Display device with diffraction grating having reduced polarization sensitivity

Abstract

To provide a display device with a diffraction grating having reduced polarization sensitivity.SOLUTION: A diffraction grating provides an optical element, for example, for in-coupling light into a waveguide or out-coupling light therefrom to the outside in a head mounted display system. These diffraction gratings may be configured to have reduced polarization sensitivity. Such a grating may, for example, in-couple or out-couple light of different polarization with a similar level of efficiency. The diffraction grating and the waveguide may include a transmissive layer and a metal layer. The diffraction grating may include a blazed grating.SELECTED DRAWING: None

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application is the sole application of U.S. Provisional Application No. 62 / 899,063, filed September 11, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY," U.S. Provisional Application No. 62 / 899,673, filed September 12, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY," and U.S. Provisional Application No. 62 / 899,673, filed September 18, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY," the disclosures of each of which are incorporated herein by reference in their entireties under 35 U.S.C. § 119(e). This application claims the benefit of priority to U.S. Provisional Application No. 62 / 902,295, entitled "METHOD OF USE IN A HIGH-FREQUENCY PHOTOMETRY AND ITS IMPROVEMENT ...

[0002] (Field) The present disclosure relates to display systems, and more particularly to augmented and virtual reality display systems. [Background technology]

[0003] (background) Description of Related Art Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as real. Virtual reality, or "VR," scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. Mixed reality, or "MR," scenarios are a type of AR scenario that typically involve virtual objects integrated into and responsive to the natural world. For example, in an MR scenario, AR image content may be perceived as occluded by or otherwise interacting with objects in the real world.

[0004] Referring to Figure 1, an augmented reality scene 10 is depicted in which a user of the AR technology sees a real-world park-like setting 20 featuring people, trees, a building in the background, and a concrete platform 30. In addition to these items, the user of the AR technology also perceives that they "see" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying, cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee, although these elements 40, 50 do not exist in the real world. The human visual perception system is complex, making it difficult to produce AR technology that facilitates a pleasant, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] The systems and methods disclosed herein address various challenges associated with AR and VR technologies. Summary of the Invention [Means for solving the problem]

[0006] (summary) For purposes of summarizing the present disclosure, certain aspects, advantages, and novel features are described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment disclosed herein. Thus, the embodiments disclosed herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein, without necessarily achieving others.

[0007] Disclosed herein is a head-mounted display system. In one configuration, the head-mounted display system can include a head-mountable frame, an optical projection system, a waveguide supported by the frame, a diffraction grating, a first layer over the diffraction grating, and a second layer including a metal disposed over the first layer. The optical projection system can be configured to output light and provide image content. The waveguide can include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide. The diffraction grating can include a material over the substrate that is different from the substrate. The diffraction grating can have a first diffraction efficiency for a first polarization of light incident thereon over a range of angles, and can also have a second diffraction efficiency for a second polarization of light incident thereon over the range of angles, the first diffraction efficiency being one to two times the second diffraction efficiency.

[0008] In another configuration, a head-mounted display system can include a head-mountable frame, an optical projection system, a waveguide supported by the frame, a diffraction grating formed in a substrate, a first layer disposed over the diffraction grating formed in the substrate, and a second layer including a metal disposed over the diffraction grating formed in the substrate. The optical projection system can be configured to output light and provide image content. The waveguide can include a substrate. The substrate can include an optically transparent material. The substrate can be configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide via the diffraction grating. The diffraction grating can have 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 the range of angles of light incident thereon, the first diffraction efficiency being one to two times the second diffraction efficiency.

[0009] In some configurations, a head-mounted display system can include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, a first diffraction grating over the substrate, which may include a material different from the substrate, a first layer disposed over the first diffraction grating, and a second layer, which may include a metal, disposed over the first diffraction grating such that the 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 the range of angles of light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency.

[0010] In some configurations, a head-mounted display system can include a head-mountable frame, an optical projection system configured to output light and provide image content, and a waveguide supported by the frame, the waveguide may include a substrate, which may include an optically transparent material, and a first diffraction grating formed in the substrate, the substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide via a first layer disposed over the first diffraction grating formed in the substrate, and a second layer, which may include a metal, disposed over the first diffraction grating formed in the substrate such that the first 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 the range of angles of light incident thereon, the first diffraction efficiency being 1 to 2 times the second diffraction efficiency.

[0011] In some configurations, a head-mounted display system includes a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, the substrate may include a first diffraction grating, the first diffraction grating may include a material different from the substrate, and a first diffraction grating disposed across the first diffraction grating such that the first diffraction grating has a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that exceeds a second diffraction efficiency for a second polarization of light over a range of angles incident thereon. and a second layer disposed over the first diffraction grating such that the first diffraction grating has a third diffraction efficiency for the second polarization over a range of angles of light incident thereon that exceeds a fourth diffraction efficiency for the first polarization over the range of angles of light incident thereon, wherein the combined diffraction efficiency of the first diffraction grating and the first and second layers collectively is configured to provide a fifth diffraction efficiency for the first polarization over the range of angles of light incident thereon, and a sixth diffraction efficiency for the second polarization over the range of angles of light incident thereon, the fifth diffraction efficiency being between 1 and 2 times the sixth diffraction efficiency.

[0012] In some configurations, a head-mounted display system may include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include an optically transparent material, a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, and a first diffraction grating formed in the substrate, the first layer disposed over the first diffraction grating formed in the substrate, the first layer having a diffraction efficiency for the first polarization of light over a range of angles that, together with the first diffraction grating, exceeds a second diffraction efficiency for a second polarization of light over a range of angles of light incident thereon. and a second layer disposed over the first diffraction grating formed in the substrate, the second layer configured, together with the first diffraction grating, to provide a third diffraction efficiency for the second polarization over a range of angles of light incident thereon that exceeds a fourth diffraction efficiency for the first polarization over the range of angles of light incident thereon, wherein the first diffraction grating, together with the first and second layers, is configured to provide a fifth diffraction efficiency for the first polarization over the range of angles of light incident thereon and a sixth diffraction efficiency for the second polarization over the range of angles of light incident thereon, the fifth diffraction efficiency being between 1 and 2 times the sixth diffraction efficiency.

[0013] In some configurations, a head-mounted display system may include a head-mountable frame; an optical projection system configured to output light and provide image content; a waveguide supported by the frame, the waveguide may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide; a first diffraction grating over the substrate, the first diffraction grating may include a material different from the substrate; and a first layer disposed over the first diffraction grating, the first layer may include a multi-layer coating, the first diffraction grating configured, together with the first layer, to have a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that exceeds a second diffraction efficiency for a second polarization of light over a range of angles incident thereon.

[0014] In some configurations, a head-mounted display system may include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, and a first diffraction grating configured to have a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that exceeds a second diffraction efficiency for a second polarization of light over a range of angles incident thereon.

[0015] In some configurations, a head-mounted display system may include a head-mountable frame; an optical projection system configured to output light and provide image content; a waveguide supported by the frame, which may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide; a first diffraction grating over the substrate, which may include a material different from the substrate, wherein the substrate may include a material having a first refractive index; a first layer disposed over the first diffraction grating, which may include a material having a second refractive index; and a material disposed over the first layer having a third refractive index between the second refractive index and the refractive index of air, wherein the first diffraction grating, together with the first layer and the material over the first layer, is configured to have a first diffraction efficiency for the first polarization over a range of angles of light incident thereon that exceeds a second diffraction efficiency for the second polarization over a range of angles of light incident thereon.

[0016] In some configurations, a head-mounted display system can include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include a substrate configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, a first diffraction grating, and a first layer disposed over the first diffraction grating such that the diffraction grating has a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that is one to two times a second diffraction efficiency for a second polarization of light over a range of angles incident thereon.

[0017] A method for fabricating a diffraction grating with reduced polarization sensitivity, the method including: forming one or more diffractive features in or on a substrate configured to direct at least a portion of light from an optical projection system to be coupled into the substrate; depositing a first layer over the one or more diffractive features; and depositing a second layer over the one or more diffractive features such that the one or more diffractive features have 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 the range of angles of light incident thereon, the first diffraction efficiency being one to two times the second diffraction efficiency.

[0018] In some configurations, a head-mounted display system can include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide may include a substrate configured to direct at least a portion of the light from the optical projection system to be coupled into the waveguide, and a first diffraction grating configured to have a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that is 1 to 2 times a second diffraction efficiency for a second polarization of light over a range of angles incident thereon.

[0019] In some configurations, a head-mounted display system may include a head-mountable frame, an optical projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide, a substrate having a refractive index less than 1.9, and a first diffraction grating configured to have a first diffraction efficiency for a first polarization of light over a range of angles incident thereon that is 1 to 2 times a second diffraction efficiency for a second polarization of light over a range of angles incident thereon. The present invention provides, for example, the following. (Item 1) 1. A head-mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by the frame, the waveguide comprising a substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide; a first diffraction grating comprising a material different from the substrate over the substrate; a first layer disposed over the first diffraction grating; a second layer comprising a metal disposed over the first diffraction grating such that the 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 the range of angles of light incident thereon, the first diffraction efficiency being one to two times the second diffraction efficiency; A head-mounted display system comprising: (Item 2) Item 1. A head-mounted display system as described in item 1, wherein the substrate comprises a material having a refractive index of at least 1.9. (Item 3) Item 10. The head-mounted display system of item 1, wherein the first diffraction grating material comprises a polymer. (Item 4) Item 1. The head-mounted display system of item 1, wherein the first grating material comprises an imprintable material. (Item 5) Item 2. The head-mounted display system according to item 1, wherein the first diffraction grating material has a refractive index of 1.4 to 1.95. (Item 6) Item 1. A head-mounted display system as described in item 1, wherein the first diffraction grating material has a lower refractive index than the substrate. (Item 7) Item 1. The head-mounted display system of item 1, wherein the first diffraction grating comprises a blazed diffraction grating. (Item 8) Item 1. The head-mounted display system of item 1, wherein the first layer comprises titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC). (Item 9) Item 1. A head-mounted display system as described in item 1, wherein the first and second polarizations comprise transverse magnetic and transverse electric polarizations, respectively. (Item 10) Item 1. A head-mounted display system as described in item 1, wherein the first and second polarizations comprise transverse electric and transverse magnetic polarizations, respectively. (Item 11) 2. The head mounted display system according to item 1, wherein the first diffraction efficiency is 1 to 1.5 times the second diffraction efficiency. (Item 12) Item 12. The head mounted display system according to item 11, wherein the first diffraction efficiency is 1 to 1.3 times the second diffraction efficiency. (Item 13) Item 13. The head mounted display system according to item 12, wherein the first diffraction efficiency is 1 to 1.2 times the second diffraction efficiency. (Item 14) Item 2. The head-mounted display system of item 1, wherein the range of angles is at least 12 degrees. (Item 15) Item 15. The head-mounted display system of item 14, wherein the range of angles is at least 22 degrees. (Item 16) Item 2. A head-mounted display system as described in item 1, wherein the angle range is between ±6 degrees relative to the plane of the substrate. (Item 17) Item 17. A head-mounted display system as described in item 16, wherein the angle range is between ±11 degrees relative to the plane of the substrate. (Item 18) Item 1. A head-mounted display system as described in item 1, wherein the waveguide is contained within an eyepiece configured to direct light to the eye of a user wearing the head-mounted display. (Item 19) 1. A head-mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by the frame, the waveguide comprising a substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide; a first diffraction grating; a first layer disposed over the first diffraction grating such that the diffraction grating has a first diffraction efficiency for a first polarization of light incident thereon over a range of angles that is one to two times a second diffraction efficiency for a second polarization of light incident thereon over the range of angles; A head-mounted display system comprising: (Item 20) 20. The head-mounted display system of claim 19, wherein the first grating on which the first layer is formed comprises a transmissive grating. [Brief explanation of the drawings]

[0020] Throughout the drawings, reference numbers are reused to indicate correspondence between referenced elements. The drawings are provided to illustrate embodiments of the features described herein and not to limit the scope thereof.

[0021] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0022] [Figure 2] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0023] [Figure 3] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus.

[0024] [Figure 4A] Figure 4A illustrates the representation of the accommodation-vergence-divergence motor response of the human visual system.

[0025] [Figure 4B] FIG. 4B illustrates examples of different accommodation and convergence states of a pair of eyes of a user.

[0026] [Figure 4C] FIG. 4C illustrates an example of a top-down view representation of a user viewing content through a display system.

[0027] [Figure 4D] FIG. 4D illustrates another example of a top-down view representation of a user viewing content through a display system.

[0028] [Figure 5] FIG. 5 illustrates aspects of an approach for simulating three-dimensional images by correcting for wavefront divergence.

[0029] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0030] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0031] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane contains an image formed using multiple different primary colors.

[0032] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each including an internal coupling optical element.

[0033] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0034] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0035] [Figure 9D] FIG. 9D illustrates an example of a wearable display system.

[0036] [Figure 10] 10A and 10B illustrate the polarization dependence of two exemplary gratings.

[0037] [Figure 11A] FIG. 11A illustrates a diagram of an example grating with a single coating that can have high efficiency for a single polarization.

[0038] [Figure 11B] FIG. 11B illustrates a diagram of an example grating with multiple coatings that may have high efficiency for more than one polarization.

[0039] [Figure 12A] FIG. 12A, for example, schematically illustrates a cross-sectional view of a portion of a waveguide having a diffraction grating disposed thereon for incoupling light into the waveguide.

[0040] [Figure 12B] FIG. 12B illustrates a cross-sectional view of a waveguide with a blazed grating disposed thereon, showing the field of view (FOV) Δα of the waveguide.

[0041] [Figure 13A] FIG. 13A illustrates different example geometries for diffractive features that can be used to form a diffraction grating.

[0042] [Figure 13B] 13B-1 and 13B-2 illustrate diagrams of one-dimensional (1D) lattices.

[0043] [Figure 13C] FIG. 13C illustrates an exemplary device having a two-dimensional (2D) array of diffractive features.

[0044] [Figure 13D] 13D-1 and 13D-2 show cross-sectional side and top views, respectively, of an exemplary 2D array of symmetric diffractive features.

[0045] [Figure 13E] FIG. 13E shows another exemplary device having a blazed 2D array of diffractive features.

[0046] [Figure 13F] 13F-1 and 13F-2 show cross-sectional side and top views, respectively, of an exemplary array of asymmetric diffractive features.

[0047] [Figure 13G-1] FIG. 13G-1 shows an example device having a 2D array of diffractive features formed in or on a substrate and blazed in two directions.

[0048] [Figure 13G-2] FIG. 13G-2 shows an example diffractive feature that directs more light in two specific directions.

[0049] [Figure 13H] FIG. 13H shows an exemplary method for forming a blazed grating.

[0050] [Figure 13I] FIG. 13I shows another exemplary method for forming a blazed grating.

[0051] [Figure 13J] FIG. 13J illustrates another exemplary method for forming a blazed grating.

[0052] [Figure 14] 14 illustrates an exemplary method for depositing a layer of material onto the diffractive features of a diffractive optical element. This layer may, in various implementations, be an optically transmissive layer.

[0053] [Figure 15] FIG. 15 illustrates exemplary diffractive features in a transmissive layer comprising multiple sub-layers and corresponding graphs of reflection from the surface of a diffractive optical element formed from such exemplary diffractive features.

[0054] [Figure 16] FIG. 16 illustrates an exemplary method for depositing layers of materials, such as dielectric and metal layers, onto a plurality of diffractive features that form a diffractive optical element, such as a diffraction grating.

[0055] [Figure 17A] 17A illustrates an example waveguide including multiple diffractive optical elements, such as diffraction gratings, that form an in-coupling optical element and an out-coupling optical element. At least one of the diffractive optical elements, e.g., the in-coupling optical element, may comprise a reduced polarization sensitivity grating.

[0056] [Figure 17B] 17B illustrates another example waveguide including multiple diffractive optical elements, such as diffraction gratings, that form the in-coupling optical element and / or the out-coupling optical element. The diffractive optical element, e.g., the in-coupling optical element, may comprise a diffraction grating that couples more TE polarization into the waveguide than TM polarization, and a diffraction grating that couples more TM polarization into the waveguide than TE polarization.

[0057] [Figure 17C] FIG. 17C illustrates another example waveguide that includes a diffractive optical element, such as a diffraction grating, that forms an internal coupling optical element that couples both TE and TM within the waveguide with high efficiency.

[0058] [Figure 17D] 17D-1-17D-4 illustrate different diffractive optical element designs that may be used, for example, as an internal coupling optical element as illustrated in FIG. 17C, and the TM and TE efficiency profiles for the different individual diffractive optical elements.

[0059] [Figure 18] FIG. 18 illustrates exemplary diffractive features that can reduce reflection losses. DETAILED DESCRIPTION OF THE INVENTION

[0060] (Detailed explanation) Although certain preferred embodiments and examples are disclosed below, the subject matter of the present invention extends to other alternative embodiments and / or uses of the invention, and modifications and equivalents thereof, beyond the specifically disclosed embodiments. Accordingly, the scope of the invention disclosed herein is not limited by any of the specific embodiments described below. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable sequence and are not necessarily limited to any particular disclosed sequence. For purposes of contrasting various embodiments with the prior art, certain aspects and advantages of these embodiments are described. Not necessarily all such aspects or advantages are achieved by any particular embodiment. Thus, for example, various embodiments may be performed in a manner that achieves or optimizes one advantage or group of advantages as taught herein, without necessarily achieving other aspects or advantages as may also be taught or suggested herein.

[0061] The AR system may display virtual content to a user or viewer while still allowing the user to see the world around them. Preferably, this content is displayed on a head-mounted display, for example, as part of eyewear that projects image information to the user's eyes. In addition, the display may also transmit light from the surrounding environment to the user's eyes, allowing a view of the surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the viewer's or user's head.

[0062] In some AR systems, virtual / augmented / composite displays with a relatively wide field of view (FOV) can enhance 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 into their eye. A waveguide with a relatively high refractive index, for example, 2.0 or greater, can provide a relatively high FOV. However, to efficiently couple light into a high-index waveguide, the diffractive optical coupling element should also have a correspondingly high refractive index. To achieve this goal, among other advantages, some displays for AR systems according to embodiments described herein include a waveguide including a relatively high refractive index (e.g., greater than or equal to 2.0) material, such as a Li-based oxide, with a separate diffraction grating formed thereon with a correspondingly high refractive index. For example, the diffraction grating may be formed directly on a Li-based oxide waveguide by patterning a surface portion of the waveguide formed from the Li-based oxide.

[0063] Some high-index diffractive optical coupling elements, such as internal or external coupling optical elements, have strong polarization dependence. For example, an internal coupling grating (ICG) for internally coupling light into a waveguide, where the diffractive optical coupling element comprises a high-index material, may receive significantly more light of a given polarization than light of another polarization. Such an element may, for example, internally couple light with TM polarization into a waveguide with approximately 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 of one polarization) and may also create coherence artifacts, reducing the uniformity of the far-field image formed by the light coupled out of the waveguide. To obtain a diffractive optical coupling element that is polarization-insensitive or at least has reduced polarization sensitivity (e.g., couples light with an efficiency that is relatively independent of polarization), some displays for AR systems according to various implementations described herein include a waveguide with a diffraction grating formed using a blazed geometry. Diffraction gratings may also be formed directly within a waveguide, which may include a high refractive index material (e.g., having a refractive index of at least 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, or up to 2.7, or any range between any of these values). Diffraction gratings may be formed within high refractive index materials, such as Li-based oxides like lithium niobate (LiNbO) or lithium tantalate (LiTaO), or zirconium oxide (ZrO), titanium dioxide (TiO), or silicon carbide (SiC), for example, by patterning the high refractive index material with a blazed geometry.

[0064] Reference will now be made to the drawings in which like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0065] FIG. 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, forming an image of the object at a different location on each eye's retina. This may be referred to as binocular disparity and may be utilized by the human visual system to provide the perception of depth. Conventional display systems simulate binocular disparity by presenting two distinct 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 as it would appear by each eye as if the virtual object were a real object at a desired depth. These images provide binocular cues that the user's visual system may interpret to derive the perception of depth.

[0066] Continuing with reference to FIG. 2 , the images 190, 200 are spaced apart from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer when the eyes are fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on slightly different views of the virtual object in the images presented to each eye 210, 220, the eyes may necessarily rotate so that the image of the object falls on a corresponding point on each eye's retina, maintaining single binocular vision. This rotation may cause the gaze of each eye 210, 220 to converge on a point in space where the virtual object is perceived to reside. As a result, providing three-dimensional images traditionally involves manipulating the convergence and divergence of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide the perception of depth.

[0067] However, creating 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 a wavefront with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and light ray divergence. The distance between the object and the eye 210 is represented in order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that 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. While only a single eye 210 is illustrated in Figures 3A-3C and other figures herein for clarity of illustration, the discussion regarding the eye 210 can apply to both eyes 210 and 220 of the viewer.

[0068] Continuing with reference to Figures 3A-3C, light from an object that a viewer's eye is fixating may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which in turn may require the lens to assume a different shape and form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as an accommodative cue, causing the shape of the eye's lens to change until a focused image is formed on the retina. For example, the accommodative cue may induce relaxation or contraction of the ciliary muscles surrounding the eye's lens, thereby modulating the force applied to the suspensory ligaments that hold the lens in place, thus changing the shape of the eye's lens and forming a focused image of the fixated object on the eye's retina (e.g., the fovea) until retinal blur of the fixated object is eliminated or minimized. The process by which the eye's lens changes shape can be referred to as accommodation, and the shape of the eye's lens required to form a focused image of a fixated object on the eye's retina (e.g., the fovea) can be referred to as the state of accommodation.

[0069] Referring now to Figure 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. Eye movement to fixate an object causes the eye to receive light from the object, which 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 vergence. The accommodation cue causes accommodation, leading the eye's lens to adopt a specific accommodation state that forms a focused image of the object on the eye's retina (e.g., the fovea). Conversely, the vergence cue causes vergence movement (eye rotation) so that the image formed on each retina of each eye is at the corresponding retinal point, maintaining single binocular vision. In these positions, the eyes can be said to be in a specific vergence state. Continuing with reference to FIG. 4A , accommodation can be understood as the process by which the eyes achieve a particular accommodation state, and convergence can be understood as the process by which the eyes achieve a particular convergence state. As shown in FIG. 4A , the accommodation and convergence states of the eyes 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.

[0070] Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of convergence-divergence and accommodation. As noted above, the convergence-divergence of the two eyes relative to one another (e.g., eye rotation such that the pupils move toward or away from one another, converging the eyes' gazes and fixating on an object) is closely coupled to accommodation of the eye's lenses. Under normal conditions, a change in the shape of the eye's lenses to change focus from one object to another at a different distance will automatically produce a corresponding change in convergence-divergence to the same distance, a relationship known as the "accommodation-divergence reflex." Similarly, a change in convergence-divergence will, under normal conditions, induce a corresponding change in lens shape.

[0071] 4B, an example of different accommodation and convergence states of the eyes is illustrated. Pair of eyes 222a fixates an object at optical infinity, while pair of eyes 222b fixates an object 221 at less than optical infinity. Notably, the convergence states of each pair of eyes are different: pair of eyes 222a points straight ahead, while pair of eyes 222 converge on 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 lenses 210a, 220a.

[0072] Unfortunately, many users of conventional "3-D" display systems may find such systems uncomfortable or may not perceive any depth perception due to a mismatch between accommodation and convergence states in these displays. As noted above, many stereoscopic or "3-D" display systems display a scene by providing a slightly different image to each eye. Such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of a scene, causing changes in the eyes' convergence states without a corresponding change in the eyes' accommodation states. Rather, images are presented by the display at a fixed distance from the eyes so that the eyes view all image information in a single accommodation state. Such an arrangement defies the "accommodation-vergence-divergence reflex" by causing changes in the convergence states without a corresponding change in the accommodation state. This mismatch is believed to cause viewer discomfort. Display systems that provide a better match between accommodation and convergence-divergence movements may produce a more realistic and comfortable simulation of three-dimensional images.

[0073] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, 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 can provide both vergence cues and matching cues for accommodation, thereby providing physiologically correct accommodation-vergence divergence matching.

[0074] 4B , two depth planes 240 are illustrated, corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, vergence-divergence cues may be provided by displaying appropriately different perspective images for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the image provided to each eye 210, 220 may have a wavefront divergence corresponding to the light field generated by a point at the distance of that depth plane 240.

[0075] In the illustrated embodiment, the distance along the z-axis of depth plane 240 containing point 221 is 1 m. As used herein, distance or depth along the z-axis may be measured with a zero point located at the exit pupil of the user's eye. Thus, depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupil of the user's eye on the optical axis of the eye with the eye 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 for the distance between the device and the exit pupil of the user's eye may be added. That value may be referred to as pupil distance and corresponds to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for pupil distance may be a normalized value generally used for all viewers. For example, pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0076] 4C and 4D, examples of matched accommodation-vergence-divergence distances and mismatched accommodation-vergence-divergence distances are illustrated, respectively. As illustrated in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may 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 image may be formed by light having a wavefront curvature corresponding to the real object on that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is focused on the retinas of those eyes. Therefore, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0077] It should be understood that the accommodation and convergence states of the eyes 210, 220 are each associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 will cause those eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state is referred to as the accommodation distance A. d Similarly, a particular convergence distance V associated with the eyes in a particular convergence state or position relative to one another may be referred to as d When the accommodation distance and the convergence distance match, the relationship between accommodation and convergence is said to be physiologically correct. This is considered the most comfortable scenario for the viewer.

[0078] However, in a stereoscopic display, the accommodation distance and the vergence distance may not always coincide. For example, as illustrated in FIG. 4D , the images displayed to the eyes 210, 220 may be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 may be in a particular accommodation state in which points 15a, 15b on that depth plane are in focus. However, the images displayed to the eyes 210, 220 may provide a convergence cue that causes the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the accommodation distance, in some embodiments, corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to the greater distance from the exit pupils of the eyes 210, 220 to point 15. The accommodation distance is different from the vergence distance. As a result, there is an accommodation-vergence-divergence mismatch. Such a mismatch may be considered undesirable and may cause discomfort to the user. The mismatch may be related to distance (e.g., V d -A d ) and can be characterized in terms of diopters.

[0079] It should be understood that in some embodiments, a reference point other than the exit pupil of the eye 210, 220 may be used to determine the distance for determining accommodation-vergence mismatch, so long as the same reference point is used for accommodation distance and vergence distance. For example, the distance may be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide in a display device) to the depth plane, etc.

[0080] Without being limited by theory, it is believed that a user may still perceive accommodation-vergence-divergence mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as physiologically correct without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6 ) presents images to a viewer with an accommodation-vergence-divergence mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0081] FIG. 5 illustrates aspects of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to a user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence that corresponds to the wavefront divergence of a 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.

[0082] 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 in a limited range of wavelengths. Consequently, in some embodiments, multiple or stacked waveguides may be utilized to provide different wavefront divergences for different depth planes and / or to output light in different ranges of wavelengths. As used herein, it should be understood that a depth plane may follow the contour of a flat or curved surface.

[0083] 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. It should be understood that display system 250 can be considered a light field display in some embodiments. Additionally, waveguide assembly 260 can also be referred to as an eyepiece.

[0084] In some embodiments, display system 250 may be configured to provide a substantially continuous cue for convergence and multiple discrete cues for accommodation. The cues for convergence may be provided by displaying different images to each of the user's eyes, and the cues for accommodation may be provided by outputting light forming images with selectable discrete amounts of wavefront divergence. In other words, display system 250 may be configured to output light with variable levels of wavefront divergence. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of waveguides 270, 280, 290, 300, and 310.

[0085] Continuing with reference to FIG. 6 , the waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may each be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, which may be configured to disperse incident light across each individual waveguide for output toward the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each input surface 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or a portion of a major 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 launched into each waveguide, outputting an entire field of cloned collimated beams directed toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0086] In some embodiments, image input devices 360, 370, 380, 390, 400 are discrete displays that each generate image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, image input devices 360, 370, 380, 390, 400 are outputs of a single multiplexed display that may send image information to each of image input devices 360, 370, 380, 390, 400 via, for example, one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0087] In some embodiments, light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520 comprising a light module 530, which may include light emitters such as light emitting diodes (LEDs). Light from the light module 530 may be directed via a beam splitter 550 to and modified by a light modulator 540, e.g., a spatial light modulator. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically, and in some embodiments, these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of waveguide assembly 260 may function as ideal lenses, relaying light injected 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 a depth plane.

[0088] 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 scan, spiral scan, Lissajous pattern, 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 injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more waveguides 270, 280, 290, 300, 310.

[0089] Controller 560 controls the operation of one or more of stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 530, and light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 contains programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 9D).

[0090] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, and 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, and 310 may each include outcoupling optical elements 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting 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 outcoupling light, and the outcoupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be, for example, a grating including diffractive optical features as discussed further herein. While shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of drawing, in some embodiments, the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and 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 outcoupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within that piece of material.

[0091] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 280 as emerging 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 350 and second 340 lenses may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third upper waveguide 290 as originating from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0092] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0093] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same multiple depth planes, with one set per depth plane. This may provide advantages for forming tiled images to provide an extended field of view at those depth planes.

[0094] Continuing with reference to FIG. 6 , the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides and output the light with an appropriate amount of divergence or collimation for the particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extracting optical elements 570, 580, 590, 600, 610 may be solid or surface features that may be configured to output light at specific angles. For example, the light-extracting optical elements 570, 580, 590, 600, 610 may be solid holograms, surface holograms, and / or diffraction gratings. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (eg, cladding layers and / or structures to form an air gap).

[0095] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues traveling through the waveguide via TIR. The light carrying the image information is thus split into several related output beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of output emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0096] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern within a host medium; 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).

[0097] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 9D) and may be in electrical communication with processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye, monitoring each eye separately.

[0098] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 260 (FIG. 6) may function similarly, and that waveguide assembly 260 includes multiple waveguides. Light 640 is launched into waveguide 270 at input surface 460 of waveguide 270 and propagates within waveguide 270 by TIR. At the point where light 640 impinges on DOE 570, a portion of the light exits the waveguide as output beam 650. Although output beams 650 are illustrated as being approximately parallel, as discussed herein, they may also be redirected to propagate to eye 210 at an angle (e.g., forming a diverging output beam) depending on the depth plane associated with waveguide 270. It should be understood that a substantially collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0099] In some embodiments, a full-color image may be formed at each depth plane by overlaying an image in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact placement of depth planes for different primary colors may be varied to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberrations.

[0100] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0101] 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.

[0102] It should be understood that references throughout this disclosure to a given color of light will be understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include one or more wavelengths of light within a range of about 620-780 nm, green light may include one or more wavelengths of light within a range of about 492-577 nm, and blue light may include one or more wavelengths of light within a range of about 435-493 nm.

[0103] In some embodiments, light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of a viewer's visual perception, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide incoupling, outcoupling, and other light redirecting structures of display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0104] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. It should be understood that stack 660 may correspond to stack 260 ( FIG. 6 ), and that the illustrated waveguides of stack 660 may correspond to portions of multiple waveguides 270, 280, 290, 300, 310, except that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0105] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the light input area on the waveguide), for example, internal coupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of an individual waveguide 670, 680, 690 (particularly if one or more internal coupling optical elements are reflective polarizing optical elements). As shown, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surfaces of the respective waveguides 670, 680, 690 (or on top of the next lower waveguide), particularly if the internal coupling optical elements are transmissive deflecting optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective so as to selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. While illustrated on one side or corner of the respective waveguides 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguides 670, 680, 690 in some embodiments.

[0106] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image input device 360, 370, 380, 390, and 400, as shown in FIG. 6 , and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to receive substantially no light from others of the in-coupling optical elements 700, 710, 720.

[0107] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of associated waveguides 670, 680, 690, respectively. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of associated waveguides 670, 680, 690, respectively, or optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0108] Waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, 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 immediately adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or 0.10 or less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0109] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. In some embodiments, the materials forming waveguides 670, 680, 690 may differ between one or more waveguides, and / or the materials forming layers 760a, 760b may differ while still maintaining the various refractive index relationships described above.

[0110] 9A, light rays 770, 780, 790 enter the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0111] In some embodiments, light rays 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0112] For example, in-coupling optical element 700 may be configured to deflect light ray 770 having a first wavelength or wavelength range while transmitting light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light ray 780 impinges on and is deflected by in-coupling optical element 710, which is configured to deflect light of the second wavelength or wavelength range. Light ray 790 is deflected by in-coupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0113] 9A , the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the in-coupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690, in-coupling the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the waveguide's corresponding optical dispersive element 730, 740, 750.

[0114] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As described above, in-coupled light rays 770, 780, 790 are deflected by in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within waveguides 670, 680, 690, respectively. Light rays 770, 780, 790 then impinge on optically dispersive elements 730, 740, 750, respectively. Optically dispersive elements 730, 740, 750 deflect light rays 770, 780, 790 to propagate toward out-coupling optical elements 800, 810, 820, respectively.

[0115] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light into the out-coupling optical elements 800, 810, 820, and in some embodiments, may also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted, and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly into the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A , the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light into the viewer's eye 210 ( FIG. 7 ). It should be understood that an OPE can be configured to increase the size of the eyebox in at least one axis, and that the EPE can increase the eyebox in an axis that intersects the axis of the OPE, e.g., orthogonal to it. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE in the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. Again, in response to striking the OPE, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, and so on. Similarly, in response to striking the EPE, a portion of the impinging light is directed out of the waveguide toward the user, and that remaining portion of the light continues to propagate through the waveguide until it again strikes an EP, at which point another portion of the impinging light is directed out of the waveguide, and so on. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an 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 beam of light.

[0116] 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optically dispersive elements (e.g., OPEs) 730, 740, 750, and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light into that waveguide (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner previously described, then continues bouncing down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, with light ray 780 impinging on and being deflected by the in-coupling optical element 710. Light ray 780 then bounces down the waveguide 680, via TIR, to its optically dispersive element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light ray 790 so that it propagates by TIR to the light dispersive element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light ray 790 to a viewer, who also receives light out-coupled from the other waveguides 670, 680.

[0117] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned, along with each waveguide's associated optically dispersive element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted-pupil systems, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0118] 9D illustrates an example of a wearable display system 60 into which the various waveguide and associated systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which diagrammatically illustrates some portions of the system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0119] 9D , display system 60 includes display 70 and various mechanical and electronic modules and systems to support the functionality of display 70. Display 70 may be coupled to a frame 80 that is wearable by a display system user or viewer 90 and configured to position display 70 in front of the user's 90's eye. Display 70, in some embodiments, may be considered an eyepiece. In some embodiments, a speaker 100 is coupled to frame 80 and configured to be positioned adjacent to the user's 90's ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). Display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones may be configured to allow a user to provide input or commands (e.g., voice menu command selections, natural language questions, etc.) to system 60 and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include ambient sensor 120a, which may be separate from frame 80 and attached to the body of user 90 (e.g., on the head, torso, limbs, etc. of user 90). Ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of user 90. For example, sensor 120a may be an electrode.

[0120] 9D , display 70 is operably coupled to local data processing module 140 by a communication link 130, such as wired or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by the user, integrated into headphones, or otherwise removably attached to user 90 (e.g., in a backpack-style configuration, in a belt-linked configuration). Similarly, sensor 120a may be operably coupled to local processor and data module 140 by a communication link 120b, such as wired or wireless connectivity. Local processing and data module 140 may comprise 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 utilized to aid in processing, caching, and storing data. Optionally, local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data may include (a) data captured from sensors (e.g., which may be operatively coupled to frame 80 or otherwise attached to user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein, and / or (b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for processing or retrieval and then passing to display 70. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on frame 80 or may be a stand-alone structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0121] 9D , in some embodiments, 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, remote data repository 160 may comprise a digital data storage facility, which may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, allowing for fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, one or more computer systems), including a CPU, GPU, etc., may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, e.g., via a wireless or wired connection.

[0122] A. Diffraction grating with reduced polarization sensitivity Providing a high-quality immersive experience to users of waveguide-based display systems, such as the various display systems configured for virtual / augmented / composite display applications described above, may depend, among other things, on various characteristics of light coupling into and / or out of the waveguide within the eyepiece of the display system. For example, a virtual / augmented / composite display with high light in-coupling and out-coupling efficiency may enhance the viewing experience by increasing the brightness of the light directed toward the user's eye. As discussed above, an internal coupling optical element, such as an internal coupling grating, may be employed to couple light into the waveguide to be guided therein by total internal reflection. Similarly, an external coupling optical element, such as an external coupling grating, may be employed to couple light guided within the waveguide out of the waveguide by total internal reflection.

[0123] For example, as described above with reference to Figures 6 and 7, display systems according to various implementations described herein may include optical elements, such as an in-coupling optical element, an out-coupling optical element, and a light-dispersing element, which may include a diffraction grating. For example, as described above with reference to Figure 7, light 640 launched into waveguide 270 at input surface 460 of waveguide 270 propagates within waveguide 270 and is guided by total internal reflection (TIR). In various implementations, at the point where light 640 impinges on out-coupling optical element 570, a portion of the light guided within the waveguide may exit the waveguide as beamlet 650. In some implementations, for example, any of optical elements 570, 580, 590, 600, 610 in Figure 6 can be configured as a diffraction grating.

[0124] To achieve desired properties for incoupling light into (or outcoupling light from) the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed from suitable materials and have suitable structures to control various optical properties, including diffractive properties such as diffraction efficiency as a function of polarization. Possibly desirable diffractive properties may include any 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), among other properties.

[0125] Some diffraction gratings have strong polarization dependence and therefore may have relatively reduced overall efficiency (due to the blocking of one polarization). In some cases, such diffraction gratings may also create coherent artifacts and reduce the uniformity of the far-field image. For example, a diffraction grating may be formed by imprinting a layer of patternable material, metallizing the patterned layer (e.g., of resist), and forming multiple diffractive features. Some grating designs formed in this way may diffract more light into a given diffraction order. Such a diffraction grating may be highly efficient for one polarization (e.g., TM or P-polarized light) but inefficient for unpolarized light.

[0126] 10A and 10B illustrate the polarization dependence of two exemplary diffraction gratings (1102, 1122). For example, FIG. 10A illustrates the diffraction efficiency as a function of the angle of incidence in degrees for the diffraction grating 1102. The diffraction grating 1102 may include a metal coating 1104 deposited on an internal coupling grating (ICG) pattern 1106 comprising patterned photoresist. The diffraction grating 1102 may be a blazed grating or another grating with asymmetric diffractive features, including, but not limited to, asymmetric morphologies with at least one straight sidewall, sloped sidewall, re-entrant (e.g., a sidewall with an acute re-entrant angle relative to the base surface) or concave sidewall, multi-step sidewall, other types of sidewall, or some combination thereof. The resulting diffraction efficiency 1108 for P-polarized light can be high (e.g., averaging approximately 70% over a range of angles of incidence from -20 to 20 degrees). However, the diffraction grating 1102 may be less efficient for S-polarized light (e.g., averaging about 20% or 30% over a range of incidence angles between -20 and 20 degrees). Thus, the diffraction grating 1102 may result in an overall lower efficiency for unpolarized light (e.g., averaging about 40% or 45% over a range of incidence angles between -20 and 20 degrees). Other efficiency values ​​within and outside the recited ranges of incidence angles are also possible.

[0127] In another example, FIG. 10B illustrates the diffraction efficiency as a function of the angle of incidence in degrees for different diffraction gratings 1122. The diffraction gratings 1122 may include blazed gratings or other gratings with asymmetric diffraction features, including, but not limited to, asymmetric morphologies with at least one straight sidewall, sloped sidewall, re-entrant (e.g., sidewalls with an acute re-entrant angle relative to the base surface) or concave sidewall, multi-step sidewall, other types of sidewall, or some combination thereof. The diffraction grating 1122 shown in FIG. 10B may have a non-metallic transmissive coating 1124, such as ZrO, TiO, or SiC, deposited on the ICG pattern 1106, e.g., comprising a patterned photoresist. The resulting diffraction efficiency 1128 for S-polarized light may be higher than the diffraction efficiency 1126 for P-polarized light. For example, S-polarized light may have an average efficiency 1128 for S-polarized light of 80%, 60%, or 40% over a range of angles of incidence from approximately -20 to 20 degrees. In another example, P-polarized light may have an average efficiency 1126 for P-polarized light of 10%, 15%, or 20% over a range of angles of incidence from approximately -20 to 20 degrees. Other efficiency values ​​within and outside the recited ranges of angles of incidence are also possible.

[0128] To provide a diffraction grating with reduced polarization sensitivity (e.g., coupling light with efficiency relatively independent of polarization), some displays for AR systems according to implementations described herein include a waveguide having a diffraction grating formed therein with multiple coatings. For example, the diffraction grating may include a patterned dielectric (e.g., patterned photoresist) having a first transmissive layer formed thereon, possibly a non-metallic (e.g., dielectric or semiconductor) coating, and a second layer comprising a metal over the first transmissive layer. In some implementations, the coated diffraction grating may achieve improved grating diffraction efficiency for a given diffraction order, while diffraction efficiency for other orders is reduced or minimized. As a result, more light may be directed to a particular given diffraction order as opposed to any of the other orders in some implementations.

[0129] 11A and 11B illustrate diagrams of an example grating with a single coating that may have high efficiency in a single polarization (e.g., TE or S-polarized light) and an example grating with multiple coatings as disclosed herein with high efficiency in both TE and TM polarization, respectively.

[0130] For example, as shown in FIG. 11A, a diffraction grating 1201 can include an ICG pattern 1202 and a transmissive layer 1204. The ICG pattern 1202 can be any suitable grating pattern, such as a sawtooth pattern. These diffractive features may comprise a patterned polymer, such as a patterned resist (e.g., photoresist), or may be formed by imprinting, such as nanoimprinting. The transmissive layer 1204 can include a non-metallic material, such as a dielectric or semiconductor material, such as ZrO, TiO, or SiC. Image 1200 shows an exemplary scanning electron micrograph of a diffraction grating, such as the diffraction grating 1201, which may have a sawtooth-pattern ICG 1202 with a TiO coating 1204. The transmissive layer 1204 (e.g., the TiO coating) was deposited using grazing angle deposition (GLAD). Thus, as shown, there is more of the transmissive layer on one side of the diffractive feature than on the other side of the diffractive feature. Table 1 shows example efficiencies associated with different types of light, including TE polarized light, TM polarized light, and unpolarized light, incident on diffraction grating 1201. As shown in Table 1, grating 1201 has increased efficiency for TE polarized light compared to TM polarized light and unpolarized light. As discussed above, such polarization-dependent efficiency may be undesirable. [Table 1]

[0131] As shown in FIG. 11B, the diffraction grating 1205 can include an ICG pattern 1202, a transparent layer 1204 formed thereon, and a metal layer 1206 formed on the transparent layer. The ICG pattern 1202 can be any suitable grating pattern, such as a blazed grating pattern like the sawtooth pattern shown. These diffractive features may comprise a patterned polymer, such as a patterned resist (e.g., photoresist), or may be formed by imprinting, such as nanoimprinting. The transparent layer 1204 can include a non-metallic material, such as a dielectric, such as ZrO or TiO, or other high-n, low-k material, such as SiC. The transparent layer 1204 (e.g., a TiO coating) was deposited using grazing angle deposition (GLAD). Thus, as shown, there is more of the transparent layer on one side of the diffractive feature than on the other side. The metal layer 1206 can include any suitable metal, such as Al, Ag, or AlSi. This metal layer may be a conformal metal layer. Image 1203 shows an example of how a metal layer 1206 can be disposed over a transmissive layer formed over the diffraction grating. Table 2 shows example efficiencies associated with different types of light, including TE polarized, TM polarized, and unpolarized light, incident on the diffraction grating 1205.

[0132] As shown in Table 2, the grating 1205 illustrated in FIG. 11B has improved efficiency for unpolarized light over the grating 1201 illustrated in FIG. 11A. The grating 1205 illustrated in FIG. 11B provides similar efficiencies for TE-polarized light, TM-polarized light, and unpolarized light. Thus, advantageously, the grating 1205 has reduced polarization sensitivity. This polarization insensitivity is achieved by using both a transparent non-metallic layer 1204, which improves TE diffraction efficiency, and a metallic layer 1206, which improves TM diffraction efficiency. By providing a first layer on the ICG pattern 1202 that improves the efficiency of TE-polarized light and a second layer that improves the efficiency of TM-polarized light, the effects of both layers can help reduce the polarization sensitivity of the grating 1205. In some implementations, increased uniformity and brighter images can be achieved. [Table 2-1] [Table 2-2]

[0133] 1. Example grid patterns 12A and 12B illustrate an example cross-sectional view of a portion of a diffraction grating 1008 formed on a substrate, which is a waveguide 1004. In the implementation shown, the blazed diffraction grating 1008 is formed in the substrate / waveguide 1004 (which, in this example, is planar). The surface of the substrate or waveguide 1004 has a surface topography with diffractive features that together form the diffraction grating 1008. The blazed diffraction grating 1008 is configured to diffract light having wavelengths within the visible spectrum such that light incident thereon is guided within the waveguide 1004 by TIR. The waveguide 1004 may be transparent and may form part of an eyepiece through which a user can see. Such a waveguide 1004 and eyepiece may be included in a head-mounted display, such as an augmented reality display. Waveguide 1004 may correspond, for example, to one of waveguides 670, 680, 690 described above with respect to Figures 9A-9C. Blazed grating 1008 may correspond, for example, to one of internal coupling optical elements 700, 710, 720 described above with respect to Figures 9A-9C. Blazed grating 1008 configured to internally couple light into waveguide 1004 may be referred to herein as an internal coupling grating (ICG). Display device 1000 may additionally include optical element 1012, which may correspond, for example, to a light dispersive element (e.g., one of light dispersive elements 730, 740, 750 shown in Figures 9A-9C) or an external coupling optical element (e.g., one of external coupling optical elements 800, 810, 820 shown in Figures 9A-9C).

[0134] In operation, when an incident light beam 1016, e.g., visible light, such as from an optical projection system providing image content, is incident on the blazed grating 1008 at an angle of incidence α measured with respect to a surface normal 1002 that is normal or orthogonal to the blazed grating or the extended surface or plane of the substrate / waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface of the waveguide on which the grating is formed (shown in FIG. 12A as extending parallel to the yx-plane), the blazed grating at least partially diffracts the incident light beam 1016 as a diffracted light beam 1024 at a diffraction angle θ measured with respect to the surface normal 1002. The diffracted light beam 1024 is incident at a critical angle θ for the occurrence of total internal reflection within the waveguide 1004. TIR Upon being diffracted at a diffraction angle θ greater than θ, the diffracted light beam 1024 propagates within the waveguide 1004 and is guided generally along a direction parallel to the x-axis and along the length of the waveguide via total internal reflection (TIR). A portion of this light guided within the waveguide 1004 may reach one of the optically dispersive elements 730, 740, 750 or one of the outcoupling optical elements (800, 810, 820, FIGS. 9A-9C) and may, for example, be diffracted again.

[0135] As described herein, in the illustrated implementation, a light beam incident at an angle in a clockwise direction relative 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 in a counterclockwise direction relative to the surface normal 1012 (i.e., to the left of the surface normal) is said to have a positive α (α>0).

[0136] A suitable combination of high-index material and / or diffraction grating 1008 structure can result in a particular range of incident angles α (Δα), referred to herein as the range of acceptance angles or field of view (FOV). One range Δα can be described by a range of angles spanning negative and / or positive values, outside of which the diffraction efficiency drops off by 10%, greater than 25%, greater than 50%, or greater than 75%, 80%, 90%, 95%, or any range between any of these values, relative to the diffraction efficiency at α=0 or some other direction. In some implementations, it may be desirable to have a Δα within a range where the diffraction efficiency is relatively high and constant; e.g., a uniform intensity of diffracted light is desired within Δα. Thus, in some implementations, Δα is related to the angular bandwidth of the diffraction grating 1008 such that an incident light beam 1016 in Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ relative to the surface normal 1002 (e.g., parallel to the yz plane), and θ is related to the angular bandwidth of the diffraction grating 1008 such that the diffracted light is guided within the waveguide 1004 under total internal reflection (TIR). TIR exceeding . In some implementations, this angle Δα range can affect the field of view seen by a user. Note that in various implementations, light can be directed onto the internal coupling grating (ICG) from both sides. For example, light can be directed through a substrate or waveguide 1004 to be incident on a reflective internal coupling grating (ICG) 1008, such as that shown in FIG. 12A . The light can be coupled into the substrate or waveguide 1004 by the internal coupling grating 1008 such that it experiences the same effect, e.g., the light is guided within the substrate or waveguide by total internal reflection. The range of incident angles α (Δα), referred to herein as the range of acceptance angles or field of view (FOV), can be affected by the refractive index of the substrate or waveguide material. In FIG. 12A , for example, the reduced angle range (Δα′) illustrates the effect of refraction of the high refractive index material on the light incident on the internal coupling grating (ICG). However, the range of angles (Δα) or FOV is larger.

[0137] FIG. 12B illustrates a cross-sectional view of an exemplary blazed diffraction grating 1008. The grating 1008 is comprised of grating features having peaks 1003 and grooves 1005. The blazed transmission grating 1008 has a surface corresponding to the substrate or waveguide surface 1004S, which has a "sawtooth" shaped pattern, as viewed from the cross-section shown. The patterned "sawtooth" is formed by first tilting a portion 1007 of the surface 1004S. In the example shown in FIG. 12B, the grating 1008 also includes a second (steeper) sloped portion 1009. In the example shown, the first sloped portion 1007 has a shallower slope than the second sloped portion 1009, which has a steeper slope. The first sloped portion 1007 is also wider than the second sloped portion 1009 in this example.

[0138] The peak 1003 has a height H, which corresponds to the distance from the bottom of the groove 1005 to the top of the peak 1003. Therefore, this value may be referred to herein as the peak height and / or groove depth and grating height or grating depth or the height of the diffraction feature of the diffraction grating. In the example shown in FIG. 12B , the bottom of the groove 1005 is formed by the intersection of first and second sloping portions 1007, 1009 of two adjacent peaks 1003. The first sloping portion 1007 is on one of the adjacent peaks 1003, and the second sloping portion 1009 is on the other adjacent peak. Similarly, the top of the peak 1003 is formed by the intersection of the first and second sloping portions 1007, 1009 at the top of the peak 1003. However, other configurations are also possible. For example, the first and second sloped portions do not necessarily intersect if, for example, the bottom of the groove 1005 has a flat base or the top of the peak 1003 includes a flat plateau, as discussed below. The blazed diffraction grating 1008 has a line spacing or pitch d, which, in some implementations, may be constant. The line spacing or pitch d may be a measure of the separation of the apexes of the peaks 1003 in a grating 1008 having, for example, a shape similar to that shown in FIG. 12B. Similarly, the line spacing or pitch d may be a measure of the separation of the deepest locations of adjacent grooves 1005. The line spacing or pitch d may also be measured from other positions on the grating feature.

[0139] The tilt can be tilted at an angle δ with respect to a plane parallel to the grating 1008 or the surface of the waveguide (e.g., the surface 1004S of the waveguide, which may extend beyond the grating or surface 1004S' of the waveguide opposite the grating in FIG. 12A). This angle δ of the first (shallower) tilted portion 1007 may be referred to herein as the blaze angle.

[0140] As illustrated in Figure 12B, the blazed diffraction grating 1008 can include grating lines or features having an asymmetric shape, e.g., with asymmetrically shaped peaks 1003 and / or grooves 1005. For example, in the diffraction grating shown in Figure 12B, the diffractive features include peaks 1003 and / or grooves 1005 with an asymmetric triangular cross-sectional shape. As discussed above, this asymmetric shape results in different slopes and / or widths of the first and second sloped portions 1007, 1009. However, other shapes are also possible.

[0141] In designs where the diffractive feature is asymmetric, e.g., where the slope of a first sloped portion is shallower while the slope of a second sloped portion is steeper, the diffractive feature may be considered to be formed from repeated slopes and steps. Such a structure may be referred to herein as a sloped step structure. In some implementations, the second portion may not be as steep as the slope. For example, the second portion may be parallel to the normal 1002.

[0142] In other implementations, the "sawtooth" pattern, e.g., the peaks 1003 and / or grooves 1005, may be symmetrical. For example, the first and second sloped portions 1007, 1009 may have the same slope and be the same width.

[0143] The cross-sectional pattern shown in Figure 12B may be referred to herein as a single-step geometry, in comparison to the multi-step structure discussed below, shown, for example, in Figure 11D.

[0144] Regardless of whether the diffractive features are asymmetric or symmetric, in some implementations, a plateau or flat portion may be located on top of the peak 1003, as discussed below. A diffraction grating 1008 comprising diffractive features having a plateau or flat portion on top of the peak 1003 is shown, for example, in Figures 10B and 11D.

[0145] Figure 12B 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 12A, 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 orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or to a surface 1004S of the waveguide 1004, e.g., a major surface or opposing planar surface 1004S' of the waveguide on which the grating is formed. In Figure 12B, the light 1016 incident on the diffraction grating 1008 is shown as being diffracted at an angle β with respect to the normal direction 1002.

[0146] According to various embodiments, when configured as an in-coupling optical element or an in-coupling grating, the grating 1008 can diffractively couple light incident into the substrate 1004, which may be a waveguide, as described above. The grating 1008 may also be configured as an out-coupling optical element, if desired, and in such embodiments, can diffractively couple light out of the substrate 1004, which may also be a waveguide, as described above.

[0147] 12A and 12B, in some implementations, the substrate 1004 comprises a polymer. For example, the polymer may include a polymerizable composition of one or more materials, such as a high-viscosity multifunctional component, a low-viscosity mono- or multifunctional component, a photoinitiator, a light stabilizer, an antioxidant, a surfactant, inorganic nanoparticles or molecular-level clusters, any combination thereof, or other materials. The substrate may comprise a polymer and have a low refractive index (e.g., 1.6 or less) or a high refractive index (e.g., greater than 1.6). The substrate 1004 may comprise, for example, an organic polymer comprised of a low refractive index (e.g., less than 1.6) or a high refractive index organic resin (e.g., greater than 1.6). Low refractive index organic polymers, such as PC, PMMA, PVA, etc., or acrylate-containing resins that can be crosslinked upon UV and / or thermal curing, may have a refractive index of 1.5 to 1.6. Some high refractive index organic polymers may have sulfur and / or aromatic groups in the acrylate crosslinking molecules.

[0148] The polymer may be patterned, e.g., etched, to fabricate a grating structure. Diffractive features of the diffraction gratings 1008, 1010, such as lines, may be formed in the substrate 1004, such as in the surface of the substrate. The diffraction features may be etched into the substrate 1004, including a polymer, for example, on one or both sides of the substrate. The substrate may, for example, include a polymer, and the diffraction grating may be formed in the polymer substrate by etching or patterning the surface of the substrate.

[0149] Thus, in some implementations, the substrate and / or waveguide may comprise a material having a refractive index between 1.4 and 2.7, for example, depending on the material. For example, the substrate may be an inorganic material such as SiO2, LiNbO3, LiTaO3, SiC, or other inorganic materials, or a glass substrate with the following materials, but not limited to: SiO2, TiO2, BO3, Li2O, La2O3, ZrO2, ZnO, Si3N4, or other glass materials. The substrate may therefore have different refractive indices, depending on the design. In some implementations, the substrate comprises a polymer, which may have a low refractive index (e.g., 1.6 or less) or a high refractive index (e.g., greater than 1.6). For example, the substrate and / or waveguide may comprise an organic polymer, such as a low refractive index (e.g., less than 1.6) or a high refractive index organic resin (e.g., greater than 1.6). Low refractive index organic polymers, such as PC, PMMA, PVA, etc., having a refractive index of 1.5-1.6, may be used, or acrylate-containing resins that can be crosslinked upon UV and / or thermal curing may be employed. Some exemplary high refractive index organic polymers may have sulfur and / or aromatic groups in the acrylate crosslinking molecules.

[0150] Thus, as explained above, in various implementations described herein, the diffraction grating 1008 and the substrate 1004 or waveguide both comprise the same material, e.g., a polymer. 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 piece or monolithic structure. For example, the substrate 1004 may comprise a waveguide, with the diffraction grating 1008 formed directly within the surface of the waveguide or substrate. In these implementations, bulk polymer material may be patterned at the surface 1004S to form the diffraction grating 1008, while the polymer material below the diffraction grating 1008 may form the waveguide. Other materials may also be used as substrates and patterned to form diffractive features therein, as discussed above. First and second layers of material may be deposited over the diffraction grating (e.g., over the diffractive features), such as a first layer that increases the diffraction efficiency for a first polarization and a second layer that increases the diffraction efficiency for a second polarization that is different from the first polarization. As discussed above, the first layer may include an optically transmissive or transparent material, and in some implementations, may include a non-metallic material such as a dielectric or semiconductor. The second layer may include a metal. Such a layer combination may increase the diffraction efficiency for both the first and second polarizations, and thus increase the diffraction efficiency for unpolarized light.

[0151] However, in some other implementations, the diffractive features, such as lines, forming the diffraction gratings 1008, 1010 may comprise a material different from that of the substrate. The bulk or substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 may therefore comprise different materials. For example, a polymer may be patterned in the surface region to form the diffraction grating 1008, while a higher refractive index material may be below the diffraction grating 1008, forming the substrate 1004. In some implementations, the patternable material from which the base pattern is formed comprises a polymer having a refractive index in the range of 1.4 to 1.95. In some implementations, the substrate comprises 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, or may be 2.4, 2.5, 2.6, 2.7, 2.8, or less, or may be within any range formed by any of these values, or may be outside these ranges. In some implementations, for example, the substrate comprises a Li-based oxide such as lithium niobate. Other materials with high refractive indices may also be used. In some implementations, the substrate may comprise, for example, silicon carbide (SiC). The substrate may comprise, for example, a crystalline, cryptocrystalline, or amorphous substrate, possibly containing, for example, Ti, Z, Hf, La, Ba, Ca, Si, or O. The substrate may comprise, for example, a high refractive index material such as a Li-based oxide (e.g., lithium niobate, LiNbO), while the diffractive features may be formed from a different material, such as a polymer, formed on the high refractive index substrate. In some implementations, this other material formed on the substrate may have, for example, a lower refractive index than the substrate.

[0152] First and second layers of material may be deposited over the diffraction grating, such as a first layer that increases the diffraction efficiency for a first polarization and a second layer that increases the diffraction efficiency for a second polarization different from the first polarization. As discussed above, the first layer may include an optically transmissive or transparent material or a non-metallic material such as a dielectric or semiconductor. The second layer may include a metal. Such a layer combination may increase the diffraction efficiency for both the first and second polarizations, and thus increase the diffraction efficiency for unpolarized light.

[0153] 12A and 12B, according to various embodiments, the diffraction grating 1008 may have various dimensions. For example, the diffractive features of the diffraction grating 1008 may have a height (H) of 10 nm to 150 nm, 100 nm to 200 nm, 150 nm to 300 nm, or 300 nm to 500 nm, or a height within a range defined by any of these values ​​(e.g., 100 nm to 600 nm), depending on the design. This height may, in some implementations, correspond to the height of the peaks 1003 and / or the depth of the grooves 1005 or regions (e.g., gaps) between the peaks. However, other heights are also possible.

[0154] The diffraction grating 1008 may have a pitch of 200 nm to 300 nm, or 300 nm to 400 nm, or 400 nm to 550 nm, or any range defined by any of these values, according to various embodiments. Other pitches are also possible.

[0155] The diffraction grating 1008 may have a blaze angle of approximately 20 to 70 degrees (shallow size) or 20 to 85 degrees and a reverse blaze angle (steep side) of 70 to 150 degrees, or any value within the range defined by these values ​​measured in the same angular direction.

[0156] Values ​​outside any of these ranges are also possible.

[0157] 13A illustrates an example geometric configuration 1302 for diffractive features in a diffraction grating 1008, such as those described above with reference to FIGS. 12A and 12B. For example, the geometric configuration can be symmetric, with straight sidewalls (e.g., the first column of the top row in FIG. 13A), sloped sidewalls (e.g., the second column of the top row, a sawtooth example), re-entrant or concave sidewalls, multi-step sidewalls (e.g., the third column of the first row), other types of sidewalls, or some combination thereof. In another example, the geometric form can be asymmetric, with at least one straight sidewall, sloped sidewall (e.g., the first and third columns of the second row in FIG. 13A ), re-entrant (e.g., a sidewall with an acute re-entrant angle relative to the base surface, also referred to as a shark tail, as shown in the third column of the second row) or concave sidewall, multi-step sidewall (e.g., the second column of the second row), other types of sidewall, or some combination thereof. Regardless of whether the diffractive feature is asymmetric or symmetric, in some implementations, a plateau or flat portion may be located at the top (e.g., peak) of the feature.

[0158] In some embodiments, the asymmetric geometry may include a profile in which a first sidewall forms an angle of 20 to 85 degrees with the substrate. In some embodiments, the second sidewall forms a different angle than the first sidewall. In some embodiments, it may be advantageous for the second sidewall to form an angle of 90 degrees or more with the substrate to provide biased deposition during substantially linear deposition onto the grating (as illustrated in FIG. 14 ), including a coating on the first sidewall but no or less coating on the second sidewall (e.g., thinner or less coverage on the second sidewall). In some embodiments, the height of the grating features can be 100 nm to 600 nm. In some embodiments, the pitch of the grating features can be 290 nm to 690 nm. Other values ​​outside these ranges are also possible.

[0159] A diffraction grating may be a one-dimensional (1D) grating or a two-dimensional (2D) grating. For example, as illustrated in FIGS. 13B-1 and 13B-2, a diffraction grating can comprise a 1D array of grating features, such as an array of lines or grooves (e.g., straight lines or grooves). Such a 1D grating may be, for example, undulating, repeating, or periodic or quasi-periodic in one direction. In some cases, a 1D array may comprise multiple parallel linear features, such as linear ridges and / or linear depressions. For example, FIG. 13B-1 shows a cross-sectional side view of an exemplary device 3300 having a series of diffractive features 3303 arranged laterally in one direction (e.g., horizontally in FIG. 13B-2). The diffractive features 3303 are undulating in one direction (e.g., horizontally in FIG. 13B-2) and are therefore referred to as 1D. FIG. 13B-2 shows a top view of the exemplary device 3300. The diffractive features 3303 can form a series of elongated longitudinal features, such as lines, that extend in one direction (e.g., vertically in FIG. 13B-2) and are arranged along and repeated in one direction (e.g., horizontally in FIG. 13B-2).

[0160] In another example, a diffraction grating can include a 2D array of grating features, such as a 2D array of protrusions, high points, or regions, and holes, gaps, or low areas between the high points, regions, or protrusions. The 2D array can, for example, resemble a checkerboard pattern in some cases. Any of the 1D arrays of structures described herein can also be arranged in two directions to form a 2D array of diffractive features. The 2D array of diffractive features can include multiple undulations in two directions. In some instances, the undulations can be periodic, while in other instances, the pitch of the undulations can vary. FIG. 13C shows an example device 3400 having a 2D array of diffractive features 3403 (e.g., diffractive features 3403 arranged laterally in two dimensions or directions). In this example, the array resembles a checkerboard pattern. These features can be referred to as protrusions, or in this case, pillars. In this example, the diffractive features 3403 are symmetrical, with sidewalls approximately perpendicular to the horizontal axis. In other embodiments, diffractive features, e.g., protrusions, can be symmetric with angled or sloped sidewalls. For example, FIGS. 13D-1 and 13D-2 show cross-sectional side and top views, respectively, of an exemplary array of symmetric diffractive features. Both the left and right sidewalls slope inward, such that the diffractive features taper, or their widths become smaller with increasing height. Thus, in this embodiment, a first sidewall is sloped in one direction and a second sidewall is sloped in a second, opposite direction. In this embodiment, the sidewall slope angle is approximately 30 degrees relative to the horizontal axis and is symmetric on both sides. In some implementations, a 2D array can include grating features formed by the orthogonal overlap of two 1D grating structures. For example, a 2D array can include the orthogonal overlap of two blazed grating structures as described with reference to FIGS. 12A and 12B. Other configurations of 1D and 2D gratings are also possible. 13A may correspond to the cross section of either a 1D or 2D grating of diffractive features. Such diffractive features may be arranged, for example, in a 1D or 2D array.

[0161] FIG. 13E shows another exemplary device 3600 having a 2D array of diffractive features 3603. The diffractive features are asymmetric in this example. FIGS. 13F-1 and 13F-2 show cross-sectional side and top views, respectively, of an exemplary array of asymmetric diffractive features. This 2D diffractive grating comprises a blazed diffractive grating. The diffractive features may be tapered, for example, in width or thickness with height. In the example shown in FIG. 13E, the diffractive feature has two sloped sidewalls or facets, one sloped more than the other, whereas in the example shown in FIGS. 13F-1 and 13F-2, one sidewall is sloped while the other, opposing sidewall, is not sloped, or any slope on the second sidewall is negligible. In both cases, the slope of one sidewall is greater than the other (if applicable), such that the diffractive feature is asymmetric and blazed. As a result, the diffractive features diffract light preferentially in one direction over another. Such diffraction gratings can be useful, for example, as in-coupling optical elements configured to diffract light received from a projector toward a light distributing element, an out-coupling optical element, or a combination of a light distributing element and an out-coupling optical element, such as a CPE or combined pupil expander-extractor. Such diffraction gratings can also be useful for out-coupling light into the eye, as opposed to facing the environment or world in front of the user and head-mounted display. In some implementations, the sidewall tilt angle is less than 30 degrees with respect to the horizontal axis on one side and greater than 80 degrees (possibly 90 degrees) on the other side. However, other tilts and tilt angles are also possible. In some instances, the diffractive features can form a 2D array of sawtooth structures, such as sawtooth nanostructures.

[0162] Thus, in various implementations, a 2D array of symmetric or asymmetric diffractive features can provide a blazed diffraction grating. As discussed above, the shape of the diffractive feature (e.g., the slope angle of the sidewalls) can determine the direction in which the grating directs or preferentially directs light. For example, a grating may direct more light toward other gratings (e.g., EPE, OPE, or CPE) and / or toward the viewer. In some instances, the diffractive feature can be faceted (e.g., blazed in multiple directions) to bias the propagation of light in two or more directions. For example, FIG. 13G-1 shows an example device 3700 having a 2D array of diffractive features 3703 formed in or on a substrate 3701. The diffractive feature 3703 has a first sidewall or facet 3703b-1 and a second sidewall or facet 3703b-2 that are sloped. Thus, the diffractive feature tapers with height, e.g., in thickness or width. The diffractive feature 3703 can be configured to preferentially direct light in a direction based on the slope angle of the first and second sidewalls or facets 3703b-1, 3703b-2. Figure 13G-2 shows an example diffractive feature that directs more light in two specific directions (as illustrated by the two thick solid arrows pointing up and to the right and down and to the left). Other implementations are also possible.

[0163] Thus, any of the structures or devices described herein, such as grating structures, may comprise 1D gratings. Similarly, any of the structures or devices described herein, such as grating structures, may comprise 2D gratings. Such 2D gratings may diffuse light. These gratings may also comprise blazed gratings. Such blazed gratings may preferentially direct light in one direction. In some implementations, a 2D grating (e.g., having one tilted facet on the diffractive features) preferentially directs light in one direction, while in other implementations, a 2D grating (e.g., having two differently tilted facets on the diffractive features) preferentially directs light in multiple directions. Similarly, any of the methods or processes described herein can be used for 1D gratings. Similarly, any of the methods or processes described herein can be used for 2D gratings. These gratings, whether 1D or 2D, may be included on a substrate and / or a waveguide, included in an eyepiece, or possibly integrated into a head-mounted display as disclosed herein. These gratings may be employed, for example, as input gratings (eg, ICG), output gratings (EPE), light distribution gratings (OPE), or combined light distribution / output gratings (eg, CPE).

[0164] The diffraction grating pattern may be formed in a substrate, which may include a waveguide. In some implementations, the patternable material includes a polymer. The pattern may be formed using photolithography, for example, where a patternable material, such as photoresist, may be deposited on a substrate, which may include a waveguide. The patternable material / photoresist may be patterned to have a geometric form such as that illustrated in FIG. 13A. Imprinting, such as nanoimprinting, may be used to pattern the patternable material. In some implementations, forming the pattern geometry in the patternable material may involve imprinting a pattern, such as a single-step "sawtooth" pattern, into photoresist (e.g., depositing photoresist on a substrate and then imprinting a blazed geometric form). After patterning, the patterned material, e.g., photoresist, may constitute a mask, such as a hard mask.

[0165] Patternable materials, such as polymers, photoresists, etc., can be imprinted with or without a residual interconnect layer thickness (RLT), or the polymer or resist pattern can be a photolithographic pattern with or without RLT. The monolithic polymer substrate can have a surface relief pattern defined on one or both sides of the waveguide. A pattern (e.g., multiple diffractive features) can additionally or alternatively be etched into the substrate (e.g., having a refractive index of 1.45-2.0) once the pattern is imprinted or otherwise formed on the substrate.

[0166] In various implementations, the patterned material (e.g., polymer or photoresist) and substrate may be etched to form a pattern in the substrate, such as that described with reference to FIG. 13A. Etching the photoresist and substrate may involve, for example, dry plasma or chemical etching and / or wet chemical etching. In some implementations, the etching may etch the material at a relatively constant rate, such that areas where the patterned photoresist is thickest result in negligible or no removal of material from the substrate, while areas where the patterned photoresist is thinnest (or absent) result in the deepest etching into the substrate.

[0167] In some other implementations, the patternable material is etched to form diffractive features in the patternable material. In such implementations, the diffractive features comprising the patternable material remain on the substrate, which does not need to be patterned.

[0168] FIG. 13H shows an exemplary method 3800 for forming a blazed grating. Method 3800 provides a template or master 3810. If the diffractive features are to be angled, tilted, or slanted, the template 3810 can be patterned to form angled structures. Various processes, e.g., etching processes, may be directional and angled to form such angled structures. Some examples of angled processes, such as angled etching processes, include ion beam milling, angled dry etching, ion etching, GLAD etching, angled etching, Faraday cage etching, etc. In some implementations, the selection of material employed for the template 3810 may aid in producing angled structures with angled sidewalls within the template. In this example, the angled structures comprise angled elongated protrusions (e.g., for a 1D grating) or angled posts (e.g., for a 2D grating). These angled elongated protrusions or angled posts may have sidewalls that are tilted in the same direction and, in some cases, may be substantially parallel. Once the template 3810 is fabricated, a layer of patternable material (e.g., a 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 a patternable material (e.g., a 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 contacted with the template with the patternable material thereon. The template can be removed, and the resist material 3805 and underlying substrate 3801 can be dry etched to form diffractive features 3803 in the substrate 3801 (or in a layer of material disposed on the substrate 3801). In various implementations, dry etching is employed as shown. The etching may be directional. In the example shown, the etching process is not angled.The resulting diffractive features 3803 formed in the substrate 3801 (or in a layer of material disposed on the substrate 3801) may have a shape, for example, blazed as a result of angled features in the mask 3805. In the example shown, the cross section of the diffractive features has a trapezoidal or generally triangular shape with two slanted sides. The sides are slanted in opposite directions. In the example shown, one side is more slanted than the other, creating an asymmetric or blazed structure. This process may be used to form 1D or 2D arrays of diffractive features.

[0169] FIG. 13I illustrates another exemplary method 3850 for forming blazed diffractive features. The mask 3855 and underlying substrate 3851 (or a layer of material disposed on the substrate 3851) can be etched (e.g., dry etched) at an angle to form diffractive features 3853 in the substrate 3851 (or a layer of material disposed on the substrate 3851). Some examples of angled directional etching processes (e.g., angled etching) include ion beam milling, angled dry etching, ion etching, GLAD etching, tilted etching, Faraday cage etching, etc. The template may include elongated protrusions (e.g., for 1D gratings) or tapered posts (e.g., for 2D gratings) with trapezoidal or approximately triangular cross-sections. These elongated protrusions or tapered posts may have sidewalls that are sloped in opposite directions. One sidewall may be more sloped than the other. Applying an angled etching process to these elongated protrusions or tapered posts can produce a blazed grating in the material underlying the elongated protrusions or tapered posts, such as a substrate or a layer of material disposed on a substrate. Blazed diffractive features with sides tilted in the same direction may be produced. In various implementations, one of the sides is more tilted than the other. This process may be used to form 1D or 2D arrays of diffractive features.

[0170] In various implementations, the resulting diffractive features may be blazed in two or more directions (e.g., as shown in FIG. 13G-1) as a result of angled features in a mask (e.g., as shown in FIG. 13H) and / or as a result of using an angled process (e.g., as shown in FIG. 13I). Diffractive features or gratings blazed in two or more directions may be produced by etching twice. In some implementations, for example, diffractive features or gratings blazed in two or more directions may be produced by etching with a first mask and then etching again with a second, different mask. In some instances, as shown in FIG. 13J, mask 3905 and substrate 3901 may be etched to form a first sidewall of diffractive feature 3903 in 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 (e.g., at an angle and / or a different orientation relative to the first sidewall) may be etched, for example, to form a second sidewall. In some implementations, after the first sidewall of the diffractive feature 3903 is formed, a planarizing layer 3907 may be added to the intermediate diffractive feature 3903 and the substrate 3901. The planarizing layer 3907, the intermediate diffractive feature 3903, and / or the substrate 3901 may be patterned and etched (e.g., at an angle relative to the first sidewall) to form a second sidewall. While the above examples are discussed in the context of patterning a substrate, in some implementations, the processes described above may be employed to pattern a layer formed on a substrate and not pattern the substrate. Alternatively, in some implementations, the processes described above may be employed to pattern a layer formed on a substrate and the substrate.

[0171] Additionally, while example methods 3800, 3850, 3900 are illustrated forming 2D arrays of asymmetric diffractive features, the methods can also be used to form 2D arrays of symmetric diffractive features (with or without angled sidewalls). The methods can also be used to form 1D arrays of diffractive features. In some instances, the diffractive features within the 1D array can be symmetric, with or without angled sidewalls. In some instances, the diffractive features within the 1D array can be asymmetric, for example, with angled sidewalls. Thus, in some cases, blazed diffractive features may be formed.

[0172] 2. Example Layer One or more transparent layers may be placed on the base pattern. For example, as illustrated in Figure 14, deposition of one or more transparent layers on the base pattern can be performed conformally (1402A, 1402B, 1402C) or directionally (1404A, 1404B, 1404C, 1406A, 1406B, 1406C).

[0173] Conformal deposition (1402A, 1402B, 1402C) can include various deposition techniques for depositing material 1412, which can result in a material layer that covers various surfaces of the underlying feature. The deposited layer can potentially be of substantially equal thickness across the base pattern geometry 1410. In some embodiments, directional deposition can include linear deposition (1404A, 1404B, 1404C) such that the deposited material 1412 is incident on the base pattern 1410 at a substantially orthogonal angle relative to the plane or horizontal or planar major surface of the substrate. In another embodiment, directional deposition can include angled deposition (1406A, 1406B, 1406C) such that the deposited material 1412 is incident on the base pattern 1410 at an angle 1414 relative to the plane or horizontal or planar major surface of the substrate. For example, the angle 1414 can be selected based on the pattern geometry. For example, the grating may be a blazed grating having a sawtooth structure, and the angle 1414 may be approximately perpendicular to the surface of the sawtooth structure such that the deposited material 1412 is deposited substantially more on portions (or specific sidewalls) of the sawtooth structure, as shown at 1406A, 1406B, 1406C.

[0174] The deposition type and base pattern geometry can affect the thickness and location of the layer of deposited material 1412. Advantageously, controlling the thickness and location of the layer of deposited material 1412 and creating a biased or angled deposition profile can enable better control for directional light emission from the ICG. As illustrated in FIGS. 13 and 14 , the pattern geometry may be asymmetric, having one or more straight sidewalls, sloped sidewalls, re-entrant or concave sidewalls, multi-step sidewalls, other sidewalls, or some combination thereof. For example, the pattern geometry may be a sawtooth with two asymmetric sloped sidewalls, as shown in 1402A, 1404A, and 1406A. In another example, the pattern geometry may have straight sidewalls and multi-step sidewalls, as shown in 1402B, 1404B, and 1406B. In another example, the pattern geometry may have re-entrant and sloped sidewalls, as shown in 1402C, 1404C, and 1406C. In the case of conformal deposition, layer 1412 may cover the top and sides of the diffractive features. In some cases, the thickness of layer 1412 may be substantially equal across different types of pattern geometries (or most of the pattern geometries). In the case of directional deposition, for some cases of linear or angled deposition, the amount deposited on the top and one or more sides may be different (e.g., see 1404B and 1406B), or the amount deposited on two different (e.g., opposing) sides may be different (e.g., see 1404A, 1404B, 1404C, 1406A, 1406B, and 1406C). In some cases, one or more sides may be exposed and have only a small amount of material deposited thereon, such as in 1406A, 1406B, and 1406C and 1404B and 1404C. Additionally, for directional deposition, the thickness of layer 1412 across different types of pattern geometries may depend more strongly on the pattern geometry. For example, for sawtooth geometry 1404A, linear directional deposition may deposit substantially more on the portion of the sawtooth 1416 with a lower slope than the portion of the sawtooth 1418 with a higher slope.In another example, for sawtooth geometry 1406A, a deposition angled approximately perpendicular to the surface 1420 of the substrate at an angle 1414 θ between 45° and 135°, or between 60° and 120°, or between 80° and 100° degrees will likely deposit more material on such surface 1420 than an angled deposition where the surface 1422 is parallel to the direction of deposition (e.g., having a small angle θ of less than 20° or 10° with respect to the surface).

[0175] The optically transmissive or transparent layer can include an optically transmissive material that can improve diffraction efficiency for polarizations such as S-polarized light or TE-polarized light. In some implementations, the transmissive layer is not a metal. In some implementations, for example, the transmissive layer is a dielectric or a semiconductor. In some examples, the transmissive layer can be a high-index dielectric such as titanium dioxide (TiO), zirconium dioxide (ZrO), SiN, ZnO, SiC, ZnTe, GaP, BP, or other material. In some examples, the high-index material 1502 may have a refractive index between 1.9 and 3.5. The transmissive material may have a refractive index greater than or equal to 2, such as 2.2, 3, 3.5, 4.0, or other high refractive index, or within any range formed by these values. In some examples, the material is a high-index material (e.g., n is greater than 2) with a low k (e.g., k is less than 0.05), such as silicon carbide (SiC).

[0176] In some embodiments, the transmissive layer can comprise multiple sublayers. For example, a sublayer can include two alternating materials. Figure 15 illustrates an example diffraction grating 1500 having alternating layers deposited on a patterned surface 1506 of a substrate. In some implementations, the sublayers form an interference coating or a bandpass filter coating. In some cases, the sublayers comprise a quarter-wave stack.

[0177] In an embodiment where the sub-layers include alternating materials, the transmissive layer can include alternating sub-layers of high refractive index material 1502 and low refractive index material 1504. For example, the high refractive index material 1502 can be TiO, or Si, N, ZnO, ZrO, which has a refractive index of 2.2. 2. The high refractive index material 1502 may include a material having a refractive index greater than or equal to 1.9 or 2, such as TiO2, SiC, ZnTe, GaP, or BP. In some embodiments, the high refractive index material 1502 may have a refractive index between 1.9 and 3.5. Additionally, in some designs, the low refractive index material 1504 may include a material having a refractive index lower than or equal to 1.9 or 2, such as less than 1.6, which may include SiO2, having a refractive index of 1.45. In some embodiments, the alternating layers may include a first layer of high refractive index material 1502, a second layer of low refractive index material 1504, and a third layer of high refractive index material 1504.

[0178] In some implementations, the thickness of one or more sublayers in a composite layer may be varied to achieve a desired reflectivity within a certain wavelength of light. For example, a transmissive layer may include a thin layer of a high-index material and a thicker layer of a low-index material. The thickness of one or more sublayers within the transmissive layer, such as a layer of low-index material, may be adjusted to increase the reflectivity of the transmissive layer at a certain wavelength. For example, the thickness of one or both sublayers may be λ / 4 times the refractive index of the material, where λ corresponds to a wavelength or range of wavelengths, or other design wavelength, that has increased reflectivity. Graph 1501 in FIG. 15 illustrates reflectivity as a function of wavelength for an exemplary diffraction grating 1500, with the thickness of the material within the transmissive layer adjusted to provide increased reflectivity 1508 within the range shown.

[0179] 15, a low refractive index material 1504, such as SiO2, is placed between layers of a high refractive index material 1502, such as TiO2, creating a highly reflective surface. By varying the thickness of one or more of the material sub-layers 1502, 1504, the diffraction grating 1500 can be configured to allow maximum reflectance within certain wavelengths, potentially acting as a color filter or providing a degree of color tuning. For example, the layer thicknesses may be configured to create ICG diffraction to select wavelengths such as blue at 450 nm over other wavelengths such as red at 650 nm.

[0180] As discussed above, one or more metal layers may be disposed over the transmissive layer. For example, as illustrated in FIG. 16, deposition of one or more metal layers onto the transmissive layer can be performed conformally (1602A, 1602B, 1602C) or directionally (1604A, 1604B, 1604C, 1606A, 1606B, 1606C). The deposition type can be the same or different from the deposition type of the transmissive layer. FIG. 16 illustrates various combinations. For example, the transmissive layer may be conformally deposited (1402A), and the metal layer may be conformally (1602A) or directionally deposited in a straight line (1604A), or directionally deposited at an angle (1606A). In another example, the transparent layer may be directionally deposited in a straight line (1404A) and the metal layer may be conformally deposited (1602B) or directionally deposited in a straight line (1604B) or directionally deposited at an angle (1606B). In another example, the transparent layer may be directionally angled (1404A) and the metal layer may be conformally deposited (1602C) or directionally deposited in a straight line (1604C) or directionally deposited at an angle (1606C).

[0181] Conformal deposition (1602A, 1602B, 1602C) can include various deposition techniques for depositing material 1612, which can result in a material layer covering different sides and portions of a transmissive layer disposed on the base pattern geometry 1410. In some embodiments, directional deposition can include linear deposition (1604A, 1604B, 1604C) such that the deposited material 1610 is incident on the transmissive layer material 1412 at a substantially orthogonal angle relative to the plane or horizontal or major planar surface of the substrate. In another embodiment, directional deposition can include angled deposition (1606A, 1606B, 1606C) such that the deposited material 1610 is incident on the transmissive layer material 1412 at an angle 1616 relative to the plane or horizontal or major planar surface of the substrate. For example, the angle 1616 can be selected based on the pattern geometry. For example, the diffraction grating can be a blazed diffraction grating having a sawtooth structure. The direction may be approximately perpendicular to the surface of the sawtooth structure, such that the deposited material 1610 is deposited substantially more on portions (or specific sidewalls) of the sawtooth structure, as shown in 1605A, 1606B, 1606C.

[0182] The deposition type and base pattern geometry can affect the thickness and location of the layer of deposited material 1612. As discussed above with reference to FIG. 14, advantageously, controlling the thickness and location of the layer of deposited material 1612 and creating a biased or angled deposition profile can enable better control for directional light emission from the ICG. As illustrated in FIGS. 13-15, the pattern geometry may be asymmetric, having straight sidewalls, sloped sidewalls, re-entrant or concave sidewalls, multi-step sidewalls, other sidewalls, or some combination thereof. In the case of conformal deposition, the thickness of the layer 1612 may be substantially equal across different types of pattern geometries (or across most of the pattern geometries). In the case of directional deposition, the thickness of the layer 1412, 1610 across different types of pattern geometries may depend more strongly on the pattern geometry. For example, for sawtooth geometry 1604A, linear directional deposition may deposit substantially more material 1612 on portions of the sawtooth with lower slopes than on portions of the sawtooth with higher slopes. In another example, for sawtooth geometry 1606A, angled deposition, generally perpendicular to the plane or horizontal or major planar surface of the substrate, may deposit more material 1612 on shallowly sloped surfaces 1420 than on steeply sloped surfaces 1422.

[0183] The metal layer can include metals or conductive materials, such as materials including aluminum, silver, gold, copper, or alloys thereof. In some designs, the metal used in the metal layer can be selected to extinguish certain wavelengths of light. For example, gold or copper can be used to extinguish light below 600 nm.

[0184] Although the permeable layer is discussed as the first layer on the base pattern and the metal layer is discussed as the second layer, the layers may be applied in any suitable order. Additionally or alternatively, one or more layers of additional material may be present between the base pattern, the permeable layer, or the metal layer. In some embodiments, one or more layers may be repeated or alternating. In some embodiments, one or more layers may be partial layers, such that material that may be part of a layer is deposited on a portion of the substrate or base pattern.

[0185] In some embodiments, an interfacial layer may be present between the metal layer and the permeable layer. The interfacial layer may increase the adhesion strength of the metal layer and the environmental reliability of the stack. For example, without the interfacial layer, a metal layer such as Ag, Au, Cu, or Al metal may delaminate from the grid during unfavorable environmental conditions such as heat and humidity. In some embodiments, the interfacial layer may include a TiO or other layer that may help bond the metal layer to the polymer surface.

[0186] Deposition of the permeable layer, metal layer, or any other layer may include physical vapor deposition (PVD). PVD may include sputtering, evaporation, or other forms of physical vapor deposition. In embodiments where conformal deposition is desired, sputtering may be used. In embodiments where directional deposition is desired, evaporation may be used. Additionally or alternatively, deposition of the permeable layer, metal layer, or any other layer may include chemical vapor deposition (CVD). CVD may include plasma-enhanced low-pressure deposition, atmospheric pressure deposition, atomic layer deposition (ALD), or other forms of chemical vapor deposition. A form of CVD may be used when conformal deposition is desired. Aspects of PVD or CVD may be varied to affect the physical properties of the deposited layer. For example, deposition thickness bias may be reduced for highly conformal processes, such as those performed at the atomic scale one monolayer at a time. In another embodiment, coating quality (e.g., in terms of grain size or density) may be affected by changes to processing temperature and pressure. The coating quality can in turn affect the n and k of the layer and the shape of adjacent layers coated on top of the deposited layer.

[0187] 3. Exemplary Waveguide Including a Diffraction Grating with Reduced Polarization Sensitivity Diffraction gratings with reduced polarization sensitivity as described above can be used in the context of AR displays. For example, a waveguide that may be part of an AR display may include a diffraction grating on one or more sides of the waveguide (such as those described with reference to FIGS. 6 and 7 ) that may serve as an internal coupling optical element, a light dispersive element, and / or an external coupling optical element. FIG. 17A illustrates an exemplary waveguide having multiple diffraction gratings, including a reduced polarization sensitivity diffraction grating, that may act as an internal coupling optical element. For example, as shown, a waveguide 1710 may include one or more internal coupling gratings (ICGs) 1712, 1714 and one or more diffraction gratings 1720, 1722 that perform light distribution and / or external coupling. In this example, the gratings 1720, 1722 may comprise pupil expander-extractor (CPE) regions, which act as both light dispersive elements and external coupling gratings. Light 1702 may be launched into one side of a waveguide 1710 through a transmissive ICG 1714. The transmissive ICG 1714 may pass the light 1702 into the waveguide 1710 and diffract light 1706. The light 1706 may propagate along the waveguide 1710 toward one or more pupil expander-extractor gratings 1720, 1722. A second reflective ICG 1712, which may be on the opposite side of the waveguide 1710, may also be configured to reflect the light 1704 back into the waveguide 1710. The reflected light 1704 may propagate along the waveguide 1710 toward one or more pupil expander-extractor gratings 1720, 1722. Advantageously, the inclusion of one or more ICGs 1712, 1714 can aid in image uniformity and / or eyebox efficiency, depending on the source light (e.g., LED, microLED, laser, polarized source, or unpolarized source).

[0188] The reflective ICG 1712 or the transmissive ICG 1714 may comprise a diffraction grating. The diffraction grating of the reflective ICG 1712 or the transmissive ICG 1714 or both may be formed in a layer on the waveguide or substrate, or within the waveguide itself. The diffraction grating may have diffractive features, for example, as described above with reference to Figures 12A-12B and 13A-13J. For example, the diffractive features of the diffraction grating may have various dimensions and symmetric or asymmetric shapes.

[0189] In some embodiments, the geometry of the diffractive features of the reflective ICG 1712 and / or the transmissive ICG 1714 can be symmetric, with straight sidewalls, sloped sidewalls, re-entrant or concave sidewalls, multi-step sidewalls (see, e.g., the third column of the first row in FIG. 13A ), other types of sidewalls, or some combination thereof. In other embodiments, the geometry can be asymmetric, with at least one straight sidewall, sloped sidewall, re-entrant (see, e.g., the third column of the second row in FIG. 13A ) or concave sidewall, multi-step sidewalls (see, e.g., the second column of the second row in FIG. 13A ), other types of sidewalls, or some combination thereof. Regardless of whether the diffractive features are asymmetric or symmetric, in some implementations, a plateau or flat portion may be located at the top (e.g., peak) of the feature. The grating may have a height greater than or less than 100 nm to 600 nm or as defined by that range. For example, the grating may have a depth or height measured from base to peak of 100 to 300 nm, 300 to 600 nm, 200 to 400 nm, 300 to 500 nm, etc., or any range defined by any of these values. The grating may have a pitch of 290 nm to 690 nm, or a pitch greater than or less than that defined by that range. If the grating is a blazed grating, the grating may have a blaze angle measured in the same angular direction, e.g., 20 to 85 degrees, 45 to 80 degrees, or another angle, and a reverse blaze angle, e.g., about 70 to 150 degrees, or any value within the range defined by these values. Values ​​outside any of these ranges are also possible.

[0190] The reflective ICG 1712 can include one or more transmissive layers 1713 and / or one or more metal layers 1711. The metal layer 1711 may be reflective. In some embodiments, the one or more transmissive layers 1713 can be efficient at diffracting TE-polarized light within one or more wavelength ranges. For example, the one or more transmissive layers can be efficient at diffracting TE-polarized light within a range of wavelengths associated with red (e.g., about 620-780 nm), a range of wavelengths associated with green (e.g., about 492-577 nm), or a range of wavelengths associated with blue (e.g., 435-493 nm). In some embodiments, the one or more metal layers 1711 can be efficient at diffracting TM-polarized light within one or more wavelength ranges. For example, the one or more metal layers may be efficient at diffracting TM-polarized light within a range of wavelengths associated with red (e.g., about 620-780 nm), a range of wavelengths associated with green (e.g., about 492-577 nm), or a range of wavelengths associated with blue (e.g., 435-493 nm). The transmissive ICG 1714 may include one or more transmissive layers 1715 as described above with reference to FIGS. 14 and 15. In some embodiments, the one or more transmissive layers may be efficient at diffracting TE-polarized light within one or more wavelength ranges. For example, the one or more transmissive layers may be efficient at diffracting TE-polarized light within a range of wavelengths associated with red (e.g., about 620-780 nm), a range of wavelengths associated with green (e.g., about 492-577 nm), or a range of wavelengths associated with blue (e.g., 435-493 nm). In some embodiments, the one or more transmissive layers 1715 may include a non-metallic material, such as a dielectric or semiconductor material, including, but not limited to, ZrO2, TiO2, or SiC. In various implementations, the diffracted light comprises the first diffraction order (e.g., +1 or -1). The majority of the diffracted light may occur within the first order.

[0191] Light received from a projector, such as an image projector, may be diffracted by one or more gratings 1712, 1714 at an angle or range of angles such that the light, or at least a portion of it, is guided within the waveguide by total internal reflection, e.g., toward a pupil expander-extractor grating. The geometry of the diffractive features, e.g., asymmetric or blazed, may preferentially direct light toward the pupil expander-extractor grating. The pupil expander-extractor grating may be configured to outcouple light from the waveguide into the user's or wearer's eye. The pupil expander-extractor grating may additionally increase the area (in two dimensions) over which light exits the waveguide. In this way, the pupil expander-extractor grating may potentially increase the eyebox in some implementations. In various designs, the projector outputs unpolarized or circularly polarized light and directs the unpolarized or circularly polarized light to the ICG for input into the waveguide. Some examples of such projectors that output unpolarized or circularly polarized light and form an image may include, for example, micro-LED projectors, digital light projectors (DLPs), and liquid crystal on silicon (LCOS)-based projectors, although others are also possible.

[0192] FIG. 17B illustrates an exemplary waveguide having multiple diffraction gratings that can act as internal coupling optical elements. For example, as shown, a waveguide 1710 may include one or more internal coupling gratings (ICGs) 1717, 1714 and one or more gratings 1720, 1722 that perform light distribution and external coupling. The gratings 1720, 1722 may comprise one or more pupil expander-extractor (CPE) regions, which act as both light dispersive elements and external coupling gratings. Light 1702 may be launched into one side of the waveguide 1710 through a transmissive ICG 1714. The transmissive ICG 1714 (e.g., comprising a transmissive grating) may pass the light 1702 into the waveguide 1710 and diffract light 1706. The transmissive ICG 1714 may have a TE diffraction efficiency that is higher than its TM efficiency. The light 1706 may be propagated along the waveguide 1710 toward one or more pupil expander-extractor gratings 1720, 1722. A second reflective ICG 1713 (e.g., the reflective ICG comprises a reflective diffraction grating), which may be in series with (e.g., matched to) the transmissive ICG 1714 and on the opposite side of the waveguide 1710, may be configured to diffract and reflect the light 1704 into the waveguide 1710. The second reflective ICG 1717 may operate in a reflective mode and may have a TM diffraction efficiency higher than its TE efficiency. The diffracted / reflected light 1704 may be propagated along the waveguide 1710 toward one or more pupil expander-extractor gratings 1720, 1722. Advantageously, the inclusion of one or more ICGs 1712, 1717 may potentially aid in image (e.g., brightness and / or color) uniformity and / or eyebox efficiency, possibly somewhat depending on the source light (e.g., LED, microLED, laser, polarized, or unpolarized source).

[0193] The transmissive ICG 1714 and / or ICG 1717 may comprise a diffraction grating. The diffraction grating of the reflective ICG 1717 or the transmissive ICG 1714 or both may be formed in a layer on the waveguide or within the waveguide or substrate itself. The diffraction grating may have diffractive features as described above with reference to FIGS. 12A-12B and 13A-13J. For example, the diffractive features of the diffraction grating may have various dimensions and different geometric forms. See, for example, FIG. 13A, which shows sawtooth (e.g., row 1, column 2 and row 2, column 1), multi-step (e.g., row 1, column 3 and row 2, column 2), and re-entrant angles (e.g., row 2, column 3 in FIG. 13A). As described herein, the diffractive features may be blazed (e.g., see row 2 in FIG. 13A) to direct light in a particular direction.

[0194] In some examples, the geometry of the diffractive features of the transmissive ICG 1714 and / or the reflective ICG 1717 can be symmetric, with straight sidewalls, sloped sidewalls, re-entrant or concave sidewalls, multi-step sidewalls, other types of sidewalls, or some combination thereof. In another example, the geometry can be asymmetric, with at least one straight sidewall, sloped sidewall, re-entrant or concave sidewall, multi-step sidewall, other types of sidewall, or some combination thereof. Regardless of whether the diffractive feature is asymmetric or symmetric, in some implementations, a plateau or flat portion may be located at the top (e.g., peak) of the feature. The grating may have a height and / or depth of 100 nm to 600 nm or heights greater than or less than those defined by the ranges (e.g., 200 to 400 nm, 205 to 350 nm, 210 to 400 nm, 350 to 500 nm, 300 to 600 nm, 400 to 600 nm, 200 to 600 nm, 200 to 500 nm, or any range formed by any of these values). The grating may have a pitch of 290 nm to 690 nm or a pitch greater than or less than those defined by the ranges. If the grating is a blazed grating, the grating may have a blaze angle, measured in the same angular direction, of, for example, about 20 to 85 degrees, and a reverse blaze angle, measured in the same angular direction, of, for example, about 70 to 150 degrees, or any value within the range defined by these values. These angles may represent internal angles measured from the base of the diffraction grating to the corresponding sidewall or surface. Values ​​outside any of these ranges are also possible.

[0195] The transmissive ICG 1714 can include one or more transmissive layers 1715 as described above with reference to FIGS. 14, 15, and 17A. The reflective ICG 1717 can also include one or more metal layers 1711. In some embodiments, the one or more metal layers 1711 can be effective in constructing a grating that is efficient at diffracting TM-polarized light within one or more wavelength ranges. For example, the inclusion of one or more metal layers can provide increased diffraction efficiency for TM-polarized light within the range of wavelengths associated with red (e.g., about 620-780 nm), the range of wavelengths associated with green (e.g., about 492-577 nm), or the range of wavelengths associated with blue (e.g., 435-493 nm). Other designs of diffraction gratings that diffract TM-polarized light or that are efficient at preferentially diffracting TM-polarized light are also possible.

[0196] Advantageously, the combination of a transmissive ICG, which preferentially diffracts TE light as it is guided into the waveguide, and a reflective ICG, which preferentially diffracts TM light as it is guided into the waveguide, provides efficient diffraction and incoupling of both TE and TM polarizations. Thus, this combination of these gratings can more efficiently diffract light, including both TE and TM polarizations, such as unpolarized light, and in the case of ICG, can couple this light into the waveguide. As explained above, in various designs, the diffracted light is within the first order, such as the +1 and / or −1 diffraction orders.

[0197] Thus, light received from a projector, such as an image projector, may be diffracted by one or more gratings 1717, 1714 at an angle or range of angles such that this light from the projector, or at least a portion thereof, is diffracted and coupled into the waveguide and directed therein by total internal reflection, e.g., toward a pupil expander-extractor grating, a light dispersive element, and / or an outcoupling optical element. The geometry of the diffractive features, e.g., asymmetric or blazed, may preferentially direct light in a particular direction, e.g., toward the pupil expander-extractor grating. The pupil expander-extractor grating may be configured to outcouple light from the waveguide into the user's or wearer's eye. The pupil expander-extractor grating may additionally increase the area (in two dimensions) over which light exits the waveguide. In this way, the pupil expander-extractor grating may potentially increase the eyebox in some implementations. In various implementations, the projector outputs unpolarized or circularly polarized light and directs this unpolarized or circularly polarized light to the ICG for input into the waveguide. Some examples of such projectors or light sources that output unpolarized or circularly polarized light and form an image may include, for example, microLEDs and microLED projectors, digital light projectors (DLPs), and liquid crystal on silicon (LCOS)-based projectors, although others are also possible.

[0198] 17C illustrates another exemplary waveguide configured to increase the efficiency of coupling light into it. The waveguide includes at least one reduced polarization sensitivity grating, which can act as an internal coupling optical element. For example, as shown, waveguide 1710 may include at least one internal coupling grating (ICG) 1730 and external coupling gratings 1720, 1722. Gratings 1720, 1722 may include pupil expander-extractor (CPE) regions, which operate as both light dispersive elements and external coupling gratings. For example, light 1702 from a projector including one or more light sources (e.g., microLEDs, lasers, LEDs) may be launched into one side of waveguide 1710 through a transmissive ICG 1730, e.g., including a transmissive grating that diffracts at least a portion of the light transmitted therethrough. The transmissive ICG 1730 passes light 1702 through its grating into the waveguide 1710 and may diffract light 1706 as it propagates through the grating. The transmissive ICG 1730 may be configured to have both high TM and high TE diffraction efficiency. The grating 1730 may be designed to diffract light incident thereon over a range of angles into a direction or within a range of angles that are totally internally reflected within the waveguide. Thus, the light 1706 may be guided or propagated along the waveguide 1710 toward one or more pupil expander-extractor gratings 1720, 1722. Advantageously, the inclusion of the transmissive ICG 1730 can aid in image uniformity and / or eyebox efficiency, depending on the source light (e.g., LED, laser, polarized, or unpolarized).

[0199] The transmissive ICG 1730 may comprise a diffraction grating. The diffraction grating of the transmissive ICG 1730 may be formed in a layer on the waveguide or substrate or within the waveguide or substrate itself, for example, on its surface. The diffraction grating may have diffractive features as described above with reference to FIGS. 12A-12B and 13A-13J. For example, the diffractive features of the diffraction grating may have various dimensions and geometries. For example, the geometry of the diffractive features can be symmetric with straight sidewalls, sloped sidewalls, re-entrant or concave sidewalls, multi-step sidewalls, other types of sidewalls, or some combination thereof. In another example, the geometry can be asymmetric with at least one straight sidewall, sloped sidewall, re-entrant or concave sidewall, multi-step sidewall, other types of sidewall, or some combination thereof. Examples of re-entrant or shark-tail shaped sidewalls can be found in FIG. 13A (e.g., second row, third column) and the third row of FIG. 14. Regardless of whether the diffractive feature is asymmetric or symmetric, in some implementations, a plateau or flat portion may be located at the top (e.g., peak) of the feature. The grating may have a height greater than or less than 100 nm to 600 nm, or a height defined by that range. As described herein, the height may be 100 to 200 nm, 200 to 300 nm, 205 to 310 nm, 210 to 310 nm, 250 to 350 nm, 300 to 400 nm, 400 to 500 nm, 500 to 600 nm, or any range formed by any of these values, and may be outside these ranges. The grating may have a pitch greater than or less than 290 nm to 690 nm, or a pitch greater than or less than that defined by that range. If the grating is a blazed grating, the grating may have a blaze angle, measured in the same angular direction, of, for example, about 20 to 85 degrees, and a counter-blaze angle, for example, about 70 to 150 degrees, or any value within the range defined by these values. As explained above, these angles may represent internal angles measured from the base of the grating to the corresponding sidewall or surface. Values ​​outside any of these ranges are also possible.

[0200] Light received from a projector, such as an image projector (e.g., comprising micro LEDs), may be diffracted by one or more gratings 1730 and directed at an angle or range of angles such that the light, or at least a portion of it, is guided within the waveguide by total internal reflection toward the pupil expander-extractor grating. The geometry of the diffractive features, e.g., asymmetry or blazing, may preferentially direct light toward the pupil expander-extractor grating. The pupil expander-extractor grating may be configured to outcouple light from the waveguide into the user's or wearer's eye. The pupil expander-extractor grating may additionally increase the area (in two dimensions) over which light exits the waveguide. In this way, the pupil expander-extractor grating may potentially increase the eyebox in some implementations. In various implementations, the projector outputs unpolarized or circularly polarized light and directs the unpolarized or circularly polarized light to the ICG for input into the waveguide. Some examples of such projectors that output unpolarized or circularly polarized light and form an image may include, for example, micro-LED projectors, digital light projectors (DLPs), and liquid crystal on silicon (LCOS)-based projectors, although others are also possible.

[0201] The transmissive ICG 1730 can include a high-index grating configured to be efficient in both TM and TE modes. For example, the ICG 1730 can have an ICG profile and / or material composition modified to obtain efficient diffraction that is insensitive to light polarization over a range of light input angles. For example, the ICG 1730 can have a diffraction efficiency in the range of 40 to 90 percent (e.g., 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, or any range between any of these values) or greater for the TE mode, and 40 to 90 percent (e.g., 50% to 60%, 60% to 70%, 70% to 80%, 80% to 90%, or any range between any of these values) or greater for the TM mode. In some embodiments, the ICG 1730 can have similar efficiency in the TE and TM modes. For example, ICG 1730 may have a TM mode efficiency within 5%, 10%, 20%, 25%, or 30% of the TE mode efficiency (or any range between any of these values). Or, ICG 1730 may have a TE mode diffraction efficiency within 5%, 10%, 20%, 25%, or 30% of the TM mode efficiency (or any range between any of these values). Thus, in various implementations, the difference in diffraction efficiency for the TE and TM modes may be 5%, 10%, 20%, 25%, or 30% of the TE mode efficiency (or any range between any of these values). Other examples are also possible. These efficiencies may be average efficiencies over a range of angles (e.g., 5 degrees, 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, or any range between any of these values). Similarly, these efficiencies may possibly be averaged over wavelengths of light in the visible spectrum, or wavelengths or wavelengths for a specific color, e.g., red, blue, or green. For example, wavelengths output by a light source in a projector, which may include multiple colored light sources, may be considered. As explained above, diffraction may occur within a diffraction mode or modes, such as a first order mode, such as the +1 and / or −1 diffraction orders.

[0202] 17D-1-17D-4 illustrate example tilted ICG profiles and compositions and corresponding polarization efficiency graphs that may be used to achieve polarization insensitivity in an internally coupled grating, such as ICG 1730 illustrated in FIG. 17C. For example, grating 1742 may produce TM and TE efficiency profile 1741 shown in the graph, grating 1744 may produce TM and TE efficiency profile 1743 shown in the graph, grating 1746 may produce TM and TE efficiency profile 1745, and grating 1748 may produce TM and TE efficiency profile 1747.

[0203] The grating 1742 illustrated in FIG. 17D-1 may include a grating having tilted diffractive features with a tilt angle of θ. The tilt angle may include an angle between 20 and 85 degrees or another angle. These angles may represent internal angles measured from the base of the grating to the corresponding sidewall or surface. In some embodiments, the duty cycle 1762A of the grating 1742 may be a percentage of the pitch of the grating. For example, the duty cycle may be 20 to 80 percent of the pitch, e.g., 50 percent of the pitch. The height 1764A of the grating may be, for example, 100 to 600 nm (e.g., 100 to 200, 200 to 300, 300 to 400, 400 to 500, 500 to 600 nanometers, or any range between any of these values). Thus, the height may be greater than, or within any range formed by any of these values, such as greater than 200 nm, 205 nm, 300 nm, 400 nm, 500 nm, 600 nm, or greater than 700 nm or 800 nm. In some embodiments, the grating 1742 may be disposed on a layer on the waveguide or substrate or within a portion of the waveguide or substrate itself (e.g., etched into the surface of the substrate). In some embodiments, the substrate may be a material having a refractive index less than 1.9, such as a refractive index in the range of 1.65 to 1.75. Similarly, the refractive index of the substrate may, in some implementations, be less than 1.4 to 1.5, 1.5 to 1.6, 1.6 to 1.7, 1.7 to 1.8, and / or 1.8 to 1.9, or within any range formed by any of these values. In some embodiments, the grating feature may comprise a material with a similar or identical refractive index as the substrate or waveguide. In the illustrated embodiment, grating 1742 comprises diffractive features having a refractive index of 1.75 on a substrate having a refractive index of 1.75. The materials used to form the diffractive features and to construct the substrate may be the same or different. The diffractive features may be etched into the substrate, or a layer of material having the same or a different (e.g., higher or lower) refractive index may be used for the diffractive features. For example, the substrate may have a lower refractive index than the material forming the diffractive features.In some cases, for example, the substrate has a refractive index less than 1.9, while the diffractive features have a refractive index greater than 1.9, or greater than 2.0 or 2.1, or 2.2 or 2.4 or 2.6 or 2.7, for example, or within any range formed by any of these values. Values ​​outside these ranges are also possible. In some embodiments, grating 1742 may be produced using a high refractive index resist and contact imprinting, or by depositing a high refractive index material and etching into the layer of material.

[0204] The TM and TE diffraction efficiency profiles (1750, 1752, respectively) associated with grating 1742 may be approximately matched over a range of incidence angles, as shown in graph 1743, and / or may be more efficient in TE and more efficient in TM at points within a range of incidence angles. In some embodiments, the average diffraction efficiency may be 40% to 60%, or 0.4 to 0.6, or at least 0.45, or 0.5, or 0.6, or 0.7, or 0.8, or 0.9, or 0.95, or 0.99 (e.g., having an average efficiency of at least 45%, 50%, 55%, 60%, 65%, 70%, 80%, 90%, 95%, or 99%, or any range formed by any of these values) over a range of angles of incidence, such as -10 degrees to 10 degrees, or over a wider or smaller range (e.g., at least 6 degrees, at least 10 degrees, 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, or any range between any of these values). In some embodiments, the diffraction efficiency averages at least 0.4 (or at least 0.45 or at least 0.50 or at least 0.55 or at least 0.6 or at least 0.65 or at least 0.7 or at least 0.8 or at least 0.9) over a range of light incidence angles of at least 30 degrees or other range of angles (e.g., at least 3 degrees, at least 6 degrees, at least 10 degrees, at least 12 degrees, at least 18 degrees, at least 20 degrees, 25 degrees, 30 degrees, 35 degrees, 40 degrees, or any range between any of these values). In some embodiments, the diffraction efficiency averages at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 over a range of light incidence angles of at least 20 degrees, or over a range of light incidence angles of at least 10 degrees. In some embodiments, the diffraction efficiency averages at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9. In some embodiments, the diffraction efficiency is at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 over a range of light incidence angles of at least 30 degrees.In some embodiments, the diffraction efficiency is at least 0.4, 0.5, 0.6, 0.7, or 0.8 over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.4, 0.5, 0.6, 0.7, or 0.8 over a range of angles of incidence of light of at least 10 degrees. The diffraction efficiency may be within any range between any of these values ​​over any of these angular ranges, or possibly over other, larger angular ranges as well. Similarly, as explained above, the average diffraction efficiency over a range of wavelengths may be within 30%, 25%, 20%, 15%, 10%, 5%, 2.5%, 1%, or any range formed by any of these values ​​over a range of angles such as 3°, 6°, 12°, 18°, 20°, 25°, 30°, 35°, 40°, or any range formed by any of these values. The diffraction efficiency may be higher for the TE mode in some designs, or higher for the TM mode in some designs. In some designs, the diffraction efficiency may be higher at some angles for the TE mode and at other angles for the TM mode.

[0205] The average diffraction efficiency may be increased using a higher refractive index material (e.g., a material with a refractive index greater than 2), as illustrated in grating 1744 of FIG. 17D-2. Grating 1744 includes a tilted grating with a geometry and features with diffractive features similar to that described with reference to FIG. 17D-1, but made of a higher refractive index material 1766, such as a 2.2 refractive index material such as TiO or a 2.6 refractive index material such as SiC. The resulting TM and TE efficiency profiles (1750, 1752, respectively) may closely match (e.g., within 30%, 20%, 15%, 10%, 8%, 5%, etc.) over a range of incidence angles, and / or may be more efficient in TE and more efficient in TM (or vice versa) at points within a range of incidence angles, as illustrated in graph 1745. In some embodiments, the average diffraction efficiency may have a peak of about 80% to 100%, or 0.8 to 0.1, over a range of incident angles from -10 degrees to 10 degrees. In some embodiments, the average diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of incident angles of light of at least 10, 20, 30, 40, 50, or 60 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of incident angles of light of at least 40 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of incident angles of light of at least 30 degrees. In some embodiments, the diffraction efficiency averages at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of light incidence angles of at least 20 degrees.In some embodiments, the diffraction efficiency is, on average, at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 10 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 10 degrees.

[0206] Similar to grating 1742, grating 1744, as illustrated in FIG. 17D-2, may include a grating having tilted diffractive features with a tilt angle of θ. The tilt angle may include an angle of 20 to 85 degrees or another angle. One side or sidewall is re-entrant, and the cross section has a sharktail shape. The cross section is in the shape of a tilted parallelogram, although other shapes are also possible. In some embodiments, the duty cycle 1762B of grating 1744 may be a percentage of the pitch of the grating. For example, the duty cycle may be 20 to 80 percent of the pitch, e.g., 50 percent of the pitch. The height 1764B of the grating may be, for example, 100 to 600 nm (e.g., 100 to 300, 200 to 400, 300 to 500, 400 to 600 nanometers, or any range between any of these values). In various implementations, the height or depth may similarly be greater than 200 nm, 205 nm, 210 nm, 250 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or any range between or outside any of these values. In some embodiments, the grating 1744 may be disposed on a layer above the waveguide or substrate, or may be part of or incorporated into the waveguide or substrate itself, for example, by etching into the substrate. In some embodiments, the substrate may comprise a material having a refractive index less than 2 or less than 1.9, such as a refractive index of 1.75. In some embodiments, the grating feature may comprise a material with a refractive index greater than that of the substrate or waveguide. In the illustrated embodiment, the grating 1744 comprises diffractive features having a refractive index of 2.2 on a substrate having a refractive index of 1.75. Values ​​outside these ranges are also possible. In some embodiments, the grating 1744 may be produced using a high refractive index resist and contact imprinting. In some embodiments, grating 1744 may be created using tilted etching, such as angled directional etching. Materials that etch preferentially in certain directions may also be employed. Some exemplary methods of etching are described in connection with Figures 13H-13J. Other methods may also be employed.Figure 13H illustrates a method for fabricating a blazed (asymmetric) diffractive feature (3803) having, for example, a sawtooth-shaped pattern with first and second sloping sidewalls sloping in opposite directions. Figure 13I illustrates a method for fabricating a blazed (asymmetric) diffractive feature (3853) having, for example, a "sharktail"-shaped cross-section with first and second sloping sidewalls sloping in the same direction. The second sidewall in Figure 13I is an example of a re-entrant sidewall or surface. Figures 17D-1-17D-4 also illustrate first and second sloping sidewalls with a second sidewall sloping in the same direction that is a re-entrant sidewall or surface. Other types of gratings with other refractive indices and material compositions are also possible.

[0207] However, contact imprinting as a mode of fabrication may be advantageous over etching due to improved efficiency and ease of fabrication. Therefore, it may be desirable to use a suitable material for use with contact imprinting techniques to produce ICG. For example, gratings 1746 and 1748 include an ICG profile with a refractive index of 1.65.

[0208] Grating 1746 includes a tilted grating with a material having a refractive index less than 2, or 1.9, or less than 1.8, e.g., 1.65, and a coating deposited on the edges of the grating using a material having a refractive index greater than 1.9 or 2, such as a material with a refractive index of 2.2, such as TiO2, or a material with a refractive index of 2.6, such as SiC. The resulting TM and TE efficiency profiles (1750 and 1752, respectively) may closely or nearly match over a range of incidence angles, as illustrated in graph 1745, and / or may be more efficient in TE and more efficient in TM at points or on average within a range of incidence angles. In some embodiments, the average diffraction efficiency may peak at about 80% to 100%, or 0.8 to 0.1, over a range of incidence angles from -10 degrees to 10 degrees. In some embodiments, the diffraction efficiency is at least 0.8 on average over a range of incidence angles of light of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.8 on average over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.8 on average over a range of angles of incidence of light of at least 10 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of angles of incidence of light of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of angles of incidence of light of at least 10 degrees.

[0209] In some embodiments, the average diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 3, 6, 10, 12, 18, 20, 30, 40, 50, or 60 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 40 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of angles of incidence of light of at least 20 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of angles of incidence of light of at least 10 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 10 degrees.

[0210] Grating 1748 also includes a blazed grating having a refractive index less than 2, or less than 1.9 or 1.8, e.g., 1.65, and a coating deposited on the edges of the grating using a material with a refractive index greater than 1.9 or 2, such as a material with a refractive index of 2.2, such as TiO2, or a material with a refractive index of 2.6, such as SiC. The resulting TM and TE efficiency profiles (1750 and 1752, respectively) may closely or nearly match over a range of incident angles, as illustrated in graph 1747, and / or may be more efficient in TE and more efficient in TM at points within a range of incident angles. In some embodiments, the average diffraction efficiency may peak at about 80% to 100%, or 0.8 to 0.1, over a range of incident angles from -10 degrees to 10 degrees. In some embodiments, the diffraction efficiency averages at least 0.8 over a range of incident angles of light of at least 30 degrees. In some embodiments, the diffraction efficiency averages at least 0.8 over a range of incident angles of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.8 on average over a range of light incident angles of at least 10 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of light incident angles of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of light incident angles of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.8 over a range of light incident angles of at least 10 degrees.

[0211] In some embodiments, the average diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 3, 6, 10, 12, 18, 20, 30, 40, 50, or 60 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 40 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, on average over a range of light incidence angles of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of angles of incidence of light of at least 20 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, on average, over a range of angles of incidence of light of at least 10 degrees, or any range formed by any of these values. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 30 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.5 or 0.6, or 0.7 or 0.8 or 0.9 or 0.95, or any range formed by any of these values, over a range of angles of incidence of light of at least 10 degrees.

[0212] Additionally, as explained above, the average diffraction efficiency over a range of wavelengths may be 30%, 25%, 20%, 15%, 10%, 5%, 2.5%, 1%, or within any range formed by any of these values ​​over a range of angles such as 3°, 6°, 12°, 18°, 20°, 25°, 30°, 35°, 40°, or any range formed by any of these values. In some designs, the diffraction efficiency may be higher for the TE mode, or in some designs, higher for the TM mode. In some designs, the diffraction efficiency may be higher at some angles for the TE mode and at other angles for the TM mode. As illustrated in Figures 17D-3 and 17D-4, an ICG such as grating 1746 or grating 1748 may include a tilted or sharktail grating, a blazed grating, or other geometric shapes. If the grating is a tilted grating, such as grating 1746, the grating may have a tilt angle, which may include, but is not limited to, an angle of 20 to 70 degrees or another angle. If the grating is a blazed grating, such as grating 1748, the grating may have a blaze angle of approximately 20 to 85 degrees (shallow side) and a reverse blaze angle (steep side) of 70 to 150 degrees, or any value within the range defined by these values, measured in the same angular direction. These angles may represent internal angles measured from the base of the grating to the corresponding sidewall or surface.

[0213] Also, as described above, various methods may be employed to fabricate the diffractive features. In some implementations, imprinting may be employed cost-effectively to form the diffractive features from a layer of polymer, possibly disposed on a substrate. An imprint template may contact the polymer layer, which may in some cases be cured using UV and / or thermal curing. Some exemplary methods of etching are also described in connection with Figures 13H-13J.

[0214] Additionally, the high refractive index material deposited on the grating feature may be biased, for example, using grazing incidence angle deposition, to provide more material on one side of the grating feature than on the other. Thus, thickness and / or coverage may be greater on a first sidewall on one side of the grating feature than on a second sidewall on the opposite side of the grating feature. In some implementations, potentially, there may be little coverage on one sidewall. For example, 90% or 95% of the second sidewall may not be covered. In some cases, deposition on a tilted diffractive feature (e.g., directional deposition) may result in a bias such that more or thicker coverage is provided on the first sidewall or side of the diffractive feature, while little is deposited on the second sidewall or side of the diffractive feature. In some cases, the topography of the underlying diffractive feature may facilitate passive bias deposition, as illustrated in FIG. 14 , for example, the second and third columns of the third row. Potentially, linear or angled directional etching, when used to deposit material onto a diffractive feature having a reentrant surface or sidewall (such as the left sidewall in the diffractive feature shown in row 3 of Figure 14), may result in little coverage on the reentrant sidewall or surface.

[0215] With reference to grating 1746, duty cycle 1778 of grating 1746 may be a percentage of the pitch of the grating. For example, the duty cycle may be 20 to 80 percent of the pitch, such as 50 percent of the pitch. Grating height 1774 may be, for example, 10 to 600 nm. In some embodiments, grating 1746 may be disposed on a substrate or waveguide, or may be part of the waveguide itself. In some embodiments, the substrate may be a material having a refractive index of 1.75. In some embodiments, the grating features may include a material with a refractive index different from the refractive index of the substrate or waveguide. In the illustrated embodiment, grating 1746 comprises diffractive features 1770 having a refractive index of 1.65 on a substrate having a refractive index of 1.75. Values ​​outside these ranges are also possible. In some embodiments, material 1772 may be deposited on diffractive features 1770. Material 1772 may have a higher refractive index than diffractive features 1770. For example, material 1772 may have a refractive index of 2.2. Other values ​​are also possible. The thickness 1776 of the material 1772 may be between about 10 and 600 nm or another value.

[0216] With reference to grating 1748, the width at the top (WT) of blazed grating feature 1780 can be greater than the width at the base (WB) of blazed grating 1784. In some embodiments, WT may be varied or may be zero. In some embodiments, WB may be varied. For example, WB may be wide enough to allow at least partial filling of the bottom width by the high refractive index coating. For example, WB may be wide enough to allow more than 50% of the width to be filled by the high refractive index coating. In some embodiments, the high refractive index coating may be applied using bias deposition such that the coating is preferentially deposited on the first sidewall over the second sidewall (e.g., a re-entrant sidewall, a vertical sidewall, or a more sloped sidewall). Advantageously, in some cases, this bias deposition may improve the overall average TM and TE efficiency.

[0217] Grating height 1782 may be, for example, 100-600 nm. In some embodiments, grating 1748 may be disposed on a substrate or waveguide, or may be part of the waveguide itself. In some embodiments, the substrate may be a material having a refractive index of 1.75. In some embodiments, the grating features may include a material with a refractive index different from that of the substrate or waveguide. In the illustrated embodiment, grating 1746 comprises diffractive features 1770 having a refractive index of 1.65 on a substrate having a refractive index of 1.75. Values ​​outside these ranges are also possible. In some embodiments, material 1772 may be deposited on diffractive features 1770. Material 1772 may have a higher refractive index than diffractive features 1770. For example, material 1772 may have a refractive index of 2.2. Other values ​​are also possible. Thickness 1786 of material 1772 may be approximately 100-600 nm or another value. Other values ​​outside these ranges are also possible.

[0218] As discussed above, in some embodiments, grating 1744 may be created using high refractive index resist and contact imprinting. In some embodiments, grating 1744 may be created using angled etching. Other types of gratings, involving other material compositions with other refractive indices, are also possible.

[0219] Advantageously, gratings such as blazed gratings with a 2.2 refractive index coating as discussed with reference to grating 1748 may have improved average diffraction efficiency and polarization insensitivity, and potentially greater manufacturability than other designs. Advantageously, ICGs such as those described with reference to FIGS. 17C and 17D-3-17D-4 can be used in conjunction with unpolarized light sources (e.g., microLED sources) in transmissive mode and in series within a waveguide stack as described above with reference to FIG. 6. This capability may enable eyepieces utilizing ICGs to have increased brightness and / or field of view. For example, more than one color of incident light may interact with each ICG at each waveguide color within the stack, which may be advantageous over conventional ICGs with high TM efficiency that are opaque and highly reflective and therefore may be spatially offset, allowing incident light to pass through each waveguide.

[0220] Similar to the waveguides shown in Figures 17A and 17B, a pair of serial (matched) ICGs or diffraction gratings with increased polarization insensitivity may be included on opposite sides of the waveguide. One of the ICGs may be a transmissive grating, and the other may be a reflective ICG. Thus, light from an image projector may be directed toward the transmissive ICG on the proximal surface of the waveguide. At least a portion of this light will be diffracted by the transmissive ICG and redirected into the waveguide at an angle such that the light is guided within the waveguide by total internal reflection. This light may be, for example, in the first diffraction order. Other light that is not diffracted, for example, in the zeroth order, may continue forward and be incident on a reflective ICG that is matched with the transmissive ICG. At least a portion of the light incident on the reflective ICG may be diffracted and thereby coupled into the waveguide and guided therein by total internal reflection. Again, in some implementations, this diffracted light corresponds to the first diffraction order of the reflective diffraction grating. In some implementations, a transmissive diffraction grating or ICG, for example, as shown in Figures 17D-1, 17D-2, 17D-3, and 17D-4, may be used. As discussed, such a grating may have reduced polarization sensitivity and increased diffraction efficiency for both TE and TM modes. Similarly, light not diffracted by the transmissive grating may be incident on a reflective ICG and diffracted into the waveguide at an angle such that at least a portion of this light is guided within the waveguide by total internal reflection. In some implementations, a reflective diffraction grating or ICG, for example, as shown in Figure 11B, may be used. As discussed, such a grating may have reduced polarization sensitivity and increased diffraction efficiency for both TE and TM modes. Such an arrangement of serial (or matched) diffraction gratings or ICGs can increase the efficiency of coupling light, such as unpolarized light, from the projector into the waveguide and eyepiece, thus potentially providing increased brightness to the viewer. Additionally, the use of two ICGs can help reduce brightness and color non-uniformity.

[0221] FIG. 18 illustrates how a transmissive ICG, such as transmissive ICG 1714 discussed with reference to FIGS. 17A and 17B, can be configured to reduce reflections and thereby potentially increase the brightness of light output by a waveguide to a user / viewer. For example, as illustrated in FIG. 18, transmissive ICG 1801 can receive light 1802 through the side of ICG 1801 that is exposed to air. Zero-order reflections of light 1804 can result in undesired reflection losses of light 1802 that arise from grating 1801, pass through one or more transmissive layers 1822, diffract into ICG 1820, and enter waveguide 1818.

[0222] Reflection losses can be reduced in the first ICG 1714 when the transmissive layer 1822 comprises one or more sublayers 1824, 1826, as discussed above. For example, as illustrated in FIG. 18 , the transmissive ICG 1803 can include a transmissive layer 1822 with one or more sublayers. The one or more sublayers can include one or more high-index sublayers 1826, such as TiO 2 , and one or more low-index sublayers 1824, such as SiO 2 . In such a configuration, the zero-order reflected light 1804 can be reduced. As discussed above, in some implementations, the sublayers 1824, 1826 or additional sublayers can comprise interference coatings, such as quarter-wave stacks. In some examples, this configuration can also reduce the first diffraction order of light 1806 in the ICG 1803. However, reducing reflection losses into the ICG, through the substrate, and towards the second ICG can improve image quality, for example, by increasing eyebox efficiency and reducing artifacts such as ghosting or coherent artifacts within the waveguide stack.

[0223] Additionally or alternatively, reflection losses can be reduced by including a material 1828 having a refractive index between that of air and one or more transmissive layers 1822 of the first ICG 1714. For example, as illustrated in FIG. 18 , the transmissive ICG 1805 can include a material 1828 having a refractive index similar to that of the ICG base pattern 1820. For example, the material 1828 may have a refractive index in the range of 1.3 to 1.5. The material 1828 can help reduce zero-order reflections 1808. In some embodiments, this configuration can also reduce the first diffraction order of light 1806 within the ICG 1803. However, an overall reduction in reflection losses can improve image quality, for example, through increased eyebox efficiency and reduced artifacts such as ghosting or coherent artifacts within the waveguide stack.

[0224] B. Additional Examples Additional Examples - Part I Example 1: A head mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by a frame, the waveguide comprising a substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide; a first diffraction grating over the substrate, the first grating comprising a material different from the substrate; a first layer disposed over the first diffraction grating; a second layer including a metal disposed over the first diffraction grating such that the 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 between 1 and 2 times the second diffraction efficiency; A head-mounted display system comprising:

[0225] Example 2: The head mounted display system of example 1, wherein the substrate comprises a lithium-based oxide.

[0226] Example 3: The head mounted display system of example 1 or 2, wherein the substrate comprises lithium niobate.

[0227] Example 4: The head mounted display system of example 1, wherein the substrate comprises silicon carbide.

[0228] Example 5: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 1.9.

[0229] Example 6: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.0.

[0230] Example 7: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.1.

[0231] Example 8: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.2.

[0232] Example 9: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.3.

[0233] Example 10: A head mounted display system according to any of the previous examples, wherein the first grating material comprises a polymer.

[0234] Example 11: A head mounted display system according to any of the previous examples, wherein the first grating material comprises an imprintable material.

[0235] Example 12: A head mounted display system according to any of the previous examples, wherein the first diffraction grating material has a refractive index between 1.4 and 1.95.

[0236] Example 13: A head mounted display system according to any of the previous examples, wherein the first grating material has a lower refractive index than the substrate.

[0237] Example 14: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a blazed diffraction grating.

[0238] Example 15: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises diffractive features comprising peaks spaced apart by grooves therebetween.

[0239] Example 16: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature comprising a plurality of straight lines.

[0240] Example 17: A waveguide according to any of the preceding examples, wherein the diffraction grating comprises diffractive features that are asymmetric.

[0241] Example 18: The head-mounted display system of any of the preceding examples, wherein the first layer comprises titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0242] Example 19: The head mounted display system of any of the previous examples, wherein the first layer comprises titanium dioxide (TiO2).

[0243] Example 20: The head mounted display system of any of the previous examples, wherein the first layer comprises zirconium dioxide (ZrO2).

[0244] Example 21: The head mounted display system of any of the previous examples, wherein the first layer comprises silicon carbide (SiC).

[0245] Example 22: A head-mounted display system as described in any of the above examples, wherein the first layer comprises a plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0246] Example 23: The head-mounted display system of Example 22, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0247] Example 24: The head-mounted display system of Example 22 or 23, wherein the plurality of sub-layers comprises only two sub-layers.

[0248] Example 25: The head-mounted display system of Example 22 or 23, wherein the plurality of sub-layers comprises at least four sub-layers.

[0249] Example 26: A head mounted display system according to any of Examples 22-25, wherein the plurality of sub-layers alternate between the first material and the second material.

[0250] Example 27: The head mounted display system of any of Examples 22-26, wherein the plurality of sub-layers comprises an interference coating.

[0251] Example 28: A head-mounted display system according to any of Examples 22-27, wherein the plurality of sub-layers comprises a quarter-wave stack.

[0252] Example 29: The head-mounted display system of any of the preceding examples, wherein the metal comprises aluminum, silver, gold, or copper.

[0253] Example 30: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations having different polarization angles.

[0254] Example 31: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations oriented in orthogonal directions.

[0255] Example 32: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise transverse magnetic and transverse electric polarizations, respectively.

[0256] Example 33: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise transverse electric and transverse magnetic polarizations, respectively.

[0257] Example 34: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0258] Example 35: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0259] Example 36: A head mounted display system according to any of the preceding examples, wherein the first diffraction efficiency is 1 to 1.5 times the second diffraction efficiency.

[0260] Example 37: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.4 times the second diffraction efficiency.

[0261] Example 38: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.3 times the second diffraction efficiency.

[0262] Example 39: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.2 times the second diffraction efficiency.

[0263] Example 40: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.1 times the second diffraction efficiency.

[0264] Example 41: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 6 degrees.

[0265] Example 42: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 12 degrees.

[0266] Example 43: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 18 degrees.

[0267] Example 44: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 22 degrees.

[0268] Example 45: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±3 degrees relative to the plane of the substrate.

[0269] Example 46: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±6 degrees relative to the plane of the substrate.

[0270] Example 47: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±9 degrees relative to the plane of the substrate.

[0271] Example 48: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±11 degrees relative to the plane of the substrate.

[0272] Example 49: A head-mounted display system described in any of the above examples, wherein the waveguide is included within an eyepiece configured to direct light to the eye of a user wearing the head-mounted display.

[0273] Example 50: A head-mounted display system as described in Example 49, wherein the eyepiece is positioned on a 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, at least a portion of the eyepiece is transparent and is positioned in front of the user's eye when the user wears the head-mounted display system, and the transparent portion allows 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.

[0274] Example 51: A head-mounted display system as described in Example 49 or 50, wherein the eyepiece lens comprises at least one waveguide, and the at least one waveguide is transparent to visible light so that a user can see through the waveguide.

[0275] Example 52: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an internal coupling optical element for coupling light from the optical projection system into the waveguide so that it is guided therein.

[0276] Example 53: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an external coupling optical element for coupling light from the optical projection system out of the waveguide, directing the light to a user's eye, and presenting the image content to a viewer.

[0277] Example 54: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an external coupling grating (EPE) configured to externally couple light from the optical projection system guided within the waveguide out of the waveguide.

[0278] Example 55: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an internal coupling grating (ICG) configured to internally couple light from the optical projection system into the waveguide.

[0279] Example 56: A head-mounted display system according to any of the preceding examples, wherein the second layer is configured to be disposed over the first layer.

[0280] Example 57: A head-mounted display system according to any of the preceding examples, further comprising a third layer disposed between the first layer and the second layer.

[0281] Example 58: A head-mounted display system as described in Example 57, wherein a third layer is configured to help join the second layer to the first layer.

[0282] Example 59: a second diffraction grating disposed over the substrate, the second diffraction grating comprising a different material than the substrate; A head-mounted display system as described in any of the above examples, comprising: a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for the first polarization over a range of angles of light incident thereon; wherein the first diffraction grating is disposed over the substrate on a first side thereof and the second diffraction grating is disposed over the substrate on a second side thereof opposite the first side thereof.

[0283] Example 60: A head-mounted display system according to any of the preceding examples, wherein the first layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0284] Example 61: A head mounted display system according to any of the previous examples, wherein the first layer is directionally deposited at an angle that lies on the one or more diffractive features.

[0285] Example 62: A head-mounted display system as described in Example 61, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0286] Example 63: A head-mounted display system as described in Example 61, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0287] Example 64: A head-mounted display system according to any of the preceding examples, wherein the second layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0288] Example 65: A head-mounted display system according to any of the preceding examples, wherein the second layer is directionally deposited at an angle that is on one or more diffractive features of the first diffraction grating.

[0289] Example 66: A head-mounted display system as described in Example 65, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0290] Example 67: A head-mounted display system as described in Example 65, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0291] Example 68: A head-mounted display system as described in any of the above examples, wherein the first diffraction grating comprises diffractive features formed in a 1D array.

[0292] Example 69: A head-mounted display system described in any of Examples 1-68, wherein the first diffraction grating comprises diffractive features formed in a 2D array.

[0293] Example 70: A head-mounted display system as described in Example 69, wherein the 2D array comprises a square array.

[0294] Example 71: A head-mounted display according to any of the above examples, wherein the diffractive features are asymmetric so as to provide a blazed grating.

[0295] Example 72: A head-mounted display as described in any of the previous examples, wherein the diffractive features have material asymmetrically deposited thereon to provide a blazed grating.

[0296] Example 73: A head-mounted display described in any of the above examples, wherein the first diffraction grating is configured to preferentially direct light in at least two directions.

[0297] Example 74: A head-mounted display according to any of the preceding examples, wherein the first diffraction grating is blazed in two directions.

[0298] Example 75: A head-mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a one-dimensional grating.

[0299] Example 76: A head-mounted display system described in any of Examples 1-75, wherein the first diffraction grating comprises a two-dimensional grating.

[0300] Example 77: a second diffraction grating disposed over the substrate, the second diffraction grating comprising a different material than the substrate; a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for the first polarization over a range of angles of light incident thereon and a fourth diffraction efficiency for the second polarization over the range of angles of light incident thereon; a first diffraction grating disposed across the substrate on a first side thereof and a second diffraction grating disposed across the substrate on a second side thereof opposite the first side thereof.

[0301] Example 78: a second diffraction grating formed in the substrate; and a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for the first polarization over a range of angles of light incident thereon and a fourth diffraction efficiency for the second polarization over the range of angles of light incident thereon; a first diffraction grating disposed across the substrate on a first side thereof and a second diffraction grating disposed across the substrate on a second side thereof opposite the first side thereof.

[0302] Example 79: A head-mounted display system described in any of the above examples, wherein the substrate is configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide via the second diffraction grating.

[0303] Example 80: A head-mounted display system described in any of the above examples, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon exceeds the fourth diffraction efficiency for the second polarization over a range of angles of light incident thereon.

[0304] Example 81: A head mounted display system according to any of the preceding examples, wherein the third diffraction efficiency is at least six times the fourth diffraction efficiency over the range of angles.

[0305] Example 82: A head-mounted display system described in any of the above examples, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon is less than the fourth diffraction efficiency for the second polarization over a range of angles of light incident thereon.

[0306] Example 83: A head mounted display system according to any of the preceding examples, wherein the fourth diffraction efficiency is at least six times the third diffraction efficiency over the range of angles.

[0307] Example 84: A head-mounted display system according to any of the preceding examples, wherein the fourth layer comprises a dielectric.

[0308] Example 85: A head-mounted display system according to any of the preceding examples, wherein the substrate comprises a material having a refractive index of 2.6 or less.

[0309] Example 86: A head-mounted display system according to any of the preceding examples, wherein the substrate comprises a material having a refractive index of 2.7 or less.

[0310] Example 87: A head-mounted display system according to any of the preceding examples, wherein the substrate comprises a material having a refractive index of 2.8 or less.

[0311] Example 88: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a dielectric.

[0312] Example 89: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 1.9 or greater.

[0313] Example 90: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 2.0 or greater.

[0314] Example 91: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 2.1 or greater.

[0315] Example 92: A head-mounted display system described in any of the above examples, further comprising a plurality of sub-layers over the first layer, the plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0316] Example 93: A head-mounted display system as described in Example 92, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0317] Example 94: A head-mounted display system as described in Example 92 or 93, wherein the plurality of sub-layers comprises only two sub-layers.

[0318] Example 95: A head-mounted display system as described in Example 92 or 93, wherein the plurality of sub-layers comprises at least four sub-layers.

[0319] Example 96: A head-mounted display system described in any of Examples 92-95, wherein the multiple sub-layers alternate between a first material and a second material.

[0320] Example 97: A head-mounted display system as described in any of Examples 92-96, wherein the plurality of sub-layers comprises an interference coating.

[0321] Example 98: A head-mounted display system described in any of Examples 92-97, wherein the plurality of sub-layers comprises a quarter-wave stack.

[0322] Example 99: A head-mounted display system described in any of Examples 92-98, wherein multiple sub-layers across the first layer form a bandpass filter.

[0323] Example 100: A head-mounted display system described in any of Examples 92-98, wherein multiple sub-layers across the first layer form a notch filter.

[0324] Example 101: A head-mounted display system described in any of Examples 92-98, wherein multiple sub-layers over the first layer form an anti-reflective (AR) coating.

[0325] Example 102: A head-mounted display system according to any of Examples 92-101, wherein the first lower refractive index material has a refractive index of 1.6 or less.

[0326] Example 103: A head-mounted display system as described in any of Examples 92-102, wherein the second, higher refractive index material has a refractive index of 1.9 or greater.

[0327] Example 104: A head-mounted display system described in any of Examples 92-103, wherein the first lower refractive index material comprises silicon dioxide.

[0328] Example 105: A head-mounted display system according to any of Examples 92-104, wherein the second higher refractive index material comprises titanium dioxide.

[0329] Example 106: A head mounted display system according to any of Examples 92-104, wherein the second higher refractive index material comprises zirconium dioxide.

[0330] Example 107: A head-mounted display system as described in any of Examples 92-104, wherein the second higher refractive index material comprises zinc oxide.

[0331] Example 108: A head-mounted display system described in any of the above examples, wherein the first diffraction grating has an average diffraction efficiency for the first polarization over the range of angles, and the second diffraction efficiency has an average diffraction efficiency for the second polarization over the range of angles.

[0332] Example 109: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 40%.

[0333] Example 110: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 50%.

[0334] Example 111: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 60%.

[0335] Example 112: A head-mounted display system according to any of the preceding examples, wherein the range of angles is at least 25 degrees.

[0336] Example 113: A head-mounted display system according to any of the preceding examples, wherein the range of angles is at least 30 degrees.

[0337] Example 114: A head-mounted display system according to any of the preceding examples, wherein the range of angles is at least 35 degrees.

[0338] Example 115: A head-mounted display system according to any of the previous examples, wherein the range of angles is at least 40 degrees.

[0339] Example 116: A head-mounted display system according to any of the above examples, wherein the angle range is between ±15 degrees relative to the plane of the substrate.

[0340] Example 117: A head-mounted display system described in any of the above examples, wherein the angle range is between ±18 degrees relative to the plane of the substrate.

[0341] Example 118: A head-mounted display system described in any of the above examples, wherein the angle range is between ±20 degrees relative to the plane of the substrate.

[0342] Example 119: A head-mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature having first and second side walls.

[0343] Example 120: A head-mounted display system as described in Example 119, wherein the first and second side walls are separated by a flat area.

[0344] Example 121: A head-mounted display system as described in Example 119, wherein the first and second side walls join to form a significant angle at the top of the diffractive feature.

[0345] Example 122: A head-mounted display system described in any of Examples 119-121, wherein at least the first side wall is inclined at an angle such that the first side wall is not as steep as the second side wall.

[0346] Example 123: A head-mounted display system described in any of Examples 119-122, wherein the first side wall is wider than the second side wall.

[0347] Example 124: A head-mounted display system described in any of Examples 119-123, wherein the first side wall forms an angle of 45° to 85° with the base of the diffractive feature.

[0348] Example 125: A head-mounted display system described in any of Examples 119-124, wherein the second side wall forms an acute re-entrant angle at the base of the diffractive feature.

[0349] Example 126: A head-mounted display system described in any of Examples 119-125, wherein the first diffraction grating has shark-tail shaped diffraction features.

[0350] Example 127: A head-mounted display system described in any of Examples 119-124, wherein the second side wall forms an obtuse re-entrant angle at the base of the diffractive feature.

[0351] Example 128: A head-mounted display system described in any of Examples 119-124, wherein the second side wall is vertical.

[0352] Example 129: A head-mounted display system described in any of Examples 119-124 or 127-128, wherein the first diffraction grating has sawtooth-shaped diffractive features.

[0353] Example 130: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a biased deposition.

[0354] Example 131: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a grazing angle deposition.

[0355] Example 132: A head-mounted display system described in any of Examples 119-131, wherein the first layer is biased to provide more coverage on the first sidewall than on the second sidewall.

[0356] Example 133: A head-mounted display system described in any of Examples 119-132, wherein the first layer covers a greater proportion of the first sidewall than the second sidewall.

[0357] Example 134: A head-mounted display system described in any of Examples 119-133, wherein the first layer is biased to provide a thicker coating on the first sidewall than on the second sidewall.

[0358] Example 135: A head-mounted display system described in any of Examples 119-134, wherein the first layer provides an averagely thicker coating on the first sidewall than on the second sidewall.

[0359] Example 136: A head-mounted display system described in any of Examples 119-135, wherein the first side wall is completely covered by the second layer.

[0360] Example 137: A head-mounted display system described in any of Examples 119-136, wherein at least a portion of the second side wall is not covered by the first layer.

[0361] Example 138: A head-mounted display system described in any of Examples 119-137, wherein the second sidewall includes an area not covered by the first layer that is greater than the first sidewall.

[0362] Example 139: A head-mounted display system described in any of Examples 119-138, wherein the second layer comprises a conformal deposition.

[0363] Example 140: A head-mounted display system described in any of Examples 119-139, wherein the first and second side walls are completely covered by the second layer.

[0364] Example 141: A head-mounted display system described in any of Examples 119-140, wherein the second layer is not biased to cover more of the first sidewall than the second sidewall.

[0365] Example 142: A head-mounted display system described in any of Examples 119-141, wherein the second layer does not provide a thicker coating on the first sidewall than on the second sidewall.

[0366] Example 143: A head-mounted display system described in any of Examples 119-142, wherein the second layer does not provide an averagely thicker coating on the first sidewall than on the second sidewall.

[0367] Example 144: A head-mounted display system described in any of Examples 119-143, wherein the second side wall is entirely covered by the second layer.

[0368] Example 145: A head-mounted display system described in any of Examples 119-144, wherein the second sidewall does not include more area not covered by the second layer than the first sidewall.

[0369] Example 146: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency for the first polarization is within 20% of the second diffraction efficiency for the second polarization.

[0370] Example 147: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency for the first polarization is within 30% of the second diffraction efficiency for the second polarization.

[0371] Example 148: A head-mounted display system described in any of the above examples, wherein the first diffraction grating on which the first and second layers are formed comprises a reflective diffraction grating.

[0372] Example 149: A head-mounted display system described in any of the above examples, wherein the first and second layers are formed on a first diffraction grating that is configured to diffract reflected light and couple the light into the waveguide so that it is guided therein by total internal reflection.

[0373] Example 150: A head-mounted display system described in any of Examples 1-148, wherein the first and second layers are formed on top of a reflective diffraction grating, the first diffraction grating being configured to diffract reflected light and couple light guided within the waveguide out of the waveguide by total internal reflection.

[0374] Example 151: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a height of 100 to 600 nanometers.

[0375] Example 152: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a height of 200 to 600 nanometers.

[0376] Example 153: A head-mounted display system described in any of the above examples, wherein the diffractive features have a height of 300 to 600 nanometers.

[0377] Example 154: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a pitch of 290 nm to 690 nm.

[0378] Example 155: A head-mounted display system described in any of the above examples, wherein the light projection system comprises micro LEDs.

[0379] Example 156: A head-mounted display system according to any of the preceding examples, wherein the optical projection system comprises a DLP or LCOS display.

[0380] Example 157: A head-mounted display system according to any of the previous examples, wherein the substrate comprises nanoparticles.

[0381] Example 158: The head mounted display system of any of the previous examples, wherein the substrate comprises inorganic nanoparticles.

[0382] Example 159: A head mounted display system according to any of the previous examples, wherein the substrate comprises a polymer.

[0383] Additional Examples - Part II Example 1: A head mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; A waveguide supported by a frame, the waveguide comprising a substrate comprising an optically transparent material and a first diffraction grating formed within the substrate, the substrate comprising: a first layer disposed over the first diffraction grating formed in the substrate; a second layer including a metal disposed over the first diffraction grating formed in the substrate such that the first 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 the range of angles of light incident thereon, the first diffraction efficiency being one to two times the second diffraction efficiency; a waveguide configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide via the waveguide; A head-mounted display system comprising:

[0384] Example 2: The head mounted display system according to Example 1, wherein the optically transparent material constituting the substrate has a refractive index of 1.45 to 2.0.

[0385] Example 3: The head mounted display system according to Example 1 or 2, wherein the transparent material constituting the substrate comprises a polymer.

[0386] Example 4: The head-mounted display system of any of the previous examples, wherein the first layer comprises titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0387] Example 5: A head mounted display system according to any of the previous examples, wherein the first layer comprises a plurality of sub-layers.

[0388] Example 6: The head mounted display system of example 5, wherein the first layer comprises a plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0389] Example 7: The head-mounted display system of Example 5 or 6, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0390] Example 8: The head mounted display system of any of Examples 5-7, wherein the plurality of sub-layers comprises only two sub-layers.

[0391] Example 9: The head mounted display system of any of Examples 5-7, wherein the plurality of sub-layers comprises at least four sub-layers.

[0392] Example 10: The head mounted display system of any of Examples 6-9, wherein the plurality of sub-layers alternate between the first material and the second material.

[0393] Example 11: The head mounted display system of any of Examples 5-10, wherein the plurality of sub-layers comprises an interference coating.

[0394] Example 12: The head mounted display system of any of Examples 5-11, wherein the plurality of sub-layers comprises a quarter wave stack.

[0395] Example 13: The head mounted display system of any of the previous examples, wherein the metal comprises aluminum, silver, gold, or copper.

[0396] Example 14: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a blazed diffraction grating.

[0397] Example 15: A head mounted display system as described in Example 14, wherein the first diffraction grating comprises diffractive features comprising peaks spaced apart by grooves therebetween.

[0398] Example 16: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature comprising a plurality of straight lines.

[0399] Example 17: A waveguide according to any of the previous examples, wherein the diffraction grating comprises diffractive features that are asymmetric.

[0400] Example 18: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations having different polarization angles.

[0401] Example 19: A head-mounted display system according to any of the previous examples, wherein the first and second polarizations comprise first and second linear polarizations oriented in orthogonal directions.

[0402] Example 20: A head-mounted display system according to any of the preceding examples, wherein the first and second polarization directions comprise transverse magnetic and transverse electric polarization, respectively.

[0403] Example 21: A head-mounted display system as described in any of Examples 1-19, wherein the first and second polarization directions comprise transverse electric and transverse magnetic polarizations, respectively.

[0404] Example 22: A head-mounted display system described in any of Examples 1-19, wherein the first diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0405] Example 23: A head-mounted display system described in any of Examples 1-19, wherein the first diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0406] Example 24: A head mounted display system according to any of the preceding examples, wherein the first diffraction efficiency is 1 to 1.5 times the second diffraction efficiency.

[0407] Example 25: A head mounted display system according to any of the preceding Examples, wherein the first diffraction efficiency is 1 to 1.4 times the second diffraction efficiency.

[0408] Example 26: A head mounted display system according to any of the preceding Examples, wherein the first diffraction efficiency is 1 to 1.3 times the second diffraction efficiency.

[0409] Example 27: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.2 times the second diffraction efficiency.

[0410] Example 28: A head mounted display system according to any of the above examples, wherein the first diffraction efficiency is 1 to 1.1 times the second diffraction efficiency.

[0411] Example 29: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 6 degrees.

[0412] Example 30: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 12 degrees.

[0413] Example 31: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 18 degrees.

[0414] Example 32: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 22 degrees.

[0415] Example 33: A head mounted display system according to any of the previous examples, wherein the angle range is between ±3 degrees relative to the plane of the substrate.

[0416] Example 34: A head mounted display system according to any of the previous examples, wherein the range of angles is between ±6 degrees relative to the plane of the substrate.

[0417] Example 35: A head mounted display system according to any of the previous examples, wherein the range of angles is between ±9 degrees relative to the plane of the substrate.

[0418] Example 36: A head mounted display system according to any of the previous examples, wherein the range of angles is between ±11 degrees relative to the plane of the substrate.

[0419] Example 37: A head-mounted display system described in any of the above examples, wherein the waveguide is included in an eyepiece configured to direct light to the eye of a user wearing the head-mounted display.

[0420] Example 38: A head-mounted display system as described in Example 37, wherein the eyepiece is positioned on a 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, at least a portion of the eyepiece is transparent and is positioned in front of the user's eye when the user wears the head-mounted display system, and the transparent portion allows 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.

[0421] Example 39: A head-mounted display system as described in Example 37 or 38, wherein the eyepiece lens comprises at least one waveguide, and the at least one waveguide is transparent to visible light so that a user can see through the waveguide.

[0422] Example 40: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an internal coupling optical element for coupling light from the optical projection system into the waveguide so that it is guided therein.

[0423] Example 41: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an external coupling optical element for coupling light from the optical projection system out of the waveguide, directing the light to a user's eye, and presenting the image content to a viewer.

[0424] Example 42: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an internal coupling grating (ICG) configured to internally couple light from the optical projection system into the waveguide.

[0425] Example 43: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an external coupling grating (EPE) configured to externally couple light from the optical projection system guided within the waveguide out of the waveguide.

[0426] Example 44: A head-mounted display system according to any of the preceding examples, wherein the second layer is configured to be disposed over the first layer.

[0427] Example 45: A head-mounted display system according to any of the preceding examples, further comprising a third layer disposed between the first layer and the second layer.

[0428] Example 46: A head-mounted display system as described in Example 45, wherein a third layer is configured to help join the second layer to the first layer.

[0429] Example 47: The waveguide comprises a second diffraction grating formed in the substrate, the substrate being configured to direct at least a portion of the light from the optical projection system to be coupled into the waveguide via the second diffraction grating, and the head mounted display system further comprises a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for a first polarization over a range of angles of light incident thereon; A head-mounted display system as described in any of the above examples, wherein a first diffraction grating is formed in the substrate on a first side of the substrate and a second diffraction grating is formed in the substrate on a second side of the substrate opposite the first side of the substrate.

[0430] Example 48: A head-mounted display system according to any of the preceding examples, wherein the first layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0431] Example 49: A head mounted display system according to any of the preceding examples, wherein the first layer is directionally deposited at an angle that lies on the one or more diffractive features.

[0432] Example 50: The head-mounted display system of Example 49, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0433] Example 51: A head-mounted display system as described in Example 49, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0434] Example 52: A head-mounted display system according to any of the preceding examples, wherein the second layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0435] Example 53: A head-mounted display system according to any of the preceding examples, wherein the second layer is directionally deposited at an angle that is on one or more diffractive features of the first diffraction grating.

[0436] Example 54: A head-mounted display system as described in Example 53, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0437] Example 55: A head-mounted display system as described in Example 53, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0438] Example 56: A head-mounted display system as described in any of the above examples, wherein the first diffraction grating comprises diffractive features formed in a 1D array.

[0439] Example 57: A head-mounted display system described in any of Examples 1-55, wherein the first diffraction grating comprises diffractive features formed in a 2D array.

[0440] Example 58: A head-mounted display system as described in Example 57, wherein the 2D array comprises a square array.

[0441] Example 59: A head-mounted display according to any of the preceding examples, wherein the diffractive features are asymmetric so as to provide a blazed grating.

[0442] Example 60: A head-mounted display according to any of the preceding examples, wherein the diffractive features have material deposited thereon asymmetrically to provide a blazed grating.

[0443] Example 61: A head-mounted display according to any of the preceding examples, wherein the first diffraction grating is configured to preferentially direct light in at least two directions.

[0444] Example 62: A head-mounted display according to any of the preceding examples, wherein the first diffraction grating is blazed in two directions.

[0445] Example 63: A head-mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a one-dimensional grating.

[0446] Example 64: A head-mounted display system described in any of Examples 1-62, wherein the first diffraction grating comprises a two-dimensional grating.

[0447] Example 65: a second diffraction grating formed in the substrate; and a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for the first polarization over a range of angles of light incident thereon and a fourth diffraction efficiency for the second polarization over the range of angles of light incident thereon; a first diffraction grating disposed across the substrate on a first side thereof and a second diffraction grating disposed across the substrate on a second side thereof opposite the first side thereof.

[0448] Example 66: a second diffraction grating disposed over the substrate, the second diffraction grating comprising a different material than the substrate; a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for the first polarization over a range of angles of light incident thereon and a fourth diffraction efficiency for the second polarization over the range of angles of light incident thereon; a first diffraction grating disposed across the substrate on a first side thereof and a second diffraction grating disposed across the substrate on a second side thereof opposite the first side thereof.

[0449] Example 67: A head-mounted display system described in any of the above examples, wherein the substrate is configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide via the second diffraction grating.

[0450] Example 68: A head-mounted display system described in any of the above examples, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon exceeds the fourth diffraction efficiency for the second polarization over that range of angles of light incident thereon.

[0451] Example 69: A head mounted display system according to any of the preceding examples, wherein the third diffraction efficiency is at least six times the fourth diffraction efficiency over the range of angles.

[0452] Example 70: A head-mounted display system described in any of the above examples, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon is less than the fourth diffraction efficiency for the second polarization over a range of angles of light incident thereon.

[0453] Example 71: A head mounted display system according to any of the preceding examples, wherein the fourth diffraction efficiency is at least six times the third diffraction efficiency over the range of angles.

[0454] Example 72: A head-mounted display system according to any of the preceding examples, wherein the fourth layer comprises a dielectric.

[0455] Example 73: A head-mounted display system according to any of the previous examples, wherein the substrate comprises a material having a refractive index of 2.6 or less.

[0456] Example 74: A head-mounted display system according to any of the preceding examples, wherein the substrate comprises a material having a refractive index of 2.7 or less.

[0457] Example 75: A head-mounted display system according to any of the preceding examples, wherein the substrate comprises a material having a refractive index of 2.8 or less.

[0458] Example 76: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a dielectric.

[0459] Example 77: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 1.9 or greater.

[0460] Example 78: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 2.0 or greater.

[0461] Example 79: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a material having a refractive index of 2.1 or greater.

[0462] Example 80: A head-mounted display system described in any of the above examples, further comprising a plurality of sub-layers over the first layer, the plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0463] Example 81: A head-mounted display system as described in Example 80, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0464] Example 82: A head-mounted display system as described in Example 80 or 81, wherein the plurality of sub-layers comprises only two sub-layers.

[0465] Example 83: A head-mounted display system as described in Example 80 or 81, wherein the plurality of sub-layers comprises at least four sub-layers.

[0466] Example 84: A head-mounted display system described in any of Examples 80-83, wherein the multiple sub-layers alternate between a first material and a second material.

[0467] Example 85: A head-mounted display system as described in any of Examples 80-84, wherein the plurality of sub-layers comprises an interference coating.

[0468] Example 86: A head-mounted display system described in any of Examples 80-85, wherein the plurality of sub-layers comprises a quarter-wave stack.

[0469] Example 87: A head-mounted display system described in any of Examples 80-86, wherein multiple sub-layers across the first layer form a bandpass filter.

[0470] Example 88: A head-mounted display system described in any of Examples 80-86, wherein multiple sub-layers across the first layer form a notch filter.

[0471] Example 89: A head-mounted display system described in any of Examples 80-86, wherein multiple sub-layers over the first layer form an anti-reflective (AR) coating.

[0472] Example 90: A head-mounted display system described in any of Examples 80-89, wherein the first lower refractive index material has a refractive index of 1.6 or less.

[0473] Example 91: A head-mounted display system described in any of Examples 80-90, wherein the second, higher refractive index material has a refractive index of 1.9 or greater.

[0474] Example 92: A head-mounted display system described in any of Examples 80-91, wherein the first lower refractive index material comprises silicon dioxide.

[0475] Example 93: A head-mounted display system according to any of Examples 80-92, wherein the second higher refractive index material comprises titanium dioxide.

[0476] Example 94: A head-mounted display system according to any of Examples 80-92, wherein the second higher refractive index material comprises zirconium dioxide.

[0477] Example 95: A head-mounted display system according to any of Examples 80-92, wherein the second higher refractive index material comprises zinc oxide.

[0478] Example 96: A head-mounted display system described in any of the above examples, wherein the first diffraction grating has an average diffraction efficiency for the first polarization over the range of angles, and the second diffraction efficiency has an average diffraction efficiency for the second polarization over the range of angles.

[0479] Example 97: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 40%.

[0480] Example 98: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 50%.

[0481] Example 99: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency averaged over the range of angles and the second diffraction efficiency averaged over the range of angles have an efficiency of at least 60%.

[0482] Example 100: A head-mounted display system according to any of the previous examples, wherein the range of angles is at least 25 degrees.

[0483] Example 101: A head-mounted display system according to any of the previous examples, wherein the range of angles is at least 30 degrees.

[0484] Example 102: A head-mounted display system according to any of the above examples, wherein the range of angles is at least 35 degrees.

[0485] Example 103: A head-mounted display system according to any of the previous examples, wherein the range of angles is at least 40 degrees.

[0486] Example 104: A head-mounted display system described in any of the above examples, wherein the angle range is between ±15 degrees relative to the plane of the substrate.

[0487] Example 105: A head-mounted display system described in any of the above examples, wherein the angle range is between ±18 degrees relative to the plane of the substrate.

[0488] Example 106: A head-mounted display system described in any of the above examples, wherein the angle range is between ±20 degrees relative to the plane of the substrate.

[0489] Example 107: A head-mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature having first and second side walls.

[0490] Example 108: A head-mounted display system as described in Example 107, wherein the first and second side walls are separated by a flat area.

[0491] Example 109: A head-mounted display system as described in Example 107, wherein the first and second side walls join to form a significant angle at the top of the diffractive feature.

[0492] Example 110: A head-mounted display system described in any of Examples 107-109, wherein at least the first side wall is inclined at an angle such that the first side wall is not as steep as the second side wall.

[0493] Example 111: A head-mounted display system described in any of Examples 107-110, wherein the first side wall is wider than the second side wall.

[0494] Example 112: A head-mounted display system described in any of Examples 107-111, wherein the first side wall forms an angle of 45° to 85° with the base of the diffractive feature.

[0495] Example 113: A head-mounted display system described in any of Examples 107-112, wherein the second side wall forms an acute re-entrant angle at the base of the diffractive feature.

[0496] Example 114: A head-mounted display system described in any of Examples 107-113, wherein the first diffraction grating has shark-tail shaped diffraction features.

[0497] Example 115: A head-mounted display system described in any of Examples 107-112, wherein the second side wall forms an obtuse re-entrant angle at the base of the diffractive feature.

[0498] Example 116: A head-mounted display system described in any of Examples 107-112, wherein the second side wall is vertical.

[0499] Example 117: A head-mounted display system described in any of Examples 107-112 or 115-116, wherein the first diffraction grating has sawtooth-shaped diffractive features.

[0500] Example 118: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a biased deposition.

[0501] Example 119: A head-mounted display system according to any of the preceding examples, wherein the first layer comprises a grazing angle deposition.

[0502] Example 120: A head-mounted display system described in any of Examples 107-119, wherein the first layer is biased to provide more coverage on the first sidewall than on the second sidewall.

[0503] Example 121: A head-mounted display system described in any of Examples 107-120, wherein the first layer covers a greater proportion of the first sidewall than the second sidewall.

[0504] Example 122: A head-mounted display system described in any of Examples 107-121, wherein the first layer is biased to provide a thicker coating on the first sidewall than on the second sidewall.

[0505] Example 123: A head-mounted display system described in any of Examples 107-122, wherein the first layer provides an averagely thicker coating on the first sidewall than on the second sidewall.

[0506] Example 124: A head-mounted display system described in any of Examples 107-123, wherein the first side wall is completely covered by the second layer.

[0507] Example 125: A head-mounted display system described in any of Examples 107-124, wherein at least a portion of the second side wall is not covered by the first layer.

[0508] Example 126: A head-mounted display system described in any of Examples 107-125, wherein the second sidewall includes an area not covered by the first layer that is greater than the first sidewall.

[0509] Example 127: A head-mounted display system described in any of Examples 107-126, wherein the second layer comprises a conformal deposition.

[0510] Example 128: A head-mounted display system described in any of Examples 107-127, wherein the first and second side walls are completely covered by the second layer.

[0511] Example 129: A head-mounted display system described in any of Examples 107-128, wherein the second layer is not biased to cover more of the first sidewall than the second sidewall.

[0512] Example 130: A head-mounted display system described in any of Examples 107-129, wherein the second layer is not biased to provide a thicker coating on the first sidewall than on the second sidewall.

[0513] Example 131: A head-mounted display system described in any of Examples 107-130, wherein the second layer does not provide an averagely thicker coating on the first sidewall than on the second sidewall.

[0514] Example 132: A head-mounted display system described in any of Examples 107-131, wherein the second side wall is entirely covered by the second layer.

[0515] Example 133: A head-mounted display system described in any of Examples 107-132, wherein the second sidewall does not include more area not covered by the second layer than the first sidewall.

[0516] Example 134: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency for the first polarization is within 20% of the second diffraction efficiency for the second polarization.

[0517] Example 135: A head-mounted display system described in any of the above examples, wherein the first diffraction efficiency for the first polarization is within 30% of the second diffraction efficiency for the second polarization.

[0518] Example 136: A head-mounted display system described in any of the above examples, wherein the first diffraction grating on which the first and second layers are formed comprises a reflective diffraction grating.

[0519] Example 137: A head-mounted display system described in any of the above examples, wherein the first and second layers are formed on a first diffraction grating that is configured to diffract reflected light and couple the light into the waveguide so that it is guided therein by total internal reflection.

[0520] Example 138: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a height of 100 to 600 nanometers.

[0521] Example 139: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a height of 200 to 600 nanometers.

[0522] Example 140: A head-mounted display system according to any of the preceding examples, wherein the diffractive features have a height of 300 to 600 nanometers.

[0523] Example 141: A head mounted display system according to any of the preceding examples, wherein the diffractive features have a pitch of 290 nm to 690 nm.

[0524] Example 142: A head-mounted display system described in any of the above examples, wherein the light projection system comprises micro LEDs.

[0525] Example 143: A head-mounted display system according to any of the previous examples, wherein the optical projection system comprises a DLP or LCOS display.

[0526] Example 144: A head mounted display system according to any of the previous examples, wherein the substrate comprises nanoparticles.

[0527] Example 145: The head mounted display system of any of the previous examples, wherein the substrate comprises inorganic nanoparticles.

[0528] Example 146: The head mounted display system of any of the previous examples, wherein the substrate comprises a polymer.

[0529] Additional Examples - Part III Example 1: A head mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by a frame, the waveguide comprising a substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide; a first diffraction grating comprising a material different from the substrate; a first layer disposed over the first diffraction grating such that the first diffraction grating has a first diffraction efficiency for a first polarization of light incident thereon over a range of angles that exceeds a second diffraction efficiency for a second polarization of light incident thereon over the range of angles; a second layer disposed over the first diffraction grating such that the first diffraction grating has a third diffraction efficiency for the second polarization of light incident thereon over the range of angles that exceeds a fourth diffraction efficiency for the first polarization of light incident thereon over the range of angles; wherein a diffraction efficiency of the combination of the first diffraction grating and the first and second layers is configured to provide a fifth diffraction efficiency for the first polarization over the range of angles of light incident thereon and a sixth diffraction efficiency for the second polarization over the range of angles of light incident thereon, wherein the fifth diffraction efficiency is between 1 and 2 times the sixth diffraction efficiency, or wherein the sixth diffraction efficiency is between 1 and 2 times the fifth diffraction efficiency.

[0530] Example 2: The head mounted display system of example 1, wherein the substrate comprises a lithium-based oxide material.

[0531] Example 3: The head mounted display system of example 1 or 2, wherein the substrate comprises a lithium niobate material.

[0532] Example 4: The head mounted display system of example 1, wherein the substrate comprises a silicon carbide material.

[0533] Example 5: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 1.9.

[0534] Example 6: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.0.

[0535] Example 7: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.1.

[0536] Example 8: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.2.

[0537] Example 9: The head mounted display system of example 1, wherein the substrate comprises a material having a refractive index of at least 2.3.

[0538] Example 10: A head mounted display system according to any of the previous examples, wherein the first grating material comprises a polymer.

[0539] Example 11: A head mounted display system according to any of the previous examples, wherein the first grating material comprises an imprintable material.

[0540] Example 12: A head mounted display system according to any of the previous examples, wherein the first diffraction grating material has a refractive index between 1.4 and 1.95.

[0541] Example 13: A head mounted display system according to any of the previous examples, wherein the first grating material has a lower refractive index than the substrate.

[0542] Example 14: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a blazed diffraction grating.

[0543] Example 15: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises diffractive features comprising peaks spaced apart by grooves therebetween.

[0544] Example 16: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature comprising a plurality of straight lines.

[0545] Example 17: A waveguide according to any of the preceding examples, wherein the diffraction grating comprises diffractive features that are asymmetric.

[0546] Example 18: The head-mounted display system of any of the preceding examples, wherein the first layer comprises titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0547] Example 19: The head mounted display system of any of the previous examples, wherein the first layer comprises titanium dioxide (TiO2).

[0548] Example 20: The head mounted display system of any of the previous examples, wherein the first layer comprises zirconium dioxide (ZrO2).

[0549] Example 21: The head mounted display system of any of the previous examples, wherein the first layer comprises silicon carbide (SiC).

[0550] Example 22: A head-mounted display system as described in any of the above examples, wherein the first layer comprises a plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0551] Example 23: The head-mounted display system of Example 22, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0552] Example 24: The head-mounted display system of Example 22 or 23, wherein the plurality of sub-layers comprises only two sub-layers.

[0553] Example 25: The head-mounted display system of Example 22 or 23, wherein the plurality of sub-layers comprises at least four sub-layers.

[0554] Example 26: A head mounted display system according to any of Examples 22-25, wherein the plurality of sub-layers alternate between the first material and the second material.

[0555] Example 27: The head mounted display system of any of Examples 22-26, wherein the plurality of sub-layers comprises an interference coating.

[0556] Example 28: A head-mounted display system according to any of Examples 22-27, wherein the plurality of sub-layers comprises a quarter-wave stack.

[0557] Example 29: A head-mounted display system according to any of the preceding examples, wherein the second layer comprises aluminum, silver, gold, or copper.

[0558] Example 30: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations having different polarization angles.

[0559] Example 31: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations oriented in orthogonal directions.

[0560] Example 32: A head-mounted display system according to any of the preceding examples, wherein the first and second polarization directions comprise transverse magnetic and transverse electric polarization, respectively.

[0561] Example 33: A head-mounted display system according to any of the preceding examples, wherein the first and second polarization directions comprise transverse electric and transverse magnetic polarizations, respectively.

[0562] Example 34: A head-mounted display system described in any of the above examples, wherein the fifth diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the sixth diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0563] Example 35: A head-mounted display system described in any of the above examples, wherein the fifth diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the sixth diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0564] Example 36: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.5 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.5 times the fifth diffraction efficiency.

[0565] Example 37: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.4 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.4 times the fifth diffraction efficiency.

[0566] Example 38: A head-mounted display system described in any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.3 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.3 times the fifth diffraction efficiency.

[0567] Example 39: A head-mounted display system described in any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.2 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.2 times the fifth diffraction efficiency.

[0568] Example 40: A head-mounted display system described in any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.1 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.1 times the fifth diffraction efficiency.

[0569] Example 41: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 6 degrees.

[0570] Example 42: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 12 degrees.

[0571] Example 43: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 18 degrees.

[0572] Example 44: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 22 degrees.

[0573] Example 45: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±3 degrees relative to the plane of the substrate.

[0574] Example 46: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±6 degrees relative to the plane of the substrate.

[0575] Example 47: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±9 degrees relative to the plane of the substrate.

[0576] Example 48: A head-mounted display system according to any of the previous examples, wherein the angle range is between ±11 degrees relative to the plane of the substrate.

[0577] Example 49: A head-mounted display system described in any of the above examples, wherein the waveguide is included within an eyepiece configured to direct light to the eye of a user wearing the head-mounted display.

[0578] Example 50: A head-mounted display system as described in Example 49, wherein the eyepiece is positioned on a frame and configured to direct light from an optical projection system into a user's eye and display augmented reality image content in the user's field of view, at least a portion of the eyepiece is transparent and is 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 providing a view of a portion of the physical environment in front of the user.

[0579] Example 51: A head-mounted display system as described in Example 49 or 50, wherein the eyepiece lens comprises at least one waveguide, and the at least one waveguide is transparent to visible light so that a user can see through the waveguide.

[0580] Example 52: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an internal coupling optical element for coupling light from the optical projection system into the waveguide so that it is guided therein.

[0581] Example 53: A head-mounted display system described in any of the above examples, wherein the waveguide comprises an external coupling optical element for coupling light from the optical projection system out of the waveguide, directing the light to a user's eye, and presenting the image content to a viewer.

[0582] Example 54: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an external coupling grating (EPE) configured to externally couple light from the optical projection system guided within the waveguide out of the waveguide.

[0583] Example 55: A head-mounted display system described in any of the above examples, wherein the first diffraction grating comprises an internal coupling grating (ICG) configured to internally couple light from the optical projection system into the waveguide.

[0584] Example 56: A head-mounted display system according to any of the preceding examples, wherein the second layer is configured to be disposed over the first layer.

[0585] Example 57: A head-mounted display system according to any of the preceding examples, comprising a third layer disposed between the first layer and the second layer.

[0586] Example 58: A head-mounted display system as described in Example 57, wherein a third layer is configured to help join the second layer to the first layer.

[0587] Example 59: a second diffraction grating disposed over the substrate, the second diffraction grating comprising a different material than the substrate; a fourth layer disposed over the second diffraction grating such that the second diffraction grating has a seventh diffraction efficiency for the first polarization over a range of angles of light incident thereon; and a first diffraction grating disposed across the substrate on a first side thereof and a second diffraction grating disposed across the substrate on a second side thereof opposite the first side thereof.

[0588] Example 60: The head-mounted display system of Example 1, wherein the first layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0589] Example 61: A head-mounted display system as described in Example 1, wherein the first layer is directionally deposited at an angle that overlies the one or more diffractive features.

[0590] Example 62: A head-mounted display system as described in Example 61, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0591] Example 63: A head-mounted display system as described in Example 61, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0592] Example 64: The head-mounted display system of Example 1, wherein the second layer is conformally deposited on one or more diffractive features of the first diffraction grating.

[0593] Example 65: A head-mounted display system as described in Example 1, wherein the second layer is directionally deposited at an angle that is on one or more diffractive features of the first diffraction grating.

[0594] Example 66: A head-mounted display system as described in Example 65, wherein the angle comprises 75 to 105 degrees relative to the planar major surface of the substrate.

[0595] Example 67: A head-mounted display system as described in Example 65, wherein the angle is 75 to 105 degrees relative to the surface of the one or more diffractive features of the first diffraction grating.

[0596] Example 68: A head-mounted display system as described in any of the above examples, wherein the first diffraction grating comprises diffractive features formed in a 1D array.

[0597] Example 69: A head-mounted display system described in any of Examples 1-68, wherein the first diffraction grating comprises diffractive features formed in a 2D array.

[0598] Example 70: A head-mounted display system as described in Example 69, wherein the 2D array comprises a square array.

[0599] Example 71: A head-mounted display according to any of the above examples, wherein the diffractive features are asymmetric so as to provide a blazed grating.

[0600] Example 72: A head-mounted display as described in any of the previous examples, wherein the diffractive features have material asymmetrically deposited thereon to provide a blazed grating.

[0601] Example 73: A head-mounted display described in any of the above examples, wherein the first diffraction grating is configured to preferentially direct light in at least two directions.

[0602] Example 74: A head-mounted display according to any of the preceding examples, wherein the first diffraction grating is blazed in two directions.

[0603] Example 75: A head-mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a one-dimensional grating.

[0604] Example 76: A head-mounted display system described in any of Examples 1-75, wherein the first diffraction grating comprises a two-dimensional grating.

[0605] Example 77: A head-mounted display system according to any of the preceding examples, wherein the light projection system comprises micro LEDs.

[0606] Example 78: A head-mounted display system according to any of the preceding examples, wherein the optical projection system comprises a DLP or LCOS display.

[0607] Example 79: A head mounted display system according to any of the preceding examples, wherein the substrate comprises nanoparticles.

[0608] Example 80: A head mounted display system according to any of the previous examples, wherein the substrate comprises inorganic nanoparticles.

[0609] Example 81: A head mounted display system according to any of the preceding examples, wherein the substrate comprises a polymer.

[0610] Additional Examples - Part IV Example 1: A head mounted display system, comprising: A head mountable frame; a light projection system configured to output light and provide image content; a waveguide supported by a frame, the waveguide comprising: a substrate comprising an optically transparent material; and a first diffraction grating formed in the substrate, the substrate configured to guide at least a portion of light from the optical projection system to be coupled into the waveguide; a first layer disposed over the first diffraction grating formed in the substrate, the first layer configured, together with the first diffraction grating, to provide a first diffraction efficiency for a first polarization of light incident thereon over a range of angles that exceeds a second diffraction efficiency for a second polarization of light incident thereon over the range of angles; a second layer disposed over the first diffraction grating formed in the substrate, the second layer configured, together with the first diffraction grating, to provide a third diffraction efficiency for the second polarization of light incident thereon over the range of angles that exceeds a fourth diffraction efficiency for the first polarization of light incident thereon over the range of angles; the first diffraction grating, together with the first and second layers, is configured to provide a fifth diffraction efficiency for a first polarization over the range of angles of light incident thereon and a sixth diffraction efficiency for a second polarization over the range of angles of light incident thereon, wherein the fifth diffraction efficiency is one to two times the sixth diffraction efficiency, or wherein the sixth diffraction efficiency is one to two times the fifth diffraction efficiency.

[0611] Example 2: The head mounted display system according to Example 1, wherein the optically transparent material constituting the substrate has a refractive index of 1.45 to 2.0.

[0612] Example 3: The head mounted display system according to Example 1 or 2, wherein the transparent material constituting the substrate comprises a polymer.

[0613] Example 4: The head-mounted display system of any of the previous examples, wherein the first layer comprises titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0614] Example 5: A head mounted display system according to any of the previous examples, wherein the first layer comprises a plurality of sub-layers.

[0615] Example 6: The head mounted display system of example 5, wherein the first layer comprises a plurality of sub-layers comprising a first higher refractive index material and a second lower refractive index material.

[0616] Example 7: The head-mounted display system of Example 5 or 6, wherein the first higher refractive index material comprises titanium dioxide (TiO2) and the second lower refractive index material comprises silicon dioxide (SiO2).

[0617] Example 8: The head mounted display system of any of Examples 5-7, wherein the plurality of sub-layers comprises only two sub-layers.

[0618] Example 9: The head mounted display system of any of Examples 5-7, wherein the plurality of sub-layers comprises at least four sub-layers.

[0619] Example 10: The head mounted display system of any of Examples 6-9, wherein the plurality of sub-layers alternate between the first material and the second material.

[0620] Example 11: The head mounted display system of any of Examples 5-10, wherein the plurality of sub-layers comprises an interference coating.

[0621] Example 12: The head mounted display system of any of Examples 5-11, wherein the plurality of sub-layers comprises a quarter wave stack.

[0622] Example 13: The head mounted display system of any of the previous examples, wherein the metal comprises aluminum, silver, gold, or copper.

[0623] Example 14: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a blazed diffraction grating.

[0624] Example 15: A head mounted display system as described in Example 14, wherein the first diffraction grating comprises diffractive features comprising peaks spaced apart by grooves therebetween.

[0625] Example 16: A head mounted display system according to any of the preceding examples, wherein the first diffraction grating comprises a diffractive feature comprising a plurality of straight lines.

[0626] Example 17: A waveguide according to any of the previous examples, wherein the diffraction grating comprises diffractive features that are asymmetric.

[0627] Example 18: A head-mounted display system according to any of the preceding examples, wherein the first and second polarizations comprise first and second linear polarizations having different polarization angles.

[0628] Example 19: A head-mounted display system according to any of the previous examples, wherein the first and second polarizations comprise first and second linear polarizations oriented in orthogonal directions.

[0629] Example 20: A head-mounted display system according to any of the preceding examples, wherein the first and second polarization directions comprise transverse magnetic and transverse electric polarization, respectively.

[0630] Example 21: A head-mounted display system as described in any of Examples 1-19, wherein the first and second polarization directions comprise transverse electric and transverse magnetic polarizations, respectively.

[0631] Example 22: A head-mounted display system described in any of Examples 1-19, wherein the fifth diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0632] Example 23: A head-mounted display system described in any of Examples 1-19, wherein the sixth diffraction efficiency comprises a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency comprises a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0633] Example 24: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.5 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.5 times the fifth diffraction efficiency.

[0634] Example 25: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.4 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.4 times the fifth diffraction efficiency.

[0635] Example 26: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.3 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.3 times the fifth diffraction efficiency.

[0636] Example 27: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.2 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.2 times the fifth diffraction efficiency.

[0637] Example 28: A head-mounted display system according to any of the above examples, wherein the fifth diffraction efficiency is 1 to 1.1 times the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.1 times the fifth diffraction efficiency.

[0638] Example 29: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 6 degrees.

[0639] Example 30: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 12 degrees.

[0640] Example 31: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 18 degrees.

[0641] Example 32: A head mounted display system according to any of the previous examples, wherein the range of angles is at least 22 degrees.

[0642] Example 33: A head mounted display system according to any ...

Claims

[Claim 1] The invention described in this specification.

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