Patent Application
20220334450
Electromagnetic radiation often is in the form of beams. To make use of such beams, they often must be directed, or steered, to where it is needed for an application. For example, this might be done for cutting and drilling, for exposing a target and measuring one or more of its properties, for free-space communications, or for Light Detection And Ranging (LIDAR). In some examples, such LIDAR systems can be used to measure the environment and provide information to other systems. In other examples, this information can be displayed for current use, and/or stored for later use.
Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details can be made and are considered included herein. Accordingly, the following embodiments are set forth without any loss of generality to, and without imposing limitations upon, any claims set forth. It is also to be understood that the terminology used herein is for describing particular embodiments only, and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Also, the same reference numerals in appearing in different drawings represent the same element. Numbers provided in flow charts and processes are provided for clarity in illustrating steps and operations and do not necessarily indicate a particular order or sequence.
Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of layouts, distances, network examples, etc., to provide a thorough understanding of various embodiments. One skilled in the relevant art will recognize, however, that such detailed embodiments do not limit the overall concepts articulated herein, but are merely representative thereof. One skilled in the relevant art will also recognize that the technology can be practiced without one or more of the specific details, or with other methods, components, layouts, etc. In other instances, well-known structures, materials, or operations may not be shown or described in detail to avoid obscuring aspects of the disclosure.
In this application, “comprises,” “comprising,” “containing” and “having” and the like can have the meaning ascribed to them in U.S. Patent law and can mean “includes,” “including,” and the like, and are generally interpreted to be open ended terms. The terms “consisting of” or “consists of” are closed terms, and include only the components, structures, steps, or the like specifically listed in conjunction with such terms, as well as that which is in accordance with U.S. Patent law. “Consisting essentially of” or “consists essentially of” have the meaning generally ascribed to them by U.S. Patent law. In particular, such terms are generally closed terms, with the exception of allowing inclusion of additional items, materials, components, steps, or elements, that do not materially affect the basic and novel characteristics or function of the item(s) used in connection therewith. For example, trace elements present in a composition, but not affecting the compositions nature or characteristics would be permissible if present under the “consisting essentially of” language, even though not expressly recited in a list of items following such terminology. When using an open-ended term in this written description, like “comprising” or “including,” it is understood that direct support should be afforded also to “consisting essentially of” language as well as “consisting of” language as if stated explicitly and vice versa.
As used herein, the term “substantially” refers to the complete or nearly complete extent or degree of an action, characteristic, property, state, structure, item, or result. For example, an object that is “substantially” enclosed would mean that the object is either completely enclosed or nearly completely enclosed. The exact allowable degree of deviation from absolute completeness may in some cases depend on the specific context. However, generally speaking the nearness of completion will be so as to have the same overall result as if absolute and total completion were obtained. The use of “substantially” is equally applicable when used in a negative connotation to refer to the complete or near complete lack of an action, characteristic, property, state, structure, item, or result. For example, a composition that is “substantially free of” particles would either completely lack particles, or so nearly completely lack particles that the effect would be the same as if it completely lacked particles. In other words, a composition that is “substantially free of” an ingredient or element may still actually contain such item as long as there is no measurable effect thereof.
As used herein, the term “about” is used to provide flexibility to a given term, metric, value, range endpoint, or the like. The degree of flexibility for a particular variable can be readily determined by one skilled in the art. However, unless otherwise expressed, the term “about” generally provides flexibility of less than 1%, and in some cases less than 0.01%. It is to be understood that, even when the term “about” is used in the present specification in connection with a specific numerical value, support for the exact numerical value recited apart from the “about” terminology is also provided.
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary.
Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 to about 5” should be interpreted to include not only the explicitly recited values of about 1 to about 5, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc., as well as 1, 1.5, 2, 2.3, 3, 3.8, 4, 4.6, 5, and 5.1 individually.
This same principle applies to ranges reciting only one numerical value as a minimum or a maximum. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
Reference throughout this specification to “an example” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one embodiment. Thus, appearances of phrases including “an example” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example or embodiment.
The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Similarly, if a method is described herein as comprising a series of steps, the order of such steps as presented herein is not necessarily the only order in which such steps may be performed, and certain of the stated steps may possibly be omitted and/or certain other steps not described herein may possibly be added to the method.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.
As used herein, comparative terms such as “increased,” “decreased,” “better,” “worse,” “higher,” “lower,” “enhanced,” and the like refer to a property of a device, component, or activity that is measurably different from other devices, components, or activities in a surrounding or adjacent area, in a single device or in multiple comparable devices, in a group or class, in multiple groups or classes, or as compared to the known state of the art. For example, a data region that has an “increased” risk of corruption can refer to a region of a memory device which is more likely to have write errors to it than other regions in the same memory device. A number of factors can cause such increased risk, including location, fabrication process, number of program pulses applied to the region, etc.
An initial overview of embodiments is provided below, and specific embodiments are then described in further detail. This initial summary is intended to aid readers in understanding the disclosure more quickly, and is not intended to identify key or essential technological features, nor is it intended to limit the scope of the claimed subject matter.
LIDAR can be used for measuring and/or imaging scenes in three dimensions (3-D). The typical data set a LIDAR system can produce is called a point cloud and can include distance/range values as a function of position within the LIDAR device field of view (FOV). Each determination of the distance value may correspond to the measurement of the time-of-flight (TOF), that is, the time it takes for one or more photons to travel from a source, to the scene, and then reflect back to a sensor.
As with typical two-dimensional (2-D) intensity imagers, conventional LIDAR systems can sample the lateral space. One class of systems that can do this is the so-called flash LIDAR, shown in
A scene can also be sampled laterally using a scanning LIDAR, shown in
One straightforward approach to beam steering for scanning LIDAR is to use reflective galvanometers, spinning polygons/prisms, or other types of actuated sub-systems. Other approaches to scanning include the use of spatial light modulators (SLMs), which are generally composed of an array of modulating elements, herein referred to as pixels. Such SLMs can include digital micromirror devices (DMDs), liquid crystal on silicon (LCoS), and others. Yet another approach is photonic integrated circuit (PIC)-based optical phased arrays (OPAs). The latter class of systems has no moving parts, and is often made in silicon and/or uses electromagnetic radiation with wavelengths around 1550 nm.
This disclosure provides systems, devices, and methods for practical, efficient beam steering that incorporate SLMs and that have significant advantages over all previously mentioned methods. Such advantages can include:
The provided systems, devices, and methods can be used with a variety of light sources. Non-limiting examples can include semiconductor lasers, solid-state lasers, fiber lasers, dye lasers, integrated photonics lasers, light-emitting diodes, thermal sources, or others, including any combination thereof. Non-limiting examples of the source operation mode can include pulsed, continuous wave, frequency-modulated, or others, including any combination thereof. Non-limiting examples of pulsed operation can use gain-switching, Q-switching, mode-locking, external-cavity modulation. In one example, the source can incorporate stabilization in order to narrow the laser linewidth, prevent mode-hopping, increase the coherence length, improve the transverse beam quality, or others, including any combination thereof. Non-limiting examples of stabilization can include optical filtering, temperature stability, optical feedback, or others, including any combination thereof.
Such devices can be used in reflection or transmission.
Solid-state SLMs (SS-SLMs) can be made using silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon-germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), aluminum arsenide (AlAs), aluminum gallium arsenide (AlxGayAs), indium gallium arsenide (InxGayAs), indium phosphide (InP), aluminum gallium indium nitride (AlGaInN), aluminum gallium indium phosphide (AlGaInP), gallium nitride (GaN), mercury cadmium telluride (HgCdTe), other III-V materials or the like, or combinations thereof.
A number of modulation techniques can be used to create the modulating region in SS-SLM pixels. In one example, quantum confining structures are used. In such structures, the quantum-confined Stark effect (QCSE) can be used to modulate the amplitude and phase response. This effect emerges when carriers (e.g. electrons, holes, excitons) are confined in the modulating region such that quantum effects are significant and change the band structure as a function of applied voltage, thereby changing the absorption and phase response of the modulating region. The modulating regions can contain one or more quantum confining structures, which may include one or more quantum wells, quantum wires, quantum dots, or combinations thereof, and can be arranged with uniform or non-uniform spacing, and can be periodically or aperiodicially placed. The quantum structures can be positioned such that at least two structures are in electronic communication (i.e. coupled), and/or such that at least one structure is not in electronic communication with other structures. For example, quantum structures in electronic communication can enable control of the overlap of electron and/or hole wavefunctions, thereby allowing better control of the modulation effects and which may include larger magnitude modulation effects. In another example, the modulating region can contain one or more superlattice structures. As an example, such structures can be created by varying doping type, doping concentration, material type, or combinations thereof. The absorption and phase spectra can be modulated, for example, through the Wannier-Stark effect by applying a voltage. As well, modulation can be accomplished in semiconductors by applying an electric field across the device, changing the carrier density through carrier injection, depletion and/or excitation (e.g. optically, electrically), inducing thermo-optic effects applied to the modulating region, or combinations thereof. Two or more modulation techniques can also be used simultaneously. Non-limiting examples can include a combination of carrier depletion and QCSE, or a combination of thermo-optic and superlattice biasing.
The actuation of SLM modulation can be done with a voltage, a current, or by exposure to electromagnetic radiation such as light. When modulating using voltage, the voltage magnitude can have a lower limit of a voltage capable of generating a detectable modulation in a signal, and otherwise can, in some examples, be less than or equal to 1.8 V, less than or equal to 3.3 V, less than or equal to 5 V, less than or equal to 10 V, less than or equal to 20 V, or less than or equal to 100 V. When modulating using a current, the current magnitude can have a lower limit of a current capable of generating a detectable modulation in a signal, and otherwise be less than or equal to 1 mA, less than or equal to 10 mA, less than or equal to 100 mA, less than or equal to 1 A, or less than or equal to 5 A or more.
In some cases, the single-pass amplitude and phase response of the SLM pixels can be small compared to what an application requires. In that case, resonance effects can be used to achieve a stronger effect. This can be accomplished by placing the modulating region in a resonator, which can be a symmetric Fabry-Perot resonator, an asymmetric Fabry-Perot resonator, a Gire-Tournois resonator, or any other suitable resonant structure capable of accepting a modulating region.
Reflecting regions, which can be partially reflecting with reflectivities less than or equal to 95%, or fully reflecting with reflectivities greater than 95%, can be positioned to reflect light and are referred to herein as a resonator structure. A reflecting region can include a variety of materials and material combinations. For example, a reflecting region can include, without limitation, metals, transparent conducting films (TCFs), conductive polymers, interference stacks, and the like, including combinations thereof. Non-limiting examples of metal reflecting region materials can include aluminium, copper, gold, silver, and the like, including metal alloys and combinations thereof. Non-limiting examples of TCFs can include transparent conductive oxides (TCOs) such as metal oxides doped with indium (e.g. indium tin oxide), fluorine, aluminum, and the like, including dopant combinations thereof. Non-limiting examples of metal oxides can include oxides of tin, cadmium, zinc, or combinations thereof. Non-limiting examples of conductive polymers can include polyacetylene, polyaniline, polypyrrole, polythiophene derivatives, or combinations thereof. The reflecting regions can also include interference stacks, which can be composed of layers that are about a quarter-wave in thickness, and can be made of silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon-germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), aluminum arsenide (AlAs), aluminum gallium arsenide (AlxGayAs), indium gallium arsenide (InxGayAs), indium phosphide (InP), aluminum gallium indium nitride (AlGaInN), aluminum gallium indium phosphide (AlGaInP), gallium nitride (GaN), mercury cadmium telluride (HgCdTe), other III-V materials or the like, or combinations thereof.
To adjust the achievable range of beam angles emerging from an SLM, for example an SS-SLM, in one example structures can be placed on the exiting face of the device. Such structures could include scatterers, grating structures, other diffractive optic structures, or microlens arrays. In the last case, the microlens array can have a pitch that is substantially equal to a integer multiple of the SLM pixel pitch, including a pitch that is equal to the SLM pixel pitch. The microlens array can be bonded to or fabricated on the SLM, and can have numerical apertures as large as 0.87, as large at 0.72, as large as 0.66, or as large as 0.29.
Achieving large angular scanning range and high angular resolution allows for larger, higher resolution imaging. The latter is enabled by keeping the beam divergence angle smaller than the angular resolution. A metric for these performance parameters can be the ratio of the SLM pixel-containing region area to individual SLM pixel area. In some examples, this ratio can be greater than 25,000,000, greater than 10,000,000, greater than 4,000,000, or greater than 2,000,000. In some examples, the angular scanning ranges can be greater than about −4° to about +4° with beam widths at 200 m away of less than about 15 mm or less than about 11 mm. In other examples, the angular scanning range can be about −12° to about +12° with beam widths at 200 m away of less than about 15 mm or less than about 11 mm.
In another example, to application of voltages to actuate modulation, contacts can be used. A contact can be one continuous plane substantially covering the SLM pixel-containing region of the device, or may be patterned. One contact can be patterned such that the optical fill factor is greater than 50%, greater than 70%, or greater than 90%. As part of the patterning, one or more etch processes can be used. A contact can be placed between the modulating region and the substrate, or between the modulating region and the device outer surface. A contact can incorporate, without limitation, metals, doped semiconductors, transparent conducting films (TCFs), conductive polymers, and the like, including combinations thereof. Non-limiting examples of metal contact region materials can include aluminium, copper, gold, silver, and others, including metal alloys and combinations thereof. Non-limiting examples of semi-conductors can include n-doped semiconductors, and/or p-doped semiconductors, where said semiconductors can include silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon-germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), aluminum arsenide (AlAs), aluminum gallium arsenide (AlxGayAs), indium gallium arsenide (InxGayAs), indium phosphide (InP), aluminum gallium indium nitride (AlGaInN), aluminum gallium indium phosphide (AlGaInP), gallium nitride (GaN), mercury cadmium telluride (HgCdTe), other III-V materials or the like, or combinations thereof. Non-limiting examples of TCFs can include transparent conductive oxides (TCOs) such as metal oxides doped with indium (e.g. indium tin oxide), fluorine, aluminum, and the like, including dopant combinations thereof. Non-limiting examples of metal oxides can include oxides of tin, cadmium, zinc, or combinations thereof. Non-limiting examples of conductive polymers can include polyacetylene, polyaniline, polypyrrole, polythiophene derivatives, or combinations thereof.
SS-SLMs can switch their modulation values faster than other types of SLMs. For example, the single-pixel switching speed of an SS-SLM can be shorter than 100 ns, shorter than 500 ns, shorter than 1 μs, shorter than 10 μs, or shorter than 100 μs. As well, the switching speed of the entire SS-SLM array can be faster than 10 kHz, 50 kHz, 100 kHz, 500 kHz, or even faster than 1 MHz.
The performance of a SLM can be improved by combining it with one or more refractive and/or diffractive optical elements (DOEs). DOEs can be binary using two or more discrete levels, provide a piecewise-continuously varying surface, be holographic, replicated, ruled, or other. One or more of the DOEs may also be directly fabricated on the SLM device. For example, this can be accomplished on an SS-SLM through masking and etching the surface. Such elements can be used to shape the beam prior to steering it with the SLM, and can, for example, reduce the average SLM power requirements and/or simplify the SLM control signals. In one example, one or more lenses are placed before the SLM to reduce the average voltages imposed on and power consumed by the SLM.
As well, refractive optics or DOEs can be used to increase functionality. In one example, the optical elements lead to the generation two or more simultaneous beams. This can be advantageous when, for example, scanning coverage over an angular FOV is required. For example, with two beams, the angular range needed to scan across the FOV can be reduced by about a factor of two. For another example, with three beams, it can be reduced by about a factor of three. In this way, the coverage of the FOV, the angular tuning range requirements, and the power per beam can be traded off to improve system performance for given application. For example, in a LIDAR application, a laser source can produce sufficient optical power such that 2-10 beams can be supported with sufficient signal-to-noise ratio (SNR) for the application. In some configurations, multiple or even all beams can be emitted along a common plane. In other configurations, one or more groups of two or more beams can be emitted along one or more common planes.
An example is shown in
In cases where the optical response to the steered beam light is also received and detected, for example as with a LIDAR application, and there are multiple beams being simultaneously emitted, a system can be configured to detect received light, including determining from which beam the light returned. Such a system can incorporate a number of detectors equal to between one and the number of beams emitted, although more detectors can be used to improve performance. This allows tradeoffs to keep the number of detectors low, and thereby allows tradeoffs in system design between performance and cost. An example is shown in
For example, consider a beam steering system, which can be incorporated into a LIDAR system, having a SLM designed to emit three beams simultaneously. Reflections of any two such beams will in general not likely arrive at the device simultaneously. In the instance that it does, the light will interfere and substantially all go back to the laser source only. More commonly, light will arrive from only one beam at a given time. In that case, that light will go back through the SLM and DOE, and be split again into multiple beams. By placing detectors properly, the split received beam can be detected and its origins deduced by the relative signal from each detector. As well, each detector can individually measure the arrival time, and such multiple measurements can be used to improve the arrival time measurement accuracy and/or precision, for example, by averaging multiple measurements. Furthermore, in some cases, this can be determined by looking at the relative detector signal powers, thereby removing the need to know the absolute power in the beams initially.
In configuration 503 showing a non-center beam path received, power is only being received in the form of the first received beam 506b. As shown, the beam steering device distributes beam 506b's power into beams 507a-507e, which are then detected by detectors 508a-508e, respectively. This provides a) between one and five signals of relative magnitudes, and b) between one and five timing measurements. Similar to configuration 502, uncorrelated noise (e.g. from the measurement system) can be averaged, and the fact that the power came from beam 506b can be determined.
In configuration 504 showing a center and non-center beam path received simultaneously, power is received simultaneously from first beam 506b and second beam 506c. Here, simultaneously means that the difference in the time of flight of beams 506b and 506c is less than the beam pulse duration. As shown, the beam steering device distributes beam 506b's and beam 506c's power into beams 507a-507e, which are then detected by detectors 508a-508e, respectively. This provides a) between one and five signals of relative magnitudes, and b) between one and five timing measurements. Similar to configuration 502, uncorrelated noise (e.g. from the measurement system) can be averaged, and the fact that the power came from both beam 506b and 506c can be determined. If the difference in time of flight between beams 506b and 506c exceeds the coherence time, then the signals will add in power. As well, if the difference in the time of flight between beams 506b and 506c is shorter than the coherent time, then the signals will interfere, and the signals detected by detectors 508a-508e will show this in the form of, for example, an interference pattern. In some cases, if the coherence time is shorter than the pulse durations, the presence of interference in the signal could be used to more accurately deduce various parameters of interest, for example, the arrival times and/or the relative velocity of the two targets associated with the returned beams.
The sensors used to detect the return signals can incorporate electronic amplification or gain. In some examples, the amplification or gain can be achieved through an avalanche process, for example by using an avalanche photodiode, or a photomultication process using, for example, a photomultiplier tube. In other examples, the amplification or gain can be achieved through a photoconductive process. In yet other examples, the amplification or gain can be achieved through the supporting detection circuit and can involve one or more transistors. In some examples, the sensor elements that have amplification or gain can be operated in Geiger mode. In other examples, the sensor elements that have amplification or gain can be operated in a substantially linear mode.
The sensors can be made using a variety of materials. Non-limiting examples can include silicon (Si), silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxynitride (SiOxNy), silicon-germanium (SiGe), germanium (Ge), gallium arsenide (GaAs), aluminum arsenide (AlAs), aluminum gallium arsenide (AlxGayAs), indium gallium arsenide (InxGayAs), indium phosphide (InP), aluminum gallium indium nitride (AlGaInN), aluminum gallium indium phosphide (AlGaInP), gallium nitride (GaN), mercury cadmium telluride (HgCdTe), other III-V materials or the like, or combinations thereof. In still other additional non-limiting examples, the sensor may contain at least one of Al, As, Ga, Ge, In, N, O, P, or Si. The material can be at least partially textured. The texturing can be done with a chemical, mechanical, or laser process, for example using a black silicon process, where the textured region is at least partially within the photocarrier generation region and where the textured region leads to enhanced photoresponse.
In some examples, the sensor can be fabricated with a CMOS process. In other examples, the sensor can be a charge-coupled device (CCD).
The sensor can be operated in an incoherent detection mode. It can also operate in a coherent detection mode, for example by interfering a portion of the source electromagnetic radiation with returned electromagnetic radiation. In the latter case, the sensor can be used to detect velocity, for example, with a single measurement. Velocity can also be determined by making multiple measurements over time and calculating velocities from that. Velocity can also be determined from Doppler shifts when operating in a coherent detection regime.
Additionally, data processing performed after acquisition can be done by a processor, which can be a single processors or multiple processors, including single core processors and multi-core processors. Non-limiting examples of processors can include central processing units (CPUs), graphics processing units (GPUs), application-specific integrated circuits (ASICs), digital signal processors (DSPs), field-programmable gate arrays (FPGAs), application-specific instruction set processors (ASIPs), and the like, including various combinations thereof. In some examples, the processor can be a custom processor designed for the data processing task. Artificial intelligence techniques can also be applied to the data.
One example subsystem includes a SLM and a DOE, where the SLM and DOE can, in some examples, be monolithically fabricated, and in other examples, can be intimately attached to form a single device. In some examples, the DOE can have lateral characteristic length that are approximately equal to or greater than the wavelength of the light used, for example 1550 nm or 2000 nm, and in other examples the lateral characteristic length scales can be substantially less than the wavelength of light. In other examples, the DOE can be a 1-D or 2-D grating. In some cases, the DOE can be aligned to the SLM with tolerances larger than the SLM element pitch, for example 1.7 μm, 2.8 μm, 5.6 μm or 11.2 μm, and in other cases it can be aligned with tolerances smaller than the SLM element pitch. In some cases, the DOE is closer to the SLM, and is not in the far-field. In some cases, the distance from the SLM to DOE can be about 10 μm, 100 μm, 1 mm, 10 mm, or 100 mm. In some examples, the DOE can be on the input face of the SLM, and serve in some examples to shape the output beam and/or split the input beam into multiple beams. In other examples, the DOE can be on the exit face of the SLM, and serve to, in addition to other functions, increase the numerical aperture of the light coming from some or all of the SLM elements to values such as 0.87, 0.72, 0.66, or 0.29, which in turn can increase the power efficiency over a wider angular FOV.
Another example subsystem includes a SLM and a microlens array, where the SLM and microlens array, in some examples, can be monolithically fabricated, and in other examples, can be intimately attached to form a single device. The microlenses can be aligned with the SLM pixels, such that a microlens covers an integer number of SLM pixels. For example, each microlens could cover between 1 and 25 SLM pixels, or could cover 1-100 SLM pixels. These microlenses can have a high numerical aperture, such as 0.87, 0.72, 0.66, or 0.29, to allow for a wide angular FOV in which diffraction efficiency is high.
In one example system, a Si-based SS-SLM comprised of vertical waveguide structures can be used that can impose substantial PM. A vertical waveguide structures can be monolithically fabricated on the SS-SLM chip, for example on the input face, in order to provide multiple diffracted beams up, for example, up to third order (i.e. 7 beams) horizontally and up to first order (i.e. 3 beams) vertically, for a total of 21 beams. The SS-SLM can be 8 mm×8 mm in size, and can have waveguides such that the pitch is about 1.0 μm×1.0 μm. Microlenses can also be fabricated, for example monolithically on the output face of the chip, in order to control the diffraction efficiency. The system can be configured for 1550 nm operation and coherent detection, where a portion of the source light is retained and interfered with received light on the sensor. The system can use the same optical path for receiving in addition to transmitting. InGaAs APD point detectors can be used to detect the multiple received beams.
In another example system, a Si-based SS-SLM can be used that has substantially constant PM and some AM. The system can be designed for 2000 nm operation. The system can be operating for incoherent detection, where a portion of the source light is retained and interfered with received light on a, for example, Ge APD linear array. Light can be received using the same optical path used for transmitting.
In another example, shown in
In another example, shown in
Below are disclosed additional systems, devices, and methods for practical, efficient beam steering that have significant advantages over other methods.
One architecture that can be used to make an optical phased array beam steering chip incorporates an array of vertical waveguides. Within each waveguide, two or more resonators may be created. In some examples, the resonators are designed so that actuating the phase response does not cause substantial changes in the amplitude response. The resonators can have similar or different resonances when not coupled, or they can have different resonances when not coupled.
The height of the vertical waveguides can be between 3 um and 50 um, between 5 um and 25 um, or between 10 um and 20 um. The waveguide widths can be about 5 um, about 2 um, about 1 um, about 0.5 um. The waveguide cross-sectional shape can be rectangular, square, round, elliptical, or any other closed shape, and that shape can contain region of one or more types of material. The waveguides can be arranged near each other, with a gap between them, the size of which can be around 2 um, around 1 um, around 0.5 um, around 0.3 um, or around 0.2 um. The gap can be filled with material with a lower refractive index than the waveguide, to allow for waveguiding. The gap can be filled with material that is electrically insulating in order to electrically isolate the waveguides from each other.
In some examples, the waveguides can contain one or more quantum wells. In other examples, the waveguides contain one or more doped layers. In some examples the waveguides can be substantially made of III-V semiconductors. In some examples the III-V can be AlAs and GaAs. In other examples the waveguides can be made of silicon.
In one example, the vertical waveguide array is shown in
On top of the waveguide a semiconductor region 908 can be formed in which circuitry can be fabricated for controlling the pixel's operation. In some examples, the control circuitry can contain one or more transistors. In some examples, the waveguide array can have region 909 disposed on it to, for example, allow for metal signal lines, vias, and electrically insulating material so that pixels can be electrically actuated and controlled.
In some examples, the regions that can be phase modulated 902a-c do so through changes in carrier concentration. This can be through any means, including but limited to carrier injection, or carrier depletion.
In one example, the regions 902a-c that may be phase modulated consist of alternating layers of p-doped and n-doped semiconductor. Between those layers there can optionally be one or more layers, one or more of which will have substantially different doping than the doping of both the alternating p-doped and n-doped layers. In some examples, the periodicity of the n- and p-doped layers will be about 100 nm, or about 50 nm, or about 30 nm.
In some examples, a region 904 of the waveguide sidewall can be p-doped such that that region 104 makes electrical contact with the p-doped layers in the regions 902a-c, and a region 905 of the waveguide sidewall can be n-doped such that that region 905 makes electrical contact with the n-doped layers in the regions 902a-c. In some examples, a voltage potential can be put across the two doped regions 904 and 905 so as to cause a change in carrier density at each n-doped and p-doped interface. In this way, the carrier density in the volume of the waveguide can be modulated, and thereby the phase modulated. The doping densities can be between 1018 cm−3 and 1022 cm−3, or between 1018 cm−3 and 1020 cm−3, or between 5×1018 cm−3 and 5×1019 cm−3. Note that the doping polarity can be switched in some examples.
One advantage the previous example offers is that fringing fields can have little impact on a neighboring waveguide, thereby mitigating this common problem with optical phase arrays that can lead to poor performance.
In another example, the waveguide may be substantially round or elliptical in cross-section, where there can be one or more regions substantially in the middle of the waveguide that are doped with one polarity, and where a bounding region of the waveguide is doped with the opposing polarity. In this case, the bounding polarity can be kept at constant electrostatic potential, and the center region(s) voltages changed to actuate the phase. This architecture can then isolate a given waveguide from the electrical signals of any nearby waveguide.
In some examples, the semiconductor in any of the previous examples can be silicon. The doping used can be phosphorus, arsenic, boron, or any other suitable doping material. In some examples, the gaps between the waveguides can be filled partially or fully with silicon dioxide, silicon oxynitride, or silicon nitride. The gaps may also be filled with metal, such as aluminum, copper, tungsten, titanium, or any suitable metal.
The waveguide circuitry is used to control the waveguide. One example of a waveguide circuit without reset 1001 is shown in
In some examples, the waveguide array could be 100 million elements or more. In general, setting different biases on each pixel in series can in some instances require signal pathways that can send data at 10's, 100's or even many 1000's of GB/s. In many instances, the fact that beam steering is being done can result in a periodicity across the array in the signal pattern required, the periodic pattern of which will be referred to as a unit cell. In examples where the steering angle is steep, that repeating unit cell can be reasonably small. In this example then, the repeated pattern allows multiple waveguide biases to be updated in parallel, reducing the data rate required by approximately the number of unit cells over the entire array. In another example, where the steering angle is shallow, the unit cell is large. However in this case, waveguides can be grouped in regions where they have substantially the same bias and biased to the same value. This way, again, multiple pixels can be updated in parallel, thereby reducing the data rate required by approximately the number of waveguides within a group with common bias.
In one example, m bias levels are used for each linear dimension. In this case, the number of updates required can be limited to m2. For example, if m=8, at most 64 clock updates will be required. If each bias imposition requires one clock tick, then a clock of 64 MHz can be sufficient to update an array of any practical size.
The beam steering chips herein described can be used such that light incident and exiting the chip do so through the substrate 1100 before and after, respectively, interacting with the beam steering optical phased array layer 1101, as shown in
In one example, 1550 nm light is steered by a silicon beam steering chip disposed on a silicon substrate. In this example, light exiting the beam steering layer, but is still in the silicon substrate, can have a range of achievable angles might be ±10°. Upon exiting the substrate, the angular range will be increased to about ±36°. In another example, the range of achievable angles might be ±15° which, upon exit from the substrate, can be increased to a range of achievable angles of ±62°.
Another benefit of using the circuit such that light travels through the substrate is that the beam steering layer is closer to the backside where thermal management can be more effectively done.
In some instances, it can be desirable to use a single beam steering chip to steer multiple beams simultaneously. One example of a way to achieve multi-laser beam steering 1200 is shown in
Below are disclosed additional systems, devices, and methods for practical, efficient beam steering that have significant advantages over other methods.
In some examples of optical phased arrays incorporating vertical waveguides, one or more tapers can be formed at the end of one or more waveguides into which light can be coupled. This can increase the light coupling efficiency. The sidewall angle from vertical of the tapers can between 0° and 5°, between 0° and 10°, between 0° and 15°, or between 0° and 30°, and can be constant along the length of the at least one taper, or the angle can vary with position. An example showing at least one taper connecting to at least one vertical waveguides is shown in
In some examples of optical phased arrays incorporating vertical waveguides, two or more nearest-neighbor waveguides can be sufficiently close to each other that an appreciable amount of optical power can cross-coupling from one waveguide to another. For example, an appreciable amount of optical power can mean more than 20%, more than 10%, more than 5% or more than 1%. Cross-coupling can be suppressed by making the mode propagation constants of nearest-neighbor waveguides dissimilar. This can be accomplished by varying the cross-sectional shape, size, and/or orientation of the two or more waveguides. Some examples 1400-1402 are shown in the top view in
In some examples of optical phased arrays incorporating vertical waveguides, at least one vertical waveguide can include one or more regions with a refractive index lower than the surrounding waveguide and that overlaps substantially with the optical mode. Each of the at least one lower refractive index regions can have one or more small dimensions in comparison to the wavelength of light. The at least one or more low refractive index region can be comprised of a material with an electrically actuatable refractive index, such that the propagation constant of the entire mode can be substantially actuated. The material in the at least one low refractive index region can also be of high electrical resistance, such that application of a bias across the at least one low refractive index region leads to very little current flow and power consumption. The high refractive index material on either side of the at least one low refractive index region can be used as electrodes for applying an electrical bias across the at least one low refractive index region.
One example of at least one low refractive index region included in at least one vertical waveguide of an optical phased array incorporating vertical waveguides is shown in
In some examples, one of the dimensions of at least one low refractive index region will be less than 200 nm. In another example, one dimension will be less than 100 nm. In yet another example, one dimension will be less than 50 nm. In still another example, one dimension will be less than 25 nm.
The material comprising the low refractive index region can be semiconductor, a dielectric, a polymer, a liquid crystal, or any suitable material, or any combination thereof. Semiconductors can include silicon, germanium, gallium arsenide, aluminum arsenide, aluminum gallium arsenide, indium phosphide, indium gallium arsenide, gallium nitride, strained variants thereof, and others. Dielectrics can include silicon dioxide, silicon nitride, silicon oxynitride, and others. Polymers can be nonlinear, electro-optic, dendritic, can contain hyperpolarizable chromophores, and can be poled. These polymers can include PMMA, polycarbonate, sol-gel, and others. Chromophores can include YLD 124, DR1, CLD1, AJL8, AJLS102, JT1, AJ307, AJ309, AJ404, and AJ-CKL1. Liquid crystals can be of the thermotropic, lyotropic, or metallotropic phases. Thermotropic phases can include the nematic phase, smectic phase, or other phases of liquid crystal. Applicable liquid crystals can be organic, and can incorporation lipids, proteins, DNA, polypeptides, and others. They can also be inorganic, and can include various oxides such as vanadium oxide, carbon nanotubes, graphene, and others. Liquid crystals can include 4-Cyano-4′-pentylbiphenyl (5CB), various biphenyl (BP) molecules such as E7, N-(4-Methoxybenzylidene)-4-butylaniline (MBBA), and others.
In some examples of optical phased arrays incorporating vertical waveguides, at least one waveguide can be designed to operate in transmission mode. In this example, the control lines and circuit elements can be at least partially placed away from the exit apertures of each vertical waveguide, to reduce the optical loss. At least one taper can be used on the inputs of the vertical waveguides in transmission mode, and optionally at the outputs of at least one of the vertical waveguides.
An example structure is shown in
In some examples of optical phased arrays, waveguides can be arranged to receive light in a direction normal to a surface upon which they are aligned. For example, waveguides arranged in an array along a surface receive light from a direction that is normal to that surface. In a more specific example, a waveguide or array of waveguides disposed on a planar substrate receive light from a direction that is normal to the plane of the support substrate, which in many cases, would be light that is transmitted through the support substrate and into the waveguides. In other cases, however, such would include light being transmitted into the waveguides and toward the support substrate. In yet another example, the light can be delivered through substrate or other material layer to the waveguide at any oblique angle that can facilitate the intended functionality of the device. In some examples, the oblique angle can be between 0° and 0.1°, between 0° and 1°, between 0° and 5°, between 0° and 10°, between 0° and 45°, or between 0° and 89°. In some examples, waveguides that receive light through the substrate upon which they are disposed can be referred to as “vertical waveguides.” In other examples, a vertical waveguide can describe a waveguide where light passes through he waveguide and into the substrate upon which they are disposed.
In some cases the support or other substrate upon which an array of waveguides is disposed may not be aligned along a 2D plane; in such cases, the direction of the light entering the waveguide can be determined from the plane established from the region upon which the waveguide sits. It is understood that the determination of directionality of transmitted light to a waveguide is well within the abilities of one of ordinary skill in the art.
This application is a continuation of U.S. patent application Ser. No. 17/009,774, filed on Sep. 1, 2020, which claims the benefit of U.S. Provisional Patent Application No. 62/869,559, filed on Jul. 1, 2019, which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62869559 | Jul 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17009774 | Sep 2020 | US |
| Child | 17674826 | US |
