PATENT DOCUMENT

Publication Number: US-11796872-B1
Application Number: US-202117459718-A
Country: US
Kind Code: B1

Title: Optical systems with pixel shifting structures

Abstract:
A display may include illumination optics, a ferroelectric liquid crystal on silicon (fLCOS) panel, and a waveguide. A twisted nematic cell may be optically interposed between the fLCOS panel and the waveguide. A birefringent crystal may be optically interposed between the cell and the waveguide. The cell may have a first state in which the cell transmits the image light with a first polarization and a second state in which the cell transmits the image light with a second polarization. The crystal may transmit the image light within spatially offset beams based on polarization. In another arrangement, a quarter waveplate may be optically interposed between the cell and the waveguide and a geometric phase grating may be optically interposed between the quarter waveplate and the waveguide. Control circuitry may toggle the cell between the first and second states to maximize the effective resolution of images at an eye box.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 illumination optics configured to produce illumination; 
 a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce light by modulating image data using the illumination; 
 a waveguide configured to propagate the light via total internal reflection; 
 an input coupling prism on the waveguide and configured to couple the light into the waveguide; 
 a twisted nematic (TN) cell optically interposed between the fLCOS panel and the input coupling prism; and 
 a birefringent crystal optically interposed between the TN cell and the input coupling prism. 
 
     
     
       2. The electronic device of  claim 1 , wherein the birefringent crystal comprises a uniaxial birefringent crystal. 
     
     
       3. The electronic device of  claim 1 , wherein the birefringent crystal comprises a biaxial birefringent crystal. 
     
     
       4. The electronic device of  claim 1 , wherein the light is incident upon the TN cell with a first linear polarization. 
     
     
       5. The electronic device of  claim 4 , wherein the TN cell has a first state in which the TN cell transmits the light to the birefringent crystal with the first linear polarization and wherein the TN cell has a second state in which the TN cell transmits the light to the birefringent crystal with a second linear polarization that is different from the first linear polarization. 
     
     
       6. The electronic device of  claim 5 , wherein the birefringent crystal is configured to transmit the light with the first linear polarization towards the input coupling prism within a first beam and wherein the birefringent crystal is configured to transmit the light with the second linear polarization towards the input coupling prism within a second beam that is spatially offset from the first beam. 
     
     
       7. The electronic device of  claim 6 , wherein the image data comprises an image frame having a pixel pitch and wherein the second beam is spatially offset from the first beam by a displacement that is less than the pixel pitch. 
     
     
       8. The electronic device of  claim 7 , further comprising:
 control circuitry coupled to the TN cell, wherein the control circuitry is configured to toggle the TN cell between the first and second states at a rate greater than or equal to 24 Hz. 
 
     
     
       9. An electronic device for displaying light, the electronic device comprising:
 a reflective display panel configured to produce light with a first linear polarization by modulating illumination using image data; 
 a twisted nematic (TN) cell configured to receive the light from the reflective display panel, wherein the TN cell has a first state in which the TN cell transmits the light with the first linear polarization and a second state in which the TN cell transmits the light with a second linear polarization that is different from the first linear polarization; 
 a uniaxial birefringent crystal configured to transmit the light with the first linear polarization within a first beam and configured to transmit the light with the second linear polarization within a second beam that is spatially offset from the first beam; 
 control circuitry configured to toggle the TN cell between the first and second states; 
 a waveguide configured to propagate the first and second beams of light via total internal reflection; and 
 an input coupling prism mounted to the surface of the waveguide, the input coupling prism being configured to receive the first and second beams of light from the uniaxial birefringent crystal and being configured to couple the first and second beams of light into the waveguide. 
 
     
     
       10. The electronic device of  claim 9 , wherein the control circuitry is configured to toggle the TN cell between the first and second states at a rate greater than or equal to 24 Hz. 
     
     
       11. The electronic device of  claim 9 , further comprising a collimating lens optically interposed between the uniaxial birefringent crystal and the input coupling prism. 
     
     
       12. An electronic device for displaying light, the electronic device comprising:
 a projector configured to modulate illumination using image data to generate light having a first linear polarization; 
 a cell configured to receive the light from the projector, wherein the cell is toggled between a first state in which the cell transmits the light with the first linear polarization and a second state in which the cell transmits the light with a second linear polarization that is different from the first linear polarization; 
 a crystal configured to transmit the light with the first linear polarization within a first beam and configured to transmit the light with the second linear polarization within a second beam that is spatially offset from the first beam; 
 a waveguide configured to propagate the first and second beams of light via total internal reflection; and 
 an input coupling prism mounted to a surface of the waveguide and configured to couple the first and second beams of light into the waveguide. 
 
     
     
       13. The electronic device of  claim 12 , wherein the cell comprises a twisted nematic cell. 
     
     
       14. The electronic device of  claim 12 , wherein the crystal comprises a uniaxial birefringent crystal. 
     
     
       15. The electronic device of  claim 12 , wherein the projector comprises a ferroelectric liquid crystal on silicon (fLCOS) panel. 
     
     
       16. The electronic device of  claim 12 , wherein the cell is toggled between the first and second states at a rate greater than or equal to 24 Hz. 
     
     
       17. The electronic device of  claim 12 , wherein the crystal is optically coupled between the cell and the input coupling prism. 
     
     
       18. The electronic device of  claim 17 , further comprising a collimating lens optically coupled between the crystal and the input coupling prism.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 63/072,003, filed Aug. 28, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to optical systems and, more particularly, to optical systems for displays. 
     Electronic devices may include displays that present images to a user&#39;s eyes. For example, devices such as virtual reality and augmented reality headsets may include displays with optical elements that allow users to view the displays. 
     It can be challenging to design devices such as these. If care is not taken, the components used in displaying content may be unsightly and bulky, can consume excessive power, and may not exhibit desired levels of optical performance. 
     SUMMARY 
     An electronic device such as a head-mounted device may have one or more near-eye displays that produce images for a user. The head-mounted device may be a pair of virtual reality glasses or may be an augmented reality headset that allows a viewer to view both computer-generated images and real-world objects in the viewer&#39;s surrounding environment. 
     The display may include a display module and a waveguide. The display module may include a spatial light modulator such as a ferroelectric liquid crystal on silicon (fLCOS) display panel and illumination optics. The illumination optics may include light sources such as light emitting diodes (LEDs) that produce illumination light. The illumination light may be provided with a linear polarization and may be transmitted to the fLCOS display panel. The fLCOS display panel may modulate image data (e.g., image frames) onto the illumination light to produce image light. The waveguide may direct the image light towards an eye box. 
     A twisted nematic (TN) cell may be optically interposed between the fLCOS display panel and the waveguide. A birefringent crystal may be optically interposed between the TN cell and the waveguide (e.g., between the TN cell and a collimating lens for the waveguide). The image light may be incident upon the TN cell with a first linear polarization. The TN cell may have a first state in which the TN cell transmits the image light with the first linear polarization. The TN cell may have a second state in which the TN cell transmits the image light with a second linear polarization that is different from the first linear polarization. The birefringent crystal may transmit the image light with the first linear polarization within a first beam. The birefringent crystal may transmit the image light with the second linear polarization within a second beam that is spatially offset from the first beam. In another suitable arrangement, a quarter waveplate may be optically interposed between the TN cell and the waveguide and a geometric phase grating may be optically interposed between the quarter waveplate and the waveguide (e.g., where the geometric phase grating is interposed between a collimating lens and the waveguide and where the quarter waveplate is interposed between the TN cell and the waveguide). The quarter waveplate may convert the first and second linear polarizations to left and right hand circular polarizations. The geometric phase grating may diffract left hand circular polarized image light onto a first output angle and may diffract right hand circular polarized image light onto a second output angle. Control circuitry may toggle the TN cell between the first and second states to maximize the effective resolution of images at the eye box. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an illustrative system having a display in accordance with some embodiments. 
         FIG.  2    is a top view of an illustrative optical system for a display having a display module that provides image light to a waveguide in accordance with some embodiments. 
         FIG.  3    is a top view of an illustrative display module having a ferroelectric liquid crystal on silicon (fLCOS) display panel in accordance with some embodiments. 
         FIG.  4    is a top view of an illustrative display having spatial pixel shifting structures that increase the effective resolution of images provided at an eye box in accordance with some embodiments. 
         FIG.  5    is a top view of an illustrative display having angular pixel shifting structures that increase the effective resolution of images provided at an eye box in accordance with some embodiments. 
         FIG.  6    is a front view of pixels of image light that illustrates how illustrative pixel shifting structures the types shown in  FIGS.  4  and  5    may increase the effective resolution of the image light in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative system having a device with one or more near-eye display systems is shown in  FIG.  1   . System  10  may be a head-mounted device having one or more displays such as near-eye displays  14  mounted within support structure (housing)  20 . Support structure  20  may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of near-eye displays  14  on the head or near the eye of a user. Near-eye displays  14  may include one or more display modules such as display modules  14 A and one or more optical systems such as optical systems  14 B. Display modules  14 A may be mounted in a support structure such as support structure  20 . Each display module  14 A may emit light  22  (sometimes referred to herein as image light  22 ) that is redirected towards a user&#39;s eyes at eye box  24  using an associated one of optical systems  14 B. 
     The operation of system  10  may be controlled using control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for controlling the operation of system  10 . Circuitry  16  may include storage such as hard disk drive storage, nonvolatile memory (e.g., electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, graphics processing units, application specific integrated circuits, and other integrated circuits. Software code (instructions) may be stored on storage in circuitry  16  and run on processing circuitry in circuitry  16  to implement operations for system  10  (e.g., data gathering operations, operations involving the adjustment of components using control signals, image rendering operations to produce image content to be displayed for a user, etc.). 
     System  10  may include input-output circuitry such as input-output devices  12 . Input-output devices  12  may be used to allow data to be received by system  10  from external equipment (e.g., a tethered computer, a portable device such as a handheld device or laptop computer, or other electrical equipment) and to allow a user to provide head-mounted device  10  with user input. Input-output devices  12  may also be used to gather information on the environment in which system  10  (e.g., head-mounted device  10 ) is operating. Output components in devices  12  may allow system  10  to provide a user with output and may be used to communicate with external electrical equipment. Input-output devices  12  may include sensors and other components  18  (e.g., image sensors for gathering images of real-world object that are digitally merged with virtual objects on a display in system  10 , accelerometers, depth sensors, light sensors, haptic output devices, speakers, batteries, wireless communications circuits for communicating between system  10  and external electronic equipment, etc.). In one suitable arrangement that is sometimes described herein as an example, the sensors in components  18  may include one or more temperature (T) sensors  19 . Temperature sensor(s)  19  may gather temperature sensor data (e.g., temperature values) from one or more locations in system  10 . If desired, control circuitry  16  may use the gathered temperature sensor data in controlling the operation of display module  14 A. 
     Display modules  14 A (sometimes referred to herein as display engines  14 A, light engines  14 A, or projectors  14 A) may include reflective displays (e.g., displays with a light source that produces illumination light that reflects off of a reflective display panel to produce image light such as liquid crystal on silicon (LCOS) displays (e.g., ferroelectric liquid crystal on silicon (fLCOS) displays), digital-micromirror device (DMD) displays, or other spatial light modulators), emissive displays (e.g., micro-light-emitting diode (uLED) displays, organic light-emitting diode (OLED) displays, laser-based displays, etc.), or displays of other types. An arrangement in which display module  14 A includes an fLCOS display is sometimes described herein as an example. Light sources in display modules  14 A may include uLEDs, OLEDs, LEDs, lasers, combinations of these, or any other desired light-emitting components. 
     Optical systems  14 B may form lenses that allow a viewer (see, e.g., a viewer&#39;s eyes at eye box  24 ) to view images on display(s)  14 . There may be two optical systems  14 B (e.g., for forming left and right lenses) associated with respective left and right eyes of the user. A single display  14  may produce images for both eyes or a pair of displays  14  may be used to display images. In configurations with multiple displays (e.g., left and right eye displays), the focal length and positions of the lenses formed by components in optical system  14 B may be selected so that any gap present between the displays will not be visible to a user (e.g., so that the images of the left and right displays overlap or merge seamlessly). 
     If desired, optical system  14 B may contain components (e.g., an optical combiner, etc.) to allow real-world image light from real-world images or objects  25  to be combined optically with virtual (computer-generated) images such as virtual images in image light  22 . In this type of system, which is sometimes referred to as an augmented reality system, a user of system  10  may view both real-world content and computer-generated content that is overlaid on top of the real-world content. Camera-based augmented reality systems may also be used in device  10  (e.g., in an arrangement in which a camera captures real-world images of object  25  and this content is digitally merged with virtual content at optical system  14 B). 
     System  10  may, if desired, include wireless circuitry and/or other circuitry to support communications with a computer or other external equipment (e.g., a computer that supplies display  14  with image content). During operation, control circuitry  16  may supply image content to display  14 . The content may be remotely received (e.g., from a computer or other content source coupled to system  10 ) and/or may be generated by control circuitry  16  (e.g., text, other computer-generated content, etc.). The content that is supplied to display  14  by control circuitry  16  may be viewed by a viewer at eye box  24 . 
       FIG.  2    is a top view of an illustrative display  14  that may be used in system  10  of  FIG.  1   . As shown in  FIG.  2   , display  14  may include one or more display modules such as display module  14 A and an optical system such as optical system  14 B. Optical system  14 B may include optical elements such as one or more waveguides  26 . Waveguide  26  may include one or more stacked substrates (e.g., stacked planar and/or curved layers sometimes referred to herein as waveguide substrates) of optically transparent material such as plastic, polymer, glass, etc. 
     If desired, waveguide  26  may also include one or more layers of holographic recording media (sometimes referred to herein as holographic media, grating media, or diffraction grating media) on which one or more diffractive gratings are recorded (e.g., holographic phase gratings, sometimes referred to herein as holograms). A holographic recording may be stored as an optical interference pattern (e.g., alternating regions of different indices of refraction) within a photosensitive optical material such as the holographic media. The optical interference pattern may create a holographic phase grating that, when illuminated with a given light source, diffracts light to create a three-dimensional reconstruction of the holographic recording. The holographic phase grating may be a non-switchable diffractive grating that is encoded with a permanent interference pattern or may be a switchable diffractive grating in which the diffracted light can be modulated by controlling an electric field applied to the holographic recording medium. Multiple holographic phase gratings (holograms) may be recorded within (e.g., superimposed within) the same volume of holographic medium if desired. The holographic phase gratings may be, for example, volume holograms or thin-film holograms in the grating medium. The grating media may include photopolymers, gelatin such as dichromated gelatin, silver halides, holographic polymer dispersed liquid crystal, or other suitable holographic media. 
     Diffractive gratings on waveguide  26  may include holographic phase gratings such as volume holograms or thin-film holograms, meta-gratings, or any other desired diffractive grating structures. The diffractive gratings on waveguide  26  may also include surface relief gratings formed on one or more surfaces of the substrates in waveguides  26 , gratings formed from patterns of metal structures, etc. The diffractive gratings may, for example, include multiple multiplexed gratings (e.g., holograms) that at least partially overlap within the same volume of grating medium (e.g., for diffracting different colors of light and/or light from a range of different input angles at one or more corresponding output angles). 
     Optical system  14 B may include collimating optics such as collimating lens  34 . Collimating lens  34  may include one or more lens elements that help direct image light  22  towards waveguide  26 . Collimating lens  34  is shown external to display module  14 A in  FIG.  2    for the sake of clarity. In general, collimating lens  34  may be formed entirely external to display module  14 A, entirely within display module  14 A, or one or more lens elements in collimating lens  34  may be formed in display module  14 A (e.g., collimating lens  34  may include both lens elements that are internal to display module  14 A and lens elements that are external to display module  14 A). Collimating lens  34  may be omitted if desired. If desired, display module(s)  14 A may be mounted within support structure  20  of  FIG.  1    while optical system  14 B may be mounted between portions of support structure  20  (e.g., to form a lens that aligns with eye box  24 ). Other mounting arrangements may be used, if desired. 
     As shown in  FIG.  2   , control circuitry  16  may control display module  14 A to generate image light  22  associated with image content (data) to be displayed to (at) eye box  24 . In the example of  FIG.  2   , display module  14 A includes illumination optics  36  and a spatial light modulator such as fLCOS display panel  40  (sometimes referred to herein simply as fLCOS panel  40 ). 
     Control circuitry  16  may be coupled to illumination optics  36  over control path(s)  42 . Control circuitry  16  may be coupled to fLCOS panel  40  over control path(s)  44 . Control circuitry  16  may provide control signals to illumination optics  36  over control path(s)  42  that control illumination optics  36  to produce illumination light  38  (sometimes referred to herein as illumination  38 ). The control signals may, for example, control illumination optics  36  to produce illumination light  38  using a corresponding illumination sequence. The illumination sequence may involve sequentially illuminating light sources of different colors in illumination optics  36 . In one suitable arrangement that is sometimes described herein as an example, the illumination sequence may be a green-heavy illumination sequence. 
     Illumination optics  36  may illuminate fLCOS display panel  40  using illumination light  38 . Control circuitry  16  may provide control signals to fLCOS display panel  40  over control path(s)  44  that control fLCOS display panel  40  to modulate illumination light  38  to produce image light  22 . For example, control circuitry  16  may provide image data such as image frames to fLCOS display panel  40 . The image light  22  produced by fLCOS display panel  40  may include the image frames identified by the image data. Control circuitry  16  may, for example, control fLCOS display panel  40  to provide fLCOS drive voltage waveforms to electrodes in the display panel. The fLCOS drive voltage waveforms may be overdriven or underdriven to optimize the performance of display module  14 A, if desired. While an arrangement in which display module  14 A includes fLCOS display panel  40  is described herein as an example, in general, display module  14 A may include any other desired type of reflective display panel (e.g., a DMD panel), an emissive display panel, etc. 
     Image light  22  may be collimated using collimating lens  34  (sometimes referred to herein as collimating optics  34 ). Optical system  14 B may be used to present image light  22  output from display module  14 A to eye box  24 . Optical system  14 B may include one or more optical couplers such as input coupler  28 , cross-coupler  32 , and output coupler  30 . In the example of  FIG.  2   , input coupler  28 , cross-coupler  32 , and output coupler  30  are formed at or on waveguide  26 . Input coupler  28 , cross-coupler  32 , and/or output coupler  30  may be completely embedded within the substrate layers of waveguide  26 , may be partially embedded within the substrate layers of waveguide  26 , may be mounted to waveguide  26  (e.g., mounted to an exterior surface of waveguide  26 ), etc. 
     The example of  FIG.  2    is merely illustrative. One or more of these couplers (e.g., cross-coupler  32 ) may be omitted. Optical system  14 B may include multiple waveguides that are laterally and/or vertically stacked with respect to each other. Each waveguide may include one, two, all, or none of couplers  28 ,  32 , and  30 . Waveguide  26  may be at least partially curved or bent if desired. 
     Waveguide  26  may guide image light  22  down its length via total internal reflection. Input coupler  28  may be configured to couple image light  22  from display module(s)  14 A into waveguide  26  (e.g., at an angle such that the image light can propagate down waveguide  26  via total internal reflection), whereas output coupler  30  may be configured to couple image light  22  from within waveguide  26  to the exterior of waveguide  26  and towards eye box  24 . Input coupler  28  may include a reflective or transmissive input coupling prism if desired. As an example, display module(s)  14 A may emit image light  22  in the +Y direction towards optical system  14 B. 
     When image light  22  strikes input coupler  28 , input coupler  28  may redirect image light  22  so that the light propagates within waveguide  26  via total internal reflection towards output coupler  30  (e.g., in the +X direction). When image light  22  strikes output coupler  30 , output coupler  30  may redirect image light  22  out of waveguide  26  towards eye box  24  (e.g., back in the −Y direction). In scenarios where cross-coupler  32  is formed at waveguide  26 , cross-coupler  32  may redirect image light  22  in one or more directions as it propagates down the length of waveguide  26 , for example. In this way, display module  14 A may provide image light  22  to eye box  24  over an optical path that extends from display module  14 A, through collimating lens  34 , input coupler  28 , cross coupler  32 , and output coupler  30 . 
     Input coupler  28 , cross-coupler  32 , and/or output coupler  30  may be based on reflective and refractive optics or may be based on holographic (e.g., diffractive) optics. In arrangements where couplers  28 ,  30 , and  32  are formed from reflective and refractive optics, couplers  28 ,  30 , and  32  may include one or more reflectors (e.g., an array of micromirrors, partial mirrors, louvered mirrors, or other reflectors). In arrangements where couplers  28 ,  30 , and  32  are based on holographic optics, couplers  28 ,  30 , and  32  may include diffractive gratings (e.g., volume holograms, surface relief gratings, etc.). 
       FIG.  3    is a top view of display module  14 A. As shown in  FIG.  3   , display module  14 A may include illumination optics  36  that provide illumination light  38  to fLCOS display panel  40 . fLCOS display panel  40  may modulate images onto illumination light  38  to produce image light  22 . 
     Illumination optics  36  may include one or more light sources  48  such as a first light source  48 A, a second light source  48 B, and a third light source  48 C. Light sources  48  may emit illumination light  52 . Prism  46  (e.g., an X-plate) in illumination optics  36  may combine the illumination light  52  emitted by each of the light sources  48  to produce the illumination light  38  that is provided to fLCOS display panel  40 . In one suitable arrangement that is sometimes described herein as an example, first light source  48 A emits red illumination light  52 A (e.g., light source  48 A may be a red (R) light source), second light source  48 B emits green illumination light  52 B (e.g., light source  48 B may be a green (G) light source), and third light source  48 C emits blue illumination light  52 C (e.g., light source  48 C may be a blue (B) light source). This is merely illustrative. In general, light sources  48 A,  48 B, and  48 C may respectively emit light in any desired wavelength bands (e.g., visible wavelengths, infrared wavelengths, near-infrared wavelengths, etc.). 
     An arrangement in which illumination optics  36  includes only one light source  48 A, one light source  48 B, and one light source  48 C is sometimes described herein as an example. This is merely illustrative. If desired, illumination optics  36  may include any desired number of light sources  48 A (e.g., an array of light sources  48 A), any desired number of light sources  48 B (e.g., an array of light sources  48 B), and any desired number of light sources  48 C (e.g., an array of light sources  48 C). Light sources  48 A,  48 B, and  48 C may include LEDs, OLEDs, uLEDs, lasers, or any other desired light sources. An arrangement in which light sources  48 A,  48 B, and  48 C are LED light sources is described herein as an example. Light sources  48 A,  48 B, and  48 C may be controlled (e.g., separately/independently controlled) by control signals received from control circuitry  16  ( FIG.  2   ) over control path(s)  42 . The control signals may, for example, control light sources  48 A,  48 B, and  48 C to emit illumination light  52  using a corresponding illumination sequence in which one or more of the light sources emits illumination light at any given time and the active light sources cycle over time. 
     Illumination light  38  may include the illumination light  52 A,  52 B, and  52 C emitted by light sources  48 A,  48 B, and  48 C, respectively. Prism  50  may provide illumination light  38  to fLCOS display panel  40 . If desired, additional optical components such as lens elements, microlenses, polarizers, prisms, beam splitters, and/or diffusers (not shown in  FIG.  3    for the sake of clarity) may be optically interposed between light sources  48 A-C and fLCOS display panel  40  to help direct illumination light  38  from illumination optics  36  to fLCOS display panel  40 . 
     Prism  50  may direct illumination light  38  onto fLCOS display panel  40  (e.g., onto different pixels P* on fLCOS display panel  40 ). Control circuitry  16  may provide control signals to fLCOS display panel  40  over control path(s)  44  that control fLCOS display panel  40  to selectively reflect illumination light  38  at each pixel location to produce image light  22  (e.g., image light having an image as modulated onto the illumination light by fLCOS display panel  40 ). As an example, the control signals may drive fLCOS drive voltage waveforms onto the pixels of fLCOS display panel  40 . Prism  50  may direct image light  22  towards collimating lens  34  of  FIG.  2   . 
     In general, fLCOS display panel  40  operates on illumination light of a single linear polarization. Polarizing structures interposed on the optical path between light sources  48 A-C and fLCOS display panel  40  may convert unpolarized illumination light into linearly polarized illumination light (e.g., s-polarized light or p-polarized illumination light). The polarizing structures may, for example, be optically interposed between prism  50  and fLCOS display panel  40 , between prism  46  and prism  50 , between light sources  48 A-C and prism  46 , within light sources  48 A-C, or elsewhere. 
     If a given pixel P* in fLCOS display panel  40  is turned on, the corresponding illumination light may be converted between linear polarizations by that pixel of the display panel. For example, if s-polarized illumination light  38  is incident upon a given pixel P*, fLCOS display panel  40  may reflect the s-polarized illumination light  38  to produce corresponding image light  22  that is p-polarized when pixel P* is turned on. Similarly, if p-polarized illumination light  38  is incident upon pixel P*, fLCOS display panel  40  may reflect the s-polarized illumination light  38  to produce corresponding image light  22  that is s-polarized when pixel P* is turned on. If pixel P* is turned off, the pixel does not convert the polarization of the illumination light, which prevents the illumination light from reflecting out of fLCOS display panel  40  as image light  22 . 
     In practice, it may be desirable to be able to increase both the field of view of and the resolution of the images in image light  22  provided to eye box  24 . In one suitable arrangement that is described herein as an example, the effective resolution of images provided to eye box  24  may be increased by performing pixel shifting operations in display  14 . 
       FIG.  4    is a top-down view showing how display  14  may perform spatial pixel shifting operations to maximize the effective resolution of images provided to eye box  24 . As shown in  FIG.  4   , display  14  may include a twisted nematic (TN) cell  220  and a birefringent crystal  222  optically interposed between display module  14 A ( FIG.  2   ) and input coupler  28  on waveguide  26 . Birefringent crystal  222  may be optically interposed between TN cell  220  and input coupler  28 . If desired, TN cell  220  and/or birefringent crystal  222  may be formed within display module  14 A of  FIG.  2    (e.g., collimating lens  34  of  FIG.  2    may be optically interposed between birefringent crystal  220  and input coupler  28 ). 
     TN cell  220  may receive image light  22  from fLCOS panel  40  ( FIG.  3   ). Image light  22  may be (linearly) polarized light such as p-polarized light or s-polarized light. An arrangement in which image light  22  is incident upon TN cell  220  as p-polarized light is described herein as an example. 
     TN cell  220  may receive control signals from control circuitry  16  ( FIG.  2   ) over control path  234 . The control signals may toggle TN cell  220  between first and second states. In the first state, TN cell  220  may transmit image light  22  without changing the polarization of image light  22 . TN cell  220  may thereby transmit p-polarized image light  22  to birefringent crystal  222  in the first state, as shown by arrow  224 . In the second state, TN cell  220  may change the polarization of image light  22  to a different linear polarization. For example, in the second state, TN cell  220  may convert the p-polarized image light  22  received from fLCOS display panel  40  into s-polarized image light  22  and may transmit the s-polarized image light  22  to birefringent crystal  222 , as shown by arrow  224 . 
     Birefringent crystal  222  (sometimes referred to herein as birefringent beam displacer  222 ) may be formed from a birefringent material such as calcite and may have a length (thickness)  232  (e.g., in the direction of the optical path). Birefringent crystal  222  may be a uniaxial birefringent crystal or a biaxial birefringent crystal, as examples. Birefringent crystal  222  may receive p-polarized image light  22  or s-polarized image light  22  from TN cell  220  (e.g., depending on the current state of TN cell  220 ). 
     Birefringent crystal  222  may spatially separate incident image light  22  based on the polarization of the image. For example, birefringent crystal  222  may output incident s-polarized image light  22  within a first beam, as shown by arrow  226 , and may output incident p-polarized image light  22  within a second beam, as shown by arrow  228 . Upon exiting birefringent crystal  222 , the second beam (e.g., the p-polarized image light  22 ) may be separated from the first beam (e.g., the s-polarized image light  22 ) by displacement  230 . The magnitude of displacement  230  may be directly proportional to the length  232  of birefringent crystal  222 , for example. 
     The p-polarized image light  22  may be spatially offset from the s-polarized image light  22  upon in-coupling to waveguide  26  by input coupler  28  (e.g., by displacement  230 ). The images conveyed by the s-polarized image light  22  may therefore be spatially offset (e.g., by displacement  130 ) from the images conveyed by the p-polarized image light  22  at eye box  24 . Control circuitry  16  may rapidly toggle TN cell  220  between the first and second states to alternate between providing input coupler  28  with p-polarized image light  22  and s-polarized image light  22 . Length  232  and thus displacement  230  may be selected so that, when the state of TN cell  220  is toggled more rapidly than the response rate of the human eye (e.g., 24 Hz or faster, 60 Hz or faster, 120 Hz or faster, 240 Hz or faster, etc.), the resulting images provided at eye box  24  exhibit an effective resolution that is greater than the resolution of that would otherwise be conveyed to eye box  24  in the absence of TN cell  220  and birefringent crystal  222 . TN cell  220  and birefringent crystal  222  of  FIG.  4    may sometimes be referred to collectively herein as spatial pixel shifting structures  225 . 
     The example of  FIG.  4    in which display  14  performs spatial pixel shifting operations is merely illustrative. In another suitable arrangement, display  14  may perform angular pixel shifting operations to maximize the effective resolution of images provided to eye box  24 . 
       FIG.  5    is a top-down view showing how display  14  may perform angular pixel shifting operations to maximize the effective resolution of images provided to eye box  24 . As shown in  FIG.  5   , birefringent crystal  222  of  FIG.  4    may be replaced by quarter waveplate  240  and geometric phase grating (GPG)  242 . Quarter waveplate  240  may be optically interposed between TN cell  220  and GPG  242 . GPG  242  may be optically interposed between quarter waveplate  240  and input coupler  28 . 
     Collimating lens  34  ( FIG.  2   ) may be optically interposed between GPG  242  and input coupler  28 , may be optically interposed between quarter waveplate  240  and GPG  242 , may be optically interposed between quarter waveplate  240  and TN cell  220 , or may be optically interposed between fLCOS display panel  40  and TN cell  220 . An arrangement in which collimating lens  34  is optically interposed between quarter waveplate  240  and GPG  242  is described herein as an example. In this example, the collimating lens may serve to focus the pupil of image light  22  onto GPG  242  (e.g., GPG  242  may be located external to display module  14 A and at or adjacent input coupler  28  and the entrance pupil of waveguide  26 ), whereas quarter waveplate  240  and TN cell  220  are located within display module  14 A. 
     Quarter waveplate  240  may convert p-polarized image light  22  (e.g., as provided by TN cell  220  when TN cell  220  is in the first state) into RHCP light that is provided to GPG  242 , as shown by arrow  252 . Quarter waveplate  240  may convert s-polarized image light  22  (e.g., as provided by TN cell  220  when TN cell  220  is in the second state) into LHCP light that is provided to GPG  242 , as shown by arrow  252 . 
     GPG  242  may diffract incident image light  22  received from quarter waveplate  240  onto a corresponding output angle θ (e.g., measured relative to the optical axis or the Y-axis as shown in  FIG.  5   ). GPG  242  may have different diffraction orders that diffract incident image light  22  in different directions based on the polarization of the incident image light. For example, GPG  242  may have a first diffraction order (e.g., a +1 diffraction order) that diffracts incident LHCP image light  22  onto output angle θ1, as shown by arrow  256 . GPG  242  may also have a second diffraction order (e.g., a −1 diffraction order) that diffracts incident RHCP image light  22  onto output angle −θ2, as shown by arrow  252 . Output angle −θ2 may be equal and opposite output angle θ1 or may be any other desired output angle. The output angles of arrows  254  and  256  may both be oriented on the same side of the optical axis if desired. 
     In one suitable arrangement that is sometimes described herein as an example, GPG  242  may include a substrate  244  and an alignment layer  246  layered onto substrate  244 . GPG  242  may include multiple liquid crystal (LC) layers  248  (e.g., a first LC layer  248 - 1 , a second LC layer  248 - 2 , and a third LC layer  248 - 3 ) layered onto alignment layer  246 . Alignment layer  246  may serve to align the LC molecules in LC layers  248  at substrate  244  (e.g., with a corresponding grating period). Each LC layer  248  may have a corresponding twist angle φ (e.g., LC layer  248 - 1  may have a first twist angle φ 1 , LC layer  248 - 2  may have a second twist angle φ 2  oriented opposite twist angle φ 1 , and LC layer  248 - 3  may have a third twist angle φ 3  oriented opposite twist angle φ 1 ). 
     In this way, the LHCP image light  22  may be angularly offset from the RHCP image light  22  upon in-coupling to waveguide  26  by input coupler  28  (e.g., by an angular displacement having a magnitude equal to |θ1|+|θ2|). The images conveyed by the LHCP image light  22  may therefore be angularly offset from the images conveyed by the RHCP image light  22  at eye box  24 . Control circuitry  16  may rapidly toggle TN cell between the first and second states to alternate between providing GPG  242  and thus input coupler  28  with LHCP image light  22  and RHCP image light  22 . GPG  242  may be configured to output image light  22  at angles θ1 and θ2 that are selected so that, when the state of TN cell  220  is toggled more rapidly than the response rate of the human eye, the resulting images provided at eye box  24  exhibit an effective resolution that is greater than the resolution of the images that would otherwise be conveyed to eye box  24  in the absence of TN cell  220 , quarter waveplate  240 , and GPG  242 . TN cell  220 , quarter waveplate  240 , and GPG  242  of  FIG.  5    may sometimes be referred to collectively herein as angular pixel shifting structures  253 . Spatial pixel shifting structures  225  of  FIG.  4    and angular pixel shifting structures  253  may sometimes be referred to collectively herein as pixel shifting structures for display  14 . 
       FIG.  6    is a front view showing how the pixel shifting structures in display  14  may provide image light  22  with an increased effective resolution at eye box  24  (e.g., as viewed at eye box  24  in the +Y direction of  FIG.  2   ). In the example of  FIG.  6   , four pixels of image light  22  are shown for the sake of clarity. In general, image light  22  and the display module may include any desired number of pixels. 
     As shown in  FIG.  6   , image light  22  may include pixels P 1 , P 2 , P 3 , and P 4  when TN cell  220  of  FIGS.  4  and  5    is in the first state (e.g., when TN cell  120  outputs p-polarized light). When TN cell  220  is in the second state (e.g., when TN cell  220  outputs s-polarized light), pixels P 1 , P 2 , P 3 , and P 4  may be displaced by displacement  260 , as shown by respective pixels P 1 ′, P 2 ′, P 3 ′, and P 4 ′. Displacement  260  may, for example, be a two-dimensional displacement that includes offset  264  parallel to the Z-axis and/or offset  262  parallel to the X-axis. Displacement  260  may be produced by a spatial displacement such as displacement  230  of  FIG.  4    (e.g., in scenarios where the pixel shifting structures include spatial pixel shifting structures  225 ) or by an angular displacement such as an angular displacement having a magnitude equal to |θ1|+|θ2| of  FIG.  5    (e.g., in scenarios where the pixel shifting structures include angular pixel shifting structures  253 ). 
     Pixels P 1 , P 2 , P 3 , and P 4  may exhibit a first pixel pitch and pixels P 1 ′, P 2 ′, P 3 ′, and P 4 ′ may also exhibit the first pixel pitch. However, the combination of pixels P 1 , P 2 , P 3 , and P 4  with pixels P 1 ′, P 2 ′, P 3 ′, and P 4 ′ may exhibit a second pixel pitch that is less than (e.g., half) the first pixel pitch. By rapidly toggling between the first and second states of TN cell  220 , image light  22  may effectively include each of pixels P 1 , P 2 , P 3 , P 4 , P 1 ′, P 2 ′, P 3 ′, and P 4 ′ (e.g., as perceived by a user at eye box  24 ) and thus the second pixel pitch, rather than only pixels P 1 , P 2 , P 3 , and P 4  and the first pixel pitch (e.g., in scenarios where pixel shifting structures are omitted from display  14 ). This may serve to increase the effective resolution of image light  22  relative to scenarios where the pixel shifting structures are omitted (e.g., to twice the resolution that image light  22  would otherwise have in the absence of the pixel shifting structures), without requiring an increase in size or processing resources for display module  14 A. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20210827
Publication Date: 20231024
Grant Date: 20231024
Priority Date: 20200828
Inventors: HE, ZIQIAN
LI, XIAOKAI
GE, ZHIBING
GUO, KAIKAI
CHEN, YUAN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/135", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0136", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1396", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133638", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2203/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/05", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/135", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133638", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/0136", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2413/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/0101", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2203/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/01", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2413/05", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1396", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0101", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/0136", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/141", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136277", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1347", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1396", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 88420992