US20210055551A1 - Dispersion compensation in volume bragg grating-based waveguide display - Google Patents

Abstract

A waveguide display includes a substrate transparent to visible light, a coupler configured to couple display light into the substrate as guided wave in the substrate, and a first VBG and a second VBG coupled to the substrate. The coupler includes a diffractive coupler, a refractive coupler, or a reflective coupler. The first VBG is configured to diffract, at a first region of the first VBG, the display light in the substrate to a first direction, and diffract, at two or more regions of the first VBG along the first direction, the display light from the first region to a second direction towards the second VBG. The second VBG is configured to couple the display light from each of the two or more regions of the first VBG out of the substrate at two or more regions of the second VBG along the second direction.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This patent application claims priority to U.S. Provisional Patent Application Ser. No. 62/891,167, filed Aug. 23, 2019, entitled “Volume Bragg Grating-Based Waveguide Display,” the disclosure of which is hereby incorporated by reference in its entirety for all purposes.
BACKGROUND
• An artificial reality system, such as a head-mounted display (HMD) or heads-up display (HUD) system, generally includes a near-eye display (e.g., in the form of a headset or a pair of glasses) configured to present content to a user via an electronic or optic display within, for example, about 10-20 mm in front of the user's eyes. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view both images of virtual objects (e.g., computer-generated images (CGIs)) and the surrounding environment by, for example, seeing through transparent display glasses or lenses (often referred to as optical see-through).
• One example of an optical see-through AR system may use a waveguide-based optical display, where light of projected images may be coupled into a waveguide (e.g., a transparent substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations. In some implementations, the light of the projected images may be coupled into or out of the waveguide using a diffractive optical element, such as a grating. Light from the surrounding environment may pass through a see-through region of the waveguide and reach the user's eyes as well.
SUMMARY
• This disclosure relates generally to volume Bragg grating-based waveguide displays for near-eye display. More specifically, disclosed herein are techniques for expanding the eyebox, reducing display haze, reducing physical size, improving optical efficiency, reducing optical artifacts, and increasing field of view of optical see-through near-eye display systems using volume Bragg grating (VBG) couplers. Various inventive embodiments are described herein, including devices, systems, methods, and the like.
• According to some embodiments, a waveguide display may include a substrate transparent to visible light, and a first VBG, a second VBG, and a third VBG coupled to the substrate. The first VBG may be configured to couple display light into the substrate as guided wave towards a first region of the second VBG. The second VBG may be configured to diffract, at the first region of the second VBG, the display light from the first VBG to a first direction (e.g., x direction), and diffract, at two or more regions of the second VBG along the first direction, the display light from the first region to a second direction (e.g., y direction) towards the third VBG. The third VBG may be configured to couple the display light from each of the two or more regions of the second VBG out of the substrate at two or more regions of the third VBG along the second direction. The first VBG and the third VBG may have a same grating vector in a plane (e.g., x-y plane) perpendicular to a surface normal direction of the substrate, and may have a same grating vector or opposite grating vectors in the surface normal (e.g., z) direction of the substrate. In some embodiments, the first region of the second VBG and the second region of the second VBG may have a same grating vector in a plane perpendicular to a surface normal direction of the substrate, and may have a same grating vector and/or opposite grating vectors in the surface normal direction of the substrate.
• In some embodiments of the waveguide display, the first VBG, the second VBG, and the third VBG may be configured to diffract the display light from a same field of view range and in a same wavelength range. Each of the first VBG, the second VBG, and the third VBG includes a reflective VBG or a transmissive VBG. In some embodiments, the third VBG may include a transmissive VBG, and the second VBG may overlap with the third VBG in a see-through region of the waveguide display.
• In some embodiments, at least one of the first VBG, the second VBG, or the third VBG may include a multiplexed VBG. The first VBG may include a first set of VBGs, the third VBG may include a second set of VBGs, and each VBG in the first set of VBGs and a corresponding VBG in the second set of VBGs may have a same grating vector in a plane perpendicular to a surface normal direction of the substrate and have a same grating vector or opposite grating vectors in the surface normal direction of the substrate, and may be configured to diffract the display light from a same field of view range and in a same wavelength range. In some embodiments, at least one of the first VBG, the second VBG, or the third VBG may include VBGs in two or more holographic material layers. In some embodiments, each of the second VBG and the third VBG may be characterized by a respective thickness less than 100 μm, and the waveguide display may be characterized by an angular resolution less than 2 arcminutes.
• In some embodiments, the waveguide display may include a polarization convertor between two holographic material layers of the two or more holographic material layers. In some embodiments, the waveguide display may include an anti-reflection layer configured to reduce reflection of ambient light into the substrate. In some embodiments, the waveguide display may include an angular-selective transmissive layer configured to reflect, diffract, or absorb ambient light incident on the angular-selective transmissive layer with an incidence angle greater than a threshold value. In some embodiments, the waveguide display may include a light source configured to generate the display light, and projector optics configure to collimate the display light and direct the display light to the first VBG.
• According to certain embodiments, a waveguide display may include a substrate transparent to visible light, a coupler configured to couple display light into the substrate as guided wave in the substrate, and a first VBG and a second VBG coupled to the substrate. The first VBG may be configured to diffract, at a first region of the first VBG, the display light in the substrate to a first direction, and diffract, at two or more regions of the first VBG along the first direction, the display light from the first region to a second direction towards the second VBG. The second VBG may be configured to couple the display light from each of the two or more regions of the first VBG out of the substrate at two or more regions of the second VBG along the second direction. Each of the first VBG and the second VBG includes a transmissive VBG or a reflective VBG. In some embodiments, the coupler may include a diffractive coupler, a refractive coupler, or a reflective coupler.
• In some embodiments, the first VBG may be characterized by a thickness less than 100 μm, and the waveguide display may be characterized by an angular resolution less than 2 arcminutes. In some embodiments, the second VBG may include a transmissive VBG, and the first VBG may overlap with the second VBG in a see-through region of the waveguide display. In some embodiments, at least one of the first VBG or the second VBG may include VBGs in two or more holographic material layers. In some embodiments, at least one of the first VBG or the second VBG includes a multiplexed VBG.
• This summary is neither intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings, and each claim. The foregoing, together with other features and examples, will be described in more detail below in the following specification, claims, and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
• Illustrative embodiments are described in detail below with reference to the following figures.
• FIG. 1 is a simplified block diagram of an example of an artificial reality system environment including a near-eye display system according to certain embodiments.
• FIG. 2 is a perspective view of an example of a near-eye display system in the form of a head-mounted display (HMD) device for implementing some of the examples disclosed herein.
• FIG. 3 is a perspective view of an example of a near-eye display system in the form of a pair of glasses for implementing some of the examples disclosed herein.
• FIG. 4 is a simplified diagram illustrating an example of an optical system in a near-eye display system.
• FIG. 5 illustrates an example of an optical see-through augmented reality system including a waveguide display for exit pupil expansion according to certain embodiments.
• FIG. 6 illustrates an example of an optical see-through augmented reality system including a waveguide display for exit pupil expansion according to certain embodiments.
• FIG. 7A illustrates the spectral bandwidth of an example of a reflective volume Bragg grating (VBG) and the spectral bandwidth of an example of a transmissive surface-relief grating (SRG).FIG. 7B illustrates the angular bandwidth of an example of a reflective VBG and the angular bandwidth of an example of a transmissive SRG.
• FIG. 8A illustrates an example of an optical see-through augmented reality system including a waveguide display and surface-relief gratings for exit pupil expansion according to certain embodiments.FIG. 8B illustrates an example of an eye box including two-dimensional replicated exit pupils according to certain embodiments.
• FIG. 9A illustrates wave vectors of light diffracted by examples of surface-relief gratings for exit pupil expansion in a waveguide display and exit pupils for multiple colors.
• FIG. 9B illustrates the field-of-view clipping by the examples of surface-relief gratings for exit pupil expansion in the waveguide display.
• FIG. 10A illustrates an example of a volume Bragg grating-based waveguide display according to certain embodiments.FIG. 10B illustrates a top view of the example of the volume Bragg grating-based waveguide display shown inFIG. 10A.FIG. 10C illustrates a side view of the example of the volume Bragg grating-based waveguide display shown inFIG. 10A.
• FIG. 11 illustrates light dispersion in an example of a volume Bragg grating-based waveguide display according to certain embodiments.
• FIG. 12A illustrates an example of a volume Bragg grating (VBG).FIG. 12B illustrates the Bragg condition for the volume Bragg grating shown inFIG. 12A.
• FIG. 13A illustrates an example of a reflective volume Bragg grating in a waveguide display according to certain embodiments.FIG. 13B illustrates an example of a reflective VBG in a waveguide display where light diffracted by the reflective VBG is not totally reflected and guided in the waveguide.FIG. 13C illustrates an example of a transmissive volume Bragg grating in a waveguide display according to certain embodiments.FIG. 13D illustrates an example of a transmissive VBG in a waveguide display where light diffracted by the transmissive VBG is not totally reflected and guided in the waveguide.
• FIG. 14A illustrates the light dispersion by an example of a reflective volume Bragg grating in a waveguide display according to certain embodiments.FIG. 14B illustrates the light dispersion by an example of a transmissive volume Bragg grating in a waveguide display according to certain embodiments.
• FIG. 15A illustrates a front view of an example of a volume Bragg grating-based waveguide display with exit pupil expansion and dispersion reduction according to certain embodiments.FIG. 15B illustrates a side view of the example of the volume Bragg grating-based waveguide display shown inFIG. 15A.
• FIG. 16A is a front view of an example of a volume Bragg grating-based waveguide display with exit pupil expansion and dispersion reduction according to certain embodiments.
• FIG. 16B is a side view of the example of the volume Bragg grating-based waveguide display shown inFIG. 16A.
• FIG. 17A illustrates the propagation of light in different colors and from different fields of view in a reflective volume Bragg grating-based waveguide display according to certain embodiments.FIG. 17B illustrates the propagation of light in different colors and from different fields of view in a transmissive volume Bragg grating-based waveguide display according to certain embodiments.
• FIG. 18 illustrates an example of a reflective volume Bragg grating-based waveguide display with exit pupil expansion and dispersion reduction according to certain embodiments.
• FIG. 19 illustrates an example of a transmissive volume Bragg grating-based waveguide display with exit pupil expansion and form-factor reduction according to certain embodiments.
• FIG. 20 illustrates another example of a transmissive volume Bragg grating-based waveguide display according to certain embodiments.
• FIG. 21 illustrates an example of a volume Bragg grating-based waveguide display with exit pupil expansion, dispersion reduction, and form-factor reduction according to certain embodiments.
• FIG. 22A illustrates another example of a volume Bragg grating-based waveguide display with exit pupil expansion, dispersion reduction, form-factor reduction, and power efficiency improvement according to certain embodiments.FIG. 22B illustrates examples of replicated exit pupils at an eyebox of the volume Bragg grating-based waveguide display shown inFIG. 22A.
• FIG. 23A illustrates an example of a volume Bragg grating-based waveguide display with exit pupil expansion, dispersion reduction, and form-factor reduction according to certain embodiments.FIG. 23B illustrates an example of a volume Bragg grating-based waveguide display with exit pupil expansion, dispersion reduction, form-factor reduction, and power efficiency improvement according to certain embodiments.
• FIG. 24A is a front view of an example of a volume Bragg grating-based waveguide display including an image projector and multiple polymer layers according to certain embodiments.FIG. 24B is a side view of the example of the volume Bragg grating-based waveguide display including the image projector and multiple polymer layers according to certain embodiments.
• FIG. 25 illustrates an example of a volume Bragg grating-based waveguide display including multiple grating layers for different fields of view and/or light wavelengths according to certain embodiments.
• FIG. 26 illustrates an example of a waveguide display including two multiplexed volume Bragg gratings and a polarization convertor between the two multiplexed volume Bragg gratings according to certain embodiments.
• FIG. 27 illustrates an example of a waveguide display including an anti-reflection layer and an angular-selective transmissive layer according to certain embodiments.
• FIG. 28 is a simplified block diagram of an example electronic system of an example near-eye display according to certain embodiments.
• The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated may be employed without departing from the principles, or benefits touted, of this disclosure.
• In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.
DETAILED DESCRIPTION
• This disclosure relates generally to volume Bragg grating (VBG)-based waveguide display for near-eye display systems. In a near-eye display system, it is generally desirable to expand the eyebox, reduce display haze, improve image quality (e.g., resolution and contrast), reduce physical size, increase power efficiency, and increase the field of view. In a waveguide-based near-eye display system, light of projected images may be coupled into a waveguide (e.g., a transparent substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations to replicate exit pupils and expand the eyebox. Two or more gratings may be used to expand the exit pupil in two dimensions. In a waveguide-based near-eye display system for augmented reality applications, light from the surrounding environment may pass through at least a see-through region of the waveguide display (e.g., the transparent substrate) and reach the user's eyes. In some implementations, the light of the projected images may be coupled into or out of the waveguide using diffractive optical elements, such as gratings. Couplers implemented using diffractive optical elements may cause dispersion between light of different colors due to the wavelength dependency of light diffraction. Therefore, images of different color components in a color image may not overlap and thus the resolution of the displayed image may be reduced. To reduce the dispersion and improve the resolution, thick transmissive and/or reflective VBG gratings may be used, which may be impractical in many cases and/or may cause significant display haze. For example, in some cases, transmissive VBG gratings with a thickness of greater than 1 mm may be used to achieve a desired resolution performance. Reflective VBG gratings with a lower thickness may be used to achieve the desired resolution performance. However, with reflection gratings, the gratings for two-dimensional pupil expansion may not overlap and thus the physical size of the waveguide display may be large.
• According to certain embodiments, two VBG gratings (or two portions of a same grating) with matching grating vectors (e.g., having the same grating vector in a plane perpendicular to a surface normal direction of the transparent substrate and having the same and/or opposite grating vectors in the surface-normal direction of the transparent substrate, but recorded in different exposure durations to achieve different diffraction efficiencies) may be used to diffract display light and expand the exit pupil in one dimension. The two VBG gratings may compensate for the dispersion of display light caused by each other to reduce the overall dispersion, due to the opposite Bragg conditions (e.g., +1 order and −1 order diffractions) at the two VBG gratings. Therefore, thin VBG gratings may be used to achieve the desired resolution. Because of the dispersion compensation, thin transmissive VBG gratings may be used to achieve the desired resolution, and the gratings for the two-dimensional pupil expansion may at least partially overlap to reduce the physical size of the waveguide display.
• In some embodiments, a first pair of VBG gratings (or two portions of a grating) may be used to expand the exit pupil in one dimension and compensate for the dispersion caused by each other, and a second pair of VBG gratings (or two portions of a grating) may be used to expand the exit pupil in another dimension and may compensate for the dispersion caused by each other. Thus, the exit pupil may be replicated in two dimensions and the resolution of the displayed images may be high in both dimensions.
• In the following description, various inventive embodiments are described, including devices, systems, methods, and the like. For the purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the disclosure. However, it will be apparent that various examples may be practiced without these specific details. For example, devices, systems, structures, assemblies, methods, and other components may be shown as components in block diagram form in order not to obscure the examples in unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques may be shown without necessary detail in order to avoid obscuring the examples. The figures and description are not intended to be restrictive. The terms and expressions that have been employed in this disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. The word “example” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.
• FIG. 1 is a simplified block diagram of an example of an artificialreality system environment100 including a near-eye display120 in accordance with certain embodiments. Artificialreality system environment100 shown inFIG. 1 may include near-eye display120, an optionalexternal imaging device150, and an optional input/output interface140, each of which may be coupled to anoptional console110. WhileFIG. 1 shows an example of artificialreality system environment100 including one near-eye display120, oneexternal imaging device150, and one input/output interface140, any number of these components may be included in artificialreality system environment100, or any of the components may be omitted. For example, there may be multiple near-eye displays120 monitored by one or moreexternal imaging devices150 in communication withconsole110. In some configurations, artificialreality system environment100 may not includeexternal imaging device150, optional input/output interface140, andoptional console110. In alternative configurations, different or additional components may be included in artificialreality system environment100.
• Near-eye display120 may be a head-mounted display that presents content to a user. Examples of content presented by near-eye display120 include one or more of images, videos, audio, or any combination thereof. In some embodiments, audio may be presented via an external device (e.g., speakers and/or headphones) that receives audio information from near-eye display120,console110, or both, and presents audio data based on the audio information. Near-eye display120 may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. A rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. A non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, near-eye display120 may be implemented in any suitable form-factor, including a pair of glasses. Some embodiments of near-eye display120 are further described below with respect toFIGS. 2 and 3. Additionally, in various embodiments, the functionality described herein may be used in a headset that combines images of an environment external to near-eye display120 and artificial reality content (e.g., computer-generated images). Therefore, near-eye display120 may augment images of a physical, real-world environment external to near-eye display120 with generated content (e.g., images, video, sound, etc.) to present an augmented reality to a user.
• In various embodiments, near-eye display120 may include one or more ofdisplay electronics122,display optics124, and an eye-trackingunit130. In some embodiments, near-eye display120 may also include one ormore locators126, one ormore position sensors128, and an inertial measurement unit (IMU)132. Near-eye display120 may omit any of eye-trackingunit130,locators126,position sensors128, andIMU132, or include additional elements in various embodiments. Additionally, in some embodiments, near-eye display120 may include elements combining the function of various elements described in conjunction withFIG. 1.
• Display electronics122 may display or facilitate the display of images to the user according to data received from, for example,console110. In various embodiments,display electronics122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, an inorganic light emitting diode (ILED) display, a micro light emitting diode (μLED) display, an active-matrix OLED display (AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one implementation of near-eye display120,display electronics122 may include a front TOLED panel, a rear display panel, and an optical component (e.g., an attenuator, polarizer, or diffractive or spectral film) between the front and rear display panels.Display electronics122 may include pixels to emit light of a predominant color such as red, green, blue, white, or yellow. In some implementations,display electronics122 may display a three-dimensional (3D) image through stereoscopic effects produced by two-dimensional panels to create a subjective perception of image depth. For example,display electronics122 may include a left display and a right display positioned in front of a user's left eye and right eye, respectively. The left and right displays may present copies of an image shifted horizontally relative to each other to create a stereoscopic effect (e.g., a perception of image depth by a user viewing the image).
• In certain embodiments,display optics124 may display image content optically (e.g., using optical waveguides and couplers) or magnify image light received fromdisplay electronics122, correct optical errors associated with the image light, and present the corrected image light to a user of near-eye display120. In various embodiments,display optics124 may include one or more optical elements, such as, for example, a substrate, optical waveguides, an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, input/output couplers, or any other suitable optical elements that may affect image light emitted fromdisplay electronics122.Display optics124 may include a combination of different optical elements as well as mechanical couplings to maintain relative spacing and orientation of the optical elements in the combination. One or more optical elements indisplay optics124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filtering coating, or a combination of different optical coatings.
• Magnification of the image light bydisplay optics124 may allowdisplay electronics122 to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field of view of the displayed content. The amount of magnification of image light bydisplay optics124 may be changed by adjusting, adding, or removing optical elements fromdisplay optics124. In some embodiments,display optics124 may project displayed images to one or more image planes that may be further away from the user's eyes than near-eye display120.
• Display optics124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or any combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and transverse chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, comatic aberration, field curvature, and astigmatism.
• Locators126 may be objects located in specific positions on near-eye display120 relative to one another and relative to a reference point on near-eye display120. In some implementations,console110 may identifylocators126 in images captured byexternal imaging device150 to determine the artificial reality headset's position, orientation, or both. Alocator126 may be an LED, a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which near-eye display120 operates, or any combination thereof. In embodiments wherelocators126 are active components (e.g., LEDs or other types of light emitting devices),locators126 may emit light in the visible band (e.g., about 380 nm to 750 nm), in the infrared (IR) band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about 10 nm to about 380 nm), in another portion of the electromagnetic spectrum, or in any combination of portions of the electromagnetic spectrum.
• External imaging device150 may include one or more cameras, one or more video cameras, any other device capable of capturing images including one or more oflocators126, or any combination thereof. Additionally,external imaging device150 may include one or more filters (e.g., to increase signal to noise ratio).External imaging device150 may be configured to detect light emitted or reflected fromlocators126 in a field of view ofexternal imaging device150. In embodiments wherelocators126 include passive elements (e.g., retroreflectors),external imaging device150 may include a light source that illuminates some or all oflocators126, which may retro-reflect the light to the light source inexternal imaging device150. Slow calibration data may be communicated fromexternal imaging device150 to console110, andexternal imaging device150 may receive one or more calibration parameters fromconsole110 to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, sensor temperature, shutter speed, aperture, etc.).
• Position sensors128 may generate one or more measurement signals in response to motion of near-eye display120. Examples ofposition sensors128 may include accelerometers, gyroscopes, magnetometers, other motion-detecting or error-correcting sensors, or any combination thereof. For example, in some embodiments,position sensors128 may include multiple accelerometers to measure translational motion (e.g., forward/back, up/down, or left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, or roll). In some embodiments, various position sensors may be oriented orthogonally to each other.
• IMU132 may be an electronic device that generates fast calibration data based on measurement signals received from one or more ofposition sensors128.Position sensors128 may be located external to IMU132, internal to IMU132, or any combination thereof. Based on the one or more measurement signals from one ormore position sensors128,IMU132 may generate fast calibration data indicating an estimated position of near-eye display120 relative to an initial position of near-eye display120. For example,IMU132 may integrate measurement signals received from accelerometers over time to estimate a velocity vector and integrate the velocity vector over time to determine an estimated position of a reference point on near-eye display120. Alternatively,IMU132 may provide the sampled measurement signals to console110, which may determine the fast calibration data. While the reference point may generally be defined as a point in space, in various embodiments, the reference point may also be defined as a point within near-eye display120 (e.g., a center of IMU132).
• Eye-trackingunit130 may include one or more eye-tracking systems. Eye tracking may refer to determining an eye's position, including orientation and location of the eye, relative to near-eye display120. An eye-tracking system may include an imaging system to image one or more eyes and may optionally include a light emitter, which may generate light that is directed to an eye such that light reflected by the eye may be captured by the imaging system. For example, eye-trackingunit130 may include a non-coherent or coherent light source (e.g., a laser diode) emitting light in the visible spectrum or infrared spectrum, and a camera capturing the light reflected by the user's eye. As another example, eye-trackingunit130 may capture reflected radio waves emitted by a miniature radar unit. Eye-trackingunit130 may use low-power light emitters that emit light at frequencies and intensities that would not injure the eye or cause physical discomfort. Eye-trackingunit130 may be arranged to increase contrast in images of an eye captured by eye-trackingunit130 while reducing the overall power consumed by eye-tracking unit130 (e.g., reducing power consumed by a light emitter and an imaging system included in eye-tracking unit130). For example, in some implementations, eye-trackingunit130 may consume less than 100 milliwatts of power.
• Near-eye display120 may use the orientation of the eye to, e.g., determine an inter-pupillary distance (IPD) of the user, determine gaze direction, introduce depth cues (e.g., blur image outside of the user's main line of sight), collect heuristics on the user interaction in the VR media (e.g., time spent on any particular subject, object, or frame as a function of exposed stimuli), some other functions that are based in part on the orientation of at least one of the user's eyes, or any combination thereof. Because the orientation may be determined for both eyes of the user, eye-trackingunit130 may be able to determine where the user is looking. For example, determining a direction of a user's gaze may include determining a point of convergence based on the determined orientations of the user's left and right eyes. A point of convergence may be the point where the two foveal axes of the user's eyes intersect. The direction of the user's gaze may be the direction of a line passing through the point of convergence and the mid-point between the pupils of the user's eyes.
• Input/output interface140 may be a device that allows a user to send action requests to console110. An action request may be a request to perform a particular action. For example, an action request may be to start or to end an application or to perform a particular action within the application. Input/output interface140 may include one or more input devices. Example input devices may include a keyboard, a mouse, a game controller, a glove, a button, a touch screen, or any other suitable device for receiving action requests and communicating the received action requests to console110. An action request received by the input/output interface140 may be communicated to console110, which may perform an action corresponding to the requested action. In some embodiments, input/output interface140 may provide haptic feedback to the user in accordance with instructions received fromconsole110. For example, input/output interface140 may provide haptic feedback when an action request is received, or whenconsole110 has performed a requested action and communicates instructions to input/output interface140. In some embodiments,external imaging device150 may be used to track input/output interface140, such as tracking the location or position of a controller (which may include, for example, an IR light source) or a hand of the user to determine the motion of the user. In some embodiments, near-eye display120 may include one or more imaging devices to track input/output interface140, such as tracking the location or position of a controller or a hand of the user to determine the motion of the user.
• Console110 may provide content to near-eye display120 for presentation to the user in accordance with information received from one or more ofexternal imaging device150, near-eye display120, and input/output interface140. In the example shown inFIG. 1,console110 may include anapplication store112, aheadset tracking module114, anartificial reality engine116, and an eye-trackingmodule118. Some embodiments ofconsole110 may include different or additional modules than those described in conjunction withFIG. 1. Functions further described below may be distributed among components ofconsole110 in a different manner than is described here.
• In some embodiments,console110 may include a processor and a non-transitory computer-readable storage medium storing instructions executable by the processor. The processor may include multiple processing units executing instructions in parallel. The non-transitory computer-readable storage medium may be any memory, such as a hard disk drive, a removable memory, or a solid-state drive (e.g., flash memory or dynamic random access memory (DRAM)). In various embodiments, the modules ofconsole110 described in conjunction withFIG. 1 may be encoded as instructions in the non-transitory computer-readable storage medium that, when executed by the processor, cause the processor to perform the functions further described below.
• Application store112 may store one or more applications for execution byconsole110. An application may include a group of instructions that, when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the user's eyes or inputs received from the input/output interface140. Examples of the applications may include gaming applications, conferencing applications, video playback application, or other suitable applications.
• Headset tracking module114 may track movements of near-eye display120 using slow calibration information fromexternal imaging device150. For example,headset tracking module114 may determine positions of a reference point of near-eye display120 using observed locators from the slow calibration information and a model of near-eye display120.Headset tracking module114 may also determine positions of a reference point of near-eye display120 using position information from the fast calibration information. Additionally, in some embodiments,headset tracking module114 may use portions of the fast calibration information, the slow calibration information, or any combination thereof, to predict a future location of near-eye display120.Headset tracking module114 may provide the estimated or predicted future position of near-eye display120 toartificial reality engine116.
• Artificial reality engine116 may execute applications within artificialreality system environment100 and receive position information of near-eye display120, acceleration information of near-eye display120, velocity information of near-eye display120, predicted future positions of near-eye display120, or any combination thereof fromheadset tracking module114.Virtual reality engine116 may also receive estimated eye position and orientation information from eye-trackingmodule118. Based on the received information,artificial reality engine116 may determine content to provide to near-eye display120 for presentation to the user. For example, if the received information indicates that the user has looked to the left,artificial reality engine116 may generate content for near-eye display120 that mirrors the user's eye movement in a virtual environment. Additionally,artificial reality engine116 may perform an action within an application executing onconsole110 in response to an action request received from input/output interface140, and provide feedback to the user indicating that the action has been performed. The feedback may be visual or audible feedback via near-eye display120 or haptic feedback via input/output interface140.
• Eye-trackingmodule118 may receive eye-tracking data from eye-trackingunit130 and determine the position of the user's eye based on the eye tracking data. The position of the eye may include an eye's orientation, location, or both relative to near-eye display120 or any element thereof. Because the eye's axes of rotation change as a function of the eye's location in its socket, determining the eye's location in its socket may allow eye-trackingmodule118 to more accurately determine the eye's orientation.
• FIG. 2 is a perspective view of an example of a near-eye display in the form of anHMD device200 for implementing some of the examples disclosed herein.HMD device200 may be a part of, e.g., a VR system, an AR system, an MR system, or any combination thereof.HMD device200 may include abody220 and ahead strap230.FIG. 2 shows atop side223, afront side225, and aright side227 ofbody220 in the perspective view.Head strap230 may have an adjustable or extendible length. There may be a sufficient space betweenbody220 andhead strap230 ofHMD device200 for allowing a user to mountHMD device200 onto the user's head. In various embodiments,HMD device200 may include additional, fewer, or different components. For example, in some embodiments,HMD device200 may include eyeglass temples and temple tips as shown in, for example,FIG. 3 below, rather thanhead strap230.
• HMD device200 may present to a user media including virtual and/or augmented views of a physical, real-world environment with computer-generated elements. Examples of the media presented byHMD device200 may include images (e.g., two-dimensional (2D) or three-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio, or any combination thereof. The images and videos may be presented to each eye of the user by one or more display assemblies (not shown inFIG. 2) enclosed inbody220 ofHMD device200. In various embodiments, the one or more display assemblies may include a single electronic display panel or multiple electronic display panels (e.g., one display panel for each eye of the user). Examples of the electronic display panel(s) may include, for example, an LCD, an OLED display, an ILED display, a μLED display, an AMOLED, a TOLED, some other display, or any combination thereof.HMD device200 may include two eyebox regions.
• In some implementations,HMD device200 may include various sensors (not shown), such as depth sensors, motion sensors, position sensors, and eye tracking sensors. Some of these sensors may use a structured light pattern for sensing. In some implementations,HMD device200 may include an input/output interface for communicating with a console. In some implementations,HMD device200 may include a virtual reality engine (not shown) that can execute applications withinHMD device200 and receive depth information, position information, acceleration information, velocity information, predicted future positions, or any combination thereof ofHMD device200 from the various sensors. In some implementations, the information received by the virtual reality engine may be used for producing a signal (e.g., display instructions) to the one or more display assemblies. In some implementations,HMD device200 may include locators (not shown, such as locators126) located in fixed positions onbody220 relative to one another and relative to a reference point. Each of the locators may emit light that is detectable by an external imaging device.
• FIG. 3 is a perspective view of an example of a near-eye display300 in the form of a pair of glasses for implementing some of the examples disclosed herein. Near-eye display300 may be a specific implementation of near-eye display120 ofFIG. 1, and may be configured to operate as a virtual reality display, an augmented reality display, and/or a mixed reality display. Near-eye display300 may include aframe305 and adisplay310.Display310 may be configured to present content to a user. In some embodiments,display310 may include display electronics and/or display optics. For example, as described above with respect to near-eye display120 ofFIG. 1,display310 may include an LCD display panel, an LED display panel, or an optical display panel (e.g., a waveguide display assembly).
• Near-eye display300 may further includevarious sensors350a,350b,350c,350d, and350eon or withinframe305. In some embodiments, sensors350a-350emay include one or more depth sensors, motion sensors, position sensors, inertial sensors, or ambient light sensors. In some embodiments, sensors350a-350emay include one or more image sensors configured to generate image data representing different fields of views in different directions. In some embodiments, sensors350a-350emay be used as input devices to control or influence the displayed content of near-eye display300, and/or to provide an interactive VR/AR/MR experience to a user of near-eye display300. In some embodiments, sensors350a-350emay also be used for stereoscopic imaging.
• In some embodiments, near-eye display300 may further include one ormore illuminators330 to project light into the physical environment. The projected light may be associated with different frequency bands (e.g., visible light, infra-red light, ultra-violet light, etc.), and may serve various purposes. For example, illuminator(s)330 may project light in a dark environment (or in an environment with low intensity of infra-red light, ultra-violet light, etc.) to assist sensors350a-350ein capturing images of different objects within the dark environment. In some embodiments, illuminator(s)330 may be used to project certain light pattern onto the objects within the environment. In some embodiments, illuminator(s)330 may be used as locators, such aslocators126 described above with respect toFIG. 1.
• In some embodiments, near-eye display300 may also include a high-resolution camera340.Camera340 may capture images of the physical environment in the field of view. The captured images may be processed, for example, by a virtual reality engine (e.g.,artificial reality engine116 ofFIG. 1) to add virtual objects to the captured images or modify physical objects in the captured images, and the processed images may be displayed to the user bydisplay310 for AR or MR applications.
• FIG. 4 is a simplified diagram illustrating an example of anoptical system400 in a near-eye display system.Optical system400 may include animage source410 andprojector optics420. In the example shown inFIG. 4,image source410 is in front ofprojector optics420. In various embodiments,image source410 may be located outside of the field of view of user'seye490. For example, one or more reflectors or directional couplers may be used to deflect light from an image source that is outside of the field of view of user'seye490 to make the image source appear to be at the location ofimage source410 shown inFIG. 4. Light from an area (e.g., a pixel or a light emitting device) onimage source410 may be collimated and directed to anexit pupil430 byprojector optics420. Thus, objects at different spatial locations onimage source410 may appear to be objects far away from user'seye490 in different viewing angles (FOVs). The collimated light from different viewing angles may then be focused by the lens of user'seye490 onto different locations onretina492 of user'seye490. For example, at least some portions of the light may be focused on afovea494 onretina492. Collimated light rays from an area onimage source410 and incident on user'seye490 from a same direction may be focused onto a same location onretina492. As such, a single image ofimage source410 may be formed onretina492.
• The user experience of using an artificial reality system may depend on several characteristics of the optical system, including field of view (FOV), image quality (e.g., angular resolution), size of the eyebox (to accommodate for eye and head movements), and brightness of the light (or contrast) within the eyebox. Field of view describes the angular range of the image as seen by the user, usually measured in degrees as observed by one eye (for a monocular HMD) or both eyes (for either biocular or binocular HMDs). The human visual system may have a total binocular FOV of about 200° (horizontal) by 130° (vertical). To create a fully immersive visual environment, a large FOV is desirable because a large FOV (e.g., greater than about 60°) may provide a sense of “being in” an image, rather than merely viewing the image. Smaller fields of view may also preclude some important visual information. For example, an HMD system with a small FOV may use a gesture interface, but the users may not see their hands in the small FOV to be sure that they are using the correct motions. On the other hand, wider fields of view may require larger displays or optical systems, which may influence the size, weight, cost, and comfort of using the HMD.
• Resolution may refer to the angular size of a displayed pixel or image element appearing to a user, or the ability for the user to view and correctly interpret an object as imaged by a pixel and/or other pixels. The resolution of an HMD may be specified as the number of pixels on the image source for a given FOV value, from which an angular resolution may be determined by dividing the FOV in one direction by the number of pixels in the same direction on the image source. For example, for a horizontal FOV of 40° and 1080 pixels in the horizontal direction on the image source, the corresponding angular resolution may be about 2.2 arc-minutes, compared with the one-arc-minute resolution associated withSnellen 20/20 human visual acuity.
• In some cases, the eyebox may be a two-dimensional box in front of the user's eye, from which the displayed image from the image source may be viewed. If the pupil of the user moves outside of the eyebox, the displayed image may not be seen by the user. For example, in a non-pupil-forming configuration, there exists a viewing eyebox within which there will be unvignetted viewing of the HMD image source, and the displayed image may vignette or may be clipped but may still be viewable when the pupil of user's eye is outside of the viewing eyebox. In a pupil-forming configuration, the image may not be viewable outside the exit pupil.
• The fovea of a human eye, where the highest resolution may be achieved on the retina, may correspond to an FOV of about 2° to about 3°. This may require that the eye rotates in order to view off-axis objects with a highest resolution. The rotation of the eye to view the off-axis objects may introduce a translation of the pupil because the eye rotates around a point that is about 10 mm behind the pupil. In addition, a user may not always be able to accurately position the pupil (e.g., having a radius of about 2.5 mm) of the user's eye at an ideal location in the eyebox. Furthermore, the environment where the HMD is used may require the eyebox to be larger to allow for movement of the user's eye and/or head relative the HMD, for example, when the HMD is used in a moving vehicle or designed to be used while the user is moving on foot. The amount of movement in these situations may depend on how well the HMD is coupled to the user's head.
• Thus, the optical system of the HMD may need to provide a sufficiently large exit pupil or viewing eyebox for viewing the full FOV with full resolution, in order to accommodate the movements of the user's pupil relative to the HMD. For example, in a pupil-forming configuration, a minimum size of 12 mm to 15 mm may be desired for the exit pupil. If the eyebox is too small, minor misalignments between the eye and the HMD may result in at least partial loss of the image, and the user experience may be substantially impaired. In general, the lateral extent of the eyebox is more critical than the vertical extent of the eyebox. This may be in part due to the significant variances in eye separation distance between users, and the fact that misalignments to eyewear tend to more frequently occur in the lateral dimension and users tend to more frequently adjust their gaze left and right, and with greater amplitude, than adjusting the gaze up and down. Thus, techniques that can increase the lateral dimension of the eyebox may substantially improve a user's experience with an HMD. On the other hand, the larger the eyebox, the larger the optics and the heavier and bulkier the near-eye display device may be.
• In order to view the displayed image against a bright background, the image source of an AR HMD may need to be sufficiently bright, and the optical system may need to be efficient to provide a bright image to the user's eye such that the displayed image may be visible in a background including strong ambient light, such as sunlight. The optical system of an HMD may be designed to concentrate light in the eyebox. When the eyebox is large, an image source with high power may be used to provide a bright image viewable within the large eyebox. Thus, there may be trade-offs among the size of the eyebox, cost, brightness, optical complexity, image quality, and size and weight of the optical system.
• FIG. 5 illustrates an example of an optical see-throughaugmented reality system500 including a waveguide display for exit pupil expansion according to certain embodiments.Augmented reality system500 may include aprojector510 and acombiner515.Projector510 may include a light source orimage source512 andprojector optics514. In some embodiments, light source orimage source512 may include one or more micro-LED devices. In some embodiments,image source512 may include a plurality of pixels that displays virtual objects, such as an LCD display panel or an LED display panel. In some embodiments,image source512 may include a light source that generates coherent or partially coherent light. For example,image source512 may include a laser diode, a vertical cavity surface emitting laser, an LED, a superluminescent LED (sLED), and/or a micro-LED described above. In some embodiments,image source512 may include a plurality of light sources (e.g., an array of micro-LEDs described above) each emitting a monochromatic image light corresponding to a primary color (e.g., red, green, or blue). In some embodiments,image source512 may include three two-dimensional arrays of micro-LEDs, where each two-dimensional array of micro-LEDs may include micro-LEDs configured to emit light of a primary color (e.g., red, green, or blue). In some embodiments,image source512 may include an optical pattern generator, such as a spatial light modulator.Projector optics514 may include one or more optical components that can condition the light fromimage source512, such as expanding, collimating, scanning, or projecting light fromimage source512 tocombiner515. The one or more optical components may include, for example, one or more lenses, liquid lenses, mirrors, free-form optics, apertures, and/or gratings. For example, in some embodiments,image source512 may include one or more one-dimensional arrays or elongated two-dimensional arrays of micro-LEDs, andprojector optics514 may include one or more one-dimensional scanners (e.g., micro-mirrors or prisms) configured to scan the one-dimensional arrays or elongated two-dimensional arrays of micro-LEDs to generate image frames. In some embodiments,projector optics514 may include a liquid lens (e.g., a liquid crystal lens) with a plurality of electrodes that allows scanning of the light fromimage source512.
• Combiner515 may include aninput coupler530 for coupling light fromprojector510 into asubstrate520 ofcombiner515.Input coupler530 may include a volume holographic grating or another diffractive optical element (DOE) (e.g., a surface-relief grating (SRG)), a slanted reflective surface ofsubstrate520, or a refractive coupler (e.g., a wedge or a prism).Input coupler530 may have a coupling efficiency of greater than 30%, 50%, 75%, 90%, or higher for visible light. Visible light coupled intosubstrate520 may propagate withinsubstrate520 through, for example, total internal reflection (TIR).Substrate520 may be in the form of a lens of a pair of eyeglasses.Substrate520 may have a flat or a curved surface, and may include one or more types of dielectric materials, such as glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA), crystal, ceramic, or the like. A thickness of the substrate may range from, for example, less than about 1 mm to about 10 mm or more.Substrate520 may be transparent to visible light.
• Substrate520 may include or may be coupled to a plurality ofoutput couplers540 each configured to extract at least a portion of the light guided by and propagating withinsubstrate520 fromsubstrate520, and direct extracted light560 to aneyebox595 where aneye590 of the user ofaugmented reality system500 may be located whenaugmented reality system500 is in use. The plurality ofoutput couplers540 may replicate the exit pupil to increase the size ofeyebox595, such that the displayed image may be visible in a larger area. Asinput coupler530,output couplers540 may include grating couplers (e.g., volume holographic gratings or surface-relief gratings), other diffraction optical elements (DOEs), prisms, etc.Output couplers540 may have different coupling (e.g., diffraction) efficiencies at different locations.Substrate520 may also allow light550 from the environment in front ofcombiner515 to pass through with little or no loss.Output couplers540 may also allow light550 to pass through with little loss. For example, in some implementations,output couplers540 may have a very low diffraction efficiency forlight550 such thatlight550 may be refracted or otherwise pass throughoutput couplers540 with little loss, and thus may have a higher intensity than extracted light560. As a result, the user may be able to view combined images of the environment in front ofcombiner515 and images of virtual objects projected byprojector510. In some implementations,output couplers540 may have a high diffraction efficiency forlight550 and may diffract light550 to certain desired directions (e.g., diffraction angles) with little loss.
• In some embodiments,projector510,input coupler530, andoutput coupler540 may be on any side ofsubstrate520.Input coupler530 andoutput coupler540 may be reflective gratings (also referred to as reflection gratings) or transmissive gratings (also referred to as transmission gratings) to couple display light into or out ofsubstrate520.
• FIG. 6 illustrates an example of an optical see-throughaugmented reality system600 including a waveguide display for exit pupil expansion according to certain embodiments.Augmented reality system600 may be similar toaugmented reality system500, and may include the waveguide display and a projector that may include a light source orimage source612 andprojector optics614. The waveguide display may include asubstrate630, aninput coupler640, and a plurality ofoutput couplers650 as described above with respect toaugmented reality system500. WhileFIG. 5 only shows the propagation of light from a single field of view,FIG. 6 shows the propagation of light from multiple fields of view.
• FIG. 6 shows that the exit pupil is replicated byoutput couplers650 to form an aggregated exit pupil or eyebox, where different fields of view (e.g., different pixels on image source612) may be associated with different respective propagation directions towards the eyebox, and light from a same field of view (e.g., a same pixel on image source612) may have a same propagation direction for the different individual exit pupils. Thus, a single image ofimage source612 may be formed by the user's eye located anywhere in the eyebox, where light from different individual exit pupils and propagating in the same direction may be from a same pixel onimage source612 and may be focused onto a same location on the retina of the user's eye.FIG. 6 shows that the image of the image source is visible by the user's eye even if the user's eye moves to different locations in the eyebox.
• In many waveguide-based near-eye display systems, in order to expand the eyebox of the waveguide-based near-eye display in two dimensions, two or more output gratings may be used to expand the display light in two dimensions or along two axes (which may be referred to as dual-axis pupil expansion). The two gratings may have different grating parameters, such that one grating may be used to replicate the exit pupil in one direction and the other grating may be used to replicate the exit pupil in another direction.
• As described above, the input and output grating couplers described above can be volume holographic gratings or surface-relief gratings, which may have very different Klein-Cook parameter Q:
• $Q=\frac{2\mathrm{\pi \lambda }d}{n{\Lambda }^2},$
• where d is the thickness of the grating, λ is the wavelength of the incident light in free space, Λ is the grating period, and n is the refractive index of the recording medium. The Klein-Cook parameter Q may divide light diffraction by gratings into three regimes. When a grating is characterized by Q<<1, light diffraction by the grating may be referred to as Raman-Nath diffraction, where multiple diffraction orders may occur for normal and/or oblique incident light. When a grating is characterized by Q>>1 (e.g., Q≥10), light diffraction by the grating may be referred to as Bragg diffraction, where generally only the zeroth and the ±1 diffraction orders may occur for light incident on the grating at an angle satisfying the Bragg condition. When a grating is characterized by Q˜1, the diffraction by the grating may be between the Raman-Nath diffraction and the Bragg diffraction. To meet Bragg conditions, the thickness d of the grating may be higher than certain values to occupy a volume (rather than at a surface) of a medium, and thus may be referred to as a volume Bragg grating. VBGs may generally have relatively small refractive index modulations (e.g., Δn≤0.05) and high spectral and angular selectivity, while surface-relief gratings may generally have large refractive index modulations (e.g., Δn≥0.5) and wide spectral and angular bandwidths.
• FIG. 7A illustrates the spectral bandwidth of an example of a volume Bragg grating (e.g., a reflective VBG) and the spectral bandwidth of an example of a surface-relief grating (e.g., a transmissive SRG). The horizontal axis represents the wavelength of the incident visible light and the vertical axis corresponds to the diffraction efficiency. As shown by acurve710, the diffraction efficiency of the reflective VBG is high in a narrow wavelength range, such as green light. In contrast, the diffraction efficiency of the transmissive SRG may be high in a very wide wavelength range, such as from blue to red light, as shown by acurve720.
• FIG. 7B illustrates the angular bandwidth of an example of a volume Bragg grating (e.g., a reflective VBG) and the angular bandwidth of an example of a surface-relief grating (e.g., a transmissive SRG). The horizontal axis represents the incident angle of the visible light incident on the grating, and the vertical axis corresponds to the diffraction efficiency. As shown by acurve715, the diffraction efficiency of the reflective VBG is high for light incident on the grating from a narrow angular range, such as about ±2.5° from the perfect Bragg condition. In contrast, the diffraction efficiency of the transmissive SRG is high in a very wide angular range, such as greater than about ±10° or wider, as shown by acurve725.
• Due to the high spectral selectivity at the Bragg condition, VBGs, such as reflective VBGs, may allow for single-waveguide design without crosstalk between primary colors, and may exhibit superior see-through quality. However, the spectral and angular selectivity may lead to lower efficiency because only a portion of the display light in the full FOV may be diffracted and reach user's eyes.
• FIG. 8A illustrates an example of an optical see-through augmented reality system including awaveguide display800 and surface-relief gratings for exit pupil expansion according to certain embodiments.Waveguide display800 may include a substrate810 (e.g., a waveguide), which may be similar tosubstrate520.Substrate810 may be transparent to visible light and may include, for example, a glass, quartz, plastic, polymer, PMMA, ceramic, or crystal substrate.Substrate810 may be a flat substrate or a curved substrate.Substrate810 may include afirst surface812 and asecond surface814. Display light may be coupled intosubstrate810 by aninput coupler820, and may be reflected byfirst surface812 andsecond surface814 through total internal reflection, such that the display light may propagate withinsubstrate810. As described above,input coupler820 may include a grating, a refractive coupler (e.g., a wedge or a prism), or a reflective coupler (e.g., a reflective surface having a slant angle with respect to substrate810). For example, in one embodiment,input coupler820 may include a prism that may couple display light of different colors intosubstrate810 at a same refraction angle. In another example,input coupler820 may include a grating coupler that may diffract light of different colors intosubstrate810 at different directions.Input coupler820 may have a coupling efficiency of greater than 10%, 20%, 30%, 50%, 75%, 90%, or higher for visible light.
• Waveguide display800 may also include afirst grating830 and asecond grating840 positioned on one or two surfaces (e.g.,first surface812 and second surface814) ofsubstrate810 for expanding incident display light beam in two dimensions in order to fill an eyebox850 (or output or exit pupil) with the display light. First grating830 may be configured to expand at least a portion of the display light beam along one direction, such as approximately in the x direction. Display light coupled intosubstrate810 may propagate in a direction shown by aline832. While the display light propagates withinsubstrate810 along a direction shown byline832, a portion of the display light may be diffracted by a portion offirst grating830 towards second grating840 as shown by aline834 each time the display light propagating withinsubstrate810 reachesfirst grating830.Second grating840 may then expand the display light fromfirst grating830 in a different direction (e.g., approximately in the y direction) by diffracting a portion of the display light toeyebox850 each time the display light propagating withinsubstrate810 reachessecond grating840.
• FIG. 8B illustrates an example of an eye box including two-dimensional replicated exit pupils.FIG. 8B shows that asingle input pupil805 may be replicated byfirst grating830 andsecond grating840 to form an aggregatedexit pupil860 that includes a two-dimensional array of individual exit pupils852. For example, the exit pupil may be replicated in approximately the x direction byfirst grating830 and in approximately the y direction bysecond grating840. As described above, output light from individual exit pupils852 and propagating in a same direction may be focused onto a same location in the retina of the user's eye. Thus, a single image may be formed by the user's eye from the output light in the two-dimensional array of individual exit pupils852.
• FIG. 9A illustrates wave vectors of light diffracted by examples of surface-relief gratings for exit pupil expansion in a waveguide display and exit pupils for multiple colors. Acircle910 may represent wave vectors of light that may be guided by the waveguide. For light with wave vectors outside ofcircle910, the light may become evanescent. Acircle920 may represent wave vectors of light that may leak out of the waveguide because the total-internal-reflection condition is not met. Thus, the ring betweencircle910 andcircle920 may represent the wave vectors of light that can be guided by the waveguide and can propagate within the waveguide through TIR.Wave vectors932 show the light dispersion caused by the input grating, where light of different colors may have different wave vectors and different diffraction angles.Wave vectors942 show the light dispersion caused by a front grating (e.g., first grating830), where light of different colors may have different diffraction angles.Wave vectors952 show the light dispersion caused by a back grating (e.g., second grating840), where light of different colors may have different diffraction angles. The wave vectors for each color may form a respective closed triangle, and the triangles for different colors may share acommon origin vertex922. Thus, the overall dispersion by the three gratings may be close to zero.
• Even though the overall dispersion by the three gratings may be zero, the dispersion by each grating may cause the reduction or clipping of the field of view of the waveguide display due to the conditions under which light may be guided by the waveguide as shown by the ring betweencircle910 andcircle920. For example, for aFOV924, the footprints of the FOV after the diffraction by the input grating may be different for different colors due to the dispersion by the input grating. In the example shown inFIG. 9A, afootprint936 of the FOV for light of a first color may be located in the ring, while a portion of afootprint934 of the FOV for light of a second color and a portion of afootprint938 of the FOV for light of a third color may fall outside of the ring and thus may not be guided by the waveguide. In addition, the footprints of the FOV after the diffraction by the front grating may be further clipped or reduced. In the example shown inFIG. 9A, a small portion of a footprint946 of the FOV for the light of the first color, a large portion of afootprint944 of the FOV for the light of the second color, and a large portion of afootprint948 of the FOV for the light of the third color may fall outside of the ring and thus may not be guided by the waveguide and diffracted by the back grating to reach the exit pupil.
• FIG. 9B illustrates the field-of-view clipping by the examples of surface-relief gratings for exit pupil expansion in the waveguide display. For example, the FOV for the light of the first color after the diffraction by the back grating may be shown by afootprint956, which may be close to the full FOV. For the light of the second color, a top portion of the FOV may be clipped after diffraction by the first grating and a right portion of the FOV may be clipped after diffraction by the front grating. Thus, the FOV for the light of the second color after the diffraction by the back grating may be shown by afootprint954, which may be much smaller than the full FOV. Similarly, for the light of the third color, a bottom portion of the FOV may be clipped after diffraction by the first grating and a left portion of the FOV may be clipped after diffraction by the front grating. Thus, the FOV for the light of the third color after the diffraction by the back grating may be shown by afootprint958, which may be much smaller than the full FOV. Thus, certain color components of the image may be missing for certain fields of view. As such, in order to achieve the full FOV for different colors, two or more waveguides and the corresponding gratings may be used. In addition, as described above, the wide bandwidth of SRGs may cause crosstalk between light of different primary colors and/or from different FOVs, and thus multiple waveguides may also be used to avoid the crosstalk.
• Due to the high spectral selectivity at the Bragg condition, VBGs, such as reflective VBGs, may allow for single-waveguide design without crosstalk between primary colors in a volume Bragg grating and may achieve a superior see-through quality. Thus,input coupler530 or640 andoutput coupler540 or650 may include a volume Bragg grating, which may be a volume hologram recorded in a holographic recording material by exposing the holographic recording material to light patterns generated by the interference between two or more coherent light beams. In volume Bragg gratings, the incident angle and the wavelength of the incident light may need to satisfy the Bragg phase-matching condition in order for the incident light to be diffracted by the Bragg grating. When a single Bragg grating is used in a waveguide-based near-eye display, the spectral and angular selectivity of the volume Bragg gratings may lead to lower efficiency because only a portion of the display light may be diffracted and reach user's eyes, and the field of view and the working wavelength range of the waveguide-based near-eye display may be limited. In some embodiments, multiplexed VBGs may be used to improve the efficiency and increase the FOV.
• FIG. 10A illustrates the front view of an example of a volume Bragg grating-basedwaveguide display1000 according to certain embodiments.Waveguide display1000 may include asubstrate1010, which may be similar tosubstrate520.Substrate1010 may be transparent to visible light and may include, for example, a glass, quartz, plastic, polymer, PMMA, ceramic, or crystal substrate.Substrate1010 may be a flat substrate or a curved substrate.Substrate1010 may include afirst surface1012 and asecond surface1014. Display light may be coupled intosubstrate1010 by aninput coupler1020, and may be reflected byfirst surface1012 andsecond surface1014 through total internal reflection, such that the display light may propagate withinsubstrate1010. As described above,input coupler1020 may include a diffractive coupler (e.g., a volume holographic grating or a surface-relief grating), a refractive coupler (e.g., a wedge or a prism), or a reflective coupler (e.g., a reflective surface having a slant angle with respect to substrate1010). For example, in one embodiment,input coupler1020 may include a prism that may couple display light of different colors intosubstrate1010 at a same refraction angle. In another example, the input coupler may include a grating coupler that may diffract light of different colors intosubstrate1010 at different directions.
• Waveguide display1000 may also include afirst grating1030 and asecond grating1040 positioned on one or two surfaces (e.g.,first surface1012 and second surface1014) ofsubstrate1010 for expanding incident display light beam in two dimensions in order to fill aneyebox1050 with the display light. First grating1030 may include one or more multiplexed volume Bragg gratings each configured to expand at least a portion of the display light beam (e.g., light corresponding to a certain field of view and/or a wavelength range) along one direction, as shown bylines1032,1034, and1036. For example, while the display light propagates withinsubstrate1010 along a direction shown byline1032,1034, or1036, a portion of the display light may be diffracted byfirst grating1030 tosecond grating1040 each time the display light propagating withinsubstrate1010 reaches first grating1030.Second grating1040 may then expand the display light fromfirst grating1030 in a different direction by diffracting a portion of the display light toeyebox1050 each time the display light propagating withinsubstrate1010 reachessecond grating1040.
• As described above,first grating1030 andsecond grating1040 may each include a multiplexed VBG that includes multiple VBGs each designed for a specific FOV range and/or wavelength range. For example,first grating1030 may include a few hundred or more VBGs (e.g., about 300 to about 1000 VBGs) recorded by a few hundred or more exposures, where each VBG may be recorded under a different condition.Second grating1040 may also include tens or hundreds of VBGs (e.g., 50 or more VBGs) recorded by tens or hundreds of exposures. First grating1030 andsecond grating1040 may each be a transmission grating or a reflection grating.
• FIGS. 10B and 10C illustrate the top and side views of volume Bragg grating-basedwaveguide display1000, respectively.Input coupler1020 may include projector optics (not shown, e.g., a lens) and a prism. Display light may be collimated and projected onto the prism by the projector optics, and may be coupled intosubstrate1010 by the prism. The prism may have a refractive index that matches the refractive index ofsubstrate1010 and may include a wedge having a certain angle such that light coupled intosubstrate1010 may be incident onsurface1012 or1014 ofsubstrate1010 at an incident angle greater than the critical angle forsubstrate1010. As such, display light coupled intosubstrate1010 may be guided bysubstrate1010 through total internal reflection, and may be diffracted by multiple regions offirst grating1030 towards second grating1040 as described above.Second grating1040 may then diffract the display light out ofsubstrate1010 at multiple regions to replicate the exit pupil.
• FIG. 11 illustrates light dispersion in an example of a volume Bragg grating-based waveguide display, such aswaveguide display1000, according to certain embodiments. As shown in the example, asphere1110 may represent wave vectors of light that may be guided by the waveguide. For light with wave vectors outside ofsphere1110, the light may become evanescent. Acone1120 may represent wave vectors of light that may leak out of the waveguide because the total-internal-reflection condition is not met. Thus, the region ofsphere1110 outside ofcone1120 may represent the wave vectors of light that can be guided by the waveguide and can propagate within the waveguide through TIR.Point1130 may represent the wave vector of the display light coupled into the waveguide by, for example, a prism.Wave vectors1140 show the light dispersion caused byfirst grating1030, where light of different colors may have different diffraction angles.Wave vectors1150 show the light dispersion caused bysecond grating1040, where light of different colors may have different diffraction angles. Thus, the light coupled out of the substrate may have some dispersion, such that the images of different colors may not perfectly overlap with each other to form one image. Therefore, the displayed image may be blurred and the resolution of the displayed image may be reduced.
• FIG. 12A illustrates an example of a volume Bragg grating1200. Volume Bragg grating1200 shown inFIG. 12A may include a transmission holographic grating that has a thickness D. The refractive index n of volume Bragg grating1200 may be modulated at an amplitude Δn, and the grating period of volume Bragg grating1200 may be Λ.Incident light1210 having a wavelength λ may be incident on volume Bragg grating1200 at an incident angle θ, and may be refracted into volume Bragg grating1200 as incident light1220 that propagates at an angle θ_nin volume Bragg grating1200.Incident light1220 may be diffracted by volume Bragg grating1200 intodiffraction light1230, which may propagate at a diffraction angle &d in volume Bragg grating1200 and may be refracted out of volume Bragg grating1200 asdiffraction light1240.
• FIG. 12B illustrates the Bragg condition for volume Bragg grating1200 shown inFIG. 12A. Volume Bragg grating1200 may be a transmissive grating. Avector1205 may represent the grating vector {right arrow over (G)}, where |{right arrow over (G)}|=2π/Λ. Avector1225 may represent the incident wave vector {right arrow over (k_l)}, and avector1235 may represent the diffract wave vector {right arrow over (k_d)}, where |{right arrow over (k_l)}|=|{right arrow over (k_d)}=2π/λ. Under the Bragg phase-matching condition, {right arrow over (k)}_l-{right arrow over (k_d)}={right arrow over (G)}. Thus, for a given wavelength λ, there may only be one pair of incident angle θ (or θ_n) and diffraction angle θ_dthat meets the Bragg condition perfectly. Similarly, for a given incident angle θ, there may be one wavelength λ that meets the Bragg condition perfectly. As such, the diffraction may occur for a small wavelength range and in a small incident angular range around a perfect Bragg condition. The diffraction efficiency, the wavelength selectivity, and the angular selectivity of volume Bragg grating1200 may be functions of thickness D of volume Bragg grating1200. For example, the full-width-half-magnitude (FWHM) wavelength range and the FWHM angular range of volume Bragg grating1200 around the Bragg condition may be inversely proportional to thickness D of volume Bragg grating1200, while the maximum diffraction efficiency at the Bragg condition may be a function of sin²(α×Δn×D), where α is a coefficient. For a reflective volume Bragg grating, the maximum diffraction efficiency at the Bragg condition may be a function of tan h²(α×Δn×D).
• As described above, in some designs, in order to achieve a large FOV (e.g., larger than) ±30° and diffract light of different colors, multiple polymer layers each including a Bragg grating for a different color (e.g., R, G, or B) and/or a different FOV may be arranged in a stack for coupling the display light to the user's eyes. In some designs, a multiplexed Bragg grating may be used, where each part of the multiplexed Bragg grating may be used to diffract light in a different FOV range and/or within a different wavelength range. Thus, in some designs, in order to achieve a desired diffraction efficiency and a large FOV for the full visible spectrum (e.g., from about 400 nm to about 700 nm, or from about 450 nm to about 650 nm), one or more thick volume Bragg gratings each including a large number of gratings (or holograms) recorded by a large number of exposures (e.g., holographic recordings), such as a few hundred or more than 1000, may be used.
• VBGs or other holographic optical elements described above may be recorded in a holographic material (e.g., photopolymer) layer. In some embodiments, the VBGs can be recorded first and then laminated on a substrate in a near-eye display system. In some embodiments, a holographic material layer may be coated or laminated on the substrate and the VBGs may then be recorded in the holographic material layer.
• In general, to record a holographic optical element in a photosensitive material layer, two coherent beams may interfere with each other at certain angles to generate a unique interference pattern in the photosensitive material layer, which may in turn generate a unique refractive index modulation pattern in the photosensitive material layer, where the refractive index modulation pattern may correspond to the light intensity pattern of the interference pattern. The photosensitive material layer may include, for example, silver halide emulsion, dichromated gelatin, photopolymers including photo-polymerizable monomers suspended in a polymer matrix, photorefractive crystals, and the like. One example of the photosensitive material layer for holographic recording is two-stage photopolymers that may include matrix precursors that can be pre-cured to form polymeric binders before holographic recording and writing monomers for holographic recording.
• In one example, the photosensitive material layer may include polymeric binders, monomers (e.g., acrylic monomers), and initiating agents, such as initiators, chain transfer agents, or photosensitizing dyes. The polymeric binders may act as the support matrix. The monomers may be dispersed in the support matrix and may serve as refractive index modulators. The photosensitizing dyes may absorb light and interact with the initiators to polymerize the monomers. Thus, in each exposure (recording), the interference pattern may cause the polymerization and diffusion of the monomers to bright fringes, thus generating concentration and density gradients that may result in refractive index modulation. For example, areas with a higher concentration of monomers and polymerization may have a higher refractive index. As the exposure and polymerization proceed, fewer monomers may be available for polymerization, and the diffusion may be suppressed. After all or substantially all monomers have been polymerized, no more new gratings may be recorded in the photosensitive material layer. In a thick VBG that includes a large number of gratings recorded in a large number of exposures, display haze may be significant.
• As described above, in some waveguide-based near-eye display systems, in order to expand the eyebox of the waveguide-based near-eye display, two output gratings (or two grating layers or two portions of a multiplexed grating) may generally be used to expand the display light in two dimensions or along two axes for dual-axis pupil expansion. Spatially separating the two output gratings and reducing the total number of exposures for each output grating may help to reduce the display haze because the see-through region (e.g., the middle) of the waveguide-based near-eye display may only include one output grating. For example, in some embodiments, the first output grating may be recorded with more exposures (e.g., >500 or >1000 times) and may be positioned outside of the see-through region of the waveguide-based near-eye display. The second output grating may be recorded with fewer exposures (e.g., <100 or <50 times) and may be positioned in the see-through region of the waveguide-based near-eye display. Thus, the display haze in the see-through region may be significantly reduced. However, because of the spatial separation of the two output gratings, the overall size of the waveguide-based near-eye display can be very large.
• The grating couplers described above may include transmissive VBGs or reflective VBGs, which may have some similar and some different characteristics. For example, as described above, the full-width-half-magnitude (FWHM) wavelength range and the FWHM angular range of a transmissive or reflective volume Bragg grating near the Bragg condition may be inversely proportional to thickness D of the transmissive or reflective volume Bragg grating. The maximum diffraction efficiency at the Bragg condition for a transmissive VBG may be a function of sin²(α×Δn×D), where α is a coefficient and Δn is the refractive index modulation, while the maximum diffraction efficiency at the Bragg condition for a reflective VBG may be a function of tan h²(α×Δn×D). In addition, the parameters (e.g., the grating tilt angles) of the transmissive and reflective volume Bragg gratings may be different in order to couple the display light into the waveguide at certain angles such that the coupled display light can be guided by the waveguide through TIR. Because of the different grating parameters, the dispersion characteristics of transmissive gratings and reflective gratings may be different.
• FIG. 13A illustrates an example of a reflective volume Bragg grating1300 in a waveguide display according to certain embodiments. The grating tilt angle α ofreflective VBG1300 may need to be within a certain range to reflectively diffract the display light. If the grating tilt angle α ofreflective VBG1300 is greater than a certain value,reflective VBG1300 may become a transmissive VBG, the distance between two consecutive locations where the display light may reach the grating may be too large (and thus the exit pupil may be sparsely replicated in the eyebox), or the display light may become evanescent. In one example, the grating tilt angle α ofreflective VBG1300 may be about 30°.
• FIG. 13B illustrates an example of areflective VBG1310 in a waveguide display where light diffracted by the reflective VBG is not totally reflected and guided in the waveguide. The grating tilt angle α ofreflective VBG1310 shown inFIG. 13B may be less than a certain value. As such, light coupled into the waveguide may be incident on the surface of the waveguide at an incident angle less than the critical angle, and thus may not be totally reflected and guided in the waveguide. The grating tilt angle α ofreflective VBG1310 may be less than about 30°. Thus, the grating tilt angle α of a reflective VBG may need to be within a certain range to reflectively diffract the display light into the waveguide such that the diffracted light may be guided by the waveguide through total internal reflection.
• FIG. 13C illustrates an example of a transmissive volume Bragg grating1350 in a waveguide display according to certain embodiments. The grating tilt angle α oftransmissive VBG1350 may also need to be within a certain range. For example, if the grating tilt angle α oftransmissive VBG1350 is lower than a certain value,transmissive VBG1350 may become a reflective VBG, the distance between two consecutive locations where the display light may reach the grating may be too large (and thus the exit pupil may be sparsely replicated in the eyebox), or the display light may become evanescent.
• FIG. 13D illustrates an example of atransmissive VBG1360 in a waveguide display where light diffracted by the transmissive VBG is not totally reflected and guided in the waveguide. The grating tilt angle α oftransmissive VBG1360 may be greater than a certain value, such as greater than about 60°. As such, light coupled into the waveguide may be incident on the surface of the waveguide at an incident angle less than the critical angle, and thus may not be totally reflected and guided in the waveguide. Thus, the grating tilt angle α of a transmissive VBG may need to be within a certain range to transmissively diffract the display light into the waveguide such that the diffracted light may be guided by the waveguide through total internal reflection.FIGS. 13A-13D show that the grating tilt angle α may be smaller for reflective gratings than for transmissive gratings.
• FIG. 14A illustrates the light dispersion by an example of a reflective volume Bragg grating1400 in a waveguide display according to certain embodiments.Reflective VBG1400 may be characterized by a grating vector k_g, a thickness d, and an average refractive index n. The surface normal direction ofreflective VBG1400 is N. The amount of light dispersion byreflective VBG1400 may be determined by:
• $\mathrm{\Delta \theta }=\frac{{\mathrm{<figure-callout\; label="\lambda "\; filenames="US20210055551A1-20210225-D00007.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0k_g\times N}{n\times dk_g·k_{\mathrm{out}}},$
• where λ₀is the wavelength of the light that perfectly meets the Bragg condition, and k_outis the wave vector of the light diffracted byreflective VBG1400. When the grating tilt angle α ofreflective VBG1400 is about 30°, the amount of light dispersion byreflective VBG1400 may be approximately:
• $\mathrm{\Delta \theta }\propto \frac{\sin 30°}{d\times \cos 30°}=\frac{0.58}{d}.$
• Thus, to achieve an angular resolution about 2 arcminutes, the thickness d ofreflective VBG1400 may be at least about 0.5 mm.
• FIG. 14B illustrates the light dispersion by an example of a transmissive volume Bragg grating1450 in a waveguide display according to certain embodiments.Transmissive VBG1450 may similarly be characterized by a grating vector k_g, a thickness d, and an average refractive index n. The surface normal direction oftransmissive VBG1450 is N. The amount of light dispersion bytransmissive VBG1450 may be determined by:
• $\mathrm{\Delta \theta }=\frac{{\mathrm{<figure-callout\; label="\lambda "\; filenames="US20210055551A1-20210225-D00007.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0k_g\times N}{n\times dk_g·k_{\mathrm{out}}},$
• where λ₀is the wavelength of the light that perfectly meets the Bragg condition, and k_outis the wave vector of the light diffracted bytransmissive VBG1450. When the grating tilt angle α oftransmissive VBG1450 is about 60°, the amount of light dispersion bytransmissive VBG1450 may be approximately:
• $\mathrm{\Delta \theta }\propto \frac{\sin 60°}{d\times \cos 60°}=\frac{1.73}{d}.$
• Thus, to achieve an angular resolution about 2 arcminutes, the thickness d oftransmissive VBG1450 may be at least about 1.5 mm, which is about three times of the thickness of a reflective VBG with the same angular resolution and may be difficult to achieve or may cause significant display haze.
• In order to reduce the thickness of the VBGs and display haze and achieve the desired resolution, dispersion compensation may be desired in a VBG-based waveguide display. According to certain embodiments, one or more pairs of gratings having matching grating vectors and operating in opposite diffraction conditions (e.g., +1 order diffraction versus −1 order diffraction) may be used to compensate for the dispersion caused by each other.
• FIGS. 15A-15B illustrates front and side views of an example of a volume Bragg grating-basedwaveguide display1500 with exit pupil expansion and dispersion reduction according to certain embodiments.Waveguide display1500 may be similar towaveguide display1000, and may include aninput coupler1520 at a different location compared withinput coupler1020.Waveguide display1500 may include asubstrate1510, and afirst grating1530 and asecond grating1540 onsubstrate1510. Asinput coupler1020,input coupler1520 may include projector optics1522 (e.g., a lens) and aprism1524. Display light may be coupled intosubstrate1510 byinput coupler1520 and may be guided bysubstrate1510. The display light may reach afirst portion1532 offirst grating1530 and may be diffracted byfirst portion1532 offirst grating1530 to change the propagation direction and reach other portions offirst grating1530, which may each diffract the display light towardssecond grating1540.Second grating1540 may diffract the display light out ofsubstrate1510 at different locations to form multiple exit pupils as described above.
• First portion1532 and each of other portions offirst grating1530 may have matching grating vectors (e.g., having a same grating vector in the x-y plane and having a same grating vector, opposite grating vectors, or both the same and opposite grating vectors in the z direction, but recorded in different exposure durations to achieve different diffraction efficiencies). Therefore, they may compensate for the dispersion of display light caused by each other to reduce the overall dispersion, due to the opposite Bragg conditions (e.g., +1 order and −1 order diffractions) for the diffractions atfirst portion1532 and each of other portions offirst grating1530. Therefore, the overall dispersion of the display light bywaveguide display1500 may be reduced in at least one direction.
• FIG. 16A is a front view of an example of a volume Bragg grating-basedwaveguide display1600 with exit pupil expansion and dispersion reduction according to certain embodiments.FIG. 16B is a side view of the example of volume Bragg grating-basedwaveguide display1600 with exit pupil expansion and dispersion reduction according to certain embodiments.Waveguide display1600 may be similar towaveguide display1500, but may include an input coupler that is different frominput coupler1520.Waveguide display1600 may include asubstrate1610 and afirst grating1630 and asecond grating1640 onsubstrate1610. The input coupler may include projector optics1620 (e.g., a lens) and a input grating1622, rather than a prism. Display light may be collimated byprojector optics1620 and projected onto input grating1622, which may couple the display light intosubstrate1610 by diffraction as described above with respect to, for example,FIGS. 5 and 6. The display light may reach afirst portion1632 offirst grating1630 and may be diffracted byfirst portion1632 offirst grating1630 to change the propagation direction and reach other portions offirst grating1630, which may each diffract the display light towardssecond grating1640.Second grating1640 may diffract the display light out ofsubstrate1610 at different locations to form multiple exit pupils as described above.
• First portion1632 and each of other portions offirst grating1630 may have matching grating vectors (e.g., having a same grating vector in the x-y plane and a same grating vector and/or opposite grating vectors in the z direction, but recorded in different exposure durations to achieve different diffraction efficiencies). Therefore, they may compensate for the dispersion of display light caused by each other to reduce the overall dispersion in one direction, due to the opposite Bragg conditions (e.g., +1 order and −1 order diffractions) for the diffractions atfirst portion1632 and each of other portions offirst grating1630. In addition, input grating1622 andsecond grating1640 may have matching grating vectors (e.g., having the same grating vector in the x-y plane and having the same or opposite grating vectors in the z direction, but recorded in different exposure durations to achieve different diffraction efficiencies), where input grating1622 may couple the display light intosubstrate1610, whilesecond grating1640 may couple the display light out of the waveguide. Therefore, input grating1622 andsecond grating1640 may compensate for the dispersion of display light caused by each other to reduce the overall dispersion in at least one direction, due to the opposite diffraction directions and opposite Bragg conditions (e.g., +1 order and −1 order diffractions) for the diffractions at input grating1622 andsecond grating1640. In this way, the dispersion byfirst portion1632 and each of other portions offirst grating1630 may be canceled out, and the dispersion by input grating1622 andsecond grating1640 may also be canceled out. Therefore, the overall dispersion of the display light bywaveguide display1600 can be minimized in any direction. As such, a higher resolution of the displayed image may be achieved.
• Thus, thinner reflective or transmissive VBGs may be used as the input and output couplers and may still achieve the desired resolution. Transmissive VBGs may also allow the first and second gratings to be at least partially overlapped to reduce the physical dimensions of the waveguide display as described in detail below.
• FIG. 17A illustrates the propagation of light from different fields of view in a reflective volume Bragg grating-basedwaveguide display1700 according to certain embodiments.Waveguide display1700 may include areflective VBG1710. Due to the grating tilt angle and thus the grating vector ofreflective VBG1710, light from a positive field of view (shown by a line1722) may have a smaller incident angle on fringes ofreflective VBG1710 and also a smaller incident angle on thetop surface1702 ofwaveguide display1700. On the other hand, light from a negative field of view (shown by a line1724) may have a larger incident angle on the fringes ofreflective VBG1710 and also a larger incident angle ontop surface1702 ofwaveguide display1700.
• FIG. 17B illustrates the propagation of light from different fields of view in a transmissive volume Bragg grating-basedwaveguide display1750 according to certain embodiments.Waveguide display1750 may include atransmissive VBG1760. Due to the grating tilt angle differences,transmissive VBG1760 may diffract light from different fields of view in different manners compared withreflective VBG1710. For example, as illustrated, light from a positive field of view (shown by a line1772) may have a smaller incident angle on fringes oftransmissive VBG1760 but a larger incident angle on the bottom surface1752 ofwaveguide display1750. On the other hand, light from a negative field of view (shown by a line1774) may have a larger incident angle on the fringes oftransmissive VBG1760 but a smaller incident angle on the bottom surface1752 ofwaveguide display1750. The manner of diffraction of light from different fields of view by a grating may affect the form factor of the waveguide display.
• FIG. 18 illustrates an example of a reflective volume Bragg grating-basedwaveguide display1800 with exit pupil expansion and dispersion reduction according to certain embodiments.Waveguide display1800 may include atop grating1805 and abottom grating1815. In the illustrated example,top grating1805 may be a reflective VBG, and bottom grating1815 may also be a reflective grating. Onbottom grating1815, anexit region1850 represents the region where display light for the full FOV at one pupil location in the eyebox (e.g., at the center the eyebox) may be coupled out of the bottom grating. As shown inFIG. 18, the top FOV ofexit region1850 represented by a line between a topright corner1822 and a topleft corner1824 may map to acurve1830 ontop grating1805, where topright corner1822 and topleft corner1824 ofexit region1850 may map to alocation1832 and alocation1834 ontop grating1805, respectively. The bottom FOV ofexit region1850 represented by a line between a bottomright corner1842 and a bottomleft corner1844 may map to acurve1810 ontop grating1805, where bottomright corner1842 and bottomleft corner1844 ofexit region1850 may map to alocation1812 and alocation1814 ontop grating1805, respectively. Thus, ifcurve1830 is below the line between topright corner1822 and topleft corner1824 ofexit region1850, there may be some FOV clipping. As such, to preserve the full FOV,curve1830 may be above the line between topright corner1822 and topleft corner1824 ofexit region1850. Therefore, the size ofwaveguide display1800 may be large.
• FIG. 19 illustrates an example of a transmissive volume Bragg grating-basedwaveguide display1900 with exit pupil expansion and form-factor reduction according to certain embodiments.Waveguide display1900 may include atop grating1905 and abottom grating1915. In the illustrated example,top grating1905 may be a reflective VBG, and bottom grating1915 may be a transmission grating. Onbottom grating1915, anexit region1950 represents the region where display light for the full FOV at one pupil location in the eyebox (e.g., at the center the eyebox) may be coupled out of the bottom grating. As shown inFIG. 19, the top FOV ofexit region1950 represented by a line between a topright corner1922 and a topleft corner1924 may map to acurve1910 ontop grating1905, where topright corner1922 and topleft corner1924 ofexit region1950 may map to alocation1912 and alocation1914 ontop grating1905, respectively. The bottom FOV ofexit region1950 represented by a line between a bottomright corner1942 and a bottomleft corner1944 may map to acurve1930 ontop grating1905, where bottomright corner1942 and bottomleft corner1944 ofexit region1950 may map to alocation1932 and alocation1934 ontop grating1905, respectively. Thus, there can be some overlap betweentop grating1905 and bottom grating1915 to reduce the overall size ofwaveguide display1900. For example,location1932 may be lower than topright corner1922 and can still be mapped to bottomright corner1942.
• FIG. 20 illustrates another example of a transmissive volume Bragg grating-basedwaveguide display2000 with animage projector2030 according to certain embodiments.Waveguide display2000 may include atop grating2005 and abottom grating2015.Top grating2005 may include a reflective VBG, and bottom grating2015 may include a transmissive VBG. The exit region onbottom grating2015 supporting the desired field of view ofwaveguide display2000 at one pupil location in the eyebox (e.g., in the center of the eyebox) is represented by anoctagon2020. Ashape2010 represents the mapping of the FOV shown byoctagon2020 to the region ontop grating2005. As described above with respect toFIG. 19, becausebottom grating2015 is a transmission grating,top grating2005 and bottom grating2015 may at least partially overlap to reduce the physical size ofwaveguide display2000.
• FIG. 21 illustrates an example of a volume Bragg grating-basedwaveguide display2100 with exit pupil expansion, dispersion reduction, and form-factor reduction according to certain embodiments.Waveguide display2100 may include asubstrate2110, which may be similar tosubstrate1610 but may be much smaller thansubstrate1610.Substrate2110 may include afirst surface2112 and asecond surface2114. Display light from a light source (e.g., LEDs) may be coupled intosubstrate2110 by aninput coupler2120, and may be reflected byfirst surface2112 andsecond surface2114 through total internal reflection, such that the display light may propagate withinsubstrate2110.Input coupler2120 may include a diffractive coupler (e.g., a volume holographic grating) and may couple display light of different colors intosubstrate2110 at different diffraction angles.
• Aswaveguide display1600,waveguide display2100 may also include afirst grating2130 and asecond grating2140 formed onfirst surface2112 and/orsecond surface2114. For example,first grating2130 andsecond grating2140 may be formed on a same surface or two different surface ofsubstrate2110.Second grating2140 may be formed in the see-through region of the waveguide display and may overlap with aneyebox2150 when viewed in the z direction (e.g., at a distance about 18 mm fromsecond grating2140 in +z or −z direction). First grating2130 andsecond grating2140 may be used for dual-axis pupil expansion to expand the incident display light beam in two dimensions to filleyebox2150 with the display light. First grating2130 may be a transmission grating or a reflection grating.Second grating2140 may include a transmission grating to at least partially overlap withfirst grating2130 and reduce the form factor ofwaveguide display2100 as described below.
• In addition,waveguide display2100 may also include athird grating2160 formed onfirst surface2112 orsecond surface2114. In some embodiments,third grating2160 andfirst grating2130 may be on a same surface ofsubstrate2110. In some embodiments,third grating2160 andfirst grating2130 may be in different regions of a same grating or a same grating material layer as shown inFIG. 16. In some embodiments,third grating2160 may be spatially separate fromfirst grating2130. In some embodiments,third grating2160 andfirst grating2130 may be recorded in a same number of exposures and under similar recording conditions (but may be recorded for different exposure durations to achieve different diffraction efficiencies), such that each VBG inthird grating2160 may match a respective VBG in first grating2130 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction). For example, in some embodiments, a VBG inthird grating2160 and a corresponding VBG infirst grating2130 may have the same grating period and the same grating slant angle (and thus the same grating vector), and the same thickness. In one embodiment,third grating2160 andfirst grating2130 may have a thickness about 20 μm and may each include about 40 or more VBGs recorded through about 40 or more exposures. In some embodiments,second grating2140 may have a thickness about 20 μm or higher, and may include about 50 or more VBGs recorded through about 50 or more exposures.
• Input coupler2120 may couple the display light from the light source intosubstrate2110. The display light may reachthird grating2160 directly or may be reflected byfirst surface2112 and/orsecond surface2114 tothird grating2160, where the size of the display light beam may be slightly larger than that atinput coupler2120. Each VBG inthird grating2160 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG tofirst grating2130. While the display light diffracted by a VBG inthird grating2160 propagates within substrate2110 (e.g., along a direction shown by a line2132) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2130 tosecond grating2140 each time the display light propagating withinsubstrate2110 reaches first grating2130.Second grating2140 may then expand the display light fromfirst grating2130 in a different direction by diffracting a portion of the display light toeyebox2150 each time the display light propagating withinsubstrate2110 reachessecond grating2140.
• Becausethird grating2160 andfirst grating2130 may be thin (e.g., about 20 μm), they may cause some dispersion, but the dispersion may not be as high as the dispersion of a grating having a thickness of, for example, 1 μm or thinner. Therefore, the fields of view for different colors may not be significantly affected by the dispersion. In addition, as described above, each VBG in third grating2160 matches a respective VBG in first grating2130 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vector in the z direction), and the two matching VBGs work under opposite Bragg conditions (e.g., +1 order diffraction versus −1 order diffraction) due to the opposite propagation directions of the display light at the two matching VBGs. For example, as shown inFIG. 21, the VBG inthird grating2160 may change the propagation direction of the display light from a downward direction to a rightward direction, while the VBG infirst grating2130 may change the propagation direction of the display light from a rightward direction to a downward direction. Thus, the dispersion caused byfirst grating2130 may be opposite to the dispersion caused bythird grating2160 to reduce or minimize the overall dispersion.
• Becausefirst grating2130 andsecond grating2140 may only have a small number (e.g., no greater than 50) of VBGs and exposures,first grating2130 may also be placed in the see-through region to overlap withsecond grating2140, thus reducing the size of the waveguide display. The total number of VBGs and exposures in a given see-through region may be less than, for example, 100 or fewer (e.g., no more than about 40 infirst grating2130 and no more than 50 in second grating2140). Thus, the display haze may be reduced significantly compared with the case where 500 or more VBGs are recorded in the see-through region.
• In some embodiments, because of the fewer exposures (e.g., smaller number of gratings in a multiplexed grating), the multiplexed grating may not be able to cover the full visible light spectrum and/or the full FOV, and thus some light information (in some spectral or FOV ranges) may be lost. According to certain embodiments, in order to improve the power efficiency and to cover a broader spectrum, additional gratings may be added at different spatial locations, such as different x, y, or z locations, to spatially multiplex the gratings. In this way, light in a broader bandwidth may be diffracted at a higher diffraction efficiency by the combination of the gratings to the eyebox. This may also help to increase the pupil replication density and make the light more uniform in the eyebox.
• FIG. 22A illustrates another example of a volume Bragg grating-basedwaveguide display2200 with exit pupil expansion, dispersion reduction, form-factor reduction, and power efficiency improvement according to certain embodiments. Aswaveguide display2100,waveguide display2200 may include asubstrate2210, which may be similar tosubstrate2110.Substrate2210 may include afirst surface2212 and asecond surface2214. Display light from a light source (e.g., LEDs) may be coupled intosubstrate2210 by aninput coupler2220, and may be reflected byfirst surface2212 andsecond surface2214 through total internal reflection, such that the display light may propagate withinsubstrate2210. As described above,input coupler2220 may include a diffractive coupler, such as a VBG, which may couple display light of different colors intosubstrate2210 at different diffraction angles.
• Aswaveguide display2100,waveguide display2200 may include afirst grating2230 and asecond grating2240 formed onfirst surface2212 and/orsecond surface2214.Waveguide display2200 may also include athird grating2260 and afourth grating2270 formed onfirst surface2212 and/orsecond surface2214.Third grating2260 andfourth grating2270 may each be a multiplexed VBG that includes multiple VBGs. In some embodiments,third grating2260,fourth grating2270, andfirst grating2230 may be on a same surface ofsubstrate2210. In some embodiments,third grating2260,fourth grating2270, andfirst grating2230 may be in different regions of a same grating or a same grating material layer.
• In some embodiments,first grating2230,third grating2260, andfourth grating2270 may each include multiple VBGs.Third grating2260 andfirst grating2230 may be recorded in multiple exposures and under similar recording conditions (but may be recorded for different exposure durations to achieve different diffraction efficiencies), such that each VBG inthird grating2260 may match a respective VBG in first grating2230 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction). For example, in some embodiments, a VBG inthird grating2260 and a corresponding VBG infirst grating2230 may have the same grating period and the same grating slant angle (and thus the same grating vector), and the same thickness.Fourth grating2270 andfirst grating2230 may also be recorded in multiple exposures and under similar recording conditions (but for different exposure durations), such that each VBG infourth grating2270 may match a respective VBG in first grating2230 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction). In some embodiments, the recording conditions for recordingthird grating2260 may be different from the recording conditions for recordingfourth grating2270, such thatthird grating2260 andfourth grating2270 may have different Bragg conditions (and different grating vectors) and thus may diffract light from different FOV ranges and/or wavelength ranges to improve the overall diffraction efficiency for visible light in a large FOV range. In some embodiments,third grating2260 andfourth grating2270 may have similar grating vectors and thus may diffract light from the same FOV ranges and/or wavelength ranges with similar or different diffraction efficiencies to improve the overall diffraction efficiency for light in certain FOV ranges and/or wavelength ranges.
• In some embodiments, M VBGs infirst grating2230 that match the M VBGs inthird grating2260 may be recorded in one area (e.g., an upper region) offirst grating2230, while the other M VBGs infirst grating2230 that match the M VBGs infourth grating2270 may be recorded in a different area (e.g., a lower region) offirst grating2230. In one example,third grating2260 andfourth grating2270 may each have a thickness about 20 μm and may each include about 20 VBGs recorded through about 20 exposures. In the example,first grating2230 may have a thickness about 20 μm and may include about 40 VBGs recorded at different regions through about 40 exposures.Second grating2240 may have a thickness about 20 μm or higher, and may include about 50 VBGs recorded through about 50 exposures.
• Input coupler2220 may couple the display light from the light source intosubstrate2210. The display light may reachthird grating2260 directly or may be reflected byfirst surface2212 and/orsecond surface2214 tothird grating2260, where the size of the display light beam may be slightly larger than that atinput coupler2220. Each VBG inthird grating2260 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG to an upper region offirst grating2230. As described above, the upper region offirst grating2230 may include VBGs that match the VBGs inthird grating2260. Therefore, while the display light diffracted by a VBG inthird grating2260 propagates within substrate2210 (e.g., along a direction shown by a line2232) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2230 tosecond grating2240 each time the display light propagating withinsubstrate2210 reaches first grating2230.
• Display light that is not diffracted by third grating2260 (e.g., due to a less than 100% diffraction efficiency or due to a small FOV range and/or wavelength range near the Bragg condition) may continue to propagate withinsubstrate2210, and may reachfourth grating2270. Each VBG infourth grating2270 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG to a lower region offirst grating2230. As described above, the lower region offirst grating2230 may include VBGs that match the VBGS infourth grating2270. Therefore, while the display light diffracted by a VBG infourth grating2270 propagates within substrate2210 (e.g., along a direction shown by a line2234) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2230 tosecond grating2240 each time the display light propagating withinsubstrate2210 reaches first grating2230.Second grating2240 may expand the display light fromfirst grating2230 in a different direction (e.g., in approximately the y direction) by diffracting a portion of the display light to an eyebox2250 (e.g., at a distance about 18 mm fromsecond grating2240 in +z or −z direction) each time the display light propagating withinsubstrate2210 reachessecond grating2240. In this way, the display light may be expanded in two dimensions to filleyebox2250.
• FIG. 22B illustrates examples of replicated exit pupils at an eyebox2280 (e.g., eyebox2250) of volume Bragg grating-basedwaveguide display2200. The exit pupils may include a first set ofexit pupils2282 replicated bygratings2260,2230, and2240, and a second set ofexit pupils2284 replicated bygratings2270,2230, and2240. In embodiments wheregratings2260 andgratings2270 have different grating vectors, the first set ofexit pupils2282 and the second set ofexit pupils2284 may correspond to different FOV ranges and/or different wavelength ranges. In embodiments wheregratings2260 andgratings2270 have similar grating vectors, the first set ofexit pupils2282 and the second set ofexit pupils2284 may correspond to a same FOV range and/or wavelength range. The first set ofexit pupils2282 and the second set ofexit pupils2284 may overlap or partially overlap. Thus, the pupil replication density may be increased, and the light may be more uniform in the eyebox, due to the diffraction of display light by two spatially multiplexed sets of VBGs.
• In addition, the dispersion may be reduced in the two dimensions due to the dual diffraction in each dimension by a pair of matching gratings that operate under opposite Bragg conditions as described above. Furthermore, display light in a broader bandwidth may be diffracted at a higher diffraction efficiency by the gratings to the eyebox because of the lower number of exposures (and thus a higher refractive index modulation Δn for each VBG). Thus, the power efficiency of the waveguide display may be improved. In some embodiments,first grating2230 andsecond grating2240 may at least partially overlap to reduce the form factor ofwaveguide display2200 as described above.
• FIG. 23 illustrates another example of a volume Bragg grating-basedwaveguide display2300 with exit pupil expansion, dispersion reduction, and form-factor reduction according to certain embodiments. Aswaveguide display2100,waveguide display2300 may include asubstrate2310, which may be similar tosubstrate2110.Substrate2310 may include afirst surface2312 and asecond surface2314. Display light from a light source (e.g., LEDs) may be coupled intosubstrate2310 by aninput coupler2320, and may be reflected byfirst surface2312 andsecond surface2314 through total internal reflection, such that the display light may propagate withinsubstrate2310. As described above,input coupler2320 may include a diffractive coupler, such as a VBG.Waveguide display2300 may also include afirst grating2330 and asecond grating2340 formed onfirst surface2312 and/orsecond surface2314. In the example shown inFIG. 23,first grating2330 andsecond grating2340 may be at different locations in the x direction, and may overlap in at least a portion of the see-through region ofwaveguide display2300. First grating2330 andsecond grating2340 may be used for dual-axis pupil expansion to expand the incident display light beam in two dimensions to fill an eyebox2350 (e.g., at a distance about 18 mm fromsecond grating2340 in +z or −z direction) with the display light. For example,first grating2330 may expand the display light beam in approximately the y direction, whilesecond grating2340 may expand the display light beam in approximately the x direction.
• In addition,waveguide display2300 may include athird grating2360 formed onfirst surface2312 and/orsecond surface2314. In some embodiments,third grating2360 andfirst grating2330 may be arranged at different locations in the y direction on a same surface ofsubstrate2310. In some embodiments,third grating2360 andfirst grating2330 may be in different regions of a same grating or a same grating material layer. In some embodiments,third grating2360 may be spatially separate fromfirst grating2330. In some embodiments,third grating2360 andfirst grating2330 may be recorded in a same number of exposures and under similar recording conditions (but may be recorded for different exposure durations to achieve different diffraction efficiencies), such that each VBG inthird grating2360 may match a respective VBG in first grating2330 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction).
• Input coupler2320 may couple the display light from the light source intosubstrate2310. The display light may propagate approximately along the x direction withinsubstrate2310, and may reachthird grating2360 directly or may be reflected byfirst surface2312 and/orsecond surface2314 tothird grating2360. Each VBG inthird grating2360 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG downward tofirst grating2330. While the display light diffracted by a VBG inthird grating2360 propagates withinsubstrate2310 along a direction (e.g., approximately in the y direction shown by a line2332) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2330 tosecond grating2340 each time the display light propagating withinsubstrate2310 reaches first grating2330.Second grating2340 may then expand the display light fromfirst grating2330 in a different direction (e.g., approximately in the x direction) by diffracting a portion of the display light toeyebox2350 each time the display light propagating withinsubstrate2310 reachessecond grating2340.Input coupler2320 andsecond grating2340 may include matching VBGs (e.g., VBGs with same grating vectors in the x-y plane and the same or opposite grating vectors in the z direction) to reduce the overall dispersion caused byinput coupler2320 andsecond grating2340. Similarly,gratings2330 and2360 may include matching VBGs (e.g., VBGs with same grating vectors in the x-y plane and having the same and/or opposite grating vectors in the z direction) to reduce the overall dispersion caused bygratings2330 and2360. Thus, the overall dispersion by the gratings inwaveguide display2300 may be reduced or minimized.
• Each offirst grating2330 andsecond grating2340 may have a thickness less than, for example, 100 μm (e.g., 20 μm), and may include, for example, fewer than 50 VBGs. Thus, any area in the optical see-through region ofwaveguide display2300 may include fewer than 100 VBGs. As such, the display haze may not be significant. In addition,first grating2330 andsecond grating2340 may at least partially overlap to reduce the form factor ofwaveguide display2300, and thus the physical dimensions ofwaveguide display2300 may be similar to the physical dimensions of a lens in a regular pair of eye glasses.
• FIG. 23B illustrates an example of a volume Bragg grating-basedwaveguide display2305 with exit pupil expansion, dispersion reduction, form-factor reduction, and power efficiency improvement according to certain embodiments. Aswaveguide display2300,waveguide display2305 may include afirst grating2335, asecond grating2345, a third grating2365, and afourth grating2375 formed on afirst surface2316 and/or asecond surface2318 of asubstrate2315. First grating2335, asecond grating2345, third grating2365, andfourth grating2375 may each include a multiplexed VBG that includes multiple VBGs. In some embodiments, third grating2365,fourth grating2375, andfirst grating2335 may be on a same surface ofsubstrate2315. In some embodiments, third grating2365,fourth grating2375, andfirst grating2335 may be in different regions of a same grating or a same grating material layer.
• Each VBG in third grating2365 may have a grating vector matching a grating vector of a respective VBG in first grating2335 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction), and each VBG infourth grating2375 may have a grating vector matching a grating vector of a respective VBG in fourth grating2335 (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction). In some embodiments, third grating2365 andfourth grating2375 may have different grating vectors and thus may diffract light from different FOV ranges and/or wavelength ranges to improve the overall diffraction efficiency for visible light in a large FOV range. In some embodiments, third grating2365 andfourth grating2375 may have similar grating vectors and thus may diffract light from the same FOV ranges and/or wavelength ranges with similar or different diffraction efficiencies to improve the overall diffraction efficiency for light in certain FOV ranges and/or wavelength ranges.
• Input coupler2325 may couple the display light from the light source intosubstrate2315. The display light may reach third grating2365 directly or may be reflected byfirst surface2316 and/orsecond surface2318 to third grating2365. Each VBG in third grating2365 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG to a left region offirst grating2335. While the display light diffracted by a VBG in third grating2365 propagates within substrate2315 (e.g., along a direction shown by a line2336) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2335 tosecond grating2345 each time the display light propagating withinsubstrate2315 reaches first grating2335.
• Display light that is not diffracted by third grating2365 (e.g., due to a less than 100% diffraction efficiency or due to a small FOV range and/or wavelength range near the Bragg condition) may continue to propagate withinsubstrate2315, and may reachfourth grating2375. Each VBG infourth grating2375 may diffract a portion of the display light within a FOV range and a wavelength range that approximately satisfies the Bragg condition of the VBG to a right region offirst grating2335. While the display light diffracted by a VBG infourth grating2375 propagates within substrate2315 (e.g., along a direction shown by a line2338) through total internal reflection, a portion of the display light may be diffracted by the corresponding VBG infirst grating2335 tosecond grating2345 each time the display light propagating withinsubstrate2315 reaches first grating2335.
• Second grating2345 may expand the display light fromfirst grating2335 in a different direction (e.g., in approximately the y direction) by diffracting a portion of the display light to an eyebox2355 (e.g., at a distance about 18 mm fromsecond grating2345 in +z or −z direction) each time the display light propagating withinsubstrate2315 reachessecond grating2345. In this way, the display light may be expanded in two dimensions to filleyebox2355. The resultant exit pupils may include a first set of exit pupils replicated bygratings2365,2335, and2345, and a second set of exit pupils replicated bygratings2375,2335, and2345. In embodiments where gratings2365 andgratings2375 have different grating vectors, the first set of exit pupils and the second set of exit pupils may correspond to different FOV ranges and/or different wavelength ranges. In embodiments where gratings2365 andgratings2375 have similar grating vectors, the first set of exit pupils and the second set of exit pupils may correspond to a same FOV range and/or wavelength range. The first set of exit pupils and the second set of exit pupils may overlap or partially overlap. Thus, the pupil replication density may be increased, and the light may be more uniform in the eyebox, due to the diffraction of display light by two spatially multiplexed sets of VBGs.
• FIG. 24A is a front view of an example of a volume Bragg grating-basedwaveguide display2400 including animage projector2420 and multiple polymer layers according to certain embodiments.FIG. 24B is a side view of the example of volume Bragg grating-basedwaveguide display2400 includingimage projector2420 according to certain embodiments.Waveguide display2400 may be similar towaveguide display1600, but may include multiple polymer layers on one or more waveguide plates, where the input grating (e.g., input grating1622), top grating (e.g., first grating1630), and bottom grating (e.g., second grating1640) may each be split into multiple gratings recorded in the multiple polymer layers, where the gratings on each polymer layer may cover different respective FOVs and light spectra, and the combination of the multiple polymer layers may provide the full FOV and spectral coverage. In this way, each polymer layer can be thin (e.g., about 20 μm to about 100 μm) and can be exposed for fewer times (e.g., less than about 100) to record fewer gratings to reduce haziness, and the overall efficiency of the multiple polymer layers can still be high for the full FOV and spectrum.
• In the example shown inFIGS. 24A and 24B,waveguide display2400 may include afirst polymer layer2412 and asecond polymer layer2414 on one or more plates or substrates. Eachpolymer layer2412 or2414 may include part of an input grating2422, atop grating2430, and abottom grating2440. Display light may be collimated and projected onto input grating2422 byimage projector2420.Input grating2422 may couple the display light into awaveguide2410 by diffraction as described above with respect to, for example,FIGS. 5 and 6. The display light may reach afirst portion2432 oftop grating2430 and may be diffracted by thefirst portion2432 oftop grating2430 to change the propagation direction and reach other portions oftop grating2430, which may each diffract the display light towards bottom grating2440. Bottom grating2440 may then diffract the display light out ofwaveguide2410 at different locations to form multiple exit pupils as described above.
• First portion2432 and each of other portions oftop grating2430 may have matching grating vectors (e.g., having the same grating vector in the x-y plane and having the same and/or opposite grating vectors in the z direction, but recorded in different exposure durations to achieve different diffraction efficiencies). Therefore, they may compensate for the dispersion of display light caused by each other to reduce the overall dispersion, due to the opposite Bragg conditions (e.g., +1 order and −1 order diffractions) for the diffractions atfirst portion2432 and each of other portions oftop grating2430. In addition, input grating2422 and bottom grating2440 may have matching grating vectors (e.g., having the same grating vector in the x-y plane and having the same or opposite grating vectors in the z direction, but recorded in different exposure durations to achieve different diffraction efficiencies), where input grating2422 may couple the display light intowaveguide2410, whilebottom grating2440 may couple the display light out ofwaveguide2410. Therefore, input grating2422 and bottom grating2440 may compensate for the dispersion of display light caused by each other to reduce the overall dispersion, due to the opposite diffraction directions and opposite Bragg conditions (e.g., +1 order and −1 order diffractions) for the diffractions at input grating2422 andbottom grating2440. In this way, the dispersion byfirst portion2432 and each of other portions oftop grating2430 may be canceled out, and the dispersion by input grating2422 and bottom grating2440 may also be canceled out. Therefore, the overall dispersion of the display light bywaveguide display2400 can be minimized in any direction. As such, a higher resolution of the displayed image may be achieved even if thepolymer layers2412 and2414 are thin and transmissive VBGs are recorded in the thin polymer layers.
• FIG. 25 illustrates an example of a volume Bragg grating-basedwaveguide display2500 including multiple grating layers for different fields of view and/or light wavelengths according to certain embodiments. Inwaveguide display2500, gratings may be spatially multiplexed along the z direction. For example,waveguide display2500 may include multiple substrates, such assubstrates2510,2512,2514, and the like. The substrates may include a same material or materials having similar refractive indexes. One or more VBGs (e.g.,VBGs2520,2522,2524, etc.) may be made on each substrate, such as recorded in a holographic material layer formed on the substrate. The VBGs may be reflection gratings or transmission gratings. The substrates with the VBGs may be arranged in a substrate stack along the z direction for spatial multiplexing. Each VBG may be a multiplexed VBG that includes multiple gratings designed for different Bragg conditions to couple display light in different wavelength ranges and/or different FOVs into or out of the waveguide.
• In the example shown inFIG. 25,VBG2520 may couple light2534 from the positive field of view into the waveguide as shown by light2544 within the waveguide.VBG2522 may couple light2530 from around 0° field of view into the waveguide as shown by light2540 within the waveguide.VBG2524 may couple light2532 from the negative field of view into the waveguide as shown by light2542 within the waveguide. As described above, each ofVBGs2520,2522, and2524 may be a multiplexed VBG with many exposures, and thus may couple light from different FOV ranges into or out of the waveguide.
• In some embodiments, because the diffraction efficiency of a transmission grating may be polarization sensitive and the incoming display light may be unpolarized, some components of the display light may not be diffracted by the grating and thus the efficiency of the waveguide display may be reduced. To improve the efficiency for unpolarized light or light in a certain polarization state, a polarization convertor and two spatially multiplexed gratings may be used to couple the display light into or out of the waveguide.
• FIG. 26 illustrates an example of awaveguide display2600 including two multiplexedvolume Bragg gratings2610 and2640 and apolarization convertor2630 between the two multiplexedvolume Bragg gratings2610 and2640 according to certain embodiments. Afirst VBG2610 may be formed on asubstrate2620 or on a surface ofpolarization convertor2630. Asecond VBG2640 may be formed on asubstrate2650 or on another surface ofpolarization convertor2630.
• Unpolarized light2602 may include s-polarized light and p-polarized light.First VBG2610 may diffract a majority of the s-polarized light and a portion of the p-polarized light as shown by diffracted light2604. Diffracted light2604 may be partially converted bypolarization convertor2630 and pass throughsecond VBG2640 without being diffracted bysecond VBG2640 as shown by transmitted light2606 because the Bragg condition is not satisfied. Theportion2608 of the p-polarized light that is not diffracted byfirst VBG2610 may pass throughpolarization convertor2630 and may be converted into s-polarized light and may be diffracted bysecond VBG2640, where the diffracted light2612 may have the same propagation direction as transmitted light2606. In this way, unpolarized light2602 may be more efficiently diffracted bywaveguide display2600.
• External light (e.g., from an external light source, such as a lamp or the sun) may be reflected at a surface of a grating coupler and back to the grating coupler, where the reflected light may be diffracted by the grating coupler to generate rainbow images. In some waveguide display, ambient light with a large incident angle outside of the see-through field of view of the waveguide display may also be diffracted by the grating couplers to generate rainbow images. According to some embodiments, additional structures, such as a reflective coating layer (e.g., for light from a large see-through FOV) and/or an antireflective coating layer (e.g., for light from a small see-through FOV), may be used in the waveguide display to reduce optical artifacts, such as rainbow effects. For example, an angular-selective transmissive layer may be placed in front of (or behind) the waveguide and the grating coupler of a waveguide display to reduce the artifacts caused by external light source. The angular-selective transmissive layer may be configured to reflect, diffract, or absorb ambient light with an incident angle greater than one half of the see-through field of view of the waveguide display, while allowing ambient light within the see-through field of view of the near-eye display to pass through and reach user's eyes with little or no loss. The angular-selective transmissive layer may include, for example, coating that may include one or more dielectric layers, diffractive elements such as gratings (e.g., meta-gratings), nanostructures (e.g., nanowires, nano-pillars, nano-prisms, nano-pyramids), and the like.
• FIG. 27 illustrates an example of awaveguide display2700 including ananti-reflection layer2750 and an angular-selective transmissive layer2740 according to certain embodiments.Waveguide display2700 may include awaveguide2710 and agrating coupler2720 at the bottom surface ofwaveguide2710.Grating coupler2720 may be similar to the grating couplers described above. External light2730 incident onwaveguide2710 may be refracted intowaveguide2710 as external light2732 and may then be diffracted by gratingcoupler2720. The diffracted light may include a 0^thorder diffraction2734 (e.g., refractive diffraction) and a −1st order diffraction (not shown). The height, period, and/or slant angle ofgrating coupler2720 may be configured such that the −1st order diffraction may be reduced or minimized for the external light.
• Waveguide display2700 may includeanti-reflection layer2750 onbottom surface2722 of gratingcoupler2720.Anti-reflection layer2750 may include, for example, one or more dielectric thin film layers or other anti-reflection layers coated onbottom surface2722, and may be used to reduce the reflection of the external light atbottom surface2722. Thus, little or no external light may be reflected atbottom surface2722 of gratingcoupler2720 back to gratingcoupler2720, and therefore the rainbow ghost that might otherwise be formed due to the diffraction of external light reflected atbottom surface2722 by gratingcoupler2720 may be reduced or minimized. Some portions of the display light may be diffracted by gratingcoupler2720 and may be coupled out ofwaveguide2710 towards user's eyes (e.g., due to −1^storder diffraction).Anti-reflection layer2750 may also help to reduce the reflection of the portions of the display light that are coupled out ofwaveguide2710 by gratingcoupler2720.
• Angular-selective transmissive layer2740 may be coated on the top surface ofwaveguide2710 or gratingcoupler2720. Angular-selective transmissive layer2740 may have a high reflectivity, high diffraction efficiency, or high absorption for incident light with an incident angle greater than a certain threshold value, and may have a low loss for incident light with an incident angle lower than the threshold value. The threshold value may be determined based on the see-through field of view ofwaveguide display2700. For example, incident light2760 with an incident angle greater than the see-through field of view may be mostly reflected, diffracted, or absorbed by angular-selective transmissive layer2740, and thus may not reachwaveguide2710. External light2730 with an incident angle within the see-through field of view may mostly pass through angular-selective transmissive layer andwaveguide2710, and may be refracted or diffracted by gratingcoupler2720.
• The angular-selective transmissive layer2740 described above may be implemented in various ways. In some embodiments, the angular-selective transmissive layer may include one or more dielectric layers (or air gap). Each dielectric layer may have a respective refractive index, and adjacent dielectric layers may have different refractive indexes. In some embodiments, the angular-selective transmissive layer may include, for example, micro mirrors or prisms, grating, meta-gratings, nanowires, nano-pillars, or other micro- or nano-structures. In some examples, the angular-selective transmissive layer may include gratings (e.g., surface-relief gratings or holographic gratings) with small grating periods formed on a substrate. The gratings may only diffract light with large incidence angles (e.g., about 75° to about 90°) and the diffracted light may propagate in directions such that the diffracted light may not reach the eyebox. The grating period may be, for example, less than 300 nm (e.g., about 200 nm) such that the angular-selective transmissive layer may not affect light within the see-through field of view. In some examples, the angular-selective transmissive layer may include micro-scale or nano-scale anisotropic structures that may reflect, diffract, or absorb incident light with large incident angles. The anisotropic structures may include, for example, large-aspect-ratio nanoparticles aligned and immersed in transparent media, nanowire arrays, certain liquid crystal materials, and the like.
• Embodiments of the invention may be used to implement components of an artificial reality system or may 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 may include, for example, 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 may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may 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 may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, for example, create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various 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.
• FIG. 28 is a simplified block diagram of an exampleelectronic system2800 of an example near-eye display (e.g., HMD device) for implementing some of the examples disclosed herein.Electronic system2800 may be used as the electronic system of an HMD device or other near-eye displays described above. In this example,electronic system2800 may include one or more processor(s)2810 and amemory2820. Processor(s)2810 may be configured to execute instructions for performing operations at a number of components, and can be, for example, a general-purpose processor or microprocessor suitable for implementation within a portable electronic device. Processor(s)2810 may be communicatively coupled with a plurality of components withinelectronic system2800. To realize this communicative coupling, processor(s)2810 may communicate with the other illustrated components across a bus2840. Bus2840 may be any subsystem adapted to transfer data withinelectronic system2800. Bus2840 may include a plurality of computer buses and additional circuitry to transfer data.
• Memory2820 may be coupled to processor(s)2810. In some embodiments,memory2820 may offer both short-term and long-term storage and may be divided into several units.Memory2820 may be volatile, such as static random access memory (SRAM) and/or dynamic random access memory (DRAM) and/or non-volatile, such as read-only memory (ROM), flash memory, and the like. Furthermore,memory2820 may include removable storage devices, such as secure digital (SD) cards.Memory2820 may provide storage of computer-readable instructions, data structures, program modules, and other data forelectronic system2800. In some embodiments,memory2820 may be distributed into different hardware modules. A set of instructions and/or code might be stored onmemory2820. The instructions might take the form of executable code that may be executable byelectronic system2800, and/or might take the form of source and/or installable code, which, upon compilation and/or installation on electronic system2800 (e.g., using any of a variety of generally available compilers, installation programs, compression/decompression utilities, etc.), may take the form of executable code.
• In some embodiments,memory2820 may store a plurality ofapplication modules2822 through2824, which may include any number of applications. Examples of applications may include gaming applications, conferencing applications, video playback applications, or other suitable applications. The applications may include a depth sensing function or eye tracking function. Application modules2822-4924 may include particular instructions to be executed by processor(s)2810. In some embodiments, certain applications or parts of application modules2822-4924 may be executable byother hardware modules2880. In certain embodiments,memory2820 may additionally include secure memory, which may include additional security controls to prevent copying or other unauthorized access to secure information.
• In some embodiments,memory2820 may include anoperating system2825 loaded therein.Operating system2825 may be operable to initiate the execution of the instructions provided by application modules2822-4924 and/or manageother hardware modules2880 as well as interfaces with awireless communication subsystem2830 which may include one or more wireless transceivers.Operating system2825 may be adapted to perform other operations across the components ofelectronic system2800 including threading, resource management, data storage control and other similar functionality.
• Wireless communication subsystem2830 may include, for example, an infrared communication device, a wireless communication device and/or chipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fi device, a WiMax device, cellular communication facilities, etc.), and/or similar communication interfaces.Electronic system2800 may include one ormore antennas2834 for wireless communication as part ofwireless communication subsystem2830 or as a separate component coupled to any portion of the system. Depending on desired functionality,wireless communication subsystem2830 may include separate transceivers to communicate with base transceiver stations and other wireless devices and access points, which may include communicating with different data networks and/or network types, such as wireless wide-area networks (WWANs), wireless local area networks (WLANs), or wireless personal area networks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16) network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN may be, for example, a Bluetooth network, an IEEE 802.15x, or some other types of network. The techniques described herein may also be used for any combination of WWAN, WLAN, and/or WPAN.Wireless communications subsystem2830 may permit data to be exchanged with a network, other computer systems, and/or any other devices described herein.Wireless communication subsystem2830 may include a means for transmitting or receiving data, such as identifiers of HMD devices, position data, a geographic map, a heat map, photos, or videos, using antenna(s)2834 and wireless link(s)2832.Wireless communication subsystem2830, processor(s)2810, andmemory2820 may together comprise at least a part of one or more of a means for performing some functions disclosed herein.
• Embodiments ofelectronic system2800 may also include one ormore sensors2890. Sensor(s)2890 may include, for example, an image sensor, an accelerometer, a pressure sensor, a temperature sensor, a proximity sensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a module that combines an accelerometer and a gyroscope), an ambient light sensor, or any other similar module operable to provide sensory output and/or receive sensory input, such as a depth sensor or a position sensor. For example, in some implementations, sensor(s)2890 may include one or more inertial measurement units (IMUs) and/or one or more position sensors. An IMU may generate calibration data indicating an estimated position of the HMD device relative to an initial position of the HMD device, based on measurement signals received from one or more of the position sensors. A position sensor may generate one or more measurement signals in response to motion of the HMD device. Examples of the position sensors may include, but are not limited to, one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU, or some combination thereof. The position sensors may be located external to the IMU, internal to the IMU, or some combination thereof. At least some sensors may use a structured light pattern for sensing.
• Electronic system2800 may include adisplay module2860.Display module2860 may be a near-eye display, and may graphically present information, such as images, videos, and various instructions, fromelectronic system2800 to a user. Such information may be derived from one or more application modules2822-4924,virtual reality engine2826, one or moreother hardware modules2880, a combination thereof, or any other suitable means for resolving graphical content for the user (e.g., by operating system2825).Display module2860 may use liquid crystal display (LCD) technology, light-emitting diode (LED) technology (including, for example, OLED, ILED, μLED, AMOLED, TOLED, etc.), light emitting polymer display (LPD) technology, or some other display technology.
• Electronic system2800 may include a user input/output module2870. User input/output module2870 may allow a user to send action requests toelectronic system2800. An action request may be a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. User input/output module2870 may include one or more input devices. Example input devices may include a touchscreen, a touch pad, microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, a game controller, or any other suitable device for receiving action requests and communicating the received action requests toelectronic system2800. In some embodiments, user input/output module2870 may provide haptic feedback to the user in accordance with instructions received fromelectronic system2800. For example, the haptic feedback may be provided when an action request is received or has been performed.
• Electronic system2800 may include acamera2850 that may be used to take photos or videos of a user, for example, for tracking the user's eye position.Camera2850 may also be used to take photos or videos of the environment, for example, for VR, AR, or MR applications.Camera2850 may include, for example, a complementary metal-oxide-semiconductor (CMOS) image sensor with a few millions or tens of millions of pixels. In some implementations,camera2850 may include two or more cameras that may be used to capture 3-D images.
• In some embodiments,electronic system2800 may include a plurality ofother hardware modules2880. Each ofother hardware modules2880 may be a physical module withinelectronic system2800. While each ofother hardware modules2880 may be permanently configured as a structure, some ofother hardware modules2880 may be temporarily configured to perform specific functions or temporarily activated. Examples ofother hardware modules2880 may include, for example, an audio output and/or input module (e.g., a microphone or speaker), a near field communication (NFC) module, a rechargeable battery, a battery management system, a wired/wireless battery charging system, etc. In some embodiments, one or more functions ofother hardware modules2880 may be implemented in software.
• In some embodiments,memory2820 ofelectronic system2800 may also store avirtual reality engine2826.Virtual reality engine2826 may execute applications withinelectronic system2800 and receive position information, acceleration information, velocity information, predicted future positions, or some combination thereof of the HMD device from the various sensors. In some embodiments, the information received byvirtual reality engine2826 may be used for producing a signal (e.g., display instructions) todisplay module2860. For example, if the received information indicates that the user has looked to the left,virtual reality engine2826 may generate content for the HMD device that mirrors the user's movement in a virtual environment. Additionally,virtual reality engine2826 may perform an action within an application in response to an action request received from user input/output module2870 and provide feedback to the user. The provided feedback may be visual, audible, or haptic feedback. In some implementations, processor(s)2810 may include one or more GPUs that may executevirtual reality engine2826.
• In various implementations, the above-described hardware and modules may be implemented on a single device or on multiple devices that can communicate with one another using wired or wireless connections. For example, in some implementations, some components or modules, such as GPUs,virtual reality engine2826, and applications (e.g., tracking application), may be implemented on a console separate from the head-mounted display device. In some implementations, one console may be connected to or support more than one HMD.
• In alternative configurations, different and/or additional components may be included inelectronic system2800. Similarly, functionality of one or more of the components can be distributed among the components in a manner different from the manner described above. For example, in some embodiments,electronic system2800 may be modified to include other system environments, such as an AR system environment and/or an MR environment.
• The methods, systems, and devices discussed above are examples. Various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods described may be performed in an order different from that described, and/or various stages may be added, omitted, and/or combined. Also, features described with respect to certain embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples that do not limit the scope of the disclosure to those specific examples.
• Specific details are given in the description to provide a thorough understanding of the embodiments. However, embodiments may be practiced without these specific details. For example, well-known circuits, processes, systems, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the embodiments. This description provides example embodiments only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the preceding description of the embodiments will provide those skilled in the art with an enabling description for implementing various embodiments. Various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the present disclosure.
• Also, some embodiments were described as processes depicted as flow diagrams or block diagrams. Although each may describe the operations as a sequential process, many of the operations may be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may have additional steps not included in the figure. Furthermore, embodiments of the methods may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the associated tasks may be stored in a computer-readable medium such as a storage medium. Processors may perform the associated tasks.
• It will be apparent to those skilled in the art that substantial variations may be made in accordance with specific requirements. For example, customized or special-purpose hardware might also be used, and/or particular elements might be implemented in hardware, software (including portable software, such as applets, etc.), or both. Further, connection to other computing devices such as network input/output devices may be employed.
• With reference to the appended figures, components that can include memory can include non-transitory machine-readable media. The term “machine-readable medium” and “computer-readable medium” may refer to any storage medium that participates in providing data that causes a machine to operate in a specific fashion. In embodiments provided hereinabove, various machine-readable media might be involved in providing instructions/code to processing units and/or other device(s) for execution. Additionally or alternatively, the machine-readable media might be used to store and/or carry such instructions/code. In many implementations, a computer-readable medium is a physical and/or tangible storage medium. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Common forms of computer-readable media include, for example, magnetic and/or optical media such as compact disk (CD) or digital versatile disk (DVD), punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read instructions and/or code. A computer program product may include code and/or machine-executable instructions that may represent a procedure, a function, a subprogram, a program, a routine, an application (App), a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements.
• Those of skill in the art will appreciate that information and signals used to communicate the messages described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.
• Terms, “and” and “or” as used herein, may include a variety of meanings that are also expected to depend at least in part upon the context in which such terms are used. Typically, “or” if used to associate a list, such as A, B, or C, is intended to mean A, B, and C, here used in the inclusive sense, as well as A, B, or C, here used in the exclusive sense. In addition, the term “one or more” as used herein may be used to describe any feature, structure, or characteristic in the singular or may be used to describe some combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example and claimed subject matter is not limited to this example. Furthermore, the term “at least one of” if used to associate a list, such as A, B, or C, can be interpreted to mean any combination of A, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.
• Further, while certain embodiments have been described using a particular combination of hardware and software, it should be recognized that other combinations of hardware and software are also possible. Certain embodiments may be implemented only in hardware, or only in software, or using combinations thereof. In one example, software may be implemented with a computer program product containing computer program code or instructions executable by one or more processors for performing any or all of the steps, operations, or processes described in this disclosure, where the computer program may be stored on a non-transitory computer readable medium. The various processes described herein can be implemented on the same processor or different processors in any combination.
• Where devices, systems, components or modules are described as being configured to perform certain operations or functions, such configuration can be accomplished, for example, by designing electronic circuits to perform the operation, by programming programmable electronic circuits (such as microprocessors) to perform the operation such as by executing computer instructions or code, or processors or cores programmed to execute code or instructions stored on a non-transitory memory medium, or any combination thereof. Processes can communicate using a variety of techniques, including, but not limited to, conventional techniques for inter-process communications, and different pairs of processes may use different techniques, or the same pair of processes may use different techniques at different times.
• The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that additions, subtractions, deletions, and other modifications and changes may be made thereunto without departing from the broader spirit and scope as set forth in the claims. Thus, although specific embodiments have been described, these are not intended to be limiting. Various modifications and equivalents are within the scope of the following claims.

Claims (22)

What is claimed is:

1. A waveguide display comprising:

a substrate transparent to visible light; and

a first volume Bragg grating (VBG), a second VBG, and a third VBG coupled to the substrate,

wherein the first VBG is configured to couple display light into the substrate as guided wave towards a first region of the second VBG;

wherein the second VBG is configured to:

diffract, at the first region of the second VBG, the display light from the first VBG to a first direction; and

diffract, at two or more regions of the second VBG along the first direction, the display light from the first region to a second direction towards the third VBG; and

wherein the third VBG is configured to couple the display light from each of the two or more regions of the second VBG out of the substrate at two or more regions of the third VBG along the second direction.

2. The waveguide display ofclaim 1, wherein the first VBG and the third VBG have a same grating vector in a plane perpendicular to a surface normal direction of the substrate.

3. The waveguide display ofclaim 1, wherein the first VBG, the second VBG, and the third VBG are configured to diffract the display light from a same field of view range and in a same wavelength range.

4. The waveguide display ofclaim 1, wherein each of the first VBG, the second VBG, and the third VBG includes a reflective VBG or a transmissive VBG.

5. The waveguide display ofclaim 1, wherein:

the third VBG includes a transmissive VBG; and

the second VBG overlaps with the third VBG in a see-through region of the waveguide display.

6. The waveguide display ofclaim 1, wherein at least one of the first VBG, the second VBG, or the third VBG includes a multiplexed VBG.

7. The waveguide display ofclaim 6, wherein:

the first VBG includes a first set of VBGs;

the third VBG includes a second set of VBGs; and

each VBG in the first set of VBGs and a corresponding VBG in the second set of VBGs have a same grating vector in a plane perpendicular to a surface normal direction of the substrate and are configured to diffract the display light from a same field of view range and in a same wavelength range.

8. The waveguide display ofclaim 6, wherein at least one of the first VBG, the second VBG, or the third VBG includes VBGs in two or more holographic material layers.

9. The waveguide display ofclaim 8, further comprising a polarization convertor between two holographic material layers of the two or more holographic material layers.

10. The waveguide display ofclaim 1, further comprising an anti-reflection layer configured to reduce reflection of ambient light into the substrate.

11. The waveguide display ofclaim 1, further comprising an angular-selective transmissive layer configured to reflect, diffract, or absorb ambient light incident on the angular-selective transmissive layer with an incidence angle greater than a threshold value.

12. The waveguide display ofclaim 1, wherein:

each of the second VBG and the third VBG is characterized by a respective thickness less than 100 μm; and

the waveguide display is characterized by an angular resolution less than 2 arcminutes.

13. The waveguide display ofclaim 1, wherein the first region of the second VBG and a second region of the two or more regions of the second VBG have a same grating vector in a plane perpendicular to a surface normal direction of the substrate.

14. The waveguide display ofclaim 1, further comprising:

a light source configured to generate the display light; and

projector optics configure to collimate the display light and direct the display light to the first VBG.

15. A waveguide display comprising:

a substrate transparent to visible light;

a coupler configured to couple display light into the substrate as guided wave in the substrate; and

a first volume Bragg grating (VBG) and a second VBG coupled to the substrate,

wherein the first VBG is configured to:

diffract, at a first region of the first VBG, the display light in the substrate to a first direction; and

diffract, at two or more regions of the first VBG along the first direction, the display light from the first region to a second direction towards the second VBG; and

wherein the second VBG is configured to couple the display light from each of the two or more regions of the first VBG out of the substrate at two or more regions of the second VBG along the second direction.

16. The waveguide display ofclaim 15, wherein:

the first VBG is characterized by a thickness less than 100 μm; and

the waveguide display is characterized by an angular resolution less than 2 arcminutes.

17. The waveguide display ofclaim 15, wherein:

the second VBG includes a transmissive VBG; and

the first VBG overlaps with the second VBG in a see-through region of the waveguide display.

18. The waveguide display ofclaim 15, wherein at least one of the first VBG or the second VBG includes VBGs in two or more holographic material layers.

19. The waveguide display ofclaim 15, wherein the coupler includes a diffractive coupler, a refractive coupler, or a reflective coupler.

20. The waveguide display ofclaim 15, wherein at least one of the first VBG or the second VBG includes a multiplexed VBG.

21. The waveguide display ofclaim 15, wherein each of the first VBG and the second VBG includes a transmissive VBG or a reflective VBG.

22. The waveguide display ofclaim 15, wherein the first region of the first VBG and a second region of the two or more regions of the first VBG have a same grating vector in a plane perpendicular to a surface normal direction of the substrate.

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