above-described systems and processes are disclosed. In other words, the embodiments described in the present disclosure provide details of arrayed imaging systems from design generation and optimization to fabrication and application to a variety of uses.
For example, the present disclosure discuss the fabrication of imaging systems, such as cameras for consumers and integrators, manufacturable with optical precision on a mass production scale. Such a camera, manufactured in accordance with the present disclosure, provides superior optics, high quality image processing, unique electronic sensors and precision packaging over existing cameras. Manufacturing techniques discussed in detail hereinafter allow nanometer precision fabrication and assembly, on a mass production scale that rivals the modern production capability of, for instance, microchip industries. The use of advanced optical materials in cooperation with precision semiconductor manufacturing and assembly techniques enables image detectors and image signal processing to be combined with precision optical elements for optimal performance and cost in mass produced imaging systems. The techniques discussed in the present disclosure allow the fabrication of optics compatible with processes generally used in detector fabrication; for example, the precision optical elements of the present disclosure may be configured to withstand high temperature processing associated with, for instance, reflow processes used in detector fabrication. The precision fabrication, and the superior performance of the resulting cameras, enables application of such imaging systems in a variety of technology areas; for example, the imaging systems disclosed herein are suitable for use in mobile imaging markets, such as hand-held or wearable cameras and phones, and in transportation sectors such as the automotive and shipping industries. Additionally, the imaging systems manufactured in accordance with the present disclosure may be used for, or integrated into, home and professional security applications, industrial control and monitoring, toys and games, medical devices and precision instruments and hobby and professional photography.
In accordance with an embodiment, multiple cameras may be manufactured as coupled units, or individual camera units can be integrated by an original equipment manufacturer (“OEM”) integrator as a multi-viewer system of cameras. Not all cameras in multi-view systems need be identical, and the high precision fabrication and assembly techniques, disclosed herein, allow a multitude of configurations to be mass produced. Some cameras in a multi-camera system may be low resolution and perform simple tasks, while other cameras in the immediate vicinity or elsewhere may cooperate to form high quality images.
In another embodiment, processors for image signal processing, machine tasks, and input/output (“I/O”) subsystems may also be integrated with the cameras using the precision fabrication and assembly techniques, or can be distributed throughout an integrated system. For instance, a single processor may be relied upon by any number of cameras, performing similar or different tasks as the processor communicates with each camera. In other applications, a single camera, or multiple cameras integrated into a single imaging system, may provide input to, or processing for, a broad variety of external processors and I/O subsystems to perform tasks and provide information or control queues. The high precision fabrication and assembly of the camera enables electronic processing and optical performance to be optimized for mass production with high quality.
Packaging for the cameras, in accordance with the present disclosure, may also integrate all packaging necessary to form a complete camera unit for off-the-shelf use. Packaging may be customized to permit mass production using the types of modern assembly techniques typically associated with electronic devices, semiconductors and chip sets. Packaging may also be configured to accommodate industrial and commercial uses such as process control and monitoring, barcode and label reading, security and surveillance, and cooperative tasks. The advanced optical materials and precision fabrication and assembly may be configured to cooperate and provide robust solutions for use in harsh environments that may degrade prior art systems. Increased tolerance to thermal and mechanical stress coupled with monolithic assemblies provides stable image quality through a broad range of stresses.
Applications for the imaging system, in accordance with an embodiment, including use in hand held devices such as phones, Global Positioning System (“GPS”) units and wearable cameras, benefit from the improved image quality and rugged utility in a precision package. The integrators for hand held devices gain flexibility and can leverage the ability to have optics, detector and signal processing combined in a single unit using precision fabrication, to provide an “optical system-on-a-chip.” Hand held camera users may gain benefit from longer battery life due to low power processing, smaller and thinner devices, and new capabilities, such as barcode reading and optical character recognition for managing information. Security may also be provided through biometric analysis such as iris identification using hand held devices with the identification and/or security processing built into the camera or communicated across a network.
Applications for mobile markets, such as transportation including automobiles and heavy trucks, shipping by rail and sea, air travel and mobile security, all may benefit from having inexpensive, high quality cameras that are mass produced. For instance, the driver of an automobile would benefit from increased monitoring abilities external to the vehicle, such as imagery behind the vehicle and to the side, providing visual feedback and/or warning, assistance with “blind spot” visualization or monitoring of cargo attached to a rack or in a truck bed. Moreover, automobile manufacturers may use the camera for monitoring internal activities, occupant behavior and location as well as providing input to safety deployment devices. Security and monitoring of cargo and shipping containers, or airline activities and equipment, with a multitude of cooperating cameras may be achieved with low cost as a result of the mass producibility of the imaging systems of the present disclosure.
Within the context of the present disclosure, an optical element is understood to be a single element that affects the electromagnetic energy transmitted therethrough in some way. For example, an optical element may be a diffractive element, a refractive element, a reflective element or a holographic element. An array of optical elements is considered to be a plurality of optical elements supported on a common base. A layered optical element is monolithic structure including two or more layers having different optical properties (e.g., refractive indices), and a plurality of layered optical elements may be supported on a common base to form an array of layered optical elements. Details of design and fabrication of such layered optical elements are discussed at an appropriate juncture hereinafter. An imaging system is considered to be a combination of optical elements and layered optical elements that cooperate to form an image, and a plurality of imaging systems may be arranged on a common substrate to form arrayed imaging systems, as will be discussed in further detail hereinafter. Furthermore, the term optics is intended to encompass any of optical elements, layered optical elements, imaging systems, detectors, cover plates, spacers, etc., which may be assembled together in a cooperative manner.
Recent interest in imaging systems such as those for use in, for instance, cell phone cameras, toys and games has spurred further miniaturization of the components that make up the imaging system. In this regard, a low cost, compact imaging system with reduced misfocus-related aberrations, that is easy to align and manufacture, would be desirable.
The embodiments described herein provide arrayed imaging systems and methods for manufacturing such imaging systems. The present disclosure advantageously provides specific configurations of optics that enable high performance, methods of fabricating wafer-scale imaging systems that enable increased yields, and assembled configurations that may be used in tandem with digital image signal processing algorithms to improve at least one of image quality and manufacturability of a given wafer-scale imaging system.
Imaging system 40 includes a processor 46 electrically connected with detector 16. Processor 46 operates to process electronic data generated by detector pixels of detector 16 in accordance with electromagnetic energy 18 incident on imaging system 40, and transmitted to the detector pixels, to produce image 48.
Imaging system 40 may work independently or cooperatively with one or more other imaging systems. For example, three imaging systems may work to view an object volume from three different perspectives to be able to complete a task of identifying an object in the object volume. Each imaging system may include one or more arrayed imaging systems, such as will be described in detail with reference to
Imaging system 10 includes a detector 16, an optics-detector interface 14, and optics 12 which cooperatively create the electronic image data. Detector 16 is, for example, a CMOS detector or a charge-coupled device (“CCD”) detector. Detector 16 has a plurality of detector pixels (not shown); each pixel is operable to create part of the electronic image data in accordance with part of electromagnetic energy 18 incident thereon. In the embodiment illustrated in
Optics-detector interface 14 may be formed on detector 16. Optics-detector interface 14 may include one or more filters, such as an infrared filter and a color filter. Optics-detector interface 14 may also include optical elements, e.g., an array of lenslets, disposed over detector pixels of detector 16, such that a lenslet is disposed over each detector pixel of detector 16. These lenslets are for example operable to direct part of electromagnetic energy 18 passing through optics 12 onto associated detector pixels. In one embodiment, lenslets are included in optics-detector interface 14 to provide chief ray angle correction as hereinafter described.
Optics 12 may be formed on optics-detector interface 14 and is operable to direct electromagnetic energy 18 onto optics-detector interface 14 and detector 16. As discussed below, optics 12 may include a plurality of optical elements and may be formed in different configurations. Optics 12 generally includes a hard aperture stop, shown later, and may be wrapped in an opaque material to mitigate stray light.
Although imaging system 10 is illustrated in
Arrayed imaging systems 10 may be fabricated as follows. A plurality of detectors 16 are formed on a common semiconductor wafer (e.g., silicon) using a process such as CMOS. Optics-detector interfaces 14 are subsequently formed on top of each detector 16, and optics 12 is then formed on each optics-detector interface 14, for example through a molding process. Accordingly, components of arrayed imaging systems 10 may be fabricated in parallel; for example, each detector 16 may be formed on the common semiconductor wafer at the same time, and then each optical element of optics 12 may be formed simultaneously. Replication methods for fabricating the components of arrayed imaging systems 10 may involve the use of a fabrication master that includes a negative profile, possibly shrinkage compensated, of the desired surface. The fabrication master is engaged with a material (e.g., liquid monomer) which may be treated (e.g., ultraviolet light “UV” cured) to harden (e.g., polymerize) and retain the shape of the fabrication master. Molding methods, generally, involve introduction of a flowable material into a mold and then cooling or solidifying the material whereupon the material retains the shape of the mold. Embossing methods are similar to replication methods, but involve engaging the fabrication master with a pliable, formable material and then optionally treating the material to retain the surface shape. Many variations of each of these methods exist in the prior art and may be exploited as appropriate to meet the design and quality constraints of the intended optical design. Specifics of the processes for forming such arrays of imaging systems 10 are discussed in more detail below.
As discussed below, additional elements (not shown) may be included in imaging system 10. For example, a variable optical element may be included in imaging system 10; such variable optical element may be useful in correcting for aberrations of imaging system 10 and/or implementing zoom functionality in imaging system 10. Optics 12 may also include one or more phase modifying elements to modify the phase of the wavefront of electromagnetic energy 18 transmitted therethrough such that an image captured at detector 16 is less sensitive to, for instance, aberrations as compared to a corresponding image captured at detector 16 without the one or more phase modifying elements. Such use of phase modifying elements may include, for example, wavefront coding, which may be used, for example, to increase a depth of field of imaging system 10 and/or implement a continuously variable zoom.
If present, the one or more phase modifying elements encodes a wavefront of electromagnetic energy 18 passing through optics 12 before it is detected by detector 16 by selectively modifying phase of a wavefront of electromagnetic energy 18. For example, the resulting image captured by detector 16 may exhibit imaging effects as a result of the encoding of the wavefront. In applications that are not sensitive to such imaging effects, such as when the image is to be analyzed by a machine, the image (including the imaging effects) captured by detector 16 may be used without further processing. However, if an in-focus image is desired, the captured image may be further processed by a processor (not shown) executing a decoding algorithm (sometimes denoted herein as “post processing” or “filtering”).
Adjacent layered optical elements 24 have a different refractive index; for example, layered optical element 24(1) has a different refractive index than layered optical element 24(2). In an embodiment of optics 22, first layered optical element 24(1) may have a larger Abbe number, or smaller dispersion, than the second layered optical element 24(2) in order to reduce chromatic aberration of imaging system 20. Anti-reflection coatings made from subwavelength features forming an effective index layer or a plurality of layers of subwavelength thicknesses may be applied between adjacent optical elements. Alternatively, a third material with a third refractive index may be applied between adjacent optical elements. The use of two different materials having different refractive indices is illustrated in
Although layered optical elements are illustrated in
Optics 22 may include one or more physical apertures (not shown). Such apertures may be disposed on top planar surfaces 26(1) and 26(2) of optics 22, for example. Optionally, apertures may be disposed on one or more layered optical element 24; for example, apertures may be disposed on planar surfaces 28(1) and 28(2) bounding layered optical elements 24(2) and 24(3). By way of example, an aperture may be formed by a low temperature deposition of metal or other opaque material onto a specific layered optical element 24. In another example, an aperture is formed on a thin metal sheet using lithography, and that metal sheet is then disposed on a layered optical element 24.
Optics 66 includes a plurality of layered optical elements 68, which may be similar to layered optical elements 24 of
Optics 66 includes a clear aperture 72 through which electromagnetic energy is intended to travel to reach detector 16; the clear aperture in this example is formed by a physical aperture 70 disposed on optical element 68(1), as shown. Areas of optics 66 outside of clear aperture 72 are represented by reference numbers 74 and may be referred to as “yards”—electromagnetic energy (e.g., 18,
In an embodiment, spaces 76 between imaging systems 62 are filled with a filler material, such as a spin-on polymer. The filler material is for example placed in spaces 76, and array 60 is then rotated at a high speed such that the filler material evenly distributes itself within spaces 76. Filler material may provide support and rigidity to imaging systems 62; if the filler material is opaque, it may isolate each imaging system 62 from undesired (stray or ambient) electromagnetic energy after separating.
Multiple embodiments of imaging system 10 are discussed herein. TABLES 1 and 2 summarize various parameters of the described embodiments. Specifics of each embodiment are discussed in detail immediately hereinafter. In TABLES 1 and 2, field of view is designated as “FOV” and chief ray angle is designated as “CRA.”
Detector 112 has a “VGA” format, which means that it includes a matrix of detector pixels (not shown) of 640 columns and 480 rows. Thus, detector 112 may be said to have a resolution of 640×480. When observed from the direction of the incident electromagnetic energy, each detector pixel has a generally square shape with each side having a length of 2.2 microns. Detector 112 has a nominal width of 1.408 mm and a nominal height of 1.056 mm. The diagonal distance across a surface of detector 112 proximate to optics 114 is nominally 1.76 mm in length.
Optics 114 has seven layered optical elements 116. Layered optical elements 116 are formed of two different materials and adjacent layered optical elements are formed of different materials. Layered optical elements 116(1), 116(3), 116(5), and 116(7) are formed of a first material having a first refractive index, and layered optical elements 116(2), 116(4), and 116(6) are formed of a second material having a second refractive index. No air gaps exist between optical elements in the embodiment of optics 114. Rays 118 represent electromagnetic energy being imaged by VGA imaging system 110; rays 118 are assumed to originate from infinity. The equation for the sag is given by Eq. (1), and the prescription of optics 114 is summarized in TABLES 3 and 4, where radius, thickness and diameter are given in units of millimeters.
where
n=1,2, . . . ,8;
r=√{square root over (x2+y2)};
c=1/Radius;
k=Conic;
Diameter=2*max(r);and
A
i=aspheric coefficients.
It may be observed from
Optics 114 is shown with a clear aperture 142 corresponding to that part of optics 114 through which electromagnetic energy travels to reach detector 112. Yards 144 outside of clear aperture 142 are represented by dark shading in
Detector 302 has a three megapixel “3 MP” format, which means that it includes a matrix of detector pixels (not shown) of 2,048 columns and 1,536 rows. Thus, detector 302 may be said to have a resolution of 2,048×1,536, which is significantly higher than that of detector 112 of
Optics 304 has four layers of optical elements in layered optical element 306 and five layers of optical elements in layered optical element 309. Layered optical element 306 is formed of two different materials, and adjacent optical elements are formed of different materials. Specifically, optical elements 306(1) and 306(3) are formed of a first material having a first refractive index; optical elements 306(2) and 306(4) are formed of a second material having a second refractive index. Layered optical element 309 is formed of two different materials, and adjacent optical elements are formed of different materials. Specifically, optical elements 309(1), 309(3) and 309(5) are formed of a first material having a first refractive index; optical elements 309(2) and 309(4) are formed of a second material having a second refractive index. Furthermore, optics 304 includes an intermediate common base 314 (e.g., formed of a glass plate) that cooperatively forms air gaps 312 within optics 304. One air gap 312 is defined by optical element 306(4) and common base 314, and another air gap 312 is defined by common base 314 and optical element 309(1). Air gaps 312 advantageously increase optical power of optics 304. Rays 308 represent electromagnetic energy being imaged by 3 MP imaging system 300; rays 308 are assumed to originate from infinity. The sag equation for optics 304 is given by Eq. (1). The prescription of optics 304 is summarized in TABLES 6 and 7, where radius, thickness and diameter are given in units of millimeters.
In order to promote illustrative clarity, only one optical element of each layered optical elements 306 and 309 are labeled in
VGA_WFC imaging system 420 has a focal length of 1.60 mm, a field of view of 62°, F/# of 1.3, a total track length of 2.25 mm, and a maximum chief ray angle of 31°. As discussed earlier, the cross hatched area shows the yard region, or the area outside the clear aperture, through which electromagnetic energy does not propagate.
VGA_WFC imaging system 420 includes optics 424 having seven-element layered optical element 116. Optics 424 includes an optical element 116(1′) that includes predetermined phase modification. That is, a surface 432 of optical element 116(1′) is formed such that optical element 116(1′) additionally functions as a phase modifying element for implementing predetermined phase modification to extend the depth of field in VGA_WFC imaging system 420. Rays 428 represent electromagnetic energy being imaged by the VGA_WFC imaging system 420; rays 428 are assumed to originate from infinity. The sag of optics 424 may be expressed using Eq. (2) and Eq. (3). Details of the prescription of optics 424 are summarized in TABLES 8-11, where radius, thickness and diameter are given in units of millimeters.
where
where
Each of plots 470, 472, and 474 includes MTF curves of the VGA_WFC imaging system 420 with and without post processing of electronic data produced by VGA_WFC imaging system 420. Specifically, plot 470 includes unfiltered MTF curves 476 and filtered MTF curves 482; plot 472 includes unfiltered MTF curves 478 and filtered MTF curves 484; and plot 474 includes unfiltered MTF curves 480 and filtered MTF curves 486. Filtered MTF curves 482, 484, and 486 represent performance of VGA_WFC imaging system 420 with post processing. As can be observed by comparing
As discussed above with respect to imaging system 10 of
It should be noted that the thickness of Surface 2, and the value of coefficient A2, change with object distance as shown in TABLE 13:
Imaging system 600 includes detector 112 and optics 604. Optics 604 includes a variable optic 616 formed on a common base 614 and layered optical elements 607(1)-607(7). A common base 614 (e.g., a glass plate) and optical element 607(1) define an air gap 612. Spacers, which are not shown in
The focal length of variable optic 616 may be varied to partially or fully correct for defocus in the VGA_AF imaging system 600. For example, the focal length of variable optic 616 may be varied to adjust the focus of imaging system 600 for different object distances. In an embodiment, a user of the VGA_AF imaging system 600 manually adjusts the focal length of variable optic 616; in another embodiment, the VGA_AF imaging system 600 automatically changes the focal length of variable optic 616 to correct for aberrations, such as defocus.
In an embodiment, variable optic 616 is formed from a material with a sufficiently large coefficient of thermal expansion (“CTE”), such as polydimethylsiloxane (“PDMS”), which has a CTE of approximately 3.1×10−4/K, deposited on common base 614. The focal length of this variable optic 616 may be varied by changing the temperature of the material, causing the material to expand or contract; causing variable optic 616 to change focal length. The temperature of the material may be changed by use of an electric heating element, which may possibly be formed into the yard region. For example, a heating element may be formed from a ring of polysilicon material surrounding the periphery of variable optic 616. In one embodiment, the heater has an inner diameter (“ID”) of 1.6 mm, an outer diameter (“OD”) of 2.6 mm and a thickness of 0.6435 mm. The heater surrounds variable optic 616, which has an OD of 1.6 mm, an edge thickness (“ET”) of 0.645 mm and a center thickness (“CT”) of greater than 0.645 mm, thereby forming a positive optical element. Polysilicon that forms the heater ring has a heat capacity of approximately 700 J/Kg·K, a resistivity of approximately 6.4×102 ΩM and a CTE of approximately 2.6×10−6/K.
Assuming that the expansion of the polysilicon heater ring is negligible with respect to that of PDMS variable optic 616, then the volume expansion of variable optic 616 is constrained in a piston-like manner. The PDMS variable optic 616 is attached to common base 614 and the ID of the heater ring, and is thereby constrained. The curvature of a top surface 615 of variable optic 616 is directly controlled therefore by the expansion of the polymer. A change in sag Δh is defined as Δh=3αΔTh where h is the original sag (CT) value, ΔT is the temperature change and α is the linear expansion coefficient of variable optic 616. For a PDMS variable optic 616 of the dimensions described above, a temperature change of 10° C. will provide a sag change of 6 microns. This calculation may provide as much as a 33% overestimate of sag change (e.g., cylindrical volume πr3 compared to spherical volume 0.66πr3) since only axial expansion is assumed, however, the modulus of the material will constrain the motion and alter the surface curvature and therefore the optical power.
For an exemplary heater ring formed from polysilicon, a current of approximately 0.3 milliamps for 1 second is sufficient to raise the temperature of the ring by 10°. Then, assuming that a majority of the heat is conducted into variable optic 616, this heat flow drives the expansion. Other heat will be lost to conduction and radiation, but the ring may be mounted upon a 200 micron glass substrate (e.g., common base 614) and further thermally isolated to minimize conduction. Other heater rings may be formed from the materials and processes used in the fabrication of thick film or thin film resistors. Alternatively, variable optic 616 may be heated from the top or bottom surfaces via a transparent resistive layer such as indium tin oxide (“ITO”). Furthermore, for suitable polymers a current may be directed through the polymer itself. In other embodiments, variable optic 616 includes a liquid lens or a liquid crystal lens.
Optics 604 forms a clear aperture 634 corresponding to that part of optics 604 through which electromagnetic energy travels to reach detector 112. Yards 636 outside of clear aperture 634 are represented by dark shading in
Comparison of
Optics 802 includes detector cover plate 810 separated from a surface 814 of detector 112 by an air gap 812. In an embodiment, air gap 812 has a thickness of 0.04 mm to accommodate lenslets of surface 814. Optional optical element cover plate 808 may be positioned adjacent to detector cover plate 810. In an embodiment, detector cover plate 810 is 0.4 mm thick. Layered optical element 804(6) is formed on optical element cover plate 808; layered optical element 804(5) is formed on layered optical element 804(6); layered optical element 804(4) is formed on layered optical element 804(5); layered optical element 804(3) is formed on layered optical element 804(4); layered optical element 804(2) is formed on layered optical element 804(3); and layered optical element 804(1) is formed on layered optical element 804(2). Layered optical elements 804 are formed of two different materials, in this example, with each adjacent layered optical element 804 being formed of different material. Specifically, layered optical elements 804(1), 804(3), and 804(5) are formed of a first material with a first refractive index, and layered optical elements 804(2), 804(4), and 804(6) are formed of a second material with a second refractive index. Rays 806 represent electromagnetic energy being imaged by VGA_W imaging system 800. A prescription for optics 802 is summarized in TABLES 15 and 16. The sag for the optics 802 is given by Eq. (1), where radius, thickness and diameter are given in units of millimeters.
VGA_S_WFC imaging system 920 includes VGA format detector 112 and optics 938. Optics 938 includes an optical element 922, which may be a glass plate, optical element 924 (which again may be a glass plate) with optical elements 928 and 930 formed on opposite sides thereof, and detector cover plate 926. Optical elements 922 and 924 form air gap 932 for a high power ray transition at optical element 928; optical element 924 and detector cover plate 926 form air gap 934 for a high power ray transition at optical element 930, and surface 940 of detector 112 and detector cover plate 926 form air gap 936.
VGA_S_WFC imaging system 920 includes a phase modifying element for introducing a predetermined imaging effect into the image. Such phase modifying element may be implemented on a surface of optical element 928 and/or optical element 930 or the phase modifying effect may be distributed among optical elements 928 and 930. In imaging system 920, primary aberrations include field curvature and astigmatism; thus, phase modification may be employed in imaging system 920 to advantageously reduce effects of such aberrations. An imaging system that is otherwise identical to system 920, but without a phase modifying element, would be referred to as the “VGA_S imaging system” (not shown). Rays 942 represent electromagnetic energy being imaged by VGA_S_WFC imaging system 920.
The sag equation for optics 938 is given by a higher-order separable polynomial phase function of Eq. (4).
where
and
Surface #3 of TABLE 17 is configured for providing a predetermined phase modification, with the parameters as shown in TABLE 19.
Plot 960 shows that the VGA_S imaging system exhibits relatively poor performance; in particular, the MTFs have relatively small values and reach zero under certain conditions. As stated above, a MTF value of zero is undesirable as it indicates loss of image data. Curves 966 of plot 962 represent the MTFs of VGA_S_WFC imaging system 920 without post filtering of electronic data produced by VGA_S_WFC imaging system 920. As may be seen by comparing plot 960 and 962, the unfiltered MTF curves 966 of VGA_S_WFC imaging system 920 have a smaller magnitude than some of the MTF curves of VGA_S imaging system. However, the unfiltered MTF curves 966 of VGA_S_WFC imaging system 920 advantageously do not reach zero, which means that VGA_S_WFC imaging system 920 preserves image information across the entire range of spatial frequencies of interest. Furthermore, the unfiltered MTF curves 966 of VGA_S_WFC imaging system 920 are all very similar. Such similarity in MTF curves allows a single filter kernel to be used by a processor (not shown) executing a decoding algorithm, as will discussed next.
As discussed above, encoding introduced by a phase modifying element in optics 938,
Each of
The Z_VGA_W imaging system 1070 includes a first optics group 1072 including a common base 1080. Negative optical element 1082 is formed on one side of common base 1080, and negative optical element 1084 is formed on the other side of common base 1080. Common base 1080 may be, for example, a glass plate. The position of optics group 1072 in imaging system 1070 is fixed.
Z_VGA_W imaging system 1070 includes a second optics group 1074 having common base 1086. Positive optical element 1088 is formed on one side of common base 1086, and plano optical element 1090 is formed on an opposite side of common base 1086. Common base 1086 is for example a glass plate. Second optics group 1074 is translatable in Z_VGA_W imaging system 1070 along an axis indicated by line 1096 between two positions. In the first position of optics group 1074, which is shown in imaging system 1070(1), imaging system 1070 has a tele configuration. In the second position of optics group 1074, which is shown in imaging system 1070(2), Z_VGA_W imaging system 1070 has a wide configuration. Prescriptions for tele configuration and wide configuration are summarized in TABLES 20-22. The sag of each optical element of Z_VGA_W imaging system 1070 is given by Eq. (1), where radius, thickness and diameter are given in units of millimeters.
Aspheric coefficients are identical for tele configuration and wide configuration.
The Z_VGA_W imaging system 1070 includes VGA format detector 112. An air gap 1094 separates a detector cover plate 1076 from detector 112 to provide space for lenslets on a surface of detector 112 proximate to detector cover plate 1076.
Rays 1092 represent electromagnetic energy being imaged by the Z_VGA_W imaging system 1070; rays 1092 originate from infinity.
Each pair of plots in
Z_VGA_LL imaging system 1220 includes a first optics group 1222 having an element 1228. Positive optical element 1230 is formed on one side of element 1228, and positive optical element 1232 is formed on the opposite side of element 1228. Element 1228 is for example a glass plate. The position of first optics group 1222 in the Z_VGA_LL imaging system 1220 is fixed.
Z_VGA_LL imaging system 1220 includes a second optics group 1224 having an optical element 1234. Negative optical element 1236 is formed on one side of element 1234, and negative optical element 1238 is formed on the other side element 1234. Element 1234 is for example a glass plate. Second optics group 1224 is translatable between two positions along an axis indicated by line 1244. In the first position of optics group 1224, which is shown in imaging system 1220(1), Z_VGA_LL imaging system 1220 has a tele configuration. In the second position of optics group 1224, which is shown in imaging system 1220(2), Z_VGA_LL imaging system 1220 has a wide configuration. It should be noted that ZEMAX® makes groups of optical elements appear to be different in the wide and tele configurations due to scaling.
The Z_VGA_LL imaging system 1220 includes a third optics group 1246 formed on VGA format detector 112. An optics-detector interface (not shown) separates third optics group 1246 from a surface of detector 112. Layered optical element 1226(7) is formed on detector 112; layered optical element 1226(6) is formed on layered optical element 1226(7); layered optical element 1226(5) is formed on layered optical element 1226(6); layered optical element 1226(4) is formed on layered optical element 1226(5); layered optical element 1226(3) is formed on layered optical element 1226(4); layered optical element 1226(2) is formed on layered optical element 1226(3); and layered optical element 1226(1) is formed on layered optical element 1226(2). Layered optical elements 1226 are formed of two different materials, with adjacent layered optical elements 1226 being formed of different materials. Specifically, layered optical elements 1226(1), 1226(3), 1226(5), and 1226(7) are formed of a first material with a first refractive index, and layered optical elements 1226(2), 1226(4), and 1226(6) are formed of a second material with a second refractive index. Rays 1242 represent electromagnetic energy being imaged by the Z_VGA_LL imaging system 1220; rays 1242 originate from infinity. The prescriptions for tele and wide configurations are summarized in TABLES 23-25. The sag for each optical element of these configurations is given by Eq. (1), where radius, thickness and diameter are given in units of millimeters.
Aspheric coefficients are identical for tele configuration and wide configuration, and they are listed in TABLE 25.
Each pair of plots in
Imaging system 1380(1) has a focal length of 3.34 millimeters, a field of view of 28°, F/# of 1.9, a total track length of 9.25 mm, and a maximum chief ray angle of 25°. Imaging system 1380(2) has a focal length of 1.71 millimeters, a field of view of 62°, F/# of 1.9, a total track length of 9.25 mm, and a maximum chief ray angle of 25°.
The Z_VGA_LL_AF imaging system 1380 includes a first optics group 1382 having an element 1388. Positive optical element 1390 is formed on one side of element 1388, and negative optical element 1392 is formed on the other side of element 1388. Element 1388 is for example a glass plate. The position of first optics group 1382 in the Z_VGA_LL_AF imaging system 1380 is fixed.
Z_VGA_LL_AF imaging system 1380 includes a second optics group 1384 having an element 1394. Negative optical element 1396 is formed on one side of element 1394, and negative optical element 1398 is formed on the opposite side of element 1394. Element 1394 is for example a glass plate. Second optics group 1384 is continuously translatable along an axis indicated by line 1400 between ends 1410 and 1412. If optics group 1384 is positioned at end 1412 of line 1400, which is shown in imaging system 1380(1), Z_VGA_LL_AF imaging system 1380 has a tele configuration. If optics group 1384 is positioned at end 1410 of line 1400, which is shown in imaging system 1380(2), Z_VGA_LL_AF imaging system 1380 has a wide configuration. If optics group 1384 is positioned in the middle of line 1400, which is shown in imaging system 1380(3), Z_VGA_LL_AF imaging system 1380 has a middle configuration. Any other zoom position between tele and wide is achieved by moving optics group 2 and adjusting the power of variable optic 1408, discussed below. The prescriptions for tele configuration, middle configuration, and wide configuration, are summarized in TABLES 26-30. The sag for each optical element of each configuration is given by Eq. (1), where radius, thickness and diameter are given in units of millimeters.
All of the aspheric coefficients, except A2 on surface 10, which is the surface of the variable optic 1408, are identical for tele configuration, middle configuration, and wide configuration (or any other zoom configuration in between tele and wide configuration), and they are listed in TABLE 29.
Aspheric coefficients A2 on surface 10 for different zoom configurations are summarized in TABLE 30.
The Z_VGA_LL_AF imaging system 1380 includes third optics group 1246 formed on VGA format detector 112. Third optics group 1246 was described above with respect to
Z_VGA_LL_AF imaging system 1380 further includes an optical element 1406 which contacts layered optical element 1226(1). A variable optic 1408 is formed on a surface of optical element 1406 opposite layered optical element 1226(1). The focal length of variable optic 1408 may be varied in accordance with a position of second optics group 1384 such that Z_VGA_LL_AF imaging system 1380 remains focused as its zoom position varies. The focal length (power) of variable optic 1408 varies to correct the defocus during zooming caused by the movement of second optics group 1384. The focal length variation of variable optic 1408 can be used not only to correct the defocus during zooming caused by the movement of second optics group 1384 as described above, but also to adjust the focus for different conjugate distances as was described in connection with VGA_AF imaging system 600 above. In an embodiment, the focal length of variable optic 1408 may be manually adjusted by, for instance, a user of the imaging system; in another embodiment, the Z_VGA_LL_AF imaging system 1380 automatically changes the focal length of variable optic 1408 in accordance with a position of second optics group 1384. For example, Z_VGA_LL_AF imaging system 1380 may include a look up table of focal lengths of variable optic 1408 corresponding to positions of second optics group 1384; Z_VGA_LL_AF imaging system 1380 may determine the correct focal length of variable optic 1408 from the lookup table and adjust the focal length of variable optic 1408 accordingly.
Variable optic 1408 is for example an optical element with an adjustable focal length. It may be a material with a sufficiently large coefficient of thermal expansion deposited on optical element 1406. The focal length of such an embodiment of variable optic 1408 is varied by varying the temperature of the material forming variable optic 1408, thereby causing the material to expand or contract; such expansion or contraction causes the focal length of variable optic 1408 to change. The temperature of the material may be changed by use of an electric heating element (not shown). As additional examples, variable optic 1408 may be a liquid lens or a liquid crystal lens.
In operation, therefore, a processor (see, e.g., processor 46 of
Rays 1402 represent electromagnetic energy being imaged by Z_VGA_LL_AF imaging system 1380; rays 1402 originate from infinity, although Z_VGA_LL_AF imaging system 1380 may image rays closer to system 1380.
Each pair of plots in
Imaging system 1620(1) has a focal length of 3.37 millimeters, a field of view of 28°, F/# of 1.7, a total track length of 8.3 mm, and a maximum chief ray angle of 22°. Imaging system 1620(2) has a focal length of 1.72 millimeters, a field of view of 60°, F/# of 1.7, a total track length of 8.3 mm, and a maximum chief ray angle of 22°.
Z_VGA_LL_WFC imaging system 1620 includes a first optics group 1622 having an element 1628. Positive optical element 1630 is formed on one side of element 1628, and an optical element 1632 is formed on the other side of element 1628. Element 1628 is for example a glass plate. The position of first optics group 1622 in the Z_VGA_LL_WFC imaging system 1620 is fixed.
Z_VGA_LL_WFC imaging system 1620 includes second optics group 1624 having an element 1634. A negative optical element 1636 is formed on one side of element 1634, and a negative optical element 1638 is formed on an opposite side of element 1634. Element 1634 is for example a glass plate. Second optics group 1624 is continuously translatable along an axis indicated by line 1640 between ends 1648 and 1650. If second optics group 1624 is positioned at end 1650 of line 1640, which is shown in imaging system 1620(1), Z_VGA_LL_WFC imaging system 1620 has a tele configuration. If optics group 1624 is positioned at end 1648 of line 1640, which is shown in imaging system 1620(2), Z_VGA_LL_WFC imaging system 1620 has a wide configuration. If optics group 1624 is positioned in the middle of line 1640, which is shown in imaging system 1620(3), Z_VGA_LL_WFC imaging system 1620 has a middle configuration.
Z_VGA_LL_WFC imaging system 1620 includes a third optics group 1626 formed on VGA format detector 112. A layered optical element 1646(7) is formed on detector 112; a layered optical element 1646(6) is formed on layered optical element 1646(7); a layered optical element 1646(5) is formed on layered optical element 1646(6); a layered optical element 1646(4) is formed on layered optical element 1646(5); a layered optical element 1646(3) is formed on layered optical element 1646(4); a layered optical element 1646(2) is formed on layered optical element 1646(3); and a layered optical element 1646(1) is formed on layered optical element 1646(2). Layered optical elements 1646 are formed of two different materials, with adjacent layered optical elements 1646 being formed of different materials. Specifically, layered optical elements 1646(1), 1646(3), 1646(5), and 1646(7) are formed of a first material with a first refractive index, and layered optical elements 1646(2), 1646(4), and 1646(6) are formed of a second material with a second refractive index. A wavefront coded surface is formed on a first surface 1674 of layered optical element 1646(1).
The prescriptions for tele configuration, middle configuration and wide configuration are summarized in TABLES 31-36. The sag for each optical element of all three configurations is given by Eq. (2). The phase function implemented by the phase modifying element is the oct form, whose parameters are given by Eq. (3) and illustrated in
The aspheric coefficients and the surface prescription for the oct form are identical for tele, middle and wide configurations, and are summarized in TABLES 34-36.
Z_VGA_LL_WFC imaging system 1620 includes a phase modifying element for implementing a predetermined phase modification. In
Performance of Z_VGA_LL_WFC imaging system 1620 may be appreciated by comparing its performance to that of Z_VGA_LL imaging system 1220 of
Unfiltered curves indicated by dashed lines represent MTFs without post filtering of electronic data produced by Z_VGA_LL_WFC imaging system 1620. As may be observed from plots 1710, 1716, and 1740, the unfiltered MTF curves have a relatively small magnitude. However, the unfiltered MTF curves advantageously do not reach zero magnitude, which means that Z_VGA_LL_WFC imaging system 1620 preserves image information over the entire range of spatial frequencies of interest. Furthermore, the unfiltered MTF curves are similar to each other. Such similarity in MTF curves allows a single filter kernel to be used by a processor executing a decoding algorithm, as will be discussed next. For example, encoding introduced by a phase modifying element (e.g., formed on surface 1674 of optical element 1646(1)) may be processed by processor 46,
Optics 1822 has seven layered optical elements 1824. Layered optical elements 1824 are formed of two different materials and adjacent layered optical elements are formed of different materials. Layered optical elements 1824(1), 1824(3), 1824(5), and 1824(7) are formed of a first material, with a first refractive index, and layered optical elements 1824(2), 1824(4) and 1824(6) are formed of a second material having a second refractive index. Two exemplary polymer materials that may be useful in the present context are: 1) a high index material (n=1.62) distributed by ChemOptics; and 2) a low index material (n=1.37) distributed by Optical Polymer Research, Inc. It should be noted that there are no air gaps in optics 1822. Rays 1830 represent electromagnetic energy being imaged by VGA_O imaging system 1820 from infinity.
Details of the prescription for optics 1822 are summarized in TABLES 37 and 38. The sag for each one of optics 1822 is given by Eq. (1), where radius, thickness and diameter are given in units of millimeters.
Detector 1832 is applied onto curved surface 1826. Optics 1822 may be fabricated independently of detector 1832. Detector 1832 may be fabricated of an organic material. Detector 1832 is for example formed or applied directly on surface 1826, such as by using an ink jet printer; alternately, detector 1832 may be applied to a substrate (e.g., a sheet of polyethylene) which is in turn bonded to surface 1826.
In an embodiment, detector 1832 has a VGA format with a 2.2 micron pixel size. In an embodiment, detector 1832 includes additional detector pixels beyond those required for the resolution of the detector. Such additional pixels may be used to relax the registration requirements of the center of detector 1832 with respect to an optical axis 1834. If detector 1832 is not accurately registered with respect to optical axis 1834, the additional pixels may allow the outline of detector 1832 to be redefined such that detector 1832 is centered with respect to optical axis 1834.
The curved image plane of VGA_O imaging system 1820 offers another degree of design freedom that may be advantageously used in VGA_O imaging system 1820. For example, curved image plane 1826 may be configured to conform to practically any surface shape, to correct for aberrations such as field curvature and/or astigmatism. As a result, it may be possible to relax the tolerances of optics 1822 and thereby decrease cost of fabrication.
It may be observed by comparing
In
First aperture 1992 captures an image while second aperture 1994 is used for integrated light level detection. Such light level detection may be used to adjust imaging system 1990 according to an ambient light intensity before capturing an image with imaging system 1990. Imaging system 1990 includes optics 2022 having a plurality of optical elements. An optical element 1998 (e.g., a glass plate) is formed with detector 1996. An optics-detector interface, such as an air gap, may separate element 1998 from detector 1996. Element 1998 may therefore be a cover plate for detector 1996.
A first air gap 2000 separates an optical element 2002 from element 1998. Positive optical element 2002 is in turn formed on one side of an optical element 2004 (e.g., a glass plate) proximate to detector 1996, and a negative optical element 2006 is formed on an opposite side of element 2004. A second air gap 2008 separates negative optical element 2006 from a negative optical element 2010. Negative optical element 2010 is formed on one side of an element 2012 (e.g., a glass plate) proximate to detector 1996; positive optical elements 2016 and 2014 are formed on an opposite side of element 2012. Positive optical element 2016 is in optical communication with first aperture 1992, and optical element 2014 is in optical communication with second aperture 1994. An element 2020 (e.g., a glass plate) is separated from optical elements 2016 and 2014 by third air gap 2018.
It may be observed from
Diffractive optical elements 2076 and 2080 may be used in place of element 2014,
Realization of arrayed imaging systems of the previous section require careful coordination of the design, optimization and fabrication of each of the components that make up the arrayed imaging systems. For example, briefly returning to
As shown in
Still referring to
Continuing to refer to
Step 3011 also includes steps to generate designs for the various components of the imaging system. Namely, step 3011 includes step 3024 to generate an optics subsystem design, step 3026 to generate an opto-mechanical subsystem design, step 3028 to generate a detector subsystem design, step 3030 to generate an image processor subsystem design and step 3032 to generate a testing routine. Steps 3024, 3026, 3028, 3030 and 3032 take into account design parameter sets for the imaging system design, and these steps may be performed in parallel, serially in any order or jointly. Furthermore, certain ones of steps 3024, 3026, 3028, 3030 and 3032 may be optional; for example, a detector subsystem design may be constrained by the fact that an off-the-shelf detector is being used in the imaging system such that step 3028 is not required. Additionally, the testing routine may be dictated by available resources such that step 3032 is extraneous.
Continuing to refer to
Step 3012 further includes a decision 3038 to determine whether the target parameters are satisfied by the imaging system. If the target parameters are not satisfied by the current imaging system design, then design parameters may be modified at a step 3039, using the set of potential design parameter modifications. For example, numerical analysis of MTF characteristics may be used to determine whether the arrayed imaging systems meet certain specifications. A specification for MTF characteristics may, for example, be dictated by the requirements of a particular application. If an imaging system design does not meet the certain specifications, specific design parameters may be changed, such as curvatures and thicknesses of individual optical elements. As another example, if chief ray angle correction is not to specification, a design of subwavelength optical elements within a detector pixel structure may be modified by changing the subwavelength feature width or thickness. If signal processing is not to specification, a kernel size of a filter may be modified, or a filter from another class or metric may be chosen.
As discussed earlier in reference to
When the calculated power coupling for the present positioning is determined to be sufficiently close to a maximum value, then, if there are remaining detector pixels to be optimized (step 3057), the above-described process is repeated, starting with step 3051. It may be understood that other parameters may be optimized, for example, power crosstalk (power that is improperly received by a neighboring detector pixel) may be optimized toward a minimum value. Further details of step 3045 are described at an appropriate junction hereinafter.
If the target and design parameters are not satisfied with the current optics subsystem design, then a decision 3066 is made to determine whether the realization process parameters may be modified to achieve performance within the target parameters. If a process modification in the realization process is feasible, then realization process parameters are modified in step 3067 based on the analysis in step 3064, optimization software (i.e., an ‘optimizer’) and/or user knowledge. The determination of whether process parameters can be modified may be made on a parameter by parameter basis or using multiple parameters. The model realization process (step 3063) and subsequent steps, as described above, may be repeated until the target parameters are satisfied or until process parameter modification is determined not to be feasible. If process parameter modification is determined not to be feasible at decision 3066, then the optics subsystem design parameters are modified, at step 3068, and the modified optics subsystem design is used at step 3062. Subsequent steps, as described above, are repeated until the target parameters are satisfied, if possible. Alternatively, design parameters may be modified (step 3068) concurrently with the modification of process parameters (step 3067) for more robust design optimization. For any given parameter, decision 3066 may be made by either a user or an optimizer. As an example, tool radius may be set at a fixed value (i.e., not able to be modified) by a user of the optimizer as a constraint. After problem analysis, specific parameters in the optimizer and/or the weighting on variables in the optimizer may be modified.
As shown in
Continuing to refer to
Still referring to
Further referring to
If the output of decision 3161 is YES, the material is suitable for replication of optical elements therewith, then the process progresses to a decision 3162, where a determination is made as to whether the arrayed optics design is compatible with the material selected at step 3161. Determination of arrayed optics design compatibility may include, for instance, examination of the curing procedure, specifically from which side of a common base arrayed optics are cured. If the arrayed optics are cured through the previously formed optics, then curing time may be significantly increased and degradations or deformations of the previously formed optics may result. While this effect may be acceptable in some designs with few layers and materials that are insensitive to over-curing and temperature increases, it may be unacceptable in designs with many layers and temperature-sensitive materials. If either decision 3161 or 3162 indicates that the intended replication process is outside of acceptable limits, then a report is generated at step 3163.
Processing blocks 3522 and 3524 operate to preprocess electronic data 3525 for noise reduction. In particular, a fixed pattern noise (“FPN”) block 3522 corrects for fixed pattern noise (e.g., pixel gain and bias, and nonlinearity in response) of detector 3520; a prefilter 3524 further reduces noise from electronic data 3525 and/or prepares electronic data 3525 for subsequent processing blocks. A color conversion block 3530 converts color components (from electronic data 3525) to a new colorspace. Such conversion of color components may be, for example, individual red (R), green (G) and blue (B) channels of a red-green-blue (“RGB”) colorspace to corresponding channels of a luminance-chrominance (“YUV”) colorspace; optionally, other colorspaces such as cyan-magenta-yellow (“CMY”) may also be utilized. A blur and filtering block 3540 removes blur from the new colorspace images by filtering one or more of the new colorspace channels. Blocks 3552 and 3554 operate to post-process data from block 3540, for example, to again reduce noise. In particular, single channel (“SC”) block 3552 filters noise within each single channel of electronic data using knowledge of digital filtering within block 3540; multiple channel (“MC”) block 3554 filters noise from multiple channels of data using knowledge of the digital filtering within blur and filtering block 3540. Prior to processed electronic data 3570, another color conversion block 3560 may for example convert the colorspace image components back to RGB color components.
As used herein, a non-homogeneous or multi-index optical element is understood as an optical element having properties that are customizable within its three dimensional volume. A non-homogeneous optical element may have, for instance, a non-uniform profile of refractive index or absorption through its volume. Alternatively, a non-homogeneous optical element may be an optical element that has one or more applied or embedded layers having non-uniform refractive index or absorption. Examples of non-uniform refractive index profiles include graded index (GRIN) lenses, or GRADIUM® material available from LightPath Technologies. Examples of layers with non-uniform refractive index and/or absorption include applied films or surfaces that are selectively altered, for example, utilizing photolithography, stamping, etching, deposition, ion implantation, epitaxy or diffusion.
The exemplary, non-homogeneous phase modifying element configuration shown in
GRIN lens 4802 has the following 3D index profile:
I=1.8+[−0.8914r2−3.0680·10−3r3+1.0064·10−2r4−4.6978·10−3r5] Eq. (5)
and has focal length=1.76 mm, F/#=1.77, diameter=1.00 mm and length=5.00 mm.
As may be seen by comparing
Certain non-homogeneous phase modifying element refractive profiles may be considered as a sum of two polynomials and a constant index, n0:
where
Thus, the variables X, Y, Z and r are defined in accordance with the same coordinate system as shown in
Phase modifying element 4202 has the following 3D index profile:
I=1.8+[−0.8914r2−3.0680·10−3r3+1.0064·10−2r4−4.6978·10−3r5],+[1.2861·10−2(X3+Y3)−5.5982·10−3(X5+Y5)] Eq. (7)
where, like GRIN lens 4802, r is radius from optical axis 4203 and X, Y and Z are as shown. In addition, like GRIN lens 4802, phase modifying element 4202 has focal length=1.76 mm, F/#=1.77, diameter=1.00 mm and length=5.00 mm.
As may be seen in comparing
Phase modifying element 4402 implements a predetermined phase modification utilizing a refractive index variation that varies as a function of position along a length of phase modifying element 4402. In phase modifying element 4402, a refractive profile is described by the sum of two polynomials and a constant index, n0, as in phase modifying element 4202, but in phase modifying element 4402, a term corresponding to the predetermined phase modification is multiplied by a factor which decays to zero along a path from front surface 4410 to back surface 4412 (e.g., from left to right as shown in
where r is defined as in Eq. (6), and Zmax is the maximum length of phase modifying element 4402 (e.g., 5 mm).
In Eq. (5)-(8), the polynomial in r is used to specify focusing power in phase modifying element 4402, and a trivariate polynomial in X, Y and Z is used to specify the predetermined phase modification. However, in phase modifying element 4402, the predetermined phase modification effect decays in amplitude over the length of phase modifying element 4402. Consequently, as indicated in
In the examples illustrated in
The multi-index optical elements of the present disclosure may in practice be used in systems that contain both homogeneous optics, as in
WALO structures may include two or more common bases (e.g., glass plates or semiconductor wafers) having arrays of optical elements formed thereon. The common bases are aligned and assembled, according to presently disclosed methods, along an optical axis to form short track length imaging systems that may be kept as a wafer-scale array of imaging systems or, alternatively, separated into a plurality of imaging systems.
The disclosed instrumentalities are advantageously compatible with arrayed imaging system fabrication techniques and reflow temperatures utilized in chip scale packaging (CSP) processes. In particular, optical elements of the arrayed imaging systems described herein are fabricated from materials that can withstand the temperatures and mechanical deformations possible in CSP processing, e.g., temperatures well in excess of 200° C. Common base materials used in the manufacture of the arrayed imaging systems may be ground or shaped into flat (or nearly flat) thin discs with a lateral dimension capable of supporting an array of optical elements. Such materials include certain solid state optical materials (e.g., glasses, silicon, etc.), temperature stabilized polymers, ceramic polymers (e.g., sol-gels) and high temperature plastics. While each of these materials may individually be able to withstand high temperatures, the disclosed arrayed imaging systems may also be able to withstand variation in thermal expansion between the materials during the CSP reflow process. For example, expansion effects may be avoided by using a low modulus adhesive at the bonding interface between surfaces.
An example analysis of imaging system 5101 is shown in
The exemplary design, as shown in
The key constraints on imaging system 5101 from TABLE 44 are a wide full field of view (“FFOV”>70°), a small total optical track (“TOTR”<2.5 mm) and a maximum chief ray angle constraint (e.g., CRA at full image height<30°). Due to the small total optical track and low chief ray angle constraints as well as the fact that imaging system 5101 has a relatively small number of optical surfaces, imaging system 5101's imaging characteristics are significantly field-dependent; that is, imaging system 5101 images much better in the center of the image than at a corner of the image.
A feature that may be added to the designs of imaging systems 5300 and 5400 is the use of a chief ray angle corrector (“CRAC”) as a part of the third and/or fourth optical element surface (e.g., optical element 5418(2) or 5430(2),
Replication methods for the disclosed wafer-scale arrays are also readily adapted for implementation of non-circular aperture optical elements, which have several advantages over traditional circular aperture geometry. Rectangular aperture geometry eliminates unnecessary area on an optical surface, which, in turn, maximizes a surface area that may be placed in contact in a bonding process given a rectilinear geometry without affecting the optical performance of an imaging system. Additionally, most detectors are designed such that a region outside the active area (i.e., the region of the detector where the detector pixels are located) is minimized to reduce package dimensions and maximize an effective die count per common base (e.g., silicon wafer). Therefore, the region surrounding the active area is limited in dimension. Circular aperture optical elements encroach into the region surrounding the active area with no benefit to the optical performance of the imaging module. The implementation of rectangular aperture modules thus allows a detector active area to be maximized for use in bonding of an imaging system.
In order to reduce encroachment of an optical element having a circular aperture into the region 5572 surrounding active area 5574 of VGA detector 5424, such an optical element may be replaced with an optical element having a rectangular aperture.
The numerous constraints of systems with short optical track lengths with controlled chief ray angles, of the type needed for practical wafer-scale imaging systems, has led to imaging systems that may not image as well as desired. Even when fabricated and assembled with high accuracy, the image quality of such short imaging systems is not necessarily as high as is desired due to various aberrations that are fundamental to short imaging systems. When optics are fabricated and assembled according to prior art wafer-scale methods, potential errors in fabrication and assembly further contribute to optical aberrations that reduce imaging performance.
Consider an imaging system 5101, shown in
When wafer-scale arrays such as those shown in
Consider the imaging system block diagram of
Specialized phase modifying element 5706 of
The only optical difference between imaging system 5700,
In comparison to imaging system 5101, consider imaging system 5700
A ray-based illustration of how addition of a surface for effecting a predetermined phase modification near an aperture stop 5712 of imaging system 5700 affects the system is shown in
In comparison, ray bundles 5772, 5774, 5776 and 5778 in the vicinity of image plane 5725 for imaging system 5700 are shown in
Specialized phase modifying element 5706 may be a form of a rectangularly separable surface profile that may be combined with the original optical surface of optical element 5106. A rectangularly separable form is given by Eq. (9):
P(x,y)=px(x)*py(y), (9)
where px=py in this example. The equation of px(x) for specialized phase modifying element 5706 shown in
p
x(x)=−564x3+3700x5−(1.18×104)x7−(5.28×105)x9, Eq. (10)
where the units of px(x) are in microns and the spatial parameter x is a normalized, unitless spatial parameter related to the (x, y) coordinates of optical element 5106 when used in units of mm Many other types of specialized surface forms may be used including non-separable and circularly symmetric.
As seen from the exit pupils of
Actual assembly tolerances of wafer-scale optics may be large compared to those of traditional optics assembly. For example, thickness variation of common bases, such as common bases 5602 and 5616 shown in
The effects of assembly errors on imaging system 5700 may be reduced through implementation of a specialized phase modifying element, as demonstrated by imaging system 5700 of
As discussed above, signal processor 5740 of imaging system 5700 may perform signal processing to remove an imaging effect, such as a blur, introduced by specialized phase modifying element 5706, from an image. Signal processor 5740 may perform such signal processing using a 2D linear filter.
The same filter illustrated in
The reason the imaging system 5700 is more insensitive to assembly errors than the imaging system 5101 is described with reference to
As discussed in prior sections, wafer-scale assembly includes placing layers of common bases containing multiple optical elements on top of each other. The imaging system so assembled may also be directly placed on top of a common base containing multiple detectors, thereby providing a number of complete imaging systems (e.g., each system including optics and detectors) which are separated during a separating operation.
This approach, however, suffers from the need for elements designed to control the spacing between individual optical elements and, possibly, between the optical assembly and the detector. These elements are usually called spacers and they usually (but not necessarily always) provide an air gap between optical elements. The spacers add cost, and reduce the yield and the reliability of the resulting imaging systems. The following embodiments remove the need for spacers, and provide imaging systems that are physically robust, easy to align and that present a potentially reduced total track length and higher imaging performance due to the higher number of optical surfaces that may be implemented. These embodiments provide the optical system designer with a wider range of distances between optical elements that may be precisely achieved.
The above described embodiments do not require the use of spacers between elements. Instead, spacing is controlled by thicknesses of several components that constitute the optical system. Referring back to
Use of replicated optical polymers further enables novel configurations in which, for example, no air gaps are required between optical elements.
A design concept illustrated in
As described previously, an advantage of selecting polymers with large differences in refractive index is the minimal curvature that is required in each surface. However, drawbacks exist to using materials with large Δn, including large Fresnel losses at each interface and high absorption typical of polymers with a refractive index exceeding 1.9. Low loss, high index polymers exist with refractive index values between 1.4 and 1.8.
It may be observed in
It is notable that the designs of imaging systems 5920 and 5960 are compatible with wafer-scale replication technologies. Use of layered materials with alternating refractive indices allows for a full imaging system with no air gaps. Use of replicated layers further allows for thinner and more dynamic aspheric curvatures in the elements created than would be possible with the use of glass common bases. Note that there is no limitation to a number of materials used, and it might be advantageous to select refractive indices that further reduce chromatic aberration from dispersion through the polymers.
A variable diameter may be incorporated into any of imaging systems 5101, 5400(2), 5920, 5960 and 5990 by exploiting variable transmittance materials. One example of this configuration would be to use, for example, an electrochromic material (for example, a combination of tungsten oxide (WO3) or Prussian blue (PB)) at an aperture stop (e.g., element 5962 of
In the fabrication of arrayed imaging systems such as those described above, it may be desirable to fabricate a plurality of features for forming optical elements (i.e., templates) as, for example, an array on a face of a fabrication master, such as an eight-inch or twelve-inch fabrication master. Examples of optical elements that may be incorporated into a fabrication master include refractive elements, diffractive elements, reflective elements, gratings, GRIN elements, subwavelength structures, anti-reflection coatings and filters.
A diamond turning process that utilizes a configuration as shown in
The following description provides methods and configurations for manufacturing a plurality of features for forming optical elements on a fabrication master, in accordance with various embodiments. Wafer-scale imaging systems (e.g., those shown in
Prior fabrication methods for wafer-scale assemblies of optical elements do not allow assembly at optical precision required to achieve high image quality; that is, while current fabrication systems allow assembly at mechanical tolerances (measured in multiples of wavelengths), they do not allow fabrication and assembly at optical tolerances (on the order of a wavelength) that are required for arrayed imaging systems such as an array of wafer-scale cameras.
It may be advantageous to directly fabricate a fully populated fabrication master that includes features thereon for forming a plurality of optical elements to eliminate, for example, the need for a stamping process to populate the fabrication master. Furthermore, it may be advantageous to fabricate all of the features for forming optical elements in one setup, so that positioning of the features with respect to one another is controlled to a high degree (e.g., nanometers). It may be further advantageous to produce higher yield fabrication masters in less time than is possible utilizing current methods.
In the following disclosure, the term “optical element” is utilized interchangeably to denote the final element that is to be formed through utilization of a fabrication master, and the features on the fabrication master itself. For example, references to “optical elements formed on a fabrication master” do not literally mean that optical elements themselves are on the fabrication master; such references denote the features intended to be utilized to form the optical elements.
The axes as defined in a conventional diamond turning process are shown in
A workpiece may be mounted on a chuck 6026, which is rotatable about the C-axis while being actuated in the X-axis on a spindle 6028. In the mean time, a cutting tool 6030 is mounted and rotated on a tool post 6032. Conversely, chuck 6026 may be mounted in place of tool post 6032 and actuated in the Z-axis while cutting tool 6030 is placed and rotated on spindle 6028. Additionally, each of chuck 6026 and cutting tool 6030 may be rotated and positioned about the B-axis.
Referring now to
Details of an inset 6042 (indicated by a dashed circle) in
Use of a STS/FTS, according to an embodiment may yield a good surface finish on the order of 3 nm Ra. Moreover, single point diamond turning (SPDT) cutting tools for STS/FTS may be inexpensive and have sufficient tool life to cut an entire fabrication master. In an exemplary embodiment, an eight-inch fabrication master 6034 may be populated with over two thousand features 6038 in one hour to three days, depending on Ra requirements that are specified during the design process, as shown in
In an embodiment, multi-axis milling/grinding may be used to form a plurality of features for forming optical elements on a fabrication master 6052, as shown in
The multi-axis milling process illustrated in
Comparing use of STS/FTS and multi-axis milling, the STS/FTS may be better suited for fabrication of shallow surfaces with low slopes, while multi-axis milling may be more suitable for fabrication of deeper surfaces and/or surfaces with higher slopes. Since surface geometry directly relates to tool geometry, optical design guidelines may encourage the specification of more effective machining parameters.
Although each of the aforedescribed embodiments have been illustrated with various components having particular respective orientations, it should be understood that the embodiments as described in the present disclosure may take on a variety of specific configurations with the various components being located in a variety of positions and mutual orientations and still remain within the spirit and scope of the present disclosure. For example, before an actual feature for forming an optical element is machined, a shape resembling the feature may be “roughed in” using, for instance, conventional cutting methods other than diamond turning or grinding. Further, cutting tools other than diamond cutting tools (e.g., high speed steel, silicon carbide, and titanium nitride) may be used.
As another example, a rotating cutting tool may be tailored to a desired shape of a feature for forming an optical element to be fabricated; that is, as shown in
As an example of the “rough in” procedure described above, a commercially available cutting tool with an appropriate diameter may be used to first machine a best-fit spherical surface, then a custom cutting tool with a specialized cutting edge (such as cutting edge 6072 may be used to form feature 6062. This “rough in” process may decrease processing time and tool wear by reducing an amount of material that must be cut by a specialized form tool.
Aspheric optical element geometry may be generated with a single plunge of a cutting tool if a form tool having an appropriate geometry is used. Presently available technologies in tool fabrication allow approximation of true aspheric shapes using a series of line and arc segments. If a geometry of a given form tool does not exactly follow a desired aspheric optical element geometry, it may be possible to measure a cut feature and then shape it on a subsequent fabrication master to account for deviation. While other optical element assembly variables, such as layer thickness of a molded optical element, may be altered to accommodate deviation in the form tool geometry, it may be advantageous to use a non-approximated, exact form tool geometry. Present diamond shaping methods limit a number of line and arc segments; that is, form tools having more than three line or arc segments may be difficult to manufacture due to the likelihood of error with one of the segments.
Each one of form tools 6076A-6076G incorporates only a portion (e.g., half) of the desired optical element geometry, as the tool rotation 6090A to 6090G creates a complete optical element geometry. It may be advantageous for the edge quality of form tools 6076A-6076G to be sufficiently high (e.g., 750× to 1000× edge quality) such that optical surfaces may be cut directly, without requiring post processing and/or polishing. Typically, form tools 6076A-6076G may be rotated on the order of 5,000 to 50,000 revolutions per minute (RPM) and plunged at such a rate that a 1 micron thick chip may be removed with each revolution of the tool; this process may allow for the creation of a complete feature for forming an optical element in a matter of seconds and a fully populated fabrication master in two or three hours. Form tools 6076A-6076G may also present the advantage that they do not have a surface slope limitation; that is, optical element geometries including slopes up to 90° may be achieved. Further, tool life for form tools 6076A-6076G may be greatly extended by the selection of an appropriate fabrication master material for the fabrication master. For example, tools 6076A-6076G may create tens of thousands to hundreds of thousands of features for forming individual optical elements in a fabrication master made of a material such as brass.
Form tools 6076A-6076G may be shaped, for example, with Focused Ion Beam (FIB) machining. Diamond shaping processes may be used to obtain true aspheric shapes having multiple changes in curvature (e.g., convex/concave), such as cutting edge 6092 of form tool 6076G. The expected curvature over edge 6092 may be, for example, less than 250 nanometers (peak to valley).
The surfaces of features for forming optical elements manufactured by direct fabrication may be enhanced with the inclusion of intentional tool marks on the feature surfaces. For example, in the C-axis mode cutting (e.g., Slow Tool Servo), an anti-reflection (AR) grating may be fabricated on the machined surface by utilizing a modified cutting tool. Further details of fabricating intentional machining marks on the machined features for affecting electromagnetic energy are described with reference to
An anti-reflection grating may be created using cutting tool 6128 in multi-axis milling, as shown in
Referring now to
It may be advantageous for an optical element to include a non-circular aperture or free form/shape geometry. For instance, a square aperture may facilitate mating of an optical element to a detector. One way to accomplish this square aperture is to perform a milling operation on the fabrication master in addition to generating a concave surface 6174. This milling operation may occur on some diameter less than the entire part diameter and may remove a depth of material to leave bosses or islands containing the desired square aperture geometry.
A milling operation to create bosses 6180 may be performed prior to creation of features for forming optical elements, although the processing order may not affect the quality of the final fabrication master. After the milling operation is performed, the entire fabrication master may be faced, thereby cutting the boss tops and annulus 6182. After the facing of fabrication master 6178, the desired optical element geometry may be directly fabricated using one of the earlier described processes, allowing for optical precision tolerances between annulus 6182 and the optical element height. Additionally, stand off features may be created between bosses 6180 that would facilitate Z alignment relative to a replication apparatus if desired.
A moldable material, such as a UV curable polymer, may be applied to fabrication master 6178′ to form a mating daughter part.
Although plurality of features 6192 are shown to be uniform in size and shape, concave features 6194 may be altered by altering the shape of modified square bosses 6178′ of fabrication master 6178′. For example, a subset of modified square bosses 6180′ may be machined to differing thicknesses or shapes by altering the milling process. In addition, a fill material (e.g., a flowable and curable plastic) may be added after modified square bosses 6180′ have been formed to further adjust the height of modified square bosses 6180′. Such fill material may be, for example, spun on to achieve acceptable flatness specifications. Convex surfaces 6184 may additionally or alternately have varied surface profiles. This technique may be beneficial for directly machining convex optical element geometry in a large array since raised bosses 6180′ provide enhanced tool clearance.
Machining of a fabrication master may take into account material characteristics of the fabrication master. Relevant material characteristics may include, but are not limited to, material hardness, brittleness, density, cutting ease, chip formation, material modulus and temperature. Characteristics of machining routines may also be considered in light of the material characteristics. Such machining routine characteristics may include, for instance, tool material, size and shape, cutting rates, feed rates, tool trajectories, FTS, STS, fabrication master revolutions per minute (“RPM”) and programming (e.g., G-code) functionality. Resulting characteristics of a surface of the finished fabrication master are dependent on the fabrication master material characteristics as well as the characteristics of the machining routine. Surface characteristics may include surface Ra, cusp size and shape, presence of burrs, corner radii and/or a shape and size of a fabricated feature for forming an optical element, for example.
When machining non-planar geometries (as often found in optical elements), the dynamics and interactions of a cutting tool and a machine tool may give rise to problems that may affect the optical quality and/or fabrication speed of populated fabrication masters. One common issue is that impact of the cutting tool with the surface of the fabrication master may cause mechanical vibration, which may result in errors in the surface shape of the resulting features. One solution to this problem is described in association with
Turning now to
Continuing to refer to
Use of a positive virtual datum, as shown in
In defining tool trajectory in implementing the virtual datum technique, it may be advantageous for interpolated virtual trajectories to have smooth, small and continuous derivatives to minimize acceleration (second derivative of a trajectory) and impulses (third and higher derivatives of the trajectory). Minimizing such abrupt changes in tool trajectory may result in surfaces with improved finish (e.g., lower Ra's) and better conformity to a desired feature sag. Furthermore, FTS machining may be employed in addition to (or instead of) the use of STS. FTS machining may provide a greater bandwidth (e.g., ten times larger or more) than STS, as it oscillates much less weight along the Z-axis (e.g., less than one pound instead of greater than one hundred pounds), although with a potential drawback of reduced finish quality (e.g., higher Ra's). However, with FTS machining, tool impact dynamics are considerably different because of the faster machining speed, and a tool may respond to sharp changes in trajectory with greater ease.
As shown in
An alternative is to reduce the number of trajectory points that are used by decreasing the resolution of the discretization. The reduced resolution in the discretization may be compensated by altering the trajectory interpolation of the machine tool. For example, linear interpolation (e.g., G-code G01) typically requires a large number of points to define a general aspheric surface. By using a higher order parameterization, such as cubic spline interpolation (e.g., G-code G01.1) or circular interpolation (e.g., G-code G02/G03), fewer points may be required to define the same tool trajectory. A second solution is to consider the surface of the fabrication master not as a single freeform surface but as a surface discretized into an array or arrays of similar features for forming optical elements. For example, a fabrication master upon which a plurality of one type of optical element is to be formed may be seen as an array of that one type of element with proper translations and rotations applied. Therefore, only that one type of element is required to be defined. Using this surface discretization, the size of the data set may be reduced; for instance, on a fabrication master with one thousand features each requiring one thousand trajectory points, the data set includes one million points, while utilizing the discretization and linear transformations approach requires the equivalent of only three thousand points (e.g., one thousand for the feature and two thousand for translation and rotation triplets).
A machining operation may leave tool marks on the surface of the machined part. For optical elements, certain types of tooling marks may increase scattering and result in deleterious electromagnetic energy loss, or cause aberrations.
where:
Continuing to refer to
Performance of fabricated features for forming optical elements may be evaluated by measurement of certain characteristics of the features. Fabrication routines for such features may be tailored, utilizing the measurements, to improve quality and/or accuracy of the features. Measurements of the features may be performed by using, for instance, white light interferometry.
To alleviate the systematic effects illustrated in
As an example of a calibration process, execution of a fabrication routine may be suspended in order to measure cut features for verification of geometry. Alternatively, such measurements may be performed while the fabrication routine continues. Measurements may then be used to implement a feedback process, to correct the fabrication routine as needed for the remaining features. Such a feedback process may, for example, compensate for cutting tool wear and other process variables that may affect yield. Measurements may be performed by, for example, a contact stylus (e.g., a Linear Variable Differential Transformer (LVDT) probe) that is actuated relative to the surface to be measured and performs single or multiple sweeps across the fabrication master. As an alternative, measurements may be performed across the aperture of a feature with an interferometer. Measurements may be performed concurrently with the cutting process, for instance, by utilizing an LVDT probe that contacts features already created, at the same time that the cutting tool is creating new features.
Continuing to refer to
Still referring to
Since the C-axis (and other axes) is encoded into the fabrication routine, a position of a feature relative to a center axis of measurement subsystem 6304 is known, or may be determined. Measurement subsystem 6304 may be triggered to measure fabrication master 6306 at a specific location or may be set to continuously sample fabrication master 6306. For instance, to allow continuous processing of fabrication master 6306, measurement subsystem 6304 may use a suitably fast pulsed (e.g., chopped or stroboscopic) laser or a flashlamp having a few microseconds duration, to effectively freeze motion of fabrication master 6306 relative to measurement subsystem 6304.
Analysis of information recorded by measurement system 6304 about characteristics of fabrication master 6306 may be performed by, for instance, pattern matching to a known result or by correlations between multiple features of the same type on fabrication master 6306. Suitable parameterization of the information and the associated correlations or pattern matching merit functions may permit control and adjustment of the machining operation using a feedback system. A first example involves measuring characteristics of a spherical concave feature in a metal fabrication master. Disregarding diffraction, an image of electromagnetic energy reflected from such a feature should be of uniform intensity and circularly bounded. If the feature is elliptically distorted, then an image at detector arrangement 6311 will show astigmatism and be elliptically bounded. Therefore, intensity and astigmatism, or lack thereof, may indicate certain characteristics of fabrication master 6306. A second example regards surface finish and surface defects. When surface finish is poor, intensity of the images may be reduced due to scattering from surface defects and an image recorded at detector arrangement 6311 may be non-uniform. Parameters that may be determined from the information recorded by measurement system 6304 and used for control include, for instance, intensities, aspect ratios, and uniformity of captured data. Any of these parameters may then be compared between two different features, between two different measurements on the same feature or between a fabricated feature and a predetermined reference parameter (such as one based upon a prior computational simulation of the feature) to determine characteristics of fabrication master 6306.
In an embodiment, combination of information from two different sensors or from an optical system at two different wavelengths assists in converting many relative measurements into absolute quantities. For example, the use of an LVDT in association with an optical measurement system can help provide a physical distance (e.g., from a fabrication master to the optical measurement system) that may be used to determine proper scaling for captured images.
In employing the fabrication master to replicate features therefrom, it may be important that the populated fabrication master is aligned precisely with respect to a replication apparatus. For example, alignment of a fabrication master in manufacturing layered optical elements, may determine alignment of different features with respect to one another and the detector. The fabrication of alignment features on the fabrication master itself may facilitate precise alignment of the fabrication master with respect to the replication apparatus. For instance, the high precision fabrication methods described above, such as diamond turning, may be used to create these alignment features simultaneously with, or during the same fabrication routine as, the features on the fabrication master. Within the context of the present application, an alignment feature is understood as a feature on the surface of the fabrication master configured to cooperate with a corresponding alignment feature on a separate object to define or indicate a separation distance, a translation and/or a rotation between the surface of the fabrication master and the separate object.
Alignment features may include, for example, features or structures that mechanically define relative position and/or orientation between the surface of the fabrication master and the separate object. Kinematic alignment features are examples of alignment features that may be fabricated using the above described methods. True kinematic alignment may be satisfied between two objects when the number of axes of motion and the number physical constraints applied between the objects total six (i.e., three translations and three rotations). Pseudo-kinematic alignment results when there are less than six axes and so alignment is constrained. Kinematic alignment features have been shown to have alignment repeatability at optical tolerances (e.g., on the order of tens of nanometers). Alignment features may be fabricated on the populated fabrication master itself but outside of the area populated by features for forming optical elements. Additionally or optionally, alignment features may include features or structures that indicate relative placement and orientation between the surface of the fabrication master and the separate object. For instance, such alignment features may be used with vision systems (e.g., microscopes) and motion systems (e.g., robotics) to relatively position the surface of the fabrication master and the separate object to enable automated assembly of arrayed imaging systems.
Different combinations of alignment features are shown in
Returning to
As one solution, rotational alignment may be achieved by the use of additional fiducials on fabrication master 6328 and/or vacuum chuck 6322. Within the context of the present application, fiducials are understood to be features formed on a fabrication master to indicate alignment of the fabrication master with respect to a separate object. These fiducials may include, but are not limited to, scribed radial lines (e.g., lines 6340 and 6340′, see
The alignment feature configurations illustrated in
Multiple differing machine tool configurations may be used to manufacture fabrication masters for the formation of optical elements. Each machine tool configuration may have certain advantages that facilitate the formation of certain types of features on fabrication masters. Additionally, certain machine tool configurations permit the utilization of specific types of tools that may be employed in the formation of certain types of features. Furthermore, the use of multiple tools and/or certain machine tool configurations facilitate the ability to do all machining operations required for the formation of a fabrication master at very high accuracy and precision without requiring the removal of a given fabrication master from the machine tool.
Advantageously to maintain optical precision, forming a fabrication master including features for forming an array of optical elements using a multi-axis machine tool may include the following sequence of steps: 1) mounting the fabrication master to a holder (such as a chuck or an appropriate equivalent thereof); 2) performing preparatory machining operations on the fabrication master; 3) directly fabricating on a surface of the fabrication master features for forming the array of optical elements; and 4) directly fabricating on the surface of the fabrication master at least one alignment feature; wherein the fabrication master remains mounted to the fabrication master holder during the performing and directly fabricating steps. Additionally or optionally, preparatory machining operations of a holder for supporting the fabrication master may be performed prior to mounting the fabrication master thereon. Examples of preparatory machining operations are to turn the outside diameter or to “face” (machine flat) the fabrication master to minimize any deflection/deformation induced by the chucking forces (and the resulting “springing” when the part comes off).
Although uncommon today, machine tools incorporating cantilevered spindles that hang vertically over a workpiece may be utilized. In a cantilevered configuration, a spindle is suspended from XY axes via an arm and a workpiece is mounted upon a Z-axis stage. A machine tool of this configuration may be advantageous for milling very large fabrication masters. Furthermore, when machining large workpieces, it may be important to measure and characterize straightness and deviations (straightness error) of axis slides. Slide deviations may typically be less than a micron but are also affected by temperature, workpiece weight, tool pressure and other stimuli. This may not be a concern for short travels; however, if machining large parts, a lookup table with a correction value may be incorporated into the software or a controller for any axis either a linear axis or a rotational axis. Hysteresis may also cause deviations in machine movements. Hysteresis may be avoided by operating an axis uni-directionally during a complete machining operation.
Multiple tools may be positionally related by performing a series of machining operations and measurements of the features formed. For example, for each tool: 1) an initial set of machine coordinates is set; 2) a first feature, such as a hemisphere, is formed on a surface using the tool; and 3) a measurement arrangement, such as an on-tool or off-tool interferometer, may be used to determine a shape of the formed test surface and any deviations therefrom. For example, if a hemisphere was cut then any deviations from a prescription (e.g., a deviation in radius and/or depth) of the hemisphere may be related to an offset between the initial set of machine coordinates and “true” machine coordinates of the tool. Using analysis of the deviation, a corrected set of machine coordinates for the tool may be determined and then set. This procedure may be performed for any number of tools. Utilizing the G-code command G92 (“coordinate system set”), coordinate system offsets may be stored and programmed for each tool. On-tool measurement subsystems, such as subsystem 6304 of
Another fabrication process that may be useful in the fabrication of optical elements on a fabrication master is Magnetorheological Finishing (MRF®) from QED Technologies, Inc. Moreover, the fabrication master may be marked with additional features other than the optical elements such as, for example, marks for orientation, alignment and identification, using one of the STS/FTS, multi-axis milling and multi-axis grinding approaches or another approach altogether.
The teachings of the present disclosure allow direct fabrication of a plurality of optical elements on, for example, an eight-inch fabrication master or larger. That is, optical elements on a fabrication master may be formed by direct fabrication rather than requiring, for instance, replication of small sections of the fabrication master to form a fully populated fabrication master. The direct fabrication may be performed by, for example, machining, milling, grinding, diamond turning, lapping, polishing, flycutting and/or the use of a specialized tool. Thus, a plurality of optical elements may be formed on a fabrication master to sub-micron precision in at least one dimension (such as at least one of X-, Y- and Z-directions) and with sub-micron accuracy in their relative positions with respect to each other. The machining configurations of the present disclosure are flexible such that a fabrication master with a variety of rotationally symmetric, rotationally non-symmetric, and aspheric surfaces may be fabricated with high positional accuracy. That is, unlike prior art methods of manufacturing a fabrication master, which involve forming one or a group of a few optical elements and replicating them across a wafer, the machining configurations disclosed herein allow the fabrication of a plurality of the optical elements as well as a variety of other features (e.g., alignment marks, mechanical spacers and identification features) across the entire fabrication master in one fabrication step. Additionally, certain machining configurations in accordance with the present disclosure provide surface features that affect electromagnetic energy propagation therethrough, thereby providing an additional degree of freedom to the designer of the optical elements to incorporate intentional machining marks into the design of the optical elements. In particular, the machining configurations disclosed herein include C-axis positioning mode machining, multi-axis milling, and multi-axis grinding, as described in detail above.
Step 8010 entails curing moldable material 8004A with fabrication master 8008A engaging common base 8006 under precise alignment using such techniques as have generally been described herein. Moldable material 8004A may be optically or thermally curable to harden moldable material 8004A as shaped by fabrication master 8008A. Depending upon a reactivity of moldable material 8004A, an activator such as ultraviolet lamp 8012 may, for example, be used as a source for ultraviolet electromagnetic energy, which may be transmitted through a translucent or transparent fabrication master 8008A. Translucent and/or transparent fabrication masters will be discussed herein below. It will be appreciated that a chemical reaction initiated by curing moldable material 8004A may cause moldable material 8004A to shrink isotropically or anisotropically in volume and/or linear dimension. For example, many common UV-curable polymers exhibit 3% to 4% linear shrinkage upon curing. Accordingly, fabrication master 8008A may be designed and machined to provide additional volume that accommodates this shrinkage. A resultant cured moldable material retains a shape of predetermined design according to fabrication master 8008A. As shown in step 8016, cured moldable material remains on common base 8006 after fabrication master 8008A is disengaged to form a first optical element 8014A of a layered optical element 8014.
In step 8018, fabrication master 8008A is replaced with a second fabrication master 8008B. Fabrication master 8008B may differ from fabrication master 8008A in predetermined shape of features for defining an array of layered optical elements. A second moldable material 8004B is deposited upon first optical element 8014A of the layered optical element or upon fabrication master 8008B. Second moldable material 8004B may be selected to yield different material properties, such as refractive index, than are provided by moldable material 8004A. Repeating steps 8002, 8010, 8016 for this layer “B” yields a cured moldable material layer forming a second optical element 8014B of the layered optical element 8014. This process may be repeated for as many layers of optical elements as are necessary to define all optics (optical elements, spacers, apertures, etc.) in a layered optical element of predetermined design.
Moldable materials are selected with regard to both optical characteristics of the materials after hardening and mechanical properties of the materials, both during and after hardening. In general, a material, when used for an optical element, should have high transmittance, low absorbance and low dispersion through a wavelength band of interest. If used for forming apertures or other optics, such as spacers, a material may have high absorbance or other optical properties not normally suitable for use with transmissive optical elements. Mechanically, a material should also be selected such that expansion of the material through an operating temperature and humidity range of an imaging system does not reduce imaging performance beyond acceptable metrics. A material should be selected for acceptable shrinkage and out-gassing during a curing process. Furthermore, a material should be able to withstand processes such as solder reflow and bump-bonding that may be used during packaging of an imaging system.
Once all individual layers of the layered optical elements have been patterned, if necessary, a layer may be applied to a top layer (e.g., the layer represented by optical element 8014B) that has protective properties and may be a desired surface on which to pattern an electromagnetic energy blocking aperture. This layer may be a rigid material, such as a glass, metal or ceramic material, or could be an encapsulating material to facilitate better structural integrity of the layered optical elements. Where a spacer is used, an array of spacers may be bonded with the common base or with a yard region of any layers of the layered optical element, with care given to insure that thru-holes in the array of spacers are properly aligned with the layered optical elements. Where an encapsulant is used, the encapsulant may be dispensed in a liquid form around the layered optical elements. The encapsulant would then be hardened and could be followed by a planarizing layer if necessary.
An initiation source, such as an ultraviolet lamp or heat source, cures in step 8036 the moldable material to a state of hardness. The moldable material may be, for example, a UV-curable acrylic polymer or copolymer. It will be appreciated that the moldable material may also be deposited and/or formed of plastic melt resin that hardens upon cooling, or from a low temperature glass. In the case of the low temperature glass, the glass is heated prior to deposition and is hardened upon cooling. The fabrication master and common base are disengaged in step 8038 to leave the moldable material on the common base.
Step 8040 is a check to determine whether all layers of layered optical elements have been fabricated. If not, anti-reflection coating layers, apertures or light blocking layers may be optionally applied in step 8042 to the layer of layered optical elements that was last formed, and the process proceeds in step 8044 with the next fabrication master or other process. Once the moldable material has been hardened and bonded onto the common base, the fabrication master is disengaged from the common base and/or vacuum chuck. The next fabrication master is selected, and the process is repeated until all intended layers have been created.
As will be described in more detail below, it may be useful to produce imaging systems that have air gaps or moving parts, in addition to the layered optical elements described immediately above. In such instances, it is possible to use an array of spacers to accommodate the air gaps or moving parts. If step 8040 determines that all layers have been fabricated, then it is possible to determine a spacer type in step 8046. If no spacer is desired, then there is a yield in step 8048 of a product (i.e., an array of layered optical elements). If a glass spacer is desired, then an array of glass spacers is bonded in step 8050 to the common base, and an aperture may be placed in step 8052 atop the layered optical elements, if required, to yield a product in step 8048. If a polymer spacer is required, then a fill polymer may be deposited in step 8054 atop the layered optical elements. The fill polymer is cured in step 8056 and may be planarized in step 8058. An aperture may be placed 8060 atop the layered optical elements, if required, to yield a product 8048.
In one embodiment, a master mold 8084 is used in combination with an optional rigid substrate 8086 to stiffen master mold 8084. For example, a master mold 8084 formed of PDMS may be supported by a metal, glass or plastic substrate 8086. As shown in
For illustrative, non-limiting purposes, the exemplary layered optical element configurations shown in
Material 8332 may be machined, molded or cast. In one example, material 8332 is molded in a polymer using a diamond-machined master.
The embodiments described herein offer advantages over existing electromagnetic detection systems, and methods of fabrication thereof, by using materials and methods that are compatible with existing fabrication processes (e.g., CMOS processes) for the manufacture of optical elements buried within detector pixels of a detector. That is, in the context of the present disclosure, “buried optical elements” are understood to be features that are integrated into a detector pixel structure for redistributing electromagnetic energy within the detector pixel in predetermined ways and are formed of materials and using procedures that may used in the fabrication of the detector pixels themselves. The resulting detectors have the advantages of potentially lower cost, higher yield and better performance. In particular, improvements in performance may be possible because the optical elements are designed with knowledge of the pixel structure (e.g., positions of metal layers and photosensitive regions). This knowledge allows a detector pixel designer to optimize an optical element specifically for a given detector pixel, thereby allowing, for example, pixels for detecting different colors (e.g., red, green and blue) to be customized for each specific color. Additionally, the integration of the buried optical element fabrication with the detector fabrication processes may provide additional advantages such as, but not limited to, better process control, less contamination, less process interruption and reduced fabrication cost.
Attention is directed to
Continuing to refer to
It is possible to take the multi-slab configuration further and replace a conventional lenslet with, for example, a dual-slab. As each one of a plurality of detector pixels is characterized by a pixel sensitivity, a multi-slab configuration may be further optimized for improved sensitivity at a wavelength of operation of a given detector pixel. A comparison of the power coupling efficiencies for a lenslet and dual-slab configurations over a range of wavelengths is shown in
An embodiment of the detector system may include additional thin film layers, as shown in
The embodiments here represented may be used individually or in combination. For example, one may use an embedded lenslet and enjoy the benefits of improved pixel sensitivity while still using conventional color filters, or one may use a thin film filter for IR-cut filtering overlaid by a conventional lenslet. However, when conventional color filters and lenslets are replaced by buried optical elements, the additional advantage of potentially integrating all steps of detector fabrication into a single fabrication facility is realized, thereby reducing the handling of detectors and possible particle contamination and, consequently, potentially increasing fabrication yields.
The embodiments of the present disclosure also present an advantage that final packaging of a detector is simplified by an absence of external optical elements. In this regard,
A cross-sectional view of a portion of buried optical elements 10605 is shown in
Filter layer group 10750 or 10755 may be a red-green-blue (RGB) type of color filter as shown in
When a thin film wavelength-selective filter such as layer group 10750 is superimposed by a subwavelength CRAC 10745, the CRAC modifies the CRA of an input beam, generally making it closer to normal incidence. In this case, the thin film filter (layer group 10750) may be nearly the same for every detector pixel (or every detector pixel of the same color, in the case when the thin film filter is used as a color-selective filter), and only the CRAC changes spatially across an array of detector pixels. Correcting CRA variation in this way presents the advantages of 1) improving the detector pixel sensitivity, because the detected electromagnetic energy travels towards the photosensitive region 10002 at an angle closer to normal incidence and, therefore, less of it is blocked by the conductive metal layers 10008, and 2) the detector pixel becomes less sensitive to the polarization state of the electromagnetic energy because the angle of incidence of the electromagnetic energy is closer to normal.
Alternatively, CRA variations in the wavelength-dependent filtering of filtering layer groups 10750 and 10755 may be mitigated by spatially varying the color correction based on the color filter response for each detector pixel. Lim, et al. in “Spatially Varying Color Correction Matrices for Reduced Noise” from the Imaging Systems Laboratory at HP Laboratories detail an application of spatially varying correction matrices to permit color correction based upon a variety of factors. The spatially varying CRA leads to a spatially varying color mixing. Since this spatially varying color mixing may be static for any one detector pixel, a static color correction matrix designed for that detector pixel may be applied using spatially coordinated signal processing.
wherein ∈1 is the dielectric function of the first material and ∈2 is the dielectric function of the second material. A new effective optical index is given by the positive square root of ∈eff. Variable f is the fractional part of the mixed material that is of the second material characterized by dielectric function ∈2. A mixing ratio of the materials is given by the ratio (1−f/f. The use of subwavelength mixed composite material layers or structures allows for spatially varying the effective index in a given layer or structure using lithographic techniques, wherein the mixing ratio is determined by the pitch of the sub-features. The use of lithographic techniques for determining a spatially-varying effective index is very powerful because even a single lithographic mask provides enough degrees of freedom in a spatially varying plane to allow for: 1) changing wavelength selectivity (color filter response) from detector pixel to detector pixel; and 2) spatially correcting for chief ray angle variations from a center detector pixel (e.g., CRA=0°) to an edge detector pixel (e.g., CRA=25°). Moreover, this spatial variation of the effective index may be done with as little as a single lithographic mask per layer. Although discussed herein with respect to modification of a single layer, multiple layers may be simultaneously modified by etching through a series of layers followed by multiple depositions.
Turning now to
The relative positions of chief ray angle corrector 10805 (10805′), metalens 10810 (10810′) and metal traces 10815 (10815′) to axis 10830 (10830′) may independently spatially vary within an arrayed set of detector pixels. For example, for each detector pixel in an array these relative positions may have a circularly symmetric and radially varying value with respect to the center of the detector pixel array.
TABLE 53 shows layer design information for an AR coating in accordance with the present disclosure. TABLE 53 includes the layer number, the layer material, the material refractive index, the material extinction coefficient, the layer full wave optical thickness (FWOT), and the layer physical thickness. These values are for the design wavelength range of 400-900 nm. Although TABLE 53 describes specific materials used in six layers, greater or fewer numbers of layers may be used and materials may be substituted, for example, BLACK DIAMOND® may be substituted for PEOX and the thicknesses changed accordingly.
TABLE 54 shows the layer design information for an IR-cut filter in accordance with the present disclosure. TABLE 54 includes the layer number, the layer material, the material refractive index, the material extinction coefficient, the layer full wave optical thickness (FWOT), and the layer physical thickness. An IR-cut filter may be incorporated into a detector pixel such as that shown in
TABLES 55-57 show layer design information for an RGB filter in accordance with the present disclosure. TABLES 55-57 include the layer number, the layer material, the material refractive index, the material extinction coefficient, the layer full wave optical thickness (FWOT), and the layer physical thickness. The individual red (TABLE 56), green (TABLE 55) and blue (TABLE 57) color filters may be jointly designed and optimized to provide for efficient and cost-effective manufacturing by limiting the number of uncommon layers. For example in TABLE 55 layers 1-5 are the layers that may be specifically optimized for a green color filter. These layers are denoted in the “Lock” column of TABLE 55 by a “No” designation. During the design and optimization process, these layers are permitted to vary in thickness. Layers 6-19 are layers that may be common to all three individual filters of the RGB filter. These layers are denoted in the “Lock” column of TABLE 55 by a “Yes” designation. In this example, layer 19 represents a 10 nm buffer or isolation layer of PEOX. Layers 14-18 of TABLE 55 represent common layers that are used as an AR coating for the photosensitive region of the detector pixel.
Variations in thickness, density or material composition of layers 10925 and 10925′ may result in variation of the amount and depth of ion implantation into layers 10930 and 10930′. Varied implantation results in changes to an optical index of a modified material layer. For example implantation of nitrogen into layers 10930 and 10930′ made of silicon dioxide results in the silicon dioxide (SiO2) being converted to silicon oxynitride (SiOxNy). In the example shown in
Continuing to refer to
Second data 11005 is fed into an optimizing module 11010 within design optimizing system 10970. Optimizing module 11010 compares second data 11005 to goals 11015, which may include user defined goals 10980, and provides a third data 11020 back to optical system model 10985. For example, if optimizing module 11010 concludes that second data 11005 does not meet goals 11015, third data 11020 prompts refinements of optical system model 10985; that is, third data 11020 may prompt adjustment of certain parameters of optical system model 10985 to result in alteration of first data 10990 and second data 11005. Design optimizing system 10970 evaluates a modified optical system model 10985 to generate new second data 11005. Design optimizing system 10970 continues to modify optical system model 10985 iteratively until goals 11015 are met, at which point design optimizing system 10970 generates an optimized optical system design 11025 that is based on optical system design 10975 as modified in accordance with third data 11020 from optimizing module 11010. One of goals 11015 may be, for example, to achieve a certain coupling value of incident electromagnetic energy into a given optical system. Design optimizing system 10970 may also generate a predicted performance 11030 that, for example, summarizes calculated performance capabilities of optimized optical system design 11025.
For example, in a detector system including buried optical elements described earlier, field angle and f/# of a particular set of imaging optics (contributing to optics data 11055) may be taken into account in designing CRAC and color filters (contributing to detector data 11060) for use with that particular set of imaging optics and, furthermore, processing of information obtained at a detector (contributing to signal processing data 11065) may be modified to complement a resulting combination of imaging optics and detector designs. Other aspects of design, such as electromagnetic energy propagation from an object through optics, may be taken into account as well. For instance, a requirement of a wide field of interest (contributing to object data 11045) and a low f/# (part of optics data 11055) lead to a need to handle incident electromagnetic energy rays with high incident angles. Consequently, optimizing process 11035 may require configuration of a CRAC to be matched to a worst case or a probabilistic distribution of incident electromagnetic energy. In other cases, some imaging systems may contain optics (contributing to optics data 11055) that purposefully distort or “remap” field points (such as classic fish-eye lenses or 360-degree panoramic lenses) so as to present unique CRAC requirements. A CRAC (and corresponding detector data 11060) for such distorted systems may be designed in conjunction with an expected remapping function corresponding to distortion represented by optics data 11055. Additionally, electromagnetic energy of different wavelengths may be distorted differently by the optics, thereby adding a wavelength-dependent component to optics data 11055. Hence color filters and CRAC or energy guiding features of the detector (part of detector data 11060) may be taken into account within trade space 11040 to account for various system characteristics pertaining to wavelength. Color filters and CRACs and energy guiding features may be combined in pixel designs (and, therefore, detector data 11060) based on the available processing (i.e., signal processing data 11065) of the sampled imagery. For instance, signal processing data 11065 may include color correction that varies spatially. Spatially varying processing including color correction and distortion correction (part of signal processing data 11065), design of the imaging optics (part of optics data 11055), and intensity and CRA variation (part of electromagnetic energy propagation data 11050) may all be jointly optimized within trade space 11040 of optimizing process 11035 so as to yield an optimized design 11080.
Continuing to refer to
Requirements 11095 may be defined by user input or selected automatically from a database by the computational system based upon a set of rules. In some cases, the various requirements may be interrelated. For example, while a layer thickness may be subject to a manufacturing limitation of a range of maximum and minimum thickness as well as a user-defined thickness range constraint, the layer thickness value used during the optimization process may be modified by an optimizer using a merit function to optimize a performance goal.
After step 11090, process 11085 advances to a step 11130 where unconstrained thin film filter designs 11135 are generated. Within the context of the present disclosure, an unconstrained thin film filter design is understood to be thin film filter designs that do not take into account constraints 11100 as specified in requirements 11095 but do consider at least some of design limitations 11120 defined in step 11090. For example, design limitations 11120, such as defining certain layers as silicon dioxide layers, may be included in the generation of unconstrained thin film filter design 11135, whereas the actual thickness of the layers of silicon dioxide may be left a freely variable parameter in step 11130. Unconstrained thin film filter design 11135 may be generated with the assistance of a thin film design program such as ESSENTIAL MACLEOD®. For example, a set of materials and a defined number of layers (i.e., design limitations 11120) from which to generate a thin film filter design may be specified in a thin film design program. The thin film design program then optimizes a selected parameter (i.e., from parameters 11125), such as thicknesses of the selected materials in each defined layer, such that a calculated transmission performance of a filter design approaches a previously defined performance goal for that filter design (i.e., performance goals 11105). Unconstrained thin film filter designs 11135 may have taken into account a variety of factors such as, for example, limitations associated with available materials, thin film layer sequencing (e.g., sequencing of high index and low index materials in a thin film filter) and sharing of a common number of layers among a set of thin film filters. Material selection and layer number definition operations may be iterated via feedback loop 11140 to provide alternative, unconstrained thin film filter designs. Additionally, the thin film design program may be set to independently optimize at least some of the alternative, unconstrained thin film filter designs. The term “unconstrained designs” generally refers to designs in which parameters of thin film layers, such as a thickness, a refractive index, or a transmission of the layers may be set to any value required to optimize performance of the design. Each of unconstrained designs 11135 generated in step 11130 may be represented by an ordered listing of materials and their associated thicknesses in the unconstrained design, as will be discussed in more detail at an appropriate juncture hereinafter.
Still referring to
Next, in a step 11155, one or more of constrained thin film filter designs 11150 are optimized to produce optimized thin film filter designs 11160 that better meet requirements 11095 in comparison to unconstrained thin film filter designs 11135 and constrained thin film filter designs 11150.
As an example, process 11085 may be used to simultaneously optimize two or more thin film filters in a variety of configurations. For instance, multiple thin film filter designs may be optimized to perform a collective function, such as color selective filtering in a CMY detector wherein different thin film filters provide filtering for the different colors. Once optimized thin film filter designs 11160 have been generated, the process ends with a step 11165. Process 11085 may be applied to the generation and optimization of thin film filter designs for a variety of functions such as, but not limited to, bandpass filtering, edge filtering, color filtering, high-pass filtering, low-pass filtering, anti-reflection, notch filtering, blocking filtering and other wavelength selective filtering.
A thin film filter design may be described, for instance, by a design table, which lists materials used, ordering of the materials in the filter and thickness of each layer of the filter. A design table for an optimized thin film filter may be generated by optimizing, for instance, the ordering of the materials and the thickness of each layer in a given thin film filter. Such a design table may be generated for each of first, second and third thin film filters 11250, 11255 and 11260 of
TABLE 61 is a design table for an exemplary CMY filter set design, in which the designs for first, second and third thin film filters 11250, 11255 and 11260 (
Using thin film filter design principles known in the art, it was determined that a nine-layer thin film filter with alternating high (“H”) and low (“L”) refractive index layers (i.e., HLHLHLHLH) would produce a satisfactory set of CMY filters, individually satisfying requirements 11095 (
An exemplary process for joint optimization of the different thin film filters in a given thin film filter set, and thereby the generation of the optimized design tables that meet requirements 11095 while providing specific correlations between the different thin film filters, is described in detail immediately hereinafter.
Referring to
Continuing to refer to
In designing a filter set using process 11085 of
Continuing to refer to
Returning to
From this set of selected smallest thickness differences developed in step 11375, the largest “smallest difference” pair and its associated layer are then selected (i.e., 33.81 nm for layer 1, in the example shown in TABLE 62) in a step 11380. In the present example, the selection of thickness difference value 33.81 nm for layer 1 further restricts layer 1 from the cyan and magenta filter designs to be fixed as a paired set of layers. This pairing procedure performed in steps 11375 and 11380 is another example of a hierarchically ordered procedural step. It has been determined that the pairing of the smallest differences rather than the pairing of the largest differences presents a smaller impact on the optimized performance of the filter design set.
Still referring to
Next, in a step 11390 the thicknesses of the remaining high index layers are optimized for each filter design to better achieve the filter design's performance goal(s), while retaining the optimized paired layer thickness determined in step 11385. TABLE 63 shows the design thickness information for the exemplary CMY filter set design following the completion of step 11390. It may be seen in TABLE 63 that the paired layer thickness for layer 1 of the cyan and magenta filter designs was determined to be 214 nm.
Returning to
TABLE 64 shows the design thickness information for the exemplary CMY filter set design following the completion of five pairing and optimization cycles of steps 11375 through 11390.
Returning briefly to
An exemplary, optimized CMY filter set design, generated in accordance with the process illustrated in
Although process 11085 (
Furthermore, in the exemplary process illustrated in
Turning now to
TABLES 66 and 67 list process sequences for two exemplary methods for manufacturing thin film color filters, such as the exemplary CMY filter set described in TABLE 64. Individual semiconductor process steps listed in TABLES 66 and 67 are well known in the art of semiconductor processing. Dielectric materials such as SiN and BLACK DIAMOND® may be deposited using known processes such as, for instance, plasma-enhanced chemical vapor deposition (PECVD). Photoresist may be spin coated on equipment designed for these functions. Masked exposure of the photoresist may be performed on commercially available lithography equipment. Photoresist removal, also known as “photoresist stripping” or “ashing” may be performed on commercially available equipment. Plasma etching may be performed using known wet or dry chemical processes.
The two process sequences defined in TABLES 66 and 67 differ in the way that plasma etching is utilized in each sequence. In the sequence listed in TABLE 66, high index layers of individual color filters that include paired thicknesses are deposited in two steps, with intervening masking and etching operations. Material is deposited to a thickness equal to a difference between a paired layer thickness and an unpaired layer thickness. Then the deposited layer is selectively masked. Where a selected thin film layer is unprotected from etching, the layer may be removed down to its interface with an underlying layer, using a selective etching process that etches the selected layer at a greater rate than the underlying layer. If the layer is removed down to its interface with an underlying layer then, due to a selectivity of the etching processes, the underlying layer remains substantially unetched. Substantially unetched means that only a negligible amount of the underlying layer is removed in the etching process. This negligible amount may be measured in terms of an absolute thickness or a relative percentage of the thickness of a layer. To maintain acceptable performance of a filter, typical values for excess etching may be as high as a few nanometers or 10%; in some cases, much less. A second deposition may then be performed to add enough material to establish the thickness of the thickest layer within a corresponding layer triplet. In a process associated with the exemplary CMY filter set design, SiN is the material that is being etched and BD is acting as a stop layer. This “etch stop” process may be performed, for example, using known CF4/O2 plasma etch processes or by the methods and apparatus discussed in, for instance, U.S. Pat. No. 5,877,090 entitled “Selective plasma etching of silicon nitride in presence of silicon or silicon oxides using mixture of NH3 or SF6 and HBr and N2” of Padmapani, et al. Optionally, wet chemical etching incorporating hot phosphoric acid, H3PO4, for selectively etching SiN, or HF or buffered oxide etchant (“BOE”) for selectively etching BD/SiO2 may also be used.
The process sequence listed in TABLE 67 illustrates a process wherein the maximum thickness of a corresponding layer triplet is deposited, and then controlled etching thins, but may not fully remove, certain layers within the triplet.
TABLE 68 lists a sequence of masking operations and specific filter(s) that are protected by each mask at each sequence step in the processes described in TABLES 66 and 67. In the exemplary CMY design, for instance, the cyan filter is always protected by the mask, the yellow filter is never protected by the mask and the magenta filter is protected during alternating masking operations.
For example, trapezoidal optical element 10210 of
It may be seen in
An exemplary definition of detector pixel geometry is summarized in TABLE 71 (dimensions in meters unless noted):
In a step 11860, input parameters and design goals, such as electromagnetic energy incidence angle, process run time and design constraints are specified. An exemplary set of input parameters and design goals is summarized in TABLE 72:
In a step 11865, an initial guess for the metalens geometry is specified. An exemplary geometry is summarized in TABLE 73:
In a step 11870, an optimizer routine modifies the metalens design in order to increase power delivered through the detector pixel to the photosensitive region. In a step 11875, performance of the modified metalens design is evaluated to determine whether the design goals, specified in step 11860, have been met. In a decision 11880, a determination is made as to whether or not the design goals have been met. If the answer to decision 11880 is YES, design goals have been met, then design process 11845 is ended in a step 11883. If the answer to decision 11880 is NO, design goals have not been met, then steps 11870 and 11875 are repeated. An exemplary evaluation of coupled power (in arbitrary units) as a function of chief ray angle (in degrees) is shown in
Another approach for providing CRA correction integrated within a detector pixel structure as a buried optical element is the use of a subwavelength prism grating (SPG). In the context of the present disclosure, a subwavelength grating is understood to be a grating with a grating period that is smaller than a wavelength, i.e.,
where Δ is a grating period, 2 is a design wavelength and n1 is a refractive index of the material forming the subwavelength grating. A subwavelength grating generally transmits only the zero-th diffraction order, while all other orders are effectively evanescent. By modifying the duty cycle (defined as W/Δ, where W is a width of a pillar within the grating) across the subwavelength grating, effective medium theory may be used to design a subwavelength grating that functions as a lens, a prism, a polarizer, etc. For purposes of CRA correction in a detector pixel, a subwavelength prism grating (SPG) may be particularly advantageous.
In the example shown in
θin=incident angle of electromagnetic energy at a first surface of the prism;
θout=output angle of electromagnetic energy at an imaginary SPG surface;
θ′out=output angle of electromagnetic energy exiting a second surface of the prism;
θA=apex angle of prism;
n1=refractive index of prism material;
n0=refractive index of the support material;
α=a first intermediate angle; and
β=a second intermediate angle.
Continuing to refer to
For example, in order to achieve an output angle of θout=16° given an input angle θin=35° using a prism formed of a material having a refractive index n1=2.0, the apex angle of the prism should be θA=18.3°, according to Eq. (16). That is, given these values for the various parameters, conventional prism 11960 would correct propagation of incident electromagnetic energy with input angle θin=35° such that the output angle from the prism would be θout=16°, which is within a cone of acceptance for a photosensitive region of, for instance, a CMOS detector. Given the apex angle of conventional prism 11960 required to achieve the necessary CRA correction, the prism height of conventional prism 11960 for a given prism base dimension is readily calculated by geometry.
Turning now to
H=(2.2 μm)tan(θA)=(2.2 μm)tan(18.3°)=0.68 μm Eq. (17)
Referring to
where
The calculated values for pillar widths Wi for values of i=1, 2, 3, . . . , 19 in the present example are summarized in TABLE 74. That is, the above list of relevant SPG parameters and TABLE 74 summarize the results of step 11948 in design process 11940 as shown in
While the calculated values above represent characteristics of an ideal SPG, it is recognized that some of the pillar widths Wi are too small to be actually manufacturable using currently available manufacturing techniques. In consideration of the manufacturability of the final design of the SPG, the minimum pillar width is set to 65 nm and the pillar height PH is set to 650 nm, since this height value represents an upper limit for currently available manufacturing processes given that the maximum aspect ratio (i.e., the ratio of the pillar height PH to the pillar width PW) should be about ten. The number of pillars N and the period are accordingly modified to simplify the SPG structure while accommodating the manufacturing constraints. The imposition of these limitations is included in step 11950 of design process 11940 shown in
The initial SPG structure design is then modified in accordance with the manufacturing constraints in a step 11952 of design process 11940.
TABLE 75 summarizes the parameters used in the simplification process. These parameters are then used to determine appropriate pillar widths in the manufacturable SPG.
The modified pillar widths in the manufacturable SPG are summarized in TABLE 76.
Step 11954 of design process 11940 involves the evaluation of the performance of the manufacturable SPG design (e.g., as summarized in TABLES 75 and 76).
While
Although each of the aforedescribed embodiments have been described in relation to a particular set of CMOS compatible processes in association with the formation of a CMOS detector pixel array and integrally formed elements including color filters, it may be readily evident to those skilled in the art that the aforedescribed methods, systems and elements may be readily adapted by substitution to other types of semiconductor processing such as BICMOS processing, GaAs processing and CCD processing. Similarly, it may be readily understood that the aforedescribed methods, systems and elements may be readily adapted to emitters of electromagnetic energy in place of detectors and still remain within the spirit and scope of the present disclosure. Furthermore, suitable equivalents may be used in place of or in addition to the various components, the function and use of such substitute or additional components being held to be familiar to those skilled in the art and are therefore regarded as falling within the scope of the present disclosure.
A surface formed of two media having different refractive indices partially reflects electromagnetic energy incident thereon. For example, a surface formed of two adjoining optical elements (e.g., within a layered optical element) having different refractive indices will partially reflect electromagnetic energy incident on the surface.
The degree to which electromagnetic energy is reflected by a surface formed of two media is proportional to the reflectance (“R”) of the surface. Reflectance is defined by Eq. (19):
where
In imaging systems, reflection of electromagnetic energy at a surface is often undesirable. For example, reflection of electromagnetic energy by two or more surfaces in an imaging system may create undesirable ghost images at a detector of the imaging system. Reflections also decrease the amount of electromagnetic energy that reaches the detector. In order to prevent undesired reflection of electromagnetic energy in the imaging systems discussed above, an anti-reflection layer may be fabricated at or on any of the surfaces of the optics (e.g., layered optical elements) in the aforedescribed arrayed imaging systems. For example, in
An anti-reflection layer may be fabricated at or on a surface of an optical element by applying a layer of an index matched material at or on the surface. The index matched material ideally (considering normally incident monochromatic electromagnetic energy) has a refractive index (“nmatched”) equal to a refractive index, which is defined by Eq. (20):
n
matched=√{square root over (n1n2)}, Eq. (20)
where n1 is the refractive index of the first medium forming the surface, and n2 is the refractive index of the second medium forming the surface. For example, if n1=1.37 and n2=1.60, then nmatched would be equal to 1.48, and an anti-reflection layer disposed at the surface would ideally have a refractive index of 1.48.
The layer of index matched material ideally has a thickness of one quarter of the wavelength of the electromagnetic energy of interest in the index matched material. Such thickness is desirable because it results in destructive interference of the electromagnetic energy of interest reflecting from the surfaces of the matched material and thereby prevents reflection at the surface. The wavelength of the electromagnetic energy in the matched material (“λmatched”) is defined by Eq. (21) as follows:
where λ0 is the wavelength of the electromagnetic energy in a vacuum. For example, assume the electromagnetic energy of interest is green light, which has a wavelength of 550 nm in a vacuum, and the refractive index of the matched material is 1.26. The green light then has a wavelength of 437 nm in the matched material, and the matched material ideally has a thickness of one quarter of this wavelength, or 109 nm
One possible matched material is a low-temperature-deposited silicon dioxide. In such case, a vapor or plasma silicon dioxide deposition system may be used to apply the matched material to a surface. Silicon dioxide may advantageously protect the surface from mechanical and/or chemical external influences in addition to serving as an anti-reflection layer.
Another possible matched material is a polymeric material. Such material may be spin coated on a surface or may be applied to a surface of an optic (e.g., a layered optical element) by molding using a fabrication master. For example, a layer of matched material may be applied to a surface of a layered optical element using the same fabrication master used to form a certain layer of the layered optical element—the fabrication master is translated the proper distance (e.g., one quarter of the wavelength of interest in the matched material) along its Z-axis (i.e., along the optical axis) to form the layer of matched material on the layered optical element. Such process is more easily applied to an optical element having a relatively low radius of curvature as compared to an optical element having a relatively high radius of curvature because curvature of an optical element results in the layer of matched material applied by the process having an uneven thickness. Alternately, a fabrication master other than the one used to form the certain layer of the layered optical element may be used to apply the layer of matched material to the layered optical element. Such a fabrication master has the necessary translation along its Z-axis (i.e., one quarter of the wavelength of interest in the matched material along the optical axis) designed into its surface features or its external alignment features.
An example of using a matched material as an anti-reflection layer is shown in
An anti-reflection layer may also be fabricated from a plurality of sub-layers, wherein the plurality of sub-layers collectively have an effective refractive index (“neff”) ideally equal to nmatched as defined by Eq. (20). Additionally, an anti-reflection layer may be advantageously fabricated from two sub-layers using the same materials used to fabricate two optical elements forming the surfaces. In
TABLE 77 summarizes an exemplary design of a two layer anti-reflection layer disposed at a surface defined by a two layers (entitled “LL1” and “LL2” below) of a layered optical element such as shown in breakout 12010(2) of
An anti-reflection layer may formed on or at a surface of an optical element by fabricating (e.g., by molding or etching) subwavelength features on the surface of the optical element. Such subwavelength features for example include recesses in the surface of the optical element wherein at least one dimension (e.g., length, width, or depth) of the recesses is smaller than the wavelength of the electromagnetic energy of interest in the anti-reflection layer. The recesses are for example filled with a filler material that has a refractive index different from that of the material used to fabricate the optical element. Such filler material may be a material, such as a polymer, that is used to form another optical element directly on the existing optic. For example, if subwavelength features are formed on a first layered optical element and a second layered optical element is to be applied directly to the first layered optical element, the filler material would be the material used to fabricate the second layered optical element. Alternately, the filler material may be air (or another gas in the environment of the optical element) if the surface of the optical element does not contact another optical element. Either way, the filler material (e.g., a polymer or air) has a different refractive index than that of the material used to fabricate the optical element. Accordingly, the subwavelength features, the filler material, and the unmodified surface of the optical element (the portion of the surface of the optical element not including subwavelength features) form an effective medium layer having an effective refractive index neff. Such effective medium layer functions as an anti-reflection layer if neff is about equal to nmatched as defined in Eq. (20). One relationship for defining an effective refractive index from a combination of two different materials is given by the Bruggeman equation, given by Eq. (22):
where, p is the volume fraction of a first constituent material A, ∈A is the complex dielectric function of first constituent material A, ∈B is the complex dielectric function of second constituent material B, and ∈e is the resultant complex dielectric function of the effective medium. The complex dielectric function, ∈, is related to the refractive index, n, and the absorption constant, k, by Eq. (23):
∈=(n+ik)2 Eq. (23)
The effective refractive index is a function of the subwavelength features' sizes and geometries as well as a fill factor of the surface of the optical element, where the fill factor is defined as the ratio of the portion of the surface that is unmodified (i.e., not having subwavelength features) to the entire surface. If the subwavelength features are small enough in relation to the wavelength of electromagnetic energy of interest, and are sufficiently evenly distributed along the surface of the optical element, the effective refractive index of the effective medium layer is approximately solely a function of the refractive indices of the filler material and the material used to fabricate the optical element
The subwavelength features may be periodic (e.g., a sine wave) or non-periodic (e.g., random). The subwavelength features may be parallel or non-parallel. Parallel subwavelength features may result in polarization state selection of electromagnetic energy passing through the effective medium layer; such polarization may or may not be desirable depending on the application.
As stated above, it is important that subwavelength features have at least one dimension that is smaller than a wavelength of electromagnetic energy of interest in the effective medium layer. In one embodiment, the subwavelength features have at least one dimension that is smaller than or equal to size which is defined by Eq. (24):
where λ0 is the wavelength of the electromagnetic energy of interest in a vacuum and neff is the effective refractive index of the effective medium layer.
A subwavelength feature may be molded in a surface of an optical element using a fabrication master having a surface defining a negative of the subwavelength features; such negative is an inverse of the subwavelength features wherein raised surfaces on the negative correspond to recesses of the subwavelength features formed on the optical element. For example,
Negative 12076 is too small to be visible on surface 12072 by the naked eye. In
If an additional optical element is to be formed proximate to surface 12086, the subwavelength features molded in surface 12086 are filled with a filler material having a different refractive index than that used to fabricate an optical element from moldable material 12078. The filler material may be a material used to fabricate the additional optical element on surface 12086; otherwise, the filler material is air or another gas of the environment of surface 12086. The subwavelength features formed in moldable material 12078 when filled with a second material, collectively form an effective medium layer that operates as an anti-reflection layer.
Subsection 12110 includes an array of four unit cells that are repeated across the surface of machined surface 6410 of
H=√{square root over (3)}W Eq. (25)
The negative defined by machined surface 6410 may be considered to have a period equal to W. It is important that at least one feature or dimension of the unit cell (e.g., Was shown in
As discussed above, an effective medium layer functioning as an anti-reflection layer may be formed on a surface of an optical element by molding subwavelength features in the surface of the optical element, and such subwavelength features may be molded using a fabrication master having a surface including a negative of the subwavelength features. Such negative may be formed on the fabrication master's surface using a variety of processes. Examples of such processes are discussed immediately hereafter.
A negative may be formed on a surface of a fabrication master by using a fly-cutting process, such as that discussed above with respect to
Another method of forming a negative on a surface of a fabrication master is by using a specialized diamond tool, such as tool tip 6104 shown in
Yet another method of forming a negative on a surface of a fabrication master is by using laser ablation. Laser ablation may be used to form a periodic or non-periodic negative. High power pulsed excimer lasers, such as KrF lasers, can be mode-locked to produce pulse energies of several micro-Joules or Q-switched to produced pulse energies exceeding 1 Joule at 248 nm to perform such laser ablation on a surface of a fabrication master. For example, surface relief structures of a negative having feature sizes smaller than 300 nm can be created using excimer laser ablation using a KrF laser as follows. The laser is focused to a diffraction-limited spot using CaF2 optics and rastered across the surface of the fabrication master. The laser pulse energy or number of pulses may be adjusted to ablate a feature (e.g., a pit) to the desired depth. The feature spacing is adjusted to achieve a fill factor corresponding to the negative design. Other lasers that may be suitable for laser oblation include an ArF laser and a CO2 laser.
A negative may be further formed on a surface of a fabrication master using an etching process. In such process, an etchant is used to etch pits in the surface of the fabrication master. Pits are associated with the grain size and configuration of the material of the fabrication master's surface; such grain size and configuration are a function of the material of the fabrication master's surface (e.g., a metal alloy), the temperature of the material, and the mechanical processing of the material. Lattice planes and defects (e.g., grain boundaries and crystallographic dislocations) of the material will affect the rate at which pits are formed. The grain boundaries and dislocations are often randomly oriented or have low coherence; accordingly, spatial distributions and sizes of pits may also be random. The sizes of the pits depend upon such characteristics as the etch chemistry, the temperature of the fabrication master and etchant, the grain size, and the duration of the etching process. Possible etchants include caustic substances such as salts and acids. As an example, consider a fabrication master having a brass surface. An etchant consisting of a solution of sodium dichromate dihydrate and sulfuric acid may be used to etch the brass surface resulting in pits having shapes including cubic and tetragonal shapes.
If an anti-reflection layer is formed on or at a surface of an optical element, the anti-reflection layer may need to be thicker near the edges of the optical element than at the center of the optical element. Such requirement is due to an increase in angle of incidence of electromagnetic energy on the surface of the optical element near its edge due to curvature of the optical element.
Optics that are formed by molding, such as single optical elements fabricated on a common base or layered optical elements (e.g., layered optical elements 24 of
In order to avoid aberrations cause by optical element shrinkage, a mold used to form an optical element may be made larger than a desired size of the optical element in order to compensate for shrinking of the optical element during its curing.
Shrinkage at sharply curved surfaces of an optical element, such as corners 12266 and 12268 of
Detector pixels, such as detector pixel 78 of
However, in certain embodiments herein, detector pixels may also be configured for “backside illumination”, and the imaging systems discussed above may be configured for use with such backside illuminated detector pixels. In backside illuminated detector pixels, electromagnetic energy enters the backside of the detector pixel and directly impinges on the photosensitive region. Accordingly, the electromagnetic energy advantageously does not travel through the series of layers to reach the photosensitive region. The metal interconnects within the layers can undesirably inhibit electromagnetic energy from reaching the photosensitive region. Imaging systems, such as those discussed above, may be applied to the backside of back illuminated detector pixels.
A backside of a detector pixel is generally covered by a thick silicon wafer during manufacturing. Such silicon wafer must be thinned, such as by etching or grinding the wafer, in order for electromagnetic energy to be able to penetrate the wafer and reach a photosensitive region.
Buried oxide layer 12304, which is fabricated of silicon dioxide, may help prevent damage to region 12306 during removal of excess silicon layer 12294. It is often difficult to precisely control etching and grinding of silicon; therefore, there is a danger that region 12306 will be damaged due to the inability to precisely stop etching or grinding of silicon wafer 12308 if region 12306 is not separated from excess silicon layer 12294. Buried oxide layer 12304 provides such separation and thereby helps prevent accidental removal of region 12306 during removal of excess silicon layer 12294. Buried oxide layer 12304 may also be advantageously used for the formation of buried optical elements, as described below, proximate to surface 12300 of detector pixel 12290.
Layers 12332 and/or 12334 may be modified to form one or more filters, such as a color filter and/or an infrared cutoff filter. In one example, layer 12334 is modified into a layered structure 12338 that acts as a color filter and/or into an infrared cutoff filter. Layers 12332 and/or 12334 may also be modified such that they help direct electromagnetic energy 18 onto photosensitive region 12336. For example, layer 12334 may be formed into a metalens that directs electromagnetic energy into photosensitive region 12336. An example of a metalens is a three-pillar metalens 12340 shown in
Metalens 12422 for directing electromagnetic energy 18 onto photosensitive region 12402 is disposed proximate to anti-reflection layer 12420. Metalens 12422 is fabricated of silicon dioxide with the exception of large pillar 12410 and small pillars 12412, which are each fabricated of silicon nitride. Large pillar 12410 has a width 12416 of 1 micron, and small pillars 12412 have a width 12428 of 120 nm Large pillar 12416 and small pillars 12412 have a depth 12418 of 300 nm Small pillars 12412 are separated from large pillar 12410 by a distance of 90 nm Detector pixel 12400 including metalens 12422 may have a quantum efficiency that is approximately 33% greater than that of an embodiment of detector pixel 12400 not including metalens 12422. Contours 12426 represent electromagnetic energy density in detector pixel 12400. As can be observed from
Anti-reflection layer 12420 and metalens 12422 may be fabricated into or on detector pixel 12400 after removing an excess silicon layer from the backside of detector pixel 12400. For example, if detector pixel 12400 is an embodiment of detector pixel 12330 of
The changes described above, and others, may be made in the imaging systems described herein without departing from the scope hereof. It should thus be noted that the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall there between.
This application is a division of U.S. application Ser. No. 12/297,608, filed Oct. 17, 2008 which is a 371 of international application no. PCT/US2007/009347 filed Apr. 17, 2007 which claims priority to U.S. provisional application Ser. No. 60/792,444, filed Apr. 17, 2006, entitled IMAGING SYSTEM WITH NON-HOMOGENEOUS WAVEFRONT CODING OPTICS; U.S. provisional application Ser. No. 60/802,047, filed May 18, 2006, entitled IMPROVED WAFER-SCALE MINIATURE CAMERA SYSTEM; U.S. provisional application Ser. No. 60/814,120, filed Jun. 16, 2006, entitled IMPROVED WAFER-SCALE MINIATURE CAMERA SYSTEM; U.S. provisional application Ser. No. 60/832,677, filed Jul. 21, 2006, entitled IMPROVED WAFER-SCALE MINIATURE CAMERA SYSTEM; U.S. provisional application Ser. No. 60/850,678, filed Oct. 10, 2006, entitled FABRICATION OF A PLURALITY OF OPTICAL ELEMENTS ON A SUBSTRATE; U.S. provisional application Ser. No. 60/865,736, filed Nov. 14, 2006, entitled FABRICATION OF A PLURALITY OF OPTICAL ELEMENTS ON A SUBSTRATE; U.S. provisional application Ser. No. 60/871,920, filed Dec. 26, 2006, entitled FABRICATION OF A PLURALITY OF OPTICAL ELEMENTS ON A SUBSTRATE; U.S. provisional application Ser. No. 60/871,917, filed Dec. 26, 2006, entitled FABRICATION OF A PLURALITY OF OPTICAL ELEMENTS ON A SUBSTRATE; U.S. provisional application Ser. No. 60/836,739, filed Aug. 10, 2006, entitled ELECTROMAGNETIC ENERGY DETECTION SYSTEM INCLUDING BURIED OPTICS; U.S. provisional application Ser. No. 60/839,833, filed Aug. 24, 2006, entitled ELECTROMAGNETIC ENERGY DETECTION SYSTEM INCLUDING BURIED OPTICS; U.S. provisional application Ser. No. 60/840,656, filed Aug. 28, 2006, entitled ELECTROMAGNETIC ENERGY DETECTION SYSTEM INCLUDING BURIED OPTICS; and U.S. provisional application Ser. No. 60/850,429, filed Oct. 10, 2006, entitled ELECTROMAGNETIC ENERGY DETECTION SYSTEM INCLUDING BURIED OPTICS. All of the aforementioned applications are incorporated herein by reference in their entireties.
| Number | Date | Country | |
|---|---|---|---|
| 60792444 | Apr 2006 | US | |
| 60802047 | May 2006 | US | |
| 60814120 | Jun 2006 | US | |
| 60832677 | Jul 2006 | US | |
| 60836739 | Aug 2006 | US | |
| 60839833 | Aug 2006 | US | |
| 60840656 | Aug 2006 | US | |
| 60850678 | Oct 2006 | US | |
| 60850429 | Oct 2006 | US | |
| 60865736 | Nov 2006 | US | |
| 60871920 | Dec 2006 | US | |
| 60871917 | Dec 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12297608 | Jan 2010 | US |
| Child | 14093802 | US |
