Display device with a 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 claims the benefit of priority of U.S. Provisional Application No. 62 / 899,063, filed on September 11, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY", U.S. Provisional Application No. 62 / 899,673, filed on September 12, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY", and U.S. Provisional Application No. 62 / 902,295, filed on September 18, 2019, entitled "DISPLAY DEVICE WITH DIFFRACTION GRATING HAVING REDUCED POLARIZATION SENSITIVITY", under 35 U.S.C. § 119(e) (Section 119(e) of the United States Patent Law), the entire disclosure of each of which is incorporated herein by reference in its entirety.

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

Background Art

[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 being real. Virtual reality, i.e., the "VR" scenario, typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and augmented reality, i.e., the "AR" scenario, typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world surrounding the user. Mixed reality, i.e., the "MR" scenario, is a type of AR scenario and typically involves virtual objects that are integrated into and responsive to the natural world. For example, in an MR scenario, AR image content can be perceived as being blocked or otherwise interacting with objects within the real world.

[0004] Referring to FIG. 1, an augmented reality scene 10 is depicted, and to a user of AR technology, a real-world park-like setting 20 characterized by people, trees, buildings in the background, and a concrete platform 30 can be seen. In addition to these items, a user of AR technology also "sees" and perceives as "visible" a robot image 40 standing on the real-world platform 30 and "virtual content" such as a flying cartoon-like avatar character 50 that appears as an anthropomorphic honeybee, but these elements 40, 50 do not exist in the real world. The human visual perception system is complex, and it is difficult to produce AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[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] (Abstract) 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 can be achieved in accordance with any particular embodiment disclosed herein. Accordingly, the embodiments disclosed herein can be embodied or carried out in a manner that necessarily does not achieve one advantage or group of advantages taught or suggested herein without achieving others.

[0007] What is disclosed herein is a head-mounted display system. In one configuration, the head-mounted display system can include a head-mountable frame, a light projection system, a waveguide supported by the frame, a diffraction grating, a first layer over the diffraction grating, and a second layer including metal disposed over the first layer. The light 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 light projection system to be coupled into the waveguide. The diffraction grating can include a material different from the substrate over the substrate. The diffraction grating can have a first diffraction efficiency for a first polarization over a certain range of angles of light incident thereon, and can also have a second diffraction efficiency for a second polarization over that range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency.

[0008] In another configuration, the head-mounted display system can include a head-mountable frame, a light projection system, a waveguide supported by the frame, a diffraction grating formed in a substrate, a first layer disposed across the diffraction grating formed in the substrate, and a second layer containing metal disposed across the diffraction grating formed in the substrate. The light 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 light projection system into the waveguide through the diffraction grating. The diffraction grating can have a first diffraction efficiency for a first polarization over a certain range of angles of light incident thereon, and can also have a second diffraction efficiency for a second polarization over that range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency.

[0009] In some configurations, the head-mounted display system includes a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide including a substrate configured to guide at least a portion of the light from the light projection system into the waveguide, a first diffraction grating that can include a material different from the substrate and disposed across the substrate, a first layer disposed across the first diffraction grating, and a second layer that can contain metal and is disposed across the first diffraction grating, wherein the first diffraction grating has a first diffraction efficiency for a first polarization over a certain range of angles of light incident thereon and a second diffraction efficiency for a second polarization over that range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency.

[0010] In some configurations, a head-mounted display system can include a head-mountable frame, a light projection system configured to output light and provide image content, and a waveguide supported by the frame. The waveguide can include a substrate that can include an optically transparent material, and a first diffraction grating formed within the substrate. The substrate can include a first layer disposed across the first diffraction grating formed within the substrate. The first diffraction grating has a first diffraction efficiency for a first polarization of light incident thereon over a range of angles and a second diffraction efficiency for a second polarization of light incident thereon over the range of angles, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency. The waveguide is configured to guide at least a portion of the light from the light projection system into the waveguide through a second layer that can include metal and is disposed across the first diffraction grating formed within the substrate.

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

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

[0013] In some configurations, a head-mounted display system includes a head-mountable frame, a light projection system configured to output light and provide image content, and a waveguide supported by the frame and configured to guide at least a portion of the light from the light projection system to be coupled into the waveguide, the waveguide including a substrate, a first diffraction grating that may include a material different from the substrate and extending across the substrate, and a first layer disposed across the first diffraction grating and including a multilayer coating, the first diffraction grating configured to have a first diffraction efficiency for a first polarization of incident light over a range of angles of incident light and a second diffraction efficiency for a second polarization of incident light over a range of angles of incident light that is greater than the first diffraction efficiency, the first layer and the first diffraction grating being configured to include each other.

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

[0015] In some configurations, a head-mounted display system includes a head-mountable frame, a light projection system configured to output light and provide image content, and a waveguide supported by the frame, the waveguide including a substrate configured to guide at least a portion of the light from the light projection system into the waveguide, a first diffraction grating extending across the substrate and including a material different from the substrate and the substrate including a material having a first refractive index, a first layer disposed across the first diffraction grating and including a material having a second refractive index, and a material disposed across the first layer and having a third refractive index between the second refractive index and the refractive index of air, the first diffraction grating being configured to have a first diffraction efficiency for a first polarization of incident light over a range of angles of incident light that is greater than a second diffraction efficiency for a second polarization of incident light over a range of angles of incident light, together with the first layer and the material across the first layer.

[0016] In some configurations, a head-mounted display system includes a head-mountable frame, a light projection system configured to output light and provide image content, and a waveguide supported by the frame, the waveguide including a substrate configured to guide at least a portion of the light from the light projection system into the waveguide, a first diffraction grating, and a first layer disposed across the first diffraction grating and configured to have a first diffraction efficiency for a first polarization of incident light over a range of angles of incident light that is 1 to 2 times a second diffraction efficiency for a second polarization of incident light over a range of angles of incident light.

[0017] A method of fabricating a diffraction grating with reduced polarization sensitivity, the method comprising: forming one or more diffraction 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 diffraction features; and depositing a second layer over the one or more diffraction features such that the one or more diffraction 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, and the first diffraction efficiency is 1 to 2 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 and including 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 over a range of angles of light incident thereon that is 1 to 2 times a second diffraction efficiency for a second polarization over the range of angles of light incident thereon.

[0019] 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 including a substrate configured to direct at least a portion of the light from the optical projection system to be coupled into the waveguide, the substrate having a refractive index of less than 1.9, and a first diffraction grating configured to have a first diffraction efficiency for a first polarization over a range of angles of light incident thereon that is 1 to 2 times a second diffraction efficiency for a second polarization over the range of angles of light incident thereon. The present invention provides, for example, the following. (Item 1) A head-mounted display system, a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide comprising a substrate configured to guide at least a part of the light from the light projection system to be coupled into the waveguide, a first diffraction grating including a material different from the substrate across the substrate, a first layer disposed across the first diffraction grating, a second layer, the second layer being such that the diffraction grating has a first diffraction efficiency for a first polarization over a certain range of angles of light incident thereon and a second diffraction efficiency for a second polarization over the certain range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency, the second layer including a metal disposed across the first diffraction grating A head-mounted display system comprising. (Item 2) The head-mounted display system according to Item 1, wherein the substrate includes a material having a refractive index of at least 1.9. (Item 3) The head-mounted display system according to Item 1, wherein the first diffraction grating material includes a polymer. (Item 4) The head-mounted display system according to Item 1, wherein the first diffraction grating material includes an imprintable material. (Item 5) 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) The head-mounted display system according to Item 1, wherein the first diffraction grating material has a refractive index lower than that of the substrate. (Item 7) The head-mounted display system according to Item 1, wherein the first diffraction grating comprises a blazed diffraction grating. (Item 8) The first layer is titanium dioxide (TiO 2 ) zirconium dioxide (ZrO 2 ) or silicon carbide (SiC), the head-mounted display system according to Item 1. (Item 9) The head-mounted display system according to Item 1, wherein the first and second polarizations each comprise transverse magnetic and transverse electric polarizations, respectively. (Item 10) The head-mounted display system according to Item 1, wherein the first and second polarizations each comprise transverse electric and transverse magnetic polarizations, respectively. (Item 11) 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) 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) 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) The head-mounted display system according to item 1, wherein the range of the angle is at least 12 degrees. (Item 15) The head-mounted display system according to item 14, wherein the range of the angle is at least 22 degrees. (Item 16) The head-mounted display system according to item 1, wherein the range of the angle is between ±6 degrees with respect to the plane of the substrate. (Item 17) The head-mounted display system according to item 16, wherein the range of the angle is between ±11 degrees with respect to the plane of the substrate. (Item 18) The head-mounted display system according to item 1, wherein the waveguide is included in an eyepiece lens configured to direct light to the eyes of a user wearing the head-mounted display. (Item 19) A head-mounted display system, a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide comprising a substrate configured to guide at least a portion of the light from the light projection system to be coupled into the waveguide, a first diffraction grating, a first layer, the first layer being arranged 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 incident light such that the first diffraction efficiency is 1 to 2 times a second diffraction efficiency for a second polarization over the range of angles of incident light, comprising. (Item 20) The head-mounted display system according to item 19, wherein the first diffraction grating on which the first layer is formed comprises a transmissive diffraction grating.

Brief Description of the Drawings

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

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DETAILED DESCRIPTION

[0060] (DETAILED DESCRIPTION) Certain preferred embodiments and examples are disclosed below, but the subject matter of the present invention extends beyond the specifically disclosed embodiments to include other alternative embodiments and / or uses of the present invention and their modifications and equivalents. Accordingly, the scope of the present invention disclosed herein is not limited by any of the specific embodiments described below. For example, in any of the methods or processes 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 the various embodiments with the prior art, certain aspects and advantages of these embodiments are described. Not all such aspects or advantages are necessarily achieved by any particular embodiment. Thus, for example, the 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 that may also be taught or suggested herein.

[0061] An AR system can still display virtual content to a user or viewer while enabling the user to see the surrounding world. Preferably, this content is displayed on a head-mounted display that is part of eyewear, for example, by projecting image information onto the user's eyes. Additionally, the display can also transmit light from the surrounding environment to the user's eyes, enabling 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 head of a viewer or user.

[0062] In some AR systems, a virtual / augmented / composite display having a relatively high field of view (FOV) can enhance the viewing experience. The FOV of a display depends on the angle of the light output by the waveguide of the eyepiece through which the image projected into the viewer's eye can be seen. For example, a waveguide having a relatively high refractive index of 2.0 or greater can provide a relatively high FOV. However, in order to efficiently couple light into a high refractive index waveguide, a diffractive optical coupling element should also correspondingly have a high refractive index. Among other advantages, to achieve this goal, some displays for an AR system according to the embodiments described herein include a waveguide that includes a material having a relatively high refractive index (e.g., greater than or equal to 2.0) with an individual diffraction grating formed thereon that correspondingly has a high refractive index, such as an Li-based oxide. For example, the diffraction grating may be formed directly on the Li-based oxide waveguide by patterning a surface portion of the waveguide formed from the Li-based oxide.

[0063] Some high refractive index diffractive optical coupling elements, such as internal or external coupling optical elements, have strong polarization dependence. For example, an internal coupling grating (ICG) for internally coupling light into a waveguide, where the diffractive optical coupling element includes a high refractive index material, can receive significantly more light of a given polarization than light of another polarization. Such an element can internally couple light with TM polarization into the waveguide, for example, at a rate of about three times that of light with TE polarization. Diffractive optical coupling elements with this type of polarization dependence can have reduced efficiency (due to the poor efficiency and overall blocking of one polarization), and can also create coherent artifacts and reduce the uniformity of the far-field image formed by the light coupled out of the waveguide. To obtain diffractive optical coupling elements that are insensitive to polarization or have at least reduced polarization sensitivity (e.g., coupling light with a relatively efficiency independent of polarization), some displays for AR systems according to various implementations described herein include waveguides with diffractive gratings formed using a blazed geometry. The diffractive grating may also be formed directly within the 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 these values). The diffractive grating may be formed, for example, by patterning a high refractive index material using a blazed geometry, such as within a Li-based oxide like lithium niobate (LiNbO3) or lithium tantalate (LiTaO3), or a high refractive index material such as zirconium dioxide (ZrO2), titanium dioxide (TiO2), or silicon carbide (SiC).

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

[0065] Figure 2 illustrates a conventional display system for simulating a three-dimensional image for a user. The user's eyes are separated, and when looking at a real object in space, each eye has a slightly different view of the object, and it should be understood that the image of the object can be formed at different locations on the retina of each eye. This can be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct images 190, 200 with slightly different views of one identical virtual object for each eye 210, 220, corresponding to the views of the virtual object that would be seen by each eye as if the virtual object were a real object at the desired depth. These images provide binocular cues that can be interpreted by the user's visual system to derive a perception of depth.

[0066] Continuing to refer to FIG. 2, the images 190, 200 are separated from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer in a state where the eye is fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the slightly different views of the virtual object within the images presented to the eyes 210, 220 respectively, the eyes can necessarily rotate so that the image of the object comes to the corresponding points on the respective retinas of the eyes and a single binocular vision is maintained. This rotation can converge the respective lines of sight of the eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, the provision of a three-dimensional image has conventionally involved being able to manipulate the convergence / divergence movement of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0067] However, generating a realistic and comfortable perception of depth is difficult. It should be understood that light from objects at different distances from the eye has wavefronts with different amounts of divergence. FIGS. 3A-3C illustrate the relationship between distance and the divergence of light rays. The distances between the object and the eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A-3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only the monocular 210 is illustrated in FIGS. 3A-3C and other figures in this specification for clarity of illustration, but the discussion regarding the eye 210 can be applied to both eyes 210 and 220 of the viewer.

[0068] Continuing to refer to FIGS. 3A-3C, light from the object on which the viewer's eye is fixated can have different degrees of wavefront divergence. Due to the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, which in turn can require the lens to take on different shapes to form a focused image on the retina of the eye. If a focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation, causing a change in the shape of the eye's lens until a focused image is formed on the retina. For example, the cue for accommodation induces relaxation or contraction of the ciliary muscle surrounding the eye's lens, thereby modulating the force applied to the zonular fibers that hold the lens, and thus changing the shape of the eye's lens until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the retina (e.g., the fovea) of the eye. 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 retina (e.g., the fovea) of the eye can be referred to as the accommodative state.

[0069] Referring now to FIG. 4A, the representation of the accommodation - vergence / divergence motion response of the human visual system is illustrated. Eye movements to fixate an object cause the eyes to receive light from the object, and the light forms an image on each of the retinas of the eyes. The presence of retinal blur in the images formed on the retinas can provide a cue for accommodation, and the relative location of the images on the retinas can provide a cue for vergence / divergence motion. The cue for accommodation causes accommodation to occur, causing the eye's lens to assume a particular accommodation state that forms a focused image of the object on the eye's retina (e.g., the fovea). On the other hand, the cue for vergence / divergence motion causes vergence / divergence motion (rotation of the eyes) to occur such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. At these positions, it can be said that the eyes are in a particular vergence / divergence motion state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eyes achieve a particular accommodation state, and vergence / divergence motion can be understood as the process by which the eyes achieve a particular vergence / divergence motion state. As shown in FIG. 4A, the accommodation and vergence / divergence motion states of the eyes can change when the user fixates on another object. For example, the accommodated state can change when the user fixates on a new object at a different depth on the z - axis.

[0070] Without being limited by theory, it is believed that an object viewer can perceive an object as "three - dimensional" due to the combination of vergence / divergence motion and accommodation. As described above, the vergence / divergence motion of the two eyes with respect to each other (e.g., the pupils move towards or away from each other, converging the lines of sight of the eyes and rotating the eyes to fixate on an object) is closely associated with the accommodation of the eye's lens. Under normal conditions, a change in the shape of the eye's lens to change focus from one object to another object at a different distance will automatically cause a corresponding change in vergence / divergence motion to the same distance under a relationship known as the "accommodation - vergence / divergence reflex". Similarly, a change in vergence / divergence motion will, under normal conditions, induce a corresponding change in the shape of the lens.

[0071] Referring now to FIG. 4B, examples of different focusing and convergence / divergence motion states of the eyes are illustrated. A pair of eyes 222a fixate on an object at optical infinity, while a pair of eyes 222b fixate on an object 221 at less than optical infinity. It should be noted that the convergence / divergence motion states of each pair of eyes are different, with a pair of eyes 222a being directed straight, while a pair of eyes 222 converge onto the object 221. The focusing states of the eyes forming each pair of eyes 222a and 222b also differ, as represented by the different shapes of the lenses 210a, 220a.

[0072] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or perceive no sense of depth, due to the mismatch between the focusing and the convergence / divergence motion states in these displays. As described above, many stereoscopic or "3-D" display systems display a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they simply provide different presentations of the scene, causing a change in the convergence / divergence motion state of the eyes, but without a corresponding change in the focusing state of those eyes. Rather, the images are presented at a fixed distance from the eyes by the display such that the eyes view all the image information in a single focusing state. Such an arrangement goes against the "focusing-convergence / divergence reflex" by causing a change in the convergence / divergence motion state without a corresponding change in the focusing state. This mismatch is thought to cause discomfort to the viewer. A display system that provides a better match between focusing and convergence / divergence motion can create a more realistic and comfortable simulation of a three-dimensional image.

[0073] While not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of an image corresponding to each of these limited number of depth planes to the eye. In some embodiments, the different presentations provide both cues for convergence / divergence motion and corresponding cues for accommodation, thereby providing a physiologically correct accommodation-convergence / divergence match.

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

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

[0076] Referring now to FIGS. 4C and 4D, examples of matched vergence accommodation - convergence / divergence movement distances and mismatched vergence accommodation - convergence / divergence movement distances are illustrated, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each of the eyes 210, 220. The image may cause the eyes 210, 220 to assume a convergence / divergence movement state in which the eyes converge on a point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to the real object in the depth plane 240. As a result, the eyes 210, 220 assume a focusing state in which the image is in focus on their retinas. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0077] It should be understood that the focusing and convergence / divergence movement states of the eyes 210, 220 are each associated with a specific distance on the z - axis. For example, an object at a specific distance from the eyes 210, 220 causes those eyes to assume a specific focusing state based on the distance of the object. The distance associated with a specific focusing state may be referred to as the focusing distance A d and may be so called. Similarly, there exists a specific convergence / divergence movement distance V d associated with a specific convergence / divergence movement state or the eyes in a particular position relative to each other. When the focusing distance and the convergence / divergence movement distance match, the relationship between focusing and convergence / divergence movement can be said to be physiologically correct. This is regarded as the most comfortable scenario for the viewer.

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

[0079] It should be understood that in some embodiments, reference points other than the exit pupils of eyes 210, 220 can also be used to determine the distance for determining the accommodation-convergence / divergence movement mismatch as long as the same reference point is used for the accommodation distance and the convergence / divergence movement distance. For example, the distance can be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc.

[0080] Although not limited by theory, it is believed that a user can physiologically perceive the accommodation - vergence / divergence motion mismatches of up to about 0.25 diopters, up to about 0.33 diopters, and up to about 0.5 diopters as being correct without the mismatch itself causing significant discomfort. In some embodiments, the display system (e.g., display system 250, FIG. 6) disclosed herein presents an image to a viewer having an accommodation - vergence / divergence motion mismatch of about 0.5 diopters or less. In some other embodiments, the accommodation - vergence / divergence motion mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation - vergence / divergence motion mismatch of the image provided by the display system is about 0.25 diopters or less, including about 0.1 diopters or less.

[0081] FIG. 5 illustrates a side view of an approach for simulating a three - dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, it will be shown that the user's other eye may be provided with image information from a similar waveguide.

[0082] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light within a limited range of wavelengths. As a result, in some embodiments, multiple or stacked waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different ranges of wavelengths. It should be understood that, as used herein, a depth plane may follow the contour of a flat or curved surface.

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

[0084] In some embodiments, the display system 250 may be configured to provide a substantially continuous cue for convergence / divergence movement and a plurality of discrete cues for depth adjustment. The cue for convergence / divergence movement may be provided by displaying different images to each of the user's eyes, and the cue for depth adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. In other words, the display system 250 may be configured to output light with a variable level of wavefront divergence. In some embodiments, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, 310.

[0085] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310, and / or a plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, respectively, configured to disperse incident light across each individual waveguide for output toward eye 210 as described herein. Light exits from output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly toward world 510 or viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams directed toward eye 210 at a particular angle (and amount of divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

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

[0087] In some embodiments, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520 that includes an optical module 530 that can include a light emitter such as a light emitting diode (LED). The light from the optical module 530 can be directed via a beam splitter 550 to a light modulator 540, such as a spatial light modulator, and thereby modified. The light modulator 540 can be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) including liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically and, in some embodiments, these image input devices can represent different optical paths and locations within a common projection system that are configured to output light into their associated waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 can function as an ideal lens while relaying the light input into the waveguides to the user's eye. In this concept, the object can be the spatial light modulator 540 and the image can 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 into the viewer's eye 210. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures are provided between the scanning fiber or fibers and one or more waveguides 270, 280, 290, 300, 310 and may, for example, 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 the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provision of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some embodiments, also be part of processing module 140 or 150 (FIG. 9D).

[0090] Continuing to refer to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar, or have another shape (e.g., curved), with major top and bottom surfaces and an edge extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external coupling optical elements 570, 580, 590, 600, 610 that are configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of the extracted light may be output by the waveguide at the location where the light propagating within the waveguide impinges on the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, that include diffractive optical features as further discussed herein. For ease of explanation and to clarify the drawings, the external coupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, but in some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces, and / or directly disposed within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material that forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that piece of material.

[0091] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (input into such waveguide 270) to the eye 210. The collimated light may represent an optically infinite focal plane. The next upper waveguide 280 may be configured to output collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane that is closer inwardly toward the eye 210 from the optically infinite. 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 generate another incremental amount of wavefront curvature so that the eye / brain interprets the light originating from the third upper waveguide 290 as originating from a second focal plane that is even closer inwardly toward the person from the optically infinite than the light from the next upper waveguide 280.

[0092] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the top waveguide 310 in the stack sends its output through all of the lenses between it and the eye for the collective focusing power that represents the focal plane closest to the person. When viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensation lens layer 620 may be disposed on top of the stack to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[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 to the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same multiple depth planes, using one set per depth plane. This can provide an advantage for forming tiled images to provide an extended field of view at those depth planes.

[0094] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light out of their respective waveguides for a particular depth plane associated with the waveguide and output this light with an appropriate amount of divergence or collimation. As a result, the waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be three-dimensional or surface features configured to output light at a specific angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be a volume hologram, a surface hologram, and / or a diffraction grating. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., a cladding layer and / or structure for forming a void).

[0095] In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 are diffraction features or “diffractive optical elements” (also referred to herein as “DOEs”) that form a diffraction pattern. Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of the beam is deflected towards the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several associated output beams that exit the waveguide at multiple locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam that bounces within the waveguide.

[0096] In some embodiments, one or more DOEs may be switchable between an “on” state where they actively diffract and an “off” state where they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets have a diffraction pattern within a host medium, and the refractive index of the microdroplets may be switched to substantially match that of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

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

[0098] Referring now to FIG. 7, an embodiment of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function similarly, and the waveguide assembly 260 includes a plurality of waveguides. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates through the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as the output beam 650. The output beams 650 are illustrated as being substantially parallel, but as discussed herein, they may also be redirected at an angle to propagate to the eye 210 depending on the depth plane associated with the waveguide 270 (e.g., to form a diverging output beam). It should be understood that a waveguide with an external coupling optical element that externally couples light to form an image that appears to be set on a depth plane at a long distance (e.g., optical infinity) from the eye 210 may be shown. Other waveguides or other sets of external coupling optical elements may output a more divergent output beam pattern, which would require the eye 210 to focus at a closer distance and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

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

[0100] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have a plurality of waveguides associated therewith. In such embodiments, it may be understood that each box in the figure, including those containing the letters G, R, or B, represents an individual waveguide, and three waveguides may be provided for each depth plane for which three primary color images are provided. The waveguides associated with each depth plane are shown adjacent to each other in this figure for ease of explanation, but it should be understood that in a physical device, all of the waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, a plurality of primary colors may be output by the same waveguide, e.g., such that only a single waveguide is provided for each depth plane.

[0101] Continuing to refer to FIG. 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may also be used in addition to or in place of one or more of red, green, or blue.

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

[0103] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light having one or more wavelengths outside of the visual perception range of the observer, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirection structures of the waveguide of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0104] Referring now to FIG. 9A, in some embodiments, light that impinges on a waveguide may need to be redirected to internally couple the light into the waveguide. An internal coupling optical element may be used to redirect and internally couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of image input devices 360, 370, 380, 390, 400 is input into the waveguide from a position that requires the light to be redirected for internal coupling.

[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 optical input area on the waveguide). For example, internal coupling optical element 700 is disposed on the major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on the major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on the major surface (e.g., the upper major surface) of waveguide 690. In some embodiments, one or more of the internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguides 670, 680, 690 (particularly, if one or more of the internal coupling optical elements are reflective deflecting optical elements). As illustrated, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface (or the upper portion of the next lower waveguide) of their respective waveguides 670, 680, 690, particularly if those internal coupling optical elements are transmissive deflecting optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the bodies of the respective waveguides 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of their respective waveguides 670, 680, 690 in some embodiments.

[0106] As shown, the internally coupled optical elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each internally coupled optical element may be offset such that its light is received without passing through another internally coupled optical element. For example, each internally coupled optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6, and may be separated (e.g., laterally spaced) from other internally coupled optical elements 700, 710, 720 such that it does not substantially receive light from other internally coupled optical elements 700, 710, 720.

[0107] Each waveguide also includes an associated light dispersing element. For example, the light dispersing element 730 is disposed on a major surface (e.g., upper major surface) of the waveguide 670, the light dispersing element 740 is disposed on a major surface (e.g., upper major surface) of the waveguide 680, and the light dispersing element 750 is disposed on a major surface (e.g., upper major surface) of the waveguide 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on the bottom major surface of the associated waveguides 670, 680, 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on both the upper and bottom major surfaces of the associated waveguides 670, 680, 690, or the light dispersing elements 730, 740, 750 may each be disposed on different ones of the upper and bottom major surfaces within different associated waveguides 670, 680, 690.

[0108] Waveguides 670, 680, 690 may be separated and isolated, for example, by a gas, liquid, and / or solid layer of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a refractive index lower than the material forming the directly adjacent ones of waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or 0.10 or less than the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light (e.g., TIR between the upper and bottom major surfaces of each waveguide) through waveguides 670, 680, 690. In some embodiments, layers 760a, 760b are formed from air. It should be understood that although not shown, the upper and bottom of the illustrated set 660 of waveguides may include the nearest cladding layer.

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

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

[0111] In some embodiments, the light rays 770, 780, 790 may have different properties, such as different wavelengths or different wavelength ranges, corresponding to different colors. The internal coupling optical elements 700, 710, 720 each deflect the incident light so that light propagates through an individual one of the waveguides 670, 680, 690 by TIR. In some embodiments, the internal coupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated internal coupling optical element.

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

[0113] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect light into its corresponding waveguide 670, 680, 690 and internally couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes light to propagate through the individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0114] Referring now to FIG. 9B, a perspective view of an embodiment of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 770, 780, 790 are each deflected by the internally coupled optical elements 700, 710, 720 and then each propagate by TIR within waveguides 670, 680, 690. The light rays 770, 780, 790 then each impinge on the light dispersion elements 730, 740, 750. The light dispersion elements 730, 740, 750 each deflect the light rays 770, 780, 790 so as to propagate towards the externally coupled optical elements 800, 810, 820.

[0115] In some embodiments, the light dispersing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPE deflects or disperses light to the external coupling optical elements 800, 810, 820, and in some embodiments, also increases the beam or spot size of the present light as it propagates to the external coupling optical elements. In some embodiments, the light dispersing elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to directly deflect light to the external coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light dispersing elements 730, 740, 750 may each be replaced with the external coupling optical elements 800, 810, 820. In some embodiments, the external coupling optical elements 800, 810, 820 are an exit pupil (EP) or an exit pupil expander (EPE) that directs light within the viewer's eye 210 (FIG. 7). It should be understood that the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, for example, is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate along the waveguide. Again, in response to a collision with the OPE, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further along the waveguide, etc. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed out of the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it impinges on the EP again, at which point another portion of the colliding light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light is "replicated" each time a portion of that light is redirected by the OPE or EPE, thereby forming a beam field of cloned light as shown in FIG. 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0116] Thus, referring to FIGS. 9A and 9B, in some embodiments, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPE) 730, 740, 750, and external coupling optical elements (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements that receive light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, the ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, then bounces along the waveguide and interacts with the light dispersion element (e.g., OPE) 730, then the external coupling optical element (e.g., EP) 800. The rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, and the ray 780 strikes the internal coupling optical element 710 and is thereby deflected. The ray 780 then bounces along the waveguide 680 via TIR and proceeds to its light dispersion element (e.g., OPE) 740, then the external coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and strikes the internal coupling optical element 720 of the waveguide 690. The internal coupling optical element 720 deflects the ray 790 such that the ray propagates, by TIR, to the light dispersion element (e.g., OPE) 750, then, by TIR, to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives the light externally coupled from the other waveguides 670, 680.

[0117] FIG. 9C illustrates a top and bottom plan view of an embodiment of a plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820 of each waveguide. However, as discussed herein, internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a particular light source to be uniquely coupled to a particular waveguide. In some embodiments, an arrangement including non-overlapping spatially separated internal coupling optical elements may be referred to as an offset pupil system, and the internal coupling optical elements within these arrangements may correspond to sub-pupils.

[0118] FIG. 9D illustrates an embodiment of a wearable display system 60 in which various waveguides and related systems disclosed herein may be integrated. In some embodiments, display system 60 is the system 250 of FIG. 6, and FIG. 6 schematically shows some parts of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

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

[0120] Continuing to refer to FIG. 9D, display 70 is operably coupled to local data processing module 140 by a communication link 130, such as a wired conductor or wireless connectivity, which may be mounted in various configurations, such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by a user, incorporated within headphones, or otherwise removably attached to user 90 (e.g., in a backpack configuration, in a belt attachment configuration). Similarly, sensor 120a may be operably coupled to local processor and data module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. Local processing and data module 140 may comprise digital memory, such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. Data may include (a) data captured from sensors such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, gyroscope, and / or other sensors disclosed herein (e.g., operably coupled to frame 80 or otherwise attachable to user 90), and / or (b) optionally, data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passage to display 70 after processing or retrieval. Local processing and data module 140 may be operably coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180 via a wired or wireless communication link, etc., such that these remote modules 150, 160 are operably coupled to each other and available as resources to local processing and data module 140.In some embodiments, the local processing and data module 140 may include one or more than one 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 than one of these sensors may be attached to the frame 80 or may be a stand-alone structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0121] Continuing to refer to FIG. 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more than one central processing unit (CPU), a graphics processing unit (GPU), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may comprise a digital data storage facility, which may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, the remote data repository 160 may include one or more than one remote server that provides information, such as information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, enabling full autonomous use from the remote module. Optionally, an external system (e.g., one or more than one processor, one or more than one computer system) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, for example, via a wireless or wired connection.

[0122] A. Diffraction Gratings with Reduced Polarization Sensitivity Providing a high-quality immersive experience to users of waveguide-based display systems, such as various display systems configured for the virtual / augmented / composite display applications described above, may depend, inter alia, on various characteristics of optical coupling into and / or out of the waveguide within the eyepiece of the display system. For example, a virtual / augmented / composite display having high internal and external coupling efficiencies may improve the viewing experience by increasing the brightness of the light directed towards the user's eye. As discussed above, internal coupling optical elements, such as internal coupling diffraction gratings, may be employed to couple light into the waveguide such that it is guided therein by total internal reflection. Similarly, external coupling optical elements, such as external coupling diffraction gratings, may be employed to couple light guided within the waveguide out of the waveguide by total internal reflection.

[0123] For example, as described above with reference to FIGS. 6 and 7, display systems according to various implementations described herein may include optical elements, such as diffraction gratings, internal coupling optical elements, external coupling optical elements, and light dispersing elements. For example, as described above with reference to FIG. 7, light 640 that is input 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 external 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 FIG. 6 can be configured as a diffraction grating.

[0124] To achieve the desired characteristics of internal coupling (or external coupling from there) of light into the waveguides 270, 280, 290, 300, 310, the optical elements 570, 580, 590, 600, 610 configured as diffraction gratings can be formed from a suitable material and have a suitable structure for controlling various optical properties, including diffraction properties such as diffraction efficiency as a function of polarization. Desirable diffraction properties that can be considered as possibilities include, among other properties, any one or more of the following, namely, spectral selectivity, angular selectivity, polarization selectivity (or non - selectivity), high spectral bandwidth, high diffraction efficiency, or wide field of view (FOV).

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

[0126] Figures 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 diffraction grating 1102. Diffraction grating 1102 can include a metal coating 1104 deposited on an internally coupled grating (ICG) pattern 1106 that comprises a patterned photoresist. Diffraction grating 1102 can be a blazed grating or another grating having asymmetric diffraction features, including an asymmetric form with at least one straight sidewall, a slanted sidewall, a concave corner (e.g., a sidewall with an acute concave corner with respect to the base surface), or a concave sidewall, a multi-step sidewall, other types of sidewalls, or some combination thereof. The resulting diffraction efficiency 1108 can be high for P-polarization (e.g., over a range of angles of incidence from -20 to 20 degrees, e.g., on average about 70%). However, diffraction grating 1102 may not be very efficient for S-polarization (e.g., over a range of angles of incidence from -20 and 20 degrees, e.g., on average about 20% or 30%). Thus, diffraction grating 1102 can result in an overall lower efficiency for unpolarized light (e.g., over a range of angles of incidence from -20 and 20 degrees, e.g., on average about 40% or 45%). Other efficiency values within and outside the recited ranges of the angle of incidence 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 grating 1122 may include, but is not limited to, at least one straight sidewall, a sloped sidewall, a concave corner (e.g., a sidewall with an acute concave corner with respect to the base surface) or a concave sidewall, a multi-step sidewall, other types of sidewalls, or a combination thereof, and may include a blazed grating or another grating having an asymmetric diffraction feature including an asymmetric form. The diffraction grating 1122 shown in FIG. 10B may have a non-metallic transmissive coating 1124 such as ZrO2, TiO2, or SiC, deposited on the ICG pattern 1106, for example, comprising a patterned photoresist. The diffraction efficiency 1128 resulting from the S-polarization may be higher than the diffraction efficiency 1126 for the P-polarization. For example, the S-polarization may have an average efficiency 1128 for S-polarization of 80%, 60%, or 40% over a range of angles of incidence from about -20 to 20 degrees. In another example, the P-polarization may have an average efficiency 1126 for P-polarization of 10%, 15%, or 20% over a range of angles of incidence from about -20 to 20 degrees. Other efficiency values within and outside the recited ranges of the angle of incidence are also possible.

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

[0129] Figures 11A and 11B respectively illustrate a diagram of an exemplary grating with a single coating that can have high efficiency in single polarization (e.g., TE or S-polarization), and an exemplary grating with a plurality of coatings as disclosed herein that has high efficiency in both TE and TM polarizations.

[0130] For example, as illustrated in FIG. 11A, the 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 diffraction 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 ZrO2, TiO2, or SiC. Image 1200 shows an exemplary scanning electron micrograph of a diffraction grating such as diffraction grating 1201 that can have a sawtooth pattern ICG 1202 with a TiO2 coating 1204. The transmissive layer 1204 (e.g., TiO2 coating) was deposited using glancing angle deposition (GLAD). Thus, as illustrated, much of the transmissive layer is on one side of the diffraction feature rather than the other side of the diffraction feature. Table 1 shows exemplary efficiencies associated with different types of light including TE polarization, TM polarization, and unpolarized light incident on diffraction grating 1201. As shown in Table 1, grating 1201 has increased efficiency in TE polarization compared to TM polarization and unpolarized light. As discussed above, such polarization-dependent efficiency may not be desirable. [Table 1]

[0131] As shown in FIG. 11B, the diffraction grating 1205 can include an ICG pattern 1202, a transmissive layer 1204 formed thereon, and a metal layer 1206 formed on the transmissive layer. The ICG pattern 1202 can be any suitable grating pattern such as a blazed grating pattern like the sawtooth pattern shown. These diffraction 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 like ZrO2 or TiO2, or other high n low k materials such as SiC. The transmissive layer 1204 (e.g., TiO2 coating) was deposited using glancing angle deposition (GLAD). Thus, as shown, much of the transmissive layer is on one side of the diffraction feature rather than the other side of the diffraction feature. 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 a way in which the metal layer 1206 can be disposed across the transmissive layer formed across the diffraction grating. Table 2 shows exemplary efficiencies associated with different types of light including TE polarization, TM polarization, and unpolarized light incident on the diffraction grating 1205.

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

Table 2-1

Table 2-2

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

[0134] During operation, an incident light beam 1016, such as from a light projection system that provides image content, for example visible light, is incident on a blazed diffraction grating 1008 at an incident angle α measured with respect to a plane normal 1002 that is normal or orthogonal to the surface or plane in which the blazed diffraction grating or substrate / waveguide extends and / or the surface 1004S of the waveguide 1004, for example the major surface of the waveguide (shown in FIG. 12A as extending parallel to the y-x plane) on which the grating is formed. The blazed diffraction grating diffracts the incident light beam 1016 as a diffracted light beam 1024, at least partially, at a diffraction angle θ measured with respect to the plane normal 1002. When the diffracted light beam 1024 is diffracted at a diffraction angle θ that exceeds the critical angle θ for the occurrence of total internal reflection within the waveguide 1004 TIR the diffracted light beam 1024 propagates within the waveguide 1004 and is generally guided via total internal reflection (TIR) along a direction parallel to the x-axis and along the length of the waveguide. A portion of this light guided within the waveguide 1004 reaches one of the light dispersion elements 730, 740, 750 or one of the external coupling optical elements (800, 810, 820, FIGS. 9A-9C) and can be diffracted again, for example.

[0135] As described herein, as in the illustrated implementation, a light beam incident at an angle in the clockwise direction (i.e., to the right of the plane normal 1002) with respect to the plane normal 1002 is said to have a negative α (α < 0), while a light beam incident at an angle in the counterclockwise direction (i.e., to the left of the plane normal) with respect to the plane normal 1012 is said to have a positive α (α > 0).

[0136] A suitable combination of the high refractive index material and / or the structure of the diffraction grating 1008 can result in a specific range (Δα) of the incident angle α, which is referred to herein as the acceptance angle or the field of view (FOV). One range Δα can be described by a certain angular range that extends to negative and / or positive values, outside of which the diffraction efficiency drops to 10%, more than 25%, more than 50%, or 75%, 80%, 90%, more than 95%, or any range between these values with respect to the diffraction efficiency at α = 0 or in some other direction. In some implementations, it may be desirable to have a Δα within a range where the diffraction efficiency is relatively high and constant, for example, a uniform intensity of the diffracted light is desired within Δα. Thus, in some implementations, Δα is associated with the angular bandwidth of the diffraction grating 1008 such that the incident light beam 1016 within Δα is efficiently diffracted by the diffraction grating 1008 at a diffraction angle θ with respect to the surface normal 1002 (e.g., in a direction parallel to the y - z plane), and θ is such that the diffracted light is guided within the waveguide 1004 under total internal reflection (TIR). TIR is exceeded. In some implementations, this angular Δα range can affect the field of view seen by the 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 to be incident on a reflective internal coupling grating (ICG) 1008 such as that shown in FIG. 12A through a substrate or a waveguide 1004. Light can be coupled into the substrate or the waveguide 1004 by the internal coupling grating 1008 such that the light is guided within the substrate or the waveguide by total internal reflection and experiences the same effect. Herein, the range (Δα) of the incident angle α, referred to as the acceptance angle or the field of view (FOV), can be affected by the refractive index of the substrate or waveguide material. In FIG. 12A, for example, a reduced angular range (Δα’) shows the effect of the refraction of the high refractive index material on the light incident on the internal coupling grating (ICG). However, the range of the angle (Δα) or the FOV is larger.

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

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

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

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

[0141] In a design where the diffraction feature is asymmetric, for example, the slope of the first sloped portion is shallower while the slope of the second sloped portion is steeper, the diffraction feature can be considered to be formed from repeated slopes and steps. Such a structure may be referred to herein as an inclined stepped structure. In some implementations, the second portion may not be as steeply sloped. For example, the second portion may be parallel to the normal 1002.

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

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

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

[0145] FIG. 12B shows an incident light beam 1016 that is incident on the grating 1008 at an angle α with respect to the normal direction 1002. (As discussed above with respect to FIG. 12A, in other embodiments, 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 or orthogonal to the extended surface of the blazed diffraction grating 1008 or the plane of the grating or waveguide and / or the surface 1004S of the waveguide 1004, e.g., the major surface or the opposing planar surface 1004S' of the waveguide on which the grating is formed. In FIG. 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 internal-coupling optical element or an internal-coupling diffraction grating, the diffraction grating 1008 can diffractively couple light incident in the substrate 1004, which can be a waveguide, as described above. The diffraction grating 1008 may optionally be configured as an external-coupling optical element, and in such embodiments, it can similarly diffractively couple light from the substrate 1004, which can be a waveguide, as described above.

[0147] Referring to FIGS. 12A and 12B, in some implementations, the substrate 1004 includes a polymer. For example, the polymer can include a polymerizable composition of one or more materials such as a high-viscosity polyfunctional component, a low-viscosity mono- or polyfunctional component, a photoinitiator, a light stabilizer, an antioxidant, a surfactant, inorganic nanoparticles or molecular-level clusters, any combination thereof, etc., or may include other materials. The substrate can include 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 can include, for example, an organic polymer consisting 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 acrylates containing resins that can be crosslinked in response to UV and / or heat curing may have a refractive index of 1.5 to 1.6. Some high refractive index organic polymers can have sulfur and / or aromatic groups in the acrylate crosslinked molecules.

[0148] The polymer can be patterned, for example, etched, and a grating structure can be processed. The diffraction characteristics of diffraction gratings 1008, 1010 such as lines are formed within the substrate 1004, such as within the surface of the substrate. The diffraction characteristics can be etched, for example, on one or both sides of the substrate, into the substrate 1004 including the polymer. The substrate can, for example, include a polymer, and the diffraction grating can be formed within the polymer substrate by etching or patterning the surface of the substrate.

[0149] Thus, in some implementations, the substrate and / or waveguide may include a material having a refractive index of, for example, 1.4 to 2.7, 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, but not limited to, the following materials, namely, SiO2, TiO2, B2O3, Li2O, La2O3, ZrO2, ZnO, Si3N4, or other glass materials. The substrate may thus have different refractive indices depending on the design. In some implementations, the substrate may include a polymer that can 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 include an organic polymer such as a low refractive index (less than a refractive index of 1.6, etc.) or a high refractive index organic resin (greater than a refractive index of 1.6). A low refractive index organic polymer having a refractive index of 1.5 to 1.6, such as PC, PMMA, PVA, etc., may be used, for example, or an acrylate containing a resin that can be crosslinked in response to UV and / or heat curing may be employed. Some exemplary high refractive index organic polymers can have sulfur and / or aromatic groups within the acrylate crosslinked molecules.

[0150] Thus, as described above, in the various implementations described herein, both the diffraction grating 1008 and the substrate 1004 or waveguide include 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 a monolithic structure. For example, the substrate 1004 may comprise a waveguide having a diffraction grating 1008 formed directly within the surface of the waveguide or substrate. In these implementations, a bulk polymer material may be patterned onto 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 the substrate, as discussed above, and may be patterned to form diffraction features therein. First and second layers of materials, 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, may be deposited across the diffraction grating (e.g., across the diffraction features). 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 combination of layers may increase the diffraction efficiency for both the first and second polarizations and thus may increase the diffraction efficiency for unpolarized light.

[0151] However, in some other implementations, the diffractive features such as lines that form the diffraction gratings 1008, 1010 may include materials different from those of the substrate. The bulk or substrate 1004 and the surface 1004S patterned to form the diffraction grating 1008 may thus include 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 that forms the substrate 1004. In some implementations, the patternable material from which the base pattern is formed includes a polymer having a refractive index in the range of 1.4 to 1.95. In some implementations, the substrate includes a high refractive index material having a refractive index of at least 1.9. The refractive index can be, for example, at least 2.0, at least 2.1, at least 2.2, or at least 2.3, and may be 2.4, 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 of these ranges. In some implementations, for example, the substrate includes a Li-based oxide such as lithium niobate. Other materials having a high refractive index may also be used. The substrate may, in some implementations, include, for example, silicon carbide (SiC). The substrate may, for example, potentially include a crystalline, cryptocrystalline, or amorphous substrate containing, for example, Ti, Z, Hf, La, Ba, Ca, Si, or O2. The substrate may include a high refractive index material such as a Li-based oxide (e.g., lithium niobate, LiNbO3), 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, some other materials formed on the substrate may have a lower refractive index than the substrate, for example.

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

[0153] Referring to FIGS. 12A and 12B, according to various embodiments, the diffraction grating 1008 may have various dimensions. For example, the diffraction characteristics 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) according to the design. This height may, in some implementations, correspond to the height of the peak 1003 and / or the depth of the groove 1005 or region (e.g., gap) between the peaks. However, other heights are also possible.

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

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

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

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

[0158] In some embodiments, the asymmetric geometric form may include a profile where the first sidewall forms an angle of 20 to 85 degrees with the substrate. In some embodiments, the second sidewall forms an angle different from 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 a biased deposition such that during a substantially straight deposition onto the grating (as illustrated in FIG. 14), the coating is included on the first sidewall but not on the second sidewall, or includes less coating on the second sidewall (e.g., a thinner or less coating on the second sidewall). In some embodiments, the height of the grating feature can be from 100 nm to 600 nm. In some embodiments, the pitch of the grating feature can be from 290 nm to 690 nm. Other values outside these ranges are also conceivable as possibilities.

[0159] The diffraction grating may be a one-dimensional (1D) grating or a two-dimensional (2D) grating. For example, as shown in FIGS. 13B-1 and 13B-2, the 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, for example, be undulating, repeating, or periodic or quasi-periodic in one direction. In some cases, the 1D array may comprise a plurality of 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 diffraction features 3303 arranged laterally in one direction (e.g., the horizontal direction in FIG. 13B-2). The diffraction features 3303 undulate in one direction (e.g., the horizontal direction in FIG. 13B-2) and are thus referred to as 1D. FIG. 13B-2 shows a top view of the exemplary device 3300. The diffraction features 3303 can form a series of elongated longitudinal features such as lines extending in one direction (e.g., the vertical direction in FIG. 13B-2). The elongated longitudinal features are arranged along one direction (e.g., the horizontal direction in FIG. 13B-2) and are repeated in that direction.

[0160] In another embodiment, the diffraction grating can include an array of protrusions or high points or regions, and lattice features such as holes, gaps, or low areas between the high points, regions, or protrusions, such as a 2D array. The 2D array can be, for example, in some cases, something like a lattice pattern. Any of the 1D arrays of the structures described herein can also be arranged in two directions to form a 2D array of diffraction features. The 2D array of diffraction features can include a plurality of 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 exemplary device 3400 having a 2D array of diffraction features 3403 (e.g., diffraction features 3403 arranged laterally in two dimensions or directions). In this embodiment, the array is similar to a lattice pattern. These features can be protrusions, or in this case, can be referred to as pillars. In this embodiment, the diffraction feature 3403 is symmetric with sidewalls that are substantially orthogonal to the horizontal axis. In other embodiments, the diffraction feature, e.g., the protrusion, can be symmetric with angled or inclined sidewalls. For example, FIGS. 13D-1 and 13D-2 show, respectively, a cross-sectional side view and a top view of an exemplary array of symmetric diffraction features. Both the left and right sidewalls are inclined inwardly such that the diffraction feature tapers or the width becomes smaller with an increase in height. Thus, in this embodiment, the first sidewall is inclined in one direction and the second sidewall is inclined in a second, opposite direction. In this embodiment, the sidewall inclination angle is about 30 degrees with respect to the horizontal axis and is symmetric on both sides. In some implementations, the 2D array can include lattice features formed by the orthogonal overlay of two 1D lattice structures. For example, the 2D array can include the orthogonal overlay of two blazed grating structures as described with reference to FIGS. 12A and 12B. Other configurations of 1D and 2D gratings are also conceivable. The geometric form 1302 shown in FIG. 13A can correspond to a cross-section of a diffraction feature of either a 1D or 2D grating. Such diffraction features can be arranged, for example, in a 1D or 2D array.

[0161] FIG. 13E shows another exemplary device 3600 having a 2D array of diffraction features 3603. The diffraction features are asymmetric in this embodiment. FIGS. 13F-1 and 13F-2 show a cross-sectional side view and a top view, respectively, of an exemplary array of asymmetric diffraction features. This 2D diffraction grating comprises a blazed diffraction grating. The diffraction features may be tapered, for example, in width or thickness with height. In the embodiment shown in FIG. 13E, the diffraction features have two sloped sidewalls or facets where one is more sloped than the other, while in the embodiments 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 diffraction features are asymmetric and blazed. As a result, the diffraction features preferentially diffract light in one direction over other directions. Such a diffraction grating may be useful as an internal coupling optical element configured to diffract light received from a projector towards a light distribution element, an external coupling optical element, or a combination of a light distribution element and an external coupling optical element, such as a CPE or a combined pupil expander-extractor. Such a diffraction grating may also be useful for externally coupling light to the eye, in contrast to the direction towards the environment or world in front of the user and the head-mounted display. The sidewall tilt angle is, in some implementations, 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 diffraction features may be able to form a 2D array of sawtooth structures, such as a sawtooth nanostructure.

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

[0163] Therefore, any of the structures or devices described in this specification, such as a lattice structure, may comprise a 1D lattice. Similarly, any of the structures or devices described in this specification, such as a lattice structure, may comprise a 2D lattice. Such a 2D lattice may be capable of diffusing light. These lattices may also comprise blazed lattices. Such blazed lattices may preferentially direct light in a certain direction. In some implementations, a 2D lattice (e.g., having one tilted facet on the diffraction feature) preferentially directs light in one direction, while in other implementations, a 2D lattice (e.g., having two tilted facets on the diffraction feature differently) preferentially directs light in multiple directions. Similarly, any of the methods or processes described in this specification may be used for a 1D lattice. Similarly, any of the methods or processes described in this specification may be used for a 2D lattice. These lattices, which are 1D or 2D, may be included on a substrate and / or waveguide, included within an eyepiece, and possibly integrated into a head-mounted display as disclosed in this specification. These lattices may be employed, for example, as an input lattice (e.g., ICG), an output lattice (EPE), a light distribution lattice (OPE), or a combined light distribution lattice / output lattice (e.g., CPE).

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

[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 may be a photolithography pattern regardless of the presence or absence of RLT. The monolithic polymer substrate may have a surface relief pattern defined on one or both sides of the waveguide. The pattern (e.g., multiple diffraction features) may, in addition or alternatively, be etched into the substrate (e.g., having a refractive index of 1.45 to 2.0), for example, once the pattern is imprinted or otherwise formed on the substrate.

[0166] In various implementations, the patterned material (e.g., a polymer or photoresist) and the substrate may be etched to form a pattern, such as that described with reference to FIG. 13A, within the substrate. Etching the photoresist and the 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 the portion of the patterned photoresist that is thickest results in negligible or no removal of material from the substrate, while the portion of the patterned photoresist that is thinnest (or non-existent) results in the deepest etching into the substrate.

[0167] In some other implementations, the patternable material is etched to form diffraction features of the patternable material. In such implementations, the diffraction features, which comprise the patternable material, remain on the substrate, which need not 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 diffraction features are to be angled, tilted, or slanted, template 3810 can be patterned to form an angled structure. Various processes, such as an etching process, can be directional and angled to form such an angled structure. Some examples of angled processes, such as an angled etching process, include ion beam milling, angled dry etching, ion etching, GLAD etching, tilted etching, Faraday cage etching, etc. In some implementations, the choice of material employed for template 3810 can assist in producing an angled structure having angled sidewalls within the template. In this example, the angled structure comprises angled elongated protrusions (e.g., for a 1D grating) or angled pillars (e.g., for a 2D grating). These angled elongated protrusions or angled pillars can have sidewalls that are tilted in the same direction and, in some cases, can be substantially parallel. Once template 3810 is processed, a layer of patternable material (e.g., a polymer, resist, photoresist, etc.) can be deposited on substrate 3801, and this layer can be imprinted using imprint template 3810. Template 3810 can be imprinted into patternable material (e.g., a resist material) 3805 on 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 diffraction features 3803 within substrate 3801 (or within a layer of material disposed on substrate 3801). In various implementations, dry etching is employed as shown. The etching can be directional. In the example shown, the etching process is not angled.The resulting diffraction feature 3803 formed within the substrate 3801 (or within a layer of material disposed on the substrate 3801) may have a certain shape, e.g., may be blazed as a result of the angled features within the mask 3805. In the illustrated embodiment, the cross-section of the diffraction feature has a trapezoidal or substantially triangular shape with two slanted sides. The sides slope in opposite directions. In the illustrated embodiment, one side is slanted more than the other side, creating an asymmetric or blazed structure. The process may be used to form a 1D or 2D array of diffraction features.

[0169] FIG. 13I shows another exemplary method 3850 of forming a blazed diffraction feature. The mask 3855 and the underlying substrate 3851 (or a layer of material disposed on the substrate 3851) are etched at an angle (e.g., dry etched) to form the diffraction feature 3853 within the substrate 3851 (or within 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 comprise elongated protrusions (e.g., for a 1D grating) or tapered pillars (e.g., for a 2D grating) with a trapezoidal or substantially triangular cross-section. These elongated protrusions or tapered pillars may have sidewalls that slope in opposite directions. One sidewall may be slanted more than the other sidewall. Applying an angled etching process to these elongated protrusions or tapered pillars may produce a blazed grating within the material underlying the elongated protrusions or tapered pillars, e.g., within the substrate or a layer of material disposed on the substrate. A blazed diffraction feature having sides slanted in the same direction may be produced. In various implementations, one of the sides is slanted more than the other side. The process may be used to form a 1D or 2D array of diffraction features.

[0170] In various implementations, the resulting diffraction features may be blazed in two or more directions as a result of the angled features within the 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). Diffraction features or gratings blazed in two or more directions may be produced by etching twice. In some implementations, for example, diffraction features or gratings blazed in two or more directions may be produced by etching using a first mask and then etching again using a second, different mask. In some instances, as shown in FIG. 13J, mask 3905 and substrate 3901 may be etched to form a first sidewall of diffraction feature 3903 within substrate 3901. Additionally, patterning may be provided to form a second sidewall. In various implementations, a second mask having a different orientation and / or shape may be used to form the second sidewall. The second mask (e.g., at an angle and / or different orientation with respect to the first sidewall) may be etched, for example, to form the second sidewall. In some implementations, after the first sidewall of diffraction feature 3903 is formed, a planarization layer 3907 may be added over the intermediate diffraction feature 3903 and substrate 3901. The planarization layer 3907, intermediate diffraction feature 3903, and / or substrate 3901 may be patterned and etched (e.g., at an angle with respect to the first sidewall) to form the second sidewall. The above examples are discussed in the context of patterning a substrate, but in some implementations, the processes described above may be employed to pattern a layer formed on the substrate without patterning the substrate. Alternatively, in some implementations, the processes described above may be employed to pattern both a layer formed on the substrate and the substrate.

[0171] Additionally, while exemplary methods 3800, 3850, 3900 are illustrated to form a 2D array of asymmetric diffraction features, the method can also be used to form a 2D array of symmetric diffraction features (regardless of the presence or absence of angled sidewalls). The method can also be used to form a 1D array of diffraction features. In some instances, the diffraction features within the 1D array can be symmetric, regardless of the presence or absence of angled sidewalls. In some instances, the diffraction features within the 1D array can be asymmetric, for example, with angled sidewalls. Thus, in some cases, blazed diffraction features may be formed.

[0172] 2. Exemplary Layer One or more transmissive layers may be disposed on the base pattern. For example, as illustrated in FIG. 14, the deposition of one or more transmissive layers onto 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 that can result in a material layer covering various surfaces of underlying features. The deposited layer can potentially be of substantially equal thickness across the base pattern geometry 1410. In some embodiments, directed deposition can include linear deposition (1404A, 1404B, 1404C) such that the material 1412 being deposited impinges on the base pattern 1410 at an angle substantially orthogonal to the plane or horizontal direction or plane major surface of the substrate. In another embodiment, directed deposition can include angled deposition (1406A, 1406B, 1406C) such that the material 1412 being deposited impinges on the base pattern 1410 at an angle 1414 with respect to the plane or horizontal direction or plane major surface of the substrate. For example, the angle 1414 can be selected based on the pattern geometry. For example, the diffraction grating can be a blazed diffraction grating having a sawtooth structure. The angle 1414 can be substantially orthogonal to the surface of the sawtooth structure such that the material 1412 being deposited deposits more substantially on a portion (or specific sidewall) of the sawtooth structure as illustrated in 1406A, 1406B, 1406C.

[0174] The deposition type and base pattern geometry can affect the thickness and placement of the layers of material 1412 being deposited. Advantageously, controlling the thickness and placement of the layers of material 1412 and generating a biased or angled deposition profile can enable better control for emitting light in a certain direction from the ICG. As illustrated in FIGS. 13 and 14, the pattern geometry may be asymmetric and have one or more straight sidewalls, angled sidewalls, concave corners or concave sidewalls, stepped sidewalls, other sidewalls, or some combination thereof. For example, the pattern geometry may be serrated with two asymmetric angled sidewalls as shown in 1402A, 1404A, 1406A. In another embodiment, the pattern geometry may have a straight sidewall and a stepped sidewall as shown in 1402B, 1404B, 1406B. In another embodiment, the pattern geometry may have a concave corner sidewall and an angled sidewall as shown in 1402C, 1404C, 1406C. In the case of conformal deposition, layer 1412 may cover the top and sides of the diffraction features. In some cases, the thickness of layer 1412 may be substantially equal across different types of pattern geometries (or a majority of the pattern geometry). In the case of directed deposition, for some cases of straight or angled deposition, the amount deposited on the top and one or more sides may be different (see, e.g., 1404B, 1406B) or the amount deposited on two different (e.g., opposite) sides may be different (see, e.g., 1404A, 1404B, 1404C, 1406A, 1406B, 1406C). In some cases, one or more sides may be exposed and have a very small amount of material deposited thereon as in 1406A, 1406B, and 1406C and 1404B and 1404C. Additionally, in the case of directed deposition, the thickness of layer 1412 across different types of pattern geometries may be more strongly dependent on the pattern geometry. For example, in the case of the serrated geometry 1404A, straight directed deposition may deposit substantially more on the portion 1416 of the serration with a lower slope than on the portion 1418 of the serration with a higher slope.In another embodiment, for the sawtooth geometry 1406A, depositions angled substantially perpendicular at an angle 1414 θ of 45° to 135° or 60° to 120° or 80° to 100° with respect to the surface 1420 of the substrate are likely to deposit more material on such a surface 1420 than depositions angled such that 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 the diffraction efficiency for polarization such as S - polarization or TE - polarization. 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 embodiments, the transmissive layer can be a high - refractive - index dielectric such as titanium dioxide (TiO2), zirconium dioxide (ZrO2), Si3N4, ZnO, SiC, ZnTe, GaP, BP, or other materials. In some embodiments, the high - refractive - index material 1502 may have a refractive index of 1.9 to 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 indices, or may be within any range formed by these values. In some embodiments, the material is a high - refractive - index material (e.g., n>2) with low k (e.g., k<0.05), such as silicon carbide (SiC).

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

[0177] In an embodiment where the sub - layer includes an alternating material, the transmissive layer can include alternating sub - layers of a high refractive index material 1502 and a low refractive index material 1504. For example, the high refractive index material 1502 can be TiO2, or Si3N4, ZnO, ZrO with a refractive index of 2.2 2. It can include materials 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 in the range of 1.9 to 3.5. Additionally, in some designs, the low refractive index material 1504 can include SiO2 having a refractive index of 1.45, or materials having a refractive index less than or equal to 1.9 or 2, such as less than 1.6. In some embodiments, the alternating layer can include a first layer of the high refractive index material 1502, a second layer of the low refractive index material 1504, and a third layer of the high refractive index material 1504.

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

[0179] In the embodiment shown in FIG. 15, a low refractive index material 1504 such as SiO2 is disposed between layers of a high refractive index material 1502 such as TiO2 to create a highly reflective surface. By varying the thickness of one or more of the sub-layers 1502, 1504 of the materials, the diffraction grating 1500 can be configured to enable maximum reflectivity within a certain wavelength and potentially serve as a color filter or provide some degree of color adjustment. For example, the layer thickness may be configured to create ICG diffraction for selecting a wavelength 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 across the transmissive layer. For example, as illustrated in FIG. 16, the 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 as or different from the deposition type of the transmissive layer. FIG. 16 illustrates various combinations. For example, the transmissive layer may be deposited conformally (1402A), and the metal layer may be deposited conformally (1602A) or directionally in a straight line (1604A), or directionally at an angle (1606A). In another embodiment, the transmissive layer may be deposited directionally in a straight line (1404A), and the metal layer may be deposited conformally (1602B) or directionally in a straight line (1604B), or directionally at an angle (1606B). In another embodiment, the transmissive layer may be deposited directionally at an angle (1404A), and the metal layer may be deposited conformally (1602C) or directionally in a straight line (1604C), or directionally at an angle (1606C).

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

[0182] The deposition type and base pattern geometry can affect the thickness and placement of the layers of material 1612 being deposited. As discussed above with reference to FIG. 14, advantageously, controlling the thickness and placement of the layers of material 1612 being deposited and generating a biased or angled deposition profile can enable better control for emitting light from the ICG in a certain direction. As illustrated in FIGS. 13 - 15, the pattern geometry may be asymmetric and have straight sidewalls, angled sidewalls, concave corners or concave sidewalls, stepped sidewalls, other sidewalls, or some combination thereof. In the case of conformal deposition, the thickness of layer 1612 may be substantially equal across different types of pattern geometries (or a majority of the pattern geometry). In the case of directional deposition, the thickness of layers 1412, 1610 across different types of pattern geometries may be more strongly dependent on the pattern geometry. For example, in the case of the sawtooth geometry 1604A, linear directional deposition may deposit substantially more on the portions of the sawtooth with a lower slope than on the portions of the sawtooth with a higher slope. In another example, in the case of the sawtooth geometry 1606A, angled deposition that is substantially orthogonal to the plane or horizontal surface or major planar surface of the substrate may deposit more material 1612 on the surface 1420 with a shallow slope than on the surface 1422 with a steep slope.

[0183] The metal layer can include a metal or conductive material such as a material including aluminum, silver, gold, copper, or an alloy thereof. In some designs, the metal used within 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] The permeable layer is discussed as the first layer on the base pattern, and the metal layer is discussed as the second layer, but the layers may be installed in any suitable order. Additionally, or alternatively, one or more additional layers of material may be present between the base pattern, the permeable layer, or the metal layers. In some embodiments, one or more layers may be repeated or interleaved. In some embodiments, one or more layers may be partial layers such that a material that may be part of the layer is deposited on a part of the substrate or the base pattern.

[0185] In some embodiments, an interface layer may be present between the metal layer and the permeable layer. The interface layer may increase the adhesion strength of the metal layer and the environmental reliability of the stack. For example, in the absence of an interface layer, a metal layer such as Ag, Au, Cu, or Al metal may peel from the lattice during unfavorable environmental conditions such as heat and humidity. In some embodiments, the interface layer can include TiO2 or other layers that may help bond the metal layer to the polymer surface.

[0186] The deposition of the transmissive layer, metal layer, or any other layer can include physical vapor deposition (PVD). PVD can 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, the deposition of the transmissive layer, metal layer, or any other layer can include chemical vapor deposition (CVD). CVD can include plasma enhanced low pressure deposition, atmospheric pressure deposition, atomic layer deposition (ALD), or other forms of chemical vapor deposition. The 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 layer being deposited. For example, the deposition thickness bias may be decreased for very conformal processes such as those performed on an atomic scale one monolayer at a time. In another embodiment, the coating quality (e.g., from the perspective of particle size or density) can be affected by changes to the processing temperature and pressure. The coating quality can, in turn, affect the n and k of the layer and the shape of the adjacent layer coated on top of the layer being deposited.

[0187] 3. Exemplary waveguides including diffraction gratings with reduced polarization sensitivity A diffraction grating having a reduced polarization sensitivity as described above can be used within the context of an AR display. For example, a waveguide, which can be part of an AR display, can include a diffraction grating that can serve as an internal coupling optical element and / or a light dispersing element and / or an external coupling optical element on one or more sides of the waveguide (such as those described with reference to FIGS. 6 and 7). FIG. 17A illustrates an exemplary waveguide having a plurality of diffraction gratings, including a reduced polarization sensitivity diffraction grating that can act as an internal coupling optical element. For example, as shown, waveguide 1710 can 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 embodiment, gratings 1720, 1722 may comprise a pupil expander - extractor (CPE) region, which operates as both a light dispersing element and an external coupling grating. Light 1702 can be introduced into one side of waveguide 1710 through transmissive ICG 1714. Transmissive ICG 1714 can pass light 1702 into waveguide 1710 and diffract light 1706. Light 1706 can propagate along waveguide 1710 towards one or more pupil expander - extractor gratings 1720, 1722. Second reflective ICG 1712, which can be on the opposite side of waveguide 1710, can also be configured to reflect light 1704 into waveguide 1710. The reflected light 1704 can propagate along waveguide 1710 towards one or more pupil expander - extractor gratings 1720, 1722. Advantageously, the inclusion of one or more ICGs 1712, 1714 can be useful for image uniformity and / or eyebox efficiency depending on the source light (e.g., LED, micro - LED, laser, polarized light source, or non - polarized light source).

[0188] The reflective ICG1712 or the transmissive ICG1714 may include a diffraction grating. The diffraction grating of either or both of the reflective ICG1712 and the transmissive ICG1714 may be formed within a waveguide or a layer on a substrate or within the waveguide itself. The diffraction grating may have diffraction characteristics as described above with reference to FIGS. 12A-12B and FIGS. 13A-13J. For example, the diffraction characteristics of the diffraction grating may have various dimensions and symmetric or asymmetric forms.

[0189] In some embodiments, the geometric form of the diffraction characteristics of the reflective ICG1712 and / or the transmissive ICG1714 can be symmetric, with straight sidewalls, slanted sidewalls, concave corners or concave sidewalls, stepped sidewalls (see, for example, the third column in the first row of FIG. 13A), other types of sidewalls, or some combination thereof. In another embodiment, the geometric form can be asymmetric, with at least one straight sidewall, slanted sidewall, concave corner (see, for example, the third column in the second row of FIG. 13A) or concave sidewall, stepped sidewalls (see, for example, the second column in the second row of FIG. 13A), other types of sidewalls, or some combination thereof. Regardless of whether the diffraction characteristics are asymmetric or symmetric, in some implementations, a flat region or flat portion may be located at the top (e.g., the peak) of the feature. The grating may have a height greater than or less than that defined by a height in the range of 100 nm to 600 nm. For example, the grating may have a depth or height measured from the base to the peak in any range defined by, for example, 100-300 nm, 300-600 nm, 200-400 nm, 300-500 nm, etc., or any of these values. The grating may have a pitch greater than or less than that defined by a pitch in the range of 290 nm to 690 nm. If the grating is a blazed grating, the grating may have a blaze angle measured in the same angular direction, for example, 20-85 degrees, 45-80 degrees, or another angle, and a reverse blaze angle of, for example, about 70-150 degrees or any value within the range defined by these values. Values outside any of these ranges are also potentially considered.

[0190] The reflective ICG1712 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, one or more transmissive layers 1713 can be efficient in diffracting TE polarization within one or more wavelength ranges. For example, one or more transmissive layers can be efficient in diffracting TE polarization within a wavelength range associated with red (e.g., about 620 - 780 nm), a wavelength range associated with green (about 492 - 577 nm), or a wavelength range associated with blue (e.g., 435 - 493 nm). In some embodiments, one or more metal layers 1711 can be efficient in diffracting TM polarization within one or more wavelength ranges. For example, one or more metal layers can be efficient in diffracting TM polarization within a wavelength range associated with red (e.g., about 620 - 780 nm), a wavelength range associated with green (about 492 - 577 nm), or a wavelength range associated with blue (e.g., 435 - 493 nm). The transmissive ICG1714 can include one or more transmissive layers 1715 as described above with reference to FIGS. 14 and 15. In some embodiments, one or more transmissive layers can be efficient in diffracting TE polarization within one or more wavelength ranges. For example, one or more transmissive layers can be efficient in diffracting TE polarization within a wavelength range associated with red (e.g., about 620 - 780 nm), a wavelength range associated with green (about 492 - 577 nm), or a wavelength range associated with blue (e.g., 435 - 493 nm). In some embodiments, one or more transmissive layers 1715 can 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 has a primary diffraction order (e.g., +1 or -1). Most of the diffracted light may occur within the primary 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 thereof, is guided within the waveguide by total internal reflection, for example, towards a pupil expander - extractor grating. The geometry of the diffraction features, such as asymmetry or blazed, may preferentially direct the light, for example, towards the pupil expander - extractor grating. The pupil expander - extractor grating may be configured to externally couple the light from the waveguide to the eye of the user or wearer. The pupil expander - extractor grating may, in addition, 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 non - polarized or circularly polarized light and directs this non - polarized or circularly polarized light towards the ICG for input into the waveguide. Some examples of such projectors that output non - polarized or circularly polarized light and form an image may include, for example, micro - LED projectors, digital light projectors (DLP), and liquid crystal on silicon (LCOS) - based projectors, although others are also possible as considered.

[0192] FIG. 17B illustrates an exemplary waveguide having a plurality of diffraction gratings that can act as an internal coupling optical element. For example, as shown, waveguide 1710 may include one or more internal coupling gratings (ICGs) 1717, 1714 and one or more gratings 1720, 1722 that perform beam splitting and external coupling. Gratings 1720, 1722 may include one or more pupil expander - extractor (CPE) regions, which operate as both a beam - dispersing element and an external coupling grating. Light 1702 can be introduced into one side of waveguide 1710 through transmissive ICG 1714. The transmissive ICG 1714 (e.g., comprising a transmissive grating) can pass light 1702 into waveguide 1710 and diffract light 1706. The transmissive ICG 1714 may have a TE diffraction efficiency higher than the TM efficiency. Light 1706 can propagate along waveguide 1710 towards 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 is in series with (e.g., aligned with) the transmissive ICG 1714 and can be on the opposite side of waveguide 1710, can be configured to diffract and reflect light 1704 into waveguide 1710. The second reflective ICG 1717 can operate in a reflection mode and may have a TM diffraction efficiency higher than the TE efficiency. The diffracted / reflected light 1704 can propagate along waveguide 1710 towards one or more pupil expander - extractor gratings 1720, 1722. Advantageously, the inclusion of one or more ICGs 1712, 1717 may potentially help with image (e.g., brightness and / or color) uniformity and / or eyebox efficiency, depending somewhat on the source light (e.g., LED, micro - LED, laser, polarized, or unpolarized source).

[0193] The transmissive ICG1714 and / or ICG1717 may include a diffraction grating. The diffraction grating of either or both of the reflective ICG1717 or the transmissive ICG1714 may be formed within a layer on the waveguide or within the waveguide or the substrate itself. The diffraction grating may have diffraction characteristics as described above with reference to FIGS. 12A-12B and FIGS. 13A-13J. For example, the diffraction characteristics of the diffraction grating may have various dimensions and different geometric forms. For example, see FIG. 13A showing sawteeth (e.g., row 1, column 2 and row 2, column 1), multi-steps (e.g., row 1, column 3 and row 2, column 2), and concave corners (e.g., row 2, column 3 of FIG. 13A). As described herein, the diffraction characteristics may be blazed (e.g., see row 2 of FIG. 13A) and direct light in a specific direction.

[0194] In some embodiments, the geometric form of the diffraction features of the transmissive ICG1714 and / or the reflective ICG1717 can be symmetric with straight sidewalls, sloped sidewalls, concave corners or concave sidewalls, multi-step sidewalls, other types of sidewalls, or some combination thereof. In another embodiment, the geometric form can be asymmetric with at least one straight sidewall, sloped sidewall, concave corner or concave sidewalls, multi-step sidewalls, other types of sidewalls, or some combination thereof. Regardless of whether the diffraction features are asymmetric or symmetric, in some implementations, a flat region or flat portion may be located at the top (e.g., peak) of the feature. The grating may have a height and / or depth greater than or less than that defined by a height in the range of 100 nm to 600 nm (e.g., 200 - 400 nm, 205 - 350 nm, 210 - 400 nm, 350 - 500 nm, 300 - 600 nm, 400 - 600 nm, 200 - 600 nm, 200 - 500 nm, or any range formed by any of these values). The grating may have a pitch greater than or less than that defined by a pitch in the range of 290 nm to 690 nm. When the grating is a blazed grating, the grating may have a blaze angle, measured in the same angular direction, of, for example, about 20 - 85 degrees and a retroblaze angle of, for example, about 70 - 150 degrees or any value within the range defined by these values. These angles can represent interior angles measured from the base of the diffraction grating to the corresponding sidewall or surface. Values outside of any of these ranges of these ranges are also potentially considered.

[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, one or more metal layers 1711 can be effective in constructing a grating that is efficient in diffracting TM polarization within one or more wavelength ranges. For example, the inclusion of one or more metal layers can provide an increased diffraction efficiency of TM polarization within a wavelength range associated with red (e.g., about 620 - 780 nm), a wavelength range associated with green (about 492 - 577 nm), or a wavelength range associated with blue (e.g., 435 - 493 nm). Other designs of diffraction gratings that diffract or are efficient in preferentially diffracting TM polarization are also conceivable as possibilities.

[0196] Advantageously, the combination of a transmissive ICG that preferentially diffracts TE light to be guided therein within a waveguide and a reflective ICG that preferentially diffracts TM light to be guided therein within a waveguide provides efficient diffraction and internal coupling of both TE and TM polarizations. Thus, this combination of gratings can diffract light more efficiently, including both TE and TM polarizations such as unpolarized light, and in the case of ICG, couple this light into the waveguide. As described above, in various designs, the diffracted light occurs within a first order such as +1 and / or -1 diffraction orders.

[0197] Therefore, the light received from a projector such as an image projector can be diffracted by one or more gratings 1717, 1714 such that the main light from the projector or at least a part thereof is diffracted and coupled into the waveguide at an angle or within an angular range and guided therein by total internal reflection towards, for example, a pupil expander - extractor grating, an optical dispersion element and / or an external coupling optical element. The geometry of the diffraction features, such as asymmetry or blazed, can preferentially direct the light in a particular direction, such as towards the pupil expander - extractor grating. The pupil expander - extractor grating may be configured to externally couple the light from the waveguide to the eye of the user or wearer. The pupil expander - extractor grating may, in addition, increase the area (in two dimensions) over which light exits the waveguide. Thus, the pupil expander - extractor grating can potentially increase the eyebox in some implementations. In various implementations, the projector outputs non - polarized or circularly polarized light and directs the non - polarized or circularly polarized light towards the ICG for input into the waveguide. Some examples of such projectors or light sources that output non - polarized or circularly polarized light and form an image can include, for example, micro - LEDs and micro - LED projectors, digital light projectors (DLPs), and liquid crystal on silicon (LCOS) - based projectors, although others are also possible as contemplated.

[0198] FIG. 17C illustrates another exemplary waveguide configured to increase the efficiency of coupling light therein. The waveguide includes at least one reduced polarization sensitivity diffraction grating that can act as an internal coupling optical element. For example, as illustrated, waveguide 1710 may include at least one internal coupling grating (ICG) 1730 and external coupling gratings 1720, 1722. Gratings 1720, 1722 may include a pupil expander - extractor (CPE) region, which operates as both a light dispersing element and an external coupling grating. For example, light 1702 from a projector comprising one or more light sources (e.g., micro - LED, laser, LED) may be input through a transmissive ICG 1730 having a transmissive diffraction grating that diffracts at least a portion of the light transmitted therethrough into one side of waveguide 1710. The transmissive ICG 1730 may pass light 1702 through its grating into waveguide 1710 and 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 efficiencies. Grating 1730 may be designed to diffract light incident thereon within a range of angles into a certain direction or within a range of angles that undergo total internal reflection within the waveguide. Thus, light 1706 may be guided or propagated along waveguide 1710 towards one or more pupil expander - extractor gratings 1720, 1722. Advantageously, the inclusion of the transmissive ICG 1730 can contribute to image uniformity and / or eyebox efficiency depending on the source light (e.g., LED, laser, polarized, or unpolarized).

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

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

[0201] The transmissive ICG1730 can include a high refractive index grating configured to be efficient in both TM and TE. For example, ICG1730 can have an ICG profile and / or material composition improved to obtain diffraction that is insensitive to the polarization of light and efficient over a certain range of input angles of light. For example, ICG1730 can have a diffraction efficiency within or above a range of 40 - 90 percent (e.g., 50% - 60%, 60% - 70%, 70% - 80%, 80% - 90%, or any range between these values) for the TE mode, and within or above a range of 40 - 90 percent (e.g., 50 - 60%, 60 - 70%, 70 - 80%, 80 - 90%, or any range between these values) for the TM mode. In some embodiments, ICG1730 can have similar efficiency in the TE and TM modes. For example, ICG1730 can have a TM mode efficiency within 5%, 10%, 20%, 25%, 30% of the TE mode efficiency (or within any range between these values). Or, ICG1730 can have a TE mode diffraction efficiency within 5%, 10%, 20%, 25%, 30% of the TM mode efficiency (or within any range between these values). Thus, in various implementations, the difference in diffraction efficiency for the TE and TM modes can be within 5%, 10%, 20%, 25%, 30% of the TE mode efficiency (or within any range between these values). Other embodiments are also possible. These efficiencies can be average efficiencies over a certain range of angles (e.g., 5 degrees, 10 degrees, 20 degrees, 30 degrees, 40 degrees, 50 degrees, or any range between these values). Similarly, these efficiencies can optionally be averaged over wavelengths, for example, wavelengths of visible spectrum light, or specific colors, such as wavelengths or multiple wavelengths related to red, blue, or green. For example, wavelengths output by a light source within a projector, which can include a plurality of colored light sources, can be considered. As described above, diffraction can occur within a certain diffraction mode or multiple modes, such as a primary mode like +1 and / or -1 diffraction orders.

[0202] Figures 17D-1 through 17D-4 illustrate exemplary tilted ICG profiles and compositions, and corresponding polarization efficiency graphs, that can be used to achieve polarization insensitivity within the internal coupling lattice of an ICG 1730, etc., as illustrated in FIG. 17C. For example, grating 1742 can generate the TM and TE efficiency profiles 1741 shown in the graph, grating 1744 can generate the TM and TE efficiency profiles 1743 shown in the graph, grating 1746 can generate TM and TE efficiency profiles 1745, and grating 1748 can generate TM and TE efficiency profiles 1747.

[0203] The grating 1742 shown in FIG. 17D-1 may include a grating having an inclined diffraction feature with an inclination angle of θ. The inclination angle may include an angle of 20 to 85 degrees or another angle. These angles may represent interior angles measured from the base of the diffraction grating to the corresponding sidewall or surface. In some embodiments, the duty cycle 1762A of the grating 1742 may be a certain 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. The height 1764A of the grating may be, for example, a height in the range of 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 200 nm, 205 nm, 300 nm, 400 nm, 500 nm, 600 nm, or greater than 700 nm or 800 nm, etc., or within any range formed by any of these values. In some embodiments, the grating 1742 may be disposed on a waveguide or on a layer on a substrate or within a part of the waveguide or the 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 one implementation, be within any range formed by 1.4 to 1.5, 1.5 to 1.6, 1.6 to 1.7, 1.7 to 1.8, and / or less than 1.8 to 1.9, or any of these values. In some embodiments, the grating feature may include a material having a refractive index similar to or the same as that of the substrate or waveguide. In the illustrated embodiment, the grating 1742 has a diffraction feature with a refractive index of 1.75 on a substrate having a refractive index of 1.75. The materials used to form the diffraction feature and to constitute the substrate may be the same or different. The diffraction feature may be etched into the substrate, or a layer of material having the same or different (e.g., higher or lower) refractive index may be used for the diffraction feature. For example, the substrate may have a refractive index lower than the material forming the diffraction feature.In some cases, for example, the substrate has a refractive index of less than 1.9, while the diffraction feature has 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, or within any range formed by any of these values. Values outside of these ranges are also considered possible. In some embodiments, the 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 a layer of the material.

[0204] The TM and TE diffraction efficiency profiles (1750, 1752 respectively), associated with the grating 1742, can approximately match over a range of incident angles, as shown in graph 1743, and / or can 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 can be 40% - 60% or 0.4 - 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 within any range formed by at least 45%, 50%, 55%, 60%, 65%, 70%, 80%, 90%, 95%, or 99%, or any of these values) over a range of incident angles such as -10 degrees to 10 degrees, or 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 is 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) on average over a range of incident angles of light of at least 30 degrees or other angular ranges (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 is at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 on average over a range of incident angles of light of at least 20 degrees, over a range of incident angles of light of at least 10 degrees. In some embodiments, the diffraction efficiency is at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 on average. 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 incident angles of light of at least 30 degrees.In some embodiments, the diffraction efficiency is at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 over an incident angle range of light of at least 20 degrees. In some embodiments, the diffraction efficiency is at least 0.4 or 0.5 or 0.6 or 0.7 or 0.8 over an incident angle range of light of at least 10 degrees. The diffraction efficiency may be within any range between any of these values, or similarly, potentially over other larger angle ranges, over any of these angle ranges. Similarly, as described above, the average diffraction efficiency over a range of wavelengths may be within a range of angles such as 3°, 6°, 12°, 18°, 20°, 25°, 30°, 35°, 40°, or any range formed by any of these values, within 30%, 25%, 20%, 15%, 10%, 5%, 2.5%, 1%, or any range formed by any of these values. The diffraction efficiency may be higher for the TE mode in some designs, or may be higher for the TM mode in some designs. In some designs, the diffraction efficiency may be higher for the TE mode at some angles and for the TM mode at other angles.

[0205] The average diffraction efficiency may be increased by using a higher refractive index material (e.g., a material having a refractive index greater than 2), such as that illustrated in grating 1744 of FIG. 17D-2. Grating 1744 is similar to that described with reference to FIG. 17D-1 and includes a tilted grating with diffraction features, geometric shapes and features, consisting of a higher refractive index material 1766, such as a 2.2 refractive index material like TiO2 or a 2.6 refractive index material like SiC. The resulting TM and TE efficiency profiles (1750, 1752, respectively) may approximately match over a range of incident angles (e.g., within 30%, 20%, 15%, 10%, 8%, 5%, etc.), and / or may be more efficient in TE and more efficient in TM (or vice versa) at points within a range of incident angles, as illustrated in graph 1745. In some embodiments, the average diffraction efficiency may have a peak of about 80% - 100% or 0.8 - 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, or any range formed by any of these values, on average, over an incident angle range 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, or any range formed by any of these values, on average, over an incident angle range 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, or any range formed by any of these values, on average, over an incident angle range 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, on average, over an incident angle range 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, averaged over an incident light angle range 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 an incident light angle range 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 an incident light angle range 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 an incident light angle range of at least 10 degrees.

[0206] Similar to grating 1742, grating 1744 as shown in FIG. 17D-2 may include a grating having a tilted diffraction feature with an inclination angle of θ. The inclination angle may include an angle of 20 to 85 degrees or another angle. One side or the sidewall is a concave corner sidewall, and the cross-section has a shark fin shape. The cross-section is in the shape of an inclined parallelogram, but other shapes are also conceivable. In some embodiments, the duty cycle 1762B of grating 1744 can be a certain percentage of the pitch of the grating. For example, the duty cycle may be 20 to 80 percent of the pitch, for example, 50 percent of the pitch. The height 1764B of the grating may be, for example, a height of 100 to 600 nm (for example, 100 to 300, 200 to 400, 300 to 500, 400 to 600 nanometers, or any range between 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 these values or outside these ranges. In some embodiments, grating 1744 may be disposed on a waveguide or a layer on a substrate, or be a part of or incorporated within the waveguide or the substrate itself, for example, by etching into the substrate. In some embodiments, the substrate may include 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 include a material with a refractive index greater than the refractive index of the substrate or the waveguide. In the illustrated embodiment, grating 1744 has a diffraction feature with a refractive index of 2.2 on a substrate having a refractive index of 1.75. Values outside these ranges are also conceivable. In some embodiments, grating 1744 may be generated using a high refractive index resist and contact imprinting. In some embodiments, grating 1744 may be generated using an inclined etching such as angled directional etching. A material that preferentially etches in a certain direction may also be employed. Some exemplary methods of etching are described in connection with FIGS. 13H-13J. Other methods may be employed.FIG. 13H shows a method of fabricating a blazed (asymmetric) diffraction feature (3803) having a serrated pattern with first and second sloped sidewalls that slope in opposite directions. FIG. 13I shows a method of fabricating a blazed (asymmetric) diffraction feature (3853) having a "shark fin" cross-section with first and second sloped sidewalls that slope in the same direction. The second sidewall in FIG. 13I is an example of a concave corner sidewall or surface. FIGS. 17D-1 - 17D-4 also show first and second sloped sidewalls having a second sidewall that slopes in the same direction and is a concave corner sidewall or surface. Other types of gratings with other material compositions and other refractive indices are also possible considerations.

[0207] However, contact imprint as a mode of fabrication can be advantageous over etching due to improved efficiency and ease of manufacture. Thus, it may be desirable to use materials suitable for use in combination with contact imprint techniques for generating ICGs. For example, gratings 1746 and 1748 include an ICG profile with a refractive index of 1.65.

[0208] Lattice 1746 includes a tilted lattice with a material having a refractive index less than 2 or less than 1.9 or less than 1.8, for example, 1.65, and a coating deposited on the edge of the lattice using a material having a refractive index greater than 1.9 or greater than 2, such as a material with a refractive index of 2.2 like TiO2 or a material with a refractive index of 2.6 like SiC. The resulting TM and TE efficiency profiles (1750 and 1752 respectively) are approximated or substantially match over a range of incident angles, as shown in graph 1745, and / or are more efficient in TE and can be more efficient in TM at points within a range of incident angles or on average. In some embodiments, the average polarization efficiency can 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 diffraction efficiency is at least 0.8 on average over an incident angle range of at least 30 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 on average over an incident angle range of at least 20 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 on average over an incident angle range of at least 10 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 30 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 20 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 10 degrees of light.

[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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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 an incident light angle range 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 an incident light angle range 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 an incident light angle range of at least 10 degrees.

[0210] The grating 1748 also includes a blazed grating having a refractive index of less than 2 or less than 1.9 or less than 1.8, for example, 1.65, and a coating deposited on the edge 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 like TiO2 or a material with a refractive index of 2.6 like SiC. The resulting TM and TE efficiency profiles (1750 and 1752, respectively) are approximately or substantially coincident over a range of incident angles, as shown 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 polarization 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 diffraction efficiency is at least 0.8 on average over an incident angle range of at least 30 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 on average over an incident angle range of at least 20 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 on average over an incident angle range of at least 10 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 30 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 20 degrees of light. In some embodiments, the diffraction efficiency is at least 0.8 over an incident angle range of at least 10 degrees of light.

[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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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, averaged over an incident light angle range 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 an incident light angle range 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 an incident light angle range 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 an incident light angle range of at least 10 degrees.

[0212] In addition, as described above, the average diffraction efficiency over a range of wavelengths can be within a range of 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°, etc., or any range formed by any of these values. The diffraction efficiency can be higher for the TE mode in some designs, or higher for the TM mode in some designs. In some designs, the diffraction efficiency can be higher for the TE mode at some angles and higher for the TM mode at other angles. As shown in FIGS. 17D-3 and 17D-4, an ICG such as grating 1746 or grating 1748 may include a tilted or serrated grating, a blazed grating, or other geometries. If the grating is a tilted grating such as grating 1746, the grating may have an inclination angle including, but 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 about 20 to 85 degrees (shallow size) and a retroblaze 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 can represent interior angles measured from the base of the diffraction grating to the corresponding sidewall or surface.

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

[0214] In addition, the high refractive index material deposited on the diffraction grating features may be biased, for example, using glancing angle deposition, to provide more material on one side of the diffraction grating feature than the other. Thus, the thickness and / or coating may be greater on the first sidewall on one side of the diffraction feature than on the second sidewall on the opposite side of the diffraction feature. In some implementations, potentially, there may be little or no coating on one sidewall. For example, 90% or 95% of the second sidewall may not be coated. In some cases, deposition onto inclined diffraction features (e.g., directional deposition) may result in a bias such that more coating or a thicker coating is provided on the first sidewall or side of the diffraction feature while little is deposited on the second sidewall or side of the diffraction feature. In some cases, the topography of underlying diffraction features may facilitate passive bias deposition, as illustrated in FIG. 14, for example, in the second and third columns of the third row. Potentially, straight or angled directional etching, when used to deposit material onto a diffraction feature having a concave corner surface or sidewall (the left sidewall within the diffraction feature shown in row 3 of FIG. 14), may result in little coating on the concave corner sidewall or surface.

[0215] Referring to grating 1746, the duty cycle 1778 of grating 1746 can be a certain percentage of the pitch of the grating. For example, the duty cycle can be 20 - 80 percent of the pitch, for example, 50 percent of the pitch. The height 1774 of the grating can be, for example, a height of 10 - 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 feature may include a material with a refractive index different from that of the substrate or waveguide. In the illustrated embodiment, grating 1746 comprises a diffraction feature 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 diffraction feature 1770. Material 1772 may have a refractive index higher than that of diffraction feature 1770. For example, material 1772 may have a refractive index of 2.2. Other values are also possible. The thickness 1776 of material 1772 may be about 10 - 600 nm or another value.

[0216] Referring to grating 1748, the width (WT) at the top of the blazed grating feature 1780 can be greater than the width (WB) at the base of the blazed grating 1784. In some embodiments, WT may be varied and 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 a high refractive index coating. For example, WB may be wide enough to allow more than 50% of the width to be filled by a 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 concave corner sidewall, a vertical sidewall, or a more inclined sidewall). Advantageously, in some cases, this bias deposition can improve the overall average TM and TE efficiency.

[0217] The height 1782 of the grating may be, for example, a height of 100 to 600 nm. In some embodiments, the 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 feature may include a material with a refractive index different from that of the substrate or waveguide. In the illustrated embodiment, the grating 1746 includes a diffraction feature 1770 having a refractive index of 1.65 on a substrate having a refractive index of 1.75. Values outside these ranges are also conceivable as possibilities. In some embodiments, the material 1772 may be deposited on the diffraction feature 1770. The material 1772 may have a refractive index higher than that of the diffraction feature 1770. For example, the material 1772 may have a refractive index of 2.2. Other values are also conceivable as possibilities. The thickness 1786 of the material 1772 may be about 100 to 600 nm or another value. Other values outside these ranges are also conceivable as possibilities.

[0218] As discussed above, in some embodiments, the grating 1744 may be generated using a high refractive index resist and contact imprinting. In some embodiments, the grating 1744 may be generated using tilt etching. Other types of gratings with other material compositions having other refractive indices are also conceivable as possibilities.

[0219] Advantageously, gratings such as blazed gratings with a refractive index coating of 2.2 as discussed with reference to grating 1748 can have improved average diffraction efficiency, and polarization insensitivity, and potentially higher manufacturability than other designs. Advantageously, the ICG as described with reference to FIGS. 17C and 17D-3-17D-4 can be used in combination with an unpolarized light source (e.g., a micro-LED source) in a transmissive mode and in series in a waveguide stack as described above with reference to FIG. 6. This capability can enable an eyepiece utilizing the ICG to have increased brightness and / or field of view. For example, a color above one of the incident lights can interact with each ICG in each waveguide color in the stack, which can be opaque and highly reflective and thus advantageously spatially offset and allow the incident light to pass through each waveguide, which can be more advantageous than a conventional ICG with high TM efficiency.

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

[0221] Figure 18 illustrates a method by which 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 to a user / viewer by a waveguide. 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 reflection of light 1804 can occur from grating 1801, pass through one or more transmissive layers 1822, diffract into ICG 1820, and enter waveguide 1818, resulting in unwanted reflection losses of light 1802.

[0222] The reflection losses can be reduced within the first ICG 1714 if the transmissive layer 1822 comprises one or more sub - layers 1824, 1826 as discussed above. For example, as illustrated in FIG. 18, transmissive ICG 1803 can include a transmissive layer 1822 with one or more sub - layers. One or more sub - layers can include one or more high - refractive - index sub - layers 1826 such as TiO2 and one or more low - refractive - index sub - layers 1824 such as SiO2. In such a configuration, the zero - order reflected light 1804 can be reduced. As discussed above, in some implementations, the sub - layers 1824, 1826 or additional sub - layers may comprise an interference coating such as a quarter - wave stack. In some embodiments, this configuration can also reduce the first - order diffraction order of light 1806 within ICG 1803. However, the reduction of reflection losses that travel through a substrate into a second ICG within the ICG can improve image quality, for example, by increased eye - box efficiency and reduction of artifacts such as afterimages or coherent artifacts within the waveguide stack.

[0223] Additionally, or alternatively, the reflection loss can be reduced by including a material 1828 having a refractive index between 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 base pattern 1820 of the ICG. 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 the zero-order reflection 1808. In some embodiments, this configuration can also reduce the first-order diffraction order of the light 1806 within the ICG 1803. However, the overall reduction in reflection loss can improve the image quality, for example, by increasing the eye box efficiency and reducing artifacts such as afterimages or coherent artifacts within the waveguide stack.

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

[0225] Example 2: The substrate is the head-mounted display system described in Example 1, which contains a lithium-based oxide.

[0226] Example 3: The substrate is the head-mounted display system described in Example 1 or 2, which contains lithium niobate.

[0227] Example 4: The substrate is the head-mounted display system described in Example 1, which contains silicon carbide.

[0228] Example 5: The substrate is the head-mounted display system described in Example 1, which contains a material having a refractive index of at least 1.9.

[0229] Example 6: The substrate is the head-mounted display system described in Example 1, which contains a material having a refractive index of at least 2.0.

[0230] Example 7: The substrate is the head-mounted display system described in Example 1, which contains a material having a refractive index of at least 2.1.

[0231] Example 8: The substrate is the head-mounted display system described in Example 1, which contains a material having a refractive index of at least 2.2.

[0232] Example 9: The substrate is the head-mounted display system described in Example 1, which contains a material having a refractive index of at least 2.3.

[0233] Example 10: The first diffraction grating material contains a polymer, and it is the head-mounted display system described in any of the above examples.

[0234] Example 11: The first diffraction grating material contains an imprintable material, and it is the head-mounted display system described in any of the above examples.

[0235] Example 12: The first diffraction grating material has a refractive index of 1.4 to 1.95, and it is the head-mounted display system described in any of the above examples.

[0236] Example 13: The first diffraction grating material is a head-mounted display system according to any of the above examples, having a refractive index lower than that of the substrate.

[0237] Example 14: The first diffraction grating is a head-mounted display system according to any of the above examples, comprising a blazed diffraction grating.

[0238] Example 15: The first diffraction grating is a head-mounted display system according to any of the above examples, having diffraction characteristics with peaks separated by grooves therebetween.

[0239] Example 16: The first diffraction grating is a head-mounted display system according to any of the above examples, having diffraction characteristics with a plurality of straight lines.

[0240] Example 17: The diffraction grating is a waveguide according to any of the above examples, having diffraction characteristics and being asymmetric.

[0241] Example 18: The first layer is a head-mounted display system according to any of the above examples, including titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0242] Example 19: The first layer is a head-mounted display system according to any of the above examples, including titanium dioxide (TiO2).

[0243] Example 20: The first layer is a head-mounted display system according to any of the above examples, including zirconium dioxide (ZrO2).

[0244] Example 21: The first layer is a head-mounted display system according to any of the above examples, including silicon carbide (SiC).

[0245] Example 22: The head-mounted display system according to any of the above examples, wherein the first layer includes a plurality of sub-layers including a first higher refractive index material and a second lower refractive index material.

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

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

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

[0249] Example 26: The 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 according to any of Examples 22-26, wherein the plurality of sub-layers includes an interference coating.

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

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

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

[0254] Example 31: The head-mounted display system according to any of the above embodiments, wherein the first and second polarizations are first and second linear polarizations oriented in orthogonal directions.

[0255] Example 32: The head-mounted display system according to any of the above embodiments, wherein the first and second polarizations are transverse magnetic and transverse electric polarizations, respectively.

[0256] Example 33: The head-mounted display system according to any of the above embodiments, wherein the first and second polarizations are transverse electric and transverse magnetic polarizations, respectively.

[0257] Example 34: The head-mounted display system according to any of the above embodiments, wherein the first diffraction efficiency has a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency has a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0258] Example 35: The head-mounted display system according to any of the above embodiments, wherein the first diffraction efficiency has a diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency has a diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0259] Example 36: The head-mounted display system according to any of the above embodiments, wherein the first diffraction efficiency is 1 to 1.5 times the second diffraction efficiency.

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

[0261] Example 38: The head-mounted display system according to any of the above embodiments, 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 above examples, wherein the angular range is at least 6 degrees.

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

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

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

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

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

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

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

[0272] Example 49: The waveguide is configured to direct light towards the eyes of a user wearing the head-mounted display, and is included within an eyepiece of the head-mounted display system according to any of the above examples.

[0273] Example 50: The eyepiece is disposed on a frame, configured to direct light from a light projection system into the user's eyes, and display augmented reality image content in the user's field of view. At least a portion of the eyepiece is transparent and, when the user wears the head-mounted display system, is disposed at a location in front of the user's eyes. The transparent portion transmits light from a part of the physical environment in front of the user to the user's eyes and provides a view of a part of the physical environment in front of the user. The head-mounted display system according to Example 49.

[0274] Example 51: The eyepiece includes the at least one waveguide, and the at least one waveguide is transparent to visible light so that the waveguide can be seen through by the user. The head-mounted display system according to Example 49 or 50.

[0275] Example 52: The waveguide includes an internal coupling optical element for coupling the light from the light projection system into the waveguide so that the light is guided therein. The head-mounted display system according to any of the above examples.

[0276] Example 53: The waveguide includes an external coupling optical element for coupling the light from the light projection system out of the waveguide, directing the light towards the user's eyes, and presenting the image content to the viewer. The head-mounted display system according to any of the above examples.

[0277] Example 54: The first diffraction grating includes an external coupling grating (EPE) configured to externally couple the light from the light projection system guided within the waveguide out of the waveguide. The head-mounted display system according to any of the above examples.

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

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

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

[0281] Example 58: The head-mounted display system according to Example 57, wherein the third layer is configured to help bond the second layer to the first layer.

[0282] Example 59: a second diffraction grating including a material different from the substrate and disposed across the substrate; a fourth layer disposed across the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for a first polarization over a certain range of angles of light incident thereon, wherein the first diffraction grating is disposed across the substrate on a first side of the substrate, and the second diffraction grating is disposed across the substrate on a second side of the substrate opposite the first side of the substrate; the head-mounted display system according to any of the above embodiments.

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

[0284] Example 61: The head-mounted display system according to any of the above embodiments, wherein the first layer is deposited directionally at an angle on one or more diffraction features.

[0285] Example 62: A head-mounted display system according to Example 61, wherein the angle includes 75 to 105 degrees with respect to the planar major surface of the substrate.

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

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

[0289] Example 66: A head-mounted display system according to Example 65, wherein the angle includes 75 to 105 degrees with respect to the planar major surface of the substrate.

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

[0291] Example 68: A head-mounted display system according to any of the above examples, wherein the first diffraction grating is formed in a 1D array and includes diffractive features.

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

[0293] Example 70: A head-mounted display system according to Example 69, wherein the 2D array includes a square array.

[0294] Example 71: The head-mounted display according to any of the above embodiments, wherein the diffraction feature is asymmetric so as to provide a blazed grating.

[0295] Example 72: The head-mounted display according to any of the above embodiments, wherein the diffraction feature has a material deposited asymmetrically thereon so as to provide a blazed grating.

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

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

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

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

[0300] Example 77: a second diffraction grating, comprising a material different from the substrate, disposed across the substrate; a fourth layer disposed across 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 and a fourth diffraction efficiency for a second polarization over the range of angles of light incident thereon; The head-mounted display system according to any of the above embodiments, wherein the first diffraction grating is disposed across the substrate on a first side of the substrate, and the second diffraction grating is disposed across the substrate on a second side of the substrate opposite the first side of the substrate.

[0301] Example 78: A second diffraction grating formed within the substrate, and The second diffraction grating has a third diffraction efficiency for a first polarization over a range of angles of light incident thereon and a fourth diffraction efficiency for a second polarization over the range of angles of light incident thereon, and a fourth layer disposed across the second diffraction grating so as to have the fourth diffraction efficiency; The head-mounted display system according to any one of the above embodiments, wherein the first diffraction grating is disposed across the substrate on a first side of the substrate, and the second diffraction grating is disposed across the substrate on a second side of the substrate opposite to the first side of the substrate.

[0302] Example 79: The head-mounted display system according to any one of the above embodiments, wherein the substrate is configured to guide at least a part of the light from the light projection system into the waveguide through the second diffraction grating.

[0303] Example 80: The head-mounted display system according to any one of the above embodiments, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon is greater than the fourth diffraction efficiency for the second polarization over the range of angles of light incident thereon.

[0304] Example 81: The head-mounted display system according to any one of the above embodiments, wherein the third diffraction efficiency is at least six times the fourth diffraction efficiency over the range of the angle.

[0305] Example 82: The head-mounted display system according to any one of the above embodiments, 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 the range of angles of light incident thereon.

[0306] Example 83: The head-mounted display system according to any one of the above embodiments, wherein the fourth diffraction efficiency is at least six times the third diffraction efficiency over the range of the angle.

[0307] Example 84: The fourth layer includes a dielectric, and is a head-mounted display system according to any of the above examples.

[0308] Example 85: The substrate includes a material having a refractive index of 2.6 or less, and is a head-mounted display system according to any of the above examples.

[0309] Example 86: The substrate includes a material having a refractive index of 2.7 or less, and is a head-mounted display system according to any of the above examples.

[0310] Example 87: The substrate includes a material having a refractive index of 2.8 or less, and is a head-mounted display system according to any of the above examples.

[0311] Example 88: The first layer includes a dielectric, and is a head-mounted display system according to any of the above examples.

[0312] Example 89: The first layer includes a material having a refractive index of 1.9 or higher, and is a head-mounted display system according to any of the above examples.

[0313] Example 90: The first layer includes a material having a refractive index of 2.0 or higher, and is a head-mounted display system according to any of the above examples.

[0314] Example 91: The first layer includes a material having a refractive index of 2.1 or higher, and is a head-mounted display system according to any of the above examples.

[0315] Example 92: The first layer further includes a plurality of sub-layers, and the plurality of sub-layers include a first material with a higher refractive index and a second material with a lower refractive index, and is a head-mounted display system according to any of the above examples.

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

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

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

[0319] Example 96: The head-mounted display system according to any one of Examples 92-95, wherein the plurality of sub-layers alternate between the first material and the second material.

[0320] Example 97: The head-mounted display system according to any one of Examples 92-96, wherein the plurality of sub-layers includes an interference coating.

[0321] Example 98: The head-mounted display system according to any one of Examples 92-97, wherein the plurality of sub-layers includes a quarter-wave stack.

[0322] Example 99: The head-mounted display system according to any one of Examples 92-98, wherein the plurality of sub-layers across the first layer forms a bandpass filter.

[0323] Example 100: The head-mounted display system according to any one of Examples 92-98, wherein the plurality of sub-layers across the first layer forms a notch filter.

[0324] Example 101: The head-mounted display system according to any one of Examples 92-98, wherein the plurality of sub-layers across the first layer forms an anti-reflection (AR) coating.

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

[0326] Example 103: The head-mounted display system according to any one of Examples 92-102, wherein the second higher refractive index material has a refractive index of 1.9 or more.

[0327] Example 104: The head-mounted display system according to any one of Examples 92-103, wherein the first lower refractive index material contains silicon dioxide.

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

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

[0330] Example 107: The head-mounted display system according to any one of Examples 92-104, wherein the second higher refractive index material contains zinc oxide.

[0331] Example 108: The head-mounted display system according to any one of the above Examples, wherein the first diffraction grating has an average diffraction efficiency for the first polarization over the range of the angle, and the second diffraction efficiency has an average diffraction efficiency for the second polarization over the range of the angle.

[0332] Example 109: The head-mounted display system according to any one of the above Examples, wherein the first diffraction efficiency averaged over the range of the angle and the second diffraction efficiency averaged over the range of the angle have an efficiency of at least 40%.

[0333] Example 110: The head-mounted display system according to any of the above embodiments, wherein the first diffraction efficiency averaged over the range of the angle and the second diffraction efficiency averaged over the range of the angle have an efficiency of at least 50%.

[0334] Example 111: The head-mounted display system according to any of the above embodiments, wherein the first diffraction efficiency averaged over the range of the angle and the second diffraction efficiency averaged over the range of the angle have an efficiency of at least 60%.

[0335] Example 112: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is at least 25 degrees.

[0336] Example 113: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is at least 30 degrees.

[0337] Example 114: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is at least 35 degrees.

[0338] Example 115: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is at least 40 degrees.

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

[0340] Example 117: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is between ±18 degrees with respect to the plane of the substrate.

[0341] Example 118: The head-mounted display system according to any of the above embodiments, wherein the range of the angle is between ±20 degrees with respect to the plane of the substrate.

[0342] Example 119: The first diffraction grating is a head-mounted display system according to any of the above embodiments, having diffraction features and including first and second sidewalls.

[0343] Example 120: The head-mounted display system according to Example 119, wherein the first and second sidewalls are separated by a flat region.

[0344] Example 121: The head-mounted display system according to Example 119, wherein the first and second sidewalls are joined so as to form a prominent angle at the upper part of the diffraction feature.

[0345] Example 122: The head-mounted display system according to any of Examples 119-121, wherein at least the first sidewall is inclined at an angle such that the first sidewall is less steep than the second sidewall.

[0346] Example 123: The head-mounted display system according to any of Examples 119-122, wherein the first sidewall is wider than the second sidewall.

[0347] Example 124: The head-mounted display system according to any of Examples 119-123, wherein the first sidewall forms an angle of 45° to 85° at the base of the diffraction feature.

[0348] Example 125: The head-mounted display system according to any of Examples 119-124, wherein the second sidewall forms an acute concave angle at the base of the diffraction feature.

[0349] Example 126: The head-mounted display system according to any of Examples 119-125, wherein the first diffraction grating has a diffraction feature in the shape of a shark's tail.

[0350] Example 127: The head-mounted display system according to any of Examples 119-124, wherein the second sidewall forms an obtuse concave angle at the base of the diffraction feature.

[0351] Example 128: The head-mounted display system according to any one of Examples 119-124, wherein the second side wall is vertical.

[0352] Example 129: The head-mounted display system according to any one of Examples 119-124 or 127-128, wherein the first diffraction grating has a sawtooth-shaped diffraction feature.

[0353] Example 130: The head-mounted display system according to any one of the above examples, wherein the first layer has a biased deposition.

[0354] Example 131: The head-mounted display system according to any one of the above examples, wherein the first layer has a glancing angle deposition.

[0355] Example 132: The head-mounted display system according to any one of Examples 119-131, wherein the first layer is biased to provide more coverage on the first side wall than on the second side wall.

[0356] Example 133: The head-mounted display system according to any one of Examples 119-132, wherein the first layer covers a larger proportion of the first side wall than the second side wall.

[0357] Example 134: The head-mounted display system according to any one of Examples 119-133, wherein the first layer is biased to provide a thicker coverage on the first side wall than on the second side wall.

[0358] Example 135: The head-mounted display system according to any one of Examples 119-134, wherein the first layer provides an average thicker coverage on the first side wall than on the second side wall.

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

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

[0361] Example 138: A head-mounted display system according to any one of Examples 119-137, wherein the second side wall includes an area not covered by more of the first layer than the first side wall.

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

[0363] Example 140: A head-mounted display system according to any one 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 according to any one of Examples 119-140, wherein the second layer is not biased to cover more of the first side wall than the second side wall.

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

[0366] Example 143: A head-mounted display system according to any one of Examples 119-142, wherein the second layer does not provide an on average thicker coating on the first side wall than on the second side wall.

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

[0368] Example 145: A head-mounted display system according to any one of Examples 119-144, wherein the second side wall does not include an area not covered by more of the second layer than the first side wall.

[0369] Example 146: The head-mounted display system according to any one 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: The head-mounted display system according to any one 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: The head-mounted display system according to any one 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: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating, on which the first and second layers are formed, comprises a reflective diffraction grating configured to diffract the reflected light and couple the light into the waveguide so as to be guided therein by total internal reflection.

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

[0374] Example 151: The head-mounted display system according to any one of the above examples, wherein the diffraction feature has a height of 100 to 600 nanometers.

[0375] Example 152: The head-mounted display system according to any one of the above examples, wherein the diffraction feature has a height of 200 to 600 nanometers.

[0376] Example 153: The diffraction feature is a head-mounted display system according to any of the above examples, having a height of 300 to 600 nanometers.

[0377] Example 154: The diffraction feature is a head-mounted display system according to any of the above examples, having a pitch of 290 nm to 690 nm.

[0378] Example 155: The light projection system is a head-mounted display system according to any of the above examples, comprising a micro LED.

[0379] Example 156: The light projection system is a head-mounted display system according to any of the above examples, comprising a DLP or LCOS display.

[0380] Example 157: The substrate is a head-mounted display system according to any of the above examples, containing nanoparticles.

[0381] Example 158: The substrate is a head-mounted display system according to any of the above examples, containing inorganic nanoparticles.

[0382] Example 159: The substrate is a head-mounted display system according to any of the above examples, containing a polymer.

[0383] Additional Example - Part II Example 1: A head-mounted display system, a head-mountable frame, a light projection system configured to output light and provide image content, a waveguide supported by the frame, the waveguide comprising a substrate containing an optically transparent material and a first diffraction grating formed in the substrate, the substrate a first layer disposed across the first diffraction grating formed in the substrate, The first diffraction grating has a first diffraction efficiency for a first polarization over a certain range of angles of light incident thereon and a second diffraction efficiency for a second polarization over that range of angles of light incident thereon, and the first diffraction efficiency is 1 to 2 times the second diffraction efficiency, and a second layer containing a metal is disposed across the first diffraction grating formed in the substrate. A waveguide configured to guide at least a part of the light from the light projection system into the waveguide. A head-mounted display system comprising the same.

[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 contains a polymer.

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

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

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

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

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

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

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

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

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

[0395] Example 13: A head-mounted display system according to any of the above examples, wherein the metal comprises aluminum, silver, gold, or copper.

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

[0397] Example 15: A head-mounted display system according to Example 14, having diffraction characteristics, wherein the first diffraction grating comprises peaks separated by grooves therebetween.

[0398] Example 16: A head-mounted display system according to any of the above examples, having diffraction characteristics, wherein the first diffraction grating comprises a plurality of straight lines.

[0399] Example 17: A waveguide according to any of the above examples, having diffraction characteristics, wherein the diffraction grating is asymmetric.

[0400] Example 18: The head-mounted display system according to any one of the above embodiments, wherein the first and second polarizations are first and second linear polarizations having different polarization angles.

[0401] Example 19: The head-mounted display system according to any one of the above embodiments, wherein the first and second polarizations are first and second linear polarizations oriented in orthogonal directions.

[0402] Example 20: The head-mounted display system according to any one of the above embodiments, wherein the first and second polarization directions are transverse magnetic and transverse electric polarizations, respectively.

[0403] Example 21: The head-mounted display system according to any one of Examples 1-19, wherein the first and second polarization directions are transverse electric and transverse magnetic polarizations, respectively.

[0404] Example 22: The head-mounted display system according to any one of Examples 1-19, wherein the first diffraction efficiency is the diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum, and the second diffraction efficiency is the diffraction efficiency for transverse electric polarization averaged across the visible light spectrum.

[0405] Example 23: The head-mounted display system according to any one of Examples 1-19, wherein the first diffraction efficiency is the diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the second diffraction efficiency is the diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum.

[0406] Example 24: The head-mounted display system according to any one of the above embodiments, wherein the first diffraction efficiency is 1 to 1.5 times the second diffraction efficiency.

[0407] Example 25: The head-mounted display system according to any one of the above embodiments, 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 one of the above examples, wherein the first diffraction efficiency is 1 to 1.3 times that of the second diffraction efficiency.

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

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

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

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

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

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

[0415] Example 33: A head-mounted display system according to any one of the above examples, wherein the angular range is between ±3 degrees with respect to the plane of the substrate.

[0416] Example 34: A head-mounted display system according to any one of the above examples, wherein the angular range is between ±6 degrees with respect to the plane of the substrate.

[0417] Example 35: A head-mounted display system according to any one of the above examples, wherein the angular range is between ±9 degrees with respect to the plane of the substrate.

[0418] Example 36: A head-mounted display system according to any of the above examples, wherein the range of the angle is between ±11 degrees with respect to the plane of the substrate.

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

[0420] Example 38: The eyepiece lens is disposed on a frame and is configured to direct light from an optical projection system into the user's eyes and display augmented reality image content in the user's field of view. At least a part of the eyepiece lens is transparent. When the user wears the head-mounted display system, the transparent part is disposed at a position in front of the user's eyes and transmits light from a part of the physical environment in front of the user to the user's eyes, providing a view of a part of the physical environment in front of the user. A head-mounted display system according to Example 37.

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

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

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

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

[0425] Example 43: The head-mounted display system according to any of the above embodiments, wherein the first diffraction grating includes an external coupling grating (EPE) configured to externally couple light from the optical projection system induced within the waveguide out of the waveguide.

[0426] Example 44: The head-mounted display system according to any of the above embodiments, wherein the second layer is configured to be disposed across the first layer.

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

[0428] Example 46: The head-mounted display system according to Example 45, wherein the third layer is configured to help bond the second layer to the first layer.

[0429] Example 47: The waveguide includes a second diffraction grating formed within the substrate, the substrate is configured to guide at least a portion of the light from the optical projection system to be coupled into the waveguide through the second diffraction grating, and the head-mounted display system further includes a fourth layer disposed across the second diffraction grating such that the second diffraction grating has a third diffraction efficiency for a first polarization over a certain range of angles of the incident light thereon. The first diffraction grating is formed within the substrate on a first side of the substrate, and the second diffraction grating is formed within the substrate on a second side of the substrate opposite to the first side of the substrate. The head-mounted display system according to any of the above embodiments.

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

[0431] Example 49: The head-mounted display system according to any of the above examples, wherein the first layer is deposited directionally at an angle on one or more diffraction features.

[0432] Example 50: The head-mounted display system according to Example 49, wherein the angle includes 75 to 105 degrees with respect to the plane major surface of the substrate.

[0433] Example 51: The head-mounted display system according to Example 49, wherein the angle is 75 to 105 degrees with respect to the surface of one or more diffraction features of the first diffraction grating.

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

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

[0436] Example 54: The head-mounted display system according to Example 53, wherein the angle includes 75 to 105 degrees with respect to the plane major surface of the substrate.

[0437] Example 55: The head-mounted display system according to Example 53, wherein the angle is 75 to 105 degrees with respect to the surface of one or more diffraction features of the first diffraction grating.

[0438] Example 56: The head-mounted display system according to any of the above examples, wherein the first diffraction grating is formed in a 1D array and has diffraction features.

[0439] Example 57: The first diffraction grating is a head-mounted display system according to any one of Examples 1-55, which is formed in a 2D array and has diffraction characteristics.

[0440] Example 58: The 2D array is a head-mounted display system according to Example 57, which includes a square array.

[0441] Example 59: The diffraction characteristics are asymmetric so as to provide a blazed grating, for a head-mounted display according to any of the above examples.

[0442] Example 60: The diffraction characteristics are for a head-mounted display according to any of the above examples, having a material deposited asymmetrically thereon so as to provide a blazed grating.

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

[0444] Example 62: The first diffraction grating is for a head-mounted display according to any of the above examples, blazed in two directions.

[0445] Example 63: The first diffraction grating is a head-mounted display system according to any of the above examples, which includes a one-dimensional grating.

[0446] Example 64: The first diffraction grating is a head-mounted display system according to any of Examples 1-62, which includes a two-dimensional grating.

[0447] Example 65: A second diffraction grating formed in the substrate, and A fourth layer disposed across 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 and a fourth diffraction efficiency for a second polarization over that range of angles of light incident thereon. A head-mounted display system according to any of the above embodiments, comprising a first diffraction grating disposed across the substrate on a first side of the substrate, and a second diffraction grating disposed across the substrate on a second side of the substrate opposite the first side of the substrate.

[0448] Example 66: A second diffraction grating disposed across the substrate and including a material different from the substrate. A fourth layer disposed across 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 and a fourth diffraction efficiency for a second polarization over that range of angles of light incident thereon. A head-mounted display system according to any of the above embodiments, further comprising a first diffraction grating disposed across the substrate on a first side of the substrate, and a second diffraction grating disposed across the substrate on a second side of the substrate opposite the first side of the substrate.

[0449] Example 67: A head-mounted display system according to any of the above embodiments, wherein the substrate is configured to guide at least a portion of the light from the light projection system into the waveguide through the second diffraction grating.

[0450] Example 68: A head-mounted display system according to any of the above embodiments, wherein the third diffraction efficiency for the first polarization over a range of angles of light incident thereon is greater than 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 above embodiments, wherein the third diffraction efficiency is at least six times the fourth diffraction efficiency over the range of angles.

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

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

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

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

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

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

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

[0459] Example 77: The head-mounted display system according to any of the above examples, wherein the first layer contains a material having a refractive index of 1.9 or more.

[0460] Example 78: The head-mounted display system according to any of the above examples, wherein the first layer contains a material having a refractive index of 2.0 or more.

[0461] Example 79: The head-mounted display system according to any of the above examples, wherein the first layer includes a material having a refractive index of 2.1 or higher.

[0462] Example 80: The head-mounted display system according to any of the above examples, further comprising a plurality of sub-layers across 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: The head-mounted display system according to Example 80, wherein the first higher refractive index material includes titanium dioxide (TiO2) and the second lower refractive index material includes silicon dioxide (SiO2).

[0464] Example 82: The head-mounted display system according to Example 80 or 81, wherein the plurality of sub-layers comprises only two sub-layers.

[0465] Example 83: The head-mounted display system according to Example 80 or 81, wherein the plurality of sub-layers comprises at least four sub-layers.

[0466] Example 84: The head-mounted display system according to any of Examples 80 - 83, wherein the plurality of sub-layers alternate between the first material and the second material.

[0467] Example 85: The head-mounted display system according to any of Examples 80 - 84, wherein the plurality of sub-layers comprises an interference coating.

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

[0469] Example 87: The head-mounted display system according to any of Examples 80 - 86, wherein the plurality of sub-layers across the first layer forms a bandpass filter.

[0470] Example 88: The head-mounted display system according to any one of Examples 80-86, wherein a plurality of sub-layers across the first layer form a notch filter.

[0471] Example 89: The head-mounted display system according to any one of Examples 80-86, wherein a plurality of sub-layers across the first layer form an anti-reflection (AR) coating.

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

[0473] Example 91: The head-mounted display system according to any one of Examples 80-90, wherein the second higher refractive index material has a refractive index of 1.9 or more.

[0474] Example 92: The head-mounted display system according to any one of Examples 80-91, wherein the first lower refractive index material contains silicon dioxide.

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

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

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

[0478] Example 96: The head-mounted display system according to any one of the above Examples, wherein the first diffraction grating has an average diffraction efficiency for the first polarization over the range of the angle, and the second diffraction efficiency has an average diffraction efficiency for the second polarization over the range of the angle.

[0479] Example 97: The head-mounted display system according to any of the above embodiments, 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: The head-mounted display system according to any of the above embodiments, 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: The head-mounted display system according to any of the above embodiments, 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: The head-mounted display system according to any of the above embodiments, wherein the range of angles is at least 25 degrees.

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

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

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

[0486] Example 104: The head-mounted display system according to any of the above embodiments, wherein the range of angles is between ±15 degrees with respect to the plane of the substrate.

[0487] Example 105: The head-mounted display system according to any of the above embodiments, wherein the range of angles is between ±18 degrees with respect to the plane of the substrate.

[0488] Example 106: The head-mounted display system according to any one of the above examples, wherein the angular range is between ±20 degrees with respect to the plane of the substrate.

[0489] Example 107: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating includes first and second side walls and has diffraction characteristics.

[0490] Example 108: The head-mounted display system according to Example 107, wherein the first and second side walls are separated by a flat region.

[0491] Example 109: The head-mounted display system according to Example 107, wherein the first and second side walls are joined so as to form a prominent angle at the top of the diffraction feature.

[0492] Example 110: The head-mounted display system according to any one of Examples 107-109, wherein at least the first side wall is inclined at an angle such that the first side wall is less steep than the second side wall.

[0493] Example 111: The head-mounted display system according to any one of Examples 107-110, wherein the first side wall is wider than the second side wall.

[0494] Example 112: The head-mounted display system according to any one of Examples 107-111, wherein the first side wall forms an angle of 45° to 85° at the base of the diffraction feature.

[0495] Example 113: The head-mounted display system according to any one of Examples 107-112, wherein the second side wall forms an acute concave angle at the base of the diffraction feature.

[0496] Example 114: The head-mounted display system according to any one of Examples 107-113, wherein the first diffraction grating has a diffraction feature in the shape of a shark fin.

[0497] Example 115: The head-mounted display system according to any one of Examples 107-112, wherein the second side wall forms an obtuse-angled concave corner at the base of the diffraction feature.

[0498] Example 116: The head-mounted display system according to any one of Examples 107-112, wherein the second side wall is vertical.

[0499] Example 117: The head-mounted display system according to any one of Examples 107-112 or 115-116, wherein the first diffraction grating has a sawtooth-shaped diffraction feature.

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

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

[0502] Example 120: The head-mounted display system according to any one of Examples 107-119, wherein the first layer is biased to provide more coverage on the first side wall than on the second side wall.

[0503] Example 121: The head-mounted display system according to any one of Examples 107-120, wherein the first layer covers a larger proportion of the first side wall than the second side wall.

[0504] Example 122: The head-mounted display system according to any one of Examples 107-121, wherein the first layer is biased to provide a thicker coating on the first side wall than on the second side wall.

[0505] Example 123: The head-mounted display system according to any one of Examples 107-122, wherein the first layer provides an average thicker coating on the first side wall than on the second side wall.

[0506] Example 124: A head-mounted display system according to any one of Examples 107-123, wherein the first sidewall is completely covered by the second layer.

[0507] Example 125: A head-mounted display system according to any one of Examples 107-124, wherein at least a part of the second sidewall is not covered by the first layer.

[0508] Example 126: A head-mounted display system according to any one of Examples 107-125, wherein the second sidewall includes an area not covered by more of the first layer than the first sidewall.

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

[0510] Example 128: A head-mounted display system according to any one of Examples 107-127, wherein the first and second sidewalls are completely covered by the second layer.

[0511] Example 129: A head-mounted display system according to any one 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 according to any one 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 according to any one of Examples 107-130, wherein the second layer does not provide an on average thicker coating on the first sidewall than on the second sidewall.

[0514] Example 132: A head-mounted display system according to any one of Examples 107-131, wherein the second sidewall is entirely covered by the second layer.

[0515] Example 133: A head-mounted display system according to any one of Examples 107-132, wherein the second side wall does not include an area not covered by more of the second layer than the first side wall.

[0516] Example 134: A head-mounted display system according to any one 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 according to any one 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 according to any one 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 according to any one of the above examples, wherein the first diffraction grating, on which the first and second layers are formed, comprises a reflective diffraction grating configured to diffract the reflected light and couple the light into the waveguide so as to be guided therein by total internal reflection.

[0520] Example 138: A head-mounted display system according to any one of the above examples, wherein the diffraction feature has a height of 100 to 600 nanometers.

[0521] Example 139: A head-mounted display system according to any one of the above examples, wherein the diffraction feature has a height of 200 to 600 nanometers.

[0522] Example 140: A head-mounted display system according to any one of the above examples, wherein the diffraction feature has a height of 300 to 600 nanometers.

[0523] Example 141: The diffraction feature is a head-mounted display system according to any of the above examples, having a pitch of 290 nm to 690 nm.

[0524] Example 142: The light projection system is a head-mounted display system according to any of the above examples, comprising a micro LED.

[0525] Example 143: The light projection system is a head-mounted display system according to any of the above examples, comprising a DLP or LCOS display.

[0526] Example 144: The substrate is a head-mounted display system according to any of the above examples, containing nanoparticles.

[0527] Example 145: The substrate is a head-mounted display system according to any of the above examples, containing inorganic nanoparticles.

[0528] Example 146: The substrate is a head-mounted display system according to any of the above examples, containing a polymer.

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

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

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

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

[0533] Example 5: The head-mounted display system according to 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 according to 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 according to 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 according to 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 according to Example 1, wherein the substrate contains a material having a refractive index of at least 2.3.

[0538] Example 10: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating material contains a polymer.

[0539] Example 11: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating material contains an imprintable material.

[0540] Example 12: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating material has a refractive index of 1.4 to 1.95.

[0541] Example 13: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating material has a refractive index lower than that of the substrate.

[0542] Example 14: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating includes a blazed diffraction grating.

[0543] Example 15: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating has diffraction characteristics including peaks separated by grooves therebetween.

[0544] Example 16: The head-mounted display system according to any one of the above examples, wherein the first diffraction grating has diffraction characteristics including a plurality of straight lines.

[0545] Example 17: The waveguide according to any one of the above examples, wherein the diffraction grating has diffraction characteristics and is asymmetric.

[0546] Example 18: The first layer is a head-mounted display system according to any of the above examples, including titanium dioxide (TiO2), zirconium dioxide (ZrO2), or silicon carbide (SiC).

[0547] Example 19: The first layer is a head-mounted display system according to any of the above examples, including titanium dioxide (TiO2).

[0548] Example 20: The first layer is a head-mounted display system according to any of the above examples, including zirconium dioxide (ZrO2).

[0549] Example 21: The first layer is a head-mounted display system according to any of the above examples, including silicon carbide (SiC).

[0550] Example 22: The first layer is a head-mounted display system according to any of the above examples, comprising a plurality of sub-layers including a first higher refractive index material and a second lower refractive index material.

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

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

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

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

[0555] Example 27: A head-mounted display system according to any one of Examples 22-26, wherein the plurality of sub-layers comprise an interference coating.

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

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

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

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

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

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

[0562] Example 34: A head-mounted display system according to any one 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: The fifth diffraction efficiency has the diffraction efficiency for transverse electric polarization averaged across the visible light spectrum, and the sixth diffraction efficiency has the diffraction efficiency for transverse magnetic polarization averaged across the visible light spectrum. The head-mounted display system according to any one of the above examples.

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

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

[0566] Example 38: The fifth diffraction efficiency is 1 to 1.3 times that of the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.3 times that of the fifth diffraction efficiency. The head-mounted display system according to any one of the above examples.

[0567] Example 39: The fifth diffraction efficiency is 1 to 1.2 times that of the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.2 times that of the fifth diffraction efficiency. The head-mounted display system according to any one of the above examples.

[0568] Example 40: The fifth diffraction efficiency is 1 to 1.1 times that of the sixth diffraction efficiency, or the sixth diffraction efficiency is 1 to 1.1 times that of the fifth diffraction efficiency. The head-mounted display system according to any one of the above examples.

[0569] Example 41: The range of the angle is at least 6 degrees. The head-mounted display system according to any one of the above examples.

[0570] Example 42: The range of the angle is at least 12 degrees. The head-mounted display system according to any one of the above examples.

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

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

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

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

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

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

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

[0578] Example 50: The eyepiece is disposed on a frame and is configured to direct light from a light projection system into the user's eyes and display augmented reality image content in the user's field of view. At least a portion of the eyepiece is transparent. When the user wears the head-mounted display system, the transparent portion is disposed in front of the user's eyes and transmits light from a portion of the physical environment in front of the user to the user's eyes, providing a view of a portion of the physical environment in front of the user. The head-mounted display system according to Example 49 includes the eyepiece.

[0579] Example 51: The head-mounted display system according to Example 49 or 50, wherein the eyepiece lens includes the at least one waveguide, and the at least one waveguide is transparent to visible light so as to be visible to the user through the waveguide.

[0580] Example 52: The head-mounted display system according to any of the above examples, wherein the waveguide includes an internal coupling optical element for coupling the light from the light projection system into the waveguide so as to be guided therein.

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

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

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

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

[0585] Example 57: The head-mounted display system according to any of the above examples, further including a third layer disposed between the first layer and the second layer.

[0586] Example 58: The head-mounted display system according to Example 57, wherein the third layer is configured to assist in bonding the second layer to the first layer.

[0587] Example 59: A second diffraction grating, which is disposed across the substrate and includes a material different from that of the substrate; A fourth layer, which is disposed across the second diffraction grating such that the second diffraction grating has a seventh diffraction efficiency for a first polarization over a certain range of angles of the light incident thereon; The head-mounted display system according to any of the above examples, wherein the first diffraction grating is disposed across the substrate on the first side of the substrate, and the second diffraction grating is disposed across the substrate on the second side of the substrate opposite to the first side of the substrate.

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

[0589] Example 61: The head-mounted display system according to Example 1, wherein the first layer is deposited directionally at an angle on one or more diffraction features.

[0590] Example 62: The head-mounted display system according to Example 61, wherein the angle includes 75 to 105 degrees with respect to the major surface of the plane of the substrate.

[0591] Example 63: The head-mounted display system according to Example 61, wherein the angle is 75 to 105 degrees with respect to the surface of one or more diffraction features of the first diffraction grating.

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

[0593] Example 65: The head-mounted display system according to Example 1, wherein the second layer is deposited directionally at an angle on one or more diffraction features of the first diffraction grating.

[0594] Example 66: The head-mounted display system according to Example 65, wherein the angle includes 75 to 105 degrees with respect to the major surface of the plane of the substrate.

[0595] Example 67: The head-mounted display system according to Example 65, wherein the angle is 75 to 105 degrees with respect to the surface of one or more diffraction features of the first diffraction grating.

[0596] Example 68: The head-mounted display system according to any of the above examples, comprising a diffraction feature, wherein the first diffraction grating is formed in a 1D array.

[0597] Example 69: The head-mounted display system according to any of Examples 1-68, comprising a diffraction feature, wherein the first diffraction grating is formed in a 2D array.

[0598] Example 70: The head-mounted display system according to Example 69, wherein the 2D array comprises a square array.

[0599] Example 71: The head-mounted display according to any of the above examples, wherein the diffraction feature is asymmetric so as to provide a blazed grating.

[0600] Example 72: The head-mounted display according to any of the above examples, having a material deposited asymmetrically thereon so as to provide a blazed grating.

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

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

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

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

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

[0606] Example 78: A head-mounted display system according to any of the above embodiments, wherein the light projection system includes a DLP or LCOS display.

[0607] Example 79: A head-mounted display system according to any of the above embodiments, wherein the substrate includes nanoparticles.

[0608] Example 80: A head-mounted display system according to any of the above embodiments, wherein the substrate includes inorganic nanoparticles.

[0609] Example 81: A head-mounted display system according to any of the above embodiments, wherein the substrate includes a polymer.

[0610] Additional Examples - Part IV Example 1: A head-mounted display system, comprising: a head-mountable frame; and a light projection system configured to output light and provide image content. A waveguide supported by a frame, the waveguide comprising: a substrate containing an optically transparent material; and a first diffraction grating formed in the substrate, the substrate being configured to guide at least a part of the light from the light projection system into the waveguide. A first layer disposed across the first diffraction grating formed in the substrate, the first layer being configured to provide a first diffraction efficiency for a first polarization of incident light over a range of angles of incident light thereon that is greater than a second diffraction efficiency for a second polarization of incident light over the same range of angles of incident light thereon, together with the first diffraction grating. A second layer disposed across the first diffraction grating formed in the substrate, the second layer being configured to provide a third diffraction efficiency for a second polarization of incident light over a range of angles of incident light thereon that is greater than a fourth diffraction efficiency for a first polarization of incident light over the same range of angles of incident light thereon, together with the first diffraction grating. The head-mounted display system comprises the above, and the first diffraction grating is configured to provide a fifth diffraction efficienc...

Claims

1. A waveguide, the waveguide comprising: a substrate configured to propagate light within said waveguide by total internal reflection; At least one diffraction grating on the substrate; Equipped with Each diffraction grating is a grating pattern on a surface of the substrate, the grating pattern comprising a material different from the substrate; and a first layer disposed over at least a portion of the grating pattern on the surface of the substrate, the first layer comprising an optically transmissive material; and a second layer including a metal disposed on the surface of the substrate over both the grating pattern and the first layer, the first layer being between the grating pattern and the second layer, the grating having a first diffraction efficiency for a TE polarization state over a range of angles of light incident on the grating and a second diffraction efficiency for a TM polarization state over the range of angles of light incident on the grating that is within ±30% of the first diffraction efficiency; Equipped with a waveguide, wherein both the first layer and the second layer are conformally disposed across the first diffraction grating and on faces of features of the first diffraction grating to conform to a shape of the first diffraction grating, and neither the first layer nor the second layer has a flat outer surface that is parallel to a surface of the waveguide.

2. The waveguide of claim 1 , wherein the substrate has a refractive index of at least 1.

9.

3. The waveguide of claim 1 , wherein the grating pattern comprises a polymer.

4. The waveguide of claim 1 , wherein the grating pattern comprises an imprintable material.

5. 2. The waveguide of claim 1, wherein the grating pattern has a refractive index between 1.4 and 1.

95.

6. The waveguide of claim 1 , wherein the grating pattern comprises a material having a refractive index lower than that of the substrate.

7. The waveguide of claim 1 , wherein the grating pattern comprises a blazed grating.

8. The first layer is made of titanium dioxide (TiO ２ ), zirconium dioxide (ZrO ２ 10. The waveguide of claim 1, comprising one or more of the following: silicon carbide (SiC);

9. 10. The waveguide of claim 1, wherein the second layer comprises one or more of aluminum, silver, gold, copper, aluminum silicate (AlSi), or an alloy of at least two of these.

10. The waveguide of claim 1 , wherein the first layer comprises at least one of a dielectric material or a semiconductor material.

11. The waveguide of claim 1 , wherein the first layer comprises a high refractive index material having a refractive index between 1.9 and 3.

5.

12. The waveguide of claim 1 , wherein the range of angles spans at least 12 degrees.

13. The waveguide of claim 1 , wherein the range of angles spans at least 22 degrees.

14. The waveguide of claim 1 , wherein the first layer comprises at least two sub-layers of different materials having different refractive indices.

15. At least one of the sub-layers is made of titanium dioxide (TiO ２ ), at least different ones of the sub-layers are made of silicon dioxide (SiO ２ 15. The waveguide of claim 14, comprising:

16. The waveguide of claim 1 , wherein the second diffraction efficiency is within ±10% of the first diffraction efficiency.

17. 2. The waveguide of claim 1, wherein the first layer includes at least three sublayers, the at least three sublayers including a first sublayer, a second sublayer, and a third sublayer, the second sublayer being disposed between the first sublayer and the third sublayer, and the refractive index of the second sublayer being lower than the refractive index of the third sublayer.

18. The second sub-layer is made of SiO ２ and the first sub-layer and the third sub-layer are TiO ２ 18. The waveguide of claim 17, wherein:

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