Compensation for liquid crystal on silicon displays

Abstract

The invention relates to compensation for liquid crystal on silicon displays. A liquid crystal on silicon (LCOS) system includes an illumination module, an LCOS, and an LCOS compensator. The illumination module is configured to generate illumination light. The LCOS is configured to receive the illumination light and modulate the illumination light into display light. The LCOS compensator may have a slow axis aligned to between-33 degrees and-77 degrees. The LCOS compensator is configured to receive the illumination light and the display light.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. nonprovisional patent application No. 18 / 908,804, filed October 8, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates generally to display technologies, and more particularly to liquid crystal on silicon (LCOS) displays. Background Technology

[0004] Modern display technologies include liquid crystal display (LCD) panels, projectors, organic light-emitting diode (OLED) arrays, liquid crystal on silicon (LCOS) displays, and even transparent displays. Common performance metrics for displays include brightness and contrast ratio. Based on size, power consumption, and desired performance specifications, certain display technologies are better suited for different situations. Summary of the Invention

[0005] According to one aspect of this disclosure, a head-mounted display (HMD) is provided, the HMD comprising: an illumination module configured to generate illumination light; a liquid crystal on silicon (LCOS) configured to receive the illumination light and modulate the illumination light into display light; an LCOS compensator having a slow axis aligned to between -48 degrees and -77 degrees, wherein the LCOS compensator is configured to receive the illumination light and the display light; and a waveguide system configured to receive the display light generated by the LCOS, wherein the waveguide system is configured to guide a virtual image contained in the display light to an eyebox region.

[0006] According to another aspect of this disclosure, a liquid crystal on silicon (LCOS) system is provided, the LCOS system comprising: an illumination module configured to generate illumination light; an LCOS configured to receive the illumination light and modulate the illumination light into display light; and an LCOS compensator having a slow axis aligned to between -33 degrees and -77 degrees, wherein the LCOS compensator is configured to receive the illumination light and the display light.

[0007] According to yet another aspect of the disclosure, a method is provided that includes emitting illumination light with an illumination system, receiving the illumination light with an LCOS system that includes an LCOS and an LCOS compensator having a slow axis, wherein the illumination light propagates through the LCOS compensator to the LCOS, and driving a calibration voltage onto the LCOS to increase a contrast ratio of display light, wherein driving the calibration voltage onto the LCOS modulates the illumination light into the display light that propagates back through the LCOS compensator. BRIEF DESCRIPTION OF DRAWINGS

[0008] Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views. Embodiments of the present disclosure are described herein with reference to the following drawings, in which:

[0009] Figure 1 A head-mounted display (HMD) that can include an LCOS system including an LCOS compensator is shown in accordance with aspects of the disclosure.

[0010] Figure 2 An example LCOS system including an LCOS and an LCOS compensator is shown in accordance with aspects of the disclosure.

[0011] Figure 3A And Figure 3B An example implementation of an LCOS compensator is shown in accordance with aspects of the disclosure.

[0012] Figure 4 A cross-section of an example LCOS system and a portion of an example LCOS is shown in accordance with aspects of the disclosure.

[0013] Figure 5 An example LCOS system including an LCOS compensator disposed between a lens and an LCOS is shown in accordance with aspects of the disclosure.

[0014] Figure 6 An example LCOS system including an LCOS compensator coupled to an LCOS is shown in accordance with aspects of the disclosure.

[0015] Figure 7 A flowchart of an example process of generating display light with an LCOS system including an LCOS compensator is shown in accordance with aspects of the disclosure. DETAILED DESCRIPTION

[0016] Embodiments of compensation for liquid crystal on silicon (LCOS) displays are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail in order to avoid obscuring the aspects.

[0017] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0018] In some embodiments of the present disclosure, the term "near-eye" can be defined to include elements configured to be placed within 50 mm of a user's eye when using the near-eye device. Thus, a "near-eye optical element" or "near-eye system" would include one or more elements configured to be placed within 50 mm of a user's eye.

[0019] In aspects of the present disclosure, visible light can be defined as having a wavelength range of about 380 nanometers (nm) to 700 nm. Non-visible light can be defined as light having a wavelength outside the range of visible light, such as ultraviolet light and infrared light. Infrared light having a wavelength range of about 700 nm to 1 millimeter (mm) includes near-infrared light. In aspects of the present disclosure, near-infrared light can be defined as having a wavelength range of about 700 nm to 1.6 micrometers (pm).

[0020] In aspects of the present disclosure, the term "transparent" can be defined as having a light transmittance greater than 90%. In some aspects, the term "transparent" can be defined as a material having a visible light transmittance greater than 90%.

[0021] LCOS displays are generally considered a micro-display technology and are sometimes used in small form-factor devices. LCOS systems generally include an illumination light that is shined onto a liquid crystal array that is applied to a silicon-based mirror substrate, which can be selectively modulated by driving an image onto different pixels in the LCOS array. LCOS systems are generally considered to have strong contrast. However, in certain situations, LCOS displays need higher contrast. One example situation is an Augmented Reality (AR) headset. In this particular situation, it is desirable to achieve a dark enough state of the display to achieve high contrast. The AR situation can be a unique situation for an LCOS display system that desires to achieve very high contrast because of the bright illumination environment (e.g., sunlight) that is incident on the AR glasses (and also through the user’s eyes) that can make the contrast of virtual images contained in the display light produced by the LCOS display system easily washed out by the bright illumination environment. High contrast for AR headsets is also important in low light environments where light leakage can be more easily seen by the eye.

[0022] In embodiments of the present disclosure, an LCOS compensator can be used to improve the contrast of the display light. The slow axis of the LCOS compensator can be passively aligned to between -33 degrees and -57 degrees. In some embodiments, the slow axis of the LCOS compensator can be about -45 degrees. This can allow the LCOS compensator to be passively aligned with respect to the LCOS display, rather than actively aligned. Active alignment in the manufacturing process can take more time and can require specialized tools. Second, active alignment can necessarily require a larger form factor because of the exclusion zone around the LCOS that can be required for the LCOS compensator to be rotated during the active alignment process.

[0023] In embodiments of the present disclosure, the LCOS compensator can be actively aligned. In some embodiments, the slow axis of the LCOS compensator can be actively aligned between -48 degrees and -77 degrees. In some embodiments, the slow axis of the LCOS compensator can be between -48 degrees and -72 degrees. In some embodiments, the slow axis of the LCOS compensator can be about -60 degrees. In some embodiments, the slow axis of the LCOS compensator can be actively aligned between -53 degrees and -77 degrees. In some embodiments, the slow axis of the LCOS compensator can be about -65 degrees.

[0024] In embodiments of the present disclosure, a combination of active alignment of LCOS compensators and voltage calibration of one or more LCOS drive voltages is utilized. In this embodiment, the LCOS compensators can be actively aligned during the manufacturing process, and voltage calibration can be applied at the final assembly of the device. Environmental temperature calibration can also be implemented to improve the device’s contrast in response to the environment.

[0025] In embodiments of the present disclosure, LCOS compensators can be passively aligned, and calibration voltages (for modulating illumination light) can be driven onto the LCOS to improve the contrast of display light produced by the LCOS. The calibration voltages can be calibrated for individual placements of the LCOS compensators, which allows the LCOS compensators to be passively aligned. The calibration voltages can be fine-tuned for each individual cell to increase contrast. In some embodiments, there are different calibration voltages for red, green, and blue (RGB) channels of the display light. In combination with the LCOS compensators being passively aligned, the calibration voltages can be applied to the LCOS compensators to improve the contrast of the display light. Figures 1 to 7 These and other embodiments are described in more detail.

[0026] Figure 1 A head-mounted display (HMD) 100 that can include an LCOS system including LCOS compensators is shown in accordance with aspects of the present disclosure. The HMD 100 includes a frame 114 coupled to arms 111A and 111B. Lens assemblies 121A and 121B are mounted to the frame 114. The lens assemblies 121A and 121B can include prescription lenses that are matched to a particular user of the HMD 100. The illustrated HMD 100 is configured to be worn on or around a head of a wearer of the HMD 100.

[0027] In Figure 1 In the illustrated HMD 100, each lens assembly 121A / 121B includes a waveguide 150A / 150B for guiding image light produced by a display 130A / 130B to an eyebox region for viewing by a user of the HMD 100. For example, the display 130A / 130B can include a liquid crystal on silicon (LCOS) display for guiding image light to a wearer of the HMD 100 to present a virtual image. The LCOS display can include an LCOS compensator.

[0028] The lens assemblies 121A and 121B can be transparent to the user to facilitate augmented reality or mixed reality to enable the user to view scene light from their surroundings while also receiving image light directed to one or both of their eyes by, for example, the waveguides 150A / 150B. The lens assemblies 121A and 121B can include two or more optical layers for different functions, such as display, eye tracking, and optical power. In some embodiments, image light from the display 130A or 130B is directed into only one eye of the wearer of the HMD 100. In an embodiment, the display 130A is used to direct image light to the waveguide 150A and the display 130B is used to direct image light to the waveguide 150B.

[0029] The frame 114 and arms 111A, 111B can include support hardware of the HMD 100 (e.g., processing logic 107), wired and / or wireless data interfaces for sending and receiving data, a graphics processor, and one or more memories for storing data and computer-executable instructions. The processing logic 107 can include circuitry, logic, instructions stored in machine-readable storage media, ASIC circuitry, FPGA circuitry, and / or one or more processors. In one embodiment, the HMD 100 can be configured to receive wired power. In one embodiment, the HMD 100 is configured to be powered by one or more batteries. In one embodiment, the HMD 100 can be configured to receive wired data including video data via a wired communication channel. In one embodiment, the HMD 100 is configured to receive wireless data including video data via a wireless communication channel. The processing logic 107 can be communicatively coupled to the network 180 to provide data to the network 180 and / or access data within the network 180. The communication channel between the processing logic 107 and the network 180 can be a wired communication channel or a wireless communication channel.

[0030] In Figure 1 In the illustrated embodiment, the HMD 100 includes a camera 147 configured to image the eyebox region. In some embodiments, the illumination module 160 can illuminate the eyebox region with near-infrared illumination light to assist the camera 147 in imaging the eyebox region for eye tracking purposes. In some embodiments, the camera 147 can include a lens assembly configured to focus image light to a complementary metal-oxide-semiconductor (CMOS) image sensor. A near-infrared filter that receives narrowband near-infrared wavelengths can be placed on the image sensor such that it is sensitive to narrowband near-infrared wavelengths while rejecting visible light and wavelengths outside of the narrowband. A near-infrared illuminator (not shown), such as a near-infrared LED or laser, that emits narrowband wavelengths can be included in the illumination module 160 to illuminate the eyebox region with narrowband near-infrared wavelengths.

[0031] Figure 2 An example LCOS system 200 is shown that includes an LCOS 239 and an LCOS compensator 233, in accordance with aspects of the present disclosure. Figure 2 This is merely an example configuration of an LCOS system, and aspects of the present disclosure can be implemented in a variety of different LCOS systems.

[0032] The example LCOS system 200 includes an illumination system 205, a pre-polarizer 210, a polarized beamsplitter (PBS) 220, an LCOS compensator 233, a lens 225, an LCOS 239, a quarter-waveplate (QWP) 240, a reflector 245, a half-waveplate (HWP) 250, a lens 255, and a waveguide system 275.

[0033] The illumination system 205 can include a light source, such as an LED or a laser. In some embodiments, the illumination system 205 includes more than one color channel, such that the display light produced by the LCOS system 200 includes a color image. In some embodiments, the illumination system 205 includes red, green, and blue (RGB) light sources that sequentially emit light, and red, green, and blue portions of the image are driven onto the LCOS 239 in correspondence with the illumination system 205 sequentially emitting red, green, and blue illumination light.

[0034] In operation, light is emitted from the illumination system 205 and propagates along an optical path 261 toward the pre-polarizer 210. The pre-polarizer 210 passes a first linear polarization orientation of the light, so the illumination light has a uniform polarization orientation. The PBS 220 is configured to reflect the first linear polarization orientation and pass a second linear polarization orientation that is orthogonal to the first linear polarization orientation. Thus, the illumination light having the first linear polarization orientation reflects off the PBS 220 and is redirected along an optical path 262 toward the LCOS 239.

[0035] In Figure 2 the illumination light propagating along the optical path 262 encounters the LCOS compensator 233 disposed between the PBS 220 and the LCOS 239. The LCOS compensator 233 is configured to receive the illumination light. The LCOS compensator 233 is configured to help provide a better dark state for display light produced by the LCOS 239.

[0036] The LCOS compensator 233 may have a slow axis passively aligned to between -33 degrees and -57 degrees. In some embodiments, the LCOS compensator 233 has a slow axis passively aligned to approximately -45 degrees. The passive alignment of the LCOS compensator 233 relative to the LCOS 239 allows a calibration voltage to be used to drive the liquid crystal in the LCOS 239 to optimal alignment to increase the contrast of the LCOS 239, which will be discussed in more detail below.

[0037] The LCOS compensator 233 may have a slow axis actively aligned to between -48 degrees and -77 degrees. In some embodiments, the LCOS compensator 233 has a slow axis actively aligned to between -48 degrees and -72 degrees. In some embodiments, the LCOS compensator 233 has a slow axis actively aligned to approximately -60 degrees. In some embodiments, the slow axis of the LCOS compensator may be between -53 degrees and -77 degrees. In some embodiments, the slow axis of the LCOS compensator may be approximately -65 degrees. The active alignment of the LCOS compensator 233 relative to the LCOS 239 allows a calibration voltage to be used to drive the liquid crystal in the LCOS 239 to optimal alignment to increase the contrast of the LCOS 239.

[0038] Figure 3A An example embodiment of the LCOS compensator 333 according to various aspects of this disclosure is shown. Figure 3A In this LCOS compensator 233, the LCOS compensator 333 has a slow axis 335 of approximately -45 degrees relative to the rubbing orientation of the indium titanium oxide (ITO) layer at -90 degrees and the silicon (Si) layer at 26 degrees. The ITO and Si layers are included within the LCOS 239. While the example LCOS compensator 333 is shown with a passively aligned slow axis 335 to approximately -45 degrees, the LCOS compensator 333 can have a passively aligned slow axis between -33 degrees and -57 degrees. In some embodiments, a calibration voltage driven onto the LCOS 239 can dictate that the LCOS compensator 233 is aligned at different angles. In some embodiments, using a calibration voltage avoids the need for mechanically rotating the LCOS compensator 233 relative to the LCOS 239.

[0039] Figure 3B Example embodiments of the LCOS compensator 334, which can be used in active alignment implementations, are shown according to various aspects of this disclosure. Figure 3B In the middle, the LCOS compensator 334 has relative to Figure 3BThe slow axis 336 is shown to be about -60 degrees and is 90 degrees relative to the indium-titanium-oxide (ITO) glass rubbing direction. In some embodiments, rubbing can be performed on a polyimide layer instead of on an ITO layer or a silicon layer. The polyimide layer can be coated on both substrates (e.g., one substrate is ITO coated glass and the other substrate is a silicon substrate with multiple layers of transistors). The ITO layer and the Si layer are included in the LCOS 239. While the example LCOS compensator 334 is shown to have a slow axis 336 actively aligned to about -60 degrees, the LCOS compensator 334 can have a slow axis actively aligned to between -48 degrees and -72 degrees. In some embodiments, the LCOS compensator 334 can have a slow axis actively aligned to between -53 degrees and -77 degrees. In some embodiments, the slow axis 336 is actively aligned to about -65 degrees. In some embodiments where the LCOS compensator 234 is actively aligned, one or more calibration voltages are also driven onto the LCOS 239 to increase the brightness contrast.

[0040] Referring back to Figure 2 , the compensated illumination light 263 encounters the LCOS 239 after propagating through the LCOS compensator 233. In some embodiments, a lens 225 can be disposed between the LCOS compensator 233 and the LCOS 239. The lens 225 can be a refractive lens. The lens 225 can be considered a field lens.

[0041] The LCOS 239 receives the compensated illumination light 263 and is configured to modulate the compensated illumination light to produce display light. An image can be driven on an LCOS pixel array of the LCOS 239. The LCOS pixel array can be arranged in rows and columns, and each LCOS pixel in the LCOS pixel array can be modulated to reflect light or block light. To generate a color image, a red image sub-frame, a green image sub-frame, and a green image sub-frame can be sequentially driven onto the LCOS 239 to generate a color image frame. The duration of the color image frame can be less than 50 milliseconds (ms). These sub-frames can be about one-third of the duration of the color image frame. In some embodiments, the duration of the color frame is about 33 ms, which corresponds to a frame rate of about 30 Hz. In some embodiments, the duration of the color frame is about 16 ms, which corresponds to a frame rate of about 60 Hz. In some embodiments, the duration of the color frame is about 8 ms, which corresponds to a frame rate of about 120 Hz.

[0042] Figure 4A cross-section of an example LCOS system 400 and a portion of an example LCOS 439 is shown in accordance with aspects of the present disclosure. The LCOS system 400 includes a driver module 470, an LCOS 439, and an LCOS compensator 433. The LCOS 439 includes a Si layer 471, a reflective layer 473, a highly-reflective (HR) coating 475, a first polyimide (PI) alignment layer 477, a liquid crystal layer 479, a second PI alignment layer 481, a transparent electrode layer 483, and a glass layer 485. The reflective layer 473 can include aluminum. For example, the transparent electrode layer 483 can include indium tin oxide (ITO). The LCOS compensator 433 can have similar characteristics as described for the LCOS compensator 233, 333, or 334.

[0043] In operation, a voltage applied between the reflective layer 473 and the transparent electrode layer 483 changes the orientation of the liquid crystals 478 in the liquid crystal layer 479. The LCOS 439 can operate in a twisted nematic (TN) mode. The TN mode is typically white, and can switch to black when a voltage is applied between the reflective layer 473 and the transparent electrode layer 483. The LCOS 439 can operate in a vertically aligned (VA) mode. Traditionally, LCOS displays have difficulty reaching a true dark state due to residual retardation, which reduces the contrast of the display light. Therefore, an LCOS compensator can be used to achieve an improved dark state that contributes to better contrast.

[0044] After an LCOS compensator is installed in an LCOS system, calibration voltage levels can be generated to maximize or significantly improve the contrast of the display light produced by the LCOS system. One or more calibration voltage levels can be driven onto the LCOS system with a passive or active alignment LCOS compensator. Because the voltage driven onto the LCOS modulates the orientation of the liquid crystals 478, the ideal dark voltage for each LCOS system can be determined by testing what voltage level provides the best dark state (as shown by optical testing). Of course, producing the darkest dark state for the LCOS system increases the contrast of the display light produced by the LCOS system. With the systems and techniques of the present disclosure, the contrast of the brightest state to the darkest state for each of the red, green, and blue channels can be higher than 1000: 1.

[0045] In Figure 4In some embodiments, the driver module 490 is configured to drive one dark voltage (or multiple dark voltages) onto the LCOS 439. The voltage can be a calibration voltage to produce the darkest dark state of the LCOS 439. In some embodiments, the ideal dark voltage is calibrated over the temperature range of the LCOS system 400 so that the dark voltage driven onto the pixels of the LCOS 439 is ideal (or close to ideal) even when temperature variations affect the LCOS system 400. The LCOS system 400 can include a temperature sensor 495 configured to provide temperature measurements to the driver module 490. In an embodiment, the red drive voltage 491, the green drive voltage 492, and the blue drive voltage 493 are calibrated over the temperature range of the LCOS system.

[0046] In some embodiments, a single calibrated dark voltage is used to drive onto the LCOS 439 for all three color channels. In some embodiments, the single calibrated dark voltage is associated with the ideal dark state of the green image subframes.

[0047] In some embodiments, the three color channels have separately calibrated drive voltages to produce the ideal dark state of each subframe. For example, the driver module 490 can be configured to (1) drive the red drive voltage 491 onto the LCOS 439 for producing a red image; (2) drive the green drive voltage 492 onto the LCOS 439 for producing a green image; and (3) drive the blue drive voltage 493 onto the LCOS 439 for producing a blue image. The red drive voltage 491, the green drive voltage 492, and the blue drive voltage 493 can be calibrated to increase the contrast of the red image, the green image, and the blue image, respectively. In some embodiments, the blue drive voltage 493 is higher than the green drive voltage 492, and the green drive voltage 492 can be higher than the red drive voltage 491. The red drive voltage 491, the green drive voltage 492, and the blue drive voltage 493 can be a function of the mechanical orientation of the LCOS compensator 233 / 433 with respect to the LCOS 239 / 439.

[0048] In Figure 4In particular, illumination light 462 encounters LCOS compensator 433. For example, illumination light 462 can be directed to LCOS compensator by PBS 220. LCOS compensator 433 receives illumination light 462 and produces compensated illumination light 463 that exits LCOS compensator 433 toward LCOS 439. The slow axis orientation of LCOS compensator 433 acts on illumination light 462 to produce compensated illumination light 463. Compensated illumination light 463 propagates through layers 485, 483, 481, and is modulated according to the orientation of liquid crystal 478. Compensated illumination light 463 continues to propagate through layers 477 and 475, is reflected by reflective layer 473 and propagates back through layers 475 and 477 and encounters liquid crystal layer 479. The light is further modulated according to the orientation of liquid crystal 478 to produce display light 464 that propagates through layers 481, 483, and 485, and then encounters LCOS compensator 433. In Figure 4 particular, display light 464 is received by LCOS compensator 433 and emerges as compensated display light 465. The slow axis orientation of LCOS compensator 433 acts on display light 464 to produce compensated display light 465. Compensated display light 465 can have a second linear polarization orientation that is orthogonal to the first linear polarization orientation of illumination light 462.

[0049] Returning to Figure 2 , compensated display light propagates along optical path 265. As shown in Figure 2 , compensated display light can have a second linear polarization orientation that is orthogonal to the first linear polarization orientation of illumination light propagating along optical path 262. Because PBS 220 is configured to pass the second linear polarization orientation and reflect the first linear polarization orientation, compensated display light (having the second linear polarization orientation) passes through PBS 220 and retains its second linear polarization orientation.

[0050] Compensated display light encounters QWP 240. QWP 240 is configured to shift the polarization axis of incident light so that linearly polarized light can be converted to circularly polarized light by QWP 240. Likewise, incident circularly polarized light can be converted to linearly polarized light by QWP 240. QWP 240 can be made of a birefringent material (e.g., quartz, an organic material sheet, or a liquid crystal). In one embodiment, QWP 240 is designed to be a so-called “zero order waveplate” such that the retardation imparted by QWP 240 remains close to a quarter wave, independent of the wavelength and angle of incidence of the incident light.

[0051] Light with a second linear polarization orientation propagating along optical path 265 is converted into circularly polarized light propagating along optical path 266 before encountering reflector 245. Reflector 245 may include a lensing curvature to help focus the compensated display light. The circularly polarized light propagating along optical path 266 is reflected by reflector 245, which changes the orientation of the light propagating along optical path 267 to circularly polarized light with the opposite orientation to that of the circularly polarized light propagating along optical path 266. The light propagating along optical path 267 is then converted into linearly polarized light by QWP 240.

[0052] like Figure 2 As shown, the light propagating along the optical path 268 is in the first linear polarization orientation and is reflected by the PBS220 toward the waveguide system 275. Figure 1 Waveguides 130A / 130B in the diagram can be examples of waveguide system 275. Light guided by PBS 220 toward waveguide system 275 maintains its first linear polarization orientation and encounters HWP 250. HWP 250 is configured to shift the polarization axis of the incident light by π / 2 (90 degrees). Thus, in some embodiments, linearly polarized light can be converted by HWP 250 into an orthogonal orientation of the linearly polarized light reflected from PBS 220 toward waveguide system 275. In other embodiments, light encountering HWP 250 can be converted into a different polarization direction, which does not necessarily have to be orthogonal to the received light. HWP 250 can be designed as a so-called "zero-order waveplate" such that the delay imparted by HWP 250 remains close to half a wave, regardless of the wavelength and angle of incidence of the incident light.

[0053] Waveguide system 275 is configured to receive display light propagating along optical path 269. Waveguide system 275 can be configured to guide a virtual image contained in the display light to the eye-fitting frame region. For example, the eye-fitting frame region may be the area occupied by the user's eyes when the user wears HMD 100.

[0054] exist Figure 2 In this configuration, lens 225 is positioned between LCOS compensator 233 and LCOS 239. However, the LCOS compensator can be positioned in different locations.

[0055] Figure 5 An example LCOS system 500 according to various aspects of this disclosure is shown, which includes an LCOS compensator 533 disposed between a lens 225 and an LCOS 239. The LCOS compensator 533 may have similar optical characteristics to those described for LCOS compensators 233 and / or 433.

[0056] Figure 6An example LCOS system 600 is shown that includes an LCOS compensator 633 coupled to an LCOS 239 in accordance with aspects of the present disclosure. In some embodiments, the LCOS compensator 633 can be laminated to the LCOS 239. The LCOS compensator 633 can have similar optical properties as described for the LCOS compensator 233 and / or 433.

[0057] Figure 7 A flowchart of an example process 700 to generate display light with an LCOS compensator in accordance with aspects of the present disclosure is shown. The order in which some or all of the process blocks appear in process 700 should not be deemed limiting. Rather, one of ordinary skill in the art, having the benefit of the present disclosure, will appreciate that some of the process blocks can be executed in a variety of orders not illustrated, or even in parallel.

[0058] In process block 705, illumination light is emitted by an illumination system (e.g., illumination system 205). The illumination system can include a light source, such as an LED or a laser. In some embodiments, the illumination system includes more than one color channel, such that the display light generated by the LCOS includes a color image. In some embodiments, the illumination system includes red, green, and blue (RGB) light sources that emit light sequentially, and red, green, and blue portions of the image are driven onto the LCOS display in accordance with the illumination system sequentially emitting red, green, and blue illumination light.

[0059] In process block 710, the illumination light is received with an LCOS system that includes an LCOS and an LCOS compensator having a slow axis. The LCOS compensator can be passively or actively aligned. The illumination light propagates through the LCOS compensator to the LCOS.

[0060] In process block 715, a calibration voltage is driven onto the LCOS to increase a contrast ratio of the display light. Driving the calibration voltage onto the LCOS modulates (through liquid crystal modulation) the illumination light into display light that propagates through the LCOS compensator. After performing process block 715, process 700 can return to process block 705.

[0061] In embodiments of the present disclosure, the LCOS compensator is actively calibrated at the factory, and the calibrated drive voltage is used to improve the brightness contrast of the LCOS system. The calibrated drive voltage can be stored in a look up table (LUT), where the calibrated drive voltage is correlated to the temperature of the LCOS system.

[0062] Embodiments of the process 700 also include driving a red drive voltage onto the LCOS for producing a red portion of the display light, and driving a blue drive voltage onto the LCOS for producing a blue portion of the display light. In this implementation, the calibration voltage recited in process block 715 can be a green drive voltage for producing a green portion of the display light. The red drive voltage, the green drive voltage, and the blue drive voltage can be calibrated to increase contrast of the red portion, the green portion, and the blue portion of the display light, respectively. In some embodiments, the blue drive voltage can be higher than the green drive voltage, and the green drive voltage can be higher than the red drive voltage. In some embodiments, the red drive voltage, the green drive voltage, and the blue drive voltage are sequentially driven onto the LCOS in a frame of the display light, where the frame has a duration of less than 50 ms.

[0063] In some embodiments of the process 700, the calibration voltage is a function of a mechanical orientation of the LCOS compensator relative to the LCOS.

[0064] In some embodiments of the process 700, the illumination light has a first linear polarization orientation, and the display light has a second linear polarization orientation that is orthogonal to the first linear polarization orientation.

[0065] Embodiments of the invention can include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which can include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and / or derivatives thereof. Artificial reality content can include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content can include video, audio, touch feedback, or some combination thereof, any of which can be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality can also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in artificial reality and / or are otherwise used in (e.g., play a game in) artificial reality. The artificial reality system that provides the artificial reality content can be implemented on a variety of platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

[0066] The term "processing logic" (e.g., logic 107) in this disclosure may include one or more processors, one or more microprocessors, one or more multi-core processors, one or more application-specific integrated circuits (ASICs), and / or one or more field-programmable gate arrays (FPGAs) that perform the operations disclosed herein. In some embodiments, memory (not shown) is integrated into the processing logic to store instructions for performing operations and / or to store data. According to embodiments of this disclosure, the processing logic may also include analog or digital circuitry for performing operations.

[0067] The term "one memory" or "multiple memories" described in this disclosure may include one or more volatile or non-volatile memory architectures. The "one memory" or "multiple memories" may be removable and non-removable media implemented using any method or technology for storing information such as computer-readable instructions, data structures, program modules, or other data. Example memory technologies may include RAM, ROM, EEPROM, flash memory, CD-ROM, digital versatile disk (DVD), high-definition multimedia / data storage disk, or other optical storage devices, magnetic cassette, magnetic tape, disk storage devices, or other magnetic storage devices, or any other non-transfer medium that can be used to store information for access by a computing device.

[0068] A network may include any network or network system, such as, but not limited to, the following: peer-to-peer network; local area network (LAN); wide area network (WAN); public network (e.g., the Internet); private network; cellular network; wireless network; wired network; a combination of wireless and wired network; and satellite network.

[0069] The communication channel may include one or more wired or wireless communications, or may be routed via one or more wired or wireless communications using the following methods: IEEE 802.11 protocol, short-range wireless protocol, Serial Peripheral Interface (SPI), or Inter-Integrated Circuit (I2C). 2C) Universal Serial Port (USB), Controller Area Network (CAN), cellular data protocols (e.g., 3G, 4G, LTE, 5G), optical communication networks, Internet Service Providers (ISP), peer-to-peer networks, Local Area Networks (LAN), Wide Area Networks (WAN), public networks (e.g., the Internet), private networks, satellite networks, or other networks.

[0070] The computing device can include a desktop computer, a laptop computer, a tablet, a phablet, a smartphone, a feature phone, a server computer, etc. The server computer can be located at a remote location in a data center, or can be stored locally.

[0071] The processes explained above are described in terms of computer software and hardware. The techniques described can constitute machine-executable instructions embodied within machine- readable storage medium used in the operation of memory, assembly language, machine code, source code, object code, scripts, or any other entity comprising a set of instructions executable by a machine. Additionally, the processes can be embodied by both hardware and software.

[0072] A tangible, non-transitory machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable / non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0073] The above description of illustrated embodiments of the application, including what is described in the abstract, is not intended to be exhaustive or to limit the application to the precise forms disclosed. While specific embodiments of, and examples for, the application are described herein for illustrative purposes, various modifications are possible within the scope of the application, as those skilled in the relevant art will recognize.

[0074] These modifications can be made in light of the above detailed description of the application. The terms used in the following claims should not be construed to limit the application to the specific embodiments disclosed in the specification and the drawings. Rather, the scope of the application is to be determined entirely by the following claims, which are to be construed in accordance with the principles of claim interpretation.

Claims

1. A head-mounted display (HMD), the HMD comprising: A lighting module configured to generate illumination light; A silicon-based liquid crystal LCOS, wherein the LCOS is configured to receive the illumination light and modulate the illumination light into display light; An LCOS compensator having a slow axis aligned to between -48 degrees and -77 degrees, wherein the LCOS compensator is configured to receive the illumination light and the display light; and A waveguide system configured to receive the display light generated by the LCOS, wherein the waveguide system is configured to guide a virtual image contained in the display light to an eye-friendly frame region.

2. The HMD according to claim 1, wherein, The illumination light has a first linear polarization orientation, and the display light has a second linear polarization orientation orthogonal to the first linear polarization orientation.

3. The HMD according to claim 1, wherein, The LCOS compensator is actively aligned.

4. A silicon-based liquid crystal LCOS system, the LCOS system comprising: A lighting module configured to generate illumination light; LCOS, the LCOS being configured to receive the illumination light and modulate the illumination light into display light; as well as An LCOS compensator having a slow axis aligned to between -33 degrees and -77 degrees, wherein the LCOS compensator is configured to receive the illumination light and the display light.

5. The LCOS system according to claim 4, wherein, The illumination light has a first linear polarization orientation, and the display light has a second linear polarization orientation orthogonal to the first linear polarization orientation.

6. The LCOS system according to claim 4, wherein, The slow axis of the LCOS compensator is actively aligned to between -48 degrees and -77 degrees.

7. The LCOS system according to claim 4, wherein, The slow axis of the LCOS compensator is actively aligned to approximately -60 degrees.

8. The LCOS system according to claim 4, wherein, The slow axis of the LCOS compensator is actively aligned to approximately -65 degrees.

9. The LCOS system according to claim 4, wherein, The slow axis of the LCOS compensator is passively aligned to between -33 degrees and -57 degrees.

10. The LCOS system according to claim 4, wherein the LCOS system further comprises: The driver module is configured to: A red driving voltage is applied to the LCOS to generate a red image; A green driving voltage is applied to the LCOS to generate a green image; and A blue driving voltage is applied to the LCOS to generate a blue image. The red driving voltage, the green driving voltage, and the blue driving voltage are calibrated to increase the contrast of the red image, the green image, and the blue image, respectively.

11. The LCOS system according to claim 10, wherein, The blue driving voltage is higher than the green driving voltage, and wherein the green driving voltage is higher than the red driving voltage.

12. The LCOS system according to claim 10, wherein, The red driving voltage, the green driving voltage, and the blue driving voltage are functions of the mechanical orientation of the LCOS compensator relative to the LCOS.

13. The LCOS system according to claim 10, wherein, The red drive voltage, the green drive voltage, and the blue drive voltage are calibrated within the temperature range of the LCOS system.

14. The LCOS system according to claim 4, wherein, The LCOS compensator is laminated onto the LCOS.

15. The LCOS system according to claim 4, further comprising: A polarization beam splitter (PBS) is configured to receive the illumination light and direct it to the LCOS, wherein the LCOS compensator is disposed between the PBS and the LCOS.

16. A method, the method comprising: Use a lighting system to emit illumination light; The illumination light is received using an LCOS system including an LCOS and an LCOS compensator with a slow axis, wherein the illumination light is propagated to the LCOS through the LCOS compensator; and A calibration voltage is driven onto the LCOS to increase the contrast of the display light, wherein driving the calibration voltage onto the LCOS modulates the illumination light into display light that propagates back through the LCOS compensator.

17. The method according to claim 16, wherein, The LCOS compensator is actively aligned between -48 degrees and -77 degrees.

18. The method according to claim 16, further comprising: A red driving voltage is driven onto the LCOS to generate the red portion of the display light, wherein the calibration voltage is a green driving voltage for generating the green portion of the display light; and A blue driving voltage is driven onto the LCOS to generate the blue portion of the display light, wherein the red driving voltage, the green driving voltage, and the blue driving voltage are calibrated to increase the contrast of the red, green, and blue portions of the display light, respectively.

19. The method according to claim 18, wherein, The blue driving voltage is higher than the green driving voltage, and wherein the green driving voltage is higher than the red driving voltage.

20. The method according to claim 18, wherein, The red driving voltage, the green driving voltage, and the blue driving voltage are sequentially driven onto the LCOS in the frames of the display light, wherein the frames have a duration of less than 50 milliseconds.

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