PATENT DOCUMENT

Publication Number: US-11927864-B2
Application Number: US-202318169263-A
Country: US
Kind Code: B2

Title: Optical systems having fLCOS display panels

Abstract:
A display may include illumination optics, a ferroelectric liquid crystal on silicon (fLCOS) panel, and a waveguide. The illumination optics may produce illumination that is modulated by the fLCOS panel to produce image light. The waveguide may direct the image light towards an eye box. The fLCOS panel may include a ferroelectric liquid crystal (fLC) layer and a backplane. In order to maximize the reflectance of the fLCOS panel and thus the optical performance of the display, the backplane may be a silver backplane or a dielectric mirror backplane. In addition, the backplane may have a cell gap that is equal to a wavelength divided by four times the birefringence of the fLC layer. In order to further optimize the optical performance of the display module, the wavelength used in determining the cell gap may be a green wavelength between 500 nm and 565 nm.

Claims:
What is claimed is: 
     
       1. A display system comprising:
 illumination optics configured to produce illumination light; 
 a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating image data using the illumination light, the fLCOS panel comprising:
 a ferroelectric liquid crystal (fLC) layer, and 
 a planar layer of silver configured to receive the illumination light through the fLC layer and configured to reflect the illumination light, the fLC layer being configured to transmit the illumination light reflected off of the planar layer of silver as the image light; and 
 
 a waveguide configured to propagate the image light. 
 
     
     
       2. The display system of  claim 1 , wherein the fLCOS panel further comprises:
 a driver flex, wherein the planar layer of silver is layered on the driver flex. 
 
     
     
       3. The display system of  claim 2 , wherein the fLCOS panel further comprises:
 electrodes selected from the group consisting of: indium tin oxide (ITO) electrodes layered on the fLC layer and index-matching indium tin oxide (IMITO) electrodes layered on the fLC layer. 
 
     
     
       4. The display system of  claim 3 , wherein the fLCOS panel further comprises:
 a glass substrate layered on the ITO electrodes. 
 
     
     
       5. The display system of  claim 4 , wherein the fLCOS panel further comprises:
 a first polyimide alignment layer interposed between the ITO electrodes and the fLC layer; and 
 a second polyimide alignment layer interposed between the fLC layer and the planar layer of silver. 
 
     
     
       6. The display system of  claim 1 , wherein the fLC layer has a birefringence and a cell gap, wherein the cell gap is equal to a distance λ divided by four times the birefringence, and wherein the distance λ is less than or equal to 530 nm. 
     
     
       7. A display system comprising:
 illumination optics configured to produce illumination light; 
 a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating the illumination light using image data; and 
 a waveguide configured to propagate the image light, the fLCOS panel comprising:
 a ferroelectric liquid crystal (fLC) layer, 
 a dielectric mirror configured to receive the illumination light through the fLC layer and configured to reflect the illumination light as the image light, and 
 a driver flex, wherein the dielectric mirror is layered on the driver flex. 
 
 
     
     
       8. The display system of  claim 7 , wherein the fLCOS panel further comprises:
 indium tin oxide (ITO) electrodes layered on the fLC layer. 
 
     
     
       9. The display system of  claim 8 , wherein the fLCOS panel further comprises:
 a glass substrate layered on the ITO electrodes. 
 
     
     
       10. The display system of  claim 9 , wherein the fLCOS panel further comprises:
 a first polyimide alignment layer interposed between the ITO electrodes and the fLC layer; and 
 a second polyimide alignment layer interposed between the fLC layer and the dielectric mirror. 
 
     
     
       11. The display system of  claim 10 , wherein the fLCOS panel further comprises:
 an anti-reflective coating on the glass substrate. 
 
     
     
       12. The display system of  claim 11 , wherein the fLC layer has a birefringence and a cell gap, wherein the cell gap is equal to a number λ divided by four times the birefringence, and wherein the number λ is less than or equal to 565 nm. 
     
     
       13. A display system comprising:
 illumination optics configured to produce illumination light; 
 a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating the illumination light using image data; and 
 a waveguide configured to propagate the image light, the fLCOS panel comprising:
 a ferroelectric liquid crystal (fLC) layer, wherein the fLC layer has a birefringence Δn, and 
 a backplane configured to receive the illumination light through the fLC layer and configured to reflect the illumination light as the image light, wherein the fLC layer has a thickness equal to a wavelength divided by four times the birefringence Δn and wherein the wavelength is between 500 nm and 565 nm. 
 
 
     
     
       14. The display system of  claim 13 , wherein the illumination optics comprise a red light source configured to generate a range of red wavelengths of the illumination light, a blue light source configured to generate a range of blue wavelengths of the illumination light, and a green light source configured to generate a range of green wavelengths of the illumination light, wherein the wavelength is a vacuum wavelength, and wherein the range of green wavelengths comprises the vacuum wavelength. 
     
     
       15. The display system of  claim 13 , wherein the backplane comprises a backplane selected from the group consisting of: a silver backplane and a silver alloy backplane. 
     
     
       16. The display system of  claim 13 , wherein the backplane comprises a dielectric mirror backplane. 
     
     
       17. The display system of  claim 13 , wherein the wavelength is between 520 nm and 530 nm. 
     
     
       18. The display system of  claim 17 , wherein the wavelength is 526 nm. 
     
     
       19. The display system of  claim 1 , wherein the planar layer of silver comprises silver alloy and is continuous across its lateral area. 
     
     
       20. The display system of  claim 1 , wherein the fLCOS panel comprises pixels and the planar layer of silver extends between the pixels.

Description:
This application is a continuation of international patent application No. PCT/US2021/047618, filed Aug. 25, 2021, which claims priority to U.S. provisional patent application No. 63/071,991, filed Aug. 28, 2020, which are hereby incorporated by reference herein in their entireties. 
    
    
     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. 
     The fLCOS display panel may include at least a ferroelectric liquid crystal (fLC) layer and a backplane. The backplane may receive the illumination light through the fLC layer. The backplane may reflect the illumination light as the image light. In order to maximize the reflectance of the fLCOS display panel and thus the optical performance of the display module, the backplane may be a silver backplane or a dielectric mirror backplane. In some cases, silver alloy may be used to improve stability. In addition, the fLCOS display panel may have a cell gap that is equal to a wavelength divided by four times the birefringence of the fLC layer. In order to further optimize the optical performance of the display module, the wavelength used in determining the cell gap may be a green wavelength between 500 nm and 565 nm. 
    
    
     
       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 cross-sectional side view of an illustrative fLCOS display panel in accordance with some embodiments. 
         FIG.  5    is a plot of ferroelectric liquid crystal (fLC) efficiency as a function of cell gap for an illustrative fLCOS display panel in accordance with some embodiments. 
         FIG.  6    is a top view of an illustrative light source having polarization recycling structures with a reflective polarizer in accordance with some embodiments. 
         FIG.  7    is a top view of an illustrative light source having polarization recycling structures with a reflective polarizer and a quarter wave plate in accordance with some embodiments. 
         FIG.  8    is a plot of optical performance (luminance as a function of incident angle) for a light source having different polarization recycling structures in accordance with some embodiments. 
         FIG.  9    is a plot of optical performance (efficiency improvement as a function of integrating cone angle) for a light source having polarization recycling structures of the types shown in  FIGS.  6  and  7    in accordance with some embodiments. 
         FIG.  10    is a cross-sectional side view of an illustrative light source having integral polarization recycling structures in accordance with some embodiments. 
         FIGS.  11  and  12    are a cross-sectional side views of an illustrative light source having polarization recycling structures separated from the emissive area of the light source by an air gap in accordance with some embodiments. 
         FIG.  13    is a cross-sectional side view of an illustrative light source having integral polarization recycling structures on a ceramic substrate in accordance with some embodiments. 
         FIG.  14    is a cross-sectional side view showing how illustrative polarization recycling structures may be shared by multiple light sources in accordance with some embodiments. 
         FIGS.  15  and  16    are cross-sectional side views of an illustrative light source having polarization recycling structures integrated with a condenser lens in accordance with some embodiments. 
         FIG.  17    is a top view of an illustrative X-plate that may be provided with interference coatings for reflecting and transmitting light from light sources in accordance with some embodiments. 
         FIG.  18    is a plot showing how polarization recycling structures may optimize optical performance (X-plate reflection as a function of wavelength) for light sources in a display module in accordance with some embodiments. 
         FIG.  19    is a timing diagram of illustrative illumination sequences that may be used by light sources to optimize power consumption in a display module in accordance with some embodiments. 
         FIG.  20    is a flow chart of illustrative steps that may be involved in controlling an fLCOS display panel to display images based on a green-heavy illumination sequence in accordance with some embodiments. 
         FIG.  21    is a flow chart of illustrative steps that may be involved in controlling light sources using a green-heavy illumination sequence in accordance with some embodiments. 
         FIG.  22    is a flow chart of illustrative steps for driving an fLCOS display panel to compensate for chromatic aberrations in a display module in accordance with some embodiments. 
         FIG.  23    is a CIE1931 color space plot that shows how illuminating an fLCOS panel using an illustrative green-heavy illumination sequence may modify the color gamut for images produced by the fLCOS panel in accordance with some embodiments. 
         FIG.  24    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.  25    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.  26    is a front view of pixels of image light that illustrates how illustrative pixel shifting structures the types shown in  FIGS.  24  and  25    may increase the effective resolution of the image light in accordance with some embodiments. 
         FIG.  27    is a timing diagram of illustrative driving voltages that may be used to drive an fLCOS display panel in accordance with some embodiments. 
         FIG.  28    is a timing diagram showing how an illustrative fLCOS display panel may be overdriven by a non-square wave driving voltage waveform in accordance with some embodiments. 
         FIG.  29    is a flow chart of illustrative steps that may be involved in overdriving an fLCOS display panel based on temperature sensor measurements in accordance with some embodiments. 
         FIG.  30    is a flow chart of illustrative steps that may be involved in overdriving an fLCOS display panel based on frame history information in accordance with some embodiments. 
         FIG.  31    is a plot of fLCOS performance (response time as a function of temperature) that shows how overdriving an fLCOS display panel based on temperature sensor measurements may minimize fLCOS response time 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 . 
       FIG.  4    is a cross-sectional side view of fLCOS display panel  40 . Four pixels P* in fLCOS display panel  40  are illustrated in  FIG.  4    for the sake of clarity. In general, fLCOS display panel  40  may include any desired number of pixels P* arranged in any desired pattern (e.g., any desired number of rows and columns). 
     As shown in  FIG.  4   , fLCOS display panel  40  may include a flexible printed circuit  74  (sometimes referred to herein as driver flex  74 ). Driver flex  74  may be layered onto substrate  76 . This is merely illustrative and, if desired, substrate  76  may be omitted. Driver flex  74  may carry control path(s)  44  ( FIG.  2   ) for driving the pixels P* in fLCOS display panel  40 , for example. 
     A backplane such as backplane  72  may be layered over driver flex  74 . Backplane  72  may serve as a reflective surface for reflecting incident illumination light  38  as corresponding image light  22 . In some scenarios, backplane  72  is an aluminum backplane made from aluminum metal. However, in practice, forming backplane  72  from aluminum may limit the overall reflective performance of fLCOS display panel  40 , thereby limiting the overall optical performance and efficiency of display module  14 A. 
     In order to increase the reflectivity of backplane  72 , backplane  72  may be formed from silver or a silver alloy (e.g., backplane  72  may be a silver backplane or a silver alloy backplane). Forming backplane  72  from silver may, for example, increase the amount of reflection in media for fLCOS display panel  40  from around 86% (in scenarios where backplane  72  is formed from aluminum) to as high as around 97%. Forming backplane  72  from silver alloy may optimize the stability of the system, for example. In another suitable arrangement, backplane  72  may be a dielectric mirror backplane. Forming backplane  72  from a dielectric mirror may also increase the reflectance of fLCOS display panel  40  relative to scenarios where an aluminum backplane is used. 
     An alignment layer such as polyimide alignment layer  70  may be layered over backplane  72 . A ferroelectric liquid crystal (fLC) layer such as fLC layer  68  may be layered over polyimide alignment layer  70 . An additional polyimide alignment layer  66  may be layered over fLC layer  68 . Polyimide alignment layers  70  and  66  may, for example, serve to align the fLC molecules in fLC layer  68  at the upper and lower surfaces of fLC layer  68 . 
     An electrode layer such as electrode layer  64  may be layered over polyimide alignment layer  66 . Electrode layer  64  may include indium tin oxide (ITO) traces or index-matching indium tin oxide (IMITO) traces, as examples. Electrode layer  64  may, for example, receive fLCOS drive voltage waveforms that control the state of each pixel P* in fLCOS display panel  40  (e.g., to reflect incident illumination light  38  of a first polarization as corresponding image light  22  of a second polarization when the pixel is turned on and to reflect illumination light  38  with the first polarization when the pixel is turned off, thereby preventing the reflected light from passing to waveguide  26  of  FIG.  2    as image light  22 ). 
     A cover layer such as cover glass  62  may be layered over electrode layer  64  (e.g., electrode layer  64  may be patterned onto the lower surface of cover glass  62 ). An optional anti-reflective coating  60  may be layered over cover glass  62  to minimize reflections at the upper surface of cover glass  62 . As shown in  FIG.  4   , illumination light  38  may pass through anti-reflective coating  60 , cover glass  62 , electrode layer  64 , polyimide alignment layer  66  and fLC layer  68 . Illumination light  38  may reflect off of backplane  72  (e.g., as image light  22  when the corresponding pixel P* is turned on). Image light  22  may then pass through fLC layer  68 , polyimide alignment layer  66 , electrode layer  64 , cover glass  62 , and anti-reflective coating  60  before passing to waveguide  26  of  FIG.  2   . 
     fLC layer  68  may have a corresponding birefringence Δn. fLC layer  68  may have a thickness  78 . Thickness  78  may sometimes be referred to herein as cell gap  78 . In general, cell gap  78  may be selected to optimize the optical efficiency of fLCOS display panel  40  at a particular wavelength. This may be performed by selecting cell gap  78  to be approximately equal to (e.g., within 5% of) λ/(4Δn), where λ is the vacuum wavelength for which optical efficiency is optimized and “/” is the division operator. 
       FIG.  5    is a plot of the optical efficiency of fLC display panel  40  as a function of cell gap  78 . As shown in  FIG.  5   , curve  80  plots the efficiency of fLC display panel  40  at blue wavelengths (e.g., at a blue wavelength such as 450 nm). Curve  82  plots the efficiency of fLC display panel  40  at green wavelengths (e.g., a green wavelength such as 532 nm). Curve  84  plots the efficiency of fLC display panel  40  at red wavelengths (e.g., a red wavelength such as 633 nm). 
     In some scenarios, cell gap  78  may be selected to have magnitude G1 (e.g., the cell gap corresponding to the intersection of curves  80  and  82 ). This may serve to optimize the efficiency of fLC display panel  40  for both blue and green wavelengths. However, the optical performance of fLCOS display panel  40  may be further optimized by increasing cell gap  78 , as shown by arrow  86 , to magnitude G2 (e.g., the cell gap corresponding to the peak of curve  82 ). By selecting cell gap  78  to have magnitude G2, the optical efficiency of fLC display panel  40  may be optimized for green wavelengths. This may serve to increase the overall optical efficiency of fLCOS display panel  40  in response to illumination light  38  relative to scenarios where cell gap  78  has magnitude G1. 
     In other words, the optical efficiency of fLC display panel  40  may be optimized when cell gap  78  of  FIG.  4    is selected to be equal to λ G /(4Δn), where λ G  is a vacuum wavelength such as a green wavelength, 526 nm, between 520 nm and 530 nm, between 510 nm and 540 nm, between 500 nm and 565 nm, less than 565 nm, less than 550 nm, less than 540 nm, less than 530 nm, greater than 500 nm, greater than 510 nm, or greater than 520 nm, as examples. Configuring cell gap  78  in this way may increase the magnitude of cell gap  78  from a magnitude G1 of around 620 nm to a magnitude G2 of around 706 nm, as one example. This may serve to increase the optical efficiency of fLC layer  68  and thus fLCOS display panel  40  by as much as 5% relative to scenarios where cell gap  78  has magnitude G1. The example of  FIG.  5    is merely illustrative. Curves  80 - 84  may have other shapes in practice. 
     In general, the light-emissive portions of light sources  48 A-C ( FIG.  3   ) emit unpolarized illumination light. The unpolarized illumination light is converted to a single linear polarization (e.g., s-polarized light or p-polarized light) in order to be reflected by fLCOS display panel  40  as image light  22 . However, if care is not taken, converting unpolarized light to light of a single linear polarization can prevent as much as half of the emitted illumination light from being converted into image light  22 , thereby limiting the overall optical efficiency of display module  14 A. If desired, light sources  48 A-C may include polarization recycling structures that increase the amount of emitted illumination light that is converted to image light  22 , thereby maximizing the optical efficiency of display module  14 A. 
       FIG.  6    is a top view of an illustrative light source  48  having polarization recycling structures. Light source  48  of  FIG.  6    may be a light source such as light source  48 A, light source  48 B, or light source  48 C of  FIG.  3   , for example. An arrangement in which light source  48  is an LED light source is described herein as an example. This is merely illustrative and, in general, light source  48  may be any desired type of light source. 
     As shown in  FIG.  6   , light source  48  may include reflector and contact layer  92 . Light source  48  may include an LED die such as LED die  90  layered over reflector and contact layer  92 . Light source  48  may also include polarization recycling structures such as polarization recycling structures  93 . In the example of  FIG.  6   , polarization recycling structures  93  include a reflective polarizer such as reflective polarizer  96  overlapping LED die  90  and a polarizer such as polarizer  94  overlapping reflective polarizer  96  (e.g., reflective polarizer  96  may be optically interposed between polarizer  94  and LED die  90 ). Polarization recycling structures  93  may, for example, be optically interposed between LED die  90  and prism  46  of  FIG.  3   . 
     Polarizer  94  may transmit light of a single linear polarization while blocking light of other polarizations. An example in which polarizer  94  transmits s-polarized light while blocking light of other polarizations is described herein as an example. This is merely illustrative and, in another suitable arrangement, polarizer  94  may transmit p-polarized light. 
     As shown in  FIG.  6   , when light source  48  is active, LED die  90  may emit unpolarized illumination light, as shown by arrow  98  (e.g., in response to control signals received from control circuitry  16  over control path  42 ( s ) of  FIG.  2   ). In scenarios where reflective polarizer  96  is omitted, polarizer  94  serves to pass s-polarized light from the illumination light (e.g., as illumination light  52  that is provided to prism  46  of  FIG.  3   ) while blocking other polarizations. This may prevent as much as half of the emitted unpolarized light from passing to prism  46  and thus fLCOS display panel  40  ( FIG.  3   ). Polarization recycling structures  93  may serve to recycle polarizations of light that would otherwise not be transmitted by polarizer  94  until at least some of the recycled light passes through polarizer  94  as illumination light  52 , thereby increasing the overall optical efficiency of the display module. 
     Reflective polarizer  96  may be, for example, a wire grid polarizer (WGP), a reflective polarizer film or coating, a cholesteric liquid crystal (LC) layer, or other structures that transmit light of a first polarization while reflecting light of a second polarization. As shown by arrow  100 , reflective polarizer  96  may transmit light of the same polarization that is transmitted by polarizer  94  (e.g., reflective polarizer  96  may transmit s-polarized light). This light may pass through polarizer  94  as a portion of the illumination light  52  that is provided to prism  46  of  FIG.  3   . At the same time, reflective polarizer  96  may reflect light of other polarizations that are not transmitted by polarizer  94 . 
     For example, as shown by arrow  102 , reflective polarizer  96  may reflect p-polarized light from the unpolarized light emitted by LED die  90 . The p-polarized light reflected by reflective polarizer  96  may reflect off of reflector and contact layer  92 , as shown by arrow  104 . Some of the p-polarized light associated with arrow  102  may be converted to s-polarized light in the process of passing through LED die  90  and reflecting off of reflector and contact layer  92 . This s-polarized light may be transmitted by reflective polarizer  96  and polarizer  94  as a portion of illumination light  52  (e.g., as shown by arrow  106 ). At the same time, the p-polarized light associated with arrow  104  may reflect back to reflector and contact layer  92 , as shown by arrow  108 . The light may continue to reflect between reflective polarizer  96  and reflector and contact layer  92  (e.g., an infinite number of times), with s-polarized light in the reflected light passing through reflective polarizer  96  and polarizer  94  (e.g., as a portion of illumination light  52 ) for each reflection (bounce). Each bounce may contribute more s-polarized light to illumination light  52 , thereby increasing the total amount of the light emitted by light source  48  that passes to prism  46  and fLCOS display panel  40  as illumination light  38  ( FIG.  3   ). This may serve to increase the overall optical efficiency of the display module relative to scenarios where reflective polarizer  96  is omitted. 
     In order to further increase the optical efficiency of the display module, polarization recycling structures  93  may include a quarter wave plate.  FIG.  7    is a diagram showing how polarization recycling structures  93  may include a quarter waveplate (QWP). As shown in  FIG.  7   , polarization recycling structures  93  may include a quarter waveplate such as quarter waveplate  120 . Quarter waveplate  120  may be optically interposed between reflective polarizer  96  and LED die  90 . 
     As shown by arrow  122  of  FIG.  7   , the unpolarized light emitted by LED die  90  may pass through quarter waveplate  120  to reflective polarizer  96 . Reflective polarizer  96  may transmit light of the same polarization that is transmitted by polarizer  94  (e.g., reflective polarizer  96  may transmit s-polarized light). As shown by arrow  124 , this s-polarized light may pass through polarizer  94  as a portion of illumination light  52 . At the same time, reflective polarizer  96  may reflect p-polarized light back towards quarter wave plate  120 , as shown by arrow  126 . 
     Quarter waveplate  120  may convert the p-polarized light reflected by reflective polarizer  96  into right-hand circularly polarized (RHCP) light that is transmitted to reflector and contact layer  92 , as shown by arrow  128 . The RHCP light transmitted by quarter waveplate  120  may reflect off of reflector and contact layer  92  as left-hand circularly polarized (LHCP) light, as shown by arrow  130 . Quarter waveplate  120  may convert the LHCP light associated with arrow  130  into s-polarized light. As shown by arrow  132 , the s-polarized light transmitted by quarter waveplate  120  may pass through reflective polarizer  96  and polarizer  94  to form a portion of illumination light  52 . Including quarter waveplate  120  in polarization recycling structures  93  may serve to increase the amount of emitted light that is converted into illumination light  52  relative to scenarios where waveplate  120  is omitted (e.g., because the LHCP light associated with arrow  130  is converted to s-polarized light without the need for additional reflections between reflective polarizer  96  and reflector and contact layer  92 ). This may serve to increase the overall optical efficiency of the display module relative to scenarios where polarization recycling structures  93  do not include quarter waveplate  120  (e.g., as shown in  FIG.  6   ). If desired, quarter waveplate  120  may have a retardation value optimized for each RGB LED respectively. For example, for red light source  48 A ( FIG.  3   ), the retardation value dΔn may be approximately λ R /4, where λ R  is the peak wavelength of red light source  48 A. Polarizer  94  may be omitted from polarization recycling structures  93  as described herein, if desired (e.g., because the reflective polarizer  96  outputs linearly polarized light). 
       FIGS.  8  and  9    are plots showing how polarization recycling structures  93  may optimize the optical performance of display module  14 A. In  FIG.  8   , the horizontal axis plots incident angle (in degrees) and the vertical axis plots the luminance of the illumination light  52  produced by light source  48 . Curve  140  of  FIG.  8    plots the luminance as a function of incident angle in scenarios where polarization recycling structures  93  are omitted (e.g., scenarios in which only a polarizer such as polarizer  94  is used to convert the unpolarized light emitted by LED die  90  into polarized light for reflection by the fLCOS display panel). 
     Curve  142  plots the luminance as a function of incident angle for the example of  FIG.  6    in which light source  48  includes polarization recycling structures  93  having reflective polarizer  94 . Curve  144  plots the luminance as a function of incident angle for the example of  FIG.  7    in which light source  48  includes polarization recycling structures  93  having both reflective polarizer  94  and quarter waveplate  120 . As shown by curves  142  and  144 , polarization recycling structures  93  may increase the luminance of light source  48  across all incident angles. Including quarter waveplate  120  may, for example, further increase the luminance of light source  48 . 
     In  FIG.  9   , the horizontal axis plots integrating cone angle and the vertical axis plots the optical efficiency improvement obtained by the display module relative to scenarios where polarization recycling structures  93  are omitted (e.g., scenarios in which only a polarizer such as polarizer  94  is used to convert the unpolarized light emitted by LED die  90  into polarized light for reflection by the fLCOS display panel). 
     Curve  146  of  FIG.  9    plots the efficiency improvement for the example of  FIG.  6    in which light source  48  includes polarization recycling structures  93  having reflective polarizer  96 . Curve  148  plots the efficiency improvement for the example of  FIG.  7    in which light source  48  includes polarization recycling structures  93  having both reflective polarizer  96  and quarter waveplate  120 . As shown by curves  148  and  146 , polarization recycling structures  93  may increase the efficiency of display module  14 A for all integrating cone angles relative to scenarios where polarization recycling structures  93  are omitted. As shown by curve  148 , including quarter waveplate  120  in polarization recycling structures  93  may further increase the optical efficiency of the display module  14 A, particularly at larger integrating cone angles. The examples of  FIGS.  8  and  9    are merely illustrative. Curves  140 - 148  may have other shapes in practice. 
     Polarization recycling structures  93  may be optically interposed between LED die  90  and prism  46  ( FIG.  3   ) in any desired manner.  FIG.  10    is a cross-sectional side view showing one illustrative example of how polarization recycling structures  93  may be integrated within light source  48 . As shown in  FIG.  10   , light source  48  may include a substrate such as patterned sapphire substrate (PSS)  150  layered over LED die  90 . Polarization recycling structures  93  may be layered over PSS  150 . 
     In another suitable arrangement, polarization recycling structures  93  may be separated from PSS  150  by an air gap.  FIG.  11    is a cross-sectional side view showing how polarization recycling structures  93  may be separated from PSS  150  by an air gap in an example where polarization recycling structures  93  include a wire grid polarizer. 
     As shown in  FIG.  11   , polarization recycling structures  93  in light source  48  may be separated PSS  150  by air gap  168 . Polarization recycling structures  93  may include a substrate such as glass layer  162  (sometimes referred to herein as cover glass layer  162 ) that is separated from PSS  150  by air gap  168 . In another suitable arrangement, layer  162  may include sapphire or other optically transparent materials if desired. Polarization recycling structures  93  may include a wire grid polarizer such as wire grid polarizer  164  (e.g., a wire grid polarizer that forms reflective polarizer  96  of  FIGS.  6  and  7   ) patterned onto the surface of glass layer  162  facing PSS  150 . If desired, the opposing surface of glass layer  162  may be covered by an optional anti-reflective layer (coating)  166 . If desired, PSS  150  may include textured surface features (e.g., surface roughness)  160  on the surface of PSS  150  at air gap  168 . Textured surface features  160  may, for example, increase light extraction efficiency and/or improve emission uniformity through glass layer  162  for light source  48  relative to scenarios where textured surface features  160  are omitted. 
     The example of  FIG.  11    in which the reflective polarizer includes wire grid polarizer  164  is merely illustrative. In another suitable arrangement, the reflective polarizer may include a reflective polarizer film.  FIG.  12    is a cross-sectional side view showing how polarization recycling structures  93  may be separated from PSS  150  by an air gap in an example where polarization recycling structures  93  include a reflective polarizer film. 
     As shown in  FIG.  12   , polarization recycling structures  93  may include reflective polarizer film  170 . Reflective polarizer film  170  may be separated from PSS  150  by air gap  168 . Reflective polarizer film  170  may form reflective polarizer  96  of  FIGS.  6  and  7   . An optional anti-reflective layer (coating)  169  may be layered onto the surface of reflective polarizer film  170  facing PSS  150 . In examples where polarization recycling structures  93  include quarter waveplate  120  ( FIG.  7   ), quarter waveplate  120  may be layered onto the bottom surface of reflective polarizer film  170  (e.g., quarter waveplate  120  may be interposed between reflective polarizer film  170  and anti-reflective layer  169  or PSS  150 ). 
     Reflective polarizer film  170  may be adhered to glass layer  162  by adhesive layer  172 . Adhesive layer  172  may include optically clear adhesive, pressure sensitive adhesive, or other adhesives, as examples. One or both of anti-reflective layers  166  and  169  may be omitted if desired. Inclusion of air gap  168  in light source  48  may, for example, allow for a fixed distance to be maintained between the reflective polarizer (e.g., wire grid polarizer  164  of  FIG.  11    or reflective polarizer film  170  of  FIG.  12   ) and LED die  90  (e.g., a distance of 200 microns or less, 100 microns or less, etc.). 
     If desired, in scenarios where light source  48  includes air gap  168 , LED die  90  and polarization recycling structures  93  may be integrated into a single LED package on a ceramic substrate.  FIG.  13    is a cross-sectional side view showing how LED die  90  and polarization recycling structures  93  may be integrated into a single LED package on a ceramic substrate. 
     As shown in  FIG.  13   , light source  48  may include LED chip  180  mounted to a substrate such as ceramic substrate  184 . Other materials may be used to form substrate  184  if desired. LED chip  180  may include LED die  90  and reflector and contact layer  92  of  FIGS.  6 ,  7 , and  10 - 12   , for example. PSS  150  may be layered over LED chip  180 . In the example of  FIG.  13   , polarization recycling structures  93  include adhesive layer  172 , reflective polarizer film  170 , and anti-reflective layer  169  layered onto the bottom surface of glass layer  162 . This is merely illustrative and, in another suitable arrangement, polarization recycling structures  93  may include wire grid polarizer  164  of  FIG.  11   . Anti-reflective layer  169  may be omitted if desired. 
     Light source  48  may include spacer and sealant  182  that couples glass layer  162  to ceramic substrate  184  (e.g., surrounding a lateral periphery of polarization recycling structures  93  and chip  180 ). Spacer and sealant  182  may hold glass layer  162  in place over chip  180  such that polarization recycling structures  93  are separated from PSS  150  by air gap  168 . 
     Polarization recycling structures  93  of  FIGS.  6 ,  7 , and  10 - 13    may be used to cover a single light source  48 . In another suitable arrangement, the same polarization recycling structures  93  may be shared by multiple light sources  48 .  FIG.  14    is a cross-sectional side view showing how multiple light sources  48  may share the same polarization recycling structures  93 . 
     As shown in  FIG.  14   , multiple light sources  48  (e.g., multiple light sources  48  that emit light of the same color and that are arranged in an array) may collectively form a light source set  199  (sometimes referred to herein as light source array  199 ). The light sources  48  in light source set  199  may be arranged in a one-dimensional array pattern or in a two dimensional array pattern, as examples. Each light source  48  in light source set  199  may produce corresponding illumination light  52  (e.g., polarized illumination light to be provided to prism  46  of  FIG.  3   ). 
     Each light source  48  in light source set  199  may include a corresponding emitter  198  mounted to a common (shared) substrate such as silicon substrate  200 . Silicon substrate  200  may, for example, be a silicon driver that drives emitters  198  to emit unpolarized illumination light (e.g., based on control signals received from control circuitry  16  over control path(s)  42  of  FIG.  2   ). The emitters  198  in light source set  199  may collectively form an emitter array  196  for light source set  199 . Each emitter  198  in emitter array  196  may include a corresponding LED die  90  and reflector and contact layer  92  of  FIGS.  6 ,  7 , and  10 - 12    (e.g., a corresponding LED chip  180  of  FIG.  13   ), for example. 
     As shown in  FIG.  14   , the same substrate such as sapphire substrate  194  may be layered over each of the emitters  198  in light source set  199 . Similarly, the same polarization recycling structures  93  may be layered over each of the emitters  198  in light source set  199 . Spacer and sealant  192  may separate polarization recycling structures  93  from sapphire substrate  194  by air gap  168 . In the example of  FIG.  14   , polarization recycling structures  93  include adhesive layer  172 , reflective polarizer film  170 , and anti-reflective layer  169  layered onto the bottom surface of glass layer  162 . This is merely illustrative and, in another suitable arrangement, polarization recycling structures  93  may include wire grid polarizer  164  of  FIG.  11   . Anti-reflective layer  169  and/or anti-reflective layer  166  may be omitted if desired. 
     If desired, light source  48  may include a condenser lens. In these arrangements, if desired, polarization recycling structures  93  may be integrated with the condenser lens.  FIGS.  15  and  16    are cross-sectional side views showing how light source  48  may include polarization recycling structures  93  integrated with a condenser lens. 
     As shown in  FIG.  15   , light source  48  may include an LED emission area  214  mounted to substrate  211 . Substrate  211  may, for example, include ceramic substrate  184  of  FIG.  13   . LED emission area  214  may include LED chip  180  and PSS  150  of  FIG.  13   , PSS  150 , LED die  90 , and reflector and contact layer  92  of  FIGS.  6 ,  7 , and  10 - 12   , etc. Light source  48  may include a lens such as condenser lens  210  overlapping LED emission area  214 . Polarization recycling structures  93  may be layered onto the bottom (e.g., planar) surface of condenser lens  210 . Spacer and sealant  182  may separate polarization recycling structures  93  from LED emission area  214  by air gap  168 . Condenser lens  210  may help to focus and/or redirect the illumination light  52  produced by light source  48 . 
     The example of  FIG.  15    in which spacer and sealant  182  polarization recycling structures  93  cover an entirety of the bottom surface of condenser lens  210  is merely illustrative. In another suitable arrangement, polarization recycling structures  93  may cover only the portion of condenser lens  210  overlapping LED emission area  214 , as shown in  FIG.  16   . In this example, spacer and sealant  182  may separate the bottom surface of condenser lens  210  from substrate  211  such that polarization recycling structures  93  are separated from LED emission area  214  by air gap  168 . 
     In the example of  FIGS.  15  and  16   , polarization recycling structures  93  include adhesive layer  172  and reflective polarizer film  170  layered onto the bottom surface of condenser lens  210 . This is merely illustrative and, if desired, polarization recycling structures  93  may include wire grid polarizer  164  of  FIG.  11    or any other desired structures. Quarter waveplate  120  of  FIG.  7    may be layered onto the bottom surface of reflective polarizer film  170  or may be otherwise optically interposed between reflective polarizer film and the LED emission area in any of the examples of  FIGS.  11 - 16   , if desired. Light source  48  may include other structures for producing polarized illumination light  52  if desired. 
     Polarizing illumination light  52  prior to passing illumination light  52  to prism  46  of  FIG.  17    may serve to optimize the optical performance of the display module. For example, as shown in the top-down view of  FIG.  17   , prism  46  in illumination optics  36  may include an X-plate formed from a first partial reflector  220  that intersects with a second partial reflector  222 . First partial reflector  220  may include coating  224 . Second partial reflector  222  may include coating  226 . Coatings  224  and  226  may sometimes be referred to herein as material interfaces and may include laminated interference films, diffractive elements that serve as a beam combiner, or other types of coatings or material interfaces. While prism  46  is sometimes referred to herein as a prism (e.g., where smaller prisms are coupled between each of the partial reflectors in the X-plate), prism  46  may include just the X-plate formed from partial reflectors  220  and  222  without also including prisms between the partial reflectors, if desired (e.g., prism  46  may be an X-plate without any prisms). 
     Coatings  224  and  226  may be wavelength-selective filters that configure partial reflectors  220  and  222  to reflect illumination light of corresponding wavelengths while transmitting light of other wavelengths. For example, coating  226  may configure partial reflector  222  to reflect illumination light of the wavelengths produced by light source  48 A (e.g., red illumination light  52 A) while transmitting illumination light of the wavelengths produced by light sources  48 B and  48 C. Coating  224  may configure partial reflector  220  to reflect illumination light of the wavelengths produced by light source  48 C (e.g., blue illumination light  52 C) while transmitting illumination light of the wavelengths produced by light sources  48 A and  48 B. The illumination light transmitted by light source  48 B (e.g., green illumination light  52 B) may be transmitted by partial reflectors  220  and  222  without being reflected. In this way, the X-plate (e.g., prism  46 ) may serve as a beam combiner that combines illumination light  52 A,  52 B, and  52 C to produce illumination light  38 . 
     Illumination light  52 A-C may be polarized illumination light (e.g., polarized illumination light as produced by polarization recycling structures  93  of  FIGS.  6 ,  7 , and  10 - 16   ). The illumination light  38  produced by prism  46  will therefore have the same polarization as illumination light  52 A-C. Polarizing illumination light  52 A-C prior to the illumination light passing through prism  46  may serve to optimize the spectral performance of illumination light  38 , for example. 
       FIG.  18    is a plot showing how polarizing illumination light  52 A-C prior to the illumination light passing through prism  46  may serve to optimize the spectral performance of illumination light  38 . The horizontal axis of  FIG.  18    plots wavelength (e.g., in nm) and the vertical axis of  FIG.  18    plots the amount of reflection performed by prism  46  (e.g., where 0% reflection corresponds to an entirety of the illumination light being transmitted by prism  46  and 100% corresponds to an entirety of the illumination light being reflected by prism  46 ). 
     Curve  230  of  FIG.  8    plots the reflection, by prism  46 , of the illumination light  52 C emitted by light source  48 C (e.g., blue illumination light) in scenarios where illumination light  52 C is unpolarized. Curve  232  plots the reflection, by prism  46 , of the illumination light  52 A emitted by light source  48 A (e.g., red illumination light) in scenarios where illumination light  52 A is unpolarized. As shown by curve  230 , partial reflector  220  and coating  224  ( FIG.  17   ) may exhibit a relatively shallow roll-off in reflecting unpolarized blue light as wavelength increases. Similarly, as shown by curve  232 , partial reflector  222  and coating  226  may exhibit a relatively shallow roll-off in reflecting unpolarized red light as wavelength decreases. 
     Curve  234  plots the reflection, by prism  46 , of the illumination light  52 C emitted by light source  48 C (e.g., blue illumination light) in scenarios where illumination light  52 C is polarized (e.g., by polarization recycling structures  93  of  FIGS.  6 ,  7 , and  10 - 16   ). Curve  236  plots the reflection, by prism  46 , of the illumination light  52 A emitted by light source  48 A (e.g., red illumination light) in scenarios where illumination light  52 A is polarized (e.g., by polarization recycling structures  93  of  FIGS.  6 ,  7 , and  10 - 16   ). 
     As shown by curve  234  and arrow  238 , providing polarized blue illumination light to prism  46  may cause partial reflector  220  and coating  224  to exhibit a steeper roll-off in reflecting blue light as wavelength increases than in scenarios where unpolarized blue light is provided to prism  46 . Similarly, as shown by curve  236  and arrow  240 , providing polarized red illumination light to prism  46  may cause partial reflector  222  and coating  226  to exhibit a steeper roll-off in reflecting red light as wavelength decreases than in scenarios where unpolarized red light is provided to prism  46 . This may serve to optimize the spectral response of the illumination light  38  output by prism  46 , for example. The example of  FIG.  18    is merely illustrative. Curves  230 - 236  may have other shapes in practice. In general, prism  46  may combine illumination light  52  of any desired wavelengths to produce illumination light  38  that is provided to fLCOS display panel  40  of  FIG.  3   . 
     In general, the efficiency of the LEDs in light sources  48  may depend on the current density used to drive the LEDs. In addition, different color LEDs exhibit peak LED efficiency at different current densities. In practice, green LEDs such as an LED in light source  48 B may reach peak LED efficiency at a lower current density than red LEDs (e.g., in light source  48 A) and/or blue LEDs (e.g., in light source  48 C). In order to reduce the overall power consumption of display module  14 A, light source  48 B may therefore be driven with a lower current density than light sources  48 A and/or  48 C. 
     The light sources  48 A-C in illumination optics  36  may be driven using a corresponding illumination sequence. The illumination sequence may specify the order in which each light source  48  is activated to produce illumination light  38 . In some scenarios, the illumination scheme is an RGBRGB illumination scheme. However, if care is not taken, driving light sources  48  using an RGBRGB illumination scheme while reducing the current density used to drive light source  48 B may cause illumination light  38  to exhibit less overall brightness at green wavelengths. This may lead to an unsightly color and brightness imbalance in the images produced at eye box  24  ( FIG.  2   ). In order to mitigate these issues while driving light source  48 B with a reduced current density, light sources  48 A-C may be driven using a green-heavy illumination sequence. 
       FIG.  19    is a timing diagram of illustrative illumination sequences that may be used to drive light sources  48 A-C. As shown in  FIG.  19   , an RGBRGB illumination sequence  250  may be used to drive light sources  48 A-C in some scenarios. RGBRGB illumination sequence  250  may involve the sequential activation of only one of light sources  48 A-C at any given time. 
     Under RGBRGB illumination sequence  250 , for a given image frame, red light source  48 A may be active for a first time period (slot)  252 , during which red light source  48 A emits red (R) illumination light  52 A of  FIGS.  3  and  17    (e.g., illumination light as polarized using polarization recycling structures  93  of  FIGS.  6 ,  7 , and  10 - 16   ). Green light source  48 B and blue light source  48 C may be inactive during the first time period  252  (e.g., green light source  48 B and blue light source  48 C may not emit any illumination light during the first time period  252 ). Green light source  48 B may be active for a subsequent second time period  252 , during which green light source  48 B emits green (G) illumination light  52 B. Red light source  48 A and blue light source  48 C may be inactive during the second time period  252  (e.g., red light source  48 A and blue light source  48 C may not emit any illumination light during the second time period  252 ). Blue light source  48 C may be active during a subsequent third time period  252 , during which blue light source  48 C emits blue (B) illumination light  52 C. Red light source  48 A and green light source  48 B may be inactive during the third time period  252  (e.g., red light source  48 A and green light source  48 B may not emit any illumination light during the third time period  252 ). Red light source  48 A may be active during a subsequent fourth time period  252 , green light source  48 B may be active during a subsequent fifth time period  252 , and blue light source  48 C may be active during a subsequent sixth time period  252  (e.g., each light source may be active during two time periods  252  for a given image frame to be displayed by display module  14 A). 
     In order to minimize power consumption by illumination optics  36 , green light source  48 B may be driven using lower current density than the green light source would have otherwise been driven under a different illumination sequence for a given field (e.g., while recovering similar visual performance). In order to recover the same overall brightness at green wavelengths as would otherwise be obtained if a higher current density were used to drive green light source  48 B, light sources  48 A-C may be driven using green-heavy illumination sequence  254  of  FIG.  19   . 
     Green-heavy illumination sequence  254  may include three time periods (slots)  256  that are used to produce illumination light  38  for a given image frame (e.g., a first time period  256 - 1 , a subsequent second time period  256 - 2 , and a subsequent third time period  256 - 3 ). Each time period  256  may correspond to an image subframe (field) that is displayed using fLCOS display panel  40 . Both red light source  48 A and green light source  48 B may be active for first time period  256 - 1 . During first time period  256 - 1 , red light source  48 A may emit red (R) illumination light  52 A and green light source  48 B may emit green (G) illumination light  52 B. Prism  46  ( FIGS.  3  and  17   ) may combine illumination light  52 A and  52 B to produce illumination light  38 . Blue light source  48 C may be inactive during first time period  256 - 1 . 
     Green light source  48 B may be active for second time period  256 - 2 . During second time period  256 - 2 , green light source  48 B may emit green illumination light  52 B. Prism  46  ( FIGS.  3  and  17   ) may produce illumination light  38  based on the green illumination light  52 B. Red light source  48 A and blue light source  48 C may be inactive during second time period  256 - 2 . 
     Both blue light source  48 C and green light source  48 B may be active for third time period  256 - 3 . During third time period  256 - 3 , blue light source  48 C may emit blue (B) illumination light  52 C and green light source  48 B may emit green illumination light  52 B. Prism  46  ( FIGS.  3  and  17   ) may combine illumination light  52 C and  52 B to produce illumination light  38 . Red light source  48 A may be inactive during third time period  256 - 3 . 
     In other words, green light source  48 B may be active during each of the time periods  256  used to display a corresponding image frame (e.g., green light source  48 B may contribute to the blue and red portions of the illumination sequence). By contributing green illumination light  52 B to illumination light  38  in each time period  256  (e.g., by increasing the total on time for green light source  40 B per image frame), the total illumination time for the green light source may be greater than in scenarios where RGBRGB illumination sequence  250  is used. This may allow green light source  48 B to be driven with lower current density without significantly sacrificing optical performance, thereby minimizing power consumption in display module  14 A. 
     The example of  FIG.  19    is merely illustrative. If desired, other green-heavy illumination sequences having any desired number of periods  256  may be used (e.g., illumination sequences where green light source  48 B is active during a greater number of time periods  256  per frame than red light source  48 A and blue light source  48 C). If desired, red light source  48 A and/or blue light source  48 C may be active during second time period  256 - 2  (e.g., where red light source  48 A is driven using less current density than during time period  256 - 1  and where blue light source  48 C is driven using less current density than during time period  256 - 3 ). Light sources  48 A-C may emit illumination light of any respective colors, in general. 
       FIG.  20    is a flow chart of illustrative steps that may be performed by system  10  to display images using a green-heavy illumination sequence such as green-heavy illumination sequence  254  of  FIG.  19   . 
     At step  260 , control circuitry  16  ( FIG.  2   ) may process image data to be displayed at eye box  24 . The image data may include a stream of image frames. Control circuitry  16  may determine whether a trigger condition has been met before beginning to display images using the green-heavy illumination sequence. 
     If desired, control circuitry  16  may determine whether the trigger condition has been met based on the content of the image data to be displayed. For example, control circuitry  16  may determine that the trigger condition has been met when one or more image frames to be displayed exhibit a saturation level that exceeds a threshold saturation level (e.g., a green saturation level that exceeds a threshold green saturation level). If desired, the green-heavy illumination sequence may be disregarded in favor of another illumination sequence (e.g., RGBRGB illumination sequence  250  of  FIG.  19   ) in scenarios where use of a green-heavy illumination sequence is unlikely to result in an improvement in power consumption and/or optical performance. This is merely illustrative and, in general, any desired trigger condition may be used (e.g., a command to begin using the green-heavy illumination sequence issued by a software call on system  10 , a command to begin using the green-heavy illumination sequence as identified by user input provided to system  10 , etc.). In some examples, the above trigger condition(s) may be used when the optical system is free of chromatic aberration. In one suitable arrangement that is sometimes described herein as an example (e.g., in scenarios where chromatic aberration is present), the trigger condition may be an ambient light level identified by ambient light sensor data collected by one or more ambient light sensors in system  10 . If desired, different green light doping ratios may be used (e.g., in the green-heavy illumination sequence) based on the current measured ambient light level (e.g., control circuitry  16  may adjust the relative amount of green illumination in each of the time periods of the illumination sequence based on the ambient light sensor data such that different relative amounts are used when different ambient light levels are detected). This may help to ensure that chromatic aberration artifacts remain invisible to the eye, for example 
     When the trigger condition has been met, processing may proceed to step  264 , as shown by arrow  262 . At step  264 , control circuitry  16  may control light sources  48 A-C to generate illumination light  38  using the green-heavy illumination sequence. Control circuitry  16  may, for example, provide driving signals to light sources  48 A-C over control path(s)  42  ( FIG.  2   ) (e.g., driving signals with a corresponding current density) that selectively activate light sources  48 A-C in accordance with the green-heavy illumination sequence (e.g., green-heavy illumination sequence  254  of  FIG.  19   ) for each image frame to be displayed. Control circuitry  16  may drive green light source  48 B with lower current density than for display of the same image data using RGBRGB illumination sequence  250 , minimizing power consumption in system  10  by meeting the peak efficiency of the green LED in green light source  48 B. 
     If desired, step  266  may be performed concurrently with step  264 . At step  266 , control circuitry  16  may provide image data to fLCOS display panel  40  ( FIG.  3   ). The image data may include image frame(s) (e.g., as processed at step  260 ). Each image frame may be used to control each pixel P* in fLCOS display panel  40  to modulate illumination light  38  (e.g., illumination light as generated in accordance with the green-heavy illumination scheme) to produce corresponding image light  22 . 
     Each image frame may be divided into sub-frames or fields to be displayed during each time period  256  of the green-heavy illumination sequence ( FIG.  19   ). For example, for a given image frame, a first sub-frame (field) of the image frame may be driven onto fLCOS display panel  40  during time period  256 - 1  of  FIG.  19    (e.g., for producing a first sub-frame in image light  22  using the polarized red and green illumination light produced during time period  256 - 1 ), a second sub-frame (field) of the image frame may be driven onto fLCOS display panel  40  during time period  256 - 2  (e.g., for producing a second sub-frame in image light  22  using the polarized green illumination light produced during time period  256 - 2 ), and a third sub-frame (field) of the image frame may be driven onto fLCOS display panel  40  during time period  256 - 3  (e.g., for producing a third sub-frame in image light  22  using the polarized green and blue illumination light produced during time period  256 - 3 ). If desired, control circuitry  16  may perform chromatic aberration compensation operations when driving fLCOS display panel  40  with the image data (optional step  268 ). 
     At step  270 , optical system  14 B ( FIG.  2   ) may direct the image light  22  produced by display module  14 A towards eye box  24 . Processing may subsequently loop back to step  260 , as shown by arrow  272 , as additional image frames are processed for display at the eye box. Control circuitry  16  may cycle through these steps rapidly enough so that each of the different-colored sub-frames appears at eye box  24  as a series of multi-color image frames to the user at eye box  24  (e.g., image frames having a corresponding color gamut and that appears visually similar to how the image frames appear to the user in scenarios where green light source  48 B is driven with higher current density using an RGBRGB illumination sequence). In this way, power consumption in display module  14 A may be minimized without significantly reducing image quality at eye box  24 . 
       FIG.  21    is a flow chart of illustrative steps that may be performed by control circuitry  16  in driving light sources  48 A-C using the green-heavy illumination sequence (e.g., green-heavy illumination sequence  254  of  FIG.  19   ). The steps of  FIG.  21    may, for example, be performed while processing step  264  of  FIG.  20    (e.g., for a given image frame to be displayed at the eye box). 
     At step  280  of  FIG.  21   , control circuitry  16  may concurrently activate (turn on) red light source  48 A and green light source  48 B to produce red illumination light  52 A and green illumination light  52 B (e.g., during time period  256 - 1  of  FIG.  19   ). This may produce a corresponding sub-frame (field) of the image frame having a color given by the combination of red illumination light  52 A and green illumination light  52 B. Blue light source  48 C may be inactive (turned off). 
     At step  282 , control circuitry  16  may activate (turn on) green light source  48 B to produce green illumination light  52 B (e.g., during time period  256 - 2  of  FIG.  19   ). This may produce a corresponding sub-frame (field) of the image frame having a green color given by green illumination light  52 B. Red light source  48 A and blue light source  48 C may be inactive (turned off). 
     At step  284 , control circuitry  16  may concurrently activate (turn on) blue light source  48 C and green light source  48 B to produce blue illumination light  52 C and green illumination light  52 B (e.g., during time period  256 - 3  of  FIG.  19   ). This may produce a corresponding sub-frame (field) of the image frame having a color given by the combination of blue illumination light  52 C and green illumination light  52 B. Red light source  48 A may be inactive (turned off). Processing may subsequently loop back to step  280 , as shown by arrow  285 , as additional image frames are displayed. The steps of  FIG.  21    are merely illustrative and may, in general, be adapted to the particular green-heavy illumination sequence that is used to produce illumination light  38 . 
       FIG.  22    is a flow chart of illustrative steps that may be performed by control circuitry  16  in performing chromatic aberration compensation operations while driving fLCOS display panel  40  with the image data (e.g., while producing image light  22  using green-heavy illumination sequence  254  of  FIG.  19   ). The steps of  FIG.  22    may, for example, be performed while processing step  268  of  FIG.  20    (e.g., for a given image frame to be displayed at the eye box). The steps of  FIG.  22    may be performed to compensate for chromatic aberrations introduced into image light  22  by collimating lens  34  and/or any other desired optical components in display module  14 A and/or optical system  14 B ( FIG.  2   ). 
     At step  290 , control circuitry  16  may identify an image frame to be driven onto fLCOS display panel  40  for producing image light  22  in response to illumination light  38 . 
     At step  292 , control circuitry  16  may decompose the image frame into a red (R) LED channel image (sub-frame), a blue (B) LED channel image (sub-frame), and a green (G) LED channel image (sub-frame), for example. 
     At step  294 , control circuitry  16  may pre-compensate the red, blue, and green LED channel images for chromatic aberration that will be introduced into image light  22  by the optical components of system  10  (e.g., control circuitry  16  may generate chromatic aberration pre-compensated red, blue, and green channel images). The amount of pre-compensation that needs to be introduced to each channel image to compensate for chromatic aberration may, for example, be determined during the design, manufacture, assembly, and/or testing of system  10  (e.g., in a manufacturing, testing, or calibration system). The pre-compensation may be performed, for example, by shifting the relative pixel position of portions of the image frame that will be subject to chromatic aberrations by different amounts across each of the color channels/fields. 
     At step  296 , control circuitry  16  may perform green redistribution operations. For example, control circuitry  16  may first modify the red illumination light from light source  48 A to a combination of red and green light from light sources  48 A and  48 B, without changing the corresponding image data used to drive fLCOS display panel  50  (sometimes referred to herein as the fLCOS display panel signal). Control circuitry  16  may then modify the blue illumination light from light source  48 C to a combination of blue and green light from light sources  48 B and  48 C, without changing the corresponding fLCOS display panel signal. The red and blue illumination light may be modified to include 1-10% green illumination, between 2-8% green illumination, between 5-20% green illumination, around 5% green illumination, or any other desired amount of green illumination (sometimes referred to herein as the green light doping ratio). Control circuitry  16  may then modify the image data used to drive fLCOS display panel  50  for the green channel, by subtracting, from the image data for the green channel, image data corresponding to the amount of green illumination that was added into the red channel (e.g., in modifying the red illumination light as described above) and the amount of green illumination that was added into the blue channel (e.g., in modifying the blue illumination light as described above). Next, any negative signal values in the modified signal may be changed to zero (e.g., a black level) and excessive green illumination values (e.g., green illumination values that exceed a threshold value) may be changed to the maximum brightness of the field (e.g., as determined by the corresponding green light doping ratio). 
     At step  298 , control circuitry  16  may drive fLCOS display panel  40  using color channel images (image data) associated with the green-heavy illumination sequence. For example, control circuitry  16  may drive fLCOS display panel  40  using an (R+G) channel image for the combination of red and green illumination light (e.g., during time period  256 - 1  of  FIG.  19   ), then using a green (G) channel image as modified during step  296  (e.g., during time period  256 - 2  of  FIG.  19   ), then using a (B+G) channel image for the combination of blue and green light (e.g., during time period  256 - 3  of  FIG.  19   ). The corresponding image light  22  produced by fLCOS display panel  40  may be pre-compensated for chromatic aberrations by the optical components along the remainder of the optical path between display module  14 A and eye box  24  ( FIG.  2   ). After passing to eye box  24 , the chromatic aberrations introduced by these optical components may cancel out the pre-compensation in the image light, thereby providing the eye box with images that are free from chromatic aberrations. Processing may subsequently loop back to step  290 , as shown by arrow  300 , as additional image frames are displayed. 
     In this way, power consumption may be minimized in display module  14 A without significantly sacrificing image quality. The green-heavy illumination sequence need not be limited to fLCOS display systems and may, in general, be used to produce image light  22  in scenarios where display module  14 A includes a DMD display panel, an emissive display panel, etc. 
     Because green light source  48 B is turned on more frequently under the green-heavy illumination sequence, the green-heavy illumination sequence may serve to shrink the overall color gamut of display module  14 A.  FIG.  23    is a CIE1931 color space plot showing how the green-heavy illumination sequence may serve to shrink the overall color gamut of display module  14 A. As shown in  FIG.  23   , display module  14 A may display images using a relatively large color gamut  312  (e.g., within overall color space  310 ) in scenarios where a green-heavy illumination sequence is not used to produce illumination light  38 . The green-heavy illumination sequence may serve to reduce the color gamut of display module  14 A to color gamut  314 , as shown by arrows  316 . Reducing the color gamut of display module  14 A to color gamut  314  may serve to reduce the power consumption of display module  14 A relative to scenarios where an RGBRGB illumination sequence is used, for example. The example of  FIG.  23    is merely illustrative. In general, color space  310 , color gamut  312 , and color gamut  314  may have other shapes. 
     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.  24    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.  24   , display  14  may include a twisted nematic (TN) cell  320  and a birefringent crystal  322  optically interposed between display module  14 A ( FIG.  2   ) and input coupler  28  on waveguide  26 . Birefringent crystal  322  may be optically interposed between TN cell  320  and input coupler  28 . If desired, TN cell  320  and/or birefringent crystal  322  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  322  and input coupler  28 ). 
     TN cell  320  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  320  as p-polarized light is described herein as an example. 
     TN cell  320  may receive control signals from control circuitry  16  ( FIG.  2   ) over control path  334 . The control signals may toggle TN cell  320  between first and second states. In the first state, TN cell  320  may transmit image light  22  without changing the polarization of image light  22 . TN cell  320  may thereby transmit p-polarized image light  22  to birefringent crystal  322  in the first state, as shown by arrow  324 . In the second state, TN cell  320  may change the polarization of image light  22  to a different linear polarization. For example, in the second state, TN cell  320  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  322 , as shown by arrow  324 . 
     Birefringent crystal  322  (sometimes referred to herein as birefringent beam displacer  322 ) may be formed from a birefringent material such as calcite and may have a length (thickness)  332  (e.g., in the direction of the optical path). Birefringent crystal  322  may be a uniaxial birefringent crystal or a biaxial birefringent crystal, as examples. Birefringent crystal  322  may receive p-polarized image light  22  or s-polarized image light  22  from TN cell  320  (e.g., depending on the current state of TN cell  320 ). 
     Birefringent crystal  322  may spatially separate incident image light  22  based on the polarization of the image. For example, birefringent crystal  322  may output incident s-polarized image light  22  within a first beam, as shown by arrow  326 , and may output incident p-polarized image light  22  within a second beam, as shown by arrow  328 . Upon exiting birefringent crystal  322 , 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  330 . The magnitude of displacement  330  may be directly proportional to the length  322  of birefringent crystal  322 , 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  330 ). The images conveyed by the s-polarized image light  22  may therefore be spatially offset (e.g., by displacement  330 ) from the images conveyed by the p-polarized 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 input coupler  28  with p-polarized image light  22  and s-polarized image light  22 . Length  332  and thus displacement  330  may be selected so that, when the state of TN cell  320  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  320  and birefringent crystal  322 . TN cell  320  and birefringent crystal  322  of  FIG.  24    may sometimes be referred to collectively herein as spatial pixel shifting structures  325 . 
     The example of  FIG.  24    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.  25    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.  25   , birefringent crystal  322  of  FIG.  24    may be replaced by quarter waveplate  340  and geometric phase grating (GPG)  342 . Quarter waveplate  340  may be optically interposed between TN cell  320  and GPG  342 . GPG  342  may be optically interposed between quarter waveplate  340  and input coupler  28 . 
     Collimating lens  34  ( FIG.  2   ) may be optically interposed between GPG  342  and input coupler  28 , may be optically interposed between quarter waveplate  340  and GPG  342 , may be optically interposed between quarter waveplate  340  and TN cell  320 , or may be optically interposed between fLCOS display panel  40  and TN cell  320 . An arrangement in which collimating lens  34  is optically interposed between quarter waveplate  340  and GPG  342  is described herein as an example. In this example, the collimating lens may serve to focus the pupil of image light  22  onto GPG  342  (e.g., GPG  342  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  340  and TN cell  320  are located within display module  14 A. 
     Quarter waveplate  340  may convert p-polarized image light  22  (e.g., as provided by TN cell  320  when TN cell  320  is in the first state) into RHCP light that is provided to GPG  342 , as shown by arrow  352 . Quarter waveplate  340  may convert s-polarized image light  22  (e.g., as provided by TN cell  320  when TN cell  320  is in the second state) into LHCP light that is provided to GPG  342 , as shown by arrow  352 . 
     GPG  342  may diffract incident image light  22  received from quarter waveplate  340  onto a corresponding output angle θ (e.g., measured relative to the optical axis or the Y-axis as shown in  FIG.  25   ). GPG  342  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  342  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  356 . GPG  342  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  352 . Output angle −θ2 may be equal and opposite output angle θ1 or may be any other desired output angle. The output angles of arrows  354  and  356  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  342  may include a substrate  344  and an alignment layer  346  layered onto substrate  344 . GPG  342  may include multiple liquid crystal (LC) layers  348  (e.g., a first LC layer  348 - 1 , a second LC layer  348 - 2 , and a third LC layer  348 - 3 ) layered onto alignment layer  346 . Alignment layer  346  may serve to align the LC molecules in LC layers  348  at substrate  344  (e.g., with a corresponding grating period). Each LC layer  348  may have a corresponding twist angle φ (e.g., LC layer  348 - 1  may have a first twist angle φ 1 , LC layer  348 - 2  may have a second twist angle φ 2  oriented opposite twist angle φ 1 , and LC layer  348 - 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 input coupler  28  GPG  342  and thus input coupler  28  with LHCP image light  22  and RHCP image light  22 . GPG  342  may be configured to output image light  22  at angles θ1 and θ2 that are selected so that, when the state of TN cell  320  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  320 , quarter waveplate  340 , and GPG  342 . TN cell  320 , quarter waveplate  340 , and GPG  342  of  FIG.  25    may sometimes be referred to collectively herein as angular pixel shifting structures  353 . Spatial pixel shifting structures  325  of  FIG.  24    and angular pixel shifting structures  353  may sometimes be referred to collectively herein as pixel shifting structures for display  14 . 
       FIG.  26    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.  26   , 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.  26   , image light  22  may include pixels P1, P2, P3, and P4 when TN cell  320  of  FIGS.  24  and  25    is in the first state (e.g., when TN cell  320  outputs p-polarized light). When TN cell  320  is in the second state (e.g., when TN cell  320  outputs s-polarized light), pixels P1, P2, P3, and P4 may be displaced by displacement  360 , as shown by respective pixels P1′, P2′, P3′, and P4′. Displacement  360  may, for example, be a two-dimensional displacement that includes offset  364  parallel to the Z-axis and/or offset  362  parallel to the X-axis. Displacement  360  may be produced by a spatial displacement such as displacement  330  of  FIG.  24    (e.g., in scenarios where the pixel shifting structures include spatial pixel shifting structures  325 ) or by an angular displacement such as an angular displacement having a magnitude equal to |θ1|+|θ2| of  FIG.  25    (e.g., in scenarios where the pixel shifting structures include angular pixel shifting structures  353 ). 
     Pixels P1, P2, P3, and P4 may exhibit a first pixel pitch and pixels P1′, P2′, P3′, and P4′ may also exhibit the first pixel pitch. However, the combination of pixels P1, P2, P3, and P4 with pixels P1′, P2′, P3′, and P4′ 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  320 , image light  22  may effectively include each of pixels P1, P2, P3, P4, P1′, P2′, P3′, and P4′ (e.g., as perceived by a user at eye box  24 ) and thus the second pixel pitch, rather than only pixels P1, P2, P3, and P4 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. 
     Control circuitry  16  ( FIG.  2   ) may drive image data onto fLCOS display panel  40  using fLCOS drive voltage waveforms (e.g., based on control signals provided to fLCOS display panel  40  over control path(s)  44  of  FIG.  2   ).  FIG.  27    is a timing diagram of two illustrative fLCOS drive voltage waveforms that may be used to drive fLCOS display panel  40 . 
     As shown in  FIG.  27   , fLCOS drive voltage waveform (curve)  370  plots the fLCOS drive voltage as a function of time for producing image light  22  with a gray level of zero. fLCOS drive voltage waveform (curve)  372  plots the fLCOS drive voltage as a function of time for producing image light  22  with a gray level of 128 (e.g., in a 256-bit field). The fLCOS drive voltage may vary between a first drive voltage V OFF  (e.g., a negative voltage level) and a second drive voltage V ON  (e.g., a positive voltage level). 
     Waveforms  370  and  372  may be at first drive voltage V OFF  prior to time TO. At time TO, waveform  370  may begin to increase to a peak at second drive voltage V ON . Waveform  370  may return to first drive voltage V OFF  at time T1. The time period between times T0 and T1 may sometimes be referred to herein as dark gap  374 . Dark gap  374  may be used to reset fLCOS display panel  40 , for example. 
     The time period between times T1 and T3 may form a duty period  380  during which at least one light source  48  (e.g., red light source  48 A of  FIG.  3   ) may be turned on to provide illumination light  38  to fLCOS display panel  40 . Because waveform  370  is at first drive voltage V OFF  during duty period  380 , the fLCOS display panel may not produce image light during duty period  380  when driven using waveform  370 . The time period between times TO and T3 may sometimes be referred to as field period  376 . Field period  376  may be associated with the illumination of fLCOS display panel  40  by a corresponding field of illumination light (e.g., illumination light of a particular color) and may include the reset time (e.g., a portion of dark gap  374 ) required to reset the fLCOS display panel to begin reflecting the field of illumination light as image light  22 . 
     At time T3, waveform  370  may to increase to a peak at second drive voltage V ON . Waveform  370  may return to first drive voltage V OFF  at time T4. The time period between times T3 and T4 may sometimes be referred to herein as the dark gap  382 . The time period between time T3 and the time when waveform  370  reaches second drive voltage V ON  may sometimes be referred to herein as reset time T_RESET. Reset time T_RESET may allow time for fLCOS display panel  40  to reset for the next field of the image. The time period between the time when waveform  370  reaches second drive voltage V ON  and time T4 may sometimes be referred to herein as off time T_OFF. The duration of dark gap  374  (e.g., off time T_OFF) may be adjusted to control the overall power consumption of display module  14 A. 
     The time period between times T4 and T5 may form a duty period  381  during which a light source other than the light source activated during duty period  380  may be turned on to provide illumination light  38  to fLCOS display panel  40 . A subsequent dark gap may begin at time T5, as waveform  370  increases back to second drive voltage V ON . This cycle may continue for each of the fields in the image frame to be displayed. The time period between times T4 and T5 may sometimes be referred to as field period  378 . 
     As shown in  FIG.  27   , waveform  372  may remain at second drive voltage V ON  after time TO and until time T2. By driving fLCOS display panel  40  at second drive voltage V ON  during a portion of duty period  380  (e.g., between times T1 and T2), fLCOS display panel  40  may reflect some of the illumination light  38  incident during duty period  380  (as image light  22 ). This may allow fLCOS display panel  40  to produce image light  22  at a higher gray level when driven by waveform  372  than when driven by waveform  370 , for example. 
     The example of  FIG.  27    is merely illustrative. In general, any desired fLCOS drive voltage waveforms may be used to drive fLCOS display panel  40  to produce any desired pixel values of any desired colors in image light  22 . If desired, the optical performance of fLCOS display panel  40  may be optimized by overdriving or underdriving the fLCOS drive voltage provided to fLCOS display panel  40 . The example of  FIG.  27    in which the drive voltage waveform follows a reset-based driving scheme is merely illustrative. In another suitable arrangement, a reset-less driving scheme may be used (e.g., there may not be dark gaps between each of the color fields and, if desired, an inverse waveform pattern may be used after each waveform pattern for charge balancing. 
       FIG.  28    is a timing diagram showing one example of how fLCOS display panel  40  may be overdriven to optimize optical performance. As shown in  FIG.  28   , fLCOS display panel  40  may be driven using fLCOS drive voltage waveform (curve)  392 . Curve  390  of  FIG.  28    plots the corresponding reflectance of fLCOS display panel  40  when driven using fLCOS drive voltage waveform  392 . 
     In the example of  FIG.  28   , fLCOS drive voltage waveform  392  has four possible voltage levels (e.g., a first drive voltage level V1, a second drive voltage level V2, a third drive voltage level V3, and a fourth drive voltage level V4). First drive voltage level V1 may be less than second drive voltage level V2, second drive voltage level V2 may be less than a voltage level of zero, third drive voltage level V3 may be greater than a voltage level of zero, and fourth drive voltage level V4 may be greater than third drive voltage level V4. This example is merely illustrative. In general, fLCOS drive voltage waveform  392  may have any desired number of possible voltage levels of any desired magnitudes. In one suitable arrangement that is sometimes described herein as an example, first drive voltage level V1 may be −1.8V, second drive voltage level V2 may be −1.5V, third drive voltage level V3 may be 1.5V, and fourth drive voltage level V4 may be 1.8V. Other drive voltage levels may be used if desired. 
     As shown by fLCOS drive voltage waveform  392 , when fLCOS display panel  40  is not being overdriven, fLCOS drive voltage waveform  392  may include square wave pulses such as square wave pulse  396  (e.g., where the fLCOS drive voltage rises from second voltage level V2 to third voltage level V3 at time TC and falls back to second voltage level V2 at time TD). Square wave pulse  396  may produce a corresponding spike in the reflectance of fLCOS display panel  40  from a reflectance of zero to a reflectance of R (e.g., a value greater than 0 and less than 1.0), as shown by curve  390 . 
     In order to overdrive fLCOS display panel  40 , control circuitry  16  may drive fLCOS display panel  40  using a non-square wave fLCOS drive voltage waveform, such as an fLCOS drive voltage waveform that includes non-square wave pulses such as non-square wave pulse  394  of fLCOS drive voltage waveform  392 . For example, at time TA, fLCOS drive voltage waveform  392  may increase from second voltage level V2 to fourth voltage level V4 (sometimes referred to herein as overdrive voltage level V4). If desired, at time TA′, fLCOS drive voltage waveform  392  may decrease to third voltage level V3. At time TB, fLCOS drive voltage waveform  392  may decrease to first voltage level V1. At time TB′, fLCOS drive voltage waveform  392  may increase back to second voltage level V2. 
     Non-square wave pulse  394  of fLCOS drive voltage waveform  392  may produce a corresponding spike in the reflectance of fLCOS display panel  40  from a reflectance of zero at time TA to a reflectance greater than reflectance R at or near time TA′ (e.g., a reflectance at or near 1.0). In other words, overdriving fLCOS display panel  40  in this way may serve to increase the reflectance of fLCOS display panel  40  relative to scenarios where fLCOS display panel  40  is not overdriven, thereby maximizing the overall optical efficiency of display module  14 A in producing image light  22 . 
     The example of  FIG.  28    is merely illustrative. In practice, curve  392  and non-square wave pulse  394  may have other shapes. In general, fLCOS display panel  40  may be overdriven using any desired non-square wave fLCOS drive voltage waveform (e.g., a waveform having non-square wave pulses that reach an overdrive voltage level such as fourth voltage level V4). Another example of a non-square wave pulse  394  that may be used to overdrive fLCOS display panel  40  is shown by dashed curve  393  of  FIG.  28   . In this example, the fLCOS drive voltage rises to voltage level V5 at time TA, drops continuously to voltage level V3 between times TA and TB, drops to voltage level V0 at time TB, and rises continuously to voltage level V2 between times TB and TB′. Voltage level V5 may be greater than 1.8V (e.g., 2.0V) and voltage level V0 may be less than −1.8V (e.g., −2.0V), as one example. The precise shape of curve  393  between times TA and TB and between times TB and TB′ may, for example, be altered to optimize the performance of fLCOS display panel  40 . The example of  FIG.  28    in which fLCOS display panel  40  is overdriven is merely illustrative and, if desired, fLCOS display panel  40  may be underdriven. Different non-square wave fLCOS drive voltage waveforms may be used to drive fLCOS display panel  40  at different times (e.g., depending on the operating conditions of display  14 ). 
     In practice, the optimal overdrive or underdrive waveform for fLCOS display panel  40  may vary as the operating temperature of fLCOS display panel  40  changes over time. If desired, control circuitry  16  may overdrive or underdrive fLCOS display panel  40  based on the temperature of display  14  (e.g., the temperature of fLCOS display panel  40 ).  FIG.  29    is a flow chart of illustrative steps that may be performed by control circuitry  16  ( FIG.  2   ) in overdriving or underdriving fLCOS display panel  40  based on the temperature of display  14 . 
     At step  400 , control circuitry  16  may gather temperature sensor data using one or more temperature sensors  19  in system  10  ( FIG.  1   ). If desired, control circuitry  16  may estimate the temperature of fLCOS display panel  40  based on the gathered temperature sensor data (e.g., using a temperature model for system  10 ). In scenarios where multiple temperature sensors  19  are used to gather temperature sensor data, the temperature sensors may be placed at different locations across system  10  if desired. Control circuitry  16  may also determine whether a trigger condition has been met before proceeding. 
     The trigger condition may be a predetermined change in the gathered temperature sensor data, may occur when the gathered temperature data reaches a threshold temperature level, may be based on the content of the image(s) to be displayed using fLCOS display panel  40 , may be based on a software call issued by one or more programs running on system  10 , may be based on a user input provided by a user of system  10 , etc. Once the trigger condition has been met, processing may proceed to step  404  as shown by arrow  402 . 
     At step  404 , control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform with which to overdrive or underdrive fLCOS display panel  40  based on the gathered temperature sensor data. For example, control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform that optimizes the optical performance (e.g., reflectance) of fLCOS display panel  40  for its current temperature (e.g., as determined while processing step  400 ). If desired, control circuitry  16  may store predetermined (optimal) non-square wave fLCOS drive voltage waveforms for different temperature values of fLCOS display panel  40  (e.g., in a look-up table or other data structure) and may identify the stored non-square wave fLCOS drive voltage waveform corresponding to the current (e.g., estimated) temperature of fLCOS display panel  40 . The stored non-square wave fLCOS drive voltage waveforms may be determined during the design, manufacture, assembly, testing, and/or calibration of system  10  if desired. 
     At step  406 , control circuitry  16  may drive fLCOS display panel  40  using the non-square wave drive voltage waveform identified while processing step  404 . Driving fLCOS display panel  40  in this way may maximize the reflectance of fLCOS display panel  40  for the current operating temperature of the display panel, for example. Control circuitry  16  may continue to overdrive fLCOS display panel  40  for a predetermined time period, until a new trigger condition is detected, for a predetermined number of frames, etc. 
     The example of  FIG.  29    in which control circuitry  16  overdrives fLCOS display panel  40  based on the temperature of display  14  is merely illustrative. In another suitable arrangement, control circuitry  16  may overdrive or underdrive fLCOS display panel  40  based on frame history information.  FIG.  30    is a flow chart of illustrative steps that may be performed by control circuitry  16  ( FIG.  2   ) in overdriving or underdriving fLCOS display panel  40  based on frame history information. 
     At step  410 , control circuitry  16  may identify frame history information for fLCOS display panel  40 . The frame history information may include, for example, information about the image frames that have been previously displayed using fLCOS display panel  40 . Control circuitry  16  may also determine whether a trigger condition has been met before proceeding. 
     The trigger condition may be a predetermined change in the gathered temperature sensor data, may occur when the gathered temperature data reaches a threshold temperature level, may be based on the content of the image(s) to be displayed using fLCOS display panel  40 , may be based on a software call issued by one or more programs running on system  10 , may be based on a user input provided by a user of system  10 , etc. In one suitable arrangement that is described herein as an example, the trigger condition may occur when the previous image frame displayed was fully on or fully off. Once the trigger condition has been met, processing may proceed to step  414  as shown by arrow  412 . 
     At step  414 , control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform with which to overdrive or underdrive fLCOS display panel  40  based on the identified frame history information. For example, control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform that optimizes the optical performance (e.g., reflectance) of fLCOS display panel  40  depending on the immediately previous image frame(s) displayed by fLCOS display panel  40  (e.g., a first fLCOS drive voltage waveform when the previous image frame was fully on, a second fLCOS drive voltage waveform when the previous image frame was fully off, etc.). 
     At step  416 , control circuitry  16  may drive fLCOS display panel  40  using the non-square wave drive voltage waveform identified while processing step  414 . Driving fLCOS display panel  40  in this way may maximize the reflectance of fLCOS display panel  40  for the current operating temperature of the display panel, for example. Control circuitry  16  may continue to overdrive fLCOS display panel  40  for a predetermined time period, until a new trigger condition is detected, for a predetermined number of frames, etc. 
     Overdriving fLCOS display panel  40  (e.g., using non-square wave fLCOS drive voltage waveforms as identified while processing step  404  of  FIG.  29    or step  414  of  FIG.  30   ) may, for example, serve to reduce the duration (width) of the dark gap of fLCOS display panel  40  relative to scenarios where fLCOS display panel  40  is driven using a square wave fLCOS drive voltage waveform. This may serve to further optimize power consumption in display module  14 A, for example. Control circuitry  16  may therefore sometimes be referred to herein as reducing the duration of the dark gap of fLCOS display panel  40  based on gathered temperature sensor data or identified frame history information. The arrangement of  FIG.  30    may be combined with the arrangement of  FIG.  29    if desired (e.g., control circuitry  16  may identify a non-square wave fLCOS drive voltage that optimizes the optical performance of fLCOS display panel  40  given both the current temperature of fLCOS display panel  40  and the frame history information of fLCOS display panel  40 ). If desired, the non-square wave drive voltage waveform to use may be selected based on the previous frame&#39;s target reflectance state and temperature information. For example, a look up table may modify the non-square wave drive voltage waveform for the current frame based on any previous state. As one example, if the previous frame was on for one-half the illumination field time, it would have a different non-square wave drive voltage for the current frame when the previous frame was on for 98% of the illumination field time. In driving fLCOS panel  40 , the percent on (duty cycle) during the illumination time may be selected to control the grey level for the field. 
     Overdriving fLCOS display panel  40  may also serve to optimize the optical performance of display module  14 A by reducing the response time of fLCOS display panel  40 .  FIG.  31    is a plot showing how overdriving fLCOS display panel  40  may reduce the response time of fLCOS display panel  40  across a wide range of operating temperatures. 
     In the example of  FIG.  31   , the horizontal axis plots the temperature of fLCOS display panel  40  (e.g., in degrees Celsius) and the vertical axis plots the response time of fLCOS display panel  40  (e.g., in microseconds). Curve  420  plots the response time of fLCOS display panel  40  when driven using square-wave fLCOS drive voltage pulses (e.g., pulses such as pulse  396  of  FIG.  28   ). As shown by curve  420 , the response time of fLCOS display panel  40  may decrease as temperature increases. 
     Curve  422  plots the response time of fLCOS display panel  40  when (over) driven using non-square-wave fLCOS drive voltage waveform pulses having a first peak voltage level (e.g., pulses such as pulse  394  of  FIG.  28    having a peak voltage given by fourth voltage level V4). Curve  424  plots the response time of fLCOS display panel  40  when (over) driven using a non-square-wave fLCOS drive voltage waveform pulses having a second peak voltage level that is higher than the first peak voltage level. The peak voltage level of the square-wave fLCOS drive voltage pulses associated with curve  420  may be 1.5V, the first peak voltage level associated with curve  422  may be 1.65V, and the second peak voltage level associated with curve  424  may be 1.8V, as one example. In general, the first peak voltage level may be any desired voltage greater than 1.5V (e.g., in scenarios where V ON  of  FIG.  27    is 1.5V), greater than 1.6V, greater than 1.7V, greater than 1.8V, etc. 
     As shown by curves  422  and  424 , overdriving fLCOS display panel  40  may serve to reduce the response time of fLCOS display panel  40  across all temperatures. As shown by curve  424 , overdriving fLCOS display panel  40  with a non-square wave fLCOS drive voltage waveform having a greater peak voltage level may serve to further decrease the response time of fLCOS display panel  40 . In this way, overdriving fLCOS display panel  40  may serve to further optimize the optical performance of display module  14 A by reducing the response time of fLCOS display panel  40  across a wide range of operating temperatures. The example of  FIG.  31    is merely illustrative. In practice, curves  420 ,  422 , and  424  may have other shapes. 
     In accordance with an embodiment, a display system is provided that includes illumination optics configured to produce illumination light; a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating image data using the illumination light, the fLCOS panel includes a ferroelectric liquid crystal (fLC) layer, and a reflective backplane configured to receive the illumination light through the fLC layer and configured to reflect the illumination light, the fLC layer being configured to transmit the illumination light reflected off of the reflective backplane as the image light; and a waveguide configured to propagate the image light. 
     In accordance with another embodiment, the fLCOS panel includes a driver flex, the silver backplane is layered on the driver flex. 
     In accordance with another embodiment, the fLCOS panel includes electrodes selected from the group consisting of: indium tin oxide (ITO) electrodes layered on the fLC layer and index-matching indium tin oxide (IMITO) electrodes layered on the fLC layer. 
     In accordance with another embodiment, the fLCOS panel includes a glass substrate layered on the ITO electrodes. 
     In accordance with another embodiment, the fLCOS panel includes a first polyimide alignment layer interposed between the ITO electrodes and the fLC layer; and a second polyimide alignment layer interposed between the fLC layer and the silver backplane. 
     In accordance with another embodiment, the backplane includes silver. 
     In accordance with another embodiment, the fLC layer has a birefringence and a cell gap, the cell gap is equal to a distance λ divided by four times the birefringence, and the distance λ is less than or equal to 530 nm. 
     In accordance with an embodiment, a display system is provided that includes illumination optics configured to produce illumination light; a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating the illumination light using image data; and a waveguide configured to propagate the image light, the fLCOS panel includes a ferroelectric liquid crystal (fLC) layer, and a dielectric mirror backplane configured to receive the illumination light through the fLC layer and configured to reflect the illumination light as the image light. 
     In accordance with another embodiment, the fLCOS panel includes a driver flex, the dielectric mirror backplane is layered on the driver flex. 
     In accordance with another embodiment, the fLCOS panel includes indium tin oxide (ITO) electrodes layered on the fLC layer. 
     In accordance with another embodiment, the fLCOS panel includes a glass substrate layered on the ITO electrodes. 
     In accordance with another embodiment, the fLCOS panel includes a first polyimide alignment layer interposed between the ITO electrodes and the fLC layer; and a second polyimide alignment layer interposed between the fLC layer and the dielectric mirror backplane. 
     In accordance with another embodiment, the fLCOS panel includes an anti-reflective coating on the glass substrate. 
     In accordance with another embodiment, the fLC layer has a birefringence and a cell gap, the cell gap is equal to a number λ divided by four times the birefringence, and the number λ is less than or equal to 565 nm. 
     In accordance with an embodiment, a display system is provided that includes illumination optics configured to produce illumination light; a ferroelectric liquid crystal on silicon (fLCOS) panel configured to produce image light by modulating the illumination light using image data; and a waveguide configured to propagate the image light, the fLCOS panel includes a ferroelectric liquid crystal (fLC) layer, the fLC layer has a birefringence Δn, and a backplane configured to receive the illumination light through the fLC layer and configured to reflect the illumination light as the image light, the fLC layer has a thickness equal to a wavelength divided by four times the birefringence Δn and the wavelength is between 500 nm and 565 nm. 
     In accordance with another embodiment, the illumination optics include a red light source configured to generate a range of red wavelengths of the illumination light, a blue light source configured to generate a range of blue wavelengths of the illumination light, and a green light source configured to generate a range of green wavelengths of the illumination light, the wavelength is a vacuum wavelength, and the range of green wavelengths includes the vacuum wavelength. 
     In accordance with another embodiment, the backplane includes a backplane selected from the group consisting of: a silver backplane and a silver alloy backplane. 
     In accordance with another embodiment, the backplane includes a dielectric mirror backplane. 
     In accordance with another embodiment, the wavelength is between 520 nm and 530 nm. 
     In accordance with another embodiment, the wavelength is 526 nm. 
     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: 20230215
Publication Date: 20240312
Grant Date: 20240312
Priority Date: 20200828
Inventors: CHEN, YUAN
LI, XIAOKAI
GE, ZHIBING
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/141", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133723", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3629", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/0408", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0491", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2340/0457", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3629", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/141", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2300/0491", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/34", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2340/0457", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136277", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/141", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13362", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/286", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B27/149", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B1/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B6/0055", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0068", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B27/0172", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133723", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3629", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/0408", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2300/0491", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2330/021", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2340/0457", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 78049777