A display device having a diffraction grating with reduced polarization sensitivity

Abstract

To provide a display device having diffraction gratings with reduced polarization sensitivity.SOLUTION: Blazed diffraction gratings provide optical elements in head-mounted display systems, for example, to in-couple light into or out-couple the light out of a waveguide. These blazed diffraction gratings may be configured to have reduced polarization sensitivity. Such gratings may, for example, in-couple or out-couple light of different polarizations with similar levels of efficiency. The blazed diffraction gratings and waveguides may be formed in a high refractive index substrate such as lithium niobate. In some implementations, the blazed diffraction gratings may include diffractive features having a feature height of 40 nm to 120 nm, for example, 80 nm. The diffractive features may be etched into the high refractive index substrate, for example, lithium niobate.SELECTED DRAWING: None

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of priority of U.S. Provisional Application No. 62 / 876,205, filed on Jul. 19, 2019, entitled "DISPLAY DEVICE HAVING DIFFRACTION GRATINGS WITH REDUCED POLARIZATION SENSITIVITY", and U.S. Provisional Application No. 62 / 902,328, filed on Sep. 18, 2019, entitled "DISPLAY DEVICE HAVING DIFFRACTION GRATINGS WITH REDUCED POLARIZATION SENSITIVITY", the contents of which are hereby incorporated by reference in their entirety. (Incorporation by Reference)

[0002] This application incorporates by reference in their entirety the following patent applications: U.S. Patent Application No. 14 / 555,585, filed on Nov. 27, 2014, and published as U.S. Patent Publication No. 2015 / 0205126 on Jul. 23, 2015; U.S. Patent Application No. 14 / 690,401, filed on Apr. 18, 2015, and published as U.S. Patent Publication No. 2015 / 0302652 on Oct. 22, 2015; U.S. Patent Application No. 14 / 212,961, filed on Mar. 14, 2014, and issued as U.S. Patent No. 9,417,452 on Aug. 16, 2016; and U.S. Patent Application No. 14 / 331,218, filed on Jul. 14, 2014, and published as U.S. Patent Publication No. 2015 / 0309263 on Oct. 29, 2015.

[0003] The present disclosure relates to display systems, and more particularly, to augmented and virtual reality display systems.

Background Art

[0004] (Description of Related Technologies) Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as being real. Virtual reality, i.e., "VR" scenarios, typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and augmented reality, i.e., "AR" scenarios, typically involve the presentation of digital or virtual image information as an augmentation to the visualization of the actual world surrounding the user. Mixed reality, i.e., "MR" scenarios, are a type of AR scenario and typically involve virtual objects that are integrated into and responsive to the natural world. For example, in an MR scenario, AR image content can be perceived as being blocked or otherwise interacting with objects within the real world.

[0005] Referring to FIG. 1, an augmented reality scene 10 is depicted, and to a user of AR technology, a real-world park-like setting 20 characterized by people, trees, buildings in the background, and a concrete platform 30 can be seen. In addition to these items, a user of AR technology also "sees" and perceives "virtual content" such as a robot figure 40 standing on the real-world platform 30 and a flying comic-like avatar character 50 that appears to be an anthropomorphic honeybee, but these elements 40, 50 do not exist in the real world. The human visual perception system is complex, and it is difficult to produce AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR and VR technologies.

Summary of the Invention

Means for Solving the Problems

[0007] In one aspect, a head-mounted display system includes a head-mountable frame, a light projection system configured to output light and provide image content, and a waveguide supported by the frame. The waveguide includes a substrate including a material having a refractive index of at least 1.9. The substrate is configured to guide at least a portion of the light from the light projection system to be coupled into the waveguide. The head-mounted display system further includes a blazed diffraction grating formed in a layer disposed within or across the substrate. The blazed diffraction grating has a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization over a range of angles of light incident thereon. The first diffraction efficiency is 1 to 2 times the second diffraction efficiency.

[0008] In another aspect, an optical waveguide includes a substrate including a material having a refractive index of at least 1.9. The substrate is configured to guide light coupled into the waveguide through total internal reflection within the waveguide. The optical waveguide further includes a blazed diffraction grating formed in a layer disposed within or across the substrate. The blazed diffraction grating has a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization over a range of angles of light incident thereon. The first diffraction efficiency is 1 to 2 times the second diffraction efficiency. The present invention provides, for example, the following. (Item 1) A head-mounted display system, a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide comprising a substrate including a material having a refractive index of at least 1.9, the substrate being configured to guide at least a part of the light from the light projection system into the waveguide, a blazed diffraction grating formed in a layer disposed within or across the substrate and comprising, the blazed diffraction grating having a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization over a range of angles of light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency, a head-mounted display system. (Item 2) The head-mounted display system according to Item 1, wherein the blazed diffraction grating is formed within the substrate and arranged to be optically in communication with the substrate. (Item 3) The head-mounted display system according to Item 1, wherein the blazed diffraction grating is disposed across the substrate and is within a layer arranged to be optically in communication with the substrate. (Item 4) The head-mounted display system according to Item 3, wherein the layer physically contacts the substrate. (Item 5) The head-mounted display system according to Item 1, wherein the material having a refractive index of at least 1.9 includes a lithium-based oxide, silicon carbide, zirconium dioxide, or titanium dioxide. (Item 6) The head-mounted display system according to Item 1, wherein the blazed diffraction grating is formed within a layer disposed across the substrate, the layer including silicon nitride, zirconium dioxide, titanium dioxide, or silicon carbide. (Item 7) The head-mounted display system according to Item 1, wherein the blazed diffraction grating is formed within a layer disposed across the substrate, the layer having a refractive index lower than that of the substrate. (Item 8) The head-mounted display system according to Item 1, wherein the material has a refractive index of at least 2.0 to 2.7. (Item 9) The head-mounted display system according to Item 1, wherein the blazed diffraction grating has a diffraction feature comprising protrusions separated by grooves therebetween. (Item 10) The blazed diffraction grating-equipped head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction feature including a plurality of straight lines. (Item 11) The head-mounted display system according to item 10, wherein the plurality of straight lines include discontinuous straight lines. (Item 12) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction feature including a plurality of pillars protruding from the surface of the substrate. (Item 13) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction feature with a tip height or groove depth of 10 to 150 nm. (Item 14) The head-mounted display system according to item 1, wherein the diffraction feature is asymmetric. (Item 15) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a pitch of 250 to 350 nm. (Item 16) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a pitch of 300 to 450 nm. (Item 17) The head-mounted display system according to item 1, wherein the substrate is planar, and the blazed diffraction grating has a blaze angle of 10 to 30 degrees with respect to the plane of the substrate. (Item 18) The head-mounted display system according to item 1, wherein the first diffraction efficiency is 1 to 1.5 times that of the second diffraction efficiency. (Item 19) The head-mounted display system according to item 1, wherein the range of the angle is at least 6 degrees. (Item 20) The head-mounted display system according to item 1, wherein the range of the angle is between ±3 degrees with respect to the plane of the substrate. (Item 21) The head-mounted display system according to item 1, wherein the first and second polarizations include first and second linear polarizations having different polarization angles. (Item 22) The head-mounted display system according to item 1, wherein the first and second polarizations include first and second linear polarizations oriented in orthogonal directions. (Item 23) The head-mounted display system according to item 1, wherein the first polarization includes one of transverse magnetic and transverse electric polarizations, and the second polarization includes the other of transverse magnetic and transverse electric polarizations. (Item 24) The first diffraction efficiency comprises the diffraction efficiency for one of the transverse magnetic polarization and the transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises the diffraction efficiency for the other of the transverse magnetic polarization and the transverse electric polarization averaged across the visible light spectrum. The head-mounted display system according to item 1. (Item 25) The blazed diffraction grating has a diffraction efficiency for the red wavelength of the light having the first polarization, which is 1 to 2 times the diffraction efficiency for the red wavelength of the second polarization. The head-mounted display system according to item 1. (Item 26) The blazed diffraction grating has a diffraction efficiency for the green wavelength of the light having the first polarization, which is 1 to 1.5 times the diffraction efficiency for the green wavelength of the second polarization. The head-mounted display system according to item 1. (Item 27) The blazed diffraction grating has a diffraction efficiency for the blue wavelength of the light having the first polarization, which is 0.7 to 1 times the diffraction efficiency for the blue wavelength of the light having the second polarization. The head-mounted display system according to item 1. (Item 28) The waveguide is included in an eyepiece lens configured to direct light toward the eyes of a user wearing the head-mounted display. The head-mounted display system according to item 1. (Item 29) The eyepiece lens is disposed on the frame, configured to direct light from the light projection system into the eyes of the user and display augmented reality image content in the user's field of view. At least a part of the eyepiece lens is transparent. When the user wears the head-mounted display system, it is disposed at a position in front of the user's eyes. The transparent portion transmits light from a part of the physical environment in front of the user to the user's eyes and provides a view of a part of the physical environment in front of the user. The head-mounted display system according to item 28. (Item 30) The eyepiece lens includes the at least one waveguide, and the at least one waveguide is transparent to visible light so that the user can see through the waveguide. The head-mounted display system according to item 28. (Item 31) The head-mounted display system according to item 1, wherein the waveguide includes an internal coupling optical element for coupling light from the light projection system into the waveguide so as to be guided therein. (Item 32) The head-mounted display system according to item 1, wherein the waveguide includes an external coupling optical element for coupling light from the light projection system out of the waveguide, directing the light toward the user's eyes, and presenting the image content to the viewer. (Item 33) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes an internal coupling grating (ICG) configured to internally couple light from the light projection system into the waveguide. (Item 34) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes an external coupling grating (EPE) configured to externally couple light from the light projection system guided within the waveguide out of the waveguide. (Item 35) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes diffraction features formed within a one-dimensional (1D) array. (Item 36) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes diffraction features formed within a two-dimensional (2D) array. (Item 37) The head-mounted display system according to item 36, wherein the two-dimensional (2D) array includes a square array. (Item 38) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes a 1D grating. (Item 39) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes a 2D grating. (Item 40) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes a 2D grating including a square array. (Item 41) The head-mounted display system according to item 1, wherein the blazed diffraction grating is configured to preferentially direct light in two or more directions. (Item 42) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes an internal coupling optical element arranged to receive light from an image source and couple the light into the substrate so as to be guided therein. (Item 43) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises a light dispersing optical element that receives light from an image source induced within the substrate and is arranged to direct the light to be coupled out of the substrate to an external coupling optical element. (Item 44) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises a light dispersing optical element that receives light from an image source induced within the substrate, diffuses the light within the waveguide, and is arranged to increase the beam size or the eye box size. (Item 45) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises an external coupling optical element that receives light from an image source induced within the substrate and is arranged to couple the light out of the substrate. (Item 46) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises a combined light dispersing / external coupling optical element that receives light from an image source induced within the substrate, diffuses the light in at least two directions, and is arranged to couple the light out of the substrate. (Item 47) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises a combined pupil expander-extractor that receives light from an image source induced within the substrate, diffuses the light, and is arranged to couple the light out of the substrate. (Item 48) An optical waveguide, a substrate including a material having a refractive index of at least 1.9, the substrate being configured to guide light coupled into the waveguide through total internal reflection within the waveguide, and a blazed diffraction grating formed within the substrate or within a layer disposed across the substrate, comprising, the blazed diffraction grating having a first diffraction efficiency for a first polarization over a range of angles for light incident thereon and a second diffraction efficiency for a second polarization over a range of angles for light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency. (Item 49) The optical waveguide according to item 48, wherein the blazed diffraction grating is formed within the substrate and arranged to be optically in communication with the substrate. (Item 50) The blazed diffraction grating is disposed across the substrate and is within a layer arranged to be optically in communication with the substrate, the optical waveguide according to item 48. (Item 51) The layer physically contacts the substrate, the optical waveguide according to item 50. (Item 52) The material having a refractive index greater than 1.9 includes a lithium-based oxide, silicon carbide, zirconium dioxide, or titanium dioxide, the optical waveguide according to item 48. (Item 53) The blazed diffraction grating is formed within a layer disposed across the substrate, the layer including silicon nitride, zirconium dioxide, titanium dioxide, or silicon carbide, the optical waveguide according to item 48. (Item 54) The blazed diffraction grating is formed within a layer disposed across the substrate, the layer having a refractive index lower than that of the substrate, the optical waveguide according to item 48. (Item 55) The blazed diffraction grating has a diffraction feature with a tip height or groove depth of 10 to 150 nm, the optical waveguide according to item 48. (Item 56) The blazed diffraction grating has a diffraction feature including a plurality of straight lines, the optical waveguide according to item 48. (Item 57) The plurality of straight lines includes discontinuous straight lines, the optical waveguide according to item 56. (Item 58) The blazed diffraction grating has a diffraction feature including a plurality of pillars protruding from the surface of the substrate, the optical waveguide according to item 48. (Item 59) The diffraction feature is asymmetric, the optical waveguide according to item 48. (Item 60) The blazed diffraction grating has a diffraction feature formed within a one-dimensional (1D) array, the optical waveguide according to item 48. (Item 61) The blazed diffraction grating has a diffraction feature formed within a two-dimensional (2D) array, the optical waveguide according to item 48. (Item 62) The two-dimensional (2D) array includes a square array, the optical waveguide according to item 61. (Item 63) The blazed diffraction grating includes a 1D grating, the optical waveguide according to item 48. (Item 64) The blazed diffraction grating includes a 2D grating, the optical waveguide according to item 48. (Item 65) The blazed diffraction grating includes a 2D grating including a square array, the optical waveguide according to item 48. (Item 66) The blazed diffraction grating is configured to preferentially direct light in two or more directions, the optical waveguide according to item 48. (Item 67) The blazed diffraction grating of claim 48, comprising an internal coupling optical element arranged to receive light from an image source and couple the light to be guided therein into the substrate. (Claim 68) The blazed diffraction grating of claim 48, comprising a light dispersing optical element arranged to receive light from an image source guided within the substrate and direct the light to be coupled out of the substrate to an external coupling optical element. (Claim 69) The blazed diffraction grating of claim 48, comprising a light dispersing optical element arranged to receive light from an image source guided within the substrate, diffuse the light within the waveguide, and increase the beam size or the eye box size. (Claim 70) The blazed diffraction grating of claim 48, comprising an external coupling optical element arranged to receive light from an image source guided within the substrate and couple the light out of the substrate. (Claim 71) The blazed diffraction grating of claim 48, comprising a combined light dispersing / external coupling optical element arranged to receive light from an image source guided within the substrate, diffuse the light in at least two directions, and couple the light out of the substrate. (Claim 72) The blazed diffraction grating of claim 48, comprising a combined pupil expander / extractor arranged to receive light from an image source guided within the substrate, diffuse the light, and couple the light out of the substrate.

Brief Description of the Drawings

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[0043] Throughout the drawings, reference numerals may be reused to indicate correspondence between the elements being referenced. The drawings are provided to illustrate example embodiments described herein and are not intended to limit the scope of the present disclosure.

DETAILED DESCRIPTION

[0044] Detailed Description An AR system can still display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, this content is displayed on a head-mounted display as part of eyewear that projects, for example, image information onto the user's eyes. In addition, the display can also transmit light from the surrounding environment to the user's eyes, enabling a view of that surrounding environment. As used herein, it should be understood that a “head-mounted” or “head-mountable” display is a display that can be mounted on the head of a viewer or user.

[0045] In some AR systems, a virtual / augmented / composite display having a relatively high field of view (FOV) can improve the viewing experience. The FOV of the display depends on the angle of the light output by the waveguide of the eyepiece through which the image projected into the viewer's eye can be seen. A waveguide having a relatively high refractive index, for example, a refractive index of 2.0 or greater, can provide a relatively high FOV. However, in order to efficiently couple light into a high refractive index waveguide, the diffractive optical coupling element should also correspondingly have a high refractive index. Among other advantages, to achieve this goal, some displays for an AR system according to the embodiments described herein include a waveguide that includes a relatively high refractive index (e.g., greater than or equal to 2.0) material having an individual diffraction grating formed thereon that correspondingly has a high refractive index, such as a Li-based oxide. For example, the diffraction grating may be formed on a Li-based oxide waveguide by directly patterning a surface portion of the waveguide formed from the Li-based oxide.

[0046] Some high refractive index diffractive optical coupling elements, such as internal or external coupling optical elements, have strong polarization dependence. For example, an internal coupling grating (ICG) for internally coupling light containing a high refractive index material into an optical waveguide can accept significantly more light of a given polarization than light of another polarization. Such an element can, for example, internally couple light with TM polarization into the optical waveguide at a rate of about three times that of light with TE polarization. Diffractive optical coupling elements with this type of polarization dependence can have reduced efficiency (due to poor efficiency and overall blocking of a certain polarization), and can also create coherent artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the optical waveguide. To obtain diffractive optical coupling elements that are insensitive to polarization or have at least reduced polarization sensitivity (e.g., coupling light with relatively polarization-independent efficiency), some displays for AR systems according to various implementations described herein include an optical waveguide with a diffraction grating formed with a blazed geometry. The diffraction grating can also be formed directly within the optical waveguide, which can contain a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7, or any value within any range between these values). The diffraction grating can be formed, for example, by patterning a high refractive index material with a blazed geometry, such as lithium niobate (LiNbO 3 ) or lithium tantalate (LiTaO 3 ) like Li-based oxides, or within a high refractive index material such as zirconium oxide (ZrO 2 ), titanium dioxide (TiO 2 ), or silicon carbide (SiC).

[0047] Reference will now be made to the figures, where like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0048] Figure 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that the user's eyes are separated, and when looking at a real object in space, each eye has a slightly different view of the object and can form an image of the object at different locations on the retina of each eye. This can be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct images 190, 200 with slightly different views of one identical virtual object for each of the eyes 210, 220, corresponding to the views of the virtual object that would be seen by each eye as if the virtual object were a real object at the desired depth. These images provide binocular cues that can be interpreted by the user's visual system to derive a perception of depth.

[0049] Continuing to refer to Figure 2, the images 190, 200 are separated from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer in a state where the eye is fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual object within the images presented to the eyes 210, 220 respectively, the eyes can necessarily rotate so that the image of the object comes to corresponding points on the respective retinas of the eyes and a single binocular vision is maintained. This rotation can converge the respective lines of sight of the eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, the provision of a three-dimensional image has conventionally involved being able to manipulate the convergence / divergence movement of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0050] However, generating realistic and comfortable perception of depth is difficult. It should be understood that light from objects at different distances from the eye has wavefronts with different divergence amounts. FIGS. 3A-3C illustrate the relationship between distance and divergence of light rays. The distances between the object and the eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A-3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only the monocular eye 210 is illustrated in FIGS. 3A-3C and other figures of this specification for clarity of illustration, but the discussion regarding the eye 210 can be applied to both eyes 210 and 220 of the viewer.

[0051] Continuing to refer to FIGS. 3A-3C, light from the object on which the viewer's eye is fixated can have different wavefront divergence degrees. Due to the different wavefront divergence amounts, the light can be focused differently by the lens of the eye, which in turn may require the lens to take on different shapes to form a focused image on the retina of the eye. If a focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation, causing a change in the shape of the lens of the eye until a focused image is formed on the retina. For example, the cue for accommodation induces relaxation or contraction of the ciliary muscle surrounding the lens of the eye, thereby modulating the force applied to the zonular fibers that hold the lens, and thus changing the shape of the lens of the eye until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the retina (e.g., fovea) of the eye. The process by which the lens of the eye changes shape can be referred to as accommodation, and the shape of the lens of the eye required to form a focused image of the fixated object on the retina (e.g., fovea) of the eye can be referred to as the accommodative state.

[0052] Referring now to FIG. 4A, the representation of the accommodation-convergence / divergence motion response of the human visual system is illustrated. Eye movements to fixate an object cause the eye to receive light from the object, and the light forms an image on each of the retinas of the eye. The presence of retinal blur in the image formed on the retina may provide a cue for accommodation, and the relative location of the image on the retina may provide a cue for convergence / divergence motion. The cue for accommodation causes accommodation to occur, causing the eye's lens to assume a particular accommodation state that forms a focused image of the object on the retina of the eye (e.g., the fovea). On the other hand, the cue for convergence / divergence motion causes a convergence / divergence motion (rotation of the eye) such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. At these positions, it can be said that the eye is in a particular convergence / divergence motion state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eye achieves a particular accommodation state, and convergence / divergence motion can be understood as the process by which the eye achieves a particular convergence / divergence motion state. As shown in FIG. 4A, the accommodation and convergence / divergence motion states of the eye can change when the user fixates on another object. For example, the accommodated state can change when the user fixates on a new object at a different depth on the z-axis.

[0053] Without being limited by theory, it is believed that an object viewer may perceive an object as "three-dimensional" due to the combination of convergence / divergence motion and accommodation. As described above, the convergence / divergence motion of the two eyes relative to each other (e.g., the movement of the pupils towards or away from each other, the rotation of the eyes that converges the lines of sight of the eyes to fixate on an object) is closely associated with the accommodation of the eye's lens. Under normal conditions, a change in the shape of the eye's lens to change focus from one object to another object at a different distance will automatically cause a corresponding change in convergence / divergence motion to the same distance under a relationship known as the "accommodation-convergence / divergence reflex". Similarly, a change in convergence / divergence motion will, under normal conditions, induce a corresponding change in the shape of the lens.

[0054] Referring now to FIG. 4B, examples of different focusing and convergence / divergence motion states of the eyes are illustrated. A pair of eyes 222a fixates on an object at optical infinity, while a pair of eyes 222b fixates on an object 221 at less than optical infinity. It should be noted that the convergence / divergence motion states of each pair of eyes are different, with the pair of eyes 222a being directed straight, while the pair of eyes 222 converge on the object 221. The focusing states of the eyes forming each pair of eyes 222a and 222b also differ, as represented by the different shapes of the lenses 210a, 220a.

[0055] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or perceive no sense of depth at all due to the mismatch between the focusing and the convergence / divergence motion states in these displays. As described above, many stereoscopic or "3-D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they merely provide different presentations of the scene, causing a change in the convergence / divergence motion state of the eyes, but without a corresponding change in the focusing state of those eyes. Rather, the images are presented at a fixed distance from the eyes by the display such that the eyes view all the image information in a single focusing state. Such an arrangement goes against the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence motion state without a corresponding change in the focusing state. This mismatch is thought to cause discomfort to the viewer. A display system that provides a better match between accommodation and convergence / divergence motion can form a more realistic and comfortable simulation of a three-dimensional image.

[0056] Although not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of an image corresponding to each of these limited number of depth planes to the eye. In some embodiments, the different presentations provide both cues for convergence / divergence motion and corresponding cues for accommodation, thereby providing a physiologically correct accommodation-convergence / divergence match.

[0057] Continuing to refer to FIG. 4B, two depth planes 240 corresponding to different distances in space from eyes 210, 220 are illustrated. For a given depth plane 240, convergence / divergence motion cues may be provided by appropriately displaying images of different viewpoints for each of eyes 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 may have a wavefront divergence corresponding to a light field generated by a point at the distance of that depth plane 240.

[0058] In the illustrated embodiment, the distance along the z-axis of depth plane 240 containing point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured using a zero point located at the exit pupil of the user's eye. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance 1 m away from the exit pupil of the user's eye on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis is measured from the front of the display of the user's eye (e.g., from the surface of a waveguide), and a value related to the distance between the device and the exit pupil of the user's eye may be added. That value may be referred to as the pupil distance and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the pupil distance may generally be a normalized value used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0059] Referring now to FIGS. 4C and 4D, examples of matched vergence accommodation - convergence / divergence movement distances and mismatched vergence accommodation - convergence / divergence movement distances are illustrated, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each of the eyes 210, 220. The image may cause the eyes 210, 220 to assume a convergence / divergence movement state in which the eyes converge on a point 15 on the depth plane 240. Additionally, the image may be formed by light having a wavefront curvature corresponding to the real object in the depth plane 240. As a result, the eyes 210, 220 assume a focus adjustment state in which the image is in focus on their retinas. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0060] It should be understood that the focus adjustment and convergence / divergence movement states of the eyes 210, 220 are each associated with a specific distance on the z - axis. For example, an object at a specific distance from the eyes 210, 220 causes those eyes to assume a specific focus adjustment state based on the distance of the object. The distance associated with a specific focus adjustment state may be referred to as the focus adjustment distance A d and may be so called. Similarly, there exists a specific convergence / divergence movement distance V d associated with a specific convergence / divergence movement state or the eyes in a particular position relative to each other. When the focus adjustment distance and the convergence / divergence movement distance match, the relationship between focus adjustment and convergence / divergence movement can be said to be physiologically correct. This is regarded as the most comfortable scenario for the viewer.

[0061] However, in a stereoscopic display, the accommodation distance and the vergence / accommodation movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210, 220 may be displayed with wavefront divergence corresponding to the depth plane 240, and eyes 210, 220 may take a specific accommodation state in which points 15a, 15b on that depth plane are in focus. However, the images displayed on eyes 210, 220 may provide a cue for vergence / accommodation movement that converges eyes 210, 220 on a point 15 that is not located on depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the vergence / accommodation movement distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The accommodation distance is different from the vergence / accommodation movement distance. As a result, there is an accommodation-vergence / accommodation movement mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch corresponds to a distance (e.g., V d -A d ) and it should be understood that it can be characterized using diopters.

[0062] It should be understood that in some embodiments, reference points other than the exit pupils of eyes 210, 220 can also be used to determine the distance for determining the accommodation-vergence / accommodation movement mismatch as long as the same reference point is used for the accommodation distance and the vergence / accommodation movement distance. For example, the distance can be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc.

[0063] Although not limited by theory, it is believed that a user can physiologically perceive vergence-accommodation mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as being correct without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents an image to a viewer having a vergence-accommodation mismatch of about 0.5 diopters or less. In some other embodiments, the vergence-accommodation mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the vergence-accommodation mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0064] FIG. 5 illustrates a side view of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it will be shown that the user's other eye may be provided with image information from a similar waveguide.

[0065] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light within a limited range of wavelengths. As a result, in some embodiments, multiple or stacked waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different ranges of wavelengths. It should be understood that, as used herein, a depth plane may follow the contour of a flat or curved surface.

[0066] FIG. 6 illustrates an example of a stack of waveguides for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that can be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It should be understood that the display system 250 may be considered a light field display in some embodiments. Additionally, the waveguide assembly 260 may also be referred to as an eyepiece.

[0067] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for convergence / divergence movement and a plurality of discrete cues for depth adjustment. The cue for convergence / divergence movement may be provided by displaying different images to each of the user's eyes, and the cue for depth adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. In other words, the display system 250 may be configured to output light with a variable level of wavefront divergence. In some embodiments, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0068] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310, and / or the plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across an individual waveguide for output toward eye 210 as described herein. Light exits from output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly toward world 510 or viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams directed toward eye 210 at a particular angle (and amount of divergence) corresponding to a depth plane associated with the particular waveguide. In some embodiments, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0069] In some embodiments, the image input devices 360, 370, 380, 390, 400 are discrete displays that each generate image information for input into their respective waveguides 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display that can send image information to each of the image input devices 360, 370, 380, 390, 400, for example, via one or more optical waveguides (such as optical fiber cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 can include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0070] In some embodiments, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520 that includes an optical module 530 that can include a light emitter such as a light emitting diode (LED). The light from the optical module 530 can be directed via a beam splitter 550 to a light modulator 540, such as a spatial light modulator, and thereby modified. The light modulator 540 can be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) including liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically and, in some embodiments, these image input devices can represent different optical paths and locations within a common projection system that are configured to output light into the associated ones of the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 can function as ideal lenses while relaying the light input into the waveguides to the user's eyes. In this concept, the object can be the spatial light modulator 540 and the image can be an image on a depth plane.

[0071] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, helical scan, Lissajous pattern, etc.) and ultimately into the viewer's eye 210. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures are provided between the scanning fiber or fibers and the one or more waveguides 270, 280, 290, 300, 310 and may, for example, redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0072] Controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, controller 560 is part of the local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may, in some embodiments, also be part of processing module 140 or 150 (FIG. 9D).

[0073] Continuing to refer to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and an edge extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external coupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of extracted light may be output by the waveguide at the location where the light propagating within the waveguide strikes the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, the external coupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, but in some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of the material forming the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that piece of material.

[0074] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (input into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to output collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to generate a slightly convex wavefront curvature such that the eye / brain interprets the light arising from the next upper waveguide 280 as arising from a first focal plane that is closer inwardly toward the eye 210 from optical infinity. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to generate another incremental amount of wavefront curvature such that the eye / brain interprets the light arising from the third upper waveguide 290 as arising from a second focal plane that is closer inwardly toward the person from optical infinity than the light from the next upper waveguide 280 was.

[0075] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the top waveguide 310 in the stack sends its output through all of the lenses between it and the eye for the collective focusing power that represents the focal plane closest to the person. When viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensation lens layer 620 may be disposed on top of the stack to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0076] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, a plurality of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or a plurality of subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, using one set per depth plane. This can provide an advantage for forming tiled images to provide an extended field of view at those depth planes.

[0077] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides for a particular depth plane associated with the waveguide and output the light with an appropriate amount of divergence or collimation. As a result, the waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be three-dimensional or surface features configured to output light at a specific angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be a volume hologram, a surface hologram, and / or a diffraction grating. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., a cladding layer and / or structure for forming a void).

[0078] In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 are diffraction features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several associated output beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam that bounces within the waveguide.

[0079] In some embodiments, one or more DOEs may be switchable between an “on” state in which they actively diffract and an “off” state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets provide a diffraction pattern within a host medium, and the refractive index of the microdroplets may be switched to substantially match that of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0080] In some embodiments, a camera assembly 630 (e.g., a digital camera including visible and infrared light cameras) may be provided to capture an image of the eye 210 and / or the tissue surrounding the eye 210, and, for example, detect user input and / or monitor the user's physiological state. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source (e.g., infrared light) that projects light onto the eye and is then reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may communicate electrically with a processing module 140 and / or 150 that can process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0081] Referring now to FIG. 7, an example of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function in a similar manner, and the waveguide assembly 260 includes a plurality of waveguides. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as the output beam 650. The output beams 650 are illustrated as being substantially parallel, but as discussed herein, they may also be redirected at an angle to propagate to the eye 210 depending on the depth plane associated with the waveguide 270 (e.g., to form a diverging output beam). It should be understood that a waveguide with an external coupling optical element that externally couples light to form an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210 may be shown. Other waveguides or other sets of external coupling optical elements may output a more divergent output beam pattern, which would require the eye 210 to focus at a closer distance and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0082] In some embodiments, a full-color image may be formed on each depth plane by overlaying the image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes an image formed using a plurality of different primary colors. The illustrated embodiment shows depth planes 240a-240f, although more or fewer depths may also be contemplated. Each depth plane may have three or more primary color images associated therewith, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are shown in the figure by different numbers associated with diopters (dpt) following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the exact placement of the depth planes for different primary colors may vary to account for differences in the focusing of light of different wavelengths by the eye. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0083] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have a plurality of waveguides associated therewith. In such embodiments, it can be understood that each box in the figure, including those containing the letters G, R, or B, represents an individual waveguide, and three waveguides may be provided for each depth plane for which three primary color images are provided. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of explanation, but it should be understood that in a physical device, all of the waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, a plurality of primary colors may be output by the same waveguide, e.g., such that only a single waveguide is provided for each depth plane.

[0084] Continuing to refer to FIG. 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may also be used in addition to, or in place of, one or more of red, green, or blue.

[0085] It should be understood that references throughout this disclosure to the color of a given light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as being that given color. For example, red light may include light of one or more wavelengths within the range of about 620 - 780 nm, green light may include light of one or more wavelengths within the range of about 492 - 577 nm, and blue light may include light of one or more wavelengths within the range of about 435 - 493 nm.

[0086] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light of one or more wavelengths outside the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirecting structures of the waveguide of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0087] Referring now to FIG. 9A, in some embodiments, light impinging on the waveguide may need to be redirected to internally couple the light into the waveguide. An internal coupling optical element may be used to redirect and internally couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a stack of a plurality or set 660 of waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image input devices 360, 370, 380, 390, 400 is input into the waveguide from a position that requires the light to be redirected for internal coupling.

[0088] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as an optical input area on the waveguide). For example, internal coupling optical element 700 is disposed on a major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the upper major surface) of waveguide 690. In some embodiments, one or more of the internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguides 670, 680, 690 (particularly, when one or more of the internal coupling optical elements are reflective deflecting optical elements). As illustrated, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface (or the upper portion of the next lower waveguide) of their respective waveguides 670, 680, 690, particularly when those internal coupling optical elements are transmissive deflecting optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the bodies of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective so as to selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690 in some embodiments.

[0089] As shown, the internally coupled optical elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each internally coupled optical element may be offset such that its light is received without passing through another internally coupled optical element. For example, each of the internally coupled optical elements 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from the other internally coupled optical elements 700, 710, 720 such that it substantially does not receive light from the other internally coupled optical elements 700, 710, 720.

[0090] Each waveguide also includes an associated light dispersing element. For example, the light dispersing element 730 is disposed on a major surface (e.g., the upper major surface) of the waveguide 670, the light dispersing element 740 is disposed on a major surface (e.g., the upper major surface) of the waveguide 680, and the light dispersing element 750 is disposed on a major surface (e.g., the upper major surface) of the waveguide 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on the bottom major surface of the associated waveguides 670, 680, 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on both the upper and bottom major surfaces of the associated waveguides 670, 680, 690, or the light dispersing elements 730, 740, 750 may each be disposed on different ones of the upper and bottom major surfaces within different associated waveguides 670, 680, 690.

[0091] Waveguides 670, 680, 690 may be separated and isolated, for example, by a gas, liquid, and / or solid layer of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a refractive index lower than the material forming the directly adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more, or 0.10 or less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light (e.g., TIR between the upper and bottom major surfaces of each waveguide) through waveguides 670, 680, 690. In some embodiments, layers 760a, 760b are formed from air. It should be understood that although not shown, the top and bottom of the illustrated set 660 of waveguides may include the nearest cladding layer.

[0092] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or identical, and the materials forming layers 760a, 760b are similar or identical. In some embodiments, the materials forming waveguides 670, 680, 690 may be different between one or more waveguides, and / or the materials forming layers 760a, 760b may still be different while maintaining the various refractive index relationships described above.

[0093] Continuing to refer to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It should be understood that light rays 770, 780, 790 may be input into waveguides 670, 680, 690 by one or more image input devices 360, 370, 380, 390, 400 (FIG. 6).

[0094] In some embodiments, the light rays 770, 780, 790 may have different properties, such as different wavelengths or different wavelength ranges, corresponding to different colors. The internal coupling optical elements 700, 710, 720 each deflect the incident light so that light propagates through an individual one of the waveguides 670, 680, 690 by TIR. In some embodiments, the internal coupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated internal coupling optical element.

[0095] For example, the internal coupling optical element 700 may be configured to selectively deflect the light ray 770 having a first wavelength or wavelength range while transmitting the light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light ray 780 impinges on the internal coupling optical element 710 configured to deflect light having a second wavelength or wavelength range, thereby being deflected. The light ray 790 is deflected by the internal coupling optical element 720 configured to selectively deflect light having a third wavelength or wavelength range.

[0096] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect light into its corresponding waveguide 670, 680, 690 and internally couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0097] Referring now to FIG. 9B, a perspective view of an embodiment of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 770, 780, 790 are each deflected by the internally coupled optical elements 700, 710, 720 and then each propagate by TIR within waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then each impinge on light dispersing elements 730, 740, 750, respectively. The light dispersing elements 730, 740, 750 deflect the light rays 770, 780, 790, respectively, so as to propagate towards external coupling optical elements 800, 810, 820, respectively.

[0098] In some embodiments, the optical dispersion elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPE deflects or disperses light to the external coupling optical elements 800, 810, 820, and in some embodiments, also increases the beam or spot size of the present light as it propagates to the external coupling optical elements. In some embodiments, the optical dispersion elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to directly deflect light to the external coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the optical dispersion elements 730, 740, 750 may be replaced with the external coupling optical elements 800, 810, 820, respectively. In some embodiments, the external coupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light within the viewer's eye 210 (FIG. 7). It should be understood that the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, for example, is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate along the waveguide. Again, in response to a collision with the OPE, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further along the waveguide, etc. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed out of the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it impinges on the EP again, at which point another portion of the colliding light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light is "replicated" each time a portion of that light is redirected by the OPE or EPE, thereby forming a beam field of cloned light as shown in FIG. 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0099] Thus, referring to FIGS. 9A and 9B, in some embodiments, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPEs) 730, 740, 750, and external coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements for receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, the ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, then bounces along the waveguide and interacts with the light dispersion element (e.g., OPE) 730, then the external coupling optical element (e.g., EP) 800. The rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, and the ray 780 collides with the internal coupling optical element 710 and is thereby deflected. The ray 780 then bounces along the waveguide 680 via TIR and proceeds to its light dispersion element (e.g., OPE) 740, then the external coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and collides with the internal coupling optical element 720 of the waveguide 690. The internal coupling optical element 720 deflects the ray 790 such that the ray propagates via TIR to the light dispersion element (e.g., OPE) 750, then via TIR to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives the light externally coupled from the other waveguides 670, 680.

[0100] FIG. 9C illustrates a top and bottom plan view of an embodiment of a plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820 of each waveguide. However, as discussed herein, internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an array comprising non-overlapping spatially separated internal coupling optical elements may be referred to as a deflected pupil system, and the internal coupling optical elements within these arrays may correspond to sub-pupils.

[0101] FIG. 9D illustrates an embodiment of a wearable display system 60 in which various waveguides and related systems disclosed herein may be integrated. In some embodiments, display system 60 is the system 250 of FIG. 6, and FIG. 6 schematically shows some portions of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of display 70.

[0102] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems for supporting the functions of the display 70. The display 70 may be wearable by a display system user or viewer 90 and may be coupled to a frame 80 configured to position the display 70 in front of the user 90's eyes. In some embodiments, the display 70 may be regarded as an eyepiece. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user 90's outer ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent to the user's other outer ear canal to provide stereo / formable sound control). The display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to enable the user to provide an input or command (e.g., selection of a voice menu command, natural language question, etc.) to the system 60 and / or to enable audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sound from the user and / or the environment). In some embodiments, the display system may also include a peripheral sensor 120a that is separate from the frame 80 and attachable to the user 90's body (e.g., on the user 90's head, torso, limbs, etc.). In some embodiments, the peripheral sensor 120a may be configured to obtain data for characterizing the physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0103] Continuing to refer to FIG. 9D, display 70 is operatively coupled to local data processing module 140 by a communication link 130 such as a wired conductor or wireless connectivity, which may be mounted in various configurations such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by a user, built into headphones, or removably attached to user 90 in some other manner (e.g., in a backpack configuration, in a belt attachment configuration). Similarly, sensor 120a may be operatively coupled to local processor and data module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. Local processing and data module 140 may comprise a digital memory such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data may include (a) data captured from sensors such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, gyroscope, and / or other sensors disclosed herein (e.g., operatively coupled to frame 80 or otherwise attachable to user 90), and / or (b) optionally, data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passage to display 70 after processing or retrieval. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180 via a wired or wireless communication link or the like such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to the frame 80 or may be a stand-alone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0104] Continuing to refer to FIG. 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility, which may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information, such as information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, one or more computer systems) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, for example, via a wireless or wired connection. (Diffraction grating having reduced polarization sensitivity)

[0105] Providing a high-quality immersive experience to users of waveguide-based display systems, such as various display systems configured for virtual / augmented / composite display applications as described above, depends, inter alia, on various characteristics of optical coupling into and / or out of the waveguide within the eyepiece of the display system. For example, a virtual / augmented / composite display having high internal and external coupling efficiencies can improve the viewing experience by increasing the brightness of the light directed towards the user's eye. As discussed above, internal coupling optical elements, such as internal coupling diffraction gratings, may be employed to couple light into the waveguide by total internal reflection so as to be guided therein. Similarly, external coupling optical elements, such as external coupling diffraction gratings, may be employed to couple light guided within the waveguide out of the waveguide by total internal reflection.

[0106] For example, as described above with reference to FIGS. 6 and 7, a display system according to various implementations described herein may include a combined pupil expander-extractor (CPE) that can include optical elements, such as internal coupling optical elements, external coupling optical elements, light dispersing elements, and / or diffraction gratings. As disclosed herein, the CPE may operate as both a light dispersing element that diffuses or disperses light within the waveguide, potentially increasing the beam size and / or the eye box, and an external coupling optical element that couples light out of the waveguide.

[0107] For example, as described above with reference to FIG. 7, light 640 that is input into waveguide 270 at the input surface 460 of waveguide 270 is guided within waveguide 270 by total internal reflection (TIR). In various implementations, at the point where light 640 impinges on external coupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as beamlets 650. In some implementations, any of optical elements 570, 580, 590, 600, 610, which may include one or more of an internal coupling optical element, an external coupling optical element, a light distribution element, or a CPE, can be configured as a diffraction grating.

[0108] To achieve the desired characteristics of internal coupling (or external coupling therefrom) of light into the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed from a suitable material and have a suitable structure for controlling various optical properties, including diffractive properties such as diffraction efficiency as a function of polarization. Desirable diffractive properties that are possible to consider include, among other properties, any one or more of the following, namely, spectral selectivity, angular selectivity, polarization selectivity (or non-selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV).

[0109] Some diffraction gratings have strong polarization dependence and thus may have a relatively reduced overall efficiency (due to the blocking of a certain polarization). Such diffraction gratings can also create coherent artifacts and reduce the uniformity of the far-field image. To provide a diffraction grating having reduced polarization sensitivity (e.g., coupling light with an efficiency that is relatively independent of polarization), some displays for an AR system according to the implementations described herein include a waveguide with a blazed diffraction grating formed therein. The blazed grating may have diffractive features, for example, having a "sawtooth" shape. In some implementations, the blazed grating can achieve an improved grating diffraction efficiency for a given diffraction order, while the diffraction efficiency of other orders is reduced or minimized. As a result, more light can be directed into a particular given diffraction order, in contrast to any of the other orders in some implementations.

[0110] FIG. 10A illustrates a partial cross-sectional view of a display device 1000, such as an eyepiece lens, comprising a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate, which is the waveguide 1004, according to some of the designs described herein. In the illustrated implementation, the blazed diffraction grating 1008 is formed within the substrate / waveguide 1004 (which is planar in this example). The surface of the substrate or waveguide 1004 has a surface topography with diffraction features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths within the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of an eyepiece lens through which a user's eye can see. Such a waveguide 1004 and eyepiece lens may be included within a head-mounted display such as an augmented reality display. The waveguide 1004 may correspond to, for example, one of the waveguides 670, 680, 690 described above with respect to FIGS. 9A - 9C. The blazed diffraction grating 1008 may correspond to, for example, one of the internal coupling optical elements 700, 710, 720 described above with respect to FIGS. 9A - 9C. The blazed diffraction grating 1008, which is configured to internally couple light into the waveguide 1004, may be referred to herein as an internal coupling grating (ICG). The display device 1000 may additionally include an optical element 1012 that may correspond to, for example, a light dispersing element (e.g., one of the light dispersing elements 730, 740, 750 shown in FIGS. 9A - 9C) or an external coupling optical element (e.g., one of the external coupling optical elements 800, 810, 820 shown in FIGS. 9A - 9C).

[0111] During operation, when an incident light beam 1016, for example, visible light from an optical projection system that provides image content, is incident on the blazed diffraction grating 1008 at an incident angle α measured with respect to the plane normal 1002, which is normal or orthogonal to the extended surface or plane of the blazed diffraction grating or the substrate / waveguide and / or the surface 1004S of the waveguide 1004, for example, the major surface of the waveguide (shown in FIG. 10A as extending parallel to the y - x plane) on which the grating is formed, the blazed diffraction grating diffracts the incident light beam 1016, at least in part, as a diffracted light beam 1024 at a diffraction angle θ measured with respect to the plane normal 1002. When the diffracted light beam 1024 is diffracted at a diffraction angle θ that exceeds the critical angle θ TIR for total internal reflection to occur within the waveguide 1004, the diffracted light beam 1024 generally propagates and is guided within the waveguide 1004 via total internal reflection (TIR) along a direction generally parallel to the x - axis and along the length of the waveguide. A portion of the light guided within the waveguide 1004 reaches one of the light dispersion elements 730, 740, 750 or one of the external coupling optical elements (800, 810, 820, FIGS. 9A - 9C) and can be diffracted again, for example.

[0112] As described herein, as in the illustrated implementation, a light beam incident at an angle in the clockwise direction (i.e., to the right of the plane normal 1002) with respect to the plane normal 1002 is said to have a negative α (α < 0), while a light beam incident at an angle in the counterclockwise direction (i.e., to the left of the plane normal) with respect to the plane normal 1002 is said to have a positive α (α > 0).

[0113] As further described elsewhere in this specification, a suitable combination of the high refractive index material and / or structure of the diffraction grating 1008 can result in an incident angle α within a particular range (Δα), herein referred to as the acceptance angle or field of view (FOV). A range Δα can be described by a range of angles extending to negative and / or positive values of α, outside of which the diffraction efficiency drops by more than 10%, more than 25%, more than 50%, or more than 75%, more than 80%, more than 90%, more than 95%, or any value within a range defined by any of these values, relative to the diffraction efficiency at α = 0 or in some other direction. In some implementations, it may be desirable to have a Δα within a range where the diffraction efficiency is relatively high and constant, for example, if a uniform intensity of the diffracted light is desired within Δα. Thus, in some implementations, Δα is associated with the angular bandwidth of the diffraction grating 1008 such that an incident light beam 1016 within Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ with respect to the surface normal 1002 (e.g., a direction parallel to the y - z plane), where θ TIR is exceeded. In some implementations, this range of the angle Δα can affect the field of view visible to the user. It should be understood that in various implementations, light can be directed onto the internal coupling grating (ICG) from both sides. For example, light can be directed through a substrate or waveguide 1004 and incident on a reflective internal coupling grating (ICG) 1008 such as that shown in FIG. 10A. The light can undergo the same effect and be coupled into the substrate or waveguide 1004 by the internal coupling grating 1008 such that the light is guided within the substrate or waveguide by total internal reflection (TIR). In this specification, the range of the incident angle α, herein referred to as the acceptance angle or field of view (FOV) range (Δα), can be affected by the refractive index of the substrate or waveguide material. In FIG. 10A, for example, a reduced range of angles (Δα’) shows the effect of refraction of the high refractive index material on the light incident on the internal coupling grating (ICG). However, the range of the angle (Δα) or FOV is larger.

[0114] FIG. 10B illustrates a cross-sectional view of an exemplary blazed transmission diffraction grating 1008. The grating 1008 comprises grating features having a cusp 1003 and a groove 1005. The blazed transmission grating 1008 comprises a surface corresponding to the surface of a substrate or waveguide 1004S having a “sawtooth” shaped pattern as visible from the cross-section shown. The patterned “sawtooth” is formed by a portion 1007 having a first slope of the surface 1004S. In the embodiment shown in FIG. 10B, the grating 1008 also includes a portion 1009 having a second (steeper) slope. In the embodiment shown, the portion 1007 having the first slope has a shallower slope than the portion 1009 having the steeper slope. The portion 1007 having the first slope is also wider than the portion 1009 having the second slope in this embodiment.

[0115] The protruding end 1003 has a height H corresponding to the distance from the bottom of the groove 1005 to the top of the protruding end 1003. Thus, this value may be referred to in this specification as the protruding end height and / or groove depth, grating height or grating depth, or the height of the diffraction characteristics of the diffraction grating. In the embodiment shown in FIG. 10B, the bottom of the groove 1005 is formed by the intersection of the first and second sloped portions 1007, 1009 of two adjacent protruding ends 1003. The first sloped portion 1007 is on one of the adjacent protruding ends 1003, and the second sloped portion 1009 is on the other adjacent protruding end. Similarly, the top of the protruding end 1003 is formed by the intersection of the first and second sloped portions 1007, 1009 at the top of the protruding end 1003. However, other configurations are also conceivable. For example, the first and second sloped portions do not necessarily intersect, for example, when the bottom of the groove 1005 has a flat base or the top of the protruding end 1003 includes a flat platform, as discussed below. The blazed diffraction grating 1008 may have a line spacing or pitch d that can be constant in some implementations. This line spacing or pitch d can be a measure of the separation of the vertices of the protruding ends 1003 within the grating 1008 having a shape similar to that shown in FIG. 10B, for example. Similarly, the line spacing or pitch d can be a measure of the separation of the deepest locations of adjacent grooves 1005. The line spacing or pitch d may be measured from other positions on the grating features.

[0116] The slope can be inclined at an angle δ with respect to a plane parallel to the surface of the grating 1008 or the waveguide (e.g., the surface 1004S of the waveguide that can extend beyond the grating or surface 1004S' of the waveguide as opposed to the grating in FIG. 10A). This angle δ of the first (shallower) sloped portion 1007 may be referred to as the blaze angle in this specification.

[0117] As shown in FIG. 10B, the blazed diffraction grating 1008 can include grating lines or features having an asymmetric shape, for example, including asymmetrically shaped protrusions 1003 and / or grooves 1005. For example, in the diffraction grating shown in FIG. 10B, the diffraction features include protrusions 1003 and / or grooves 1005 having an asymmetric triangular cross-sectional shape. As discussed above, this asymmetric shape results in different slopes and / or widths of the first and second sloped portions 1007, 1009. However, other shapes are also conceivable.

[0118] In a design where the diffraction feature is asymmetric, for example, the slope of the first sloped portion is shallower while the slope of the second sloped portion is steeper, the diffraction feature can be considered to be formed from repeated slopes and steps. Such a structure may be referred to herein as an inclined step structure. In some implementations, the second portion may be less steeply sloped, for example, the second portion may be parallel to the normal 1002.

[0119] However, in other implementations of the "sawtooth" pattern, the protrusions 1003 and / or grooves 1005 may be symmetric. For example, the first and second sloped portions 1007, 1009 may have the same slope and the same width.

[0120] The cross-sectional pattern shown in FIG. 10B may be referred to herein as a single-step geometry as compared to the multi-step structure discussed below. The multi-step structure is shown, for example, in FIG. 11D.

[0121] Regardless of whether the diffraction feature is asymmetric or symmetric, in some implementations, a mesa or flat portion may be located on top of the protrusion 1003 as discussed below. A diffraction grating 1008 having a diffraction feature with a mesa or flat portion on top of the protrusion 1003 is shown, for example, in FIGS. 11B and 11D.

[0122] FIG. 10B shows an incident light beam 1016 that is incident on grating 1008 at an angle α with respect to the normal direction 1002. (As discussed above with respect to FIG. 10A, in other embodiments, light can pass through substrate or waveguide 1004 and be incident on grating 1008 from the other side.) As discussed above, the normal 1002 is normal or orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface or the opposing planar surface 1004S' of the waveguide on which the grating is formed. In FIG. 10B, the light 1016 incident on the diffraction grating 1008 is shown to be diffracted at an angle β with respect to the normal direction 1002.

[0123] According to various embodiments, when configured as an internal coupling optical element or an internal coupling diffraction grating, the diffraction grating 1008 can diffractively couple the light incident in the substrate 1004, which can be a waveguide as described above. The diffraction grating 1008 may optionally be configured as an external coupling optical element, and in such embodiments, it can similarly diffractively couple the light from the substrate 1004, which can also be a waveguide as described above.

[0124] Referring to FIGS. 10A and 10B, in some implementations, the substrate 1004 includes a high refractive index material having a refractive index of at least 1.9. The refractive index can be, for example, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and can be 2.4 or less, 2.5 or less, 2.6 or less, 2.7 or less, 2.8 or less, or can be within any range formed by any of these values, or can be outside of these ranges. In some implementations, for example, the substrate includes a Li-based oxide. In various embodiments disclosed herein, the diffraction features of the diffraction grating 1008 may be formed on the surface of the substrate 1004. The diffraction features can be formed within the substrate 1004, such as within a waveguide, or across the substrate 1004, such as across a waveguide, and can be formed within any of separate layers that are optically in communication with the substrate 1004, such as configured to couple light into or out of the substrate 1004. In the illustrated embodiment, the diffraction features of the diffraction grating 1008, such as lines, are formed within the substrate 1004, such as within the surface of the substrate. The diffraction features can be etched into the substrate 1004, which includes a high refractive index material, such as a Li-based oxide. The substrate can include, for example, lithium niobate, and the diffraction grating can be formed within the lithium niobate substrate by etching or patterning the surface of the substrate. Other materials having a high refractive index can also be used. For example, lithium oxides, such as lithium tantalate (LiTaO 3 ) and the like, which contain lithium, can also be employed as the substrate. Silicon carbide (SiC) is another option for the substrate material. The embodiments are not so limited. In other embodiments, the diffraction features of the diffraction grating 1008 can be formed within a separate layer that is disposed across the substrate 1004, such as physically contacting it. For example, zinc oxide (ZnO) having a thickness of less than 200 nm, silicon nitride (Si 3 N 4 ), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2) A thin film coating such as silicon carbide (SiC) may be disposed over an existing high refractive index substrate. The thin film coating may be patterned to form diffraction features. However, in some implementations, diffraction features such as the lines of diffraction grating 1008 may be formed from a different material than that of the substrate. The substrate may include, for example, a Li-based oxide (e.g., lithium niobate LiNbO 3 or lithium tantalate LiTaO 3 ) and other high refractive index materials, however, the diffraction features may be formed from different materials such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), or other materials described herein. In some implementations, other materials formed on the substrate may have a lower refractive index. In some cases, substrate 1004 may include, for example, silica glass (e.g., doped silica glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium dioxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials based on materials having a suitable refractive index different from that of the material of the Li-based oxide feature 1008 and substantially optically transparent to visible light, such as those described above (including amorphous high refractive index glass substrates).

[0125] However, as described above, in various implementations described herein, both the diffraction grating 1008 and the substrate 1004 or waveguide include the same material, e.g., a Li-based oxide. In some implementations, the diffraction grating 1008 is directly patterned into the substrate 1004 such that the diffraction grating 1008 and the substrate 1004 form a single piece or monolithic structure. For example, the substrate 1004 comprises a waveguide having a diffraction grating 1008 formed directly within the surface of the waveguide or substrate. In these implementations, a bulk Li-based oxide material may be patterned on the surface 1004S to form the diffraction grating 1008, while the Li-based oxide material below the diffraction grating 1008 may form the waveguide. Further, in some other implementations, the bulk or substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 include different Li-based oxides. For example, the bulk Li-based oxide material patterned in the surface region to form the diffraction grating 1008 may be formed from a first Li-based oxide material, while the Li-based oxide material below the diffraction grating 1008 forming the substrate 1004 or substrate region may be formed from a second Li-based oxide material different from the first Li-based oxide material. As discussed above, in some other implementations, the diffraction grating 1008 is made of a different high refractive index material such as zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), etc., and the material below the diffraction grating 1008 forming the substrate 1004 or substrate region may be formed from a second material different from the first material coated as a thin film such as LiTaO 3 , LiNbO 3 , etc.

[0126] In the embodiments illustrated in FIGS. 10A and 10B, the diffraction grating 1008 may include a plurality of blazed diffraction grating lines that extend in a first horizontal or y - direction and are periodically repeated in a second horizontal or x - direction. The diffraction grating lines can be, for example, straight and continuous lines extending in the y - direction. However, the embodiments are not so limited. In some implementations, the diffraction grating lines can be, for example, discontinuous lines in the y - direction. In some other implementations, the discontinuous lines can form a plurality of pillars protruding from the surface of the grating substrate. In some implementations, at least some of the diffraction grating lines can have different widths in the x - direction.

[0127] In the illustrated embodiments, the diffraction grating lines of the diffraction grating 1008 have a sawtooth profile with a certain profile, for example, asymmetric opposing side surfaces that form different angles with respect to the plane of the substrate. However, the embodiments are not so limited, and in other implementations, the diffraction grating lines can have symmetric opposing side surfaces that form similar angles with respect to the plane of the substrate.

[0128] Referring to FIGS. 10A and 10B according to various embodiments, the diffraction grating 1008 may have various dimensions. For example, according to embodiments, the diffraction features of the diffraction grating 1008 may have a height (H) that is a height within a range defined by 10 nm or 40 nm to 150 nm or 200 nm, 50 nm to 110 nm, 60 nm to 100 nm, 70 nm to 90 nm, or about 80 nm, or any of these values. This height may correspond to the height of the tip 1003 and / or the depth of the groove 1005. Such a height with a blazed geometry in a high refractive index material can provide a diffraction grating with reduced polarization sensitivity. However, other heights are also possible.

[0129] According to various embodiments, the diffraction grating 1008 may have a pitch of 250 nm to 350 nm, 300 nm to 400 nm, 250 nm to 450 nm, or a pitch within any range defined by any of these values. Other pitches are also conceivable as possibilities.

[0130] The diffraction grating 1008 may have a blaze angle (shallow side) of about 10 to 70 degrees and a reverse blaze angle (steep side) of 140 to 70 degrees, or any value within the range defined by these values. Values outside these ranges are also conceivable as possibilities.

[0131] As shown in FIGS. 11A - 11D, a blazed diffraction grating of either single - stage or multi - stage geometry may be formed. In the examples shown in FIGS. 11A - 11D, the grating is formed by depositing a blazed photoresist and then etching and patterning the photoresist.

[0132] FIG. 11A illustrates the formation of a single - stage blazed grating 1106 in a substrate 1104, which can be a waveguide 1004 (FIG. 10A). A patternable material such as a photoresist 1102 may be deposited on the substrate 1104, which may include the waveguide 1004. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grating. The step of forming the blazed geometry in the photoresist 1102 may, in some implementations, involve imprinting a pattern such as a single - stage "sawtooth" pattern into the photoresist 1102 (e.g., depositing the photoresist on the substrate 1104 and then imprinting the blazed geometry). The photoresist 1102 may include a mask such as a hard mask. The patterned photoresist 1102 and the substrate 1104 are then etched to form the blazed pattern in the substrate 1106. The step of etching the photoresist 1102 and the substrate 1104 may, for example, involve dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching illustrated in FIG. 11A etches away the material at a relatively constant rate such that the portion where the patterned photoresist was thickest results in a relatively small removal of material from the substrate, e.g., negligible or no removal, while the portion where the patterned photoresist was thinnest (or did not exist) results in a relatively large removal of material from the substrate or the deepest etching into the substrate.

[0133] FIG. 11B is a scanning electron micrograph of a blazed photoresist grating 1112, where the blazed grating pattern is formed in the photoresist 1104, for example, by imprinting the photoresist using a patterned master. The diffraction grating 1112 shown has a single - stage blazed geometry.

[0134] FIG. 11C illustrates the formation of a multi - stepped blazed grating 1156 within a substrate 1154, which can be a waveguide 1004 (FIG. 10A). A patternable material such as a photoresist 1152 can be deposited on the substrate 1154. The patternable material / photoresist 1152 is patterned to have the shape of the blazed grating. The step of forming the blazed photoresist 1152 may, in some implementations, involve imprinting a pattern such as a multi - stepped "sawtooth" pattern into the photoresist 1152 (e.g., depositing the photoresist on the substrate 1154 and then imprinting the blazed geometry). The patterned photoresist 1152 and the substrate 1154 can then be etched to form a multi - stepped blazed substrate 1156. The photoresist 1152 may comprise a mask such as a hard mask. The patterned photoresist 1152 and the substrate 1154 can then be etched to form a blazed pattern within the substrate 1156. The step of etching the photoresist 1152 and the substrate 1154 may, for example, involve dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching illustrated in FIG. 11C etches away the material at a relatively constant rate such that the portion where the patterned photoresist was thickest results in a relatively small removal of material from the substrate, e.g., negligible or no removal, while the portion where the blazed photoresist was thinnest (or non - existent) results in a relatively large removal of material from the substrate or the deepest etching into the substrate.

[0135] FIG. 11D is a scanning electron micrograph of a blazed photoresist grating 1162, where the blazed grating pattern is formed on a photoresist 1164, for example, by imprinting the photoresist using a patterned master. The diffraction grating 1162 may have a multi - stepped blazed geometry. The width of the tip 1003 is shown to be about 200 nm.

[0136] As shown in FIG. 11E, the blazed geometry of a diffraction grating formed within a high refractive index substrate such as grating 1008 of FIGS. 10A and 10B can be varied to have different heights and / or blaze angles. In particular, FIG. 11E illustrates a first diffraction grating 1170 (e.g., geometry 1) having a first shape and a first height (which may be about 80 nm in some implementations). FIG. 11E also illustrates a second diffraction grating 1180 (e.g., geometry 2) having a second shape and a second height (which may be lower than the first height and may be about 35 nm for some designs). As will be discussed at least in connection with FIG. 13, varying the geometry of a blazed diffraction grating can vary the performance characteristics of the grating. For example, geometry 1 with a height (or depth) of 80 nm may provide lower polarization sensitivity than geometry 2 with a height (or depth) of 35 nm.

[0137] FIGS. 12A - 12F show scanning electron microscope photographs (SEM) of various blazed diffraction gratings formed within a substrate. The substrates and gratings of FIGS. 12A - 12F are merely illustrative examples, and in general, feature sizes, pitch, angles, and other characteristics may be varied to achieve desired performance characteristics.

[0138] FIGS. 12A - 12C show a lithium niobate (LiNbO 3 ) substrate having an upper surface with a blazed geometry (e.g., a blazed diffraction grating). FIG. 12A shows a lithium niobate (LiNbO 3)SEM image 1200 of a blazed diffraction grating formed in a substrate, where the height of the steps or tips of the blazed grating is measured to be approximately 31.90 nm. The angle δ of the surface with a first (shallower) inclination with respect to the plane of the substrate is approximately 12.1 degrees. (This angle δ may be referred to as the blaze angle in this specification.) FIG. 12B shows SEM image 1202 of the blazed grating from a different perspective. FIG. 12B shows a pitch (e.g., the distance between the minimum values of the tips or steps or grooves) measured to be approximately 331.8 nm. In the SEM image 1204 shown in FIG. 12C, lithium niobate (LiNbO 3 )The blazed grating formed in the substrate is shown to have a tip or step height that is measured to be approximately 46.26 nm. The angle δ of the surface with a first (shallower) inclination with respect to the plane of the substrate is approximately 19.5 degrees. (This angle δ may be referred to as the blaze angle in this specification.)

[0139] FIG. 12D shows SEM image 1206 of a silicon substrate that has been etched to form a blazed diffraction grating therein. The height of the blazed diffraction feature in the example of FIG. 12D, e.g., the height of the tip or the depth of the groove, is measured to be approximately 63.80 nm. The width of the tip is measured to be approximately 167.5 nm. The "steep" angle of the tip, e.g., the angle of the second, steeper inclined portion, is measured to be approximately 53.0 degrees (with respect to the extended plane of the substrate). The "shallow" angle of the tip, e.g., the angle δ of the first, shallower inclined portion (which may be referred to as the blaze angle), is measured to be approximately 27.9 degrees (with respect to the extended plane of the substrate).

[0140] FIG. 12E shows a SEM image 1208 of a silicon substrate that is etched to form a multi-level blazed diffraction grating therein. In the embodiment of FIG. 12D, the height of the multi-level blazed feature, e.g., the height of the tip or the depth of the groove, is measured to be about 66.85 nm. The width of the multi-level blazed feature or tip is measured to be about 206.9 nm (e.g., the width excluding any spacing between adjacent multi-level features). The overall "shallow" angle of the tip, determined based on the height of the tip relative to the distance from the base of the tip to the top of the tip, is measured to be about 22.5 degrees (relative to the plane in which the substrate extends). The "steep" angle, e.g., the angle of the second, more steeply inclined portion of the tip, is measured to be about 68.8 degrees (relative to the plane in which the substrate extends).

[0141] FIG. 12F shows a SEM image 1210 of a substrate formed from glass having a refractive index (RI) of 1.8. The imaged substrate has a blazed diffraction grating formed therein with a step or feature height of about 87.09 nm.

[0142] In general, varying the geometry of a blazed diffraction grating such as grating 1008 in FIGS. 10A and 10B can modify the performance characteristics of the grating. In at least some implementations, for example, a diffraction grating (e.g., a diffractive optical coupling element that couples light internally or externally, relatively independently of the polarization of the light) that is less sensitive to the polarization of light can be obtained by suitably adjusting parameters of the grating such as the thickness of the grating or the height of the diffraction feature. A diffraction grating having reduced polarization sensitivity can have a higher overall efficiency (e.g., can couple more light than a grating that is more sensitive to polarization), and since a polarization-sensitive grating can introduce unwanted coherent artifacts and reduce, for example, the uniformity of a far-field image produced by an eyepiece of a head-mounted display, it can provide a more uniform image for the viewer.

[0143] FIG. 13 illustrates, for example, the polarization sensitivity of various blazed diffraction gratings. In particular, FIG. 13 illustrates the TM / TE internal coupled grating diffraction efficiency (DE) ratio as a function of the angle of incidence. The TM / TE ICG DE ratio may correspond to, for example, the internal coupling efficiency for transverse magnetic (TM) polarization divided by the internal coupling efficiency for transverse electric (TE) polarization. The angle of incidence may be, for example, the angle of incidence α as referenced in FIGS. 10A and 10B.

[0144] Plot 1300 illustrates the TM / TE ratio as a function of the angle of incidence α for a blazed diffraction grating formed in a photoresist disposed on a lithium niobate substrate. As shown in plot 1300, the diffraction grating formed from the blazed photoresist on the lithium niobate substrate may be relatively polarization sensitive, having, for example, an efficiency for TM polarization that exceeds the efficiency for TE polarization within a range of angles of incidence by a factor of 3 to 4.

[0145] Plot 1302 illustrates the TM / TE ratio as a function of the angle of incidence α for a blazed diffraction grating (such as diffraction grating 1180 having the geometry 2 shown in FIG. 11E) comprising diffraction features formed in a lithium niobate substrate having a feature or tip height (or groove depth) H of 35 nm. As shown in plot 1302, the diffraction grating with a 35 nm etched feature height is not as polarization sensitive as the blazed grating formed in a photoresist layer deposited on the lithium niobate substrate. Over most of the measured range of angles of incidence, the diffraction grating with a 35 nm etched feature height only slightly favors TM polarization over TE polarization at a ratio of about 1.5 to 2.0 or 2.2 (for example, the grating thus has a slightly reduced polarization sensitivity).

[0146] Plot 1304 illustrates the TM / TE ratio as a function of the angle of incidence α for a blazed diffraction grating (such as diffraction grating 1170 having the geometry 1 shown in FIG. 11E) with diffraction features formed within a lithium niobate substrate having a feature or tip height (or groove depth) H of 80 nm. As shown in Plot 1304, a diffraction grating with an etched diffraction feature height of 80 nm has a TM / TE diffraction efficiency ratio of approximately 1 over a wide range of angles of incidence (e.g., the grating has a reduced polarization sensitivity, e.g., is substantially insensitive to polarization).

[0147] FIG. 14 illustrates the TM / TE diffraction efficiency of a blazed diffraction grating formed within a lithium niobate substrate having a feature height of 80 nm for different colors of light (e.g., for green light, blue light, and red light). As shown in FIG. 14, the TM / TE diffraction efficiency ratio (of diffraction grating 1170) is approximately 1 over a wide range of angles of incidence for both green and blue light. In addition, for red light, the TM / TE diffraction efficiency ratio is generally approximately 1.5 and increases above 2 for a certain angle of incidence (but less than 2.5).

[0148] FIG. 15 illustrates the average diffraction efficiency of a blazed diffraction grating formed within lithium niobate with a feature height of 80 nm for green, blue, and red light as a function of the angle of incidence. The average diffraction efficiency can indicate, for example, the efficiency of the diffraction grating in internal coupling (or external coupling) unpolarized light.

[0149] In addition to the general reduction in efficiency and brightness, a diffraction grating that is highly sensitive to polarization can also create coherent artifacts and reduce the uniformity of the far-field image produced by the eyepiece lens in a head-mounted display that directs image content to the user's eye.

[0150] FIG. 16 shows the distribution of light output from an eyepiece lens with an internal coupling grating, which comprises a blazed diffraction grating formed in a photoresist deposited on a lithium niobate substrate, for internally coupling light into a waveguide-based eyepiece lens and a light redirection element (orthogonal pupil expander) and an external coupling optical element (exit pupil expander). As shown in FIG. 16, the eyepiece lens with an internal coupling optical element comprising a blazed diffraction grating in a photoresist deposited on a lithium niobate substrate can produce a coherent uniformity of about 9.45% for non-polarized input and about 11.3% for linearly polarized input. The graph and image of FIG. 16 are obtained from a 500-micron-thick Z-cut lithium niobate substrate having thereon a layer of photoresist patterned by imprinting to form the internal coupling grating. FIG. 16 shows non-uniformities within the far-field image 1600. In this example, the plotted uniformity score is a mathematical value derived from analyzing the pixel values of an image captured over an area, giving an indication of the non-uniformity within the values captured at different sampling spatial frequencies over the image. Lower values indicate a more uniform color distribution over the field of view of the captured or desired image.

[0151] FIG. 17 shows the distribution of light output from an eyepiece lens having an internal coupling grating including a blazed diffraction grating formed in a lithium niobate substrate for internally coupling light into a waveguide-based eyepiece lens and an optical re-directing element (orthogonal pupil expander) and an external coupling optical element (exit pupil expander). As shown in FIG. 17, the internal coupling optical element including the blazed diffraction grating having a feature height (apex height or groove depth) of 80 nm formed by etching in the lithium niobate substrate can have an improved coherent uniformity such as about 8.1% for non-polarized input and about 8.35% for linearly polarized input. The graph and image of FIG. 17 are obtained from a 500 micron thick Z-cut lithium niobate substrate with a blazed diffraction grating etched therein. The EPE and OPE are also etched into the substrate. FIG. 17 shows a reduction in non-uniformity in the far-field image 1700 relative to the far-field image 1600.

[0152] Therefore, a blazed grating formed in a high refractive index substrate such as lithium niobate having a dimension such as a thickness within the range of about 40 - 120, or 60 - 100, or 70 - 90, or 80 nanometers, or any value between any of these values, can provide reduced polarization sensitivity.

[0153] The structure and its manufacturing method may be different from those of the embodiments specifically described above. For example, the blazed grating may be used as an external coupling optical element (e.g., EPE) and / or an optical re-directing optical element (e.g., OPE). In addition, instead of a diffraction grating, other types of diffractive optical elements may be formed, for example, in a high refractive index substrate. For example, lithium tantalate (e.g., LiTaO 3Different high refractive index materials such as, etc. may be used for the waveguide and the diffraction features formed therein. As discussed above, in some other implementations, the waveguide and the diffraction features formed therein may include other high refractive index materials such as silicon carbide or high refractive index amorphous glass. Additionally, in some implementations, the diffraction grating 1008 includes different high refractive index materials or coatings such as zinc oxide (ZnO), silicon nitride (Si 3 N 4 ), zirconium dioxide (ZrO 2 ), titanium dioxide (TiO 2 ), silicon carbide (SiC), etc., and the material below the one forming the substrate 1004 or the substrate region may include a second high refractive index material such as LiTaO 3 , LiNbO 3 , etc. (Diffraction Grating with 2D Array of Diffraction Features)

[0154] Various implementations of diffraction gratings with reduced polarization sensitivity can be implemented as a one-dimensional (1D) array of diffraction features, e.g., as lines as described above. For example, FIG. 10A shows a cross-sectional side view of an exemplary device 1000 having a series of diffraction features 1012 having a "sawtooth" shape with sloped sidewalls and arranged laterally in one direction (e.g., the first horizontal or x direction in FIG. 10A). The diffraction features 1012 undulate in one direction (e.g., the first horizontal or x direction in FIG. 10A) or extend in one direction (e.g., the second horizontal or y direction in FIG. 10A) and are thus referred to as 1D. As a further example of a 1D diffraction feature, FIG. 11B shows a perspective view of a blazed photoresist grating configured as a 1D array. The diffraction features 1012 (FIG. 10A) can form a series of elongated longitudinal features such as lines extending in one direction (e.g., the second horizontal or y direction in FIG. 10A). The elongated longitudinal features are arranged along one direction (e.g., the first horizontal or x direction in FIG. 10A) and repeated in that direction.

[0155] In some embodiments, the array of structures can also be arranged in two directions to form a two-dimensional (2D) array of diffraction features. The 2D array of diffraction features can include undulations in two directions. In some instances, the undulations can be periodic, while in other instances, the pitch of the undulations can vary in at least one direction. According to various examples described herein, the diffraction features have opposing sidewalls that are asymmetrically angled or tilted. According to various examples described herein, the diffraction features can be tapered. In some implementations, the diffraction features can have opposing sidewalls that are substantially angled or tilted. In some implementations, the opposing sidewalls can be tilted in the same direction, while in other implementations, the opposing sidewalls can be tilted in opposing directions. In some other implementations, the diffraction features can have one of the opposing sidewalls that is substantially tilted, while having the other sidewall that is substantially perpendicular or orthogonal to the horizontal axis or tilted less than at least the other sidewall. In various examples of the 2D diffraction features described herein, the 2D diffraction features can be waveguides, formed within or on the underlying substrate, as described above with respect to various examples of the 1D diffraction features. For example, the 2D diffraction features can be formed by etching into the underlying substrate or patterning a separate layer formed thereon. Thus, the 2D diffraction features can be formed from the same or different materials as the substrate material, similar to what was described above with respect to various 2D diffraction features. Other variations and configurations are also possible as contemplated.

[0156] FIG. 18 shows an exemplary device 3600 having a 2D array of diffraction features 3603 (e.g., diffraction features 3603 arranged laterally in two dimensions or directions). In this example, the array is similar to a lattice pattern. The diffraction features 3603 can be referred to as protrusions. The diffraction features have angled sidewalls that are tilted in opposing directions. One of the sidewall tilts can have a tilt that is less than the other sidewall tilt. The result of this configuration is that the diffraction features are blazed.

[0157] The diffraction features in the illustrated embodiment of FIG. 18 are asymmetric in at least one lateral direction. FIGS. 18A and 18B show, respectively, a cross-sectional side view and a top view of an exemplary array of asymmetric diffraction features. The present 2D diffraction grating comprises a blazed diffraction grating. The diffraction features may be tapered in height, for example, in thickness. In the embodiment shown in FIG. 18, the diffraction features have sidewalls or facets with two opposing slopes, one slope being greater than the other and inclined in opposite directions, while in the embodiments shown in FIGS. 18A and 18B, one sidewall is sloped while the other opposing sidewall is substantially vertical or has a slope on the second sidewall that is not sloped or is negligible. In both cases, the slope of one of the opposing sidewalls exceeds that of the other of the opposing sidewalls such that the diffraction features are asymmetric and blazed. As a result, the diffraction features diffract light preferentially in one direction over the other. Such a diffraction grating can be useful as an internal coupling optical element configured to diffract light received from a projector, for example, towards a light distribution element, an external coupling optical element, or a combination of a light distribution element and an external coupling optical element, such as a combined pupil expander-extractor (CPE). Such a diffraction grating can be useful for externally coupling light to the eye, in contrast to the direction towards the front environment or world of the user and the head-mounted display. The sidewall tilt angle is, in some implementations, less than 30 degrees relative to the horizontal axis on one side and greater than 80 degrees (e.g., 80-90 degrees) on the other side. However, other tilts and tilt angles are also possible. In some instances, the diffraction features can form a 2D array of sawtooth structures such as sawtooth nanostructures.

[0158] Thus, in various implementations, a 2D array of symmetric or asymmetric diffraction features can serve as a blazed diffraction grating. As discussed above, the shape of the diffraction grating (e.g., the tilt angle of the sidewalls) can determine the direction in which the grating directs light or preferentially directs light towards it. For example, the grating may direct more light towards other gratings (e.g., EPE, OPE, or CPE) and / or towards the viewer. In some instances, the diffraction features can be faceted and bias the propagation of light in two or more directions (e.g., blazed in multiple directions). For example, FIG. 19A shows an exemplary device 3700 having a 2D array of diffraction features 3703 formed within or on a substrate 3701. The diffraction feature 3703 has a first sidewall or facet 3703b-1 and a second sidewall or facet 3703b-2 that is tilted. Thus, the diffraction feature is, for example, tapered in height. The diffraction feature 3703 can be configured to preferentially direct light in a direction based on the tilt angles of the first and second sidewalls or facets 3703b-1, 3703b-2. FIG. 19B shows an exemplary diffraction feature that directs more light in two specific directions (as illustrated by the two thick solid arrows directed upwards to the right and downwards to the left). Other embodiments are also possible.

[0159] Therefore, any of the structures or devices described in this specification, such as a lattice structure, may comprise a 1D lattice. Similarly, any of the structures or devices described in this specification, such as a lattice structure, may comprise a 2D lattice. Such a 2D lattice may be capable of diffusing light. These lattices may also comprise blazed lattices. Such blazed lattices may preferentially direct light in a certain direction. In some implementations, a 2D lattice (e.g., having one tilted facet on the diffraction feature) preferentially directs light in one direction, while in other implementations, a 2D lattice (e.g., having two tilted facets with different diffraction features) preferentially directs light in multiple directions. Similarly, any of the methods or processes described in this specification may be used for a 1D lattice. Similarly, any of the methods or processes described in this specification may be used for a 2D lattice. These 1D or 2D lattices may be included within or on a substrate and / or waveguide, within an eyepiece lens, and possibly integrated within a head-mounted display, as disclosed in this specification. These lattices may be employed as an input lattice (e.g., ICG), an output lattice (EPE), a light distribution lattice (OPE), or a combined light distribution / output lattice (e.g., CPE).

[0160] Figure 20A shows an exemplary method 3800 of forming a blazed grating. Method 3800 includes the step of providing a template or master 3810. If the diffraction features are to be angled, tilted, or sloped, the template 3810 can be patterned to form an angled structure. Various processes, such as an etching process, can be directed and angled to form such an angled structure. Some examples of angling processes such as an angled etching process include ion beam milling, angled dry etching, ion etching, GLAD etching, tilted etching, Faraday cage etching, etc. In some implementations, the choice of material employed for the template 3810 can assist in producing an angled structure having angled sidewalls within the template. In this example, the angled structure comprises angled elongated protrusions (e.g., for a 1D grating) or angled pillars (e.g., for a 2D grating). These angled elongated protrusions or angled pillars can have sidewalls that are tilted in the same direction and, in some cases, can be substantially parallel. Once the template 3810 is processed, a layer of patternable material (e.g., polymer, resist, photoresist, etc.) can be deposited on the substrate 3801, and this layer can be imprinted using the imprint template 3810. The template 3810 can be imprinted into the patternable material (e.g., resist material) 3805 on the substrate 3801 to form a mask 3805 for the substrate. In other implementations, the patternable material can be deposited on the template, and the substrate can be brought into contact with the template with the patternable material thereon. The template can be removed, and the resist material 3805 and the underlying substrate 3801 can be dry etched to form the diffraction features 3803 within the substrate 3801. In various implementations, dry etching is employed as shown. The etching can be directional. In the example shown, the etching process is not angled.Diffraction features 3803 resulting from being formed within substrate 3801 (or within a layer of material disposed on substrate 3801) may have a certain shape and, for example, may be blazed as a result of angled features within mask 3805. In the illustrated embodiment, the cross-section of the diffraction feature has a trapezoidal or substantially triangular shape with two slanted sides. The sides slope in opposite directions. In the illustrated embodiment, one side is more angled than the other, creating a blazed structure. This process may be used to form a 1D or 2D array of diffraction features.

[0161] FIG. 20B shows another exemplary method 3850 of forming blazed diffraction features. Mask 3855 and underlying substrate 3851 are etched at an angle (e.g., dry etching) to form diffraction features 3853 within substrate 3851 (or within a layer of material disposed on substrate 3851). In an angled etching process, the direction of the etching solution forms an angle that is tilted with respect to the surface normal direction of substrate 3851, which may be due to either a tilt at the inflow angle of the etching solution or a tilt on the surface of substrate 3851. Some examples of angled directional etching processes (e.g., angled etching) include ion beam milling, angled dry etching, ion etching, GLAD etching, inclined etching, Faraday cage etching, etc. The template may comprise elongated protrusions (e.g., for a 1D grating) or tapered columns (e.g., for a 2D grating) having a trapezoidal or substantially triangular cross-section. These elongated protrusions or tapered columns may have sidewalls that are tilted in opposite directions. One sidewall may be more angled than the other. Applying an angled etching process to these elongated protrusions or tapered columns may produce a blazed grating within a material, e.g., within the underlying substrate or a layer of material disposed on the substrate of the elongated protrusions or tapered columns. Blazed diffraction features having sides tilted in the same direction may be produced. In various implementations, one of the sides is more angled than the other. This process may be used to form a 1D or 2D array of diffraction features.

[0162] In various implementations, the resulting diffraction features may be blazed in two or more directions (e.g., as shown in FIG. 19A) as a result of the angled features within the mask (e.g., as shown in FIG. 20A) and / or as a result of using an angling process (e.g., as shown in FIG. 20B). Diffraction features or gratings blazed in two or more directions may be produced by etching twice. In some implementations, for example, diffraction features or gratings that are blazed in two or more directions may be produced by etching using a first mask and then again using a second, different mask. In some instances, as shown in FIG. 21, mask 3905 and substrate 3901 may be etched to form a first sidewall of diffraction feature 3903 within substrate 3901. Additionally, patterning may be provided to form a second sidewall. In various implementations, a second mask having a different orientation and / or shape may be used to form the second sidewall. The second mask (e.g., at an angle and / or in a different orientation with respect to the first sidewall) may be etched, for example, to form the second sidewall. In some implementations, after the first sidewall of diffraction feature 3903 is formed, a planarization layer 3907 may be added over the intermediate diffraction feature 3903 and substrate 3901. The planarization layer 3907, intermediate diffraction feature 3903, and / or substrate 3901 may be patterned and etched (e.g., at an angle with respect to the first sidewall) to form the second sidewall. The above examples are discussed in the context of patterning a substrate, but in some implementations, the processes described above may be employed to pattern a layer formed on the substrate rather than the substrate. Alternatively, in some implementations, the processes described above may be employed to pattern both a layer formed on the substrate and the substrate.

[0163] Additionally, while exemplary methods 3800, 3850, 3900 are illustrated to form a 2D array of asymmetric diffraction features, the methods can also be used to form a 2D array of symmetric diffraction features (regardless of the presence or absence of angled sidewalls). The methods can also be used to form a 1D array of diffraction features. In some instances, the diffraction features in the 1D array can be symmetric, regardless of the presence or absence of angled sidewalls. In some instances, the diffraction features in the 1D array can be asymmetric, for example, with angled sidewalls. Thus, in some cases, blazed diffraction features may be formed. Additional Examples - Part I: (Example 1) A head-mounted display system, A head-mountable frame, and An optical projection system configured to output light and provide image content, A waveguide supported by the frame, the waveguide comprising a substrate including a material having a refractive index of at least 1.9 and a blazed diffraction grating formed in the substrate, the substrate being configured to guide at least a portion of the light from the optical projection system into the waveguide, Comprising, the blazed diffraction grating having a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization over a range of angles of light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency, a head-mounted display system. (Example 2) The material having a refractive index of at least 1.9 includes a lithium-based oxide, the head-mounted display system according to Example 1. (Example 3) The material having a refractive index of at least 1.9 includes lithium niobate, the head-mounted display system according to Example 1 or 2. (Example 4) The head-mounted display system according to Example 1 or 2, wherein the material has a refractive index of at least 1.9 and includes lithium tantalate. (Example 5) The head-mounted display system according to Example 1, wherein the material has a refractive index of at least 1.9 and includes silicon carbide. (Example 6) The head-mounted display system according to Example 1, wherein the material has a refractive index of at least 1.9 and includes zirconium dioxide. (Example 7) The head-mounted display system according to Example 1, wherein the material has a refractive index of at least 1.9 and includes titanium dioxide. (Example 8) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.0 to 2.7. (Example 9) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.1 to 2.7. (Example 10) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.2 to 2.7. (Example 11) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.3 to 2.7. (Example 12) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.4 to 2.7. (Example 13) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.5 to 2.7. (Example 14) The head-mounted display system according to any of the above Examples, wherein the material has a refractive index of at least 2.6 to 2.7. (Example 15) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having protruding ends separated by grooves therebetween. (Example 16) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having a plurality of straight lines. (Example 17) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having a protruding end height or groove depth of 40 to 120 nm. (Example 18) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having a protruding end height or groove depth of 60 to 100 nm. (Example 19) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having a protruding end height or groove depth of 70 to 90 nm. (Example 20) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and having a protruding end height or groove depth of about 80 nm. (Example 21) The diffraction feature is asymmetric, and it is a head-mounted display system according to any of the above embodiments. (Example 22) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having a pitch of 250 to 350 nm. (Example 23) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having a pitch of 300 to 450 nm. (Example 24) The substrate is planar, and the blazed diffraction grating has a blaze angle of 10 to 30 degrees with respect to the plane of the substrate, and it is a head-mounted display system according to any of the above embodiments. (Example 25) The substrate is planar, and the blazed diffraction grating has a blaze angle of 15 to 25 degrees with respect to the plane of the substrate, the head-mounted display system according to any of the above embodiments. (Example 26) The substrate is planar, and the blazed diffraction grating has a blaze angle of about 19.5 degrees with respect to the plane of the substrate, the head-mounted display system according to any of the above embodiments. (Example 27) The first diffraction efficiency is 1 to 1.5 times that of the second diffraction efficiency, the head-mounted display system according to any of the above embodiments. (Example 28) The first diffraction efficiency is 1 to 1.4 times that of the second diffraction efficiency, the head-mounted display system according to any of the above embodiments. (Example 29) The first diffraction efficiency is 1 to 1.3 times that of the second diffraction efficiency, the head-mounted display system according to any of the above embodiments. (Example 30) The first diffraction efficiency is 1 to 1.2 times that of the second diffraction efficiency, the head-mounted display system according to any of the above embodiments. (Example 31) The first diffraction efficiency is 1 to 1.1 times that of the second diffraction efficiency, the head-mounted display system according to any of the above embodiments. (Example 32) The range of the angle is at least 6 degrees, the head-mounted display system according to any of the above embodiments. (Example 33) The range of the angle is at least 12 degrees, the head-mounted display system according to any of the above embodiments. (Example 34) The range of the angle is at least 18 degrees, the head-mounted display system according to any of the above embodiments. (Example 35) The range of the angle is at least 22 degrees, the head-mounted display system according to any of the above embodiments. (Example 36) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±3 degrees with respect to the plane of the substrate. (Embodiment 37) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±6 degrees with respect to the plane of the substrate. (Embodiment 38) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±9 degrees with respect to the plane of the substrate. (Embodiment 39) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±11 degrees with respect to the plane of the substrate. (Embodiment 40) The head-mounted display system according to any one of the above embodiments, comprising first and second polarizations that are first and second linear polarizations having different polarization angles. (Embodiment 41) The head-mounted display system according to any one of the above embodiments, comprising first and second polarizations that are first and second linear polarizations oriented in orthogonal directions. (Embodiment 42) The head-mounted display system according to any one of the above embodiments, wherein the first and second polarizations each comprise transverse magnetic and transverse electric polarizations. (Embodiment 43) The head-mounted display system according to any one of the above embodiments, wherein the first and second polarizations each comprise transverse electric and transverse magnetic polarizations. (Embodiment 44) The head-mounted display system according to any one of the above embodiments, wherein the first diffraction efficiency comprises the diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises the diffraction efficiency for transverse electric polarization averaged across the visible light spectrum. (Embodiment 45) The first diffraction efficiency includes the diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency includes the diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum. The head-mounted display system according to any of the above embodiments. (Example 46) The blazed diffraction grating has a diffraction efficiency for the red wavelength of light having a first polarization that is 1 to 2 times the diffraction efficiency for the red wavelength of light having a second polarization. The head-mounted display system according to any of the above embodiments. (Example 47) The blazed diffraction grating has a diffraction efficiency for the green wavelength of light having a first polarization that is 1 to 1.5 times the diffraction efficiency for the green wavelength of light having a second polarization. The head-mounted display system according to any of the above embodiments. (Example 48) The blazed diffraction grating has a diffraction efficiency for the blue wavelength of light having a first polarization that is 0.7 to 1 times the diffraction efficiency for the blue wavelength of light having a second polarization. The head-mounted display system according to any of the above embodiments. (Example 49) The waveguide is included in the eyepiece lens and is configured to direct light to the eyes of a user wearing the head-mounted display. The head-mounted display system according to any of the above embodiments. (Example 50) The eyepiece lens is disposed on a frame and is configured to direct light from a light projection system into the eyes of a user and display augmented reality image content in the user's field of view. At least a portion of the eyepiece lens is transparent, and when the user wears the head-mounted display system, it is disposed in front of the user's eyes. The transparent portion transmits light from a part of the physical environment in front of the user to the user's eyes and provides a view of a part of the physical environment in front of the user. The head-mounted display system according to Example 49. (Example 51) The eyepiece includes the at least one waveguide, and the at least one waveguide is transparent to visible light so that a user can see through the waveguide, the head-mounted display system according to Embodiment 49 or 50. (Embodiment 52) The waveguide includes an internal coupling optical element for coupling the light from the light projection system into the waveguide so that the light is guided therein, the head-mounted display system according to any of the above embodiments. (Embodiment 53) The waveguide includes an external coupling optical element for coupling the light from the light projection system out of the waveguide, directing the light to the user's eye, and presenting the image content to the viewer, the head-mounted display system according to any of the above embodiments. (Embodiment 54) The blazed diffraction grating includes an internal coupling grating (ICG) configured to internally couple the light from the light projection system into the waveguide, the head-mounted display system according to any of the above embodiments. (Embodiment 55) The blazed diffraction grating includes an external coupling grating (EPE) configured to externally couple the light from the light projection system guided within the waveguide out of the waveguide, the head-mounted display system according to any of the above embodiments. (Embodiment 56) An optical waveguide, A substrate including a material having a refractive index of at least 1.9, the substrate being configured to guide the light coupled into the waveguide within the waveguide through total internal reflection, and A blazed diffraction grating formed within the substrate, and Comprising, the blazed diffraction grating has a first diffraction efficiency for a first polarization over a range of angles for the light incident thereon, and a second diffraction efficiency for a second polarization over a range of angles for the light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency, an optical waveguide. (Embodiment 57) The optical waveguide described in Example 56, wherein the material has a refractive index greater than 1.9 and includes a lithium-based oxide. (Example 58) The optical waveguide described in Example 56 or 57, wherein the material has a refractive index greater than 1.9 and includes lithium niobate. (Example 59) The optical waveguide described in Example 56 or 57, wherein the material has a refractive index greater than 1.9 and includes lithium tantalate. (Example 60) The optical waveguide described in Example 56, wherein the material has a refractive index greater than 1.9 and includes silicon carbide. (Example 61) The optical waveguide described in Example 56, wherein the material has a refractive index greater than 1.9 and includes zirconium dioxide. (Example 62) The optical waveguide described in Example 56, wherein the material has a refractive index greater than 1.9 and includes titanium dioxide. (Example 63) The blazed diffraction grating has a tip height or groove depth of 40 to 120 nm and has diffraction characteristics, and is the optical waveguide described in any one of Examples 56 - 62. (Example 64) The blazed diffraction grating has a tip height or groove depth of 60 to 100 nm and has diffraction characteristics, and is the optical waveguide described in any one of Examples 56 - 63. (Example 65) The blazed diffraction grating has a tip height or groove depth of 70 to 90 nm and has diffraction characteristics, and is the optical waveguide described in any one of Examples 56 - 64. (Example 66) The blazed diffraction grating has a tip height or groove depth of about 80 nm and has diffraction characteristics, and is the optical waveguide described in any one of Examples 56 - 65. (Example 67) The diffraction characteristics are asymmetric, and it is the optical waveguide described in any one of Examples 56 - 66. (Example 68) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a one-dimensional (1D) array and has diffraction characteristics. (Example 69) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a two-dimensional (2D) array and has diffraction characteristics. (Example 70) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a two-dimensional (2D) array having a square array and has diffraction characteristics. (Example 71) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a two-dimensional (2D) array, has diffraction characteristics, and the blazed diffraction grating includes a 1D grating. (Example 72) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a two-dimensional (2D) array, has diffraction characteristics, and the blazed diffraction grating includes a 2D grating. (Example 73) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is formed in a two-dimensional (2D) array, has diffraction characteristics, the blazed diffraction grating includes a square array, and includes a 2D grating. (Example 74) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, which is configured to preferentially direct light in at least two directions. (Example 75) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, blazed in two directions. (Example 76) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, comprising an internal coupling optical element arranged to receive light from an image source and couple the light to be guided therein into the substrate. (Example 77) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, comprising a light dispersing optical element arranged to receive light from an image source guided in the substrate and direct the light to be coupled out of the substrate to an external coupling optical element. (Example 78) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, comprising a light dispersing optical element arranged to receive light from an image source guided in the substrate, diffuse the light in the waveguide, and increase the beam size or the eye box size. (Example 79) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, comprising an external coupling optical element arranged to receive light from an image source guided in the substrate and couple the light out of the substrate. (Example 80) The blazed diffraction grating is a head-mounted display system according to any one of Examples 1-55 or an optical waveguide according to any one of Examples 56-67, comprising a combined light dispersing / external coupling optical element arranged to receive light from an image source guided in the substrate, diffuse the light in at least two directions, and couple the light out of the substrate. (Example 81) The blazed diffraction grating includes a combined pupil expander-extractor that receives light from an image source induced within the substrate, diffuses the light, and is arranged to couple the light out of the substrate, and is the head-mounted display system according to any one of Examples 1-55 or the optical waveguide according to any one of Examples 56-67. Additional Examples - Part II: (Example 1) A head-mounted display system, a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide comprising a substrate including a material having a refractive index of at least 1.9, the substrate being configured to guide at least a portion of the light from the light projection system to be coupled into the waveguide, a layer disposed across the substrate, a blazed diffraction grating formed within the layer, and the blazed diffraction grating has a first diffraction efficiency for a first polarization over a range of angles of light incident thereon and a second diffraction efficiency for a second polarization over a range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency, the head-mounted display system. (Example 2) The substrate material having a refractive index of at least 1.9 includes a lithium-based oxide, the head-mounted display system according to Example 1. (Example 3) The material having a refractive index of at least 1.9 includes lithium niobate, the head-mounted display system according to Example 1 or 2. (Example 4) The material having a refractive index of at least 1.9 includes lithium tantalate, the head-mounted display system according to Example 1 or 2. (Example 5) The material having a refractive index greater than 1.9 includes silicon carbide, the head-mounted display system according to Example 1. (Example 6) The head-mounted display system according to Example 1, wherein the material has a refractive index greater than 1.9 and includes titanium dioxide. (Example 7) The head-mounted display system according to Example 1, wherein the material has a refractive index greater than 1.9 and includes zirconium dioxide. (Example 8) The head-mounted display system according to any one of the above examples, wherein the layer includes zinc oxide. (Example 9) The head-mounted display system according to any one of the above examples, wherein the layer includes silicon nitride. (Example 10) The head-mounted display system according to any one of the above examples, wherein the layer includes zirconium dioxide. (Example 11) The head-mounted display system according to any one of the above examples, wherein the layer includes titanium dioxide. (Example 12) The head-mounted display system according to any one of the above examples, wherein the layer includes silicon carbide. (Example 13) The head-mounted display system according to any one of the above examples, wherein the layer has a refractive index lower than that of the substrate. (Example 14) The head-mounted display system according to any one of the above examples, wherein the substrate material has a refractive index of at least 2.0 to 2.7. (Example 15) The head-mounted display system according to any one of the above examples, wherein the substrate material has a refractive index of at least 2.1 to 2.7. (Example 16) The head-mounted display system according to any one of the above examples, wherein the substrate material has a refractive index of at least 2.2 to 2.7. (Example 17) The head-mounted display system according to any one of the above examples, wherein the substrate material has a refractive index of at least 2.3 to 2.7. (Example 18) The substrate material is a head-mounted display system according to any of the above embodiments, having a refractive index of at least 2.3 to 2.4. (Example 19) The substrate material is a head-mounted display system according to any of the above embodiments, having a refractive index of at least 2.3 to 2.5. (Example 20) The substrate material is a head-mounted display system according to any of the above embodiments, having a refractive index of at least 2.6 to 2.7. (Example 21) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having protruding ends separated by grooves therebetween. (Example 22) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having a plurality of straight lines. (Example 23) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having a protruding end height or groove depth of 40 to 120 nm. (Example 24) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having a protruding end height or groove depth of 60 to 100 nm. (Example 25) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having a protruding end height or groove depth of 70 to 90 nm. (Example 26) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction characteristics and having a protruding end height or groove depth of about 80 nm. (Example 27) The diffraction characteristic is an asymmetric waveguide according to any of the above embodiments. (Example 28) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having a pitch of 250 to 350 nm. (Example 29) The blazed diffraction grating is a head-mounted display system according to any of the above embodiments, having a pitch of 300 to 450 nm. (Example 30) The substrate is planar, and the blazed diffraction grating has a blaze angle of 10 to 30 degrees with respect to the plane of the substrate, which is a head-mounted display system according to any of the above embodiments. (Example 31) The substrate is planar, and the blazed diffraction grating has a blaze angle of 15 to 25 degrees with respect to the plane of the substrate, which is a head-mounted display system according to any of the above embodiments. (Example 32) The substrate is planar, and the blazed diffraction grating has a blaze angle of about 19.5 degrees with respect to the plane of the substrate, which is a head-mounted display system according to any of the above embodiments. (Example 33) The first diffraction efficiency is 1 to 1.5 times that of the second diffraction efficiency, which is a head-mounted display system according to any of the above embodiments. (Example 34) The first diffraction efficiency is 1 to 1.4 times that of the second diffraction efficiency, which is a head-mounted display system according to any of the above embodiments. (Example 35) The first diffraction efficiency is 1 to 1.3 times that of the second diffraction efficiency, which is a head-mounted display system according to any of the above embodiments. (Example 36) The first diffraction efficiency is 1 to 1.2 times that of the second diffraction efficiency, which is a head-mounted display system according to any of the above embodiments. (Example 37) The first diffraction efficiency is 1 to 1.1 times that of the second diffraction efficiency, which is a head-mounted display system according to any of the above embodiments. (Example 38) The head-mounted display system according to any one of the above embodiments, wherein the angular range is at least 6 degrees. (Example 39) The head-mounted display system according to any one of the above embodiments, wherein the angular range is at least 12 degrees. (Example 40) The head-mounted display system according to any one of the above embodiments, wherein the angular range is at least 18 degrees. (Example 41) The head-mounted display system according to any one of the above embodiments, wherein the angular range is at least 22 degrees. (Example 42) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±3 degrees with respect to the plane of the substrate. (Example 43) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±6 degrees with respect to the plane of the substrate. (Example 44) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±9 degrees with respect to the plane of the substrate. (Example 45) The head-mounted display system according to any one of the above embodiments, wherein the angular range is between ±11 degrees with respect to the plane of the substrate. (Example 46) The head-mounted display system according to any one of the above embodiments, comprising first and second linear polarizations having different polarization angles. (Example 47) The head-mounted display system according to any one of the above embodiments, comprising first and second linear polarizations oriented in orthogonal directions. (Example 48) The head-mounted display system according to any one of the above embodiments, wherein the first and second polarization directions each comprise transverse magnetic and transverse electric polarizations. (Example 49) The first and second polarization directions are respectively the head-mounted display system according to any of the above embodiments, each having horizontal electric and horizontal magnetic polarizations. (Example 50) The first diffraction efficiency is the diffraction efficiency for horizontal magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency is the diffraction efficiency for horizontal electric polarization averaged across the visible light spectrum, of the head-mounted display system according to any of the above embodiments. (Example 51) The first diffraction efficiency is the diffraction efficiency for horizontal electric polarization averaged across the visible light spectrum, and the second diffraction efficiency is the diffraction efficiency for horizontal magnetic polarization averaged across the visible light spectrum, of the head-mounted display system according to any of the above embodiments. (Example 52) The waveguide is included in an eyepiece lens configured to direct light to the eyes of a user wearing the head-mounted display, of the head-mounted display system according to any of the above embodiments. (Example 53) The eyepiece lens is disposed on a frame, configured to direct light from a light projection system into the user's eyes and display augmented reality image content in the user's field of view. At least a part of the eyepiece lens is transparent. When the user wears the head-mounted display system, it is disposed at a location in front of the user's eyes. The transparent part transmits light from a part of the physical environment in front of the user to the user's eyes and provides a view of a part of the physical environment in front of the user, of the head-mounted display system described in Example 52. (Example 54) The eyepiece lens includes the at least one waveguide, and the at least one waveguide is transparent to visible light so that the user can see through the waveguide, of the head-mounted display system described in Example 52 or 53. (Example 55) The waveguide is the head-mounted display system according to any of the above embodiments, and includes an internal coupling optical element for coupling the light from the light projection system into the waveguide so as to be guided therein. (Example 56) The waveguide is the head-mounted display system according to any of the above embodiments, and includes an external coupling optical element for coupling the light from the light projection system out of the waveguide, directing the light toward the user's eyes, and presenting the image content to the viewer. (Example 57) The blazed diffraction grating is the head-mounted display system according to any of the above embodiments, and includes an internal coupling grating (ICG) configured to internally couple the light from the light projection system into the waveguide. (Example 58) The blazed diffraction grating is the head-mounted display system according to any of the above embodiments, and includes an external coupling grating (EPE) configured to externally couple the light from the light projection system induced in the waveguide out of the waveguide. (Example 59) An optical waveguide, A substrate including a material having a refractive index of at least 1.9, the substrate being configured to guide the light coupled into the waveguide through total internal reflection within the waveguide; A layer disposed across the substrate; A blazed diffraction grating formed within the layer; The optical waveguide includes a blazed diffraction grating having a first diffraction efficiency for a first polarization over a range of angles for light incident thereon and a second diffraction efficiency for a second polarization over a range of angles for light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency. (Example 60) The optical waveguide according to Example 59, wherein the material having a refractive index greater than 1.9 includes a lithium-based oxide. (Example 61) The optical waveguide according to Example 59 or 60, wherein the material having a refractive index greater than 1.9 includes lithium niobate. (Example 62) An optical waveguide according to Example 59 or 60, wherein the material has a refractive index greater than 1.9 and includes lithium tantalate. (Example 63) An optical waveguide according to Example 59, wherein the material has a refractive index greater than 1.9 and includes silicon carbide. (Example 64) An optical waveguide according to Example 59, wherein the material has a refractive index greater than 1.9 and includes titanium dioxide. (Example 65) An optical waveguide according to Example 59, wherein the material has a refractive index greater than 1.9 and includes zirconium dioxide. (Example 66) An optical waveguide according to any one of Examples 59 - 65, wherein the layer includes zinc oxide. (Example 67) An optical waveguide according to any one of Examples 59 - 66, wherein the layer includes silicon nitride. (Example 68) An optical waveguide according to any one of Examples 59 - 67, wherein the layer includes zirconium dioxide. (Example 69) An optical waveguide according to any one of Examples 59 - 68, wherein the layer includes titanium dioxide. (Example 70) An optical waveguide according to any one of Examples 59 - 69, wherein the layer includes silicon carbide. (Example 71) An optical waveguide according to any one of Examples 59 - 70, wherein the layer has a refractive index lower than that of the substrate. (Example 72) The blazed diffraction grating has a tip height or groove depth of 40 - 120 nm and has diffraction characteristics, and is an optical waveguide according to any one of Examples 59 - 71. (Example 73) The blazed diffraction grating has a tip height or groove depth of 60 - 100 nm and has diffraction characteristics, and is an optical waveguide according to any one of Examples 59 - 72. (Example 74) The blazed diffraction grating is an optical waveguide according to any of Examples 59 - 73, having a tip height or groove depth of 70 - 90 nm and having diffraction characteristics. (Example 75) The blazed diffraction grating is an optical waveguide according to any of Examples 59 - 74, having a tip height or groove depth of about 80 nm and having diffraction characteristics. (Example 76) The diffraction characteristics are asymmetric, and it is an optical waveguide according to any of Examples 59 - 75. (Example 77) The blazed diffraction grating is a head - mounted display system according to any of Examples 1 - 58 or an optical waveguide according to any of Examples 59 - 76, having diffraction characteristics and being formed in a one - dimensional (1D) array. (Example 78) The blazed diffraction grating is a head - mounted display system according to any of Examples 1 - 58 or an optical waveguide according to any of Examples 59 - 76, having diffraction characteristics and being formed in a two - dimensional (2D) array. (Example 79) The blazed diffraction grating is a head - mounted display system according to any of Examples 1 - 58 or an optical waveguide according to any of Examples 59 - 76, having diffraction characteristics and being formed in a two - dimensional (2D) array having a square array. (Example 80) The blazed diffraction grating is a head - mounted display system according to any of Examples 1 - 58 or an optical waveguide according to any of Examples 59 - 76, having diffraction characteristics and being formed in a two - dimensional (2D) array, and the blazed diffraction grating has a 1D grating. (Example 81) The blazed diffraction grating is a head - mounted display system according to any of Examples 1 - 58 or an optical waveguide according to any of Examples 59 - 76, having diffraction characteristics and being formed in a two - dimensional (2D) array, and the blazed diffraction grating has a 2D grating. (Example 82) The blazed diffraction grating is formed within a two-dimensional (2D) array, has diffraction characteristics, and the blazed diffraction grating comprises a 2D grating with a square array, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 83) The blazed diffraction grating is configured to preferentially direct light in at least two directions, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 84) The blazed diffraction grating is blazed in two directions, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 85) The blazed diffraction grating is provided with an internal coupling optical element that receives light from an image source and is arranged to couple the light so as to be guided therein within the substrate, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 86) The blazed diffraction grating is provided with a light dispersion optical element that receives light from an image source guided within the substrate and is arranged to direct the light to be coupled out of the substrate to an external coupling optical element, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 87) The blazed diffraction grating is provided with a light dispersion optical element that receives light from an image source guided within the substrate, diffuses the light within the waveguide, and is arranged to increase the beam size or the eye box size, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 88) The blazed diffraction grating includes an external coupling optical element that receives light from an image source induced within the substrate and is arranged to couple the light out of the substrate, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 89) The blazed diffraction grating includes a combined light dispersion / external coupling optical element that receives light from an image source induced within the substrate, diffuses the light in at least two directions, and is arranged to couple the light out of the substrate, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Example 90) The blazed diffraction grating includes a combined pupil expander-extractor that receives light from an image source induced within the substrate, diffuses the light, and is arranged to couple the light out of the substrate, and is a head-mounted display system according to any one of Examples 1-58 or an optical waveguide according to any one of Examples 59-76. (Additional Considerations)

[0164] In the foregoing specification, the invention has been described with reference to its specific embodiments. However, it will be apparent that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a limiting sense.

[0165] In fact, the systems and methods of the present disclosure each have several innovative aspects, and it should be understood that none of them alone participates in or is required for the desirable attributes disclosed herein. The various features and processes described above can be used independently of each other or combined in various ways. All possible combinations and sub-combinations are intended to fall within the scope of the present disclosure.

[0166] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented separately in multiple embodiments or in any suitable sub-combination. Further, features may be described above as acting in certain combinations and may, further, be initially claimed as such, but one or more features from a claimed combination may, in some cases, be deleted from the combination and the claimed combination may be directed to a sub-combination or variation of a sub-combination. No single feature or group of features is necessary or essential to all embodiments.

[0167] In particular, conditional statements used in this specification such as "can", "could", "might", "may", "e.g.", and equivalents are generally intended to convey that one embodiment includes certain features, elements, and / or steps while other embodiments do not, unless otherwise specifically stated or understood within the context in which they are used. Thus, such conditional statements are generally not intended to imply that features, elements, and / or steps are required in any way for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether these features, elements, and / or steps are to be included or implemented in any particular embodiment, regardless of the author's input or prompting. The terms "comprising", "including", "having", and equivalents are synonyms and are used inclusively in a non-limiting manner, not excluding additional elements, features, acts, operations, etc. Also, the term "or", when used, for example, to connect a list of elements, is used in its inclusive sense (and not in its exclusive sense) such that the term "or" means one, some, or all of the elements in the list. Additionally, the articles "a", "an", and "the" as used in this application and the appended claims should be construed to mean "one or more" or "at least one" unless otherwise defined. Similarly, operations may be depicted in the drawings in a particular order, but it should be recognized that such operations need not be performed in the particular order shown or in a sequential order, nor do all of the illustrated operations need to be performed, in order to achieve a desired result. Further, the drawings may schematically depict one or more exemplary processes in the form of flowcharts. However, other operations not depicted may also be incorporated into the exemplary methods and processes schematically illustrated. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the illustrated operations.Additionally, the operations may be rearranged or reordered in other embodiments. In certain situations, multitasking and parallel processing may be advantageous. Further, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0168] Accordingly, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the disclosure, principles, and novel features disclosed herein.

Claims

1. A head-mounted display system, wherein the head-mounted display system comprises: a frame capable of being mounted on the head; an optical projection system configured to provide image content by outputting light; a waveguide supported by the frame, the waveguide comprising a substrate, the substrate being configured to guide at least a part of the light from the optical projection system into the waveguide; a blazed diffraction grating formed in the surface of the substrate; and; the substrate includes a material having a refractive index of at least 1.9, the material including a lithium-based oxide, silicon carbide, zirconium dioxide, or titanium dioxide; the blazed diffraction grating has a first diffraction efficiency across the visible spectrum of light for a first polarization over a range of angles of light incident on the blazed diffraction grating, the blazed diffraction grating has a second diffraction efficiency across the visible spectrum of light for a second polarization over a range of angles of light incident on the blazed diffraction grating, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency; the blazed diffraction grating has diffraction features with a tip height or groove depth of 10 nm to 150 nm, a head-mounted display system.

2. The head-mounted display system according to claim 1, wherein the blazed diffraction grating is arranged to be optically in communication with the substrate.

3. The head-mounted display system according to claim 1, wherein the material has a refractive index of at least 2.0 to 2.

7.

4. The head-mounted display system according to claim 1, wherein the diffraction features include tips separated by grooves therebetween.

5. The head-mounted display system according to claim 1, wherein the diffraction features include a plurality of straight lines.

6. The head-mounted display system according to claim 1, wherein the diffraction features include a plurality of columns protruding from the surface of the substrate.

7. The head-mounted display system according to claim 1, wherein the diffraction features are asymmetric.

8. The head-mounted display system according to claim 1, wherein the blazed diffraction grating has a pitch of 250 nm to 350 nm.

9. The blazed diffraction grating has a pitch of 300 nm to 450 nm, and the head-mounted display system according to claim 1.

10. The substrate is planar, and the blazed diffraction grating has a blaze angle of 10 degrees to 30 degrees with respect to the major plane of the substrate, and the head-mounted display system according to claim 1.

11. The range of the angle is at least 6 degrees, and the head-mounted display system according to claim 1.

12. The first polarization and the second polarization include a first linear polarization and a second linear polarization having different polarization angles, and the head-mounted display system according to claim 1.

13. The first polarization and the second polarization include a first linear polarization and a second linear polarization oriented in orthogonal directions, and the head-mounted display system according to claim 1.

14. The first polarization includes one of transverse magnetic polarization and transverse electric polarization, and the second polarization includes the other of the transverse magnetic polarization and the transverse electric polarization, and the head-mounted display system according to claim 1.

15. The first diffraction efficiency includes a diffraction efficiency for one of transverse magnetic polarization and transverse electric polarization averaged across the visible spectrum of the light, and the second diffraction efficiency includes a diffraction efficiency for the other of the transverse magnetic polarization and transverse electric polarization averaged across the visible spectrum of the light, and the head-mounted display system according to claim 1.

16. The blazed diffraction grating has a diffraction efficiency for the red wavelength of the light having the first polarization that is 1 to 2.5 times the diffraction efficiency for the red wavelength of the second polarization, and the head-mounted display system according to claim 1.

17. The blazed diffraction grating has a diffraction efficiency for the green wavelength of the light having the first polarization that is 1 to 1.5 times the diffraction efficiency for the green wavelength of the second polarization, and the head-mounted display system according to claim 1.

18. The blazed diffraction grating has a diffraction efficiency for the blue wavelength of the light having the first polarization that is 0.7 to 1 times the diffraction efficiency for the blue wavelength of the light having the second polarization. The first diffraction efficiency across the visible spectrum of the light is the average diffraction efficiency for the blue wavelength, red wavelength, and green wavelength of the light having the first polarization, The second diffraction efficiency across the visible spectrum of the light is the average diffraction efficiency for the blue wavelength, red wavelength, and green wavelength of the light having the second polarization, the head-mounted display system according to claim 1.

19. The waveguide is included in an eyepiece lens configured to direct light to the eyes of a user wearing the head-mounted display system, the head-mounted display system according to claim 1.

20. An optical waveguide, wherein the optical waveguide A substrate configured to guide light coupled into the waveguide within the waveguide through total internal reflection, A blazed diffraction grating formed in the surface of the substrate Comprising, The substrate includes a material having a refractive index of at least 1.9, the material including a lithium-based oxide, silicon carbide, zirconium dioxide, or titanium dioxide, The blazed diffraction grating has a first diffraction efficiency across the visible spectrum of light for a first polarization over a range of angles for light incident on the blazed diffraction grating, the blazed diffraction grating has a second diffraction efficiency across the visible spectrum of the light for a second polarization over a range of angles for light incident on the blazed diffraction grating, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency, The blazed diffraction grating comprises diffraction features having a tip height or groove depth of 10 nm to 150 nm, an optical waveguide.

21. The blazed diffraction grating is arranged to be optically in communication with the substrate, the optical waveguide according to claim 20.

22. The diffraction features comprise a plurality of continuous or discontinuous straight lines, the optical waveguide according to claim 20.

23. The diffraction features comprise a plurality of pillars protruding from the surface of the substrate, the optical waveguide according to claim 20.

24. The diffraction features are asymmetric, the optical waveguide according to any one of claims 20, 22 to 23.

25. The diffraction features are formed in a one-dimensional (1D) array or a two-dimensional (2D) array, the optical waveguide according to claim 20.

26. The diffractive feature is formed within a two-dimensional (2D) array comprising a square array, the optical waveguide according to claim 20.

27. The blazed diffraction grating comprises a 1D grating or a 2D grating, the optical waveguide according to claim 25.

28. The blazed diffraction grating comprises the 2D grating comprising a square array, the optical waveguide according to claim 27.

29. The blazed diffraction grating is configured to direct light in two or more directions, the optical waveguide according to claim 20.

30. The blazed diffraction grating is an internal coupling optical element arranged to receive light from an image source and couple the light into the substrate such that the light is guided within the substrate, and an external coupling optical element arranged to receive light from the image source guided within the substrate and couple the light out of the substrate and comprises one or both of them, the optical waveguide according to claim 20.

31. The blazed diffraction grating is arranged to receive light from an image source guided within the substrate, and increase the beam size or the eye box size by directing the light to an external coupling optical element such that the light is coupled out of the substrate, or by diffusing the light within the waveguide and comprises a light dispersing optical element arranged to perform the above, the optical waveguide according to claim 20.

32. The blazed diffraction grating is arranged to receive light from an image source guided within the substrate, diffuse the light, and comprises a combined pupil expander extractor arranged to couple the light out of the substrate, the optical waveguide according to claim 20.

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