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 July 19, 2019, entitled "DISPLAY DEVICE HAVING DIFFRACTION GRATINGS WITH REDUCED POLARIZATION SENSITIVITY", and U.S. Provisional Application No. 62 / 902,328, filed on September 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 November 27, 2014, and published as U.S. Patent Publication No. 2015 / 0205126 on July 23, 2015; U.S. Patent Application No. 14 / 690,401, filed on April 18, 2015, and published as U.S. Patent Publication No. 2015 / 0302652 on October 22, 2015; U.S. Patent Application No. 14 / 212,961, filed on March 14, 2014, and issued as U.S. Patent No. 9,417,452 on August 16, 2016; and U.S. Patent Application No. 14 / 331,218, filed on July 14, 2014, and published as U.S. Patent Publication No. 2015 / 0309263 on October 29, 2015.

[0003] This 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 are driving the development of systems for so-called "virtual reality" or "augmented reality" experiences, where digitally reproduced images or parts thereof are presented to the user in a manner that appears, or can be perceived, as real. Virtual reality, or "VR," scenarios typically involve the presentation of digital or virtual imagery without transparency to other real-world visual inputs, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual imagery as an extension of the user's visualization of the real world around them. Mixed reality, or "MR," scenarios, are a type of AR scenario that typically involves virtual objects integrated into and responding to the natural world. For example, in an MR scenario, AR imagery may be perceived as being obscured by, or interacting with, objects in the real world in a different way.

[0005] Referring to Figure 1, an augmented reality scene 10 is depicted, and the user of AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. In addition to these items, the user of AR technology also perceives "virtual content" such as a robot figure 40 standing on the real-world platform 30 and a flying cartoon-like avatar character 50 that looks like an anthropomorphic bumblebee, although these elements 40 and 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 related to AR and VR technologies. [Overview of the Initiative] [Means for solving the problem]

[0007] In one aspect, the head-mounted display system comprises a head-mountable frame, a light projection system configured to emit light and provide image content, and a waveguide supported by the frame. The waveguide comprises a substrate containing 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 couple into the waveguide. The head-mounted display system also comprises a blazed diffraction grating formed in 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 on it, and a second diffraction efficiency for a second polarization over a range of angles of light incident on it. The first diffraction efficiency is 1 to 2 times that of the second diffraction efficiency.

[0008] In another aspect, the optical waveguide comprises a substrate containing 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 also comprises a blazed diffraction grating formed in or across the substrate. The blazed diffraction grating has a first diffraction efficiency for a first polarization over an angular range for light incident on it, and a second diffraction efficiency for a second polarization over an angular range for light incident on it. The first diffraction efficiency is 1 to 2 times that of the second diffraction efficiency. The present invention provides, for example, the following: (Item 1) A head-mounted display system, A frame that can be mounted on the head, A light projection system configured to output light and provide image content, A waveguide supported by the frame, wherein the waveguide comprises a substrate containing a material having a refractive index of at least 1.9, and the substrate is configured to guide at least a portion of the light from the light projection system into the waveguide, A blazed diffraction grating formed within the substrate or in a layer arranged across the substrate. Equipped with, A head-mounted display system wherein 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 being 1 to 2 times the second diffraction efficiency. (Item 2) The head-mounted display system according to item 1, wherein the blazed diffraction grating is formed in the substrate and arranged to communicate optically with the substrate. (Item 3) The head-mounted display system according to item 1, wherein the blazed diffraction grating is arranged across the substrate and in a layer that is arranged to communicate optically with the substrate. (Item 4) The aforementioned layer is in physical contact with the substrate, as described in item 3, for the head-mounted display system. (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 in a layer arranged across the substrate, and the layer comprises 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 in a layer arranged across the substrate, and the layer has a lower refractive index than 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 diffraction features with tips separated by grooves between them. (Item 10) The blazed diffraction grating has diffraction features comprising multiple straight lines, as described in item 1, for the head-mounted display system. (Item 11) The head-mounted display system according to item 10, wherein the plurality of straight lines comprises discontinuous straight lines. (Item 12) The head-mounted display system according to item 1, wherein the blazed diffraction grating has diffraction features comprising a plurality of columns protruding from the surface of the substrate. (Item 13) The blazed diffraction grating has diffraction features having a tip height or groove depth of 10 to 150 nm, as described in item 1, for the head-mounted display system. (Item 14) The head-mounted display system described in item 1, wherein the diffraction features are asymmetric. (Item 15) The blazed diffraction grating has a pitch of 250 to 350 nm, as described in item 1 for the head-mounted display system. (Item 16) The blazed diffraction grating has a pitch of 300-450 nm and is used in the head-mounted display system described in item 1. (Item 17) The head-mounted display system according to item 1, wherein the substrate is planar, and the blazed diffraction grating has a blazing 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 head-mounted display system according to item 1, wherein the first diffraction efficiency includes a diffraction efficiency for one of transverse magnetic polarization and transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency includes a diffraction efficiency for the other of transverse magnetic polarization and transverse electric polarization averaged across the visible light spectrum. (Item 25) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction efficiency for the red wavelength of light having the first polarization, which is 1 to 2 times the diffraction efficiency for the red wavelength of the second polarization. (Item 26) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction efficiency for the green wavelength of light having the first polarization, which is 1 to 1.5 times the diffraction efficiency for the green wavelength of the second polarization. (Item 27) The head-mounted display system according to item 1, wherein the blazed diffraction grating has a diffraction efficiency for the blue wavelength of light having the first polarization, which is 0.7 to 1 times the diffraction efficiency for the blue wavelength of light having the second polarization. (Item 28) The head-mounted display system according to item 1, wherein the waveguide is included in an eyepiece lens configured to direct light toward the eyes of a user wearing the head-mounted display. (Item 29) The head-mounted display system according to item 28, wherein the eyepiece is positioned on the frame and configured to direct light from the light projection system into the user's eye and display augmented reality image content in the user's field of view, and at least a portion of the eyepiece is transparent and positioned in front of the user's eye when the user wears the head-mounted display system, the transparent portion allowing light from a portion of the physical environment in front of the user to pass through to the user's eye and provide a view of a portion of the physical environment in front of the user. (Item 30) The head-mounted display system according to item 28, wherein the eyepiece comprises the at least one waveguide, the at least one waveguide being transparent to visible light so that the user can see through the waveguide. (Item 31) The head-mounted display system according to item 1, wherein the waveguide comprises an internal coupling optical element for coupling light from the light projection system into the waveguide so that it is guided therein. (Item 32) The head-mounted display system according to item 1, wherein the waveguide comprises an external coupling optical element for coupling light from the light projection system out of the waveguide, directing the light towards the user's eye, and presenting the image content to the viewer. (Item 33) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises an internally coupled grating (ICG) configured to internally couple light from the optical projection system into the waveguide. (Item 34) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises an externally coupled grating (EPE) configured to externally couple light from the optical projection system induced in the waveguide to the outside of the waveguide. (Item 35) The blazed diffraction grating has diffraction features formed within a one-dimensional (1D) array, as described in item 1, for the head-mounted display system. (Item 36) The blazed diffraction grating has diffraction features formed within a two-dimensional (2D) array, as described in item 1, for the head-mounted display system. (Item 37) The two-dimensional (2D) array comprises a square array, as described in item 36, in the head-mounted display system. (Item 38) The blazed diffraction grating is a head-mounted display system according to item 1, comprising a 1D grating. (Item 39) The blazed diffraction grating is a head-mounted display system according to item 1, comprising a 2D grating. (Item 40) The blazed diffraction grating comprises a 2D grating with a square array, as described in item 1, for the head-mounted display system. (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 internally coupled optical element that receives light from an image source and couples 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 includes a light-dispersing optical element that receives light from an image source induced within the substrate and directs the light to an external coupling optical element so as to couple the light outward from the substrate. (Item 44) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes light-dispersing optical elements arranged to receive light from an image source induced in the substrate, diffuse the light in the waveguide, and increase the beam size or eyebox size. (Item 45) The head-mounted display system according to item 1, wherein the blazed diffraction grating includes an external coupling optical element that receives light from an image source induced within the substrate and couples the light out of the substrate. (Item 46) The head-mounted display system according to item 1, comprising a blazed diffraction grating that receives light from an image source induced within the substrate, diffuses the light in at least two directions, and comprises a combination of optically dispersed / externally coupled optical elements arranged to couple the light outward from the substrate. (Item 47) The head-mounted display system according to item 1, wherein the blazed diffraction grating comprises a combined pupil expander-extractor positioned to receive light from an image source induced within the substrate, diffuse the light, and couple the light out of the substrate. (Item 48) An optical waveguide, A substrate comprising a material having a refractive index of at least 1.9, wherein the substrate is configured to guide light coupled into the waveguide within the waveguide via total internal reflection, A blazed diffraction grating formed within the substrate or in a layer arranged across the substrate. Equipped with, An optical waveguide wherein the blazed diffraction grating has a first diffraction efficiency for a first polarization over an angular range for light incident thereon, and a second diffraction efficiency for a second polarization over an angular range for light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency. (Item 49) The blazed diffraction grating is formed in the substrate and arranged to communicate optically with the substrate, as described in item 48, in the optical waveguide. (Item 50) The optical waveguide according to item 48, wherein the blazed diffraction grating is arranged across the substrate and in a layer that is arranged to communicate optically with the substrate. (Item 51) The layer is an optical waveguide as described in item 50, which is in physical contact with the substrate. (Item 52) The optical waveguide according to item 48, wherein the material having a refractive index greater than 1.9 includes a lithium-based oxide, silicon carbide, zirconium dioxide, or titanium dioxide. (Item 53) The blazed diffraction grating is formed in a layer arranged across the substrate, the layer comprising silicon nitride, zirconium dioxide, titanium dioxide, or silicon carbide, as described in item 48 of the optical waveguide. (Item 54) The blazed diffraction grating is formed in a layer arranged across the substrate, the layer having a lower refractive index than the substrate, as described in item 48 of the optical waveguide. (Item 55) The blazed diffraction grating is an optical waveguide according to item 48, having diffraction features with a tip height or groove depth of 10 to 150 nm. (Item 56) The blazed diffraction grating is an optical waveguide according to item 48, having diffraction features comprising multiple straight lines. (Item 57) The optical waveguide described in item 56 comprises discontinuous straight lines. (Item 58) The optical waveguide according to item 48, wherein the blazed diffraction grating has diffraction features comprising a plurality of columns protruding from the surface of the substrate. (Item 59) The diffraction features are asymmetric, as described in item 48 for the optical waveguide. (Item 60) The blazed diffraction grating is an optical waveguide as described in item 48, having diffraction features formed within a one-dimensional (1D) array. (Item 61) The blazed diffraction grating is an optical waveguide according to item 48, having diffraction features formed within a two-dimensional (2D) array. (Item 62) The two-dimensional (2D) array is an optical waveguide as described in item 61, comprising a square array. (Item 63) The blazed diffraction grating is an optical waveguide as described in item 48, comprising a 1D grating. (Item 64) The blazed diffraction grating is an optical waveguide as described in item 48, comprising a 2D grating. (Item 65) The blazed diffraction grating comprises a 2D grating with a square array, as described in item 48, for the optical waveguide. (Item 66) The blazed diffraction grating is configured to preferentially direct light in two or more directions, as described in item 48, for the optical waveguide. (Item 67) The optical waveguide according to item 48, wherein the blazed diffraction grating includes an internally coupled optical element that receives light from an image source and couples the light into the substrate so as to be guided therein. (Item 68) The optical waveguide according to item 48, wherein the blazed diffraction grating receives light from an image source induced within the substrate and includes an optically dispersive optical element positioned to direct the light so as to couple it outward from the substrate to an external coupling optical element. (Item 69) The optical waveguide according to item 48, wherein the blazed diffraction grating includes an optical element that receives light from an image source induced in the substrate, diffuses the light within the waveguide, and is arranged to increase the beam size or eyebox size. (Item 70) The optical waveguide according to item 48, wherein the blazed diffraction grating includes an external coupling optical element that receives light from an image source induced within the substrate and couples the light out of the substrate. (Item 71) The optical waveguide according to item 48, wherein the blazed diffraction grating receives light from an image source induced within the substrate, diffuses the light in at least two directions, and comprises a combination of optical dispersion / external coupling optical elements arranged to couple the light outward from the substrate. (Item 72) The optical waveguide according to item 48, wherein the blazed diffraction grating comprises a combined pupil expander-extractor positioned to receive light from an image source induced within the substrate, diffuse the light, and couple the light out of the substrate. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 illustrates the user's view of augmented reality (AR) through an AR device.

[0010] [Figure 2] Figure 2 illustrates a conventional display system for simulating a three-dimensional image for the user.

[0011] [Figure 3] Figures 3A-3C illustrate the relationship between the radius of curvature and the radius of focus.

[0012] [Figure 4A] Figure 4A illustrates the representation of the accommodation-convergence-divergence motion response of the human visual system.

[0013] [Figure 4B] Figure 4B illustrates examples of different near and far accommodative states and convergence / divergence motion states of a user's pair of eyes.

[0014] [Figure 4C] Figure 4C illustrates an example of how the upper and lower figures represent a user viewing content through a display system.

[0015] [Figure 4D] Figure 4D illustrates another embodiment of the representation of the upper and lower figures of a user viewing content through a display system.

[0016] [Figure 5] Figure 5 illustrates aspects of an approach to simulating a 3D image by correcting wavefront divergence.

[0017] [Figure 6] Figure 6 illustrates an example of a waveguide stack for outputting image information to the user.

[0018] [Figure 7] Figure 7 illustrates an example of an output beam produced by a waveguide.

[0019] [Figure 8] Figure 8 illustrates an embodiment of a stacked waveguide assembly in which each depth plane includes an image formed using multiple different primary colors.

[0020] [Figure 9A] Figure 9A shows a cross-sectional side view of an embodiment of a stacked waveguide set, each including an internally coupled optical element.

[0021] [Figure 9B] Figure 9B shows a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A.

[0022] [Figure 9C] Figure 9C shows top and bottom plan views of the embodiment of the multiple stacked waveguides shown in Figures 9A and 9B.

[0023] [Figure 9D] Figure 9D illustrates an embodiment of a wearable display system.

[0024] [Figure 10A] Figure 10A schematically illustrates a cross-sectional view of a portion of a waveguide, which has a diffraction grating placed on it for internal coupling of light within the waveguide.

[0025] [Figure 10B] Figure 10B shows a cross-sectional view of a waveguide with a blazed diffraction grating positioned above it, indicating the waveguide's field of view (FOV) Δα.

[0026] [Figure 11A] Figure 11A illustrates the etching process for forming a waveguide, which has a single-stage blazed diffraction grating placed on top of it.

[0027] [Figure 11B] Figure 11B is a scanning electron micrograph of a single-stage blazed photoresist grating.

[0028] [Figure 11C] Figure 11C illustrates the etching process for forming a waveguide having a multi-stage blazed diffraction grating placed on top of it.

[0029] [Figure 11D] Figure 11D is a scanning electron micrograph of a multi-stage blazed photoresist grating.

[0030] [Figure 11E] Figure 11E illustrates cross-sectional side views of two different blazed geometric shapes for diffraction gratings.

[0031] [Figure 12A] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon. [Figure 12B] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon. [Figure 12C] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon. [Figure 12D] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon. [Figure 12E] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon. [Figure 12F] Figures 12A-12F show scanning electron micrographs of various substrates with different blazed geometric shapes and blazed diffraction gratings formed thereon.

[0032] [Figure 13] Figure 13 is a plot of the ratio of the diffraction efficiency of transversely magnetic (TM) polarization to the diffraction efficiency of transversely electric (TE) polarization as a function of the angle of incidence for various diffraction gratings with different blazed geometric shapes.

[0033] [Figure 14] Figure 14 is a plot of the ratio of the diffraction efficiency of transversely magnetic (TM) polarization to the diffraction efficiency of transversely electric (TE) polarization as a function of the angle of incidence with respect to the diffraction grating, with diffraction features having a tip height or groove depth of 80 nm for green, blue, and red wavelengths.

[0034] [Figure 15] Figure 15 is a plot of diffraction efficiency for diffraction gratings with a tip height or groove depth of 80 nm for green, blue, and red wavelengths.

[0035] [Figure 16] Figure 16 illustrates the coherent uniformity of a blazed photoresist diffraction grating with respect to unpolarized and linearly polarized inputs.

[0036] [Figure 17] Figure 17 illustrates the coherent uniformity of a blazed diffraction grating etched in a lithium niobate substrate for unpolarized and linearly polarized inputs.

[0037] [Figure 18] Figure 18 is a perspective view of a two-dimensional (2D) diffraction grating with a two-dimensional array of blazed diffraction features.

[0038] [Figure 18A] Figures 18A and 18B are cross-sectional and plan views, respectively, of a 2D diffraction grating having a two-dimensional array of blazed diffraction features. [Figure 18B] Figures 18A and 18B are cross-sectional and plan views, respectively, of a 2D diffraction grating having a two-dimensional array of blazed diffraction features.

[0039] [Figure 19A] Figure 19A is a perspective view of a 2D diffraction grating having a two-dimensional array of diffraction features blazed in two directions.

[0040] [Figure 19B] Figure 19B illustrates how light is preferentially directed in different directions by a 2D diffraction grating having a two-dimensional array of diffraction features blazed in two directions.

[0041] [Figure 20A] Figures 20A and 20B are schematic diagrams illustrating a method for manufacturing a blazed diffraction grating using a master template. [Figure 20B] Figures 20A and 20B are schematic diagrams illustrating a method for manufacturing a blazed diffraction grating using a master template.

[0042] [Figure 21] Figure 21 is a schematic diagram of a method for manufacturing blazed diffraction gratings using different master templates.

[0043] Throughout the drawings, reference numbers may be reused to indicate correspondences between the referenced elements. The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of this disclosure. [Modes for carrying out the invention]

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

[0045] In some AR systems, virtual / enhanced / composite displays with a relatively wide field of view (FOV) can improve the viewing experience. The FOV of a display depends on the angle of light output by the eyepiece waveguide through which the viewer sees the projected image in their eyes. Waveguides with a relatively high refractive index, e.g., 2.0 or higher, 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 have a correspondingly high refractive index. Among the advantages, to achieve this objective, some displays for AR systems according to embodiments described herein include waveguides made of a relatively high refractive index (e.g., above or equal to 2.0) material, such as a Li-based oxide, on which a separate diffraction grating is formed, with a correspondingly high refractive index. 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, exhibit strong polarization dependence. For example, an internal coupling grating (ICG) for internally coupling light containing a high-refractive-index material into a waveguide can accept significantly more light of a given polarization than light of another polarization. Such an element can internally couple light with TM polarization into a waveguide at, for example, about three times the rate of light with TE polarization. Diffractive optical coupling elements with this type of polarization dependence may have reduced efficiency (due to poor efficiency and general blocking for certain polarizations) and may create coherent artifacts, reducing the uniformity of the far-field image formed by light coupled out of the waveguide. To obtain a diffractive optical coupling element that is insensitive to polarization, or at least has reduced polarization sensitivity (e.g., coupling light with relatively polarization-independent efficiency), some displays for AR systems, according to the various implementations described herein, include a waveguide with a diffraction grating formed together with a blazed geometric shape. Diffraction gratings may also be formed directly within a waveguide, which may contain high refractive index materials (e.g., having refractive indices 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 range between these values). Diffraction gratings may also be formed within high refractive index materials such as lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or zirconium oxide (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC), for example, by patterning the high refractive index material with a blazed geometric shape.

[0047] Here, similar reference numbers will refer to the same parts throughout the document. Unless otherwise indicated, the drawings are schematic and not necessarily drawn to exact scale.

[0048] Figure 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that when a user's eyes are spaced apart and viewing a real object in space, each eye may have a slightly different view of the object and may form an image of the object in different locations on the retina of each eye. This may be called binocular parallax and can be used by the human visual system to provide a sense of depth. Conventional display systems simulate binocular parallax by presenting two distinctly different images 190, 200, one for each eye 210, 220, with slightly different views of the same virtual object, corresponding to the view of the virtual object that each eye would see as a real object at a desired depth. These images provide binocular cues that the user's visual system can interpret to derive a sense of depth.

[0049] Continuing with Figure 2, images 190 and 200 are spaced 230 units away from eyes 210 and 220 on the z-axis. The z-axis is parallel to the viewer's optical axis when the eye is fixated on an object at optical infinity directly in front of the viewer. Images 190 and 200 are flat and at a fixed distance from eyes 210 and 220. Based on slightly different views of the virtual object in the images presented to eyes 210 and 220, the eyes may necessarily rotate so that the image of the object comes to the corresponding point on the respective retina of the eye, maintaining monobiocular vision. This rotation can converge the lines of sight of eyes 210 and 220 to a point in space where the virtual object is perceived to exist. As a result, the provision of three-dimensional images involves providing binocular cues that can conventionally manipulate the convergence and divergence movements of the user's eyes 210 and 220, which the human visual system interprets to provide depth perception.

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

[0051] Continuing to refer to Figures 3A-3C, light from an object that the viewer's eye is fixated on may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which may require the lens to take on different shapes and form a focused image on the retina. 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 eye's lens 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 eye's lens, thereby modulating the force applied to the suspensory ligament that holds the lens, and thus changing the shape of the eye's lens until the retinal blur of the fixed object is eliminated or minimized, thereby forming a focused image of the fixed object on the retina (e.g., the fovea). The process by which the lens of the eye changes shape may be called accommodation, and the shape of the lens required to form a focused image of the object being fixed on onto the retina of the eye (e.g., the fovea) may be called the accommodative state.

[0052] Referring here to Figure 4A, the representation of the accommodation-convergence-divergence response of the human visual system is illustrated. Eye movement to fixate on an object causes the eye to receive light from the object, and the light forms an image on each of the eye's retinas. The presence of retinal blur in the image formed on the retina can provide a cue for accommodation, and the relative location of the image on the retina can provide a cue for convergence-divergence movement. The cue for accommodation causes accommodation, prompting the lens of the eye to assume a specific accommodative state in which a focused image of the object is formed on the eye's retina (e.g., the fovea). On the other hand, the cue for convergence-divergence movement causes convergence-divergence movement (rotation of the eye) so that the image formed on each retina of each eye is at the corresponding retinal point that maintains monobiocular vision. At these positions, the eye can be said to be in a specific convergence-divergence state. Continuing to refer to Figure 4A, accommodation can be understood as the process by which the eye achieves a specific state of accommodation, and convergence / divergence can be understood as the process by which the eye achieves a specific state of convergence / divergence. As shown in Figure 4A, the state of accommodation and convergence / divergence of the eye can change when the user fixates on a different 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] While not limited by theory, it is thought that viewers of objects may perceive them as "three-dimensional" due to a combination of convergence / divergence movements and accommodation. As described above, the convergence / divergence movements of two eyes relative to each other (for example, eye rotations that cause the pupils to move toward or away from each other, converging the lines of sight and fixing on an object) are closely related to the accommodation of the eye's lens. Under normal conditions, a change in the shape of the eye's lens to shift focus from one object to another at a different distance will automatically produce a corresponding change in convergence / divergence movements to the same distance, under a relationship known as the "accommodation-convergence / divergence reflex." Similarly, a change in convergence / divergence movements will, under normal conditions, induce a corresponding change in the shape of the lens.

[0054] Referring now to Figure 4B, embodiments of different accommodation and convergence / divergence states of the eyes are illustrated. A pair of eyes 222a fixate on an object at optical infinity, while a pair of eyes 222b fixate on an object 221 below optical infinity. It is noteworthy that the convergence / divergence states of each pair of eyes are different, with the pair of eyes 222a pointing straight ahead, while the pair of eyes 222 converges on the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a and 220a.

[0055] Unfortunately, many users of conventional "3-D" display systems find such systems uncomfortable or completely fail to perceive depth due to the mismatch between the accommodation and convergence / divergence states in these displays. As mentioned above, many stereoscopic or "3-D" display systems display scenes by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they, above all, simply provide different presentations of scenes and cause changes in the convergence / divergence states of the eyes, but without corresponding changes in the accommodation states of those eyes. Rather, the images are presented by the display at a fixed distance from the eyes so that the eyes perceive all image information in a single accommodation state. Such arrangements go against the "accommodation-convergence / divergence reflex" by causing changes in the convergence / divergence state without corresponding changes in the accommodation state. This mismatch is thought to cause discomfort to the viewer. A display system that provides a better match between distance accommodation and convergence / divergence motion can create a more realistic and comfortable simulation of three-dimensional images.

[0056] While not limited by theory, the human eye is typically thought to be capable of interpreting a finite number of depth planes and providing depth perception. Consequently, a highly realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both cues for convergence-divergence movements and matching cues for accommodation, thereby providing a physiologically correct accommodation-convergence-divergence movement match.

[0057] Continuing with Figure 4B, two depth planes 240 are illustrated, corresponding to different spatial distances from eyes 210 and 220. With respect to a given depth plane 240, convergence and divergence motion cues may be provided by displaying appropriately different viewpoint images for each eye 210 and 220. In addition, with respect to a given depth plane 240, the light forming the image provided to each eye 210 and 220 may have wavefront divergence corresponding to a light field generated by a point at a distance in that depth plane 240.

[0058] In the illustrated embodiment, the distance along the z-axis of the depth plane 240 containing point 221 is 1 m. As used herein, the distance along the z-axis, or depth, may be measured using a zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m from the exit pupil of the user's eye on the optical axis of those eyes, with the eyes pointed toward optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the display in front of the user's eye (e.g., from the surface of the waveguide) and a value relating to the distance between the device and the exit pupil of the user's eye may be added. This value may be called the pupil distance and corresponds to the distance between the exit pupil of the user's eye and the user-worn display in front of the eye. In practice, the value relating to 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 from the front of the display.

[0059] Referring here to Figures 4C and 4D, embodiments of coincident accommodation-convergence-divergence distance and mismatched accommodation-convergence-divergence distance are illustrated, respectively. As shown in Figure 4C, the display system may provide images of virtual objects to each eye 210, 220. The images can cause the eyes 210, 220 to assume a convergence-divergence state in which the eyes converge on point 15 on the depth plane 240. In addition, the images may be formed by light having a wavefront curvature corresponding to the real object in its depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the images are in focus on the retinas of their eyes. Thus, the user can perceive the virtual object as being at point 15 on the depth plane 240.

[0060] It should be understood that the accommodation and convergence / divergence movements of eyes 210 and 220 are each associated with a specific distance on the z-axis. For example, an object at a specific distance from eyes 210 and 220 will cause those eyes to adopt a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state is the accommodation distance A. d It can be called a specific convergence-divergence distance V associated with the eyes in a specific convergence-divergence movement state or relative position. d However, such a scenario exists. When the accommodation distance and the convergence / divergence distance match, the relationship between accommodation and convergence / divergence can be said to be physiologically correct. This is considered the most comfortable scenario for the viewer.

[0061] However, in stereoscopic displays, the accommodation distance and the convergence / divergence distance do not always coincide. For example, as illustrated in Figure 4D, the images displayed to eyes 210 and 220 may be displayed with wavefront divergence corresponding to the depth plane 240, and eyes 210 and 220 may take on a specific accommodation state in which points 15a and 15b on their depth plane are in focus. However, the images displayed to eyes 210 and 220 may provide cues for convergence / divergence movements that cause eyes 210 and 220 to converge on point 15, which is not located on the depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of eyes 210 and 220 to the depth plane 240, while the convergence / divergence distance corresponds to a larger distance from the exit pupils of eyes 210 and 220 to point 15. The accommodation distance is different from the convergence / divergence distance. As a result, there is a mismatch in accommodation-convergence / divergence motion. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch is due to distance (e.g., V d -A d Please understand that this corresponds to and 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 may also be used to determine distances for determining the mismatch between accommodative and convergence / divergence movements, insofar as the same reference points are used for accommodative distance and convergence / divergence distance. For example, distances may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of a display device) to the depth plane, etc.

[0063] While not limited by theory, it is conceivable that users may still perceive physiologically correct accommodation-convergence / divergence mismatches of up to approximately 0.25 diopters, up to approximately 0.33 diopters, and up to approximately 0.5 diopters, without the mismatch itself causing significant discomfort. In some embodiments, the display systems disclosed herein (e.g., display system 250, Figure 6) present images to the viewer having accommodation-convergence / divergence mismatches of about 0.5 diopters or less. In some other embodiments, the accommodation-convergence / divergence mismatch of the images provided by the display system is about 0.33 diopters or less. In yet more embodiments, the accommodation-convergence / divergence mismatch of the images provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0064] Figure 5 illustrates an aspect of an approach to simulating a three-dimensional image by correcting wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output that 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. In addition, it will be illustrated 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 wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light with a limited range of wavelengths. As a result, in some embodiments, multiple or stacked waveguides may be used to provide different wavefront divergences for different depth planes, and / or to output light with different ranges of wavelengths. It should be understood that, as used herein, depth planes can follow the contours of flat or curved surfaces.

[0066] Figure 6 illustrates an embodiment of a waveguide stack for outputting image information to a user. The display system 250 includes a waveguide stack or stacked waveguide assembly 260, which may be used 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. In addition, 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 substantially continuous cues for convergence-divergence motion and a plurality of discrete cues for near accommodation. The cues for convergence-divergence motion may be provided by displaying different images to each of the user's eyes, and the cues for near accommodation 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 specific depth plane and be provided by a specific waveguide among 270, 280, 290, 300, and 310.

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

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

[0070] In some embodiments, the light introduced into waveguides 270, 280, 290, 300, and 310 is provided by an optical projector system 520 comprising an optical module 530, which may include an optical emitter such as a light-emitting diode (LED). The light from the optical module 530 may be directed and modified via a beam splitter 550 to an optical modulator 540, for example, a spatial light modulator. The optical modulator 540 may be configured to change the perceived intensity of the light introduced into waveguides 270, 280, 290, 300, and 310, thereby encoding the light with image information. Embodiments of the spatial light modulator include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. Image input devices 360, 370, 380, 390, and 400 are graphically illustrated, and it should be understood that in some embodiments, these image input devices may represent different optical paths and locations within a common projection system, configured to output light into associated waveguides 270, 280, 290, 300, and 310. In some embodiments, the waveguides of waveguide assembly 260 may function as ideal lenses, relaying the light input into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540, and the image may be an image on the 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 in various patterns (e.g., raster scanning, helical scanning, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310, and ultimately to 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 multiple scanning fibers or multiple bundles of scanning fibers, each configured to input light into the associated waveguide 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, and 310. It should also be understood that one or more intervening optical structures may be provided between the scanning fiber or multiple fibers and one or more waveguides 270, 280, 290, 300, and 310, for example, to redirect light emitted from the scanning fiber into one or more waveguides 270, 280, 290, 300, and 310.

[0072] The 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 optical modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) to coordinate the timing and delivery of image information to the 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 wired or wireless communication channels. In some embodiments, the controller 560 may be part of the processing module 140 or 150 (Figure 9D).

[0073] Continuing with Figure 6, waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, and 310 may each be planar or have another shape (e.g., curved), with major upper and lower surfaces and edges extending between their major upper and lower surfaces. In the illustrated configuration, waveguides 270, 280, 290, 300, and 310 may each include external coupling optical elements 570, 580, 590, 600, and 610, respectively, configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as externally coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light can be output by the waveguide at the point where 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 the sake of clarity and to facilitate the explanation, they are shown positioned on the bottom main 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 positioned on the top and / or bottom main 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 mounted on a transparent substrate and formed within a layer of material that forms 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 inside the material piece.

[0074] Continuing with reference to Figure 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to emit 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 (injected into such waveguide 270) to the eye 210. The collimated light may represent the optical infinity focal plane. The next upper waveguide 280 may be configured to emit 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 some convex wavefront curvature so that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. 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 produce a different, gradually increasing wavefront curvature so that the eye / brain interprets the light originating from the third upper waveguide 290 as originating from a second focal plane that is closer inward toward the person from optical infinity than the light originating from the next upper waveguide 280.

[0075] Other waveguide layers 300, 310 and lenses 330, 320 are configured similarly, with the highest waveguide 310 in the stack emitting its output through all the lenses between it and the eye for a convergent focusing force representing the focal plane closest to the person. When viewing / interpreting light originating from the other side world 510 of the stacked waveguide assembly 260, a compensating lens layer 620 may be positioned on top of the stack to compensate for the convergent forces of the lower lens stacks 320, 330, 340, 350 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, and 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, and 310 may be configured to output images set on the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, and 310 may be configured to output images set on the same multiple depth planes, using one set per depth plane. This may offer the advantage of forming tiled images that provide an extended field of view in those depth planes.

[0077] Continuing with Figure 6, the external coupling optical elements 570, 580, 590, 600, and 610 may be configured to redirect light outward from their individual waveguides for specific depth planes associated with the waveguides, and to output the light with an appropriate amount of divergence or collimation. As a result, waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, and 610, which 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, and 610 may be three-dimensional or surface features that can be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, and 610 may be three-dimensional holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, and 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming voids).

[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 DOEs have sufficiently low diffraction efficiency such that only a portion of the beam light is deflected toward the eye 210 at each intersection of the DOEs, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is therefore split into several associated emission beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of emission toward the eye 210 with respect to this particular collimated beam bouncing 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 where microdroplets have a diffraction pattern within the host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index 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 light and infrared light cameras) may be provided to capture images of the eye 210 and / or the surrounding tissues, for example, to detect user input and / or monitor the user's physiological state. As used herein, the camera may be any image-capturing device. In some embodiments, the camera assembly 630 may include the image-capturing device and a light source that projects light (e.g., infrared light) onto the eye, which is then reflected by the eye and can be detected by the image-capturing device. In some embodiments, the camera assembly 630 may be mounted on a frame 80 (Figure 9D) and may communicate with processing modules 140 and / or 150 that can process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be used per eye to monitor each eye separately.

[0081] Referring here to Figure 7, an embodiment of an outgoing beam output by a waveguide is shown. Although one waveguide is illustrated, other waveguides within the waveguide assembly 260 (Figure 6) may function similarly, and it should be understood that the waveguide assembly 260 includes multiple waveguides. Light 640 is introduced into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates through the waveguide 270 by TIR. At the point where the light 640 collides on the DOE 570, a portion of the light exits the waveguide as an outgoing beam 650. The outgoing beams 650 are illustrated as substantially parallel, but as discussed herein, they may also be redirected to propagate towards the eye 210 at a certain angle (e.g., forming a divergent outgoing beam), depending on the depth plane associated with the waveguide 270. It should be understood that a nearly parallel emitted beam may represent a waveguide with an externally coupled optical element that externally couples the light to form an image that appears to be set on the depth plane at a distance from the eye 210 (e.g., optical infinity). Other waveguides or other sets of externally coupled optical elements may output a more divergent emitted beam pattern, which would require the eye 210 to adjust to a closer distance and focus onto the retina, 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 in each depth plane by overlaying an image onto each of the primary colors, for example, three or more primary colors. Figure 8 illustrates an embodiment of a stacked waveguide assembly in which each depth plane includes an image formed using several different primary colors. The illustrated embodiment shows depth planes 240a–240f, but more or fewer depths may also be considered. Each depth plane may have three or more associated primary color images, 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 indicated in the figure by different numbers relating to diopters (dpt) following the letters G, R, and B. As merely an embodiment, the numbers following each of these letters indicate diopters (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 depth planes relating to different primary colors may vary to account for differences in the focusing of light of different wavelengths on the eye. For example, different primary color images relating to 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, each primary color light may be output by a single dedicated waveguide, and as a result, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure, including the letters G, R, or B, can be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images provided for each depth plane. 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 waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, for example, so that only a single waveguide may be provided for each depth plane.

[0084] Continuing to refer to Figure 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 be used in addition to or replace one or more of red, green, or blue.

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

[0086] In some embodiments, the light source 530 (Figure 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. In addition, internal coupling, external coupling, and other light redirection structures of the waveguide of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, for example, for imaging and / or user stimulation applications.

[0087] Referring here to Figure 9A, in some embodiments, light impacting a waveguide may need to be redirected to internally couple that light into the waveguide. Internal coupling optical elements may be used to redirect and internally couple the light into its corresponding waveguide. Figure 9A illustrates cross-sectional side views of embodiments of multiple or set 660 stacked 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. It should be understood that a stack 660 may correspond to a stack 260 (Figure 6), and the illustrated waveguides of a stack 660 may correspond to a portion of multiple 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 requiring the light to be redirected for internal coupling.

[0088] The illustrated set of stacked waveguides 660 includes waveguides 670, 680, and 690. Each waveguide includes associated internal coupling optical elements (which may also be referred to as optical input areas on the waveguide), for example, internal coupling optical element 700 is located on the main surface of waveguide 670 (e.g., the upper main surface), internal coupling optical element 710 is located on the main surface of waveguide 680 (e.g., the upper main surface), and internal coupling optical element 720 is located on the main surface of waveguide 690 (e.g., the upper main surface). In some embodiments, one or more of the internal coupling optical elements 700, 710, and 720 may be located on the bottom main surfaces of individual waveguides 670, 680, and 690 (particularly when one or more internal coupling optical elements are reflective deflection optical elements). As illustrated, the internal coupling optical elements 700, 710, and 720 may be located on the upper main surface (or the upper part of the following lower waveguide) of their individual waveguides 670, 680, and 690, in particular when their internal coupling optical elements are transmissive deflection optical elements. In some embodiments, the internal coupling optical elements 700, 710, and 720 may be located within the body of the individual waveguides 670, 680, and 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, and 720 are wavelength-selective, such as selectively redirecting one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their individual waveguides 670, 680, and 690, it should be understood that in some embodiments, the internal coupling optical elements 700, 710, and 720 may be located within other areas of their individual waveguides 670, 680, and 690.

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

[0090] Each waveguide also includes associated optical dispersion elements, for example, optical dispersion element 730 is located on the main surface (e.g., upper main surface) of waveguide 670, optical dispersion element 740 is located on the main surface (e.g., upper main surface) of waveguide 680, and optical dispersion element 750 is located on the main surface (e.g., upper main surface) of waveguide 690. In some other embodiments, optical dispersion elements 730, 740, and 750 may be located on the bottom main surfaces of the associated waveguides 670, 680, and 690, respectively. In some other embodiments, optical dispersion elements 730, 740, and 750 may be located on both the top and bottom main surfaces of the associated waveguides 670, 680, and 690, respectively, or optical dispersion elements 730, 740, and 750 may be located on different top and bottom main surfaces within different associated waveguides 670, 680, and 690.

[0091] Waveguides 670, 680, and 690 may be separated and isolated by, for example, gaseous, liquid, and / or solid layers 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 lower refractive index than the material forming the directly adjacent waveguides 670, 680, and 690). Preferably, the refractive index of the material forming layers 760a and 760b is 0.05 or greater, or 0.10 or less, than the refractive index of the material forming waveguides 670, 680, and 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the upper and lower main surfaces of each waveguide). In some embodiments, layers 760a, 760b are formed from air. It should be understood that the upper and lower parts of the illustrated set of waveguides 660 may include the immediate cladding layer, although not shown.

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

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

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

[0095] For example, the internally coupled optical element 700 may be configured to selectively deflect a ray 770 having a first wavelength or wavelength range while transmitting rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted ray 780 collides with an internally coupled optical element 710 configured to deflect light of the second wavelength or wavelength range, and is deflected by it. The ray 790 is deflected by an internally coupled optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

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

[0097] Referring now to Figure 9B, a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A is illustrated. As described above, the internally coupled rays 770, 780, and 790 are deflected by the internally coupled optical elements 700, 710, and 720, respectively, and then propagate by TIR within waveguides 670, 680, and 690, respectively. The rays 770, 780, and 790 then collide with the optical dispersion elements 730, 740, and 750, respectively. The optical dispersion elements 730, 740, and 750 deflect the rays 770, 780, and 790 so that they propagate toward the externally coupled optical elements 800, 810, and 820, respectively.

[0098] In some embodiments, the light dispersion elements 730, 740, and 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light to the external coupling optical elements 800, 810, and 820, and in some embodiments, they can also increase the beam or spot size of the light as it propagates to the external coupling optical elements. In some embodiments, the light dispersion elements 730, 740, and 750 may be omitted, and the internal coupling optical elements 700, 710, and 720 may be configured to deflect light directly to the external coupling optical elements 800, 810, and 820. For example, referring to Figure 9A, the light dispersion elements 730, 740, and 750 may be replaced by the external coupling optical elements 800, 810, and 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 into the viewer's eye 210 (Figure 7). It should be understood that the OPEs may be configured to increase the dimensions of the eyebox along at least one axis, and the EPEs may increase the eyebox along an axis intersecting, for example, orthogonal to the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impacting the OPE to an EPE in the same waveguide, while allowing the rest of the light to continue propagating along the waveguide. Again, in response to the impact on the OPE, another portion of the remaining light is redirected to the EPE, and the rest of that portion continues to propagate further along the waveguide, etc. Similarly, in response to the impact on the EPE, a portion of the impacting light is directed out of the waveguide toward the user, and the rest of that light continues to propagate through the waveguide until it impacts the EP again, at which point another portion of the impacting light is directed out of the waveguide, and so on. As a result, a single beam of internally coupled light is "duplicated" each time a portion of its light is redirected by the OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the light beam.

[0099] Therefore, referring to Figures 9A and 9B, in some embodiments, the set of waveguides 660 includes, for each primary color, waveguides 670, 680, 690, internally coupled optical elements 700, 710, 720, optical dispersion elements (e.g., OPE) 730, 740, 750, and externally coupled optical elements (e.g., EP) 800, 810, 820. Waveguides 670, 680, 690 may be stacked with air gaps / cladding layers between each one. The internally coupled optical elements 700, 710, 720 redirect or deflect the incident light into their waveguides (using different internally coupled optical elements that receive light of different wavelengths). The light then propagates within the individual waveguides 670, 680, 690 at angles that will result in a TIR. In the embodiment shown, a ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, and then continues to bounce along the waveguide, interacting with the optical dispersion element (e.g., OPE) 730 and then the external coupling optical element (e.g., EP) 800. Rays 780 and 790 (e.g., green and red light, respectively) pass through waveguide 670, with ray 780 colliding with the internal coupling optical element 710, thereby being deflected. Ray 780 then bounces along waveguide 680 via TIR, proceeding to its optical dispersion element (e.g., OPE) 740 and then the external coupling optical element (e.g., EP) 810. Finally, ray 790 (e.g., red light) passes through waveguide 690 and colliding with the optical internal coupling optical element 720 of waveguide 690. The internal optical coupling element 720 deflects the ray 790 so that it propagates by TIR to the optical dispersion element (e.g., OPE) 750, and then by 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 externally coupled light from other waveguides 670, 680.

[0100] Figure 9C illustrates upper and lower plan views of embodiments of the multiple stacked waveguides shown in Figures 9A and 9B. As shown, waveguides 670, 680, and 690 may be vertically aligned with the associated optical dispersion elements 730, 740, and 750 and associated external coupling optical elements 800, 810, and 820 of each waveguide. However, as discussed herein, the internal coupling optical elements 700, 710, and 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced, as seen in the upper and lower figures). As further discussed herein, this non-overlapping spatial arrangement facilitates the ingress 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, arrangements including non-overlapping, spatially separated internal coupling optical elements may be referred to as pupil-shifting systems, where the internal coupling optical elements in these arrangements may correspond to subpupils.

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

[0102] Continuing with reference to Figure 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functions of the display 70. The display 70 may be attached to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the user 90's eyes. In some embodiments, the display 70 may be considered an eyepiece. In some embodiments, a speaker 100 is attached to the frame 80 and configured to be positioned adjacent to the user 90's ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent to the user's other ear canal to provide stereo / shapeable sound control). The display system 60 also includes one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands (e.g., selection of voice menu commands, natural language questions, 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 also be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include a peripheral sensor 120a, separate from the frame 80, which can be attached 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 characterizing the user 90's physiological state. For example, the sensor 120a may be an electrode.

[0103] Continuing to refer to Figure 9D, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as a wired cable or wireless connectivity, which may be mounted in various configurations, such as being fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, built into headphones, or otherwise detachably attached to the user 90 (e.g., in a backpack configuration, in a belt-mounted configuration). Similarly, the sensor 120a may be operably coupled to the local processor and data module 140 by a communication link 120b, such as a wired cable or wireless connectivity. The local processing and data module 140 may include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be used to assist in data processing, caching, and storage. Optionally, the 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 image acquisition devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (for example, operably coupled to frame 80 or otherwise attached to user 90), and / or (b) possibly data obtained and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passage to display 70 after processing or reading. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180 via wired or wireless communication links, etc., so that these remote modules 150, 160 are operably coupled to each other and available as resources to the local processing and data module 140.In some embodiments, the local processing and data module 140 may include one or more of the following: an image acquisition 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 mounted on the frame 80 or may be in a standalone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0104] Continuing to refer to Figure 9D, in some embodiments, the remote processing module 150 may comprise 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 comprise digital data storage equipment, 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 comprise one or more remote servers that provide information, for example, augmented reality content, for generating data for the local processing and data modules 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 modules, enabling fully autonomous use from the remote modules. Optionally, an external system (e.g., one or more processors, one or more computer systems), including a CPU, GPU, etc., may perform at least part of the processing (e.g., generate image information, process data) and provide information to and receive information from modules 140, 150, and 160, for example, via a wireless or wired connection. (Diffraction grating with reduced polarization sensitivity)

[0105] Providing users of waveguide-based display systems, such as various display systems configured for the virtual / enhanced / composite display applications described above, depends, among other things, on the various properties of optical coupling in and / or out of the waveguide within the eyepiece of the display system. For example, virtual / enhanced / composite displays with high optical internal and external coupling efficiencies can improve the viewing experience by increasing the brightness of the light directed to 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 so that it is induced therein by total internal reflection. Similarly, external coupling optical elements, such as external coupling diffraction gratings, may be employed to couple light induced in the waveguide out of the waveguide by total internal reflection.

[0106] For example, as described above with reference to Figures 6 and 7, the display system, according to the various implementations described herein, may include a combined pupil expander-extractor (CPE) which may include optical elements, such as an internally coupled optical element, an externally coupled optical element, a light-dispersing element, and / or a diffraction grating. As disclosed herein, the CPE may act as both a light-dispersing element, which diffuses or disperses light within the waveguide and potentially increases the beam size and / or eyebox, and an externally coupled optical element, which couples light out of the waveguide.

[0107] For example, as described above with reference to Figure 7, light 640, which is introduced into the waveguide 270 at the input surface 460 of the waveguide 270, propagates and is induced within the waveguide 270 by total internal reflection (TIR). In various implementations, at the point where light 640 collides with the external coupling optical element 570, a portion of the light induced within the waveguide may exit the waveguide as a beamlet 650. In some implementations, any of the optical elements 570, 580, 590, 600, and 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 desirable characteristics of the internal coupling of light into (or external coupling of light from) the waveguides 270, 280, 290, 300, and 310, the optical elements 570, 580, 590, 600, and 610, which are configured as diffraction gratings, can be formed from suitable materials and have suitable structures for controlling various optical properties, including diffraction properties such as diffraction efficiency as a function of polarization. Possible desirable diffraction properties may include, among other things, one or more of the following: 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 a strong polarization dependence and therefore may have a relatively reduced overall efficiency (due to the blocking of certain polarizations). Such diffraction gratings may also create coherent artifacts and reduce the uniformity of far-field images. To provide a diffraction grating with reduced polarization sensitivity (e.g., coupling light with relatively polarization-independent efficiency), some displays for AR systems, according to the implementations described herein, include a waveguide with a blazed diffraction grating formed therein. The blazed grating may have diffraction features, for example, a “sawtooth” shape. In some implementations, the blazed grating may achieve improved grating diffraction efficiency with respect to a given diffraction order, while diffraction efficiency for other orders is reduced or minimized. As a result, more light may be directed into a particular given diffraction order, in contrast to any of the other orders in some implementations.

[0110] Figure 10A illustrates a partial cross-sectional view of a display device 1000, such as an eyepiece, comprising a waveguide 1004 and a blazed diffraction grating 1008 formed on a substrate which is the waveguide 1004, according to several designs described herein. In the shown implementation, the blazed diffraction grating 1008 is formed within the substrate / waveguide 1004 (which is planar in this embodiment). 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 in the visible spectrum so that light incident on it is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of an eyepiece through which the user's eye can see. Such a waveguide 1004 and eyepiece may be incorporated within a head-mounted display, such as an augmented reality display. Waveguide 1004 may correspond to, for example, one of waveguides 670, 680, and 690 as described above with respect to Figures 9A-9C. Blazed diffraction grating 1008 may correspond to, for example, one of internally coupled optical elements 700, 710, and 720 as described above with respect to Figures 9A-9C. Blazed diffraction grating 1008 configured to internally couple light into waveguide 1004 may be referred to herein as an internally coupled grating (ICG). Display device 1000 may also include optical element 1012, which may correspond to, for example, an optical dispersion element (for example, one of optical dispersion elements 730, 740, and 750 shown in Figures 9A-9C) or an externally coupled optical element (for example, one of externally coupled optical elements 800, 810, and 820 shown in Figures 9A-9C).

[0111] When operating, when an incident light beam 1016, for example visible light from a light projection system providing image content, is incident on the blazed diffraction grating 1008 at an incident angle α measured with respect to a surface normal 1002 which is normal to or perpendicular to the main surface of the waveguide (shown in Figure 10A as extending parallel to the yx plane) on which the grating is formed, the blazed diffraction grating diffracts the incident light beam 1016 at a diffraction angle θ measured with respect to the surface normal 1002, at least partially, as a diffracted light beam 1024. The diffracted light beam 1024 reaches a critical angle θ for the occurrence of total internal reflection within the waveguide 1004. TIR When diffracted at a diffraction angle θ exceeding θ, the diffracted light beam 1024 propagates and is guided within the waveguide 1004 via total internal reflection (TIR) ​​generally along the direction parallel to the x-axis and along the length of the waveguide. A portion of this light guided within waveguide 1004 reaches one of the optical dispersion elements 730, 740, 750 or one of the external coupling optical elements (800, 810, 820, Figures 9A-9C), where it can be diffracted again, for example.

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

[0113] As further described herein, preferred combinations of high refractive index materials and / or structures of the diffraction grating 1008 may result in a specific range (Δα) of incident angle α, which is referred herein to as the range of the receiving angle or field of view (FOV). A range Δα may be described by a range of angles extending to negative and / or positive values ​​of α, whereout of this range, the diffraction efficiency decreases 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 the range defined by any of these values, compared to the diffraction efficiency at α=0 or in some other direction. In some implementations, having a range Δα in which the diffraction efficiency is relatively high and constant may be desirable, for example, if a uniform intensity of diffracted light is desired within Δα. Therefore, in some implementations, Δα is associated with the angular bandwidth of the diffraction grating 1008 so that the incident light beam 1016 in Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ with respect to the surface normal 1002 (e.g., the direction parallel to the yz plane), and θ is associated with the angular bandwidth of the diffraction grating 1008 so that the diffracted light is guided in the waveguide 1004 under total internal reflection (TIR). TIR This exceeds [a certain value]. In some implementations, this angle Δα range can affect the field of view visible to the user. It should be understood that in various implementations, light can be directed onto an internally coupled grating (ICG) from both sides. For example, light can be directed through a substrate or waveguide 1004 and incident onto a reflective internally coupled grating (ICG) 1008, such as that shown in Figure 10A. The light can be coupled into the substrate or waveguide 1004 by the internally coupled grating 1008, for example, so that the light is guided into the substrate or waveguide by total internal reflection. The range of incident angle α (Δα), referred herein to as the range of the receiving angle or field of view (FOV), can be influenced by the refractive index of the substrate or waveguide material. In Figure 10A, for example, the reduced angle range (Δα') shows the effect of refraction by a high refractive index material on light incident on an internally coupled grating (ICG). However, the angle (Δα) or FOV range is larger.

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

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

[0116] The inclination can be tilted at an angle δ with respect to a plane parallel to the grid 1008 or the surface of the waveguide (for example, surface 1004S of the waveguide, which may extend beyond the grid or surface 1004S' of the waveguide, as opposed to the grid in Figure 10A). This angle δ of the first (shallower) inclined portion 1007 may be referred to herein as the blaze angle.

[0117] As illustrated in Figure 10B, the blazed diffraction grating 1008 may include grating lines or features having an asymmetrical shape, for example, comprising asymmetrically shaped protrusions 1003 and / or grooves 1005. For example, in the diffraction grating shown in Figure 10B, the diffraction features comprise protrusions 1003 and / or grooves 1005 having an asymmetrical triangular cross-sectional shape. As discussed above, this asymmetrical shape results in different inclinations and / or widths of the first and second inclined portions 1007, 1009. However, other shapes are also possible.

[0118] In designs where the diffraction features are asymmetric, for example, where the slope of the first inclined portion is shallower and the slope of the second inclined portion is steeper, the diffraction features can be considered to be formed from repeating inclinations and steps. Such a structure may be referred to herein as an inclined step structure. In some implementations, the second portion may be so steep as to have no inclination, for example, the second portion may be parallel to the normal 1002.

[0119] However, in other implementations of the “sawtooth” pattern, the tips 1003 and / or grooves 1005 may be symmetrical. For example, the first and second inclined portions 1007, 1009 may have the same inclination and the same width.

[0120] The cross-sectional pattern shown in Figure 10B may be referred to herein as a single-stage geometric shape in comparison to the multi-stage structure discussed below. The multi-stage structure is shown, for example, in Figure 11D.

[0121] Regardless of whether the diffraction features are asymmetric or symmetric, in some implementations, the solenoid or planar portion may be located above the tip 1003, as discussed below. A diffraction grating 1008 having diffraction features with the solenoid or planar portion above the tip 1003 is shown, for example, in Figures 11B and 11D.

[0122] Figure 10B shows an incident light beam 1016 incident on the grating 1008 at an angle α with respect to the normal direction 1002. (As discussed above with respect to Figure 10A, in other embodiments, the light can pass through the substrate or waveguide 1004 and be incident on the diffraction grating 1008 from the other side.) As discussed above, the normal 1002 is normal to or perpendicular to the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, for example, the main surface or opposing plane surface 1004S' of the waveguide on which the grating is formed. In Figure 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 internally coupled optical element or an internally coupled diffraction grating, the diffraction grating 1008 can diffract and couple light incident on the substrate 1004, which may be a waveguide, as described above. The diffraction grating 1008 may optionally be configured as an externally coupled optical element, in which case it can diffract and couple light from the substrate 1004, which may similarly be a waveguide, as described above.

[0124] Referring to Figures 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 may be 2.4 or less, 2.5 or less, 2.6 or less, 2.7 or less, 2.8 or less, or within any range formed by any of these values, or 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 may be formed either within the substrate 1004, for example, within a waveguide, or within a separate layer formed across the substrate 1004, for example, within a waveguide and optically communicating with the substrate 1004, for example, 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 may be etched into the substrate 1004, for example, a high refractive index material such as a Li-based oxide. The substrate may contain, for example, lithium niobate, and the diffraction grating may be formed within the lithium niobate substrate by etching or patterning the surface of the substrate. Other materials having a high refractive index may also be used. For example, other materials containing lithium, such as lithium oxide, e.g., lithium tantalate (LiTaO3), may be used as the substrate. Silicon carbide (SiC) is another option for the substrate material. The embodiment is not limited thereto. In other embodiments, the diffraction features of the diffraction grating 1008 may be formed in a separate layer, for example, physically in contact with, the substrate 1004. For example, thin film coatings of zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), etc., with a thickness of less than 200 nm, may be placed 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 the diffraction grating 1008 may be formed from a material different from that of the substrate.The substrate may include, for example, a high refractive index material such as a Li-based oxide (e.g., lithium niobate LiNbO3 or lithium tantalate LiTaO3), however, the diffraction features may be formed from different materials such as a coating of zinc oxide (ZnO), zirconium dioxide (ZrO2), titanium dioxide (TiO2), silicon carbide (SiC), or other materials described herein. In some implementations, the other material formed on the substrate may have a lower refractive index. In some cases, the substrate 1004 may include materials such as silica glass (e.g., doped silica glass), silicon oxynitride, transition metal oxides (e.g., hafnium oxide, tantalum oxide, zirconium oxide, niobium oxide, aluminum oxide (e.g., sapphire)), plastics, polymers, or other materials that are substantially optically transparent to visible light and have a suitable refractive index as described above, different from the material of the Li-based oxide feature 1008 (including amorphous high refractive index glass substrates).

[0125] However, as described above, in the various implementations described herein, both the diffraction grating 1008 and the substrate 1004 or waveguide contain the same material, for example, a Li-based oxide. In some implementations, the diffraction grating 1008 is patterned directly into the substrate 1004 such that the diffraction grating 1008 and the substrate 1004 form a single sub-piece or monolithic structure. For example, the substrate 1004 comprises a waveguide having a diffraction grating 1008 formed directly within the waveguide or the surface of the 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 beneath the diffraction grating 1008 may form the waveguide. Furthermore, in some other implementations, the bulk or substrate 1004 and surface 1004S patterned to form the diffraction grating 1008 contain different Li-based oxides. For example, the bulk Li-based oxide material that is patterned on 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 that forms 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 may consist of different high refractive index materials such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), and silicon carbide (SiC), and the material below the diffraction grating 1008 that forms the substrate 1004 or substrate region may be formed from a second material different from the first material that is coated as a thin film, such as LiTaO3 or LiNbO3.

[0126] In the embodiments illustrated in Figures 10A and 10B, the diffraction grating 1008 may include a plurality of blazed diffraction grating lines that are extended in a first horizontal or y-direction and periodically repeated in a second horizontal or x-direction. The diffraction grating lines can be, for example, linear and continuous lines extending in the y-direction. However, embodiments are not limited thereto. 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 embodiment, the diffraction grating lines of the diffraction grating 1008 have a sawtooth profile, for example, an asymmetrical opposing surface that forms a different angle with respect to the plane of the substrate. However, the embodiment is not limited thereto, and in other implementations, the diffraction grating lines may have a symmetrical opposing surface that forms a similar angle with respect to the plane of the substrate.

[0128] Referring to Figures 10A and 10B, which illustrate various embodiments, the diffraction grating 1008 may have various dimensions. For example, the diffraction features of the diffraction grating 1008 may have a height (H) that, according to embodiments, 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 blaze geometry in a high refractive index material may provide a diffraction grating with reduced polarization sensitivity. However, other heights may also be considered as possibilities.

[0129] The diffraction grating 1008 may, according to various embodiments, have a pitch of 250 nm to 350 nm, 300 nm to 400 nm, 250 nm to 450 nm, or any range defined by any of these values. Other pitches are also possible.

[0130] The diffraction grating 1008 may have a blaze angle of approximately 10–70 degrees (shallow size) and an inverse blaze angle of 140–70 degrees (steep side), or any value within the range defined by these values. Values ​​outside these ranges are also possible.

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

[0132] Figure 11A illustrates the formation of a single-stage blazed grid 1106 within a substrate 1104, which may be a waveguide 1004 (Figure 10A). A patternable material such as a photoresist 1102 may be deposited on the substrate 1104, which may contain a waveguide 1004. The patternable material / photoresist 1102 is patterned to have the shape of a blazed grid. In some implementations, the step of forming the blazed geometric shape within the photoresist 1102 may involve imprinting a pattern, such as a single-stage "sawtooth" pattern, into the photoresist 1102 (for example, depositing the photoresist on the substrate 1104 and then imprinting the blazed geometric shape). The photoresist 1102 may include a mask, such as a rigid mask. The patterned photoresist 1102 and substrate 1104 can then be etched to form a blazed pattern within the substrate 1106. The step of etching the photoresist 1102 and the substrate 1104 may involve, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching illustrated in Figure 11A may etch away material at a relatively constant rate such that the areas where the patterned photoresist was thickest result in relatively small amounts of material removal from the substrate, e.g., negligible or no removal, while the areas where the patterned photoresist was thinnest (or absent) result in relatively large amounts of material removal from the substrate or deep etching into the substrate.

[0133] Figure 11B is a scanning electron microscope image of a blazed photoresist grating 1112, where the blazed grating pattern is formed within the photoresist 1104, for example, by imprinting the photoresist using a patterned master. The diffraction grating 1112 shown has a single-stage blazed geometric shape.

[0134] Figure 11C illustrates the formation of a multi-stage blazed grid 1156 within a substrate 1154, which may be a waveguide 1004 (Figure 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 a blazed grid. In some implementations, the step of forming the blazed photoresist 1152 may involve imprinting a pattern, such as a multi-stage "sawtooth" pattern, into the photoresist 1152 (for example, depositing the photoresist on the substrate 1154 and then imprinting the blazed geometric shape). The patterned photoresist 1152 and substrate 1154 can then be etched to form a multi-stage blazed substrate 1156. The photoresist 1152 may be equipped with a mask, such as a rigid mask. The patterned photoresist 1152 and substrate 1154 may then be etched to form a blazed pattern within the substrate 1156. The step of etching the photoresist 1152 and substrate 1154 may involve, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching illustrated in Figure 11C may etch and remove material at a relatively constant rate, such that the areas where the patterned photoresist was thickest result in relatively small amounts of material removal from the substrate, e.g., negligible or no removal, while the areas where the blazed photoresist was thinnest (or absent) result in relatively large amounts of material removal from the substrate or deep etching into the substrate.

[0135] Figure 11D is a scanning electron microscope image of a blazed photoresist grating 1162, where the blazed grating pattern is formed on the photoresist 1164, for example, by imprinting the photoresist using a patterned master. The diffraction grating 1162 may have a multi-stage blazed geometric shape. The width of the tip 1003 is shown to be approximately 200 nm.

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

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

[0138] Figures 12A–12C show a lithium niobate (LiNbO3) substrate with an upper surface having the shape of a blazed diffraction grating (e.g., blazed geometric shape). Figure 12A is an SEM image 1200 of the blazed diffraction grating formed in the lithium niobate (LiNbO3) substrate, where the step height or tip height of the blazed grating is measured to be approximately 31.90 nm. The angle δ of the first (shallower) inclined surface with respect to the plane of the substrate is approximately 12.1 degrees. (This angle δ may be referred to herein as the blaze angle.) Figure 12B shows an SEM image 1202 of the blazed grating from a different viewpoint. Figure 12B shows the pitch (e.g., the distance between the minimum values ​​of the tips or steps or grooves) which is measured to be approximately 331.8 nm. In the SEM image 1204 shown in Figure 12C, the blazed lattice formed within the lithium niobate (LiNbO3) substrate is shown to have protrusions or steps, measured to be approximately 46.26 nm. The angle δ of the first (shallower) inclined surface with respect to the plane of the substrate is approximately 19.5 degrees. (This angle δ may be referred to herein as the blaze angle.)

[0139] Figure 12D shows an SEM image 1206 of a silicon substrate etched to form a blazed diffraction grating therein. In the embodiment of Figure 12D, the height of the blazed diffraction feature, e.g., the tip height or groove depth, 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 plane over which the substrate extends). The “shallow” angle of the tip, e.g., the angle δ of the first shallower inclined portion (which may be called the blaze angle), is measured to be approximately 27.9 degrees (with respect to the plane over which the substrate extends).

[0140] Figure 12E shows an SEM image 1208 of a silicon substrate etched to form a multi-stage blazed diffraction grating therein. The height of the multi-stage blazed feature in the embodiment of Figure 12D, e.g., the tip height or groove depth, is measured to be approximately 66.85 nm. The width of the multi-stage blazed feature or tip is measured to be approximately 206.9 nm (e.g., width not including any spacing between adjacent multi-stage features). The overall "shallow" angle of the tip, determined based on the tip height relative to the distance from the base to the top of the tip, is measured to be approximately 22.5 degrees (with respect to the plane over which the substrate extends). The "steep" angle, e.g., the angle of a second, steeper inclined portion of the tip, is measured to be approximately 68.8 degrees (with respect to the plane over which the substrate extends).

[0141] Figure 12F shows an SEM image 1210 of a substrate formed from glass with a refractive index (RI) of 1.8. The imaged substrate has a blazed diffraction grating formed within it, with a step or feature height of approximately 87.09 nm.

[0142] In general, varying the geometric shape of a blazed diffraction grating, such as grating 1008 in Figures 10A and 10B, can alter the performance characteristics of the grating. In at least some implementations, diffraction gratings that are less sensitive to the polarization of light (e.g., diffractive optical coupling elements that internally or externally couple light relatively independently of its polarization) can be obtained by suitably adjusting grating parameters such as the grating thickness or the height of the diffraction features. A diffraction grating with reduced polarization sensitivity may have higher overall efficiency (e.g., it may couple more light than a more polarization-sensitive grating), and a polarization-sensitive grating may introduce undesirable coherent artifacts, reducing the uniformity of the far-field image produced by, for example, the eyepiece of a head-mounted display, thus providing a more uniform image for the viewer.

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

[0144] Plot 1300 illustrates the TM / TE ratio as a function of the incident angle α with respect to a blazed diffraction grating formed in a photoresist placed on a lithium niobate substrate. As shown in plot 1300, the diffraction grating formed from the blazed photoresist on the lithium niobate substrate is relatively sensitive to polarization; for example, it may have an efficiency with respect to TM polarization that is 3 to 4 times higher than the efficiency of the grating with respect to TE polarization within a range of incident angles.

[0145] Plot 1302 illustrates the TM / TE ratio as a function of the incident angle α for blazed diffraction gratings (diffraction grating 1180, etc., having geometric shape 2 shown in Figure 11E) with diffraction features formed within a lithium niobate substrate having a feature or tip height (or groove depth) H of 35 nm. As shown in Plot 1302, diffraction gratings with an etched feature height of 35 nm are less sensitive to polarization than blazed gratings formed within a photoresist layer deposited on a lithium niobate substrate. Across most of the measured range of incident angles, diffraction gratings with an etched feature height of 35 nm are only slightly more favorable to TM polarization than TE polarization, by a ratio of approximately 1.5–2.0 or 2.2 (e.g., the grating thus has slightly reduced polarization sensitivity).

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

[0147] Figure 14 illustrates the TM / TE diffraction efficiency of a blazed diffraction grating formed in a lithium niobate substrate with a feature height of 80 nm for different colored light (e.g., green, blue, and red light). As shown in Figure 14, the TM / TE diffraction efficiency ratio (of diffraction grating 1170) is approximately 1 over a wide range of incident angles for both green and blue light. In addition, for red light, the TM / TE diffraction efficiency ratio is generally approximately 1.5 and increases to over 2 for certain incident angles (but not to 2.5).

[0148] Figure 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, for example, represent the efficiency of the diffraction grating in internally coupled (or externally coupled) unpolarized light.

[0149] In addition to general reductions in efficiency and brightness, certain highly polarization-sensitive diffraction gratings can also create coherent artifacts and reduce the uniformity of far-field images produced by eyepieces in head-mounted displays that direct image content towards the user's eye.

[0150] Figure 16 shows the distribution of light output from an eyepiece equipped with an internal coupling grating, which includes a blazed diffraction grating formed in a photoresist deposited on a lithium niobate substrate to internally couple light into a waveguide-based eyepiece and an optical redirection element (orthogonal pupil expander) and an external coupling optical element (exit pupil expander). As shown in Figure 16, the eyepiece with an internal coupling optical element, which includes a blazed diffraction grating in a photoresist deposited on a lithium niobate substrate, can produce coherent uniformity of approximately 9.45% for unpolarized input and approximately 11.3% for linearly polarized input. The graphs and images in Figure 16 were obtained from a 500-micron thick Z-cut lithium niobate substrate having a layer of photoresist on which it is patterned by imprinting to form an internal coupling grating. Figure 16 shows non-uniformity in the far-field image 1600. In this embodiment, the plotted uniformity score is a mathematical value derived from analyzing the pixel values ​​of an image captured over a certain area, and indicates non-uniformity in the captured values ​​at different sampling spatial frequencies across the image. Lower values ​​indicate a more uniform color distribution across the captured or desired image field of view.

[0151] Figure 17 shows the distribution of light output from an eyepiece equipped with an internal coupling grating, which includes a blazed diffraction grating formed in a lithium niobate substrate for internal coupling of light into a waveguide-based eyepiece and an optical redirection element (orthogonal pupil expander) and an external coupling optical element (exit pupil expander). As shown in Figure 17, the internal coupling optical element, equipped with a blazed diffraction grating with a feature height (tip height or groove depth) of 80 nm formed by etching in a lithium niobate substrate, can have improved coherent uniformity, such as approximately 8.1% coherent uniformity for unpolarized inputs and approximately 8.35% coherent uniformity for linearly polarized inputs. The graphs and images in Figure 17 were obtained from a 500-micron thick Z-cut lithium niobate substrate with a blazed diffraction grating etched in the substrate. EPE and OPE are also etched in the substrate. Figure 17 shows the reduction in non-uniformity in far-field image 1700 compared to far-field image 1600.

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

[0153] The structure and its manufacturing method may differ from those embodiments specifically described above. For example, the blazed grating may be used as an externally coupled optical element (e.g., EPE) and / or an optical redirection optical element (e.g., OPE). In addition, other types of diffractive optical elements may be formed, for example, within a high refractive index substrate instead of a diffraction grating. For example, different high refractive index materials such as lithium tantalate (e.g., LiTaO3) may be used for the waveguide and the diffractive features formed therein. As discussed above, in some other implementations, the waveguide and the diffractive features formed therein may include silicon carbide or other high refractive index materials such as high refractive index amorphous glass. In addition, in some implementations, the diffraction grating 1008 may include different high refractive index materials or coatings such as zinc oxide (ZnO), silicon nitride (Si3N4), zirconium dioxide (ZrO2), titanium dioxide (TiO2), and silicon carbide (SiC), and the material beneath the substrate 1004 or the material forming the substrate region may include a second high refractive index material such as LiTaO3 or LiNbO3. (Diffraction grating with a two-dimensional (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, for example, as lines, as described above. For example, Figure 10A shows a cross-sectional side view of exemplary device 1000 having a series of diffraction features 1012 that may have a “sawtooth” shape with inclined sidewalls and are arranged laterally in one direction (e.g., a first horizontal or x-direction in Figure 10A). The diffraction features 1012 are undulating in one direction (e.g., a first horizontal or x-direction in Figure 10A) or elongating in one direction (e.g., a second horizontal or y-direction in Figure 10A), and are therefore referred to as 1D. As a further embodiment of 1D diffraction features, Figure 11B shows a perspective view of a blazed photoresist grating configured as a 1D array. The diffraction feature 1012 (Figure 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 Figure 10A). The elongated longitudinal features are arranged along one direction (e.g., the first horizontal or x-direction in Figure 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 relief in two directions. In some instances, the relief can be periodic, while in other instances, the pitch of the relief can vary in at least one direction. According to various embodiments described herein, the diffraction features have opposing sidewalls that are asymmetrically angled or inclined. According to various embodiments described herein, the diffraction features may be tapered. In some implementations, the diffraction features can have opposing sidewalls that are substantially angled or inclined. In some implementations, the opposing sidewalls may be inclined in the same direction, while in other implementations, the opposing sidewalls may be inclined in the opposite direction. In some other implementations, the diffraction features can have one of the opposing sidewalls that is substantially inclined, while the other sidewall is substantially perpendicular or orthogonal to the horizontal axis, or inclined at least less than the other sidewall. In various embodiments of the 2D diffraction features described herein, the 2D diffraction features can be formed in or on an underlying substrate, which may be a waveguide, as described above with respect to various embodiments of the 1D diffraction features. For example, the 2D diffraction features can be formed by patterning a separate layer that is etched into or formed on the underlying substrate. Thus, the 2D diffraction features can be formed from the same or different material as the substrate material, as described above with respect to various 2D diffraction features. Other modifications and configurations are also possible.

[0156] Figure 18 shows an exemplary device 3600 having a 2D array of diffraction features 3603 (for example, diffraction features 3603 arranged laterally in two dimensions or directions). In this embodiment, the array is analogous to a grid pattern. The diffraction features 3603 may be referred to as projections. The diffraction features have inclined sidewalls that are inclined in opposite directions. One of the sidewall inclinations may have a slope less than the other sidewall inclination. The result of this configuration is that the diffraction features are blazed.

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

[0158] Therefore, in various implementations, a 2D array of symmetric or asymmetric diffraction features can function 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 to bias the propagation of light in two or more directions (e.g., blazed in multiple directions). For example, Figure 19A shows an exemplary device 3700 having a 2D array of diffraction features 3703 formed in or on a substrate 3701. The diffraction feature 3703 has a first sidewall or facet 3703b-1 and a tilted second sidewall or facet 3703b-2. Thus, the diffraction feature is tapered in height, for example, in thickness. The diffraction feature 3703 can be configured to preferentially direct light in directions based on the tilt angles of the first and second sidewalls or facets 3703b-1, 3703b-2. Figure 19B shows an exemplary diffraction feature that directs more light in two specific directions (as illustrated by two thick solid arrows pointing upwards to the right and downwards to the left). Other embodiments are also possible.

[0159] Therefore, any of the structures or devices described herein, such as lattice structures, may comprise a 1D lattice. Similarly, any of the structures or devices described herein, such as lattice structures, may comprise a 2D lattice. Such a 2D lattice can diffuse light. These lattices may also comprise a blazed lattice. Such a blazed lattice 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 differently on the diffraction feature) preferentially directs light in multiple directions. Similarly, any of the methods or processes described herein can be used for a 1D lattice. Similarly, any of the methods or processes described herein can be used for a 2D lattice. These 1D or 2D lattices may be contained in or on a substrate and / or waveguide, contained in an eyepiece, and possibly integrated into a head-mounted display, as disclosed herein. These gratings may be used as input gratings (e.g., ICG), output gratings (EPE), distribution gratings (OPE), or combined distribution gratings / output gratings (e.g., CPE).

[0160] Figure 20A shows an exemplary method 3800 for forming a blazed lattice. Method 3800 includes the step of providing a template or master 3810. If the diffraction features are to be angled, tilted, or inclined, the template 3810 can be patterned to form an angled structure. Various processes, such as etching processes, may be directed and angled to form such an angled structure. Some embodiments of angled processes, such as angled etching processes, include ion beam milling, angled dry etching, ion etching, GLAD etching, tilt etching, Faraday cage etching, etc. In some implementations, the choice of material employed for the template 3810 may help produce an angled structure having angled sidewalls within the template. In this embodiment, the angled structure comprises angled extension projections (e.g., for a 1D lattice) or angled columns (e.g., for a 2D lattice). These angled extension projections or angled columns may have sidewalls that are inclined in the same direction and, in some cases, may 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 on it. The template can be removed, and the resist material 3805 and the underlying substrate 3801 can be dry-etched to form diffraction features 3803 within the substrate 3801. In various implementations, dry etching is employed as shown. The etching may be directional. In the shown embodiment, the etching process is not angled.The diffraction features 3803 resulting from the formation within the substrate 3801 (or within a layer of material placed on the substrate 3801) may have a certain shape, for example, they may be blazed as a result of angled features within the mask 3805. In the shown embodiment, the cross-section of the diffraction feature has a trapezoidal or substantially triangular shape with two inclined sides. The sides are inclined in opposite directions. In the shown embodiment, one side is inclined more than the other to create a blazed structure. This process may be used to form a 1D or 2D array of diffraction features.

[0161] Figure 20B shows another exemplary method 3850 for forming blazed diffraction features. The mask 3855 and the underlying substrate 3851 are etched at an angle (e.g., dry etching) to form diffraction features 3853 within the substrate 3851 (or within a layer of material placed on the substrate 3851). In the angled etching process, the direction of the etching solution forms an angle tilted with respect to the surface normal direction of the substrate 3851, which may result from either a tilt in the inflow angle of the etching solution or a tilt on the surface of the substrate 3851. Some embodiments of angled directional etching processes (e.g., angled etching) include ion beam milling, angled dry etching, ion etching, GLAD etching, tilt etching, Faraday cage etching, etc. The template may comprise elongated projections (e.g., for a 1D grid) or tapered columns (e.g., for a 2D grid) having a trapezoidal or substantially triangular cross-section. These elongated projections or tapered columns may have side walls tilted in the opposite direction. One sidewall may be inclined more than the other. Applying an angled etching process to these extensional projections or tapered columns can produce a blazed lattice within a material, such as a substrate or layer of material placed on top of the substrate beneath the extensional projections or tapered columns. Blazed diffraction features having sides inclined in the same direction may be produced. In various implementations, one of the sides is inclined more 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 Figure 19A) as a result of angled features in the mask (e.g., as shown in Figure 20A) and / or as a result of using an angled process (e.g., as shown in Figure 20B). The diffraction features or gratings blazed in two or more directions may be produced by etching twice. In some implementations, for example, the diffraction features or gratings blazed in two or more directions may be produced by etching using a first mask and then etching again using a second different mask. In some instances, as shown in Figure 21, the mask 3905 and substrate 3901 may be etched to form a first sidewall of the diffraction feature 3903 within the substrate 3901. In addition, 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. A second mask (for example, at a certain angle and / or a different orientation with respect to the first sidewall) may be etched, for example, to form a second sidewall. In some implementations, after the first sidewall of the diffraction feature 3903 is formed, a planaring layer 3907 may be added to the intermediate diffraction feature 3903 and the substrate 3901. The planaring layer 3907, the intermediate diffraction feature 3903, and / or the substrate 3901 may be patterned and etched (for example, at a certain angle with respect to the first sidewall) to form a second sidewall. The above embodiments are discussed in the context of patterning a substrate, but in some implementations, the process described above may be employed to pattern layers formed on the substrate rather than the substrate itself. Alternatively, in some implementations, the process described above may be employed to pattern layers formed on the substrate and the substrate itself.

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

[0164] In the aforementioned specification, the present invention has been described with reference to its specific embodiments. However, it will become 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 should therefore be considered illustrative, not restrictive.

[0165] In fact, each of the systems and methods described herein has several innovative aspects, and it should be understood that none of them alone are involved in or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of each other or in various combinations. All possible combinations and secondary combinations are intended to fall within the scope of this disclosure.

[0166] Some features described herein in the context of a separate embodiment may also be implemented in a 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 preferred secondary combination. Furthermore, features described above as acting in a combination and further claimed as such, but one or more features from the claimed combination may, in some cases, be removed from the combination, and the claimed combination may be subject to secondary combinations or variations of secondary combinations. No single feature or group of features is required or essential in any embodiment.

[0167] In particular, conditional statements used herein, such as “can,” “could,” “might,” “may,” “e.g.,” and equivalents, should be understood to generally convey that one embodiment includes certain features, elements, and / or steps, while other embodiments do not, unless otherwise specifically stated or understood in the context in which they are used. Therefore, 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 included or should be implemented in any particular embodiment, whether or not they are input or prompted by the author. The terms “comprising,” “including,” “having,” and equivalents are synonyms and are used in a non-restrictive manner to encompass additional elements, features, actions, behaviors, etc. Furthermore, 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) so that the term "or" means one, some, or all of the elements in the list. In addition, the articles "a," "an," and "the," as used in this application and the attached claims, should be interpreted as meaning "one or more" or "at least one" unless otherwise specified. Similarly, while actions may be depicted in drawings in a particular order, it should be recognized that such actions do not need to be performed in a particular order or sequential order shown, or that not all illustrated actions need to be performed, in order to achieve the desired result. Furthermore, drawings may graphically depict one or more exemplary processes in the form of flowcharts. However, other actions not depicted may also be incorporated into the graphically illustrated exemplary methods and processes. For example, one or more additional actions may be performed before, after, simultaneously with, or in between any of the illustrated actions.In addition, the operations may be rearranged or rearranged in other embodiments. In some situations, multitasking and parallel processing may be advantageous. Furthermore, 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 described program components and systems may generally be integrated together in a single software product or packaged in multiple software products. In addition, other implementations are also within the scope of the following claims. In some cases, the actions enumerated in the claims may be performed in a different order and still achieve the desired results.

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

Claims

1. An optical waveguide, wherein the optical waveguide is A substrate configured to guide light coupled into the optical waveguide through total internal reflection within the optical waveguide, A diffraction grating formed on the surface of the substrate Equipped with, The diffraction grating comprises a plurality of protrusions, each of which includes a first side wall and a second side wall opposite the first side wall, the first side wall forming a first inclination angle with respect to the surface of the substrate, the second side wall forming a second inclination angle with respect to the surface of the substrate, the first inclination angle being greater than the second inclination angle. The diffraction grating has a first diffraction efficiency for light having a first state over an angular range with respect to light incident on the diffraction grating, and the diffraction grating has a second diffraction efficiency for light having a second state over the angular range with respect to light incident on the diffraction grating. The first state is a transverse magnetic polarization state, and the second state is a transverse electric polarization state. An optical waveguide in which the first diffraction efficiency is 1 to 2 times that of the second diffraction efficiency.

2. The optical waveguide according to claim 1, wherein the substrate has 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 range between any of these values.

3. The optical waveguide according to claim 1, wherein both the first diffraction efficiency and the second diffraction efficiency are for green light.

4. The optical waveguide according to claim 1, wherein the diffraction grating has diffraction features having a tip height or groove depth of about 35 nm, and the ratio of the first diffraction efficiency to the second diffraction efficiency is about 1.5 to about 2.0 over the range of the angle.

5. The optical waveguide according to claim 1, wherein the diffraction grating has diffraction features having a tip height or groove depth of about 80 nm, and the ratio of the first diffraction efficiency to the second diffraction efficiency is about 1.0 to about 1.3 over the range of the angle.

6. The optical waveguide according to claim 1, wherein the substrate comprises one or more of lithium-based oxides, silicon carbide, zirconium dioxide, or titanium dioxide.

7. The optical waveguide according to claim 1, wherein the diffraction grating has diffraction characteristics having a tip height or groove depth of 10 nm to 150 nm.

8. The optical waveguide according to claim 1, wherein the diffraction grating comprises a plurality of protrusions arranged in a two-dimensional (2D) array.

9. The optical waveguide according to claim 8, wherein the diffraction grating comprises the plurality of protrusions arranged within a square array.

10. The optical waveguide according to claim 8, wherein the diffraction grating comprises the plurality of protrusions arranged within a grating pattern.

11. The optical waveguide according to claim 1, wherein the diffraction grating is configured to direct light in two or more directions.

12. The diffraction grating is An internal coupling optical element is arranged to receive light from an image source and couple the light into the substrate so that the light is guided within the substrate, An external coupling optical element is arranged to receive light from an image source induced within the substrate and to couple the light out of the substrate, Optical dispersion elements and Having one or more of the following, The aforementioned light-dispersing optical element receives light from an image source induced within the substrate, The light is directed towards an external coupling optical element so that it is coupled to the outside of the substrate, By diffusing the aforementioned light within the optical waveguide, the beam size or eyebox size can be increased. An optical waveguide according to claim 1, arranged to perform one or more of the following:

13. The optical waveguide according to claim 1, wherein the plurality of protrusions are tapered in thickness with increasing height.

14. The optical waveguide according to claim 1, wherein the plurality of protrusions are arranged to preferentially direct light based on the first tilt angle and the second tilt angle.

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