Patent Application
20210405255
This disclosure relates to metamaterial lenses to control deflection in transmissive and reflective structures. Additionally, this disclosure relates to electronic displays including red, green, and blue (RGB) electronic displays.
Various embodiments, systems, apparatuses, and methods are described herein that relate to the controlled deflection of incident optical radiation. Examples are described herein for reflective optical systems that reflect incident optical radiation. Examples are also described herein for optically transmissive optical systems that refract, deflect, or otherwise modify optical radiation passing therethrough. In some examples, electronic displays, such as RGB LED displays, include variations of the metalenses described herein. Additionally, the presently described metalenses can be used in combination with waveguides for optical transmission and/or near eye displays (NEDs), such as head mounted displays (HMD) and wearable displays. An input coupler may be formed using a variation of the metalenses described herein to couple an image source to a waveguide. The waveguide may convey the optical radiation forming the images to an output coupler that includes another metalens according to one of the embodiments described herein.
The output coupling metalens may deflect and focus the optical radiation (e.g., based on frequency and/or with a frequency selective filter) to form an image visible to one eye of a user. In some embodiments, the output coupling metalens may be used to deflect and focus the optical radiation as a stereo image or as a duplicated image on both eyes of the user or even on the eyes of multiple users.
According to various embodiments, an electronic display may include a multi-pixel light-emitting diode (LED) display layer to generate optical radiation at various wavelengths (e.g., different visible colors of light) using at least three different colors of LED subpixels (e.g., red, green, and blue subpixels for an RGB display). A metalens layer may include a plurality of metalens subpixels. Each metalens subpixel may correspond to one of the LED subpixels. In some embodiments, a multi-frequency metalens subpixel may be responsive to multiple frequencies allowing a single multi-frequency metalens subpixel to be used for each pixel of the RGB display.
The metalens subpixels deflect the optical radiation from each corresponding LED subpixel at a target deflection angle for focusing, image replication, color separation, and/or other deflection purposes. Each metalens subpixel comprises an array (e.g., a two-dimensional array for two-dimensional LED subpixels) of passive deflector elements with varying diameters. The passive deflector elements extend from a substrate (e.g., normal to, substantially normal to, or at an angle with respect to the substrate). The passive deflector elements are arranged in a repeating pattern of deflector element diameters with constant and/or frequency-dependent interelement on-center spacings.
Various embodiments of the metalenses described herein may be used in combination with an imaging sensor, such as a charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensor array. For example, various embodiments of the metalenses described herein may be utilized in place of frequency masks, filters, microlenses, and other optical elements of CCD and CMOS digital image sensors. Frequency selective metalenses can be tuned (i.e., configured with specific deflector element dimensions and patterns) to filter and/or deflect (e.g., refract or reflect) optical radiation received by each pixel or subpixel in a digital imaging sensor.
The repeating pattern of deflector element diameters may include passive deflector elements having any number of different diameters. Some of the illustrated examples include passive deflector elements with six different diameters arranged in a repeating pattern with constant on-center spacing. In other embodiments, the number of passive deflector elements with different diameters may be fewer than six or more than six (e.g., 8, 10, or even dozens of different diameters). In some embodiments, the height to which each passive deflector element extends from the substrate in a given metalens subpixel is constant. In fact, in some embodiments, the height to which each passive deflector element extends from the substrate may be constant for all the metalens subpixels, regardless of the operational frequency thereof. Thus, while the repeating pattern of diameters of deflector elements may vary based on the operational frequency, the heights of the deflector elements may all be the same.
As described herein, the passive deflector elements may be polarization-independent or polarization-dependent. For a given frequency, the polarization-dependent passive deflector elements may extend from the substrate to a shorter height than the polarization-independent passive deflector elements, while the pattern of deflector element diameters may remain substantially the same.
Accordingly, polarization-independent passive deflector elements may have a height-to-diameter (height:diameter) aspect ratio that is greater than 1. That is, the height of each polarization-independent passive deflector element is generally greater than the diameter thereof. In contrast, polarization-dependent passive deflector elements may have a height:diameter aspect ratio that is less than 1. That is, the height of each polarization-dependent passive deflector element may generally be less than the diameter thereof.
Metalens embodiments utilizing polarization-dependent passive deflector elements may also include a polarizing filter to polarize the optical radiation before it is deflected by the deflector elements. For example, a polarizing layer may be positioned on the substrate between the substrate and the polarization-dependent passive deflector elements. In such embodiments, the polarization-dependent passive deflector elements may extend from the substrate through the polarizing layer or extend from the polarizing layer on the substrate. In some embodiments, the substrate and the polarizing layer may be combined or described in combination as a polarizing substrate.
The exact shape and size of the deflector elements may depend on the manufacturing process utilized and target operational characteristics. In many embodiments, including the illustrated embodiments, the deflector elements are substantially cylindrical and extend normal to (e.g., perpendicular to) the plane of the underlying substrate. The cylindrical deflector elements can be described as having a diameter (D), a height (H), and an on-center nearest neighbor interelement spacing (P). A metalens subpixel may include many unit cells, where each unit cell includes a cylindrical deflector element extending from a substrate. A metalens subpixel may be formed by combining many unit cells in a two-dimensional array with varying diameters of cylindrical deflector elements (e.g., in a repeating pattern of deflector element diameters).
In some embodiments, the cylindrical deflector elements include a cavity or depression formed therein. The cavity may be cylindrical and only extend partially into the cylindrical deflector elements. For example, the depth of the cavity may be half the height of the cylindrical deflector elements, less than half the height of the cylindrical deflector elements, or more than half the height of the cylindrical deflector elements. In some embodiments, the cavity may be filled with air or another material that has a different electromagnetic permittivity than the deflector element.
While many of the metalenses described herein are described in the context of an electronic display, metalenses may be used for other purposes and applications. In various embodiments, a metalens includes an array of passive deflector elements with varying diameters that extend from a substrate with a repeating pattern of deflector element diameters. The interelement on-center spacings of the passive deflector elements may be selected as a function of an operational wavelength of the optical metalens. Each passive deflector element has a height and a width that are each less than a smallest wavelength within the operational bandwidth.
The repeating pattern of deflector element diameters within the optical metalens includes passive deflector elements having at least six different diameters. Again, the passive deflector elements may be polarization-independent in some embodiments. When used in combination with a polarizer or polarizing layer, the passive deflector elements may be polarization-dependent.
In one specific embodiment, an optical metalens configured to deflect a wavelength of red light includes a repeating pattern of deflector element diameters ranging from 80 nanometers to 220 nanometers. The exact heights and spacing may vary based on the wavelength, target deflection response, and manufacturing processes. However, in one specific embodiment the height of the deflector elements is 280 nanometers with nearest neighbor interelement spacing of approximately 230 nanometers. In another specific embodiment, the height of the deflector elements is 220 nanometers with nearest neighbor interelement spacings of approximately 250 nanometers.
Again, while the specific dimensions and spacing characteristics may vary based on the wavelength, target deflection response, and/or manufacturing processes, specific examples are provided herein to facilitate a complete understanding of the systems, methods, and apparatuses described herein. In one embodiment, the optical metalens is configured to deflect a wavelength of green light and has a repeating pattern of passive polarization-independent deflector elements with diameters ranging from 80 nanometers to 150 nanometers. In one embodiment, the optical metalens is configured to deflect a wavelength of blue light and has a repeating pattern of passive polarization-independent deflector elements with diameters ranging from 40 nanometers to 140 nanometers, or a narrower range in some embodiments (e.g., 80 to 140 nanometers). In one specific embodiment, an optical metalens for a wavelength of blue light has a repeating pattern of deflector elements with diameters ranging from 80 nanometers to 140 nanometers.
In some embodiments, each metalens or metalens subpixel includes a plurality of unit cells arranged in a one-dimensional or two-dimensional array. In some embodiments, each unit cell may include a single deflector element and the array of deflector elements may be configured for a single frequency response (or narrowband frequency response). In other embodiments, each unit cell may include multiple deflector elements such that the array of deflector elements provides a multi-frequency response.
In another embodiment, a metalens is used within a transmissive medium to form a frequency selective optical filter. For example, the frequency selective optical filter may be conceptually described as a two-dimensional array of subwavelength unit cells, where each unit cell includes an optically transmissive medium and an array of passive deflector elements with varying diameters arranged therein. The interelement on-center spacings of the passive deflector elements can be selected to reflect optical radiation within a target bandwidth to a focal point. Optical radiation outside of the target bandwidth (e.g., a narrow bandwidth of optical radiation of 10-100 nanometers) is deflected or passed through the optically transmissive medium.
An understanding of traditional optical lenses may be helpful to understand the possible applications and functions of various embodiments and applications of the metalenses described herein. Traditional optical lenses and mirrors (e.g., glass or acrylic lenses) are formed with a curvature to modify the optical path of incident optical radiation. Multiple lenses and/or mirrors may be combined with various indices of refraction, curvatures, coatings, and other features to achieve specific optical goals.
Metamaterial-based lenses and mirrors may be formed as relatively thin (e.g., <1mm) elements that provide controlled deflection without curved surfaces. As described herein, a substrate surface may be configured as a transmissive surface to allow optical radiation to pass therethrough, or as a reflective surface to reflect optical radiation therefrom. Subwavelength-scale features may be patterned on a surface of the substrate to deflect incident optical radiation in a controlled manner to obtain a target optical radiation output at any angle between 0° to 180°. Such a device is referred to herein as a metalens. Various embodiments and variations of metalenses are described herein. Metalenses are broadly defined herein to encompass both transmissive and reflective devices.
In some embodiments, subwavelength-scale features may be formed on more than one surface of the substrate. For example, subwavelength-scale features may be formed on a receiving side of a transmissive substrate and an output side of the transmissive substrate. A metalens may be used to deflect optical radiation within free space (e.g., air) or to couple optical radiation between free space and another transmissive medium, such as a waveguide, traditional optical lenses, a fiber optic transmission line, or the like.
In various embodiments, a surface (or multiple surfaces) of the substrate is patterned with an array of deflector elements. According to various embodiments calculated, estimated, modeled, or optimized to achieve specific target deflection patterns, the array of deflector elements may be uniformly spaced, periodically spaced, aperiodically spaced, and/or arranged in repeating patterns of the same.
Each deflector element in the array of deflector elements may have subwavelength dimensions, such that the deflector element array collectively exhibits metamaterial behaviors for a relatively narrow band of optical radiation (e.g., a target operational bandwidth). In some embodiments, the deflector elements may extend substantially orthogonal to the planar surface of the substrate. In applications in which the metalens is used in combination with an RGB LED display, the fall off or cutoff frequency of the narrowband response may not be as critical since the frequencies of the red, green, and blue light are relatively far apart on the frequency spectrum.
The contact surface of a deflector element contacting the substrate may be a circle, oval, square, rectangle, an n-sided polygon, or another shape. The deflector element may extend from the planar surface to a height that is greater than a length or width dimension of the deflector element. For example, each of the deflector elements may have a circular contact surface with a diameter less than the smallest wavelength within the operational bandwidth and extend from the substrate as a pillar to a height, H. In various embodiments, the height, H, may also be less than the smallest wavelength within the operational bandwidth. The deflector elements may be described as subwavelength, as having subwavelength features, as having subwavelength dimensions, and/or as having subwavelength interelement spacings.
In some embodiments, each deflector element may be a non-circular pillar extending from a substrate or positioned within a substrate (e.g., as illustrated and described herein in the context of a frequency-selective filter). For example, each deflector element may have a square, rectangular, oval, hexagonal, or other shape profile and extend from the substrate to a predetermined height. In some embodiments, each of the deflector elements in a deflector element array may extend to the same height. In other embodiments, the heights of various deflector elements may vary randomly, form a slope relative to the planar surface of the substrate, and/or conform to a repeating pattern.
In some embodiments, each deflector element may be a pillar or nanopillar (e.g., a circular or non-circular pillar) formed from titanium dioxide, polycrystalline silicon (poly-Si), and/or silicon nitride that extends from, for example, a silicon dioxide substrate or magnesium fluoride substrate. Such pillars, including both circular and non-circular variations, may be referred to as nanopillars due to their subwavelength characteristics and nanometer dimensions. In some embodiments, the substrate may comprise multiple layers of substrates with different refractive indices and/or comprise different combinations of materials. For example, in some embodiments, the substrate may comprise a Bragg reflector formed as a sequence of layers of two or more different optical materials having different refractive indices. In various embodiments, the deflector elements are passive subwavelength deflectors that are polarization independent.
The deflection pattern generated by the metalens may be influenced or controlled by careful selection of pillar height, diameter, spacing, and pattern arrangement on the substrate. Metalenses may have a deflector element array configured to generate a converging deflection pattern, a diverging deflection pattern, or another target deflection pattern to achieve a specific deflection goal.
In some embodiments, a metalens includes an array of passive, polarization-independent deflector elements extending from a transmissive substrate. The metalens may be incorporated as part of a laser-based scanning illumination engine to output collimated optical radiation along one dimension of an output surface of the metalens in response to received optical radiation incident at varying angles of incidence on a corresponding dimension of a receiving surface of the metalens (e.g., a “receive surface” of a metalens).
In another embodiment, the angle of output optical radiation may vary based on the location on the output surface of the metalens. The spatially varied output angles of deflected optical radiation may be configured to form multiple depth planes, pupil replication, or expansion of a viewing “eyebox.”
In some embodiments, a single metalens may be responsive to multiple colors of optical radiation sufficient for combination in full-color optical displays. Multiple different functionalities may be combined within a single lens to respond to different states of polarization (e.g., for spatial-multiplexing or time-multiplexing). In other embodiments, multiple metalenses may be stacked, spatially multiplexed, time-multiplexed, or otherwise arranged for use in full-color optical displays. For example, three different metalenses may be stacked for use in an RGB optical display.
The stacked metalenses may include a first metalens configured with an array of deflector elements with dimensions to deflect red optical radiation, a second metalens configured with an array of deflector elements with dimensions to deflect green optical radiation, and a third metalens configured with an array of deflector elements with dimensions to deflect blue optical radiation. In some embodiments, a metalens may be used in place of injection optics for a laser-based scanning illumination engine or LED microdisplay coupled to a waveguide. The metalens may be used to efficiently deflect incident optical radiation from a laser source into a waveguide for total internal reflection.
Variations of the systems and methods described herein may be used or adapted for use in near-to-eye (NTE) displays, such as NTE displays used in wearable technology, smart glasses, augmented reality headsets, virtual reality headsets, heads-up displays, and the like. For example, a metalens may be used as part of an NTE display to collimate optical radiation into parallel rays for delivery to the eye of the user at “infinite focus.” Similarly, a metalens may be used as part of an NTE display to deliver optical radiation to the eye of the user at target angles that vary spatially along the surface of the metalens to cause an image to appear to originate from a target focal depth plane.
In other embodiments, a metalens may be used as part of an NTE display to duplicate source images and cause the duplicated source images to appear as if they originate from different positions in the visual field, for example, to facilitate pupil replication or expansion of the effective “eyebox” of the NTE display. The metalens may be used to expand the source image of an NTE display to have a wider range of divergence angles (e.g., act as a diffuser) to provide a wider effective field of view.
Variations of the systems and methods described herein may be used or adapted for use in light-field displays. As used herein, the term “light-field display” is used to describe any of a wide variety of displays using various technologies to render a three-dimensional image field to one or more users without the use of polarized or active-shutter glasses. Light-field displays deliver an image to each eye of the user at slightly different perspectives to provide binocular disparity for depth perception. The different images transmitted to the eyes of the user cause the user to perceive the image as a three-dimensional image. As an example, a lenticular lens overlaid on a digital display may be used to deliver different images to each eye of the user. Three-dimensional displays using lenticular lens technology have fundamentally limited fields of view.
The presently described systems and methods relating to metalenses can be used to create advanced light-field displays that can be viewed from different perspectives simultaneously by multiple users. Similarly, metalenses can be used to create advanced light-field displays that deliver an image from different perspectives as a single user moves through the visual field. The metalenses may deliver variations of an image to different spatial locations within the visual field to provide the user with a natural-appearing three-dimensional image that accounts for motion, parallax, occlusion, and/or accommodation.
Some three-dimensional displays use a two-dimensional array of microlenses (e.g., a microlens array or “MLA”) with lenslets that span multiple pixels of the underlying electronic display. In such embodiments, the microlenses cause the user to perceive only one of the underlying pixels based on the position of the user's eye relative to each respective lenslet. The metalens-based approaches described herein avoid undesirable field-of-view, reduced fill factor, and other optical deficiencies fundamentally associated with microlens solutions. Specifically, three-dimensional displays utilizing metalenses to deliver different images (e.g., different perspectives of an image) to different locations within the visual field provide an improved optical performance, a finer pitch, and a lower-profile than comparable microlens-based solutions.
According to various embodiments, the metalenses described herein may be fabricated using any of a wide variety of suitable manufacturing techniques, including without limitation nanoimprinting manufacturing techniques, CMOS fabrication techniques, and/or ultraviolet lithography processes. Relatively low aspect ratios (e.g., the ratio of the height to the width of each nanopillar deflector element) allow for relatively faster, cheaper, and higher fidelity manufacturing than competing technologies. For example, the array of nanopillar deflector elements and the underlying substrate may use resonant modes that are electromagnetically coupled to form a metalens that is ultrathin (e.g., less than one wavelength). In some of the specific embodiments described herein, metalenses have been demonstrated to have transmission efficiencies in excess of 85% using devices having a thicknesses of less than one-half (½) of the operational wavelength.
In various embodiments, an array of polarization-independent, passive deflector elements patterned on a transmissive or reflective substrate may be adapted to deflect a relatively narrow band of coherent optical radiation (e.g., from a laser light source) in a prescribed direction, arbitrarily based on the origin of the optical radiation (e.g., pixel-by-pixel variation), and/or collimated to provide an effective “infinite focus.”
In other embodiments, an array of polarization-dependent, passive deflector elements may be patterned on a transmissive or reflective substrate for use with a relatively wide band of noncoherent optical radiation (e.g., from an LED light source) in a prescribed direction, arbitrarily based on the origin of the optical radiation (e.g., pixel-by-pixel variation), and/or collimated to provide an effective “infinite focus.”
As described herein, an array of nanopillar deflector elements may have a repeating pattern of pillars with varying diameters, interelement spacings, and/or heights. The repeating pattern of nanopillar deflector elements may be repeated multiple times to provide a metasurface lens, such as a metalens subpixel with a target surface area that corresponds to the surface area of an LED subpixel of an RGB pixel of an RGB LED display. The diameters, interelement spacings, and/or heights of the pillars in each array of nanopillar deflector elements may vary based on the frequency/wavelength/color of the corresponding LED subpixel. Accordingly, a metalens for a single pixel of an RGB display may include three different single-frequency arrays of nanopillar deflector elements that are “stitched” or otherwise positioned adjacent to one another to form a multifrequency metalens with metalens subpixels for each LED pixel. The stitched multifrequency metalens may be replicated for each pixel of the RGB display. In some instances, stitched multifrequency metalenses may exhibit some crosstalk between the different single-frequency arrays of nanopillar deflector elements.
In other embodiments, an entire RGB display may be covered with three different metalens layers. A first metalens layer with a first pattern of nanopillars may be provided to deflect optical radiation having a first frequency. A second metalens layer with a second pattern of nanopillars may be provided to deflect optical radiation having a second frequency. A third metalens layer with a third pattern of nanopillars may be provided to deflect optical radiation having a third frequency. In some instances, the vertical stacking of three metalens layers may reduce the overall efficiency of light transmission due to multi-layer reflections and other losses.
In another embodiment, a multifrequency metalens for a multicolor display (e.g., an RGB display, a two-color display, or another display) may be embodied as an in-plane spatially multiplexed array of frequency-specific nanopillars intermingled with one another. The spatially multiplexed array of frequency-specific nanopillars may comprise a plurality of sub-unit-cells with a number of pillars equal to or greater than the number of independent frequencies to be deflected. The periodicity of the sub-unit-cells is subwavelength and selected for zero-order diffraction. Accordingly, the periodicity of the sub-unit-cells may be selected to be less than the smallest wavelength of the frequencies to be deflected. For example, if the smallest wavelength to be deflected is 550 nanometers, the largest periodicity for zero-order diffraction is approximately 360 nanometers, and so the largest periodicity of the sub-unit-cells is approximately 180 nanometers (e.g., the Nyquist limit). For blue light with a wavelength less than 500 nanometers, the largest periodicity for zero-order diffraction would be even smaller, and accordingly, the largest periodicity of the sub-unit-cells would be smaller still.
In some embodiments, to achieve an acceptable phase shift of each of the independent frequencies to be deflected (e.g., a range from 0 to 2π), the height of the individual pillars may be slightly taller than in other embodiments to accommodate for relatively close spacing defined by the calculated largest possible periodicity of the sub-unit-cells for zero-order diffraction. For example, a pillar height between approximately 200 nanometers and 400 nanometers may be suitable, depending on the specific frequencies to be deflected. In one example, the individual pillars have a height of approximately 300 nanometers.
For a selected height and periodicity, a simulator or calculation module may simulate or calculate the transmission and transmitted phase shift of each of the frequencies to be deflected for a range of pillar diameters in each sub-unit-cell. Suitable pillar diameters may be selected to achieve target performance metrics and/or controllability. For example, pillar diameters may be selected to provide a transmission of at least 0.7 (e.g., 70%) and a phase shift within a range of 0 to 2π to provide full control of deflection. In some embodiments and applications, lower or higher transmission thresholds may be acceptable and/or partial deflection control may be sufficient (e.g., less than 2π phase shift).
The difference between a target field and a simulated field provides a figure of merit that can be calculated as |ttargete−iϕ
In one simulation of a design for a dual-frequency response metalens for 650 nanometers and 550 nanometers, a 300 nanometers pillar height was selected with a sub-unit-cell periodicity of 180. The simulated diffraction efficiency of the first order was 0.93 and 0.92 for the wavelengths 550 nanometers and 650 nanometers, respectively. Each repeated unit cell of the simulated metalens provided a phase shift range of more than 2π via six unique sub-unit-cells with two pillars of varying diameters in each sub-unit-cell.
The generalized descriptions of the systems and methods herein may be utilized and/or adapted for utilization in a wide variety of industrial, commercial, and personal applications. Similarly, the presently described systems and methods may be used in conjunction with or utilize existing computing devices and infrastructures. Some of the infrastructure that can be used with embodiments disclosed herein is already available, such as general-purpose computers, computer programming tools and techniques, digital storage media, and communication links. A computing device or controller may include a processor, such as a microprocessor, a microcontroller, logic circuitry, or the like.
A processor may include one or more special-purpose processing devices, such as application-specific integrated circuits (ASICs), a programmable array logic (PAL), a programmable logic array (PLA), a programmable logic device (PLD), a field-programmable gate array (FPGA), or another customizable and/or programmable device. The computing device may also include a machine-readable storage device, such as non-volatile memory, static RAM, dynamic RAM, ROM, CD-ROM, disk, tape, magnetic, optical, flash memory, or another machine-readable storage medium. Various aspects of certain embodiments may be implemented using hardware, software, firmware, or a combination thereof.
The components of the disclosed embodiments, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Furthermore, the features, structures, and operations associated with one embodiment may be applied to or combined with the features, structures, or operations described in conjunction with another embodiment. In many instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of this disclosure. The embodiments of the systems and methods provided within this disclosure are not intended to limit the scope of the disclosure but are merely representative of possible embodiments. In addition, the steps of a method do not necessarily need to be executed in any specific order or even sequentially, nor do the steps need to be executed only once.
As illustrated, the metalens may be configured to transmissively deflect the incident optical radiation as collimated deflected optical radiation 420 that transmits in a uniform direction along the length of the metalens 400. In such an embodiment, the array of deflector elements may be patterned on a substrate with dimensions, spacings, and heights to compensate for the different angle of incidence of the optical radiation 410 as the scanning mirror is rotated.
In an alternative embodiment illustrated in
In the illustrated example, the spacing, P, between the centers of adjacent nanopillars 620 is 456 nanometers. The height, H, of each nanopillar 620 may be 150 nanometers. The diameters, D, of the nanopillars 620 in the array of nanopillars may vary from approximately 160 nanometers to 340 nanometers. The specific pattern of diameters of nanopillars, spacings, and heights may be selected to attain a target deflection pattern (e.g., angle of deflection, dispersion, collimation, convergence, etc.).
In the illustrated example, the substrate 610 may be SiO2 with an index of refraction of approximately 1.45. The deflector element, illustrated as cylindrical nanopillar 620, may be poly-Si with an index of refraction of approximately 3.8. The air 630 or other surrounding fluid (gas, oil, liquid, etc.) or other material may have a relatively low index of refraction. For example, the air 630 may have an index of refraction of approximately 1.0.
For coherent illumination sources, such as laser illumination sources, each of the deflector elements in an array of deflector elements may be cylindrical (e.g., nanopillars) and operate in the resonance mode with a height, H, that is less than or equal to the smallest diameter, D, in the array of deflector elements. Such deflector elements can be described as having an aspect ratio of less than one (e.g., H/D<1). Accordingly, the deflector elements of a metalens illuminated using laser light may be cylindrical nanopillars and operate in the resonance mode with an aspect ratio of less than approximately one.
The cylindrical deflector element 621 may extend into a region of free space 631 that is filled with air or another fluid. The diameter of the cylindrical deflector element 621 and the diameter of the cylindrical cavity 622 may each be selected based on a target frequency response. A metalens may be formed as a two-dimensional array of unit cells of cylindrical deflector elements 621 having varying diameters within a range of diameters selected for a target deflection pattern within an operational frequency range.
According to various embodiments, any of a wide variety of illumination sources may be utilized, including LEDs, microLEDs, OLED, and the like. As compared to laser light sources, LED illumination sources have a relatively broad frequency band that is not spatially coherent. The incoherent light from the LED array 720 is polarized by the polarizing filter 710. The polarized light from the polarization filter 710 is deflected by the metalens 730. The metalens 730 may include pillars with rectangular or cylindrical shapes that are polarization-dependent to receive and deflect the polarized optical radiation after it passes through the polarizing filter 710. In some embodiments, the metalens 730 and the polarizing filter 710 may be laminated on top of, for example, a two-dimensional array of LEDs.
In alternative embodiments, a metalens may include polarization-dependent rectangular pillars, but omit the polarizer 710 shown in
By way of comparison, the deflector elements of a metalens which are illuminated using laser light, according to various embodiments described herein, may be cylindrical (e.g., nanopillars) and operate in the resonance mode with a height:diameter aspect ratio of approximately less than one. In contrast, the deflector elements of a metalens illuminated using incoherent light (e.g., from an array of LEDs) passed through a polarization filter may be rectangular (polarization-dependent) and operate in the resonance mode with a height:diameter aspect ratio of less than approximately one.
In contrast with the previously described embodiments, the deflector elements of the metalens 830, which are illuminated using incoherent light without a polarizing filter, as illustrated in
In some embodiments, as described herein in the context of pixel or subpixel duplication, light field generation, 3D-image generation, and/or the like, light from each LED subpixel in a given RGB pixel may be directed in the same direction, different directions, or subdivided for transmission to two different locations.
Simplified patterns of deflector elements 940 are shown for each of a green subpixel metalens 941, a blue subpixel metalens 942, and a red subpixel metalens 943. Each subpixel metalens 941, 942, and 943 includes deflector elements with repeating patterns of diameters and interelement spacings selected to provide a target deflection angle. An example of the repeating pattern of nanopillars on a substrate 950 is illustrated as well. The number of pillars, pattern of diameters, range of diameters, and other characteristics of the individual pillars in each repeating pattern may vary according to the specific operational frequency and target deflection angle or deflection pattern.
The following specific examples of on-center spacings, P, heights, H, and diameters, D, are provided with respect to the patterns of deflector elements 940 and the example repeating pattern of nanopillars on the substrate 950. According to one specific embodiment, the deflector elements of the green subpixel metalens 941 may have a height, H, of approximately 210 to 280 nanometers and on-center spacings, P, of approximately 160 to 2000 nanometers for green light having a wavelength of, for example, approximately 550 nanometers. The height, H, and on-center spacings, P, may be adjusted or specified based on the specific frequency or frequency range of the green light.
In the illustrated embodiment, the deflector elements of the green subpixel metalens 941 have a height, H, of approximately 260 nanometers with on-center spacings, P, of approximately 180 nanometers. In a different embodiment, the deflector elements of the green subpixel metalens 941 may be configured with a height, H, of approximately 220 nanometers with on-center spacings, P, of approximately 190 nanometers. The repeating pattern of deflector elements may include deflector elements having diameters between 80 nanometers and 150 nanometers, for example. The total size (length and width) of the green subpixel metalens 941 may be selected to correspond to the dimensions of a green subpixel 921 of the LED display 920. In applications in which the metalens 931 is used for imaging, the total size (length and width) of the green subpixel metalens 941 may be selected to correspond to the dimensions of a green photosensor of an imaging sensor array.
In the illustrated example, the diameters, D, of the nanopillars in each repeating row of nanopillars in the green subpixel metalens 941 range from approximately 80 nanometers and 140 nanometers to attain phase shifts approaching or exceeding a 2π range. As described above, some embodiments may use a wider range of diameters (e.g., 80 nanometers to 150 nanometers) to attain a suitable range of attainable phase shifts for a particular application. A target pattern of phase shifts across the two-dimensional arrangement of repeating rows of nanopillars in the green subpixel metalens 941 may be selected to achieve a target deflection pattern. Furthermore, the number of nanopillars in each row of repeating nanopillars of varying diameters may be determined based on the target deflection pattern and the specific frequency or frequency range of green light. The total number of rows and columns of repeating patterns of nanopillars of varying diameters may depend on the total length and width of the green subpixel metalens 941.
The deflector elements of the blue subpixel metalens 942 may have a height, H, of approximately 210 to 260 nanometers and on-center spacings, P, of approximately 160 to 200 nanometers for blue light having a wavelength of, for example, approximately 490 nanometers. Again, the height, H, and on-center spacings, P, may be adjusted or specified based on the specific frequency or frequency range of the blue light. In the illustrated embodiment, the deflector elements of the blue subpixel metalens 942 have a height, H, of approximately 260 nanometers with on-center spacings, P, of approximately 180 nanometers. The diameters, D, of the nanopillars in each repeating row of nanopillars in the blue subpixel metalens 942 may range between approximately 40 nanometers and 140 nanometers to attain phase shifts exceeding a 2π range.
A target pattern of phase shifts across the two-dimensional arrangement of repeating rows of nanopillars in the blue subpixel metalens 942 may be selected to achieve a target deflection pattern (e.g., reflection angle or refraction angle). Furthermore, the number of nanopillars in each row of repeating nanopillars of varying diameters may be determined based on the target deflection pattern and/or the specific frequency or frequency range of blue light. The total number of rows and columns of repeating patterns of nanopillars of varying dimensions may depend on the total length and width of the blue subpixel metalens 942.
In one specific embodiment, the deflector elements of the blue subpixel metalens 942 may be configured with a height, H, of approximately 220 nanometers, on-center spacings, P, of approximately 180 nanometers, and repeating pattern of deflector element diameters between 80 nanometers and 140 nanometers. As in other embodiments, the total size (length and width) of the blue subpixel metalens 942 may be selected to correspond to the dimensions of a blue subpixel 922 of the LED display 920. In applications in which the metalens 931 is used for imaging, the total size (length and width) of the blue subpixel metalens 942 may be selected to correspond to the dimensions of a blue photosensor of an imaging sensor array.
The deflector elements of the red subpixel metalens 943 may have a height, H, of approximately 210 to 280 nanometers and on-center spacings, P, of 210-280 nanometers for red light having a wavelength of, for example, approximately 635 nanometers. In the specific illustration, the red subpixel metalens 943 has a height, H, of 260 nanometers and on-center spacings, P, of 230 nanometers. Again, the height, H, and on-center spacings, P, may be adjusted or specified based on the specific frequency or frequency range of the red light. Moreover, the total size (length and width) of the red subpixel metalens 943 may be selected to correspond to the dimensions of a red subpixel 923 of the LED display 920. In applications in which the metalens 931 is used for imaging, the total size (length and width) of the red subpixel metalens 943 may be selected to correspond to the dimensions of a red photosensor of an imaging sensor array.
In the illustrated embodiment, the deflector elements of the red subpixel metalens 943 have a height, H, of approximately 260 nanometers with on-center spacings, P, of approximately 230 nanometers. In a different embodiment, the deflector elements of the red subpixel metalens 943 may be configured with a height, H, of approximately 220 nanometers with on-center spacings, P, of approximately 250 nanometers. The repeating pattern of deflector elements may include deflector elements having diameters between 80 nanometers and 220 nanometers, for example.
In the illustrated example, the diameters, D, of the nanopillars in each repeating row of nanopillars in the red subpixel metalens 943 range from approximately 100 nanometers to 210 nanometers to attain phase shifts exceeding a 2π range. In a different embodiment, the diameters of the nanopillars used in the red subpixel metalens 943 range from approximately 80 nanometers to 220 nanometers to provide a wider range of attainable phase shifts. A target pattern of phase shifts across the two-dimensional arrangement of repeating rows of nanopillars in the red subpixel metalens 943 may be selected to achieve a target deflection pattern (e.g., reflection angle or refraction angle). Furthermore, the number of nanopillars in each row of repeating nanopillars of varying diameters may be determined based on the target deflection pattern and/or the specific frequency or frequency range of red light. The total number of rows and columns of repeating patterns of nanopillars of varying dimensions may depend on the total length and width of the red subpixel metalens 943.
In the illustrated example, as described above, the heights of the nanopillars for each of the red, green, and blue subpixel metalenses 943, 941, and 942 are the same. In alternative embodiments, the heights of the nanopillars of each different color subpixel metalens may be different. Additionally, the example LED display 920 includes green, blue, and red pixels 921, 922, and 923. However, it is appreciated that alternative display color schemes are possible, as are LED displays that include more than three subpixels per pixel (e.g., MultiPrimary displays, such as those using RGBY, RGBW, or RGBYC subpixels). In such embodiments, a tuned metalens may include any number of “subpixel metalenses” or “metalens subpixels” to match the number and/or colors of subpixels used in the MultiPrimary LED display.
A row of nanopillars of varying widths that is repeated along the length and/or width of a given subpixel metalens may be referred to as a nanopillar row. The on-center spacing, P, of adjacent nanopillars in a nanopillar row may be constant, as described herein. In some embodiments, on-center spacing, P, of adjacent nanopillars in a nanopillar row may be a function of the frequency of light to be deflected (e.g., refracted or reflected). Accordingly, on-center spacing, P, of adjacent nanopillars in a nanopillar row for a subpixel metalens for a blue subpixel may be different than the on-center spacing, P, of adjacent nanopillars in a nanopillar row for a subpixel metalens for a red or green subpixel.
The spacing between nanopillars in adjacent nanopillar rows (e.g., across a width of a subpixel metalens or along the length of the subpixel metalens) may be the same as the on-center spacing, P, of adjacent nanopillars in an individual nanopillar row of the subpixel metalens. Alternatively, the spacing between nanopillars in adjacent nanopillar rows (e.g., across a width of a subpixel metalens or along the length of the subpixel metalens) may be different than the on-center spacing, P, of adjacent nanopillars in an individual nanopillar row of the subpixel metalens.
The difference between the target field and the simulated field provides a figure of merit that can be calculated as |ttargete−iϕ
In
As shown in
As illustrated in
As shown in
Various embodiments of the presently described metalenses (both refractive-type and reflective-type) may be used in combination with a wide variety of image sensing arrays, including RGB image sensing arrays using CCD and CMOS technologies. One or more metalenses may be used to provide the functionality of traditional microlens focusing, color filtering, infrared filtering, and/or other filtering and refracting functions. In some embodiments, the same metalens or an additional metalens may be used as the primary focusing lens for an imaging device and/or to supplement a traditional primary focusing lens of an imaging device.
This disclosure has been made with reference to various embodiments, including the best mode. However, those skilled in the art will recognize that changes and modifications may be made to the various embodiments without departing from the scope of the present disclosure. While the principles of this disclosure have been shown in various embodiments, many modifications of structure, arrangements, proportions, elements, materials, and components may be adapted for a specific environment and/or operating requirements without departing from the principles and scope of this disclosure. These and other changes or modifications are intended to be included within the scope of the present disclosure.
This disclosure is to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope thereof. Likewise, benefits, other advantages, and solutions to problems have been described above with regard to various embodiments. However, benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element.
This application claims benefit of and priority to U.S. Provisional Patent Application No. 63/120,546 filed on Dec. 2, 2020 titled “Metalenses for Optical Displays” and U.S. Provisional Patent Application No. 63/046,094 filed on Jun. 30, 2020 also titled “Metalenses for Optical Displays,” each of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63120546 | Dec 2020 | US | |
| 63046094 | Jun 2020 | US |
