WO2020205101A1

WO2020205101A1 - Electronic device displays with holographic angular filters

Info

Publication number: WO2020205101A1
Application number: PCT/US2020/020064
Authority: WO
Inventors: Scott M. DELAPP; Vikrant BHAKTA; Hyungryul CHOI
Original assignee: Apple Inc.
Priority date: 2019-03-29
Filing date: 2020-02-27
Publication date: 2020-10-08

Abstract

An electronic device may include a light source that emits light, A holographic angular filter may transmit a first portion of the light while diffracting a second portion of the light towards a light sink. A prism may receive the first portion and may direct the first portion towards a spatial light modulator. The spatial light modulator may reflect the first portion towards projection optics as image light. The projection optics may direct the image light towards an eye box. The first portion may be incident upon the prism at relatively low incident angles. The second portion may be incident upon the prism at relatively high incident angles. The holographic angular filter may mitigate propagation of stray light into the projection optics, thereby maximizing a contrast ratio of the image light at the eye box while occupying less volume within the device than other light baffling techniques.

Description

Electronic Device Disnlavs with Holographic Annular Filters

This application claims priority to U.S. patent application No. 16/802,176, filed on February 26, 2020, and U.S. provisional patent application No. 62/826,838, filed on March 29, 2019, which are hereby incorporated by reference herein in their entireties.

Background

[0001] This relates generally to electronic devices and, more particularly, to electronic devices with displays.

[0002] Electronic devices often include displays. For example, a head-mounted device such as a pair of virtual reality or mixed reality glasses may have a display for displaying images for a user. The display may include a spatial light modulator with pixels that produce images for the user. An optical system provides illumination for the spatial light modulator so that the user can view the images.

[0003] It can be challenging to form optical systems for devices such as head-mounted devices. If care is not taken, stray light in the optical system can undesirably limit the contrast ratio of the images viewed by the user.

Summary

[0004] An electronic device such as a head-mounted display device may include a display system. The display system may include a light source that emits light. A holographic angular filter may transmit a first portion of the light while diffracting a second portion of the light towards a light sink. A prism may receive the first portion of the light and may direct the first portion of the light to a spatial light modulator such as a digital micromirror device (DMD) or a liquid crystal on silicon (LCOS) chip. The spatial light modulator may reflect the first portion of the light towards projection optics as image light. The projection optics may direct the image light towards an eye box.

[0005] The first portion of the light may be incident upon an input surface of the prism at relatively low incident angles with respect to a normal axis of the input surface. The second portion of the light may be incident upon the input surface at relatively high incident angles with respect to the normal axis. The holographic angular filter may include holograms such as volume holograms that are configured to diffract incident light at the relatively high incident angles towards the light sink. This may mitigate propagation of high incident angle light and corresponding stray light into the projection optics and towards the eye box, thereby maximizing a contrast ratio of the image light received at the eye box. The volume holograms may be embedded within or formed on a surface of a waveguide at the input surface of the prism if desired. The volume holograms may include different sets of holograms that are configured to diffract different wavelengths of the light emitted by the light source. If desired, an image sensor or other light detecting element may generate image data in response to the second portion of the light diffracted by the holographic angular filter. Control circuitry may process the image data to perform feedback operations on the light source.

[0006] In another suitable arrangement, the display system may include an emissive display panel. The holographic angular filter may diffract high incident angle light emitted by the display panel to the light sink while transmitting low incident angle light emitted by the display panel to optical components. The optical components may direct the low incident angle light towards an eye box. The holographic angular filter may include waveguides that propagate the diffracted light towards the light sink via total internal reflection. If desired, the holographic angular filter may include multiple holographic grating structures and/or multiple waveguides for propagating the diffracted light in different directions. Use of holographic angular filters for mitigating high incident angle light and the corresponding stray light that the high incident angle light produces may serve to maximize contrast ratio at the eye box without requiring as much volume within the device as other light baffling techniques.

Brief Description of the Drawings

[0007] FIG. 1 is a diagram of an illustrative electronic device having a display in accordance with an embodiment

[0008] FIG. 2 is a diagram of illustrative optical system components for providing illumination to a digital micromirror device and directing image light to an eye box for viewing by a user in accordance with some embodiments.

[0009] FIG. 3 is a diagram of illustrative optical system components having a digital micromirror device and a holographic angular filter for directing high incident angle light towards a light sink to optimize contrast of image light provided to an eye box in accordance with some embodiments.

[0010] FIG. 4 is a diagram of an illustrative waveguide having a holographic angular filter for directing high incident angle light towards a light sink in accordance with some embodiments.

[0011] FIG. 5 is a plot of diffraction efficiency as a function of incident angle for holograms that diffract light of different wavelengths in a holographic angular filter in accordance with some embodiments.

[0012] FIG. 6 is a diagram of illustrative optical system components for providing illumination to a liquid crystal on silicon chip and directing image light to an eye box for viewing by a user in accordance with some embodiments.

[0013] FIG. 7 is a diagram of illustrative optical system components having a liquid crystal on silicon chip and a holographic angular filter for directing high incident angle light towards a light sink in accordance with some embodiments.

[0014] FIG. 8 is a flow chart of illustrative steps that may be performed in adjusting a light source based on high incident angle light that has been diffracted by a holographic angular filter in accordance with some embodiments.

[0015] FIG. 9 is a diagram showing how holographic angular filters may be used to direct light from an emissive display towards a light sink in accordance with some embodiments.

[0016] FIG. 10 is a diagram showing how holographic angular filters of the type shown in FIG, 9 may direct light in multiple directions in accordance with some embodiments.

Detailed Descriptfon

[0017] Head-mounted devices and other electronic devices may be used for virtual reality and mixed reality (augmented reality) systems. These devices may include portable consumer electronics (e.g., portable electronic devices such as cellular telephones, tablet computers, glasses, other wearable equipment), head-up displays in cockpits, vehicles, etc., display-based equipment (projectors, televisions, etc.), or other devices. Devices such as these may include displays and other optical components. Device configurations in which virtual reality and/or mixed reality content is provided to a user (viewer) with a head- mounted display device are described herein as an example. This is, however, merely illustrative. Any suitable equipment may be used in providing a user with visual content such as virtual reality and/or mixed reality content

[0018] A head-mounted device such as a pair of augmented reality glasses that is worn on the head of a user may be used to provide a user with computer-generated content that is overlaid on top of real-world content. The real-world content may be viewed directly by a user through a transparent portion of an optical system. The optical system may be used to route images from one or more pixel arrays in a display system to the eyes of a user. A waveguide such as a thin planar waveguide formed from a sheet of transparent material such as glass or plastic or other light guides may be included in the optical system to convey image light from the pixel arrays to the user. The display system may include reflective displays such as liquid-crystal-on-silicon displays, microelectromechanical systems (MEMs) displays (sometimes referred to as digital micromirror devices), emissive displays, or other types of displays.

[0019] A schematic diagram of an illustrative electronic device such as a head-mounted device is shown in FIG. 1. As shown in FIG. 1, head-mounted device 10 (sometimes referred to herein as head-mounted display 10 or head-mounted display device 10) may have a head- mountable support structure such as support structure 20. The components of head-mounted device 10 may be supported by support structure 20. Support structure 20, which may sometimes be referred to as a housing, may be configured to form a frame of a pair of glasses (e.g., left and right temples and other frame members), may be configured to form a helmet, may be configured to form a pair of goggles, or may have other head-mountable

configurations.

[0020] The operation of device 10 may be controlled using control circuitry 16. Control circuitry 16 may include storage and processing circuitry for controlling the operation of device 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 may be stored on storage in circuitry 16 and run on processing circuitry in circuitry 16 to implement operations for device 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.).

[0021] Device 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 device 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 device 10 with user input. Input-output devices 12 may also be used to gather information on the environment in which device 10 is operating. Output components in input-output devices 12 may allow device 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 device 10, accelerometers, depth sensors, light sensors, haptic output devices, speakers, batteries, wireless communications circuits for communicating between device 10 and external electronic equipment, etc.).

[0022] As shown in FIG. 1, input-output devices 12 may include one or more displays in a display system such as display system 14. Display system 14, which may sometimes be referred to as a display, may be used to display images for a user of device 10. Display system 14 may include a light source such as light source 14A that produces illumination 22 (sometimes referred to herein as light 22 or illumination light 22). Light source 14A may be based on light-emitting diodes, lasers (e.g., vertical cavity surface emitting lasers or other diode lasers), or other light emitting devices. Light source 14A may include multiple light emitting devices that emit light of different wavelengths (e.g., in different color channels). Each light emitting device in light source 14A may be individually (independently) controllable if desired. Illumination 22 may pass through optical system 14B and reflect off of spatial light modulator 14C. Spatial light modulator 14C may be a liquid-crystal-on- silicon (LCOS) device, a microelectromechanical systems (MEMs) device (e.g., a device with an array of micromirrors, sometimes referred to as a digital micromirror device (DMD)), or other spatial light modulators.

[0023] Spatial light modulator 14C has an array of individually adjustable pixels P. During operation, control circuitry 16 can use spatial light modulator 14C to produce an image that is illuminated by illumination 22. Corresponding image light 22R (e.g., illumination 22 that has reflected from pixels P in spatial light modulator 14C and that therefore corresponds to a computer-generated (virtual) image formed by spatial light modulator) may be directed to eye boxes such as eye box 24 by optical system 14B for viewing by the eyes of a user. Optical system 14B may direct image light 22R to eye box 24 via output optics 26. Output optics 26 may include lenses, prisms, waveguides, output couplers (e.g., holographic output couplers), and/or other components. In one suitable arrangement that is sometimes described herein as an example, output optics 26 may include a waveguide that receives image light 22R from optical system 14B (e.g., via an input coupler such as an input coupling prism or a holographic input coupler), that propagates the received image light 22R via the principle of total internal reflection, and that outputs image light 22R to eye box 24 using an output coupler (e.g., a holographic output coupler).

[0024] Optical system 14B of FIG. 1 may use prisms, mirrors, beamsplitters, holograms (e.g., volume holograms, surface holograms, etc.), gratings (e.g., electrically tunable gratings), lenses, waveguides, polarizers, polarizing beam splitters, and/or other optical components. Optical system 14B may use components such as these to pass light 22 to spatial light modulator 14C while directing reflected image light 22R to output optics 26 and eye box 24. Optical system 14B and/or output optics 26 may include lens structures (one or more discrete lenses and/or optical structures with an associated lens power) so that a viewable image is formed for the user in eye box 24. If desired, optical system 14B may contain components (e.g., an optical combiner, etc.) to allow real-world image light 25 (e.g., real-world images or real-world objects such as real-world object 28) to be combined optically with virtual (computer-generated) images such as virtual images in image light 22R. In this type of system, which is sometimes referred to as an augmented reality system, a user of device 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 which a camera captures real-world images of object 28 and this content is digitally merged with virtual content on display 14C). Display system 14 may be used in a virtual reality system (e.g., a system without merged real-world content) and/or any suitable type of system.

[0025] The example of FIG. 1 in which display system 14 includes a reflective-type display such as spatial light modulator 14C is merely illustrative. In another suitable arrangement, display system 14 may include an emissive-type display in which light source 14A is formed from a display panel of organic light emitting diodes, micro light emitting diodes, or other light emitting components (e.g., where the light emitting elements of the display panel are arranged in an array that is controlled to produce images). In these arrangements, optical system 14B may route light 22 emitted by the display panel to output optics 26 without reflecting the light off of spatial light modulator 14C (e.g., spatial light modulator 14C may be omitted).

[0026] An illustrative configuration for a portion of optical system 14B that may be used to pass illumination 22 to spatial light modulator 14C while directing reflected image light 22R from spatial light modulator 14C to output optics such as output optics 26 is shown in FIG. 2. In the example of FIG. 2, spatial light modulator 14C includes a digital micromirror device (DMD) such as DMD 32. This is merely illustrative and, in general, other types of spatial light modulators may be used.

[0027] As shown in FIG. 2, optical system 14B may include coupled prisms such as a first prism 36 and a second prism 38. Surface 45 of prism 36 may be mounted to surface 44 of prism 38. Prisms 36 and 38 may be mounted over DMD 32. Optical system 14B may include projection optics 30 and a baffle structure such as baffle 34. Projection optics 30 may include one or more lenses or other optical components that direct image light from optical system 14B towards output optics 26 of FIG. 1.

[0028] Light 22 may be received from light source 14A (FIG. 1 ). Light 22 may be collimated by one or more collimating lenses 50. While only a single collimating lens is shown in FIG. 2 for the sake of clarity, any desired number of lenses or other optical components may be interposed between light source 14A and optical system 14B or, in another possible arrangement, collimating lens 50 may be omitted. If desired, a blocking structure having an aperture may be used to help limit the angular spread of light 22 prior to passing the light to optical system 14B.

[0029] Collimating lens 50 may direct light 22 towards input surface 42 of prism 36 as input beam 56. Input beam 56 may include relatively low incident angle light (e.g., the portion of input beam 56 lying between arrows 54 of FIG. 2) and relatively high incident angle light (e.g., the portion of input beam 56 lying between the upper-most arrow 54 and the upper-most arrow 58 and the portion of input beam 56 lying between the lower-most arrow 54 and the lower-most arrow 58 in FIG. 2). The low incident angle light in input beam 56 (sometimes referred to herein as low incident angle light 54) is incident on input surface 42 at a relatively low incident angle (e.g., an angle measured with respect to normal axis 48 of input surface 42). The high incident angle light in beam 56 (sometimes referred to herein as high incident angle light 58) is incident on input surface 42 at a relatively high incident angle with respect to normal axis 48 (e.g., an angle that is greater than a minimum threshold angle). The angle with which light is incident upon input surface 42 with respect to normal axis 48 may sometimes be referred to herein as incident angle Ai. While high incident angle light 58 is shown schematically by two arrows in FIG. 2 for the sake of clarity, the high incident angle light includes an angular spread of incident light (e.g., a beam) extending from arrows 54 to arrows 58. Similarly, while low incident angle light 54 is shown schematically by two arrows in FIG. 2 for the sake of clarity, the low incident angle light includes an angular spread (beam) of incident light extending between arrows 54.

[0030] As shown in FIG. 2, input beam 56 may reflect off of surface 45 of prism 36 (e.g., via total internal reflection) towards surface 40 of prism 36. Beam 56 may reflect off of surface 40 of prism 36 (e.g., off of a reflective element such as a mirror located at surface 40, via total internal reflection, etc.) towards DMD 32. Beam 56, after reflecting off of surface 40, may pass through surface 45, surface 44 of prism 38, prism 38, and surface 39 of prism 38 to pixel P* of DMD 32. The example of FIG. 2 illustrates the operation of a single pixel P* on beam 56 for the sake of clarity. However, in general, similar operations are performed at each pixel across the lateral area of DMD 32 (e.g., for each of pixels P of FIG. 1).

[0031] Each pixel in DMD 32 may include a respective micromirror (e.g., a MEMS-based micromirror) that is individually rotated between two or three predetermined positions such as an“ON” state and an“OFF” state. Control circuitry 16 of FIG. 1 may individually adjust the state of each pixel based on the images to be displayed using display system 14. The operation of pixel P* of FIG. 2 may be illustrative of the operation of each pixel in DMD 32.

[0032] When pixel P* is in the‘ON” state, pixel P* may direct the beam 56 that has been reflected off of surface 40 of prism 36 into projection optics 30. For example, the

micromirror in pixel P* may reflect beam 56 towards surface 44 of prism 38 at an angle such that the beam reflects off of surface 44 of prism 38 as reflected light 62, which passes through projection optics 30 towards output optics 26 of FIG. 1 (e.g., reflected light 62 may form image light 22R of FIG. 1). When pixel P* is in the“OFF” state, pixel P* may direct the beam 56 that has been reflected off of surface 40 of prism 36 towards baffle 34. For example, the micromirror in pixel P* may reflect beam 56 as reflected light 66, which is directed towards baffle 34 by prism 38. Baffle 34 may include light absorbing materials and/or textured structures that effectively extinguish light 66 to prevent light 66 from being received at eye box 24. By adjusting pixel P* between at least the“ON” and‘OFF’ states in this way, pixel P* may either direct input beam 56 towards projection optics 30 and the eye box or may direct input beam 56 outside of the projection optics (i.e., towards baffle 34) so that the beam is not received at the eye box.

[0033] In practice, the pixels in DMD 32 such as pixel P* can only rotate through a relatively small angle of rotation (e.g., +/- 17 degrees or other values). This limited angle of rotation means that the angular content of input beam 56 needs to be tightly controlled. If care is not taken, high incident angle portions of input beam 56 such as high incident angle light 58 can be reflected into projection optics 30 or elsewhere even when pixel P* is in the ‘OFF” state. This can undesirably limit the contrast ratio of the image light provided at the eye box.

[0034] For example, in the“OFF’ state, pixel P* may reflect high incident angle light 58 into prism 38 at an angle such that prism 38 directs the reflected high incident angle at angles that are pointed away from baffle 34, as shown by stray light 64. Some of stray light 64 may pass through projection optics 30 and to the eye box or elsewhere in the optical system. At the same time, some high incident angle light from input beam 56 may also pass directly through prisms 36 and 38 into projection optics 30, as shown by dash-dotted arrow 60 (e.g., because incident angles associated with arrow 60 may be too steep to reflect off of surface 45 by total internal reflection). Projection optics 30 may convey stray light 64 and the incident light associated with arrow 60 to the eye box, thereby providing some light to the user for pixel P* even though pixel P* is in the‘OFF” state and should otherwise appear black. This may serve to undesirably limit the contrast ratio of the image displayed at eye box 24.

[0035] In order to eliminate stray light in projection optics 30 when pixel P* is in the ‘OFF’ state, optical system 14B may be provided with a holographic angular filter. FIG. 3 is a diagram showing how optical system 14B may include a holographic angular filter. As shown in FIG. 3, a holographic angular filter such as holographic angular filter 76 may be formed at input surface 42 of prism 36.

[0036] 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. The photosensitive optical material (sometimes referred to as a grating medium) may include volume holographic media such as photopolymers, gelatin such as dichromated gelatin, silver halides, holographic polymer dispersed liquid crystal, or other suitable volume holographic media. The optical interference pattern may create a holographic grating that, when illuminated with a given light source, diffracts light to create a three-dimensional

reconstruction of the holographic recording. The diffractive grating (hologram) may be a non-switchable diffractive grating that is encoded with a permanent interference pattern, as an example.

[0037] Holographic angular filter 76 may include one or more diffractive grating structures such as one or more holograms. The holograms may include surface holograms and/or volume holograms such as volume phase holographic gratings (VPHG). Examples in which holographic angular filter 76 includes volume phase holographic gratings (sometimes referred to herein simply as holograms) are described herein as an example. Holograms in

holographic angular filter 76 exhibit a diffraction efficiency that is strongly dependent upon angle of incidence. Each hologram in holographic angular filter 76 may redirect (diffract) incident light of a particular wavelength (e.g., spread of wavelengths) and a particular incident angle (e.g., spread of incident angles) at a corresponding output angle (e.g., at a spread of output angles). For example, each hologram may diffract incident light that is Bragg-matched (or near Bragg-matched but at a lower diffraction efficiency) with that hologram (e.g., each hologram may have a grating frequency and orientation defined by the spatial modulation of refractive index in the grating medium, which determine which incident angle(s) and wavelength(s) of light are diffracted by that hologram in a particular output direction). The holograms in holographic angular filter 76 may include reflective holograms and/or transmissive holograms.

[0038] The holograms in holographic angular filter 76 may be configured to diffract high incident angle light 58 towards a light sink such as light sink 70, as shown by diffracted beams 74 (e.g., the holograms may have grating frequencies and directions that configure the holograms to diffract high incident angle light 58 as diffracted beams 74). Holographic angular filter 76 may include different holograms (e.g., spatially multiplexed holograms) for diffracting light of each wavelength included in input beam 56. For example, in scenarios where light source 14A of FIG. 1 transmits light 22 with red, green, and blue light sources, holographic angular filter 76 may include holograms that diffract red light, holograms that diffract green light, and holograms that diffract blue light as diffracted beams 74. If desired, each hologram in holographic angular filter 76 may be superimposed on the same volume of grating medium. In another suitable arrangement, holographic angular filter 76 may include multiple layers of grating medium and each layer may include one or more holograms for holographic angular filter 76.

[0039] Light sink 70 may be located outside of projection optics 30 so that diffracted beams 74 are not conveyed to the eye box by the projection optics. Light sink 70 may include light absorbers, baffles, light traps, opaque structures, matte structures, black structures, and/or any other desired structures that prevent diffracted beams 74 from propagating to projection optics 30. If desired, light sink 70 may include an image sensor such as image sensor 72. Image sensor 72 may capture images (e.g., image signals) of diffracted beams 74.

[0040] In tiiis way, holographic angular filter 76 may serve as an angular filter that filters out high incident angle light 58 from passing into prism 36. This may allow low incident angle light 54 to continue to pass through prisms 36 and 38, to reflect off of pixel P* in the “OFF” state, and to propagate towards baffle 34 without any portion of input beam 56 passing to projection optics 30 or the eye box. This may help to ensure that pixel P* correctly appears as black to the user when pixel P* in the“OFF” state, thereby maximizing contrast ratio for the image.

[0041] The example of FIG. 3 is merely illustrative. If desired, holographic angular filter 76 may be separated from prism 36 (e.g., holographic angular filter 76 need not be mounted to input surface 42). Holographic angular filter 76 may be located elsewhere in optical system 14B. The holograms in holographic angular filter 76 may be located across the entire lateral area of holographic angular filter 76 (e.g., in the Z-Y plane of FIG. 3) or may be located only within the portions of holographic angular filter 76 that are illuminated by high incident angle light 58. In another suitable arrangement, holographic angular filter 76 may be formed within a waveguide.

[0042] FIG. 4 is a diagram showing how holographic angular filter 76 may be formed within a waveguide. As shown in FIG. 4, holographic angular filter 76 may include holographic grating structures 88 embedded within waveguide 80. Waveguide 80 may, for example, include two transparent waveguide substrates located on either side of holographic grating structures 88 (e.g., holographic grating structures 88 may be sandwiched between the transparent waveguide substrates). Holographic grating structures 88 may include a grating medium and one or more holograms recorded therein. Holographic grating structures 88 may extend across some or all of the lateral area of waveguide 80 (e.g., in the Z-Y plane of FIG. 4). Surface 84 of waveguide 80 may be mounted to input surface 42 of prism 36 (FIG. 3) or, if desired, waveguide 80 may be separated from prism 36 and may be mounted with surface 84 facing input surface 42.

[0043] Holographic grating structures 88 are not Bragg-matched to low incident angle light 54. Low incident angle light 54 will therefore pass through waveguide 80 and holographic grating structures 88 without being diffracted (e.g., holographic grating structures 88 may be transparent to low incident angle light 54). At the same time, holographic grating structures 88 may be configured to diffract high incident angle light 58 from input beam 56 (e.g., portions of input beam 56 at incident angles with respect to normal axis 48 that lie between arrows 54 and 58) towards light sink 82 at surface 86 of waveguide 80, as shown by diffracted light 90. For example, holographic grating structures 88 may diffract high incident angle light 58 towards light sink 82 at an angle such that diffracted light 90 propagates up the length of waveguide 80 (e.g., in the direction of the Y-axis) via total internal reflection. Light sink 82 may include light absorbers, baffles, light traps, opaque structures, matte structures, black structures, and/or any other desired structures. When diffracted light 90 reaches light sink 82, light sink 82 may extinguish the diffracted light to prevent the diffracted light from propagating elsewhere in the optical system such as into projection optics 30 of FIG. 3. If desired, waveguide 80 may include an output coupler (e.g., holographic output couplers, prisms, angled edges of waveguide 80, mirrors, etc.) that direct diffracted light 90 out of waveguide 80 and into light sink 82. If desired, light sink 82 may include an image sensor such as image sensor 92 that gathers images of diffracted light 90. Waveguide 80 may be relatively thin (e.g., 1 mm or less in the X dimension). Using a waveguide such as waveguide 80 may, for example, allow for more control over the diffracted light relative to scenarios where the waveguide is omitted (e.g., as shown in FIG. 3).

[0044] The example of FIG. 4 is merely illustrative. In practice, waveguide 80 and holographic grating structures 88 extend across a lateral plane (e.g., in the Z-Y plane of FIG. 4). Holographic grating structures 88 may diffract high incident angle light 58 in any desired directions towards light sink 82 (e.g., the holographic grating structures may direct the high incident angle light pointing in the -Z direction upwards towards light sink 82, may direct the high incident angle light pointing in the +Z direction downwards towards light sink 82, etc.). Light sink 82 may be separated from surface 86 of waveguide 80, may be formed on end 91 of waveguide 80, and/or may be formed elsewhere on waveguide 80. In the arrangement of FIG. 4, holographic grating structures 88 include reflective holograms. In another suitable arrangement, holographic grating structures 88 may include transmissive holograms. If desired, holographic grating structures 88 may be layered onto surface 86 of waveguide 80 (e.g., such that waveguide 80 is interposed between the holographic grating structures and prism 36 of FIG. 3). In this arrangement, the holographic grating structures may include transmissive holograms that diffract the high incident angle light into waveguide 80 for propagation to light sink 82. In yet another suitable arrangement, holographic grating structures 88 may be layered onto surface 84 of waveguide 80 (e.g., such that holographic grating structures 88 are interposed between waveguide 80 and prism 36 of FIG. 3).

Waveguide 80 and holographic grating structures 80 may be curved if desired.

[0045] In practice, the holograms in holographic angular filter 76 exhibit a diffraction efficiency that is strongly dependent upon the angle of incidence. This property is illustrated in the plot of FIG. 5, which plots the diffraction efficiency of holographic angular filter 76 as a function of angle of incidence Ai (e.g., as measured with respect to normal axis 48 of FIGS. 2 and 4). As shown in FIG. 5, curve 100 plots the diffraction efficiency of a first hologram that diffracts light of a first wavelength, curve 102 plots the diffraction efficiency of a second hologram that diffracts light of a second wavelength, and curve 104 plots the diffraction efficiency of a third hologram that diffracts light of a third wavelength.

[0046] The diffraction efficiency of each hologram is high (e.g., greater than a minimum threshold value) only over a corresponding limited range of incidence angles Ai which are near the Bragg angle of that hologram. For example, the hologram associated with curve 100 exhibits a high diffraction efficiency over a range of incidence angles around Bragg angle Ail, the hologram associated with curve 102 exhibits a high diffraction efficiency over a range of incidence angles around Bragg angle Ai2, and the hologram associated with curve 104 exhibits a high diffraction efficiency over a range of incidence angles around Bragg angle Ai3. Each hologram appears as transparent (e.g., the diffraction efficiency is effectively zero) for light at incident angles that are far from the corresponding Bragg angle.

[0047] Holographic angular filter 76 may include multiple holograms for each wavelength of light in input beam 56, such that the angular filter collectively exhibits satisfactory diffraction efficiency (e.g., a diffraction efficiency greater than a threshold efficiency) over the range of incident angles extending from incident angle Aimin to incident angle Aimax. For example, holographic angular filter 76 may include a first set of holograms that diffract light of the same wavelength as the hologram associated with curve 100 but that collectively exhibit satisfactory diffraction efficiency across the entire range of incident angles from Aimin to Aimax. Similarly, holographic angular filter 76 may include a second set of holograms that diffract light of the same wavelength as the hologram associated with curve 102 but that collectively exhibit satisfactory diffraction efficiency across the entire range of incident angles from Aimin to Aimax. Likewise, holographic angular filter 76 may include a third set of holograms that diffract light of the same wavelength as the hologram associated with curve 104 but that collectively exhibit satisfactory diffraction efficiency across the entire range of incident angles from Aimin to Aimax.

[0048] Holographic angular filter 76 may include sets of holograms such as these for each wavelength or range of wavelengths in input beam 56. For example, in scenarios where input beam 56 includes red, green, and blue light (e.g., where light source 14A of FIG. 1 includes red, green, and blue light emitting devices), holographic angular filter 76 may include a first set of holograms that diffract the red light (e.g., where each hologram in the first set diffracts red light incident at a respective incident angle or range of incident angles between Aimin and Aimax), holographic angular filter 76 may include a second set of holograms that diffract the green light (e.g., where each hologram in the second set diffracts green light incident at a respective incident angle or range of incident angles between Aimin and Aimax), and holographic angular filter 76 may include a third set of holograms that diffract the blue light (e.g., where each hologram in the third set diffracts blue light incident at a respective incident angle or range of incident angles between Aimin and Aimax).

[0049] Incident angles Aimin and Aimax may be defined by the range of angles in high incident angle light 58. For example, incident angle Aimin may correspond to the incident angle of the upper-most arrow 54 in FIGS. 2-4 whereas incident angle Aimax may correspond to the incident angle of the upper-most arrow 58 in FIGS. 2-4. This example is merely illustrative. In general, any desired number of wavelengths (or ranges of

wavelengths) may be used in the input light and diffracted by holographic angular filter 76. Curves 100-104 may, in practice, have other shapes (e.g., shapes dependent upon the thickness of the grating medium and the refractive index modulation).

[0050] The example of FIG. 5 only illustrates a single range of incident angles Ai that are diffracted by holographic angular filter 76 for the sake of clarity. Holographic angular filter 76 may also include holograms that similarly diffract light between incident angles -Aimin and -Aimax (e.g., corresponding to incident light between the lower-most arrow 54 and the lower-most arrow 58 of FIGS. 2-4). This example only illustrates diffraction performed by the holographic angular filter for incident light within a single plane (e.g., within the X-Y plane of FIGS. 2-4). However, in general, holographic angular filter 76 may diffract incident light across the entire lateral area of the filter (e.g., within the Z-Y plane of FIGS. 2-4). In other words, low incident angle light 54 may be defined in the Z-Y plane by a circle or ellipse of light at relatively low incident angles about normal axis 48, whereas high incident angle light 58 is defined in the Z-Y plane by a two-dimensional ring of light at relatively high incident angles about low incident angle light 54 and normal axis 48. Holographic angular filter 76 may include holograms that diffract incident light towards the light sink for each wavelength of input beam 56 and for each incident angle in the two-dimensional ring of light about normal axis 48.

[0051] In the example of FIGS. 2-4, spatial light modulator 14C is a digital micromirror device. This is merely illustrative. In another suitable arrangement, spatial light modulator 14C may include a liquid crystal on silicon (LCOS) chip. FIG. 6 is a diagram showing how optical system 14B may direct light off of an LCOS chip and towards the eye box.

[0052] As shown in FIG. 6, spatial light modulator 14C may include LCOS chip 110.

Coupled prisms 116 (e.g., a first prism 116-1 and a second prism 116-2) may be mounted over LCOS chip 110. A polarizing beam splitter such as polarizing beam splitter 118 may be mounted between prisms 116-1 and 116-2. A retarder such as quarter wave plate 114 may be mounted to surface 115 of prism 116-2. A reflective element such as mirror 112 may be mounted to quarter wave plate 114. A polarizer such as polarizer 124 may be mounted to input surface 117 of prism 116-2. LCOS chip 110 may be mounted at bottom surface 119 of prism 116-1 or may otherwise be mounted adjacent to prism 116-1 with surface 119 facing LCOS chip 110.

[0053] Input beam 56 may be received at polarizer 124. Polarizer 124 may pass a first polarization of the input beam (e.g., s-polarized light in input beam 56) into prism 116-2 while extinguishing other polarizations in input beam 56. Polarizing beam splitter 118 may be configured to transmit light of a second polarization (e.g., p-polarized light) while reflecting light of the first polarization (e.g., s-polarized light). This is merely illustrative and, in another suitable arrangement, polarizer 124 may transmit p-polarized light and polarizing beam splitter 118 may reflect p-polarized light while transmitting s-polarized light.

[0054] Polarizer 124 and/or polarizing beam splitter 118 may exhibit high extinction ratios. However, high extinction for broadband light sources is typically achievable over a relatively small angular range. If light is incident on polarizer 124 and polarizing beam splitter 118 at excessively large incident angles, such as high incident angle light 58, the unwanted polarization can leak through polarizer 124 and polarizing beam splitter 118, as shown by stray light 122. Stray light 122 may be propagated by projection optics 30 into the eye box, thereby undesirably limiting the contrast ratio in the image displayed at the eye box.

[0055] At the same time, polarizer 124 may pass a first polarization of low incident angle light 54 as polarized light 54^*. Polarized light 54’ may reflect off of polarizing beam splitter 118 towards surface 115 of prism 116-2. Polarized light 54* may pass through quarter wave plate 114 and reflect off of mirror 112 and into prism 116-2 as reflected light 54” having the second polarization. Polarizing beam splitter 118 may transmit reflected light 54” to pixel P** of LCOS chip 110. The example of FIG. 6 illustrates the operation of a single pixel P** on beam 56 for the sake of clarity. However, in general, similar operations are performed at each pixel across the lateral area of LCOS chip 110 (e.g., for each pixel P of FIG. 1).

[0056] LCOS chip 110 modulates light via pixel-by-pixel polarization changes. When pixel P** is in the“ON” state, pixel P** reflects the reflected light 54” towards polarizing beam splitter 118 with the first polarization. Polarizing beam splitter 118 thereby reflects this light through projection optics 30, as shown by arrow 120. When pixel P** is in the‘OFF” state, pixel P** reflects light 54” towards polarizing beam splitter 118 with the second

polarization. Polarizing beam splitter 118 thereby transmits this light, which reflects off of mirror 112 as reflected light with the first orientation. The reflected light is then reflected by polarizing beam splitter 118 towards polarizer 124, where it is directed elsewhere in the display system.

[0057] In order to optimize contrast ratio in the displayed image, holographic angular filter 76 may be included in optical system 14B of FIG. 6 for redirecting high incident angle light 58 towards a light sink. FIG. 7 is a diagram showing how holographic angular filter 76 may be integrated into the optical system 14B of FIG. 6. As shown in FIG. 7, holographic angular filter 76 may be mounted to polarizer 124. Holographic angular filter 76 of FIG. 7 may include holograms that diffract each wavelength of input beam 56 at each incident angle of high incident angle light 58 as diffracted beams 74 towards light sink 70 (e.g., holographic angular filter 76 may include multiple holograms as described above in connection with FIGS. 2-5). This may allow low incident angle light 54 to propagate through projection optics 30 (e.g., when pixel P** is in the“ON” state) without passing high incident angle light 58 to projection optics 30 (e.g., as shown by stray light 122 of FIG. 6).

[0058] The example of FIG. 7 is merely illustrative. If desired, holographic angular filter 76 may be formed within waveguide 80 of FIG. 4 (e.g., waveguide 80 of FIG. 4 may be mounted to polarizer 124 of FIG. 7). Holographic angular filter 76 need not be mounted to polarizer 124 and may, if desired, be separated from polarizer 124. In another suitable arrangement, holographic angular filter 76 may be interposed between polarizer 124 and prism 116-2.

[0059] In practice, different holograms may exhibit greater diffraction efficiency for some polarizations than for others. Holographic angular filter 76 may include holograms that are optimized to diffract light of the first polarization that are multiplexed (e.g., stacked over or spatially superimposed with) holograms that are optimized to diffract light of the second polarization. In another suitable arrangement, the holograms may also be used to help polarizer 124 filter out light of a particular polarization. For example, in scenarios where polarizer 124 is configured to transmit s-polarized light, the holograms in holographic angular filter 76 may be optimized to diffract p-polarized light towards light sink 70.

[0060] In scenarios where light sink 70 of FIGS. 3 and 7 includes image sensor 72 or in scenarios where light sink 82 of FIG. 4 includes image sensor 92, control circuitry 16 (FIG.

1) may use image data captured by the image sensor to adjust the light source that produced input beam 56 (e.g., to adjust light source 14A using an active feedback scheme). FIG. 8 is a flow chart of illustrative steps that may be processed by device 10 in performing active feedback using image sensors.

[0061] At step 130, control circuitry 16 may control light source 14A (FIG. 1) to emit light 22 towards optical system 14B in multiple color channels (e.g., in red, blue, and green color channels using respective red, blue, and green light emitting devices in light source 14A).

[0062] At step 132, holographic angular filter 76 may diffract high incident angle light 58 towards one or more image sensors (e.g., holographic angular filter 76 may direct diffracted beams 74 towards image sensor 72 of FIGS. 3 and 7 or may direct diffracted light 90 to image sensor 92 of FIG. 4).

[0063] At step 134, the image sensor may capture images of the diffracted beams (e.g., the image sensor may generate image signals in response to the diffracted beams). The image sensor may pass the captured images to control circuitry 16. [0064] At step 136, control circuitry 16 may identify changes in relative brightness between color channels based on the images captured by the image sensor. For example, over time, different light emitting devices (color channels) in light source 14A may reduce in brightness over time more quickly than other light emitting devices (color channels) in light source 14A. These types of changes may, for example, alter the white point of the images displayed to the user over time. Control circuitry 16 may identify these changes in relative brightness based on the captured images.

[0065] At step 138, control circuitry 16 may adjust light source 14A based on the identified changes in relative brightness (e.g., to compensate for the changes in relative brightness between the color channels). For example, in scenarios where the light source emits red, green, and blue light and the captured images indicate that the red channel has reduced in brightness relative to the green and blue channels, control circuitry 16 may reduce the brightness of the green and blue channels or may boost the current provided to the red light emitting device in light source 14A to compensate for the change in relative brightness.

Processing may loop back to step 130, as shown by arrow 139, and light source 14A may emit light 22 that has been compensated for the change in relative brightness between the channels. This may help to ensure that the images are provided with a consistent white point over time.

[0066] Performing active feedback operations using the diffracted high incident angle light 58 may allow the control circuitry to isolate the cause of the changes in relative brightness to changes associated with light source 14A (e.g., rather than changes associated with components in optical system 14B or spatial light modulator 14C). This may help to ensure that adjustments to light source 14A will provide the displayed images with a consistent white point over time. The example of FIG. 8 is merely illustrative. In general, control circuitry 16 may perform any desired adjustments to display system 14 based on any desired properties measured in the images captured by the image sensors. While elements 72 and 92 are sometimes described herein as image sensors, tins is merely illustrative. In general, elements 72 and/or 92 may also be implemented using other types of light detecting elements (e.g., light sensors) such as photodiodes or other light sensors that include photodiodes. The use of image sensors in elements 72 and 92 may, for example, be particularly effective when a pulsar-type illumination is used to illuminate the display system. With other illumination schemes, simple energy detectors may be sufficient for elements 72 and 92 to capture and gather information from the diffracted light for use in performing the feedback operations of FIG. 8 (e.g., for monitoring and compensating for changes in LED performance over time).

[0067] In the example of FIGS. 2-7, display system 14 includes a reflective spatial light modulator 14C such as DMD 32 of FIGS. 2-4 or LCOS chip 110 of FIGS. 6 and 7. This is merely illustrative. In another suitable arrangement, display system 14 may include an emissive display panel such as emissive display panel 140 of FIG. 9.

[0068] As shown in FIG. 9, display system 14 may include emissive display panel 140. Display panel 140 may be a micro-light-emitting-diode (uLED) display, an organic light- emitting diode display, or other display panel having pixels that emit illumination 22 from within the display panel (e.g., without reflecting the illumination off of a reflective spatial light modulator). The example of FIG. 9 illustrates the operation of a single pixel P*** in display panel 140 for the sake of clarity. However, in general, similar operations are performed at each pixel across the lateral area of display panel 140.

[0069] Pixel P*** may emit light 22 towards optical components 148. A holographic angular filter such as holographic angular filter 152 may be used to filter out high incident angle portions of the light 22 emitted by pixel P*** (e.g., to prevent scattering of stray light in the display system and to maximize contrast ratio for the displayed image). As shown in FIG. 9, light 22 emitted by pixel P*** may include low incident angle light 22L (e.g., light at relatively low incident angles about normal axis 142 of holographic angular filter 152) and high incident angle light 22H (e.g., light at relatively high incident angles about low incident angle light 22L and normal axis 142).

[0070] Holographic angular filter 152 may include a first waveguide 146- 1 and a second waveguide 146-2. First waveguide 146-1 may include holographic grating structures 154. Second waveguide 146-2 may include holographic grating structures 156. Holographic grating structures 154 and 156 may each include reflective and/or transmissive holograms. In the example of FIG. 9, holographic grating structures 154 and 156 include reflective holograms. The example of FIG. 9 in which holographic grating structures 154 and 156 are embedded within waveguides 146-1 and 146-2 is merely illustrative and, if desired, holographic grating structures 154 may be formed on surface 145 of waveguide 146-1 or may be interposed between waveguides 146-1 and 146-2. Similarly, holographic grating structures 156 may be formed on surface 144 of waveguide 146-2 or may be interposed between waveguides 146-1 and 146-2. Waveguide 146-1 and holographic grating structures 154 may be omitted if desired. Holographic grating structures 154 may be layered over holographic grating structures 156 (e.g., at a surface of waveguide 146-2 or within waveguide 146-2) or may be superimposed with holographic grating structures 156 in the same volume of grating medium if desired. Holographic grating structures 154 and 156 may include different sets of holograms for diffracting light of different incident angles and wavelengths (e.g., holographic grating structures 154 and/or 156 may include different sets of holograms such as tiie sets of holograms in holographic angular filter 76 of FIGS. 2-7).

[0071] As shown in FIG. 9, holographic grating structures 156 may be configured to diffract high incident angle light 22H towards a surface of waveguide 146-2 as diffracted light 158, such that diffracted light 158 propagates along the length of waveguide 146-2 (e.g., along the X-axis of FIG. 9) to light sink 160 via total internal reflection. Light sink 160 may include light absorbers, baffles, light traps, opaque structures, matte structures, black structures, and/or any other desired structures that prevent diffracted light 158 from propagating other optical components 148 or eye box 24. Light sink 160 may be formed adjacent to or mounted to the periphery of waveguide 146-1 and/or waveguide 146-2.

[0072] Light 22 that has not been diffracted by holographic grating structures 156 may be transmitted to holographic grating structures 154. Holographic grating structures may be configured to diffract high incident angle light 22H towards a surface of waveguide 146-1 such that the diffracted light propagates along the height of waveguide 146-2 (e.g., along the Z-axis of FIG. 9) to light sink 160. Light sink 160 may, for example, surround all four lateral sides of waveguides 146-1 and 146-2 in the Z-X plane of FIG. 9.

[0073] Holographic grating structures 154 and 156 may be transparent to low angle light 22L. Low angle light 22L may pass through waveguides 146-1 and 146-2 as light 150.

Other optical components 148 (e.g., portions of optical system 14B or output optics 26 of FIG. 1) may direct light 150 to eye box 24, as shown by arrow 150’. In this way, holographic angular filter 152 may filter out high incident angle light emitted by display panel 140, thereby minimizing stray light in the system and maximizing contrast ratio.

[0074] FIG. 10 is a front view of holographic angular filter 152 of FIG. 9 (e.g., as viewed in the direction of arrow 162 of FIG. 9). As shown in FIG. 10, light sink 160 may extend around the periphery of holographic angular filter 152. Low incident angle light 22L (FIG. 9) may be transmitted through lateral surface 145 of waveguide 146-1 within circular or elliptical region 174. High incident angle light 22H (FIG. 9) may be incident upon holographic angular filter 152 within ring-shaped region 179. Holographic grating structures 156 of FIG. 9 may be configured to diffract the portion of high incident angle light 22H to the left of vertical axis 172 towards light sink 160, as shown by arrow 176, and may be configured to diffract the portion of high incident angle light 22H to the right of vertical axis 172 towards light sink 160, as shown by arrow 176^*. At the same time, holographic grating structures 154 of FIG. 9 may be configured to diffract the portion of high incident angle light 22H above horizontal axis 170 towards light sink 160, as shown by arrow 178, and may be configured to diffract the portion of high incident angle light 22H below horizontal axis 170 towards light sink 160, as shown by arrow 178^*. In this way, the holographic angular filter may filter high incident angle light 22H at any incident angle (e.g., within ring-shaped region 179) towards the light sink. Holographic angular filter 76 of FIGS. 2-7 may similarly diffract high incident angle light in two-dimensional ring-shaped regions towards light sink 70 (FIGS. 3 and 7) or light sink 82 (FIG. 4). Use of holographic angular filters such as holographic angular filter 76 of FIGS. 2-7 and holographic angular filter 152 of FIGS. 9 and 10 may allow display system 14 to mitigate high incident angle light and the corresponding stray light that the high incident angle light produces. This may, for example, serve to maximize contrast ratio at the eye box without requiring as much volume within the device as other light baffling techniques.

[0075] A physical environment refers to a physical world that people can sense and/or interact with without aid of electronic systems. Physical environments, such as a physical park, include physical articles, such as physical trees, physical buildings, and physical people. People can directly sense and/or interact with the physical environment, such as through sight, touch, hearing, taste, and smell.

[0076] In contrast, a computer-generated reality (CGR) environment refers to a wholly or partially simulated environment that people sense and/or interact with via an electronic system (e.g., an electronic system including the display systems described herein). In CGR, a subset of a person’s physical motions, or representations thereof, are tracked, and, in response, one or more characteristics of one or more virtual objects simulated in the CGR environment are adjusted in a manner that comports with at least one law of physics. For example, a CGR system may detect a person’s head turning and, in response, adjust graphical content and an acoustic field presented to the person in a manner similar to how such views and sounds would change in a physical environment. In some situations (e.g., for accessibility reasons), adjustments to characteristic(s) of virtual object(s) in a CGR environment may be made in response to representations of physical motions (e.g., vocal commands).

[0077] A person may sense and/or interact with a CGR object using any one of their senses, including sight, sound, touch, taste, and smell. For example, a person may sense and/or interact with audio objects that create 3D or spatial audio environment that provides the perception of point audio sources in 3D space. In another example, audio objects may enable audio transparency, which selectively incorporates ambient sounds from the physical environment with or without computer-generated audio. In some CGR environments, a person may sense and/or interact only with audio objects. Examples of CGR include virtual reality and mixed reality.

[0078] A virtual reality (VR) environment refers to a simulated environment that is designed to be based entirely on computer-generated sensory inputs for one or more senses.

A VR environment comprises a plurality of virtual objects with which a person may sense and/or interact. For example, computer-generated imagery of trees, buildings, and avatars representing people are examples of virtual objects. A person may sense and/or interact with virtual objects in the VR environment through a simulation of the person’s presence within the computer-generated environment, and/or through a simulation of a subset of the person’s physical movements within the computer-generated environment.

[0079] In contrast to a VR environment, which is designed to be based entirely on computer-generated sensory inputs, a mixed reality (MR) environment refers to a simulated environment that is designed to incorporate sensory inputs from the physical environment, or a representation thereof, in addition to including computer-generated sensory inputs (e.g., virtual objects). On a virtuality continuum, a mixed reality environment is anywhere between, but not including, a wholly physical environment at one end and virtual reality environment at the other end.

[0080] In some MR environments, computer-generated sensory inputs may respond to changes in sensory inputs from the physical environment. Also, some electronic systems for presenting an MR environment may track location and/or orientation with respect to the physical environment to enable virtual objects to interact with real objects (that is, physical articles from the physical environment or representations thereof). For example, a system may account for movements so that a virtual tree appears stationery with respect to the physical ground. Examples of mixed realities include augmented reality and augmented virtuality.

[0081] An augmented reality (AR) environment refers to a simulated environment in which one or more virtual objects are superimposed over a physical environment, or a representation thereof. For example, an electronic system for presenting an AR environment may have a transparent or translucent display through which a person may directly view the physical environment. The system may be configured to present virtual objects on the transparent or translucent display, so that a person, using the system, perceives the virtual objects superimposed over the physical environment. Alternatively, a system may have an opaque display and one or more imaging sensors that capture images or video of the physical environment, which are representations of the physical environment. The system composites the images or video with virtual objects, and presents the composition on the opaque display. A person, using the system, indirectly views the physical environment by way of the images or video of the physical environment, and perceives the virtual objects superimposed over the physical environment. As used herein, a video of the physical environment shown on an opaque display is called“pass-through video,” meaning a system uses one or more image sensor(s) to capture images of the physical environment, and uses those images in presenting the AR environment on the opaque display. Further alternatively, a system may have a projection system that projects virtual objects into the physical environment, for example, as a hologram or on a physical surface, so that a person, using the system, perceives the virtual objects superimposed over the physical environment

[0082] An augmented reality environment also refers to a simulated environment in which a representation of a physical environment is transformed by computer-generated sensory information. For example, in providing pass-through video, a system may transform one or more sensor images to impose a select perspective (e.g., viewpoint) different than the perspective captured by the imaging sensors. As another example, a representation of a physical environment may be transformed by graphically modifying (e.g., enlarging) portions thereof, such that the modified portion may be representative but not photorealistic versions of the originally captured images. As a further example, a representation of a physical environment may be transformed by graphically eliminating or obfuscating portions thereof.

[0083] An augmented virtuality (AV) environment refers to a simulated environment in which a virtual or computer-generated environment incorporates one or more sensory inputs from the physical environment The sensory inputs may be representations of one or more characteristics of the physical environment. For example, an AV park may have virtual trees and virtual buildings, but people with faces photorealistically reproduced from images taken of physical people. As another example, a virtual object may adopt a shape or color of a physical article imaged by one or more imaging sensors. As a further example, a virtual object may adopt shadows consistent with the position of the sun in the physical

environment

[0084] There are many different types of electronic systems that enable a person to sense and/or interact with various CGR environments. Examples include head mounted systems, projection-based systems, heads-up displays (HUDs), vehicle windshields having integrated display capability, windows having integrated display capability, displays formed as lenses designed to be placed on a person’s eyes (e.g., similar to contact lenses),

headphones/earphones, speaker arrays, input systems (e.g., wearable or handheld controllers with or without haptic feedback), smartphones, tablets, and desktop/laptop computers. A head mounted system may have one or more speakers) and an integrated opaque display. Alternatively, a head mounted system may be configured to accept an external opaque display (e.g., a smartphone). The head mounted system may incorporate one or more imaging sensors to capture images or video of the physical environment, and/or one or more microphones to capture audio of the physical environment. Rather than an opaque display, a head mounted system may have a transparent or translucent display. The transparent or translucent display may have a medium through which light representative of images is directed to a person’s eyes. The display may utilize digital light projection, OLEDs, LEDs, uLEDs, liquid crystal on silicon, laser scanning light source, or any combination of these technologies. The medium may be an optical waveguide, a hologram medium, an optical combiner, an optical reflector, or any combination thereof. In one embodiment, the transparent or translucent display may be configured to become opaque selectively.

Projection-based systems may employ retinal projection technology that projects graphical images onto a person’s retina. Projection systems also may be configured to project virtual objects into the physical environment, for example, as a hologram or on a physical surface. The display systems having holographic optical filters described herein may be used for these types of systems and for any other desired display arrangements.

[0085] In accordance with an embodiment, a display system is provided that includes a light source configured to emit light, a spatial light modulator, a prism configured to direct a first portion of the light towards the spatial light modulator, the spatial light modulator is configured to reflect the first portion of the light as image light, optical components configured to direct the image light towards an eye box, a light sink and a holographic angular filter, the holographic angular filter is configured to diffract a second portion of the light towards the light sink while transmitting the first portion of the light towards the prism.

[0086] In accordance with another embodiment, the first portion of the light is incident upon a surface of the prism at a first set of incident angles with respect to a normal axis of the surface, the second portion of the light is incident upon the surface at a second set of incident angles with respect to the normal axis, and the incident angles in the second set are greater than the incident angles in the first set.

[0087] In accordance with another embodiment, the holographic angular filter includes a hologram selected from the group consisting of: a transmissive hologram and a reflective hologram.

[0088] In accordance with another embodiment, the holographic angular filter is transparent to the first portion of the fight.

[0089] In accordance with another embodiment, the display system includes a waveguide, the holographic angular filter includes holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and the waveguide is configured to propagate the diffracted second portion of the fight towards the light sink via total internal reflection.

[0090] In accordance with another embodiment, the holographic grating structures are embedded within the waveguide.

[0091] In accordance with another embodiment, the holographic grating structures are mounted to a surface of the waveguide.

[0092] In accordance with another embodiment, the waveguide is interposed between the holographic grating structures and the surface of the prism.

[0093] In accordance with another embodiment, the spatial fight modulator includes a digital micromirror device (DMD).

[0094] In accordance with another embodiment, the display system includes a baffle, the DMD includes an array of micromirrors, each micromirror in the array having a first state at which that micromirror is configured to direct the first portion of the fight towards the baffle and a second state at which that mirror is configured to direct the first portion of the light towards the optical components.

[0095] In accordance with another embodiment, the display system includes a waveguide, the holographic angular filter includes holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and the waveguide is configured to propagate the diffracted second portion of the light towards the light sink via total internal reflection.

[0096] In accordance with another embodiment, the spatial light modulator includes a liquid crystal on silicon (LCOS) chip.

[0097] In accordance with another embodiment, the display system includes a polarizer mounted to the surface of the prism, a beam splitting polarizer mounted to a first additional surface of the prism and a reflective element mounted to a second additional surface of the prism, the holographic optical element is configured to transmit the first portion of the light into the prism through the polarizer, the beam splitting polarizer is configured to reflect the first portion of the light towards the reflective element, and the reflective element is configured to reflect the first portion of the light towards the LCOS chip.

[0098] In accordance with another embodiment, the polarizer is configured to transmit a first polarization of the first portion of the light, the reflective element is configured to diffract a second polarization of the second portion of the light with greater diffractive efficiency than the first polarization of the second portion of the light, and the second polarization is different than the first polarization.

[0099] In accordance with another embodiment, the display system includes a waveguide, the holographic angular filter includes holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and the waveguide is configured to propagate the diffracted second portion of the light towards the light sink via total internal reflection.

[00100] In accordance with another embodiment, the holographic angular filter includes a first set of holograms configured to diffract a first wavelength of the second portion of the light, and the holographic angular filter includes a second set of holograms configured to diffract a second wavelength of the second portion of the light, the second wavelength being different from the first wavelength.

[00101] In accordance with another embodiment, each hologram in the first set is configured to diffract the first wavelength of the second portion of the light at a respective one of the incident angles in the second set of incident angles, and each hologram in the second set is configured to diffract the second wavelength of the second portion of the light at a respective one of the incident angles in the second set of incident angles.

[00102] In accordance with another embodiment, the holographic angular filter includes a grating medium and the first set of holograms are superimposed with the second set of holograms within the same volume of the grating medium.

[00103] In accordance with another embodiment, the holographic angular filter includes a first grating medium and a second grating medium at least partially overlapping the first grating medium, the first set of holograms are recorded in the first grating medium, and the second set of holograms are recorded in the second grating medium.

[00104] In accordance with another embodiment, the display system includes a light detecting element at the light sink, the imager sensor is configured to gather image data from the second portion of the light that has been diffracted by the holographic angular filter and control circuitry, the control circuitry is configured to adjust the light source based on the image data gathered by the light detecting element.

[00105] In accordance with another embodiment, the light source is configured to emit the light in a plurality of color channels, the control circuitry is configured to identify a relative difference in brightness between the color channels in the second portion of the light, and the control circuitry is configured to adjust at least one color channel in the plurality of color channels based on the identified relative difference in brightness.

[00106] In accordance with an embodiment, a display system is provided that includes a display panel having an array of pixels configured to emit image light, optical components configured to direct a first portion of the image light towards an eye box, a light sink and a holographic angular filter mounted between the display panel and the optical components, the holographic angular filter is configured to diffract a second portion of the image light towards the light sink while transmitting the first portion of the image light, the second portion of the image light being incident upon the holographic angular filter at a greater incident angle with respect to a normal axis of the holographic angular filter than the first portion of the image light.

[00107] In accordance with another embodiment, the display includes a waveguide, the holographic angular filter includes holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and the waveguide is configured to propagate the second portion of the light diffracted by the grating structures towards the light sink via total internal reflection.

[00108] In accordance with another embodiment, the display includes an additional waveguide overlapping the waveguide, the holographic angular filter includes additional holographic grating structures configured to diffract the second portion of the light towards a surface of the additional waveguide, and the additional waveguide is configured to propagate the second portion of the light diffracted by the additional grating structures towards the light sink via total internal reflection.

[00109] In accordance with another embodiment, the holographic grating structures are configured to diffract the second portion of the light in a direction parallel to a first axis, and the additional holographic grating structures are configured to diffract the second portion of the light in a direction parallel to a second axis perpendicular to the first axis.

[00110] In accordance with another embodiment, the light sink is mounted along a peripheral edge of the waveguide.

[00111] In accordance with an embodiment, a head-mounted display device is provided that includes a light source configured to emit light, a spatial light modulator, a prism configured to receive the light at an input surface and configured to direct the light towards the spatial light modulator, the spatial light modulator is configured to reflect the light, projection optics configured to direct the light reflected by the spatial light modulator towards an eye box and a set of volume holograms coupled to the input surface of the prism, the set of volume holograms is configured to optimize a contrast ratio of the image light by diffracting, away from the projection optics, a portion of the light incident upon the input surface at incident angles greater than a minimum threshold incident angle relative to a normal axis of the input surface.

[00112] In accordance with another embodiment, the spatial light modulator includes a spatial light modulator selected from the group consisting of: a digital microminor device and a liquid crystal on silicon chip.

[00113] In accordance with another embodiment, the head-mounted display device includes a waveguide mounted to the input surface of the prism, the set of volume holograms is configured to diffract the portion of the incident light towards a surface of the waveguide and the waveguide is configured to propagate the diffracted portion of the incident light via total internal reflection.

[00114] In accordance with another embodiment, the head-mounted display device includes an image sensor configured to gather image data in response to the diffracted portion of the incident light propagated by the waveguide.

[00115] 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.

Claims

Claims What is Claimed is:

1. A display system, comprising:

a light source configured to emit light;

a spatial light modulator;

a prism configured to direct a first portion of the light towards the spatial light modulator, wherein the spatial light modulator is configured to reflect the first portion of the light as image light;

optical components configured to direct the image light towards an eye box;

a light sink; and

a holographic angular filter, wherein the holographic angular filter is configured to diffract a second portion of the light towards the light sink while transmitting the first portion of the light towards the prism.

2. The display system defined in claim 1 , wherein the first portion of the light is incident upon a surface of the prism at a first set of incident angles with respect to a normal axis of the surface, wherein the second portion of the light is incident upon the surface at a second set of incident angles with respect to the normal axis, and wherein the incident angles in the second set are greater than the incident angles in the first set.

3. The display system defined in claim 2, wherein the holographic angular filter comprises a hologram selected from the group consisting of: a transmissive hologram and a reflective hologram.

4. The display system defined in claim 2, wherein the holographic angular filter is transparent to the first portion of the light

5. The display system defined in claim 2, further comprising:

a waveguide, wherein the holographic angular filter comprises holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and wherein the waveguide is configured to propagate the diffracted second portion of the light towards the light sink via total internal reflection.

6. The display system defined in claim 5, wherein the holographic grating structures are embedded within the waveguide.

7. The display system defined in claim 5, wherein the holographic grating structures are mounted to a surface of the waveguide.

8. The display system defined in claim 7, wherein the waveguide is interposed between the holographic grating structures and the surface of the prism.

9. The display system defined in claim 2, wherein the spatial light modulator comprises a digital micromirror device (DMD).

10. The display system defined in claim 9, further comprising:

a baffle, wherein the DMD comprises an array of micromirrors, each micromirror in the array having a first state at which that micromirror is configured to direct the first portion of the light towards the baffle and a second state at which that mirror is configured to direct the first portion of the light towards the optical components.

11. The display system defined in claim 10, further comprising:

12. The display system defined in claim 2, wherein the spatial light modulator comprises a liquid crystal on silicon (LCOS) chip.

13. The display system defined in claim 12, further comprising:

a polarizer mounted to the surface of the prism;

a beam splitting polarizer mounted to a first additional surface of the prism; and

a reflective element mounted to a second additional surface of the prism, wherein the holographic optical element is configured to transmit the first portion of the light into the prism through the polarizer, the beam splitting polarizer is configured to reflect the first portion of the light towards the reflective element, and the reflective element is configured to reflect the first portion of the light towards the LCOS chip.

14. The display system defined in claim 13, wherein the polarizer is configured to transmit a first polarization of the first portion of the light, wherein the reflective element is configured to diffract a second polarization of the second portion of the light with greater diffractive efficiency than the first polarization of the second portion of the light, and wherein the second polarization is different than the first polarization.

15. The display system defined in claim 12, further comprising:

16. The display system defined in claim 2, wherein the holographic angular filter comprises a first set of holograms configured to diffract a first wavelength of the second portion of the light, and wherein the holographic angular filter comprises a second set of holograms configured to diffract a second wavelength of the second portion of the light, the second wavelength being different from the first wavelength.

17. The display system defined in claim 16, wherein each hologram in the first set is configured to diffract the first wavelength of the second portion of the light at a respective one of the incident angles in the second set of incident angles, and wherein each hologram in the second set is configured to diffract the second wavelength of the second portion of the light at a respective one of the incident angles in the second set of incident angles.

18. The display system defined in claim 16, wherein the holographic angular filter comprises a grating medium and wherein the first set of holograms are superimposed with the second set of holograms within the same volume of the grating medium.

19. The display system defined in claim 16, wherein the holographic angular filter comprises a first grating medium and a second grating medium at least partially overlapping the first grating medium, wherein the first set of holograms are recorded in the first grating medium, and wherein the second set of holograms are recorded in the second grating medium.

20. The display system defined in claim 1 , further comprising:

a light detecting element at the light sink, wherein the imager sensor is configured to gather image data from the second portion of the light that has been diffracted by the holographic angular filter; and

control circuitry, wherein the control circuitry is configured to adjust the light source based on the image data gathered by the light detecting element.

21. The display system defined in claim 16, wherein the light source is configured to emit the light in a plurality of color channels, wherein the control circuitry is configured to identify a relative difference in brightness between the color channels in the second portion of the light, and wherein the control circuitry is configured to adjust at least one color channel in the plurality of color channels based on the identified relative difference in brightness.

22. A display system, comprising:

a display panel having an array of pixels configured to emit image light;

optical components configured to direct a first portion of the image light towards an eye box;

a light sink; and

a holographic angular filter mounted between the display panel and the optical components, wherein the holographic angular filter is configured to diffract a second portion of the image light towards the light sink while transmitting the first portion of the image light, the second portion of the image light being incident upon the holographic angular filter at a greater incident angle with respect to a normal axis of the holographic angular filter than the first portion of the image light.

23. The display system defined in claim 22, further comprising: a waveguide, wherein the holographic angular filter comprises holographic grating structures configured to diffract the second portion of the light towards a surface of the waveguide, and wherein the waveguide is configured to propagate the second portion of the light diffracted by the grating structures towards the light sink via total internal reflection.

24. The display system defined in claim 23, further comprising:

an additional waveguide overlapping the waveguide, wherein the holographic angular filter comprises additional holographic grating structures configured to diffract the second portion of the light towards a surface of the additional waveguide, and wherein the additional waveguide is configured to propagate the second portion of the light diffracted by the additional grating structures towards the light sink via total internal reflection.

25. The display system defined in claim 24, wherein the holographic grating structures are configured to diffract the second portion of the light in a direction parallel to a first axis, and wherein the additional holographic grating structures are configured to diffract the second portion of the light in a direction parallel to a second axis perpendicular to the first axis.

26. The display system defined in claim 23, wherein the light sink is mounted along a peripheral edge of the waveguide.

27. A head-mounted display device comprising:

a light source configured to emit light;

a spatial light modulator,

a prism configured to receive the light at an input surface and configured to direct the light towards the spatial light modulator, wherein the spatial light modulator is configured to reflect the light;

projection optics configured to direct the light reflected by the spatial light modulator towards an eye box; and

a set of volume holograms coupled to the input surface of the prism, wherein the set of volume holograms is configured to optimize a contrast ratio of the image light by diffracting, away from the projection optics, a portion of the light incident upon the input surface at incident angles greater than a minimum threshold incident angle relative to a normal axis of the input surface.

28. The head-mounted display device defined in claim 27, wherein the spatial light modulator comprises a spatial light modulator selected from the group consisting of: a digital micromirror device and a liquid crystal on silicon chip.

29. The head-mounted display device defined in claim 28, further composing:

a waveguide mounted to the input surface of the prism, wherein the set of volume holograms is configured to diffract the portion of the incident light towards a surface of the waveguide and wherein the waveguide is configured to propagate the diffracted portion of the incident light via total internal reflection.

30. The head-mounted display device defined in claim 29, further composing:

an image sensor configured to gather image data in response to the diffracted portion of the incident light propagated by the waveguide.