Metasurfaces with light-redirecting structures including multiple materials and methods for processing the same

Abstract

To provide favorable metasurfaces with light-redirecting structures including multiple materials and methods for processing the same.SOLUTION: Display devices include waveguides with metasurfaces as in-coupling and / or out-coupling optical elements. The metasurfaces may be formed on a surface of the waveguide and may include a plurality or an array of sub-wavelength-scale (e.g., nanometer-scale) protrusions. The individual protrusions may include horizontal and / or vertical layers of different materials which may have different refractive indices, allowing enhanced manipulation of light redirecting properties of the metasurfaces. Some configurations and combinations of materials may advantageously allow broadband metasurfaces. Manufacturing methods described herein provide vertical and / or horizontal layers of different materials in a desired configuration or profile.SELECTED DRAWING: Figure 13

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit of U.S. Provisional Application No. 62 / 933,246, filed on November 8, 2019, entitled "METASURFACES WITH LIGHT - REDIRECTING STRUCTURES INCLUDING MULTIPLE MATERIALS AND METHODS FOR FABRICATING", which is hereby incorporated by reference in its entirety.

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

Background Art

[0003] 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 is perceived to be real. Virtual reality, i.e., "VR" scenarios, typically involve the presentation of digital or virtual image information without transparency to other actual real - world visual inputs, and augmented reality, i.e., "AR" scenarios, typically involve the presentation of digital or virtual image information as an augmentation to the visualization of the actual world around the user. Mixed reality or "MR" scenarios are a type of AR scenario that typically involves virtual objects integrated into and responsive to the natural world. For example, an MR scenario may include AR image content that appears to be blocked or otherwise interact with real - world objects.

[0004] Referring to FIG. 1, an augmented reality scene 10 is depicted. To a user of AR technology, a real-world park-like setting 20 featuring people, trees, and buildings in the background, and a concrete platform 30 are visible. The user also "sees" "virtual content" such as a robot image 40 standing on the real-world platform 30 and an avatar character 50 like a flying comic that appears anthropomorphic like a honeybee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The generation of AR technology, which promotes a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements, is difficult because the human visual perception system is complex. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0005] Some aspects include an optical system. The optical system includes an optical waveguide and optical elements on the surface of the optical waveguide. The optical elements are configured to redirect light having a certain wavelength and include a plurality of spaced-apart protrusions disposed on the optical waveguide. Each protrusion includes a first vertical layer comprising a first material and a second vertical layer comprising a second material different from the first material.

[0006] The optical element may be a metasurface. The first material and the second material may have different refractive indices. The first vertical layer may define a U-shaped cross-sectional profile, and the second material may fill the U-shaped internal volume. Each protrusion may further include an intermediate vertical layer disposed between the first vertical layer and the second vertical layer, the intermediate vertical layer comprising a third material different from the first material and the second material. Both the intermediate vertical layer and the second vertical layer may have a U-shaped cross-sectional profile. The plurality of protrusions may include at least one of a nanobeam and a pillar. The protrusions of the plurality of protrusions may be separated from each other by a sub-wavelength spacing. As used herein, a sub-wavelength dimension is less than the wavelength of light, preferably visible light (e.g., visible light as disclosed herein for which the metasurface is configured to receive and redirect within a display system). The wavelength may correspond to blue light, green light, or red light.

[0007] Some aspects include a method of manufacturing an optical element for redirecting light. The method includes providing a plurality of spaced-apart placeholders on a waveguide, conformally depositing a first blanket layer comprising a first material over the placeholders and the waveguide, preferentially removing a horizontally oriented portion of the first blanket layer to expose at least a portion of the placeholders, and selectively etching the placeholders with respect to the first blanket layer to form a plurality of vertically oriented protrusions comprising the first material. The plurality of vertically oriented protrusions are configured to redirect light.

[0008] The vertically oriented protrusions may form a metasurface, and the vertically oriented protrusions have a spacing less than the wavelength of light. The vertically oriented protrusions may comprise at least one of a nanobeam and a pillar. The wavelength may correspond to blue light, green light, or red light. Providing a placeholder may include depositing a layer of resist on a waveguide and patterning the resist to define the placeholder. Patterning the resist may include performing at least one of photolithography, electron beam lithography, and nanoimprint lithography. Conformally depositing a first layer may include depositing the first layer by atomic layer deposition. The method may further include conformally depositing a second blanket layer on the first blanket layer, the second blanket layer comprising a second material different from the first material, and the second blanket layer being conformally deposited prior to preferentially removing horizontally oriented portions. Preferentially removing horizontally oriented portions may include removing the horizontally oriented portions of the second layer and the first layer. The first blanket layer may extend along the sidewalls of the placeholder and define an open volume therebetween, and further include filling the open volume with a filling material prior to preferentially removing horizontally oriented portions. Selectively etching the placeholder may include retaining the filling material. The filling material may have a refractive index different from that of the first material. Preferentially removing horizontally oriented portions may include performing chemical mechanical polishing. The method may further include annealing the remaining portion of the first blanket layer prior to selectively etching the placeholder. Selectively etching the placeholder may include including at least one of wet etching and plasma etching.

[0009] Some aspects include an optical system. The optical system includes an optical waveguide and optical elements on the surface of the optical waveguide. The optical elements are configured to redirect light having a certain wavelength and include a plurality of protrusions disposed on the optical waveguide. Each protrusion includes a lower horizontal layer on the optical waveguide, the lower horizontal layer comprising a first material, and an upper layer on the lower horizontal layer, the upper horizontal layer comprising a second material different from the first material.

[0010] The optical element may include a metasurface. The first material and the second material may have different refractive indices. Each protrusion may further include an intermediate horizontal layer disposed between the upper layer and the lower layer, the intermediate layer comprising a third material different from the first material and the second material. The plurality of protrusions may include at least one of nanobeams and pillars. The plurality of protrusions may be separated from each other by a sub-wavelength spacing less than the wavelength of the light. The wavelength may correspond to blue light, green light, or red light. At least one of the first material and the second material may include a sulfur compound. The sulfur compound may be molybdenum sulfide.

[0011] Some aspects include a method of manufacturing an optical element. The method includes forming a metasurface, which includes depositing a lower blanket layer on the optical waveguide, the lower blanket layer comprising a first material, depositing an upper blanket layer on the lower blanket layer, the upper blanket layer comprising a second material different from the first material, forming an etching mask over the upper blanket layer, the etching mask exposing unmasked portions of the upper blanket layer, removing the unmasked portions of the upper blanket layer and the lower blanket layer to form a plurality of protrusions that make up the remaining portions of the lower and upper layers, the protrusions being configured to redirect light.

[0012] The vertically oriented protrusions may form a metasurface, and the vertically oriented protrusions have a sub-wavelength spacing less than the wavelength of light. The vertically oriented protrusions may comprise at least one of a nanobeam and a pillar. The wavelength may correspond to blue light, green light, or red light. The method may further include converting at least one of the lower layer and the upper layer of each protrusion to a different material by exposing the plurality of protrusions to an atmosphere comprising species for incorporation into at least one of the lower layer and the upper layer. Converting the lower layer or the upper layer may include at least one of sulfidation and selenization. The lower layer and the upper layer may be deposited by at least one of physical vapor deposition, chemical vapor deposition, and atomic layer deposition. At least one of the lower layer and the upper layer may have a thickness of 5 nanometers or less. The method may further include depositing a third layer on the upper layer before forming the etching mask, the third layer comprising a third material different from the first material and the second material, and forming the etching mask includes forming the etching mask across the third layer. The present invention provides, for example, the following. (Item 1) An optical system, a waveguide, and an optical element on the surface of the waveguide, the optical element being configured to redirect light having a certain wavelength, the optical element comprising a plurality of spaced-apart protrusions disposed on the waveguide, each protrusion comprising a first vertical layer comprising a first material, and a second vertical layer comprising a second material different from the first material and comprising a plurality of spaced-apart protrusions and comprising an optical element and comprising an optical system. (Item 2) The optical system according to item 1, wherein the optical element is a metasurface. (Item 3) The optical system according to item 1, wherein the first material and the second material have different refractive indices. (Item 4) The optical system according to item 1, wherein the first vertical layer defines a U-shaped cross-sectional profile, and the second material fills the internal volume of the U shape. (Item 5) Each protrusion further includes an intermediate vertical layer disposed between the first vertical layer and the second vertical layer, and the intermediate vertical layer includes a third material different from the first material and the second material. The optical system according to item 1. (Item 6) The optical system according to item 5, wherein both the intermediate vertical layer and the second vertical layer have a U-shaped cross-sectional profile. (Item 7) The optical system according to item 1, wherein the plurality of protrusions includes at least one of a nanobeam and a pillar. (Item 8) The optical system according to item 1, wherein the protrusions of the plurality of protrusions are separated from each other by a sub-wavelength interval less than the wavelength of the light. (Item 9) The optical system according to item 1, wherein the wavelength corresponds to blue light, green light, or red light. (Item 10) A method of manufacturing an optical element for redirecting light, the method comprising: Providing a plurality of spaced-apart placeholders on a waveguide; Conformally depositing a first blanket layer comprising a first material on the placeholders and the waveguide; Preferentially removing a horizontally oriented portion of the first blanket layer to expose at least a portion of the placeholder; Selectively etching the placeholder with respect to the first blanket layer to form a plurality of vertically oriented protrusions comprising the first material, the plurality of vertically oriented protrusions being configured to redirect light. A method including. (Item 11) The method according to item 10, wherein the vertically oriented protrusions form a metasurface and the vertically oriented protrusions have a spacing less than the wavelength of the light. (Item 12) The method according to item 11, wherein the vertically oriented protrusions comprise at least one of a nanobeam and a pillar. (Item 13) The method according to item 11, wherein the wavelength corresponds to blue light, green light, or red light. (Item 14) The method according to item 10, wherein providing the placeholder includes depositing a layer of resist on the waveguide and patterning the resist to define the placeholder. (Item 15) The method according to item 14, wherein patterning the resist includes performing at least one of photolithography, electron beam lithography, and nanoimprint lithography. (Item 16) The method according to item 10, wherein conformally depositing the first layer includes depositing the first layer by atomic layer deposition. (Item 17) The method according to item 10, further comprising conformally depositing a second blanket layer on the first blanket layer, the second blanket layer comprising a second material different from the first material, and the second blanket layer being conformally deposited prior to preferentially removing horizontally oriented portions. (Item 18) The method according to item 17, wherein preferentially removing horizontally oriented portions includes removing horizontally oriented portions of the second layer and the first layer. (Item 19) The method according to item 10, wherein the first blanket layer extends along sidewalls of the placeholder, defines an open volume therebetween, and further includes filling the open volume with a filling material prior to preferentially removing horizontally oriented portions. (Item 20) The method according to item 19, wherein selectively etching the placeholder includes holding the filling material in place. (Item 21) The method according to item 19, wherein the filling material has a refractive index different from that of the first material. (Item 22) The method according to item 10, wherein preferentially removing the horizontally oriented portion includes performing chemical mechanical polishing. (Item 23) The method according to item 10, further comprising annealing the remaining portion of the first blanket layer prior to selectively etching the placeholder. (Item 24) The method according to item 10, wherein selectively etching the placeholder includes at least one of wet etching and plasma etching. (Item 25) An optical system, a waveguide, an optical element on the surface of the waveguide, the optical element being configured to redirect light having a certain wavelength, and the optical element a plurality of protrusions disposed on the waveguide, each protrusion a lower horizontal layer on the waveguide, the lower horizontal layer comprising a first material, and an upper horizontal layer on the lower horizontal layer, the upper horizontal layer comprising a second material different from the first material, comprising a plurality of protrusions comprising an optical element comprising an optical system. (Item 26) The optical system according to item 25, wherein the optical element comprises a metasurface. (Item 27) The optical system according to item 25, wherein the first material and the second material have different refractive indices. (Item 28) Each protrusion further comprises an intermediate horizontal layer disposed between the upper layer and the lower layer, the intermediate layer comprising a third material different from the first material and the second material, the optical system according to item 25. (Item 29) The plurality of protrusions comprises at least one of a nanobeam and a pillar, the optical system according to item 25. (Item 30) The plurality of protrusions are separated from each other by a sub-wavelength spacing less than the wavelength of the light, the optical system according to item 25. (Item 31) The wavelength corresponds to blue light, green light, or red light, the optical system according to item 25. (Item 32) At least one of the first material and the second material comprises a sulfur compound, the optical system according to item 25. (Item 33) The sulfur compound is molybdenum sulfide, the optical system according to item 32. (Item 34) A method of manufacturing an optical element, the method comprising: Forming a metasurface, wherein forming the metasurface comprises: Depositing a lower blanket layer on a waveguide, the lower blanket layer comprising a first material, and Depositing an upper blanket layer on the lower blanket layer, the upper blanket layer comprising a second material different from the first material, and Forming an etching mask over the upper blanket layer, the etching mask exposing unmasked portions of the upper blanket layer, and Removing the unmasked portions of the upper blanket layer and the lower blanket layer to form a plurality of protrusions that constitute the remaining portions of the lower layer and the upper layer, the protrusions being configured to redirect light Including, Including, the method. (Item 35) The method according to item 34, wherein the vertically oriented protrusions form a metasurface, and the vertically oriented protrusions have a sub-wavelength spacing less than the wavelength of the light. (Item 36) The method according to item 35, wherein the vertically oriented protrusions comprise at least one of a nanobeam and a pillar. (Item 37) The method according to item 35, wherein the wavelength corresponds to blue light, green light, or red light. (Item 38) The method according to item 34, further comprising converting at least one of the lower layer and the upper layer of each protrusion into a different material by exposing the plurality of protrusions to an atmosphere comprising a species for incorporation into at least one of the lower layer and the upper layer. (Item 39) The method according to item 38, wherein converting the lower layer or the upper layer comprises at least one of sulfidation and selenization. (Item 40) The method according to item 34, wherein the lower layer and the upper layer are deposited by at least one of physical vapor deposition, chemical vapor deposition, and atomic layer deposition. (Item 41) The method according to item 34, wherein at least one of the lower layer and the upper layer has a thickness of 5 nanometers or less. (Item 42) The method according to item 34, further comprising depositing a third layer on the upper layer before forming the etching mask, the third layer comprising a third material different from the first material and the second material, and forming the etching mask comprises forming the etching mask over the third layer.

Brief Description of the Drawings

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[0037] Detailed Description An AR and / or VR system can display virtual content to a user or viewer. For example, this content may be displayed on a head-mounted display as part of eyewear that projects image information onto the user's eyes. Additionally, if the system is an AR system, the display may also transmit light from the surrounding environment through the user's eyes, enabling a view of that surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the head of a viewer or user.

[0038] In some display systems, one or more waveguides, such as a stack of waveguides, may be configured to form virtual images on a plurality of virtual depth planes (also simply referred to herein as "depth planes") and be perceived as being at different distances away from the user. In some implementations, light containing image information may be internally coupled into the waveguides, propagate through the waveguides, and then be externally coupled (e.g., towards the viewer's eyes). Different waveguides in the stack of waveguides may have an optical structure (e.g., an external coupling optical element) that simulates the wavefront divergence of light propagating from an object at a different distance from the user's eyes to the user's eyes. In some implementations, as an alternative to or in addition to the waveguide optical structure for providing refractive power, the display system may also include one or more lenses that provide, or additionally provide, refractive power or a desired amount of wavefront divergence. The light carrying the image information may be provided by an image source and be internally coupled into the individual waveguides by the internal coupling optical elements of each waveguide. The internal coupling and external coupling optical elements may be diffractive optical elements that include a metasurface.

[0039] It should be understood that internal and external coupling optical elements preferably meet various performance criteria, for example, to provide good image quality and / or high power efficiency. For example, different waveguides can be configured to output light of different colors or wavelengths. As a result, in some implementations, the internal and / or external coupling optical elements redirect light (internally or externally couple the light, respectively) with high selectivity and high efficiency with respect to a desired wavelength, while redirecting light with low efficiency with respect to other wavelengths. As another example, it may be desirable for the internal and / or external coupling optical elements to redirect light away from those optical elements at a particular angle and / or receive incident light at a particular angle for redirection. Preferably, the redirection of light at a particular desired wavelength and / or in a particular desired direction or therefrom is achieved with high efficiency. These and various other performance parameters of the metasurface can be adjusted by appropriately designing the structure that defines the metasurface.

[0040] Advantageously, the systems and methods described herein provide optical elements such as internal and / or external coupling optical elements, which in some implementations enable a high degree of freedom in adjusting the performance characteristics of the optical elements by enabling a high degree of freedom in modifying properties associated with the materials forming the optical elements. A metasurface is typically formed from a single material. Some of the systems and methods described herein provide individual constituent structures of the metasurface, which include multiple materials at highly precise locations and ratios. For example, the protrusions forming the metasurface may have horizontal and / or vertical layers (e.g., concentric vertical layers) of different materials, such as materials having different refractive indices. Advantageously, the inclusion of multiple materials within individual protrusions of the metasurface provides more customization in metasurface design and may enable, for example, improved control of the scattering response (e.g., amplitude, phase shift, etc.) of the metasurface. It should be understood that the metasurface may form various structures and provide controlled redirection or scattering of incident electromagnetic radiation, including light at visible wavelengths. In some implementations, the multilayered metasurface protrusions form broadband achromatic metalenses, broadband beam polarizers, broadband achromatic waveplates, broadband polarizers, and / or any other metasurface in which a similar scattering response is desired across a desired (e.g., broad) range of incident wavelengths.

[0041] Reference is now made to the drawings, in which like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale. Exemplary display system

[0042] FIG. 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 can form an image of the object at different locations on the retina of each eye. This can be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct images 190, 200 with slightly different views of one identical virtual object for each of the eyes 210, 220, corresponding to the views of the virtual object that would be seen by each eye as if the virtual object were a real object at the desired depth. These images provide binocular cues that the user's visual system interprets to derive a perception of depth.

[0043] 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 in the images presented to the eyes 210, 220 respectively, the eyes can necessarily rotate so that the images of the object come to corresponding points on the respective retinas of the eyes and a single binocular vision is maintained. This rotation can converge the respective lines of sight of the eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, the provision of a three-dimensional image has conventionally involved being able to manipulate the convergence and divergence movements of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide a perception of depth.

[0044] However, generating realistic and comfortable perception of depth is difficult. It should be understood that light from objects at different distances from the eye has wavefronts with different divergence amounts. FIGS. 3A - 3C illustrate the relationship between distance and divergence of light rays. The distances between the object and the eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A - 3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. Only the single eye 210 is illustrated in FIGS. 3A - 3C and various 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.

[0045] Continuing to refer to FIGS. 3A - 3C, the light from the object on which the viewer's eye is fixated can have different wavefront divergence degrees. Due to the different wavefront divergence amounts, the light can be focused differently by the eye's lens, which in turn may require the lens to take on different shapes to form a focused image on the retina of the eye. If the focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation to cause a change in the shape of the eye's lens until the focused image is formed on the retina. For example, the cue for accommodation triggers 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., 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 the fixated object on the retina (e.g., fovea) of the eye can be referred to as the accommodative state.

[0046] Referring now to FIG. 4A, the representation of the accommodation-convergence / divergence movement response of the human visual system is illustrated. The movement of the eyes to fixate on an object causes 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 convergence / divergence movement. The cue for accommodation results in causing accommodation and 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 convergence / divergence movement causes a convergence / divergence movement (rotation of the eyes) 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 convergence / divergence movement state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eyes achieve a particular accommodation state, and convergence / divergence movement can be understood as the process by which the eyes achieve a particular convergence / divergence movement state. As shown in FIG. 4A, the accommodation and convergence / divergence movement 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 along the z-axis.

[0047] Although not limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of convergence / divergence motion and accommodation. As described above, the mutual convergence / divergence movement of the two eyes (e.g., the rotation of the eyes such that the pupils move towards or away from each other, converging the lines of sight of the eyes to fixate on an object) is closely associated with the accommodation of the eye's lens. Under normal conditions, changing the shape of the eye's lens to change focus from one object to another at different distances will automatically cause a corresponding change in convergence / divergence motion to the same distance under a relationship known as the "accommodation-convergence / divergence reflex". Similarly, a change in convergence / divergence motion will trigger a corresponding change in the shape of the lens under normal conditions.

[0048] Referring now to FIG. 4B, an example of different accommodation and convergence / divergence states of the eyes is illustrated. The pair of eyes 222a fixates on an object at optical infinity, while the pair of eyes 222b fixates on an object 221 at less than optical infinity. It should be noted that the convergence / divergence states of each pair of eyes are different, with the pair of eyes 222a being straight ahead, while the pair of eyes 222 converges on the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b also differ, as represented by the different shapes of the lenses 210a, 220a.

[0049] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or perceive no sense of depth due to the inconsistency between the depth adjustment and the convergence / divergence motion state 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 accommodation state of their 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 accommodation state. Such an arrangement violates the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence motion state without a corresponding change in the accommodation state. This inconsistency is thought to cause viewer discomfort. A display system that provides better alignment between accommodation and convergence / divergence motion can create a more realistic and comfortable simulation of a three-dimensional image.

[0050] Although not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eyes. In some implementations, the different presentations may provide both a cue for convergence / divergence motion and a corresponding cue for accommodation, thereby providing a physiologically correct accommodation-convergence / divergence alignment.

[0051] Continuing to refer to FIG. 4B, two depth planes 240 are illustrated that correspond to different distances in space from eyes 210, 220. For a given depth plane 240, a vergence / divergence motion cue 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.

[0052] In the illustrated implementation, 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, 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 (e.g., 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 is referred to as the pupil distance and may correspond 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.

[0053] Referring now to FIGS. 4C and 4D, examples of consistent vergence-accommodation-convergence / divergence movement distances and inconsistent 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 eye 210, 220. The image may cause the eyes 210, 220 to assume a vergence-accommodation-convergence / divergence state in which the eyes converge on a point 15 on the depth plane 240. Additionally, the image may be formed by light having a wavefront curvature corresponding to the real object in the depth plane 240. As a result, the eyes 210, 220 assume an accommodation 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.

[0054] It should be understood that the accommodation and vergence-accommodation-convergence / divergence 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 accommodation state based on the distance of the object. The distance associated with a specific accommodation state may be referred to as the accommodation distance A d Similarly, there exists a specific vergence-accommodation-convergence / divergence distance V d or a position relative to each other associated with the eyes in a specific vergence-accommodation-convergence / divergence state. When the accommodation distance and the vergence-accommodation-convergence / divergence distance are consistent, the relationship between accommodation and vergence-accommodation-convergence / divergence may be said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0055] However, in a stereoscopic display, the focusing adjustment distance and the vergence / accommodation movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may be in a specific focusing adjustment state where points 15a, 15b on that depth plane are in focus. However, the images displayed on eyes 210, 220 may provide a cue for vergence / accommodation movement that converges eyes 210, 220 on points 15 that are not located on depth plane 240. As a result, in some implementations, the focusing adjustment distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the vergence / accommodation movement distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to points 15. The focusing adjustment distance is different from the vergence / accommodation movement distance. As a result, there is a focusing adjustment - vergence / accommodation movement mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch corresponds to a distance (e.g., V d -A d ) and it should be understood that it can be characterized using diopters.

[0056] It should be understood that in some implementations, as long as the same reference point is used for the focusing adjustment distance and the vergence / accommodation movement distance, reference points other than the exit pupils of eyes 210, 220 may be used to determine the distance in order to determine the focusing adjustment - vergence / accommodation movement mismatch. 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.

[0057] Although not limited by theory, it is believed that the user can still perceive vergence-accommodation divergence mismatches of up to 0.25 diopters, up to 0.33 diopters, and up to about 0.5 diopters that are physiologically correct without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents an image having a vergence-accommodation divergence mismatch of about 0.5 diopters or less to a viewer. In some other embodiments, the vergence-accommodation divergence mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the vergence-accommodation divergence mismatch of the image provided by the display system is 0.25 diopters or less, including about 0.1 diopters or less.

[0058] 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 implementations, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, the user's other eye would be illustrated as being provided with image information from a similar waveguide.

[0059] In some implementations, 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 implementations, multiple or stacked waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light within different ranges of wavelengths. It will be understood that as used herein, a depth plane may be a plane or may follow the contour of a curved surface.

[0060] FIG. 6 illustrates an example of a stack of waveguides for outputting image information to a user. Display system 250 includes a stack or stacked waveguide assembly 260 of waveguides that can be utilized to provide 3D perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It should be understood that in some implementations, display system 250 may be regarded as a light field display. Additionally, waveguide assembly 260 may also be referred to as an eyepiece.

[0061] In some implementations, 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, display system 250 may be configured to output light with a variable level of wavefront divergence. In some implementations, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of waveguides 270, 280, 290, 300, 310.

[0062] 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 implementations, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310 and / or the plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310 and may each be configured to disperse incident light across an individual waveguide to output it towards 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 implementations, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a part of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly towards world 510 or viewer's eye 210). In some implementations, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of collimated beams that are cloned and directed towards eye 210 at a particular angle (and amount of divergence) corresponding to a particular depth plane associated with the particular waveguide. In some implementations, 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.

[0063] In some implementations, 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, for example, via one or more optical waveguides (such as optical fiber cables) to each of the image input devices 360, 370, 380, 390, 400. It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0064] In some implementations, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520, which may include an optical module 530 that may include a light emitter such as a light emitting diode (LED). The light from the optical module 530 may be directed and modified by a beam splitter 550 and an optical modulator 540, such as a spatial light modulator. The optical modulator 540 may be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) and liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically and, in some implementations, these image input devices may represent the optical paths and locations within a common projection system configured to output light into the associated ones of the waveguides 270, 280, 290, 300, 310. In some implementations, the waveguides of the waveguide assembly 260 may function as an ideal lens while relaying the light input into the waveguides to the user's eye. In this concept, the object may be the spatial light modulator 540 and the image may be an image on a depth plane.

[0065] In some implementations, the display system 250 may be a scanning fiber display that includes one or more scanning fibers configured to project light into one or more waveguides 270, 280, 290, 300, 310 in various patterns (e.g., raster scan, helical scan, Lissajous pattern, etc.) and ultimately into the viewer's eye 210. In some implementations, 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 may be provided between the scanning fiber or fibers and one or more waveguides 270, 280, 290, 300, 310 to, for example, redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0066] Controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 530, and light modulator 540. In some implementations, 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 provisioning of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some implementations, the controller may be a single monolithic device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some implementations, also be part of processing module 140 or 150 (FIG. 9D).

[0067] 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 a major top surface and a bottom surface and an edge extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external coupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide out of the waveguide and outputting the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of 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, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, they are shown disposed on the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, but in some implementations, 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 implementations, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of the material forming the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be a monolithic piece of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that piece of material.

[0068] 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 such 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 lens 350 and the second lens 340 may be configured to generate another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is closer inwardly toward the person from the optically infinite than the light from the next upper waveguide 280 was.

[0069] 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 representing 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 compensating 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.

[0070] In some implementations, 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, with one set per depth plane. This can provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0071] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from their respective waveguides for a particular depth plane associated with the waveguide and output the light with an appropriate amount of divergence or collimation. As a result, waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610, which output light with different amounts of divergence depending on the associated depth plane. In some implementations, the light extraction optical elements 570, 580, 590, 600, 610 may be three-dimensional or surface features, which may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some implementations, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming voids).

[0072] In some implementations, the external coupling optical elements 570, 580, 590, 600, 610 are "diffractive optical elements", i.e., diffractive features that form a diffraction pattern (also referred to herein as a "DOE"). 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 exiting the waveguide at various locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam bouncing within the waveguide.

[0073] In some implementations, one or more DOEs may be switchable between an “on” state that actively diffracts and an “off” state that does not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which microdroplets have a diffraction pattern in a host medium and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0074] In some implementations, a camera assembly 630 (e.g., a digital camera including visible and infrared light cameras) may be provided to capture an image of the eye 210 and / or 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 implementations, the camera assembly 630 may include an image capture device and a light source (e.g., infrared light) that projects light onto the eye and is then reflected by the eye and detected by the image capture device. In some implementations, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may communicate electrically with a processing module 140 and / or 150 that can process image information from the camera assembly 630. In some implementations, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0075] Referring now to FIG. 7, an example of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function 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 within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as the output beam 650. The output beam 650 is illustrated as being substantially parallel, but as discussed herein, it may also be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging output beam) depending on the depth plane associated with the waveguide 270. 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 in a depth plane at a long distance (e.g., optical infinity) from the eye 210 may be shown for the substantially parallel output beam. 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.

[0076] In some implementations, a full-color image may be formed on each depth plane by overlaying the image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an embodiment of a stacked waveguide assembly, and 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 diopter following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some implementations, to account for differences in the focusing of light of different wavelengths by the eye, the exact location of the depth planes for different primary colors may vary. For example, the 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.

[0077] In some implementations, the light of each primary color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such an embodiment, each box in the figure, including those containing the letters G, R, or B, may be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this 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.

[0078] Continuing to refer to FIG. 8, in some implementations, 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 instead of one or more of red, green, or blue.

[0079] It is to be understood that references throughout this disclosure to the color of a given light include light of one or more wavelengths within the range of wavelengths of the light that is perceived by a viewer as that given color. For example, red light may include light of one or more wavelengths within the range of about 620 - 780 nm, green light may include light of one or more wavelengths within the range of about 492 - 577 nm, and blue light may include light of one or more wavelengths within the range of about 435 - 493 nm.

[0080] In some implementations, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the visual perception range of a viewer, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirecting structures of the waveguide of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications.

[0081] Referring now to FIG. 9A, in some implementations, 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 stack 660 of multiple or a set of waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, but it should be understood that light from one or more of the image input devices 360, 370, 380, 390, 400 is input into the waveguide from a position that requires the light to be redirected for internal coupling.

[0082] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as an optical input area on the waveguide). For example, internal coupling optical element 700 is disposed on a major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the upper major surface) of waveguide 690. In some implementations, 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 (in particular, 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 of their respective waveguides 670, 680, 690 (or the upper portion of the next lower waveguide), and in particular, those internal coupling optical elements are transmissive deflecting optical elements. In some implementations, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguides 670, 680, 690. In some implementations, 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 implementations.

[0083] As shown, the internally coupled optical elements 700, 710, 720 may be laterally offset from each other. In some implementations, 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 receives substantially no light from the other internally coupled optical elements 700, 710, 720.

[0084] Each waveguide also includes an associated light dispersing element. For example, light dispersing element 730 is disposed on a major surface (e.g., upper major surface) of waveguide 670, light dispersing element 740 is disposed on a major surface (e.g., upper major surface) of waveguide 680, and light dispersing element 750 is disposed on a major surface (e.g., upper major surface) of waveguide 690. In some other embodiments, 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, 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 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.

[0085] 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 implementations, 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 immediate waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is less than the refractive index of the material forming waveguides 670, 680, 690 by 0.05 or more, or by 0.10 or more. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote 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 implementations, 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 an immediate cladding layer.

[0086] 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 implementations, 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.

[0087] 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).

[0088] In some implementations, 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 implementations, 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 associated internal coupling optical elements.

[0089] For example, the internal coupling optical element 700 may be configured to selectively deflect the light ray 770 having a first wavelength or wavelength range while transmitting the light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light ray 780 impinges on the internal coupling optical element 710 configured to selectively 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.

[0090] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect light into its corresponding waveguide 670, 680, 690 and internally couple the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0091] 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 the waveguides 670, 680, 690. The light rays 770, 780, 790 then each impinge on the light dispersing elements 730, 740, 750. The light dispersing 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.

[0092] In some implementations, the light dispersing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some implementations, the OPEs deflect or disperse light to the external coupling optical elements 800, 810, 820, and in some implementations, also increase the beam or spot size of the present light as it propagates to the external coupling optical elements. In some implementations, the light dispersing elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to deflect light directly 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 implementations, the external coupling optical elements 800, 810, 820 are an exit pupil (EP) or an exit pupil expander (EPE) that directs light to the viewer's eye 210 (FIG. 7). The OPE may be configured to increase the size of the eyebox in at least one axis, and it should be understood that 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 remainder of the light to continue to propagate along the waveguide. In response to a collision with the OPE, again, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further along the waveguide or the like. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed from the waveguide towards the user, and the remainder of that light continues to propagate through the waveguide until it impinges again on the EP, at which point another portion of the colliding light is directed from 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 implementations, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0093] Thus, referring to FIGS. 9A and 9B, in some implementations, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPEs) 730, 740, 750, and external coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements for receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated embodiment, the ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above and then bounces along the waveguide, interacting with the light dispersion element (e.g., OPE) 730 and 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. The ray 780 impinges on the internal coupling optical element 710 and is thereby deflected. The ray 780 then bounces along the waveguide 680 via TIR and will proceed to its light dispersion element (e.g., OPE) 740 and then the external coupling optical element (e.g., EP) 810. Finally, the ray 790 (e.g., red light) passes through the waveguide 690 and impinges on 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 and then by TIR to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives the externally coupled light from the other waveguides 670, 680.

[0094] FIG. 9C illustrates top and bottom plan views of an embodiment of a plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820 of each waveguide. However, as discussed herein, internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a specific light source to be uniquely coupled to a specific waveguide. In some implementations, an array that includes non-overlapping spatially separated internal coupling optical elements may be referred to as a defocused pupil system, and the internal coupling optical elements within these arrays may correspond to sub-pupils.

[0095] 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 implementations, display system 60 is the system 250 of FIG. 6, which schematically shows some parts of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of display 70.

[0096] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems for supporting the functions of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the user 90's eyes. In some implementations, the display 70 may be regarded as an eyepiece. In some implementations, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user 90's outer ear canal (in some implementations, another speaker, not shown, may also be optionally positioned adjacent to the user's other outer ear canal to provide stereo / formable sound control). The display system 60 may also include one or more microphones 110 or other devices that may detect sound. In some implementations, the microphone is configured to enable the user to provide an input or command to the system 60 (e.g., selection of an audio menu command, natural language question, etc.) and / or 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 implementations, the display system 60 may further include one or more outwardly directed environmental sensors 112 configured to detect objects, stimuli, people, animals, places, or other aspects of the world around the user. For example, the environmental sensor 112 may include one or more cameras, which may be positioned facing outward to capture an image similar to at least a portion of the user 90's normal field of view. In some implementations, the display system may also include a peripheral sensor 120a, which is separate from the frame 80 and may be attached to the user 90's body (e.g., the user 90's head, torso, limbs, etc.). The peripheral sensor 120a may, in some implementations, be configured to obtain data characterizing the physiological state of the user 90.For example, the sensor 120a may be an electrode.

[0097] Continuing to refer to FIG. 9D, display 70 is operatively coupled to local data processing module 140 by a communication link 130, such as a wired conductor or wireless connectivity, which may be mounted in various configurations, such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by a user, embedded within headphones, or removably attached to user 90 in some other manner (e.g., in a backpack-style configuration, a belt-coupled configuration). Similarly, sensor 120a may be operatively coupled to local data processing module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. Local processing and data module 140 may comprise a digital memory, such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, local processor and data module 140 may include one or more processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data may include a) data captured from sensors (image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., operatively coupled to frame 80 or otherwise attachable to user 90)), and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for passage to display 70 after processing or retrieval. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via a wired or wireless communication link, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some implementations, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be attached to the frame 80 or may be of an independent structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0098] Continuing to refer to FIG. 9D, in some implementations, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some implementations, the remote data repository 160 may include a digital data storage facility, which may be available through the Internet or other networking configurations in a "cloud" resource configuration. In some implementations, the remote data repository 160 may include one or more remote servers that provide information, such as information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some implementations, all data is stored and all computations are performed in the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system, including, for example, one or more processors, one or more computer systems, including CPUs, GPUs, 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. Exemplary metasurface

[0099] Figures 10A and 10B respectively illustrate cross-sectional side views and top and bottom views of an example of a metasurface 2002 according to several embodiments. The substrate 2000 has a surface 2000a on which a metasurface 2002 comprising a plurality of metasurface unit cells 2010 is disposed. Each unit cell 2010 includes one or more protrusions comprising a material extending upward from the surface 2000a. As shown, in some implementations, the unit cell 2010 includes two protrusions 2020a, 2020b. In some implementations, the protrusions 2020a, 2020b may take the form of self-standing columns. In some other implementations, the protrusions 2020a, 2020b may take the form of nanobeams that extend laterally. When the unit cell 2010 includes two or more protrusions, the protrusions 2020a, 2020b may be of different sizes (e.g., one may be wider than the other), as shown. The protrusions 2020a, 2020b may be formed of an optically transmissive material.

[0100] Continuing to refer to FIG. 10A, the protrusions 2020a, 2020b may be ridges (or nanobeams) that extend laterally in and out of the page and define a trench between neighboring protrusions. In some implementations, the protrusions 2020a, 2020b may be linear. In some implementations, the protrusions 2020a, 2020b may be continuous along their length, which may have the advantage of providing high diffraction efficiency. In some other implementations, the protrusions 2020a, 2020b may be intermittent along their length, e.g., the protrusions 2020a, 2020b may each extend along a line and have gaps within the protrusions 2020a, 2020b along those lines.

[0101] The unit cell 2010 may repeat at regular intervals across the surface 2000a and the protrusions 2020a, 2020b may also be parallel to each other. The unit cell 2010 may have a width P, which is the distance between the same points of directly adjacent unit cells 2010. In some implementations, P may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. It should be understood that P can be regarded as the pitch of the unit cell 2010 and may be substantially constant across the lattice formed by those unit cells. In some other embodiments, P may vary across the surface 2000a.

[0102] Preferably, the refractive index of the material forming the protrusions 2020a, 2020b is different from (e.g., higher than) the refractive index of the substrate 2000. In some implementations, the protrusions 2020a, 2020b or other structures (e.g., pillars or other shapes) may include a plurality of materials having different refractive indices, some of which may individually be higher or lower than the refractive index of the substrate 2000. In some implementations, the substrate 2000 may be a waveguide and may correspond to waveguides 270, 280, 290, 300, 310 (FIG. 6) and / or waveguides 670, 680, and 690 (FIG. 9A). In such applications, the substrate preferably has a relatively high refractive index, e.g., 1.5, 1.6, 1.7, 1.8, 1.9, or higher, which can provide the advantage of increasing the field of view of a display that forms an image by outputting light from the substrate 2000. Examples of materials for forming the substrate 2000 include glass (e.g., doped glass), lithium niobate, plastic, polymer, sapphire, or other optically transparent materials. In some implementations, the refractive index of the material forming the protrusions 2020a, 2020b (or the effective refractive index if the protrusions 2020a, 2020b or other nanostructures include a plurality of materials) may be 2.0 or higher, 2.5 or higher, 3.0 or higher, 3.3 or higher, or 3.5 or higher. Examples of materials for forming the protrusions 2020a, 2020b include silicon-containing materials (e.g., amorphous or polysilicon, and silicon nitride), oxides, and gallium phosphide. Examples of oxides include titanium oxide, zirconium dioxide, silicon dioxide, and zinc oxide. In some implementations, the material or combination of materials forming the protrusions 2020a, 2020b is the same, which has the advantage of simplifying the processing of the metasurface 2002.

[0103] Continuing to refer to FIGS. 10A and 10B, one of the protrusions 2020b has a width NW greater than the other width NW of the illustrated protrusion 2020a. 1 Greater width NW 2 In some implementations, the widths NW 1 and NW2 is within the range of 10 nm to 1 μm, including 10 nm to 300 nm, for each NW 1 is, as described above, NW 2 exceeds. As shown, the protrusions 2020a, 2020b may be separated by a gap within the range of 10 nm to 1 μm width, including 10 nm to 300 nm width. Also, as shown, the protrusions 2020a, 2020b have a height h nw which, in some implementations, may be within the range of 10 nm to 1 μm, including 10 nm to 450 nm. Preferably, the heights of the protrusions 2020a, 2020b are substantially equal.

[0104] Continuing to refer to FIGS. 10A and 10B, the metasurface 2002 illustrated in these figures can function in transmission mode. The light rays 2021a, 2021b are redirected in response to propagating through the metasurface 2002 formed by the protrusions 2020a, 2020b. As shown, the light ray 2021a is incident on the metasurface 2002 at an angle α with respect to the normal of the surface 2000a. Preferably, the angle α is within the angular bandwidth for the metasurface 2002 such that the light ray 2021a is redirected by the metasurface 2002 and propagates within the substrate 2000 at an angle that facilitates total internal reflection within the substrate 2000. As shown, the light ray 2021b is redirected to create an angle θ TIR with respect to the normal of the surface 2000a. Preferably, the angle θ TIR is within the range of angles that facilitate total internal reflection within the substrate 2000. As disclosed herein, in some implementations, the metasurface 2002 is utilized as an internal coupling optical element (e.g., as one or more than one of the internal coupling optical elements 700, 710, 720 (FIG. 9A)) and may internally couple the incident light such that light propagates through the substrate 2000 via total internal reflection.

[0105] The metasurface 2002 will also deflect light impinging thereon from within the substrate 2000. Utilizing this functionality, in some implementations, instead of or in addition to forming internal coupling optical elements at different locations on the surface 2000a, the metasurfaces disclosed herein may be applied to form external coupling optical elements such as one or more of the external coupling optical elements 570, 580, 590, 600, 610 (FIG. 6) or 800, 810, 820 (FIG. 9B). It should be understood that if different waveguides have different associated primary colors, the external coupling optical elements and / or internal coupling optical elements associated with each waveguide may have geometric sizes and / or periodicities specific to the wavelength or color of the light configured to propagate through the waveguide. Thus, different waveguides may have metasurfaces with different geometric sizes and / or periodicities. As an example, metasurfaces for internally or externally coupling red, green, or blue light may have geometric sizes and / or periodicities (pitches) configured to redirect or diffract light at wavelengths of, for example, 638 nm, 520 nm, and 455 nm, respectively. In some implementations, the geometric sizes and periodicities of the protrusions 2020a, 2020b and the unit cell 2010 increase as the wavelength gets longer, and / or the height or thickness of one or both of the protrusions 2020a, 2020b also increases as the wavelength gets longer.

[0106] In some implementations, when the metasurface 2002 is utilized as an external coupling optical element, the metasurface 2002 may have a geometric size and / or pitch that imparts a refractive force on the light diffracted by the metasurface. For example, the metasurface may be configured to emit light in a divergent or convergent direction from the metasurface. Different portions of the metasurface may have different pitches, which, for example, deflect different light rays in different directions such that the light rays diverge or converge.

[0107] In some other implementations, the metasurface 2002 may redirect light such that the light propagates away from the metasurface 2002 as collimated light rays. For example, if collimated light impinges on the metasurface 2002 at similar angles, the metasurface 2002 may have a consistent geometric size and a consistent pitch across the entirety of the metasurface 2002 and redirect the light at similar angles.

[0108] As described above, two protrusions 2020a, 2020b are shown for ease of discussion, but the metasurface 2002 may include unit cells 2010 with more than one or two protrusions per unit cell 2010. Additionally, the protrusions may have various shapes. In some implementations, the protrusions may be cylindrical and / or rounded.

[0109] Referring to FIGS. 11A - 12B, additional metasurface design considerations will be discussed in more detail. FIG. 11A illustrates a unit cell 1110 of an exemplary metasurface 1102 with substantially cylindrical protrusions or posts 1120 formed on a substrate 1100, which may be similar to the substrate 2000 (FIGS. 10A - 10B). The metasurface 1102 may include a regular array of unit cells 1110 equally spaced along the x - and y - axes and / or an array of unit cells 1110 having a first spacing along the x - axis and a different spacing along the y - axis. Each post 1120 of the metasurface in this example comprises a single material.

[0110] FIG. 12A similarly illustrates a unit cell 1210 of an exemplary metasurface 1202 including substantially cylindrical structures or posts 1220 formed on a substrate 1200, which may be similar to the substrate 2000 (FIGS. 10A - 10B). However, the posts 1220 of the metasurface 1202 include an outer layer 1222 comprising a first material and an inner layer 1224 comprising a second material having a different refractive index.

[0111] Figures 11B and 12B are phase maps illustrating the optical properties of exemplary configurations of metasurfaces 1102 and 1202, respectively. The phase map in FIG. 11B corresponds to a metasurface having cylindrical pillars 1120 comprising titanium dioxide, with a height of 600 nm and a unit cell pitch U of 200 nm. The phase map in FIG. 12B corresponds to a metasurface having cylindrical pillars 1220 comprising an outer layer 1222 of titanium dioxide and an inner layer 1224 of air, with a height of 600 nm and a unit cell pitch U of 390 nm. As shown in FIG. 11B, an array of pillars 1120 comprising a single material has a relatively low degree of design freedom, since modifications to the metasurface can be limited to changes in the material, diameter, spacing, and height of the pillars 1120, which can each, for example, vary the wavelength-dependent phase shift resulting from the metasurface.

[0112] As shown in FIG. 12B, the phase map corresponding to metasurface 1202 has a profile that is substantially different from the phase map corresponding to metasurface 1102, due at least in part to the inclusion of an outer layer 1222 and an inner layer 1224 of a material different from the material of the outer layer 1222. Thus, the ability to produce a metasurface that includes multiple materials within a nanostructure (e.g., pillars, nanobeams, etc.) introduces even more degrees of freedom into metasurface design. For example, these additional degrees of freedom can include the number of layers, the materials that make up each layer, and the thickness of each individual layer. Further, the layers may be formed by a deposition process, which allows for precise control of their thickness and location. Thus, a metasurface with a multilayer structure as described herein advantageously allows for finer tuning of metasurface performance.

[0113] Figures 13 and 14 illustrate cross-sectional views of exemplary configurations of multilayer metasurfaces 1302, 1402. FIG. 13 illustrates a metasurface 1302 with a protrusion 1320 formed by a plurality of vertically oriented portions 1322, 1324, 1326, 1328. In some implementations, the vertically oriented layers 1322, 1324, 1326, 1328 may have a concentric U-shaped profile as seen in a cross-sectional side view, and the central portion 1328 may include one or more layers 1322, 1324, 1326 that extend along opposing sidewalls and across the bottom surface of the central portion 3028 such that each of the layers 1322, 1324, 1326 forms a U-shaped profile. In some implementations, the protrusion 1320 may have a uniform size, and each unit cell 1310 may include a single protrusion 1320. As discussed in the foregoing and some other implementations, each unit cell 1310 may include a plurality of protrusions 1320 with different protrusions having different physical dimensions (e.g., width) within the unit cell. For example, one protrusion 1320 of unit cell 1310 may be larger than another protrusion of the unit cell (e.g., two protrusions 1320 of the unit cell may correspond to protrusions 2020a, 2020b (FIGS. 10A-10B)). The protrusions described herein may be formed from one, two, three, or more laminated layers.

[0114] FIG. 14 illustrates a metasurface 1402 with unit cells 1410 formed from protrusions 1420, each including a plurality of horizontally oriented layers 1422, 1424, 1426. As discussed herein, each unit cell may include one or more protrusions 1420. In some implementations, each unit cell 1310 includes a plurality of protrusions 1420. As illustrated, unit cell 1410 may include two protrusions 1420 having different widths. Each protrusion 1420 may be formed from a plurality of horizontally oriented layers 1422, 1424, 1426, which may define a stack of such layers.

[0115] Referring to both FIGS. 13 and 14, the protrusions 1320, 1420 may be pillars having, for example, a rectangular, circular, or elliptical profile when viewed from above, such as a nanobeam, or may have other shapes. The spacing between adjacent protrusions 1320 or 1420 is relatively small for visible light (e.g., blue light, green light, red light, etc.), and may be, for example, a sub-wavelength spacing (e.g., a nanometer-scale spacing). In some implementations, the pitch of the unit cell may be in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. Further, in some implementations, the thickness of some layers may be relatively thin, such as about 5 nm or less. It should be understood that either the horizontal or vertical layer may be implemented in a unit cell configuration such as a unit cell comprising a single protrusion or a plurality of protrusions, a unit cell comprising protrusions that are uniformly sized or sized differently, a unit cell comprising protrusions that are uniformly spaced or spaced differently, etc.

[0116] Referring again to FIGS. 13 and 14, the protrusions 1320, 1420 may include one or more than one of a silicon-containing material (e.g., amorphous or polysilicon, and silicon nitride), an oxide, gallium phosphide, or air (e.g., like the inner central portion 1328 of the protrusion 1320) and other different materials. Examples of the oxide include titanium oxide, zirconium dioxide, silicon dioxide, and zinc oxide. In some implementations, all the layers of each protrusion 1320, 1420 may comprise different materials having different refractive indices. In some other implementations, one or more than one material may be repeated or may have the same refractive index. For example, in the metasurfaces 1302 and 1402, the layers 1322 and 1326, 1322 and 1328, 1324 and 1328, or the layers 1422 and 1426 may comprise the same material or may have the same refractive index. However, adjacent layers preferably have different refractive indices.

[0117] An exemplary method of manufacturing meta - surfaces 1302 and 1402 will be described here.

[0118] Figures 15A - 15G illustrate an exemplary process for manufacturing a meta - surface 1502 that includes protrusions 1520 (Figure 15G) having a vertically - oriented layer of material. In some implementations, the meta - surface 1502 may be similar to or the same as the meta - surface 1302 of Figure 13, and the protrusions 1520 may be similar to or the same as the protrusions 1320.

[0119] Referring to Figure 15A, a substrate 1500 may be provided to assist in the formation of the final protrusions. The substrate 1500 may be made of an optically - transmissive material such as glass, polymer (e.g., plastic), or the like, and may be similar to or the same as the substrate 2000 (Figures 10A - 10B), 1300 (Figure 13), or 1400 (Figure 14). In some implementations, the substrate 1500 may be a waveguide.

[0120] Continuing to refer to Figure 15A, a plurality of placeholders 1530 having a separation W and a height H are formed. In some implementations, W corresponds to the width of the final protrusions 1520 (Figure 15G), and H is higher than the desired height of the protrusions 1520. The placeholders 1530 may comprise various materials such as a resist material (e.g., a polymer resist) or any other suitable material that is selectively etchable with respect to the components of the protrusions. The placeholders may be a linear structure (e.g., for forming nanobeams therebetween) or may be a layer having an opening with a square, circular, elliptical, or other profile (e.g., for forming pillars therebetween). In some implementations, the placeholders 1530 may be formed by depositing a layer of resist on the substrate 1500 and subsequently patterning the resist by photolithography, electron - beam lithography, nano - imprint lithography, or the like to form the placeholders 1530.

[0121] Referring now to FIG. 15B, a first blanket layer 1522 is deposited over substrate 1500 and placeholder 1530 by a conformal deposition process. Preferably, the first blanket layer 1522 is deposited with a substantially uniform thickness T 1 therewith. The thickness T 1 may be sub-wavelength thickness, e.g., nanometer-scale thickness. The first blanket layer 1522 may be made of a material that will form the outer layer of the protrusions 1520 of the completed metasurface 1502 (FIG. 15G).

[0122] Referring now to FIG. 15C, a second blanket layer 1524 may be deposited over the first blanket layer 1522 (e.g., on and in contact with the first blanket layer 1522). The second blanket layer 1524 may be a material different from the material constituting the first blanket layer 1522 and may have a different refractive index. The second blanket layer 1524 may also be deposited by a conformal deposition process such that the second blanket layer 1524 has a substantially uniform thickness T 2 thereof. The thickness T 2 may likewise be sub-wavelength thickness, e.g., nanometer-scale thickness.

[0123] Referring now to FIG. 15D, a third blanket layer 1526 may be conformally deposited over the second blanket layer 1524 at a substantially uniform thickness T 3 . The third blanket layer 1526 preferably comprises a different material with a different refractive index than the material constituting the second blanket layer 1524. For example, the third blanket layer may comprise the same material as the first blanket layer 1522, or may have the same refractive index, or may have a refractive index different from both the first blanket layer 1522 and the second blanket layer 1524. The thickness T 3 may likewise be sub-wavelength thickness, e.g., nanometer-scale thickness. It should be understood that the third blanket layer 1526 may define an open volume 1527.

[0124] Referring now to FIG. 15E, the open volume 1527 (FIG. 15D) may be provided with a filling 1528. In some implementations, the filling 1528 may be, in effect, a fourth layer that is deposited across the third blanket layer 1526 until the fourth layer substantially occupies the entirety of the volume 1527. In some implementations, the filling 1528 may be deposited by atomic layer deposition. In some other implementations, the filling 1528 is preferably deposited by relatively high-speed deposition, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). After the filling is deposited, the total thickness T t of all the deposited layers (e.g., 1522, 1524, 1526, 1528) is preferably less than half of the width W between the placeholders 1530 (e.g., T t ≦W / 2). In some embodiments, the filling 1528 is air and no material is substantially deposited into the opening 1527.

[0125] Referring now to FIG. 15F, the horizontally oriented portions of the layers 1522, 1524, 1526, 1528 disposed above the placeholder 1530 may be removed by a process such as chemical mechanical polishing (CMP), etching (e.g., liquid and / or plasma etching), milling, or any other suitable subtractive manufacturing process. In some implementations, a portion of the placeholder 1530 may likewise be removed by a subtractive manufacturing process. Preferably, sufficient material is removed so that the entire width of each placeholder is exposed and not vertically covered by any of the layers 1522, 1524, 1526, 1528. In some implementations, the remaining structure may be annealed and / or modified, for example, to increase its mechanical integrity.

[0126] After subtractive manufacturing exposes placeholder 1530, placeholder 1530 may be removed to provide metasurface 1502 depicted in FIG. 15G. As discussed herein, placeholder 1530 preferably comprises a material that is selectively etchable with respect to the materials of layers 1522, 1524, 1526, 1528. Placeholder 1530 may comprise a material removable by wet etching, plasma etching, or similar methods. For example, placeholder 1530 may comprise a resist material that is soluble in a solvent and does not dissolve the materials of layers 1522, 1524, 1526, and 1528. Thus, the solvent may be used to remove the exposed placeholder of FIG. 15F and form metasurface 1502 of FIG. 15G. In some implementations, one or more layers (e.g., first layer 1522 or innermost layer 1528) may be modified (e.g., convertible to a different material) by a process such as sulfidation or other ion exchange methods. In some implementations, it should be understood that protrusions 1520 may be a substitute for protrusions 2020a, 2020b of metasurface 2002 (FIGS. 10A-10B).

[0127] Again, referring to FIGS. 15B and 15E, it should be understood that in some implementations, the manufacturing method may proceed to directly fill volume 1527 (FIG. 15E) after forming the structure of FIG. 15B without forming additional intervening layers, such as the additional layers of FIGS. 15C-15D. In some other implementations, one or more of additional blanket layers 1524, 1526 (FIGS. 15C and 15D, respectively) may be formed before proceeding to fill volume 1527. In yet other implementations, additional blanket layers may be deposited after forming additional blanket layers 1524, 1526 and before proceeding to FIG. 15E.

[0128] Referring again to FIGS. 15B - 15E, an example of a conformal deposition process for forming the various layers (e.g., layers 1522, 1524, 1526) of the protrusion 1520 is atomic layer deposition (ALD). Preferably, the layers are deposited with a substantially uniform thickness, which is substantially uniform along the sidewalls and upper surface of the placeholder 1530, and along the substrate surface between the placeholders 1530. The thickness may be sub - wavelength thickness, e.g., nanometer - scale thickness. In some implementations, the thickness may be less than 200 nm, including within the range of 5 nm to 200 nm, less than 100 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 10 nm, 10 nm to 20 nm, 20 nm to 50 nm, 50 nm to 100 nm, or less than 5 nm. In some embodiments, the respective thicknesses of the constituent layers 1520 are substantially equal. In some other embodiments, at least some of the thicknesses of the layers may be different.

[0129] FIGS. 16A - 16F illustrate an exemplary process for manufacturing a metasurface 1602 or 1602' that includes a horizontally stratified protrusion 1620 (FIG. 16F). In some implementations, the metasurface 1602 may be similar to or the same as the metasurface 1402 of FIG. 14.

[0130] Referring to FIG. 15A, a substrate 1500 may be provided to assist in the formation of the final protrusion 1620 (FIG. 16F). The substrate 1600 may include an optically transparent material such as glass, polymer (e.g., plastic), or the like, and may be similar to or the same as the substrate 2000 (FIGS. 10A - 10B), 1300 (FIG. 13), or 1400 (FIG. 14). In some implementations, the substrate 1500 may be a waveguide.

[0131] Referring now to FIG. 16B, a plurality of blanket layers 1622, 1624, 1626 are sequentially deposited across substrate 1600. Since the layers can be formed on a flat substrate surface, the requirements regarding conformality can be relaxed relative to the process of FIGS. 15A - 15G, and layers 1622, 1624, 1626 may be deposited by conformal or non - conformal deposition methods. For example, layers 1622, 1624, 1626 may be deposited by methods such as physical vapor deposition, chemical vapor deposition, atomic layer deposition, or the like. In some implementations, for depositing thin layers (e.g., layers with a thickness of 5 nm or less) and / or when precise control of the thickness is desired, layers 1622, 1624, 1626 may be deposited by ALD. Preferably, layers 1622, 1624, 1626 blanket - coat an area in which a plurality of protrusions 1620 (FIG. 16F) will be formed therein.

[0132] Three layers 1622, 1624, 1626 are depicted, but it should be understood that the process of FIGS. 16A - 16F may include more or fewer depositions than three layers. Layers 1622, 1624, 1626 may each have the same thickness or may have different thicknesses. Preferably, each individual blanket layer 1622, 1624, 1626 has a substantially uniform thickness across its entire extent. The thickness of each layer may be sub - wavelength thick, e.g., on the nanometer scale. In some implementations, one or more of the blanket layers 1622, 1624, 1626 may each have a thickness less than 100 nm, including within the range of 5 nm to 200 nm, 5 nm to 100 nm, 5 nm to 50 nm, 5 nm to 10 nm, 10 nm to 20 nm, 20 nm to 50 nm, or 50 nm to 100 nm. In some implementations, one or more of the blanket layers 1622, 1624, 1626 may each have a thickness of about 5 nm or less. The thickness of each of the blanket layers 1622, 1624, 1626 is selected such that the total thickness of all the combined blanket layers equals the desired height of the protrusions 1620 of the finished metasurface 1602 or 1602' (FIGS. 16E and 16F, respectively). Each blanket layer 1622, 1624, 1626 preferably comprises a material having a different refractive index than the directly adjacent layer of layers 1622, 1624, 1626. Additionally, layer 1622 preferably has a refractive index different from that of the substrate 1600. In some implementations, layers 1622 and 1626 (or other non - consecutive layers if more than three layers are included) may comprise the same material or may have the same refractive index.

[0133] After all desired layers 1622, 1624, 1626 have been deposited across substrate 1600, the deposited layers may be patterned. Referring now to FIG. 16C, an etching mask may be formed across upper layer 1626, defining protrusions 1620 (FIG. 16E). The etching mask may include a plurality of mask features 1630, which may be formed by selectively depositing one or more layers of a definable material and then patterning that material to define the mask features 1630. It should be understood that the mask features 1630 may comprise any suitable material that is resistant to a subtractive manufacturing process for etching the blanket layers 1622, 1624, 1626. For example, the mask features 1630 may include a resist, a hard mask, or other suitable etching mask material. In some implementations, a layer of resist material may be deposited over layer 1626 and then patterned, for example, by photolithography, imprinting, etc. As a result, in some implementations, the mask features 1630 are resist features.

[0134] In some other implementations, a layer of etching mask material is deposited over layer 1626 and a resist layer is subsequently deposited over the etching mask material. The resist layer is patterned in a pattern that is subsequently transferred downwardly with respect to the layer of etching mask material, defining the mask features 1630 within the layer of etching mask material.

[0135] As can be seen in the figures above and below, it should be understood that the mask features 1630 have a shape corresponding to the desired shape of the protrusions 1620. For example, if the protrusions 1620 of the metasurface 1602 or 1602' are to be nanobeams, the mask 1630 may include linear sections having the same width and length as the desired nanobeams in a plane parallel to the substrate 1600. If the protrusions 1620 are pillars, the mask 1630 has the same two-dimensional shape as the desired nanobeams.

[0136] After forming the mask feature 1630, a subtractive manufacturing method may be applied to remove portions of the blanket layers 1622, 1624, 1626 not covered by the mask 1630, as shown in FIG. 16D. The subtractive manufacturing method used to produce the configuration of FIG. 16D may include a directed or non-directed etching process, such as wet etching, plasma etching, or the like. After etching the blanket layers 1622, 1624, 1626, the mask features 1630 are removed (e.g., by applying a solvent to dissolve those features or by ashing), and a metasurface 1602 including protrusions 1620 with horizontally oriented layers 1622, 1624, 1626 may be formed, as shown in FIG. 16E.

[0137] In some implementations, the metasurface 1602 of FIG. 16E may be in a desired configuration. In some other implementations, one or more than one of the layers 1622, 1624, 1626 may be modified (e.g., can be converted to a different material). The modification may include processes such as sulfidation or selenization or other ion exchange processes. For example, the protrusions 1620 may be exposed to an atmosphere with a concentration of a chemical substance that will be incorporated into an appropriate layer. In some implementations, an ion exchange process may be desirable where the protrusions 1620 are difficult to deposit by typical deposition methods (and thus not desirable to form as one of the layers 1622, 1624, and 1626), and may be formed by ion exchange from a material that is more easily deposited. In the exemplary metasurface 1602' of FIG. 16F, the central layer 1624 may be converted to a modified central layer 1624' by ion exchange. However, other layers (e.g., layers 1622 and / or 1626) may similarly be modified as desired. For example, one of the layers 1622, 1624, 1626 may be deposited as a molybdenum compound (e.g., molybdenum oxide or the like) and exposed to a sulfur atmosphere to convert the molybdenum compound to molybdenum sulfide. It should be understood that in some implementations, the protrusions 1520 may be a substitute for the protrusions 2020a, 2020b of the metasurface 2002 (FIGS. 10A - 10B).

[0138] Various exemplary embodiments of the present invention are described herein. By way of non - limiting example, these examples are referred to. They are provided to illustrate broader and applicable aspects of the present invention. Various changes may be made to the invention as described, and equivalents may be substituted without departing from the spirit and scope of the invention.

[0139] For example, advantageously, it is utilized with an AR display that provides an image across multiple depth planes, although the augmented reality content disclosed herein may also be displayed by a system that provides an image on a single depth plane. Additionally, advantageously, while applied to a metasurface, the multilayer structures and related manufacturing methods disclosed herein may be applied to form other optical structures, including diffraction gratings formed from protrusions, that are larger than the wavelength of visible light.

[0140] In addition, many modifications may be made to adapt a particular situation, material, substance composition, process, process act, or step to the purposes, spirit, or scope of the present invention. Further, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein has discrete components and features that can be readily separated from, or combined with, the features of any of several other embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

[0141] The present invention includes methods that may be implemented using such a device. The method may include the act of providing such a suitable device. Such providing may be done by a user. In other words, the act of "providing" merely requires the user to obtain, access, approach, position, set up, activate, power on, or otherwise act so as to provide the required device in the method. The methods described herein may be performed in any order of the described events that is logically possible, and in the order of the described events.

[0142] Exemplary aspects of the present invention are described above, along with details regarding material selection and manufacture. Regarding other details of the present invention, these are to be understood in conjunction with the aforementioned reference patents and publications and are generally known or understood in the art. The same may also apply to the method-based aspects of the present invention from the perspective of additional acts as commonly or logically employed.

[0143] In addition, the present invention has been described with reference to several embodiments that optionally incorporate various features, but the present invention is not limited to what is described or illustrated as would be considered for each variation of the invention. Various modifications may be made to the present invention as described, and equivalents may be substituted (whether described herein or not, or whether included for the sake of brevity), without departing from the spirit and scope of the present invention. In addition, when a range of values is provided, it is to be understood that all intervening values between the upper and lower limits of that range, as well as any other stated value or intervening values within the stated range, are included within the present invention.

[0144] Also contemplated is that any optional feature of a variation of the invention described herein may be described and claimed independently or in combination with any one or more of the features described herein. Reference to items in the singular includes the possibility that there are multiple identical items. More specifically, as used herein and in the claims associated therewith, the singular forms "a", "an", "said", and "the" include plural referents unless otherwise specified. In other words, the use of the articles enables "at least one" of the items of the subject matter in the above description and in the claims associated with the present invention. Further, it should be noted that such claims may be drafted to exclude any optional element. Thus, the text is intended to serve as a preamble for the use of exclusive terms such as "merely", "only", and equivalents, or the use of "negative" limitations, in connection with the recitation of elements of the claims.

[0145] Unless such exclusive terms are used, the term "comprising" in the claims associated with the present invention shall be construed to allow the inclusion of any additional elements, whether or not a given number of elements are recited in such claims, or the addition of features may be regarded as transforming the nature of the elements recited in such claims. Unless specifically defined herein, all technical and scientific terms used herein shall be given the broadest possible generally understood meaning while maintaining the validity of the claims.

Claims

[Claim 1] The invention described in this specification.

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