NZ787902A - Metasurfaces with asymmetric gratings for redirecting light and methods for fabricating - Google Patents

Abstract

Complex human visual perception leads to problems in creating natural-feeling AR and VR representations. Described herein is an optical system comprising an optically transmissive substrate comprising a metasurface, the metasurface comprising a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view a laterally-elongated first nanobeam having a first width and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width and a reflector, wherein the grating is between the reflector and the substrate.

Description

METASURFACES WITH ASYMMETRIC GRATINGS FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING Priority Claim This application claims the benefit of priority under 35 U.S.C. § 119(e) of: U.S.

Provisional Application No. 62/333,067, filed on May 6, 2016; and U.S. Patent Application No. 62/474,432, filed on March 21, 2017. The entire disclosure of each of these priority documents is incorporated herein by reference.

] This application is a divisional of New Zealand Patent Application No. 747834, the entire contents of which are orated herein by reference. oration by Reference This application incorporates by reference the entirety of each of the following patent publications: U.S. Publication No. 2015/0016777; U.S. Publication No. 2015/0178939; and U.S.

Publication No. 2015/0346490.

BACKGROUND Field The present disclosure relates to optical devices, including augmented reality imaging and visualization systems.

Description of the Related Art Modern computing and display technologies have facilitated the development of s 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 wherein they seem to be, or may be perceived as, real. A virtual reality, or "VR", scenario typically involves the presentation of l or l image information without transparency to other actual real-world visual input; an ted reality, or "AR", scenario typically involves presentation of digital or l image information as an augmentation to visualization of the actual world around the user. A mixed reality, or "MR", scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and sive to, the natural world.

For e, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.

Referring to Figure 1, an ted reality scene 10 is depicted. The user of an AR technology sees a orld park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user also perceives that he/she "sees" "virtual content" such as a robot statue 40 ng upon the real-world platform 30, and a flying cartoon-like avatar character 50 which seems to be a personification of a bumble bee. These elements 50, 40 are "virtual" in that they do not exist in the real world. Because the human visual perception system is complex, it is nging to produce AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges related to AR and VR technology.

SUMMARY In some embodiments, an optical system comprises an optically transmissive substrate comprising a metasurface which comprises a grating sing a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second am having a second width larger than the first width. The heights of the first and the second nanobeams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 µm where the refractive index is 3.3 or less.

In some other embodiments, an optical system comprises an optically transmissive substrate comprising a metasurface which ses a grating comprising a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap. The second nanobeam has a second width larger than the first width. The optical system also ses a reflector. The reflector and the substrate are on opposite sides of the grating.

In yet other embodiments, a method for forming a metasurface comprises providing an optically transmissive substrate; providing an optically transmissive layer over the substrate; and ning the optically transmissive layer to define a grating comprising a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second am spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width. The s of the first and the second ams are: 10 nm to 450 nm where a refractive index of the substrate is more than 3.3; and 10 nm to 1 µm where the refractive index is 3.3 or less.

In some other embodiments, a method for forming a metasurface comprises providing an optically transmissive substrate and forming a grating comprising a plurality of unit cells.

Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width. The method also comprises providing a layer of tive al in the gap and between the unit cells.

In some other embodiments, a method for forming a metasurface ses providing an optically transmissive substrate; and forming a grating comprising a plurality of unit cells.

Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width. The method further ses ting a layer of optically transmissive spacer material in the gap and between the unit cells; and depositing a reflective layer on the layer of spacer material, wherein the spacer material separates the grating from the reflective layer.

In yet other embodiments, an l system comprises an optically transmissive substrate comprising a metasurface which comprises a grating comprising a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width. A pitch of the unit cells is 10 nm to 1 µm.

In some other embodiments, a method for forming a metasurface comprises ing an optically transmissive substrate; providing an optically transmissive layer over the ate; and patterning the optically transmissive layer to define a grating comprising a plurality of unit cells. Each unit cell comprises a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width. A pitch of the unit cells is 10 nm to 1 µm.

In yet other embodiments, an optical system comprises an optically transmissive substrate sing a evel metasurface. The multilevel metasurface ses a g comprising a plurality of multilevel unit cells. Each unit cell comprises, on a lowermost level of the unit cell, a laterally-elongated, first lowermost level nanobeam having a first width; and a laterally-elongated, second lowermost level nanobeam having a second width, where the second width is larger than the first width. On an uppermost level of the unit cell is a laterally-elongated, first uppermost level nanobeam above the first lowermost level nanobeam; and a laterally-elongated, second uppermost level nanobeam above the second lowermost level am.

In some other embodiments, a method for forming a metasurface comprises providing an optically transmissive substrate; providing an optically issive layer over the substrate; and patterning the optically transmissive layer to define a plurality of repeating units. Each repeating unit ses a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced-apart from the first nanobeam by a gap, the second am having a second width larger than the first width. The method also ses depositing an optically transmissive material on the first and second nanobeams and into the gaps between the nanobeams to form spaced apart plateaus of the optically transmissive material above the nanobeams. [0016A] In one broad form, an aspect of the present invention seeks to provide an optical system comprising: an optically transmissive ate comprising a metasurface, the metasurface comprising: a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first am by a gap, the second nanobeam having a second width larger than the first width; and a reflector, wherein the grating is between the reflector and the substrate. [0016B] In one embodiment the reflector is spaced apart from the grating. [0016C] In one ment the grating is embedded in an optically transmissive material. [0016D] In one embodiment the optically transmissive material spaces the reflector apart from the g. [0016E] In one embodiment the substrate comprises: a second metasurface on a side of the substrate opposite the metasurface, the second metasurface comprising: a second grating comprising a plurality of second unit cells, each second unit cell comprising, as seen in a top-down view: a laterally-elongated third nanobeam; and a lly-elongated fourth nanobeam spaced apart from the third nanobeam by a gap, wherein the fourth nanobeam is wider than the third nanobeam. [0016F] In one ment the unit cells are laterally-elongated and are parallel to each other. [0016G] In one embodiment the metasurface is configured to diffract incident light of a visible wavelength into a first diffraction order.

] In one embodiment the second width is 10 nm to 1 µm. [0016I] In one embodiment the second width is 10 nm to 300 nm. [0016J] In one embodiment a pitch of the unit cells is 10 nm to 1 µm.

] In one embodiment the pitch of the unit cells is 10 nm to 500 nm. [0016L] In one embodiment the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 µm. [0016M] In one embodiment the gap is 10 nm to 300 nm wide.

] In one embodiment the optically transmissive substrate ses a glass. [0016O] In one embodiment the first and second am comprises n. [0016P] In one embodiment the first and second nanobeam comprises silicon e. [0016Q] In one embodiment the optically transmissive substrate and the metasurface form a polarizing beam splitter. [0016R] In one embodiment the optically transmissive substrate is a waveguide plate. [0016S] In one embodiment the l system further comprises a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the substrates. [0016T] In one embodiment the rface is an incoupling optical element, further comprising an image injection device configured to project light to the incoupling optical element, n the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection. [0016U] In one embodiment the metasurface is an outcoupling optical element, wherein the rface is configured to extract light out of the ate. [0016V] In one broad form, an aspect of the present invention seeks to provide a method for forming a metasurface, the method comprising: providing an optically transmissive substrate; forming a g on the substrate, the grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width; and providing a layer of tive material on the grating, the layer of reflective material extending into the gap and between the unit cells, wherein the grating is between the reflector and the substrate. [0016W] In one embodiment providing the layer of reflective material comprises depositing reflective material between and over the first and second nanobeams. [0016X] In one embodiment the reflective material comprises aluminum. [0016Y] In one embodiment forming the grating comprises: depositing an optically transmissive layer over the substrate; and patterning the optically issive layer to define the g. [0016Z] In one embodiment patterning the optically transmissive layer comprises: providing a resist layer over the optically issive layer; defining a pattern in the resist layer; and transferring the pattern from the resist layer to the optically transmissive layer.

Additional and other objects, es, and ages of the invention are described in the detail ption, figures and claims.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a user’s view of augmented reality (AR) through an AR .

Figure 2 illustrates a conventional display system for simulating three-dimensional imagery for a user.

Figures 3A-3C illustrate relationships between radius of ure and focal radius.

Figure 4A illustrates a representation of the accommodation-vergence response of the human visual system.

Figure 4B illustrates examples of different accommodative states and vergence states of a pair of eyes of the user.

Figure 4C illustrates an example of a representation of a wn view of a user viewing content via a display system.

Figure 4D illustrates another example of a representation of a top-down view of a user viewing content via a y system.

Figure 5 illustrates aspects of an approach for simulating three-dimensional imagery by modifying wavefront divergence.

Figure 6 illustrates an example of a waveguide stack for outputting image ation to a user.

Figure 7 illustrates an example of exit beams outputted by a waveguide.

Figure 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors.

Figure 9A illustrates a cross-sectional side view of an example of a set of d waveguides that each includes an incoupling optical element.

Figure 9B illustrates a perspective view of an example of the plurality of stacked waveguides of Figure 9A.

Figure 9C rates a top-down plan view of an example of the plurality of stacked waveguides of Figures 9A and 9B.

Figure 9D illustrates an e of wearable display .

Figures 10A and 10B illustrate es of cross-sectional side and top-down views, tively, of a metasurface.

Figure 11A illustrates an example of a cross-sectional side view of a rface configured to function in a reflective mode.

Figure 11B illustrates an example of a cross-sectional, top-down view of the metasurface of Figure 11A as viewed on the plane 11B of Figure 11A.

Figure 12 rates an example of a cross-sectional side view of another metasurface configured to function in a reflective mode.

Figure 13 illustrates an example of a cross-sectional, top-down view of the metasurface of Figure 12 as viewed on the plane 13 of Figure 12.

Figure 14A illustrates an example of a sectional side view of a substrate having both transmissive and reflective metasurface.

Figure 14B illustrates an example of a top-down view of the metasurface of Figure Figure 14C illustrates an example of a top-down view of the metasurface of Figure 14A viewed on the plane 14C of Figure 14A.

Figures 15A-15E illustrate an example of a process flow for forming a metasurface.

Figures 16A and 16B illustrate scanning on micrographs of a metasurface.

Figure 17 illustrates an example of a plot showing the diffraction efficiency versus angle of incidence of light for a transmissive metasurface.

Figures 18A – 18C illustrate examples of plots showing the ction efficiency versus angle of incidence of light for a reflective metasurface. The wavelengths of incident light are different for each of Figures 18A – 18C.

Figures 19A and 19B illustrate examples of plots showing the polarization ivity of the metasurface of Figures 10A and 10B.

Figure 20 illustrates plots of amplitude and phase shift versus am width for the metasurface of Figures 10A and 10B.

Figure 21A illustrates an example of a cross-sectional side view of a multilevel metasurface.

Figure 21B illustrates an e of a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in Figure 21A.

Figure 22A illustrates an example of a cross-sectional side view of a multilevel metasurface.

Figure 22B illustrates an example of a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in Figure 22A.

Figures 23A-23D illustrate an example of a process flow for forming multilevel metasurfaces.

The gs are provided to rate example ments described herein and are not intended to limit the scope of the disclosure. It will be appreciated that the drawings are schematic and not necessarily drawn to scale.

DETAILED DESCRIPTION Metasurfaces, metamaterial surfaces, provide opportunities to realize virtually flat, aberration-free optics on much r scales, in comparison with geometrical optics. Without being limited by , in some embodiments, metasurfaces include dense arrangements of surface structures that function as resonant optical antennas. The resonant nature of the light-surface structure interaction es the ability to manipulate optical wave-fronts. In some cases, the metasurfaces may allow the ement of bulky or difficult to manufacture optical components with thin, planar elements formed by simple patterning processes.

One type of a conventional optical element is a blaze grating, which may be desirable in some applications for having high selectivity in cting light. These gratings, however, typically have sloped surfaces and may be nging to manufacture. Advantageously, in some embodiments, metasurfaces are disclosed that are able to ct light, similar to a blazed grating, in the visible range while having a relatively flat response over a wide range of incoming angles, and while providing a more easily manufactured structure.

The metasurfaces may take the form of an asymmetric grating formed by a plurality of repeating unit cells. Each unit cell comprises two laterally-elongated protrusions, which may be also ed to as nanobeams or nanowires, with one protrusion being wider than the other. As used herein, a protrusion, nanobeam or nanowire, is an elongated volume of material, e.g., a single substantially neous material. It will be appreciated that these elongated structures are not limited to any particular cross-sectional shape. In some embodiments, the cross-sectional shape is rectangular.

Preferably, the nanobeams have a sub-wavelength width and spacing from one another. For e, the widths of the nanobeams may be less than the wavelengths of light that the metasurface is configured to redirect. In some embodiments, the units cells formed by the nanobeams may be on or proximate the e of an optically transmissive substrate, e.g., a waveguide.

In some embodiments, the metasurfaces may work in a transmission mode in which light is incident on the metasurface from a first side of the metasurface, propagates through the metasurface, and subsequently propagates away from the metasurface on an opposite side of the metasurface. The light ates away from the rface in a direction different from the incident direction of the light on the first side.

In some other embodiments, the metasurface may work in a reflective mode in which the light is incident from the first side of the metasurface, and is reflected back on the first side to propagate away from the metasurface. In the reflective mode, the metasurface may include nanobeams embedded within a tive layer. In some other embodiments, the nanobeams may be embedded within a spacer layer, and a reflective layer may be provided directly on the spacer layer, on a side of the metasurface te the first side.

Preferably, the features forming the metasurface are ured to redirect light, e.g. by diffraction. In some embodiments, the light is visible light having a wavelength in the range of 350 nm to 800 nm. In some embodiments, the metasurface is configured to diffract nt light of a visible ngth into a first diffraction order In some embodiments, the widths of the nanobeams forming the unit cells are in the range of 10 nm to 1 µm, including 10 nm to 300 nm or 10 nm to 250 nm. The nanobeams may be separated by a gap in the range of 5 nm to 1 µm wide, including 10 nm to 1 µm wide or 10 nm to 300 nm wide. The pitch of the unit cells (that is, the distance between identical points in ly neighboring unit cells) may be in the range of 10 nm to 1 µm, including 10 nm to 500 nm, or 300 nm to 500 nm. In some embodiments, the heights of the nanobeams may be in the range of 10 nm to 1 µm, including 10 nm to 500 nm or 10 nm to 450 nm.

It has been found that the ions of features of the unit cells may vary depending upon the properties of the materials used to form the metasurface. For example, the height of the nanobeams may vary depending upon the refractive index of the material used for those nanobeams.

In some embodiments, the heights of the nanobeams may be 10 nm to 450 nm where a refractive index of the al is more than 3.3; and 10 nm to 1 µm where the refractive index is 3.3 or less. As another example, the height of the nanobeams may be 10 nm to 450 nm where the nanobeams are formed of silicon (e.g., amorphous or polysilicon).

In some embodiments, the metasurface is a multilevel (e.g., bi-level) structure having unit cells with relatively narrow and relatively wide nanobeams as noted above on a lowermost level, and a second optically transmissive al between the nanobeams on the lowermost level. The metasurface may also include a second level formed by a second optically transmissive al disposed on top surfaces of the nanobeams. The material on the second level may be localized on the top surfaces of the nanobeams and may form spaced apart plateaus of the al, as seen in a cross-sectional view taken along a plane orthogonal to the length axis of the nanobeams. In some embodiments, the heights of the material on the second level may be in the range of 10 nm to 1 µm, ing 10 nm to 600 nm.

It will be appreciated that, in some embodiments, the metasurface selectively redirects some wavelengths of light, while being transmissive to other wavelengths of light. Such properties are typically engineered with structures on micron scales (e.g., in photonics crystal fibers or distributed bragg reflectors), while various embodiments herein include ries on nano-scales (e.g. -100x r scales), and provide selective redirection of light in the visible part of the electromagnetic spectrum. In some embodiments, the nanobeams may be formed on the surface of the ate a single level, thereby providing a simple to cture structure. ageously, the metasurfaces may be formed using patterning and deposition processes, e.g., lithography and chemical etching. In some ments, the metasurfaces may be patterned using nanoimprinting, thereby avoiding costly lithography and etch processes.

Metasurfaces formed according to various embodiments provide one or more of the following advantages. For example, the metasurfaces may have a relatively large angular bandwidth over which it may redirect or diffract light. In addition, the metasurfaces may have a good diffraction efficiency over this bandwidth. For example, the ction efficiency may be 25% or more, 30% or more, or 40% or more, over an angular bandwidth (FWHM) of 40°, or 50° (as measured from the normal to a e).

Moreover, the diffraction efficiency over the angular bandwidth may be advantageously flat, e.g., varying by less than 25%, 20%, 15%, or 10% over the angular bandwidth. The metasurfaces may also have a large tion angle, which may advantageously be d to incouple light within the angular bandwidth by redirecting the light such that it propagates at angles suitable for total internal reflection (TIR). In addition, the advantages noted above may be realized in a number of wavelengths of light corresponding to different component colors for g images. For example, the wavelengths may correspond to the colors red, green, and blue (e.g. wavelengths of 455 nm, 520 nm, and 638 nm). In a reflective mode, the metasurface may provide color selective beam shaping with a high extinction ratio (e.g., 5 or more, 10 or more, 20 or more). In some embodiments, the metasurfaces exhibit strong polarization dependence and may function as a polarization beam splitter. For example, for light of different polarizations, the metasurface may exhibit extinction ratios of 5 or more, 7 or more, or 9 or more.

In some embodiments, the waveguides supporting the metasurfaces may form direct view display devices or ye display devices, with the waveguides configured to receive input image information and generate an output image based on the input image information. These devices may be wearable and tute eyewear in some embodiments. The input image information received by the waveguides can be encoded in multiplexed light streams of different wavelengths (e.g., red, green and blue light) that are incoupled into one or more waveguides. Incoupled light may propagate through the waveguide due to total internal reflection. The incoupled light may be outcoupled (or outputted) from the waveguide by one or more outcoupling optical ts.

In some embodiments, the metasurfaces be the incoupling and/or outcoupling optical ts. The compactness and planarity of the metasurface allows for a compact waveguide, and for a t stack of ides where multiple waveguides form a stack. In addition, the high wavelength ivity of the rface allows for a high degree of precision in incoupling and/or outcoupling light, which can provide high image quality in applications where the light ns image information. For example, the high selectivity may reduce channel crosstalk in configurations in which full color images are formed by outputting light of different colors or wavelengths at the same time.

Reference will now be made to the Figures, in which like reference numbers refer to like features throughout.

Example Display Systems Various embodiments disclosed herein may be implemented in optical devices to steer or redirect light, and may be particularly advantageously employed as parts of display systems. In some embodiments, the display systems take the form of eyewear (e.g., they are le), which may advantageously provide a highly immersive VR or AR experience. For example, displays containing waveguides for displaying multiple depth planes, e.g. a stack of waveguides (one waveguide or set of waveguides for each depth plane), may be configured to be worn positioned in front of the eyes of a user, or . In some ments, multiple waveguides, e.g. two stacks of ides, one for each eye of a viewer, may be utilized to e different images to each eye.

Figure 2 illustrates a conventional display system for simulating three-dimensional imagery for a user. It will be appreciated that a user’s eyes are spaced apart and that, when looking at a real object in space, each eye will have a slightly different view of the object and may form an image of the object at different locations on the retina of each eye. This may be referred to as binocular disparity and may be utilized by the human visual system to provide a perception of depth. Conventional y systems simulate binocular disparity by presenting two distinct images 190, 200 with slightly ent views of the same virtual object—one for each eye 210, 220—corresponding to the views of the virtual object that would be seen by each eye were the virtual object a real object at a desired depth. These images provide lar cues that the user’s visual system may interpret to derive a perception of depth.

With continued reference to Figure 2, the images 190, 200 are spaced from the eyes 210, 220 by a distance 230 on a z-axis. The z-axis is parallel to the optical axis of the viewer with their eyes fixated on an object at optical infinity directly ahead of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on the ly different views of a virtual object in the images presented to the eyes 210, 220, respectively, the eyes may naturally rotate such that an image of the object falls on corresponding points on the retinas of each of the eyes, to maintain single binocular vision. This on may cause the lines of sight of each of the eyes 210, 220 to converge onto a point in space at which the virtual object is perceived to be t. As a result, providing three-dimensional imagery conventionally involves providing binocular cues that may manipulate the vergence of the user’s eyes 210, 220, and that the human visual system interprets to provide a perception of depth.

Generating a realistic and comfortable perception of depth is challenging, however. It will be appreciated that light from objects at different distances from the eyes have wavefronts with different s of divergence. Figures 3A-3C illustrate relationships between distance and the divergence of light rays. The distance between the object and the eye 210 is represented by, in order of decreasing distance, R1, R2, and R3. As shown in Figures 3A-3C, the light rays become more ent as distance to the object decreases. Conversely, as distance increases, the light rays become more collimated. Stated another way, it may be said that the light field produced by a point (the object or a part of the object) has a spherical wavefront curvature, which is a function of how far away the point is from the eye of the user. The curvature ses with decreasing distance between the object and the eye 210.

While only a single eye 210 is illustrated for clarity of illustration in Figures 3A-3C and other figures herein, the discussions regarding eye 210 may be applied to both eyes 210 and 220 of a viewer.

With continued reference to Figures 3A-3C, light from an object that the viewer’s eyes are fixated on may have different s of wavefront divergence. Due to the different amounts of wavefront divergence, the light may be focused differently by the lens of the eye, which in turn may require the lens to assume different shapes to form a d image on the retina of the eye. Where a focused image is not formed on the retina, the resulting retinal blur acts as a cue to odation that causes a change in the shape of the lens of the eye until a focused image is formed on the retina. For example, the cue to accommodation may trigger the ciliary muscles surrounding the lens of the eye to relax or contract, thereby modulating the force applied to the suspensory ligaments holding the lens, thus g the shape of the lens of the eye to change until retinal blur is ated or minimized, thereby forming a focused image of the object of fixation on the retina/fovea of the eye. The process by which the lens of the eye s shape may be referred to as accommodation, and the shape of the lens of the eye required to form a focused image of the object of fixation on the retina/fovea of the eye may be referred to as an accommodative state.

With reference now to Figure 4A, a entation of the accommodation-vergence 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, with the light forming an image on each of the retinas of the eyes. The presence of l blur in the image formed on the retina may provide a cue to accommodation, and the relative locations of the image on the retinas may provide a cue to ce.

The cue to accommodation causes odation to occur, resulting in the lenses of the eyes each assuming a particular accommodative state that forms a focused image of the object on the retina/fovea of the eye. On the other hand, the cue to vergence causes vergence movements ion of the eyes) to occur such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. In these positions, the eyes may be said to have assumed a particular vergence state. With continued reference to Figure 4A, accommodation may be understood to be the process by which the eye achieves a particular accommodative state, and vergence may be understood to be the process by which the eye achieves a particular vergence state. As indicated in Figure 4A, the accommodative and vergence states of the eyes may change if the user fixates on another object. For example, the accommodated state may change if the user fixates on a new object at a different depth on the z-axis.

Without being limited by theory, it is believed that s of an object may perceive the object as being "three-dimensional" due to a combination of vergence and accommodation. As noted above, vergence movements (e.g., rotation of the eyes so that the pupils move toward or away from each other to converge the lines of sight of the eyes to fixate upon an object) of the two eyes relative to each other are closely associated with accommodation of the lenses of the eyes. Under normal conditions, changing the shapes of the lenses of the eyes to change focus from one object to another object at a ent distance will automatically cause a matching change in vergence to the same ce, under a relationship known as the "accommodation-vergence ." Likewise, a change in vergence will trigger a ng change in lens shape under normal conditions.

With reference now to Figure 4B, examples of different accommodative and vergence states of the eyes are rated. The pair of eyes 222a are fixated on an object at optical infinity, while the pair eyes 222b are d on an object 221 at less than optical infinity. Notably, the vergence states of each pair of eyes is different, with the pair of eyes 222a directed straight ahead, while the pair of eyes 222 converge on the object 221. The accommodative states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of the lenses 210a, 220a.

Undesirably, many users of conventional "3-D" display systems find such conventional systems to be uncomfortable or may not ve a sense of depth at all due to a mismatch between accommodative and vergence states in these displays. As noted above, many stereoscopic or "3-D" display systems display a scene by providing slightly ent images to each eye. Such systems are ortable for many viewers, since they, among other things, simply provide different presentations of a scene and cause changes in the vergence states of the eyes, but without a corresponding change in the accommodative states of those eyes. Rather, the images are shown by a display at a fixed distance from the eyes, such that the eyes view all the image information at a single accommodative state. Such an arrangement works against the "accommodation-vergence reflex" by causing changes in the vergence state without a matching change in the accommodative state. This mismatch is believed to cause viewer discomfort. Display systems that provide a better match between accommodation and vergence may form more realistic and comfortable simulations of dimensional imagery.

Without being d by theory, it is ed that the human eye typically may interpret a finite number of depth planes to provide depth perception. Consequently, a highly believable simulation of perceived depth may be achieved by providing, to the eye, different presentations of an image ponding to each of these limited numbers of depth planes. In some embodiments, the different presentations may provide both cues to ce and matching cues to accommodation, thereby providing physiologically correct accommodation-vergence matching.

With continued reference to Figure 4B, two depth planes 240, corresponding to different distances in space from the eyes 210, 220, are illustrated. For a given depth plane 240, vergence cues may be provided by the displaying of images of appropriately different perspectives for each eye 210, 220. In addition, for a given depth plane 240, light forming the images provided to each eye 210, 220 may have a wavefront ence corresponding to a light field produced by a point at the distance of that depth plane 240.

In the rated embodiment, the distance, along the z-axis, of the depth plane 240 ning the point 221 is 1 m. As used herein, distances or depths along the z-axis may be measured with a zero point located at the exit pupils of the user’s eyes. Thus, a depth plane 240 located at a depth of 1 m corresponds to a distance of 1 m away from the exit pupils of the user’s eyes, on the optical axis of those eyes. As an approximation, the depth or distance along the z-axis may be measured from the display in front of the user’s eyes (e.g., from the surface of a waveguide), plus a value for the distance between the device and the exit pupils of the user’s eyes. That value may be called the eye relief and corresponds to the distance between the exit pupil of the user’s eye and the y worn by the user in front of the eye. In practice, the value for the eye relief may be a normalized value used lly for all viewers. For example, the eye relief may be d to be 20 mm and a depth plane that is at a depth of 1 m may be at a distance of 980 mm in front of the display.

With reference now to s 4C and 4D, es of matched accommodationvergence distances and mismatched accommodation-vergence distances are illustrated, respectively. As illustrated in Figure 4C, the y system may provide images of a virtual object to each eye 210, 220.

The images may cause the eyes 210, 220 to assume a vergence state in which the eyes converge on a point 15 on a depth plane 240. In addition, the images may be formed by a light having a wavefront curvature corresponding to real objects at that depth plane 240. As a result, the eyes 210, 220 assume an accommodative state in which the images are in focus on the retinas of those eyes. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

It will be appreciated that each of the accommodative and vergence states of the eyes 210, 220 are associated with a ular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 causes those eyes to assume particular accommodative states based upon the distances of the object. The distance associated with a particular accommodative state may be referred to as the accommodation distance, Ad. Similarly, there are particular vergence c es, Vd, associated with the eyes in particular vergence states, or positions relative to one another. Where the accommodation distance and the vergence distance match, the relationship between accommodation and vergence may be said to be physiologically correct. This is considered to be the most comfortable scenario for a viewer.

In stereoscopic displays, however, the accommodation distance and the vergence distance may not always match. For example, as illustrated in Figure 4D, images displayed to the eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and the eyes 210, 220 may assume a particular odative state in which the points 15a, 15b on that depth plane are in focus. However, the images yed to the eyes 210, 220 may provide cues for ce that cause the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, the odation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the vergence distance corresponds to the larger distance from the exit pupils of the eyes 210, 220 to the point 15, in some embodiments. The accommodation distance is different from the vergence distance. Consequently, there is an accommodation-vergence mismatch. Such a mismatch is considered undesirable and may cause discomfort in the user. It will be appreciated that the mismatch ponds to ce (e.g., Vd – Ad) and may be characterized using diopters.

Without being limited by theory, it is believed that users may still perceive accommodation-vergence mismatches of up to 0.25 r, up to 0.33 diopter, and up to about 0.5 diopter as being physiologically correct, without the mismatch itself causing significant discomfort. In some embodiments, display systems disclosed herein (e.g., the display system 250, Figure 6) are configured to present images to the viewer using light with wavefront divergence and images with binocular cues that e an odation-vergence mismatch of 0.5 diopter or less. In some other embodiments, the y systems are configured to present images to the viewer using light with wavefront divergence and images with binocular cues that provide an accommodation-vergence mismatch of 0.33 diopter or less. In yet other embodiments, the display systems are configured to present images to the viewer using light with wavefront divergence and images with binocular cues that provide an accommodation-vergence mismatch of 0.25 diopter or less, including about 0.1 r or less.

In some embodiments, it will be appreciated that a reference point other than exit pupils of the eyes 210, 220 may be ed for determining distance, so long as the same reference point is utilized for the odation distance and the ce distance. For example, the distances could be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., a waveguide of the display ) to the depth plane, and so on.

Figure 5 illustrates s of an approach for simulating three-dimensional imagery by modifying wavefront divergence. The display system includes a ide 270 that is configured to receive light 770 that is encoded with image information, and to output that light to the user’s eye 210.

The waveguide 270 may output the light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of a light field produced by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, it will be illustrated that the other eye of the user may be provided with image information from a similar waveguide.

In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or d number of depth planes and/or the waveguide may be configured to output light of a limited range of wavelengths. Consequently, in some embodiments, a plurality or stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and/or to output light of ent ranges of wavelengths.

Figure 6 illustrates an example of a waveguide stack for outputting image information to a user. A y system 250 includes a stack of waveguides, or stacked waveguide assembly, 260 that may be utilized to provide three-dimensional perception to the eye/brain using a plurality of waveguides 270, 280, 290, 300, 310. It will be appreciated that the y system 250 may be considered a light field display in some embodiments. In addition, the waveguide assembly 260 may also be ed to as an eyepiece.

In some embodiments, the display system 250 may be configured to e substantially continuous cues to vergence and multiple te cues to accommodation. The cues to ce may be provided by displaying different images to each of the eyes of the user, and the cues to accommodation may be provided by outputting the light that forms the images with discrete amounts of wavefront divergence. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of the waveguides 270, 280, 290, 300, With continued reference to Figure 6, the ide assembly 260 may also include a plurality of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and/or the plurality of lenses 320, 330, 340, 350 may be ured to send image information to the eye with various levels of wavefront curvature or light ray divergence. Each waveguide level may be associated with a particular depth plane and may be ured to output image information corresponding to that depth plane. Image injection devices 360, 370, 380, 390, 400 may function as a source of light for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each of which may be ured, as described herein, to distribute incoming light across each respective waveguide, for output toward the eye 210. Light exits an output surface 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into a ponding input surface 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of a corresponding waveguide, or may be part of a major surface of the corresponding waveguide (that is, one of the waveguide surfaces ly facing the world 510 or the viewer’s eye 210). In some embodiments, a single beam of light (e.g. a collimated beam) may be ed into each waveguide to output an entire field of cloned collimated beams that are directed toward the eye 210 at particular angles (and s of divergence) corresponding to the depth plane ated with a particular waveguide. In some ments, a single one of the image ion devices 360, 370, 380, 390, 400 may be associated with and inject light into a plurality (e.g., three) of the waveguides 270, 280, 290, 300, 310.

In some embodiments, the image injection devices 360, 370, 380, 390, 400 are discrete ys that each e image information for injection into a corresponding waveguide 270, 280, 290, 300, 310, respectively. In some other embodiments, the image injection devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display which may, e.g., pipe image information via one or more optical conduits (such as fiber optic cables) to each of the image injection devices 360, 370, 380, 390, 400. It will be appreciated that the image information provided by the image injection s 360, 370, 380, 390, 400 may include light of different wavelengths, or colors (e.g., different component colors, as discussed herein).

In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which comprises a light module 530, which may include a light emitter, such as a light emitting diode (LED). The light from the light module 530 may be directed to and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to change the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 to encode the light with image ation. Examples of spatial light tors include liquid crystal ys (LCD) including a liquid crystal on silicon (LCOS) displays. It will be appreciated that the image injection devices 360, 370, 380, 390, 400 are illustrated schematically and, in some embodiments, these image injection devices may represent different light paths and locations in a common projection system configured to output light into associated ones of the waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may on as ideal lens while relaying light injected into the waveguides out to the user’s eyes. In this conception, the object may be the spatial light modulator 540 and the image may be the image on the depth plane.

In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous patterns, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the eye 210 of the viewer. In some ments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or a plurality of the waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may schematically represent a ity of scanning fibers or a plurality of bundles of scanning , each of which are configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more optical fibers may be ured to transmit light from the light module 530 to the one or more waveguides 270, 280, 290, 300, 310. It will be appreciated that one or more intervening optical structures may be ed between the scanning fiber, or fibers, and the one or more waveguides 270, 280, 290, 300, 310 to, e.g., redirect light exiting the scanning fiber into the one or more waveguides 270, 280, 290, 300, 310.

A ller 560 controls the operation of one or more of the stacked waveguide assembly 260, including operation of the image injection devices 360, 370, 380, 390, 400, the light source 530, and the light modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transitory medium) that regulates the timing and provision of image information to the waveguides 270, 280, 290, 300, 310 according to, e.g., any of the various schemes disclosed herein. In some embodiments, the controller may be a single integral device, or a distributed system connected by wired or wireless communication ls. The controller 560 may be part of the processing modules 140 or 150 (Figure 9D) in some embodiments.

With continued reference to Figure 6, the waveguides 270, 280, 290, 300, 310 may be configured to ate light within each tive waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, 310 may each be planar or have another shape (e.g., curved), with major top and bottom surfaces and edges extending between those major top and bottom surfaces. In the illustrated configuration, the ides 270, 280, 290, 300, 310 may each include upling optical elements 570, 580, 590, 600, 610 that are configured to extract light out of a waveguide by redirecting the light, propagating within each respective waveguide, out of the waveguide to output image information to the eye 210. Extracted light may also be referred to as out-coupled light and the out-coupling optical elements light may also be referred to light extracting optical elements. An extracted beam of light may be outputted by the waveguide at locations at which the light propagating in the waveguide strikes a light extracting optical t. The out-coupling optical elements 570, 580, 590, 600, 610 may, for e, be gratings, ing diffractive optical features, as discussed further herein. While rated disposed at the bottom major surfaces of the waveguides 270, 280, 290, 300, 310, for ease of description and drawing clarity, in some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 may be disposed at the top and/or bottom major surfaces, and/or may be disposed directly in the volume of the ides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 may be formed in a layer of material that is attached to a transparent substrate to form 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 out-coupling optical elements 570, 580, 590, 600, 610 may be formed on a surface and/or in the interior of that piece of material.

With continued reference to Figure 6, as sed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light to form an image ponding to a particular depth plane. For example, the waveguide 270 nearest the eye may be ured to deliver collimated light (which was injected into such waveguide 270), to the eye 210. The collimated light may be representative of the optical infinity focal plane. The next waveguide up 280 may be configured to send out collimated light which passes h the first lens 350 (e.g., a negative lens) before it may reach the eye 210; such first lens 350 may be configured to create a slight convex wavefront curvature so that the eye/brain interprets light coming from that next waveguide up 280 as coming from a first focal plane closer inward toward the eye 210 from optical infinity. Similarly, the third up waveguide 290 passes its output light through both the first 350 and second 340 lenses before reaching the eye 210; the combined optical power of the first 350 and second 340 lenses may be configured to create another incremental amount of wavefront curvature so that the eye/brain interprets light coming from the third waveguide 290 as coming from a second focal plane that is even closer inward toward the person from l infinity than was light from the next waveguide up 280.

The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power entative of the closest focal plane to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing/interpreting light coming from the world 510 on the other side of the d waveguide assembly 260, a compensating lens layer 620 may be disposed at the top of the stack to compensate for the aggregate power of the lens stack 320, 330, 340, 350 below.

Such a uration provides as many perceived focal planes as there are available waveguide/lens pairings. Both the out-coupling l elements of the waveguides and the focusing aspects of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, either or both may be dynamic using electro-active features.

In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same ity of depth planes, with one set for each depth plane. This may provide ages for forming a tiled image to provide an expanded field of view at those depth planes.

With continued reference to Figure 6, the out-coupling optical elements 570, 580, 590, 600, 610 may be configured to both redirect light out of their respective waveguides and to output this light with the appropriate amount of divergence or collimation for a ular depth plane associated with the waveguide. As a result, waveguides having different ated depth planes may have different configurations of out-coupling l elements 570, 580, 590, 600, 610, which output light with a different amount of divergence depending on the associated depth plane. In some embodiments, the light extracting l elements 570, 580, 590, 600, 610 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extracting optical elements 570, 580, 590, 600, 610 may be volume ams, surface holograms, and/or diffraction gratings. In some embodiments, the es 320, 330, 340, 350 may not be lenses; rather, they may simply be spacers (e.g., cladding layers and/or structures for forming air gaps).

In some embodiments, the out-coupling optical elements 570, 580, 590, 600, 610 are diffractive features that form a diffraction pattern, or "diffractive optical element" (also referred to herein as a "DOE"). Preferably, the DOE’s have a sufficiently low ction efficiency so that only a portion of the light of the beam is deflected away toward the eye 210 with each intersection of the DOE, while the rest continues to move through a waveguide via TIR. The light carrying the image information is thus divided into a number of related exit beams that exit the waveguide at a multiplicity of locations and the result is a fairly uniform pattern of exit emission toward the eye 210 for this particular collimated beam ng around within a waveguide.

In some embodiments, one or more DOEs may be switchable between "on" states in which they actively diffract, and "off" states in which they do not significantly diffract. For ce, a switchable DOE may se a layer of r dispersed liquid crystal, in which microdroplets comprise a diffraction pattern in a host medium, and the refractive index of the microdroplets may be switched to ntially match the refractive index of the host material (in which case the pattern does not appreciably diffract incident light) or the microdroplet may be ed to an index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible light and infrared light s) may be provided to capture images of the eye 210 and/or tissue around the eye 210 to, e.g., detect user inputs and/or to monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source to project light (e.g., infrared light) to the eye, which may then be reflected by the eye and detected by the image e device. In some embodiments, the camera ly 630 may be attached to the frame 80 (Figure 9D) and may be in electrical communication with the processing modules 140 and/or 150, which may process image information from the camera assembly 630. In some embodiments, one camera ly 630 may be utilized for each eye, to separately monitor each eye.

With reference now to Figure 7, an example of exit beams outputted by a waveguide is shown. One ide is illustrated, but it will be appreciated that other waveguides in the waveguide assembly 260 (Figure 6) may function similarly, where the waveguide assembly 260 includes multiple waveguides. Light 640 is injected into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At points where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as exit beams 650. The exit beams 650 are illustrated as substantially parallel but, as discussed herein, they may also be redirected to propagate to the eye 210 at an angle (e.g., g divergent exit beams), depending on the depth plane associated with the waveguide 270. It will be appreciated that substantially parallel exit beams may be indicative of a waveguide with out-coupling optical elements that out-couple light to form images that appear to be set on a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of out-coupling optical elements may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance to bring it into focus on the retina and would be interpreted by the brain as light from a distance closer to the eye 210 than l infinity.

In some embodiments, a full color image may be formed at each depth plane by ying images in each of the component colors, e.g., three or more component colors. Figure 8 illustrates an example of a stacked waveguide assembly in which each depth plane includes images formed using multiple different component colors. The illustrated embodiment shows depth planes 240a – 240f, although more or fewer depths are also contemplated. Each depth plane may have three or more ent color images ated with it, including: a first image of a first color, G; a second image of a second color, R; and a third image of a third color, B. Different depth planes are indicated in the figure by different numbers for diopters (dpt) following the letters G, R, and B. Just as examples, the numbers following each of these letters indicate rs (1/m), or inverse distance of the depth plane from a viewer, and each box in the figures represents an individual component color image. In some embodiments, to account for differences in the eye’s focusing of light of different wavelengths, the exact placement of the depth planes for different component colors may vary. For e, different component 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 may decrease chromatic aberrations.

In some embodiments, light of each component color may be outputted by a single ted ide and, consequently, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figures including the letters G, R, or B may be tood to represent an individual waveguide, and three waveguides may be provided per depth plane where three component color images are ed per depth plane. While the waveguides associated with each depth plane are shown adjacent to one another in this drawing for ease of description, it will be appreciated that, in a physical , the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple component colors may be outputted by the same ide, such that, e.g., only a single waveguide may be provided per depth plane.

With continued nce to Figure 8, in some embodiments, G is the color green, R is the color red, and B is the color blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or may replace one or more of red, green, or blue.

It will be appreciated that references to a given color of light throughout this sure will be understood to encompass light of one or more wavelengths within a range of wavelengths of light that are perceived by a viewer as being of that given color. For example, red light may include light of one or more wavelengths in the range of about 620–780 nm, green light may include light of one or more wavelengths in the range of about 492–577 nm, and blue light may include light of one or more wavelengths in the range of about 3 nm.

In some embodiments, the light source 530 e 6) may be configured to emit light of one or more wavelengths outside the visual perception range of the viewer, for example, infrared and/or ultraviolet wavelengths. In addition, the in-coupling, out-coupling, and other light cting structures of the waveguides of the display 250 may be configured to direct and emit this light out of the display towards the user’s eye 210, e.g., for imaging and/or user stimulation applications.

With reference now to Figure 9A, in some embodiments, light ing on a waveguide may need to be redirected to in-couple that light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. Figure 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of d waveguides that each includes an in-coupling optical element. The waveguides may each be configured to output light of one or more ent wavelengths, or one or more different ranges of wavelengths. It will be appreciated that the stack 660 may correspond to the stack 260 (Figure 6) and the illustrated waveguides of the stack 660 may correspond to part of the plurality of waveguides 270, 280, 290, 300, 310, except that light from one or more of the image injection devices 360, 370, 380, 390, 400 is injected into the waveguides from a position that requires light to be redirected for in-coupling.

The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated in-coupling optical t (which may also be referred to as a light input area on the waveguide), with, e.g., in-coupling optical element 700 disposed on a major e (e.g., an upper major surface) of waveguide 670, in-coupling l element 710 disposed on a major surface (e.g., an upper major surface) of waveguide 680, and pling optical element 720 ed on a major surface (e.g., an upper major surface) of waveguide 690. In some embodiments, one or more of the in-coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the respective waveguide 670, 680, 690 (particularly where the one or more in-coupling optical ts are reflective, deflecting optical elements). As illustrated, the in-coupling optical elements 700, 710, 720 may be disposed on the upper major e of their respective waveguide 670, 680, 690 (or the top of the next lower waveguide), particularly where those in-coupling optical elements are transmissive, deflecting optical elements. In some embodiments, the in-coupling optical elements 700, 710, 720 may be disposed in the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the in-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. While rated on one side or corner of their tive waveguide 670, 680, 690, it will be appreciated that the in- coupling optical elements 700, 710, 720 may be disposed in other areas of their respective waveguide 670, 680, 690 in some embodiments.

As illustrated, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each pling optical element may be offset such that it receives light without that light passing through another pling optical element. For e, each incoupling optical element 700, 710, 720 may be configured to receive light from a different image injection device 360, 370, 380, 390, and 400 as shown in Figure 6, and may be separated (e.g., laterally spaced apart) from other in-coupling optical elements 700, 710, 720 such that it substantially does not e light from the other ones of the in-coupling optical elements 700, 710, 720.

Each ide also es associated light distributing elements, with, e.g., light distributing elements 730 disposed on a major surface (e.g., a top major surface) of waveguide 670, light buting elements 740 disposed on a major surface (e.g., a top major surface) of waveguide 680, and light distributing elements 750 disposed on a major surface (e.g., a top major surface) of waveguide 690.

In some other embodiments, the light distributing elements 730, 740, 750, may be disposed on a bottom major surface of associated waveguides 670, 680, 690, respectively. In some other embodiments, the light distributing elements 730, 740, 750, may be disposed on both top and bottom major surface of associated waveguides 670, 680, 690, respectively; or the light distributing elements 730, 740, 750, may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

The waveguides 670, 680, 690 may be spaced apart and separated by, e.g., gas, liquid, and/or solid layers of material. For example, as illustrated, layer 760a may separate ides 670 and 680; and layer 760b may separate waveguides 680 and 690. In some embodiments, the layers 760a and 760b are formed of low tive index materials (that is, materials having a lower tive index than the material forming the immediately adjacent one of waveguides 670, 680, 690). Preferably, the refractive index of the material g the layers 760a, 760b is 0.05 or more, or 0.10 or less than the refractive index of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that facilitate total internal reflection (TIR) of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed of air. While not illustrated, it will be iated that the top and bottom of the illustrated set 660 of waveguides may e immediately neighboring cladding .

Preferably, for ease of manufacturing and other considerations, the al forming the waveguides 670, 680, 690 are similar or the same, and the material forming the layers 760a, 760b are similar or the same. In some embodiments, the material forming the ides 670, 680, 690 may be different between one or more waveguides, and/or the material forming the layers 760a, 760b may be different, while still holding to the various refractive index relationships noted above.

With continued reference to Figure 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It will be iated that the light rays 770, 780, 790 may be ed into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (Figure 6).

In some embodiments, the light rays 770, 780, 790 have different ties, e.g., different wavelengths or different ranges of wavelengths, which may correspond to different colors. The in-coupling optical elements 700, 710, 720 each deflect the incident light such that the light propagates h a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, the incoupling optical elements 700, 710, 720 each selectively deflect one or more particular wavelengths of light, while transmitting other wavelengths to an underlying waveguide and associated incoupling optical element.

For example, in-coupling l element 700 may be configured to deflect ray 770, which has a first wavelength or range of wavelengths, while transmitting rays 780 and 790, which have different second and third wavelengths or ranges of wavelengths, tively. The itted ray 780 impinges on and is ted by the in-coupling optical element 710, which is configured to deflect light of a second wavelength or range of wavelengths. The ray 790 is deflected by the in-coupling optical element 720, which is configured to selectively deflect light of third wavelength or range of wavelengths.

With continued reference to Figure 9A, the deflected light rays 770, 780, 790 are deflected so that they propagate through a corresponding waveguide 670, 680, 690; that is, the incoupling optical ts 700, 710, 720 of each waveguide deflects light into that corresponding waveguide 670, 680, 690 to in-couple light into that corresponding waveguide. The light rays 770, 780, 790 are deflected at angles that cause the light to propagate through the respective ide 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the tive waveguide 670, 680, 690 by TIR until impinging on the waveguide’s corresponding light distributing ts 730, 740, 750.

With reference now to Figure 9B, a perspective view of an example of the plurality of stacked waveguides of Figure 9A is illustrated. As noted above, the pled light rays 770, 780, 790, are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the light distributing elements 730, 740, 750, respectively. The light distributing elements 730, 740, 750 deflect the light rays 770, 780, 790 so that they propagate towards the out-coupling optical elements 800, 810, 820, respectively.

In some embodiments, the light distributing elements 730, 740, 750 are orthogonal pupil expanders (OPE’s). In some embodiments, the OPE’s deflect or distribute light to the out-coupling optical elements 800, 810, 820 and, in some embodiments, may also se the beam or spot size of this light as it propagates to the out-coupling optical elements. In some ments, the light distributing elements 730, 740, 750 may be omitted and the in-coupling l elements 700, 710, 720 may be configured to t light directly to the out-coupling optical elements 800, 810, 820. For example, with reference to Figure 9A, the light distributing elements 730, 740, 750 may be replaced with out-coupling optical elements 800, 810, 820, respectively. In some ments, the out-coupling optical elements 800, 810, 820 are exit pupils (EP’s) or exit pupil expanders ) that direct light in a viewer’s eye 210 (Figure 7). It will be appreciated that the OPE’s may be configured to increase the dimensions of the eye box in at least one axis and the EPE’s may be to increase the eye box in an axis crossing, e.g., orthogonal to, the axis of the OPEs. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to ue to propagate down the waveguide. Upon impinging on the OPE again, another portion of the remaining light is redirected to the EPE, and the remaining portion of that n continues to propagate further down the waveguide, and so on. Similarly, upon striking the EPE, a portion of the ing light is directed out of the waveguide towards the user, and a remaining portion of that light continues to propagate through the waveguide until it strikes the EP again, at which time another portion of the ing light is directed out of the waveguide, and so on. Consequently, a single beam of incoupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, y g a field of cloned beams of light, as shown in Figure 6. In some embodiments, the OPE and/or EPE may be configured to modify a size of the beams of light.

Accordingly, with reference to s 9A and 9B, in some embodiments, the set 660 of waveguides es waveguides 670, 680, 690; in-coupling optical elements 700, 710, 720; light distributing elements (e.g., OPE’s) 730, 740, 750; and out-coupling optical elements (e.g., EP’s) 800, 810, 820 for each component color. The waveguides 670, 680, 690 may be stacked with an air gap/cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light (with different in-coupling optical elements receiving light of different wavelengths) into its waveguide. The light then propagates at an angle which will result in TIR within the tive waveguide 670, 680, 690.

In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700, and then continues to bounce down the ide, cting with the light distributing element (e.g., OPE’s) 730 and then the out-coupling optical element (e.g., EPs) 800, in a manner described earlier.

The light rays 780 and 790 (e.g., green and red light, respectively) will pass through the waveguide 670, with light ray 780 impinging on and being deflected by in-coupling optical element 710. The light ray 780 then bounces down the waveguide 680 via TIR, proceeding on to its light buting element (e.g., OPEs) 740 and then the out-coupling optical element (e.g., EP’s) 810. y, light ray 790 (e.g., red light) passes through the ide 690 to impinge on the light in-coupling optical elements 720 of the waveguide 690. The light in-coupling optical elements 720 deflect the light ray 790 such that the light ray propagates to light distributing element (e.g., OPEs) 750 by TIR, and then to the upling optical element (e.g., EPs) 820 by TIR. The out-coupling optical element 820 then finally out-couples the light ray 790 to the viewer, who also receives the out-coupled light from the other waveguides 670, 680.

Figure 9C illustrates a top-down plan view of an example of the plurality of stacked waveguides of Figures 9A and 9B. As illustrated, the waveguides 670, 680, 690, along with each waveguide’s associated light distributing element 730, 740, 750 and associated out-coupling optical element 800, 810, 820, may be vertically aligned. However, as sed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned; rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart as seen in the top-down view). As discussed further , this nonoverlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a -one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrangements including nonoverlapping spatiallyseparated pling optical elements may be referred to as a d pupil system, and the in-coupling optical elements within these arrangements may correspond to sub pupils.

Figure 9D illustrates an example of wearable display system 60 into which the various waveguides and related systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of Figure 6, with Figure 6 schematically showing some parts of that system 60 in r detail. For example, the waveguide assembly 260 of Figure 6 may be part of the display 70.

With continued reference to Figure 9D, the display system 60 includes a display 70, and various mechanical and electronic modules and systems to support the functioning of that display 70.

The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and which is configured to position the display 70 in front of the eyes of the user 90. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned nt the ear canal of the user 90 (in some embodiments, r speaker, not shown, may optionally be positioned nt the other ear canal of the user to provide stereo/shapeable sound control). The display system 60 may also e one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone is configured to allow the user to provide inputs or commands to the system 60 (e.g., the selection of voice menu commands, natural language questions, etc.), and/or may allow audio communication with other persons (e.g., with other users of similar display systems. The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sounds from the user and/or environment). In some embodiments, the display system may also include a peripheral sensor 120a, which may be separate from the frame 80 and ed to the body of the user 90 (e.g., on the head, torso, an extremity, etc. of the user 90). The peripheral sensor 120a may be configured to acquire data characterizing a physiological state of the user 90 in some embodiments. For example, the sensor 120a may be an electrode.

With continued reference to Figure 9D, the display 70 is ively coupled by communications link 130, such as by a wired lead or wireless connectivity, to a local data sing module 140 which may be mounted in a variety of configurations, such as y attached to the frame 80, y attached to a helmet or hat worn by the user, embedded in ones, or otherwise removably attached to the user 90 (e.g., in a backpack-style configuration, in a belt-coupling style configuration).

Similarly, the sensor 120a may be operatively coupled by communications link 120b, e.g., a wired lead or ss tivity, to the local processor and data module 140. The local processing and data module 140 may comprise a hardware processor, as well as digital memory, such as non-volatile memory (e.g., flash memory or hard disk drives), both of which may be utilized to assist in the processing, caching, and storage of data. ally, the local processor and data module 140 may include one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing re, and so on.

The data may include data a) captured from sensors (which may be, e.g., operatively coupled to the frame 80 or otherwise ed to the user 90), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, radio devices, gyros, and/or other sensors disclosed herein; and/or b) acquired and/or processed using remote processing module 150 and/or remote data repository 160 (including data relating to virtual content), possibly for passage to the y 70 after such processing or retrieval. The local processing and data module 140 may be operatively coupled by communication links 170, 180, such as via a wired or wireless communication links, to the remote sing module 150 and remote data tory 160 such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 may e one or more of the image capture devices, microphones, inertial measurement units, accelerometers, ses, GPS units, radio devices, and/or gyros. In some other embodiments, one or more of these sensors may be attached to the frame 80, or may be standalone structures that communicate with the local processing and data module 140 by wired or wireless communication pathways.

With continued reference to Figure 9D, in some embodiments, the remote processing module 150 may comprise one or more processors configured to analyze and process data and/or image information, for instance including one or more central processing units (CPUs), graphics sing units (GPUs), dedicated processing hardware, and so on. In some embodiments, the remote data tory 160 may comprise a digital data storage facility, which may be available through the internet or other king configuration in a "cloud" resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers, which provide ation, e.g., information for generating augmented reality content, to the local processing and data module 140 and/or the remote processing module 150. In some embodiments, all data is stored and all computations are performed in the local processing and data , allowing fully autonomous use from a remote module. Optionally, an e system (e.g., a system of one or more processors, one or more computers) that includes CPUs, GPUs, and so on, may perform at least a portion of processing (e.g., generating image information, processing data) and provide information to, and receive information from, modules 140, 150, 160, for instance via wireless or wired connections.

Metasurfaces Figures 10A and 10B illustrate examples of sectional side and top down views, respectively, of a rface 2002 according to some embodiments. A substrate 2000 has a surface 2000a on which a metasurface 2002 comprising a plurality of metasurface unit cells 2010 is disposed.

The unit cells each include a plurality of nanobeams 2020a, 2020b formed of an optically ssive material. The nanobeams 2020a, 2020b may be ridges (or nanowires), which are laterally ted into and out of the page and define trenches between neighboring nanobeams. In some embodiments, the nanobeams 2020a, 2020b may be linear. Preferably, the nanobeams 2020a, 2020b are continuous along their lengths, which can have benefits for providing a high diffraction efficiency. In some other embodiments, the nanobeams 2020a, 2020b may be discontinuous along their lengths, e.g., the nanobeams 2020a, 2020b may each extend along a line, with gaps in the nanobeams 2020a, 2020b along those lines.

The unit cells 2010 may repeat at regular intervals across the surface 2000a, and may be parallel to one another such that the nanobeams 2020a, 2020b are also parallel to one r.

The unit cells 2010 may have a width P, which is the distance between identical points of directly neighboring unit cells 2010. In some embodiments, 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 will be iated that P may be considered the pitch of the unit cells 2010 and may be ntially constant across a grating formed by those unit cells. In some other embodiments, P may vary across the surface 2000a.

Preferably, the refractive index of the material forming the nanobeams 2020a, 2020b is higher than the refractive index of the ate 2000. In some embodiments, the substrate 2000 may be a waveguide, and may correspond to the waveguides 270, 280, 290, 300, 310 (Figure 6) and/or waveguides 670, 680, and 690 (Figure 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 benefits for increasing the field of view of a display that forms an image by outputting light from that substrate 2000. Examples of materials for forming the substrate 2000 include glass (e.g., doped glass), m niobate, plastic, a polymer, sapphire, or other optically transmissive material. In some embodiments, the refractive index of the material forming the nanobeams 2020a, 2020b 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 g the nanobeams 2020a, 2020b include silicon-containing materials (e.g., amorphous or polysilicon, and n nitride), oxides, and gallium phosphide. Examples of oxides include titanium oxide, ium oxide, and zinc oxide. Preferably, the material g the nanobeams 2020a, 2020b is the same, which has advantages for simplifying fabrication of the metasurface 2002.

With continued nce to Figures 10A and 10B, one of the ams 2020b has a width NW2 that is larger than the width NW1 of the other of the illustrated nanobeams 2020a. In some embodiments, the widths NW1 and NW2 are each in the range of 10 nm to 1 µm, ing 10 nm to 300 nm, with NW1 being r than NW2 as noted above. As illustrated, the nanobeams 2020a, 2020b may be separated by a gap in the range of 10 nm to 1 µm wide, including10 nm to 300 nm wide. As also illustrated, the nanobeams 2020a, 2020b have a height hnw , which may be in the range of 10 nm to 1 µm, including 10 nm to 450 nm. Preferably, the s of the nanobeams 2020a, 2020b are substantially equal.

As disclosed herein, the various dimensions of es of the unit cells 2010 and nanobeams 2020a, 2020b may vary depending upon the properties of the materials used to form the metasurface 2002 and the properties of surrounding structures, such as the ate 2000. In some embodiments, the height hnw of the nanobeams 2020a, 2020b may vary depending upon the refractive index of the material used for those nanobeams. In some embodiments, the heights of the nanobeams may be 10 nm to 450 nm where a refractive index of the al is more than 3.3; and 10 nm to 1 µm where the refractive index is 3.3 or less. As another example, the height of the nanobeams may be 10 nm to 450 nm where the nanobeams are formed of silicon (e.g., amorphous or polysilicon).

With continued nce to Figures 10A and 10B, the metasurface 2002 illustrated in these figures works in the transmissive mode. Light rays 2021a, 2021b are cted upon propagating through the metasurface 2002 formed by the nanobeams 2020a, 2020b. As illustrated, the light ray 2021a is incident on the metasurface 2002 at an angle α relative to the normal to the surface 2000a. Preferably, the angle α is within the r bandwidth for the metasurface 2002 such that the light ray 2021a is redirected by the metasurface 2002 to propagate within the substrate 2000 at angles that facilitate total internal tion within that substrate 2000. As illustrated, the light ray 2021b is redirected such that it makes out an angle θTIR with the normal to the surface 2000a. Preferably, the angle θTIR is within a range of angles that facilitate total internal reflection within the substrate 2000. As disclosed herein, in some ments, the metasurface 2002 may be utilized as an incoupling optical element (e.g., as one or more of the incoupling optical elements 700, 710, 720 (Figure 9A)) to incouple incident light such that the light propagates through the substrate 2000 via total internal reflection.

The rface 2002 will also deflect light ing on it from within the substrate 2000. Taking advantage of this functionality, in some embodiments, the metasurfaces disclosed herein may be applied to form outcoupling optical elements, such as one or more of the outcoupling optical elements 570, 580, 590, 600, 610 (Figure 6) or 800, 810, 820 (Figure 9B) instead of, or in addition to, forming an incoupling optical element at different locations on the surface 2000a. Where different waveguides have different associated component colors, it will be iated that the outcoupling l elements and/or the incoupling optical elements associated with each waveguide made have a geometric size and/or periodicity specific for the wavelengths or colors of light that the waveguide is ured to propagate. Thus, different waveguides may have metasurfaces with different ric sizes and/or periodicities. As examples, the metasurfaces for incoupling or outcoupling red, green, or blue light may be have geometric sizes and/or periodicities (pitches) configured to redirect or diffract light at ngths of, e.g., 638 nm, 520 nm, and 455 nm, respectively. In some ments, the geometric size and periodicity of the nanobeams 2020a, 2020b and unit cells 2010 increases as wavelengths become longer, and the height or thickness of one or both of the nanobeams 2020a, 2020b also increase as wavelengths become longer.

In some ments, where the metasurface is 2002 are utilized as pling optical elements, the rfaces 2002 may have geometric sizes and/or s that cause the rfaces to impart optical power onto the cted light. For example, the metasurfaces may be configured to cause light to exit the metasurface in diverging or ging directions. Different portions of the metasurface may have different pitches, which cause different light rays to deflect in different directions, e.g., so that the light rays diverge or converge.

In some other embodiments, the metasurface 2002 may redirect light such that the light propagates away from the metasurface 2002 as collimated rays of light. For example, where colliminated light es on the metasurface 2002 at similar angles, the metasurface 2002 may have consistent geometric sizes and a consistent pitch across the entirety of the metasurface 2002 to redirect the light at similar angles.

With reference now to Figures 11A-11B, the metasurface 2002 may deflect light in a "reflective mode" where the redirected light s on the same side of the metasurface 2002 before and after impinging on the metasurface. Figure 11A rates an example of a cross-sectional side view of a metasurface configured to function in a reflective mode, and Figure 11B illustrates an example of a crosssectional , top-down view of the metasurfaces of Figure 11A as viewed on the plane 11B. As shown, the nanobeams 2020a, 2020b of the metasurface 2002 may be embedded in a reflective layer 2100. The tive layer 2100 may be formed of a reflective material, e.g., a metal, such as aluminum, silver, gold, and . Preferably, the material forming the reflective layer 2100 fills the spaces between the nanobeams 2020a, 2020b and between the unit cells 2010. In addition, the height or thickness hr of the reflective layer 2100 may be greater than the height hnw of the nanobeams 2020a, 2020b. In some embodiments, the height hr may be 150 nm or thicker, or 1 μm or thicker. Preferably, the reflective layer 2100 is sufficiently thick to block incident light, with hr being greater than the l depth of the layer 2100. It will be appreciated that the ranges of the dimensions of the various features forming a unit cell 2010 are similar to that discussed herein with respect to Figures 10A and 10B.

With reference now to Figures 12-13, another example of a reflective mode metasurface is illustrated. Figure 12 illustrates an example of a cross-sectional side view of the metasurface 2002 configured to function in a reflective mode, and Figure 13 rates an example of a cross-sectional, top-down view of the metasurface of Figure 12 as viewed on the plane 13 of Figure 13.

As illustrated, the ams 2020a, 2020b are embedded in an optically transmissive spacer layer 2110.

In these embodiments, the reflective layer 2100 is disposed directly on the surface of the spacer layer 2110 opposite the substrate 2000. The spacer layer 2110 has a height or thickness hsl which is greater than the height of the nanobeams 2020a, 2020b by a height hs, thereby spacing the nanobeams 2020a, 2020b from reflective layer 2100 by a distance equal to hs. In some embodiments, the height h s may be within the range of 5 nm to 1 μm, including 10 nm to 300 nm. It will be iated that examples of suitable materials for the spacer layer 2100 can include material that may be deposited by spin on coat, including poly(methyl methacrylate) (PMMA), spin-on glass, e-beam resist or photo-resist, and polymer. In some embodiments, the spacer layer has a refractive index of 1 to 2.

In some embodiments, the substrate 2000 may be provided with both transmissive metasurfaces and reflective metasurfaces. Figure 14A illustrates an example of a cross-sectional side view of the substrate 2000 having transmissive and reflective metasurfaces 2002a, 2002b, respectively.

In some embodiments, the transmissive and reflective metasurfaces 2002a, 2002b may be on opposing sides of the substrate. Figure 14B illustrates an example of a top-down view of the metasurface 2002a of Figure 14A. Figure 14C illustrates an example of a top-down view of the metasurface 2002b of Figure 14A viewed on the plane 14C of Figure 14A.

With reference to Figure 14A, metasurface 2002a includes a ity of unit cells 2010a which include nanobeams 2020a, 2020b. Similarly, the metasurface 2002b includes a plurality of unit cells 2010b which include nanobeams 2020c, 2020d. As with the nanobeams 2020a, 2020b, one of the nanobeams 2020c, 2020d is wider than the other. As sed herein, the ions of the features of the unit cells 2010a, 2010b may be selected based upon the wavelengths of light that the metasurfaces are configured to ct, and the desired degree of redirection. Where the metasurface is are configured to redirect light of different wavelengths, the widths of the nanobeams 2020a and 2020c may be different from one another, and/or the widths of the nanobeams 2020b and 2020d may be different from one another. For example, the metasurface 2002a may be configured to redirect light corresponding to the color green, while the metasurface 2002b may be configured to redirect light corresponding to the color red. In some embodiments, such an arrangement in which each rface is ured to ct light of a different range of wavelengths may advantageously reduce the size of a waveguide stack in which ent waveguides are used to propagate light of different wavelengths. Advantageously, the metasurfaces 2002a, 2002b may be used as ling optical elements and/or outcoupling optical ts to allow a single waveguide to be used to guide light ponding to different component colors, thereby ng the use of one waveguide.

As rated, the metasurface 2002a functions in the transmissive mode and selectively redirects light ray 2040a, while allowing light ray 2040b to propagate through the metasurface without being redirected. The light ray 2040b then impinges on the reflective-mode metasurface 2002b, which reflects the light ray 2040b such that it propagates in a d direction (which is different from the direction expected for a specular reflector).

With reference now to Figures 15A-15E, an example of a process flow for forming a transmissive metasurface is illustrated. With reference to Figure 15A, a layer 2020 of an optically transmissive material for forming the nanobeams 2020a, 2020b is deposited on the substrate 2000. The deposition may be accomplished using, e.g., a vapor deposition process such as chemical vapor deposition (CVD), including plasma-enhanced chemical vapor deposition. Subsequently, with reference to Figure 15B, a selectively definable material, e.g., a resist (such as a nanoimoprint resist) is deposited on the layer 2022. The resist 2022 may be deposited by jet g (e.g., inkjet printing), which may provide advantages for g exceptionally thin layers, and also layers with varying composition and/or thickness. .

With reference to Figure 15C, an imprint template or master 2024 is brought into contact with the resist 2022 to pattern that resist. In some other embodiments, the pattern in the im print template 2024 may be formed by, e.g., raphy, including e-beam lithography or EUV lithography.

With reference to Figure 15D, the pattern formed in the resist layer 2022 is transferred to the optically transmissive layer 2020. It will be appreciated that this pattern transfer may be accomplished using an etch selective for the material forming the optically transmissive layer 2020 relative to other exposed materials. In some embodiments, the pattern transfer etch may be an anisotropic etch, such as a reactive ion etch. Subsequently, in some embodiments, the resist layer 2022 may be removed using, e.g., an ashing s.

With reference now to Figure 15E, a plurality of unit cells 2010 comprising nanobeams 2020a, 2020b are formed. It will be appreciated that while shown schematically as having similar widths for ease of illustration, the nanobeams 2020a, 2020b have different widths, as disclosed herein.

Figures 16A and 16B illustrate ng electron microscope images of a metasurface. The metasurface was formed generally as described with t to Figures 15A-15E, with the resist being patterned by electron beam lithography. ageously, highly uniform rows of material corresponding to the nanobeams 2020a, 2020b were formed. As shown in Figure 16B, each nanobeam has a substantially uniform cross-sectional shape, as seen in the illustrated side view.

While not illustrated, it will be appreciated that reflective-mode metasurfaces may be formed h onal processing of the structure shown in Figure 15E. For example, a reflective material may be deposited in the open volumes between the nanobeams 2020a, 2020b, and over those ams to form the structure illustrated in Figures 11A and 11B. In some other ments, the nanobeams 2020a, 2020b may be formed by etching trenches in the reflective layer and subsequently filling the trenches with the material of the nanobeams 2020a, 2020b.

As another example, the structure illustrated in Figure 12 may be formed by ting a layer of optically-transmissive spacer material on and between the nanobeams 2020a, 2020b.

The reflective layer may subsequently be ted on the spacer layer. In some embodiments, the depositions may be accomplished using vapor deposition processes, e.g., chemical vapor deposition (CVD) processes and/or physical vapor deposition (PVD) processes.

As discussed herein, metasurfaces according to various embodiments provide highly m diffraction ency over a wide range of innocent angles. Figure 17 illustrates an e of a plot showing the diffraction efficiency versus angle of incidence of light for a transmissive metasurface.

Advantageously, the diffraction efficiency over a span of angles ranging about 50° is highly uniform.

High uniformity is also ed by various embodiments of a reflective metasurface.

Figures 18A – 18C illustrate examples of plots g the diffraction efficiency versus angle of incidence of light for a reflective rface. The wavelengths of incident light are different for each of Figures 18A – 18C. Advantageously, the plots are highly flat over a large range of incident . In addition, the plots are advantageously similar for different wavelengths corresponding to the colors red, green, and blue. Such uniformity may be beneficially applied to display systems which utilize different component colors. The uniformity of the diffraction may aid in the formation of high quality images images with high color accuracy.

It has also been found that the diffraction efficiency of the metasurfaces is highly dependent upon the polarization of the instant light. s 19A and 19B illustrate examples of plots showing the polarization sensitivity of the transmissive rface of Figures 10A and 10B. As shown in Figure 19A, the diffraction efficiency is high for incident light with a polarization that is parallel to the ams forming the asymmetric rating. However, light with a polarization that is perpendicular to the nanobeams has low diffraction efficiency. Given this sensitivity to polarization, as noted , the metasurface may ageously be utilized as a polarizing beam splitter. Preferably, the metasurface provides extinction ratios of 5 or more, 7 or more, or 9 or more for light of different polarizations.

As discussed herein, the amplitude and phase of light redirected by the metasurfaces disclosed herein are dependent upon the wdiths of the nanobeams g the metal surfaces. Figure 20 illustrates plots of amplitude and phase shift versus nanobeam width for the metasurface of Figures 10A and 10B. As indicated by the plots, the widths of the nanobeams or nanowires may be adjusted to manipulate the amplitude and phase of the redirected light.

With reference now to Figure 21A, in some embodiments, the metasurface may include a multilevel asymmetric grating. Figure 21A illustrates an example of a sectional side view of a multilevel metasurface 2008 that includes a plurality of levels of optically transmissive materials. It will be appreciated that the cross-sectional side view is taken on a plane orthogonal to the elongate axis of the illustrated nanobeams 2020a, 2020b. Nanobeams 2020a, 2020b are formed on the surface 2000a of the ate 2000. As rated, in some embodiments, the metasurface 2008 is a bi-level structure having lowermost and uppermost levels 2012, 2014, respectively. The lowermost level 2012 includes the nanobeams 2020a, 2020b formed of a first optically transissive al and masses 2030c of a second optically transmissive material between the nanobeams 2020a, 2020b. The uppermost level 2014 may be directly ally adjacent the nanobeams 2020a, 2020b and includes uppermost level nanobeams 2030a of the second optically transmissive al formed directly on the nanobeams 2020a and uppermost level nanobeams 2030b of the second optically issive material formed directly on the nanobeams 2020b. It will be appreciated that the uppermost level nanobeams 2030a, 2030b of the second optically transmissive al may t the nanobeams 2020a, 2020b. As illustrated, on the uppermost level 2014, the nanobeams 2030a, 2030b of the second optically transmissive material may be localized on the surface of the nanobeams 2020a, 2020b, forming plateaus of material spaced apart from other localized deposits (or plateaus) of the second optically transmissive material.

With continued reference to Figure 21A, ably, the refractive index of the second optically transmissive al forming the nanobeams 2030a, 2030b and masses 2030c is higher than the refractive index of both the first optically transissive material forming the nanobeams 2020a, 2020b, and the material forming the ate 2000. In some embodiments, the refractive index of the first optically transissive material forming the nanobeams 2020a, 2020b is lower than or similar to the refractive index of the material forming the substrate 2000.

With continued reference to Figure 21A, the first optically transissive material of the nanobeams 2020a, 2020b is preferably a material that may be patterned, e.g., by lithography and etch processes. More preferably, the first optically transmissive material is a nanoimprint resist that may be patterned by nanoimprinting. As discussed herein, the second optically transmissive material forming the nanobeams 2030a, 2030b and masses 2030c may have a higher refractive index than both the first optically transissive material of the nanobeams 2020a, 2020b and the material g the ate 2000. In some embodiments, the refractive index of the second optically transmissive material is higher than 1.6, 1.7, 1.8, or 1.9. Examples of materials for the second optically transmissive al include semiconductor materials, including silicon-containing materials, and oxides. Examples of siliconcontaining materials include silicon nitride and silicon carbide. Examples of oxides include titanium oxide, zirconium oxide, and zinc oxide. In some embodiments, the second optically transmissive al may have lower l transparency than these oxides. For example, the second optically transmissive material may be silicon or its derivatives. In some embodiments, the first and second lly transmissive materials are amorphous solid state materials, or lline solid state als. Without being limited by theory, amorphous materials may be desirable in some applications, since they may be formed at lower temperatures and over a wider range of surfaces than some crystalline als. In some embodiments, each of the first and second optically transmissive materials forming the es 2020a, 2020b, 2030a, 2030b, 2030c may be one of an amorphous or crystalline semiconductor al.

As discussed above, in some embodiments, the widths NW1, NW2 of the nanobeams 2020a, 2020b, respectively, forming the unit cells 2010 may be in the range of 10 nm to 1 µm, including 10 nm to 300 nm or 10 nm to 250 nm. The nanobeams 2020a, 2020b of a unit cell 2010 may be separated by a gap in the range of 5 nm to 1 µm wide, including 10 nm to 1 µm wide or 10 nm to 300 nm wide. The pitch P of the unit cells 2010 may be in the range of 10 nm to 1 µm, including 10 nm to 500 nm, or 300 nm to 500 nm. In some ments, the heights hnw of the nanobeams 2020a, 2020b may be in the range of 10 nm to 1 µm, ing 10 nm to 500 nm or 10 nm to 450 nm. The heights hm of the masses 2030c may be in the range of 10 nm to 1 µm, including 10 nm to 600 nm. Preferably, the heights of the nanobeams 2030a, 2030b and masses 2030c are substantially similar.

It has been found that the dimensions of features of the unit cells may vary depending upon the properties of the materials used to form the metasurface. For example, the height of the nanobeams may vary depending upon the refractive index of the material used for those ams. In some embodiments, the heights of the nanobeams may be 10 nm to 450 nm where a refractive index of the al is more than 3.3; and 10 nm to 1 µm where the refractive index is 3.3 or less. As another example, the height of the nanobeams may be 10 nm to 450 nm where the nanobeams are formed of silicon (e.g., amorphous or polysilicon). In some embodiments, the heights of the material of the ams 2030a, 2030b and masses 2030c may be in the range of 10 nm to 1 µm, ing 10 nm to 600 nm.

Within the above noted ranges of dimensions, it will be appreciated that, in some embodiments, the metasurface may on in a primarily reflective mode or a primarily transmissive mode, depending upon the appropriate selection of dimensions in conjunction with materials for the features 2030a, 2030b, 2030c. For example, for a given wavelength of light, the thickness of the features 2030a, 2030b, 2030c for a metasurface 2008 working in the reflective mode may be lower than the thickness of the features 2030a, 2030b, 2030c for a metasurface working in the transmissive mode. In addition, in either the transmissive or reflective mode, the use of a higher refractive index material for the es 2030a, 2030b, 2030c may allow a reduction in the thickness of those features while achieving similar light redirecting properties.

With continued reference to Figure 21A, the metasurface 2008 is working in the reflective mode, with incident light ray 2200 impinging on the metasurface 2008 and being redirected by diffraction at an angle such that it propagates through the substrate 2000 by total internal reflection. In some embodiments, the s of the features 2030a, 2030b, 2030c may be lower than the heights of the ams 2020a, 2020b, as illustrated. It will be appreciated that light may be understood to pass twice through rfaces working in the reflective mode (once as the incident light impinges on the metasurface, and a second time as it is reflected through and away from the metasurface), thereby allowing for features 2030a, 2030b, 2030c and nanobeams 2020a, 2020b with lower heights than a metasurface working in the issive mode with similar light cting capabilities.

With reference now to Figure 21B, an example is illustrated of a plot of ission and reflection as a function of the angle of incidence of light for a metasurface having the l structure shown in Figure 21A. Various diffraction orders of transmitted and reflected light are indicated by "T" and "R," respectively. In this example, the ams 2020a, 2020b are formed of an optically transmissive resist and the features 2030a, 2030b, 2030c are formed of titanium oxide. Titanium oxide has an advantageously high refractive index of 2.6, which can facilitate reductions in the thicknesses or heights of the features 2030a, 2030b, 2030c and nanobeams 2020a, 2020b relative to lower tive index materials. For each unit cell, the width of the nanobeam 2020a is 50 nm; the width of the nanobeam 2020b is 110 nm; the gap n the nanobeams 2020a and 2020b is 40 nm; the heights of the nanobeams 2020a, 2020b are 100 nm; the heights of the features 2030a, 2030b, 2030c are 50 nm; and the pitch of the unit cells 2010 is 382 nm.

With continued reference to Figure 22B, the percentage of light incident on the metasurface 2008 that is reflected and undergoes first order diffraction to angles suitable for TIR (R1) is about 25% for an incident angle of 0°, and varies between 25% and 42% for incident angles from about - ° to about 10°. As illustrated, zero order reflection is advantageously low. Where the metasurface 2008 is utilized in a display device such as a display system 250 (Figure 6) that utilizes a tive spatial light modulator, zero order reflection may undesirably cause reflection of light back to the l light modulator, which then reflects the light back to the viewer, thereby causing undesirable image artifacts such as ghosting. Consequently, a low amount zero order reflection may be desirable in such applications. In addition, as illustrated, a portion of the incident light is transmitted (T0) and another portion of the incident light undergoes negative first order ction (R-1).

With reference now to Figure 22A, a metasurface 2008 operating in the transmissive mode is illustrated. Notably, in this ment, the metasurface 2008 is similar to that shown in Figure 21A, except for the s of the features 2030a, 2030b, 2030c, and optionally the material forming these features 2030a, 2030b, 2030c. As illustrated, the heights of the masses 2030c (and the corresponding heights of the nanobeams 2030a, 2030b) may be greater than the heights of the nanobeams 2020a, 2020b in some embodiments. In the illustrated embodiment, the light ray 2200 propagates through the rface 2008 and is diffracted into an angle such that it propagates through the substrate 2000 by total internal reflection.

With reference now to Figure 22B, an example is illustrated of a plot of transmission and reflection as a function of the angle of incidence of light for a metasurface having the general structure shown in Figure 22A. As above, ction orders of transmitted and reflected light are indicated by "T" and "R," respectively. For each unit cell, the width of the nanobeam 2020a is 50 nm; the width of the am 2020b is 110 nm; the gap between the nanobeams 2020a and 2020b is 50 nm; the heights of the nanobeams 2020a, 2020b are 150 nm; the s of the features 2030a, 2030b, 2030c are 190 nm; and the pitch of the unit cells 2010 is 382 nm. In this example, the nanobeams 2020a, 2020b are formed of an lly transmissive resist and the es 2030a, 2030b, 2030c are formed of n nitride, which has a refractive index of 2.0.

With continued reference to Figure 22B, the tage of light incident on the metasurface that is transmitted and undergoes negative first order diffraction to angles suitable for TIR (T- 1) is about 35% for an incident angle of 0°, and varies between 35% and 56% for incident angles from about -10° to about 10°. Zero order reflection remains advantageously low. As also illustrated, a portion of the incident light is transmitted (T0) without being redirected, and another portion of the nt light undergoes positive first order diffraction (T1).

With reference now to Figures 23A-23D, an example of a process flow for forming the metasurface 2008 is illustrated. With reference to Figure 14A, a layer 2020 of a first material, e.g., resist (such as a nanoimoprint resist) is deposited on substrate 2000. The layer 2020 is preferably optically transmissive and may be deposited by, e.g., spin coating. In some embodiments, the layer 2020 may be deposited by jet coating (e.g., inkjet printing), which may e advantages for forming exceptionally thin layers, and also layers with varying composition and/or thickness.

With reference to Figure 23B, an imprint template or master 2024 is brought into contact with the resist layer 2020 to pattern that layer. It will be appreciated that the pattern in the imprint te 2024 may be a negative of the pattern of nanobeams of the metasurface to be formed. The pattern in the imprint template 2024 may be formed by, e.g., lithography, including e-beam lithography or EUV lithography. Advantageously, the same template 2024 may be reused to pattern resist on multiple ates, thereby reducing per-unit fabrication costs for the eventually-formed rfaces.

After contacting the imprint template 2024, the resist 2020 assumes the pattern defined by the openings in the template 2024. In some embodiments, the resist 2020 may be cured, e.g., by exposure to light (such as UV light) and/or heat, to lize the resist. The template 2024 may then be retracted, to leave a patterned resist having nanobeams 2020a, 2020b, as shown in Figure 23C. In some other embodiments, the pattern in the resist layer may be transferred to an ying layer of material (e.g., as shown in Figures 15A-15E) and the resist may be removed, thereby forming the nanobeams 2020a, 2020b in that underlying layer of al.

With reference now to Figure 23D, a second material is subsequently deposited on the ams 2020a, 2020b to form the nanobeams 2030a, 2030b. Examples of materials for the second material include semiconductor materials, including silicon-containing materials such as n, silicon nitride, silicon carbide; oxides, including zirconium oxide, zinc oxide, and titanium oxide; and optically transmissive s. As disclosed herein, the second material 2030 is preferably an optically transmissive material. The second material 2030 may be deposited by s ses, including t depositions, directional depositions, and spin or jet coating. Examples of blanket depositions include chemical vapor deposition (CVD), in which the resist is exposed to mutually reactive precursors simultaneously present in a deposition chamber ning the substrate 2000, and atomic layer deposition (ALD), in which the resist is alternately exposed to precursors. ALD may provide advantages for precisely controlling the thickness of deposited layers, where high precision is desired, and also for depositing materials at low temperatures. Examples of directional depositions e evaporation and sputtering to deliver the second material preferentially onto the top surfaces of the nanobeams 2020a, 2020b and the ate 2000.

It will be appreciated that substrates 2000 having metasurfaces according to various embodiments disclosed herein may be used to form display systems, such as the system 1000 (Figure 6) disclosed herein. For example, the metasurfaces may be utilized as ling and/or outcoupling optical elements as noted herein. In some embodiments, after fabrication of the metasurface, the waveguide 2000 may be optically coupled to a light pipe, such as a light pipe for injecting image information into the waveguide. The light pipe may be an optical fiber in some embodiments. Examples of light pipes e the image ion devices 200, 202, 204, 206, 208 (Figure 6) and scanning optical fibers. In some embodiments, a plurality of waveguides each having metasurfaces 2010 may be provided, and each of these waveguides may be optically coupled to one or more image injection devices. s example embodiments of the invention are bed herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the invention. Various changes may be made to the invention described and equivalents may be substituted without departing from the true spirit and scope of the invention.

For example, while advantageously ed with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by systems that e images on a single depth plane, and/or with virtual reality displays. In some embodiments where multiplexed image information (e.g. light of different colors) is directed into a waveguide, multiple metasurfaces may be provided on the ide, e.g., one rface active for each color of light. In some ments, the pitch or periodicity, and/or geometric sizes, of the nanobeams, or nanobeams, forming the metasurface may vary across a metasurface. Such a metasurface may be active in redirecting light of different ngths, depending upon the geometries and pitches at the locations where that light impinges on the metasurfaces. In some other ments, the geometries and pitches of metasurface features are configured to vary such that ted light rays, even of r wavelengths, propagate away from the metasurface at different angles. It will also be appreciated that multiple separated metasurfaces may be disposed across a substrate surface, with each of the metsurfaces having the same geometries and pitches in some embodiments, or with at least some of the metasurfaces having different geometries and/or pitches from other metasurfaces in some other embodiments.

Various terms specifying orientation are utilized herein. For e, the nanobeams may be bed as being on or over a substrate, and may be described as having a height (or thickness). It will be appreciated that these terms relate to the nanobeams and substrate when placed in a reference orientation in which the substrate is vertically below the nanobeams. In such an orientation, a height describes a vertical dimension, while a gap, pitch, or width describe a lateral ion, e.g., extending in a plane facing (e.g., substantially el to) the surface of the substrate on which the nanobeams are disposed. It will be appreciated, however, that the nanobeams and substrates are not limited in their relative orientations and may be positioned in other orientations relative to one another.

Also, while advantageously applied to displays, such as wearable displays, the metasurfaces may be applied to various other devices in which a compact, low-profile light cting element is desired. For e, the metal surfaces may be applied to form light redirecting parts of optical plates (e.g., glass plates), optical fibers, microscopes, sensors, watches, s, and image projection devices generally.

In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. Further, as will be appreciated by those with skill in the art that each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other l embodiments without departing from the scope or spirit of the present inventions. All such modifications are ed to be within the scope of claims associated with this disclosure.

The invention includes methods that may be med using the subject devices.

The methods may comprise the act of providing such a suitable device. Such provision may be performed by the user. In other words, the "providing" act merely requires the user obtain, access, approach, position, set-up, activate, power-up or otherwise act to provide the requisite device in the t method.

Methods d herein may be carried out in any order of the recited events which is logically possible, as well as in the recited order of events.

Example aspects of the invention, together with details regarding material selection and manufacture have been set forth above. As for other details of the present invention, these may be appreciated in connection with the above-referenced patents and publications as well as generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed.

For ease of description, s words ting the relative positions of features are used herein. For example, various features may be bed as being "on," "over," at the "side" of, "higher" or "lower" other features. Other words of relative position may also be used. All such words of relative position assume that the aggregate ure or system formed by the features as a whole is in a certain orientation as a point of reference for ption es, but it will be appreciated that, in use, the structure may be positioned sideways, flipped, or in any number of other ations.

In addition, though the invention has been described in reference to several examples optionally incorporating various features, the invention is not to be limited to that which is described or indicated as plated with respect to each variation of the invention. Various changes may be made to the invention described and lents (whether recited herein or not included for the sake of some brevity) may be substituted without departing from the true spirit and scope of the invention. In addition, where a range of values is provided, it is understood that every ening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention.

Also, it is plated that any optional feature of the inventive variations described may be set forth and d independently, or in combination with any one or more of the features described herein. Reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in claims associated hereto, the singular forms "a," "an," "said," and "the" include plural referents unless the specifically stated ise. In other words, use of the es allow for "at least one" of the subject item in the description above as well as claims associated with this disclosure. It is further noted that such claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely," "only" and the like in connection with the tion of claim elements, or use of a "negative" limitation.

Without the use of such exclusive terminology, the term "comprising" in claims associated with this disclosure shall allow for the inclusion of any additional element--irrespective of whether a given number of elements are enumerated in such claims, or the addition of a feature could be regarded as transforming the nature of an t set forth in such claims. Except as specifically defined herein, all technical and ific terms used herein are to be given as broad a commonly tood meaning as le while maintaining claim validity.

The breadth of the t invention is not to be limited to the examples provided and/or the subject specification, but rather only by the scope of claim language associated with this disclosure The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

We

Claims (10)

Claim:

1. An optical system comprising: an optically transmissive substrate comprising a metasurface, the metasurface comprising: a grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view: a laterally-elongated first nanobeam having a first width; and a lly-elongated second nanobeam spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width; and a reflector, wherein the grating is between the reflector and the substrate.

2. The l system of Claim 1, wherein the reflector is spaced apart from the grating.

3. The optical system of Claim 2, wherein the grating is embedded in an optically transmissive al.

4. The optical system of any one of the Claims 1 to 3, wherein the optically transmissive material spaces the reflector apart from the grating.

5. The optical system of any one of the Claims 1 to 4, wherein the substrate comprises: a second metasurface on a side of the substrate te the metasurface, the second metasurface comprising: a second grating comprising a plurality of second unit cells, each second unit cell comprising, as seen in a wn view: a laterally-elongated third nanobeam; and a laterally-elongated fourth nanobeam spaced apart from the third nanobeam by a gap, wherein the fourth am is wider than the third nanobeam.

6. The optical system of any one of the Claims 1 to 5, wherein the unit cells are laterallyelongated and are parallel to each other.

7. The optical system of any one of the Claims 1 to 6, wherein the metasurface is configured to ct incident light of a visible wavelength into a first diffraction order.

8. The optical system of any one of the Claims 1 to 7, n the second width is 10 nm to 1 µm. 9. The l system of Claim 8, wherein the second width is 10 nm to 300 nm. 10. The optical system of any one of the Claims 1 to 9, wherein a pitch of the unit cells is 10 nm to 1 µm. 11. The optical system of Claim 10, wherein the pitch of the unit cells is 10 nm to 500 nm. 12. The optical system of any one of the Claims 1 to 11, wherein the first nanobeam and the second nanobeam are separated by a gap of 10 nm to 1 µm. 13. The optical system of Claim 12, wherein the gap is 10 nm to 300 nm wide. 14. The l system of any one of the Claims 1 to 13, wherein the optically transmissive substrate comprises a glass. 15. The optical system of any one of the Claims 1 to 14, wherein the first and second nanobeam comprises silicon. 16. The optical system of Claim 15, wherein the first and second nanobeam comprises silicon nitride. 17. The optical system of any one of the Claims 1 to 16, wherein the optically transmissive substrate and the metasurface form a polarizing beam splitter. 18. The optical system of Claim 10, wherein the optically transmissive substrate is a waveguide plate. 19. The optical system of Claim 18, further comprising a stack of the optically transmissive substrates, wherein dimensions of features of the unit cells varies between the ates. 20. The optical system of any one of the Claims 1 to 19, wherein the metasurface is an incoupling optical element, r comprising an image injection device configured to project light to the incoupling optical element, wherein the metasurface is configured to redirect the light to propagate the light through the substrate by total internal reflection. 21. The optical system of any one of the Claims 1 to 20, wherein the metasurface is an outcoupling optical element, wherein the metasurface is configured to extract light out of the substrate. 22. A method for forming a metasurface, the method comprising: providing an optically transmissive substrate; forming a grating on the substrate, the grating comprising a plurality of unit cells, each unit cell comprising, as seen in a top-down view: a laterally-elongated first nanobeam having a first width; and a laterally-elongated second am spaced apart from the first nanobeam by a gap, the second nanobeam having a second width larger than the first width; and providing a layer of tive material on the grating, the layer of reflective material extending into the gap and between the unit cells, wherein the grating is n the reflector and the ate. 23. The method of Claim 22, wherein providing the layer of reflective material ses depositing reflective material n and over the first and second nanobeams. 24. The method of Claim 23, wherein the tive material ses aluminum. 25. The method of any one of the Claims 22 to 24, wherein forming the grating comprises: ting an optically transmissive layer over the substrate; and ning the optically transmissive layer to define the grating. 26. The method of Claim 25, wherein patterning the optically transmissive layer comprises: providing a resist layer over the optically transmissive layer; defining a pattern in the resist layer; and transferring the pattern from the resist layer to the lly transmissive layer. FIG, 8 FIG, 34 9, 859m), mocmmhg, 5 $0 mwmxu 3 3 “gamma $2: cm GE mgm commvoEEoqu mwmwm

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