Metasurfaces for redirecting light and fabricating methods

Abstract

To provide favorable metasurfaces for redirecting light and fabricating methods.SOLUTION: A display system comprises a waveguide having light incoupling or light outcoupling optical elements formed of a metasurface. The metasurface is of a multilevel (e.g., bi-level) structure having a first level defined by spaced protrusions formed of a first optically transmissive material and a second optically transmissive material between the protrusions. The metasurface also includes a second level formed by the second optically transmissive material. The protrusions on the first level may be patterned by nanoimprinting the first optically transmissive material, and the second optically transmissive material may be deposited over and between the patterned protrusions. The widths of the protrusions and the spacing between the protrusions may be selected to diffract light, and a pitch of the protrusions may be 10-600 nm.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] (Priority application) This application claims the benefit of U.S. Provisional Patent Application No. 62 / 252,315, filed November 6, 2015, entitled "METASURFACES FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING," and U.S. Provisional Patent Application No. 62 / 252,929, filed November 9, 2015, entitled "METASURFACES FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING," the entirety of each of which is incorporated herein by reference.

[0002] (Incorporated by reference) This application also incorporates by reference in its entirety each of U.S. Application No. 14 / 331,218 (Magic Leap Admin. No. 20020.00), U.S. Application No. 14 / 641,376 (Magic Leap Admin. No. 20014.00), U.S. Provisional Application No. 62 / 012,273 (Magic Leap Admin. No. 30019.00), and U.S. Provisional Application No. 62 / 005,807 (Magic Leap Admin. No. 30016.00).

[0003] The present disclosure relates to augmented and virtual reality imaging and visualization systems. [Background technology]

[0004] Modern computing and display technology has facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images, or portions thereof, are presented to a user in a manner that appears or can be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. For example, referring to FIG. 1 , an augmented reality scene 1100 is depicted in which a user of the AR technology sees a real-world park-like setting 1100 featuring people, trees, and buildings in the background, as well as a concrete platform 1120. In addition to these items, the user of the AR technology also perceives as "seeing" a robotic figure 1110 standing on the real-world platform 1120 and a flying, cartoon-like avatar character 1130 that appears to be an anthropomorphic bumblebee, although these elements 1130, 1110 do not exist in the real world. The human visual perception system is complex, making it difficult to create VR or AR technologies that facilitate comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

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

[0006] In some embodiments, a method for forming an optical waveguide includes providing an optically transparent resist layer over an optically transparent substrate. The resist is patterned with a pattern comprising protrusions and intervening gaps, the protrusions having a pitch in the range of 10 nm to 600 nm. An optically transparent material is deposited on the protrusions and in the gaps between the protrusions.

[0007] In some other embodiments, a method of fabricating a display device includes providing a waveguide comprising a metasurface. The metasurface comprises a plurality of spaced apart protrusions formed from a first optically transmissive material and a second optically transmissive material spanning and between the spaced apart protrusions. The waveguide may be optically coupled to a light pipe.

[0008] In yet another embodiment, a display system comprises a waveguide and an optical incoupling optical element disposed on a surface of the waveguide, the optical incoupling optical element comprising a multilevel metasurface having a pitch and comprising a plurality of spaced apart protrusions formed from a first optically transmissive material and a second optically transmissive material spanning and between the spaced apart protrusions.

[0009] In some other embodiments, a display system comprises a waveguide and a light outcoupling optical element disposed on a surface of the waveguide, the light outcoupling optical element comprising a multilevel metasurface having a pitch and comprising a plurality of spaced apart protrusions formed from a first optically transmissive material and a second optically transmissive material spanning and between the spaced apart protrusions.

[0010] In yet another embodiment, a display system includes a waveguide and an optical incoupling optical element disposed on a surface of the waveguide, the optical incoupling optical element comprising a metasurface including a plurality of spaced apart protrusions formed from a first optically transmissive material and an optically transmissive resist between the spaced apart protrusions.

[0011] In some other embodiments, a display system comprises a waveguide and a light outcoupling optical element disposed on a surface of the waveguide, the light outcoupling optical element comprising a metasurface comprising a plurality of spaced apart protrusions formed from a first optically transmissive material and an optically transmissive resist between the spaced apart protrusions.

[0012] Additional and other objects, features, and advantages of the present invention are set forth in the detailed description, drawings, and claims. The present invention provides, for example, the following. (Item 1) 1. A method for forming an optical waveguide, the method comprising: Steps for forming metasurfaces Including, The step of forming the metasurface comprises: providing an optically transparent resist layer over an optically transparent substrate; patterning the resist with a pattern comprising protrusions and intervening gaps, the protrusions having a pitch in the range of 10 nm to 600 nm; depositing an optically transparent material on the protrusions and in the gaps between the protrusions; A method comprising: (Item 2) Item 10. The method of claim 1, wherein the optically transparent material is amorphous. (Item 3) Item 10. The method of item 1, wherein the step of depositing the optically transmissive material forms spaced apart plateaus of the optically transmissive material above the protrusions. (Item 4) Item 10. The method of item 1, wherein the optically transparent material has a higher refractive index than either the patterned resist or the substrate. (Item 5) 5. The method according to claim 4, wherein the refractive index of the optically transparent material is higher than 1.7. (Item 6) Item 5. The method according to item 4, wherein the optically transparent material is a resist. (Item 7) Item 10. The method of claim 1, wherein the optically transparent substrate is a waveguide. (Item 8) Item 10. The method of item 1, wherein patterning the resist comprises imprinting the pattern into the resist. (Item 9) Item 10. The method of item 1, wherein depositing the optically transparent material comprises spin-coating the optically transparent material onto the patterned resist. (Item 10) Item 10. The method of item 1, wherein depositing the optically transparent material comprises conformal or directional deposition of the optically transparent material. (Item 11) Item 11. The method of item 10, wherein the conformal deposition comprises chemical vapor deposition or atomic layer deposition of the optically transparent material. (Item 12) Item 11. The method of item 10, wherein the directional deposition comprises evaporation or sputtering of the optically transparent material. (Item 13) Item 2. The method according to item 1, wherein the total width is within a range of 300 to 500 nm. (Item 14) Item 2. The method according to item 1, wherein the step of depositing an optically transparent material deposits the optically transparent material above the protrusion to a thickness of 10 nm to 1 μm. (Item 15) Item 10. The method of claim 1, wherein the protrusion comprises steps at two levels. (Item 16) 1. A display system comprising: A waveguide; an optical incoupling optical element disposed on a surface of the waveguide, the optical incoupling optical element comprising a multilevel metasurface, the multilevel metasurface comprising: a plurality of spaced apart protrusions having a pitch and formed from a first optically transmissive material; a second optically transparent material across and between the spaced apart protrusions; and an optical incoupling optical element comprising: A display system comprising: (Item 17) Item 17. The display system of item 16, wherein the pitch of the protrusions varies across the surface of the waveguide. (Item 18) Item 17. The display system of item 16, further comprising an image injection device configured to inject light comprising image information into the waveguide. (Item 19) Item 17. The display system of item 16, wherein the waveguide is one of a stack of waveguides, each of the stacks of waveguides having an associated multilevel metasurface. (Item 20) 20. The display system of claim 19, wherein the associated multilevel metasurfaces of at least some of the waveguides are configured to redirect light in a different wavelength range than the associated multilevel metasurfaces of the other waveguides. (Item 21) Item 17. The display system of item 16, wherein the first optically transmissive material comprises a resist. (Item 22) Item 17. The display system of item 16, wherein the space between each protrusion and its nearest neighbor defines an overall width of 10 to 600 nm. (Item 23) Item 17. The display system of item 16, wherein the second optically transparent material forms the spaced apart plateaus across the protrusions. (Item 24) Item 17. The display system of item 16, wherein the first and second optically transmissive materials are amorphous. (Item 25) Item 17. The display system of item 16, wherein the second optically transmissive material has a higher refractive index than either the first optically transmissive material or the material forming the waveguide. (Item 26) Item 26. The display system of item 25, wherein the second optically transmissive material has a refractive index greater than 1.7. (Item 27) Item 26. The display system of item 25, wherein the optically transmissive material comprises a semiconductor. (Item 28) Item 28. The display system of item 27, wherein the optically transmissive material comprises silicon. (Item 29) Item 29. The display system of item 28, wherein the optically transmissive material comprises silicon nitride or silicon carbide. (Item 30) Item 26. The display system of item 25, wherein the optically transmissive material comprises an oxide. (Item 31) Item 26. The display system of item 25, wherein the optically transmissive material comprises a metal oxide. (Item 32) Item 32. The display system of item 31, wherein the optically transmissive material comprises titanium oxide, zirconium oxide, or zinc oxide. (Item 33) Item 17. The display system of item 16, wherein the metasurface is a bi-level metasurface. (Item 34) Item 17. The display system of item 16, wherein the metasurface is a tri-level or higher level metasurface. (Item 35) 1. A display system comprising: A waveguide; an optical outcoupling optical element disposed on a surface of the waveguide, the optical outcoupling optical element comprising a multilevel metasurface, the multilevel metasurface comprising: a plurality of spaced apart protrusions having a pitch and formed from a first optically transmissive material; a second optically transparent material across and between the spaced apart protrusions; and a light outcoupling optical element comprising: A display system comprising: (Item 36) Item 36. The display system of item 35, wherein the pitch of the protrusions varies across the surface of the waveguide. (Item 37) Item 36. The display system of item 35, further comprising an image injection device configured to inject light comprising image information into the waveguide. (Item 38) Item 36. The display system of item 35, wherein the waveguide is one of a stack of waveguides, each of the stacks of waveguides having an associated multilevel metasurface. (Item 39) Item 39. A display system as described in Item 38, wherein the associated multilevel metasurfaces of at least some of the waveguides are configured to redirect light in a different wavelength range than the associated multilevel metasurfaces of the other waveguides. (Item 40) Item 36. The display system of item 35, further comprising an optical in-coupling optical element disposed on a surface of the waveguide, wherein both the optical in-coupling optical element and the optical out-coupling optical element comprise a multi-level metasurface. (Item 41) Item 36. The display system of item 35, wherein the space between each protrusion and its nearest neighbor defines an overall width of 200 to 500 nm. (Item 42) Item 36. The display system of item 35, wherein the second optically transmissive material forms the spaced apart plateaus across the protrusions. (Item 43) Item 36. The display system of item 35, wherein the first and second optically transmissive materials are amorphous. (Item 44) Item 36. The display system of item 35, wherein the first optically transparent material is a nanoimprint resist. (Item 45) Item 36. The display system of item 35, wherein the second optically transmissive material has a higher refractive index than either the first optically transmissive material or the material forming the waveguide. (Item 46) Item 46. The display system of item 45, wherein the second optically transmissive material has a refractive index greater than 1.7. (Item 47) Item 47. The display system of item 46, wherein the optically transmissive material comprises a semiconductor. (Item 48) Item 48. The display system of item 47, wherein the optically transmissive material comprises silicon. (Item 49) Item 49. The display system of item 48, wherein the optically transmissive material comprises silicon nitride or silicon carbide. (Item 50) Item 47. The display system of item 46, wherein the optically transmissive material comprises an oxide. (Item 51) Item 51. The display system of item 50, wherein the optically transmissive material comprises a metal oxide. (Item 52) Item 52. The display system of item 51, wherein the optically transmissive material comprises titanium oxide, zirconium oxide, or zinc oxide. (Item 53) Item 36. The display system of item 35, wherein the waveguide is formed from a material having a refractive index of 1.6 or higher. (Item 54) Item 36. The display system of item 35, wherein the protrusion is a single-level structure. (Item 55) Item 36. The display system of item 35, wherein the protrusion is a stepped multi-level structure. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0014] [Figure 2] FIG. 2 illustrates an example of a wearable display system.

[0015] [Figure 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0016] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0017] [Figure 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0018] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0019] [Figure 7] FIG. 7 shows an example of an output beam output by a waveguide.

[0020] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0021] [Figure 9A] FIG. 9A illustrates an example of a cross-sectional side view of a set of stacked waveguides, each including an internal coupling optical element.

[0022] [Figure 9B] FIG. 9B illustrates an example of a perspective view of multiple stacked waveguides of FIG. 9A.

[0023] [Figure 10A] FIG. 10A illustrates an example of a cross-sectional side view of a metasurface.

[0024] [Figure 10B] FIG. 10B shows plots of the transmission and reflection spectra for a metasurface having the general structure shown in FIG. 10A.

[0025] [Figure 11] 11A-11B show cross-sectional side-view examples of metasurfaces that incoupling light into a waveguide.

[0026] [Figure 12] 12A-12B show cross-sectional side view examples of metasurfaces for coupling light out of a waveguide.

[0027] [Figure 13]13A-13B show an example of a metasurface operating in transmission mode.

[0028] [Figure 14] 14A-14D illustrate an example process flow for forming a metasurface.

[0029] [Figure 15] FIG. 15 illustrates an enlarged cross-sectional view of the patterned material on the first level of the metasurface.

[0030] [Figure 16-1] 16A1 and 16B-16C illustrate examples of cross-sectional side views of a metasurface structure in which a second material is deposited to different thicknesses across an underlying pattern of protrusions.

[0031] [Figure 16-2] FIG. 16A2 shows plots of the transmission and reflection spectra for a metasurface having the general structure shown in FIG. 16A1.

[0032] [Figure 17] 17A-17C illustrate examples of cross-sectional side views of metasurface structures, where the second material is a resist deposited by spin or jet coating.

[0033] [Figure 18] 18A-18B illustrate examples of cross-sectional side views of metasurfaces having more than two levels.

[0034] [Figure 19] 19A-19D illustrate an example process flow for forming a metasurface having more than two levels.

[0035] The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of the present disclosure. It should be understood that the drawings are schematic and are not necessarily drawn to scale. DETAILED DESCRIPTION OF THE INVENTION

[0036] Metasurfaces, which are metamaterials of reduced dimensions, offer the opportunity to achieve flat and aberration-free optics at a much smaller scale than geometric optics. Without being limited by theory, in some embodiments, metasurfaces comprise a dense array of surface structures that function as resonant optical antennas. The resonant nature of the light-surface structure interaction provides the ability to manipulate the optical wavefront.

[0037] However, while metasurfaces are typically formed using very high refractive index materials, their typical applications are otherwise limited to infrared wavelengths due to their inherently high absorption. For example, metasurfaces for beam shaping have been developed for near-infrared light using high-refractive-index opaque materials such as silicon wafers. However, these metasurface structures based on high-refractive-index materials can undesirably absorb large amounts of impinging light (e.g., 40% or more) when transmitting visible-wavelength light across the thickness of the structure. Visible-wavelength transparent materials such as silicon nitride, with a refractive index of approximately 2, are not considered to have a sufficiently high refractive index to support the optical resonances desired for effectively manipulating optical wavefronts.

[0038] Metasurfaces also face challenges in their fabrication. Given the size of the surface structures that form the metasurface and their characteristic features that are less than the wavelength of the incident light, lithography and etching processes are typically used to fabricate the surface. However, such processes and equipment used for these processes are cost-prohibitive, especially when the metasurface extends across a large surface area that can be thousands of times larger than the characteristic size of the metamaterial structures.

[0039] Advantageously, according to some embodiments disclosed herein, multilevel metasurfaces enable the use of relatively low-index materials while providing highly wavelength-selective redirection of light, including light in the visible portion of the optical spectrum. Preferably, the metasurfaces selectively redirect some wavelengths of light while transmitting other wavelengths of light. While such properties are typically engineered using micron-scale structures (e.g., in crystal fibers or distributed Bragg reflectors), various embodiments herein include nanoscale (e.g., 10-100 times smaller) multilevel geometries to provide selective redirection of light in the visible portion of the electromagnetic spectrum. Such metasurfaces with multilevel functionality offer advantages over stacked architectures of single-functional layers. Furthermore, metasurface structures can be formed by patterning using nanoimprinting, thereby avoiding costly lithography and etching processes.

[0040] In some embodiments, the metasurface is a multilevel (e.g., bilevel) structure having a first level defined by spaced protrusions formed from a first optically transmissive material and a second optically transmissive material between the protrusions. The metasurface also includes a second level formed by a second optically transmissive material disposed on the upper surfaces of the protrusions. The first and second optically transmissive materials may be formed on an optically transmissive substrate, e.g., a waveguide. The first and second optically transmissive materials may be deposited on a substrate. In some embodiments, the first and second optically transmissive materials may be amorphous or crystalline. In some embodiments, the pitch of the protrusions and the height of the first and second levels are configured to redirect light, e.g., by diffraction. In some embodiments, the metasurface may be a three-level or higher structure, where the protrusions take the form of steps and include a second optically transmissive material on both sides and on the upper surface of the protrusions.

[0041] In some embodiments, the pitch of the protrusions is about 10 nm to 1 μm, 10 to 600 nm, about 200 to 500 nm, or about 300 to 500 nm, and the height of each level is about 10 nm to 1 μm, about 10-500 nm, about 50-500 nm, or about 100-500 nm. It should be understood that the pitch of the protrusions and the height (or thickness) of each level may be selected depending on the wavelength of light desired to be redirected and the angle of redirection. In some embodiments, the pitch is less than the wavelength of light the metasurface is configured to redirect. In some embodiments, the second optically transparent material partially or completely occupies the space between the protrusions but does not extend above the protrusions. In some embodiments, the width of the protrusions, as well as the pitch and height of each level, may be selected based on the wavelength of light desired to be redirected and the angle of redirection. By way of example, the protrusions may have a width of about 10 nm to 1 μm, including 10 to 250 nm.

[0042] As disclosed herein, protrusions on a first level, i.e., a level below the upper level of a three or higher level structure, may be patterned by lithography and etching in some embodiments. More preferably, the protrusions may be patterned by nanoimprinting a first optically transparent material. A second optically transparent material may then be deposited between (and, in some embodiments, over) the patterned protrusions. Deposition may be accomplished by various processes, including directional deposition, blanket deposition (e.g., conformal deposition), and spin or jet coating. In some embodiments, the second optically transparent material is deposited to a thickness such that material rests between and on top of the protrusions, forming a plateau of material across each of the protrusions, leaving gaps between the plateau on the upper level and the protrusions on the lower level. In some other embodiments, deposition is allowed to proceed to the extent that the gaps between the protrusions are filled. In still other embodiments, deposition of the second optically transparent material is allowed to proceed to the extent that a continuous layer of the second optically transparent material is formed on the second level.

[0043] In some embodiments, the waveguide may form a direct-view or eyepiece display device, where the waveguide is configured to receive input image information and generate an output image based on the input image information. These devices may be wearable and, in some embodiments, constitute eyewear. The input image information received by the waveguide may be encoded into multiplexed light streams of different wavelengths (e.g., red, green, and blue light) that are internally coupled into one or more waveguides. The internally coupled light may propagate through the waveguide due to total internal reflection. The internally coupled light may be outcoupled (or output) from the waveguide by one or more outcoupling optical elements.

[0044] Advantageously, metasurfaces may be formed on waveguides and may be incoupling and / or outcoupling optical elements. The compactness and planarity of metasurfaces allow for stacks of compact waveguides, where multiple waveguides form a stack, rather than just compact waveguides. In addition, the high wavelength selectivity of metasurfaces allows for high precision incoupling and / or outcoupling light, which can provide high image quality in applications where the light contains image information. For example, high selectivity can reduce channel crosstalk in configurations where a full-color image is formed by simultaneously outputting light of different colors or wavelengths.

[0045] It should be understood that a metasurface may, in some embodiments, selectively redirect light by reflection or diffraction. For example, a metasurface may reflect one or more wavelengths of light while transmitting other wavelengths of light. Advantageously, redirecting light in such a "reflection mode" provides tight control and high specificity of the wavelengths of light redirected by reflection or diffraction. In some other embodiments, a metasurface may function in a "transmission mode," selectively redirecting one or more wavelengths of light while also transmitting light at other wavelengths, without substantially changing the path of those other wavelengths of light.

[0046] Reference is now made to the drawings, wherein like reference numerals refer to like features throughout.

[0047] Exemplary Display Systems The various embodiments disclosed herein may generally be implemented as a display system. In some embodiments, the display system takes the form of eyewear (e.g., they are wearable), which may advantageously provide a more immersive VR or AR experience. For example, a display containing a waveguide for displaying multiple depth planes, e.g., a stack of waveguides (one waveguide or set of waveguides per depth plane), may be configured to be positioned in front of and worn by a user or viewer. In some embodiments, multiple waveguides, e.g., two stacks of waveguides, one for each viewer's eye, may be utilized to provide different images to each eye.

[0048] FIG. 2 illustrates an example of a wearable display system 80. The display system 80 includes a display 62 and various mechanical and electronic modules and systems to support the functionality of the display 62. The display 62 may form eyewear and be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 directly in front of the user's 60 eyes. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user's 60 ear canal (in some embodiments, another speaker, not shown, is positioned adjacent to the user's other ear canal to provide stereo / shapeable sound control). In some embodiments, the display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphones are configured to allow a user to provide input or commands to the system 80 (e.g., voice menu command selections, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of similar display systems). In some embodiments, the display system may include one or more cameras (not shown), which may be mounted to the frame 64 or otherwise attached to the user 60. The cameras may be positioned and oriented to capture images of the surrounding environment in which the user 60 is located.

[0049] 2, the display 62 is operatively coupled 68, such as by wired leads or wireless connectivity, to a local data processing module 70, which may be mounted in a variety of configurations, such as fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, embedded within headphones, or otherwise removably attached to the user 60 (e.g., in a backpack-style configuration, a belt-coupled configuration). The local processing and data module 70 may include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes data a) captured from sensors (e.g., which may be operatively coupled to frame 64 or otherwise attached to user 60), such as image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, and / or gyroscopes, and / or b) obtained and / or processed using a remote processing module 72 and / or a remote data repository 74, possibly for passage to display 62 after such processing or readout. Local processing and data module 70 may be operatively coupled to remote processing module 72 and remote data repository 74 by communication links 76, 78, such as via wired or wireless communication links, such that these remote modules 72, 74 are operatively coupled to each other and available as resources to local processing and data module 70. In some embodiments, location processing and data module 70 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on the frame 64 or may be freestanding structures that communicate with the location processing and data module 70 via wired or wireless communication paths.

[0050] 2, in some embodiments, remote processing module 72 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 74 may comprise a digital data storage facility that may be available through the Internet or other networking configuration in a "cloud" resource configuration. In some embodiments, all data is stored and all calculations are performed within the local processing and data module, allowing for fully autonomous use from the remote module.

[0051] The perception of an image as "three-dimensional" or "3-D" can be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 5, 7, one for each eye 4, 6, are output to the user. The images 5, 7 are spaced from the eyes 4, 6 by a distance 10 along an optical axis, or z-axis, parallel to the viewer's line of sight. The images 5, 7 are flat, and the eyes 4, 6 can focus on the images by assuming a single accommodative state. Such a system relies on the human visual system to combine the images 5, 7 and provide the perception of depth for the combined image.

[0052] However, it should be appreciated that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that viewers of an object may perceive the object as “three-dimensional” due to a combination of vergence and accommodation. Vergence movement of the two eyes relative to one another (i.e., the rolling movement of the pupils toward or away from one another to converge the gaze of the eyes and fixate on an object) is closely linked to the focusing of the eye’s lens (or “accommodation”). Under normal conditions, changing the focus of the eye’s lens, or accommodating the eye to change focus from one object to another at different distances, will automatically produce a matching change in vergence to the same distance, a relationship known as the “accommodation-vergence reflex.” Similarly, changes in vergence-divergence will, under normal conditions, induce matching changes in accommodation. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of the scene, but the eyes view all image information in a single, accommodated state, countering the "accommodation-vergence-divergence reflex." Display systems that offer better matching between accommodation and vergence-divergence may produce more realistic and comfortable simulations of three-dimensional images.

[0053] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. Referring to FIG. 4 , objects at various distances from eyes 4 and 6 on the z-axis are accommodated by eyes 4, 6 such that the objects are in focus. The eyes 4, 6 assume particular accommodated states and focus on objects at different distances along the z-axis. Consequently, a particular accommodated state may be said to be associated with a particular one of depth planes 14 having an associated focal length such that an object or portion of an object at a particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image for each eye 4, 6, and by providing a different presentation of an image corresponding to each of the depth planes. While shown as separate for clarity of illustration, it should be understood that the fields of view of eyes 4, 6 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular accommodative state.

[0054] The distance between an object and eye 4 or 6 can also change the amount of divergence of light from that object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between an object and eye 4 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and eye 4 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the viewer's eye 4 decreases. While only a single eye 4 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 4 may apply to both eyes 4 and 6 of a viewer.

[0055] Without being limited by theory, it is believed that the human eye can typically interpret a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations can be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on different depth planes and / or based on the observation of different image features on different depth planes that are out of focus.

[0056] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 1000 includes a stack of waveguides or stacked waveguide assembly 178 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 182, 184, 186, 188, 190. In some embodiments, display system 1000 is system 80 of FIG. 2, and FIG. 6 shows some portions of system 80 in more detail. For example, waveguide assembly 178 can be part of display 62 of FIG. 2.

[0057] Continuing with reference to FIG. 6 , the waveguide assembly 178 may also include multiple features 198, 196, 194, 192 between the waveguides. In some embodiments, the features 198, 196, 194, 192 may be lenses. The waveguides 182, 184, 186, 188, 190 and / or multiple lenses 198, 196, 194, 192 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. Image injection devices 200, 202, 204, 206, 208 may act as light sources for the waveguides and may be utilized to inject image information into waveguides 182, 184, 186, 188, 190, each configured to disperse incident light across each respective waveguide for output toward eye 4, as described herein. Light exits output surfaces 300, 302, 304, 306, 308 of image injection devices 200, 202, 204, 206, 208 and is injected into corresponding input surfaces 382, ​​384, 386, 388, 390 of waveguides 182, 184, 186, 188, 190. In some embodiments, the input surface 382, ​​384, 386, 388, 390 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 144 or the viewer's eye 4). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed toward the eye 4 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 200, 202, 204, 206, 208 may be associated with and launch light into multiple (e.g., three) waveguides 182, 184, 186, 188, 190.

[0058] In some embodiments, image input devices 200, 202, 204, 206, 208 are each discrete displays that generate image information for input into corresponding waveguides 182, 184, 186, 188, 190, respectively. In some other embodiments, image input devices 200, 202, 204, 206, 208 are outputs of a single multiplexed display that may, for example, send image information to each of image input devices 200, 202, 204, 206, 208 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by image input devices 200, 202, 204, 206, 208 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0059] In some embodiments, the image injection devices 200, 202, 204, 206, 208 may be the output end of a scanning fiber display system, where the image injection devices 200, 202, 204, 206, 208 move or scan across the surfaces of corresponding input surfaces 382, ​​384, 386, 388, 390 of the waveguides 182, 184, 186, 188, 190 to inject image information into those waveguides. An example of such a scanning fiber system is disclosed in U.S. Patent Application No. 14 / 641,376, which is incorporated herein by reference. In some embodiments, more than one of the image injection devices 200, 202, 204, 206, 208 may be replaced by scanning fibers.

[0060] Continuing with reference to FIG. 6 , controller 210 controls the operation of stacked waveguide assembly 178 and image injection devices 200, 202, 204, 206, 208. In some embodiments, controller 210 is part of local data processing module 70. Controller 210 includes programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provisioning of image information to waveguides 182, 184, 186, 188, 190, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 210 may, in some embodiments, be part of processing module 70 or 72 ( FIG. 1 ).

[0061] 6 , the waveguides 182, 184, 186, 188, and 190 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 182, 184, 186, 188, and 190 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 182, 184, 186, 188, and 190 may each include one or more outcoupling optical elements 282, 284, 286, 288, and 290 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide and outputting image information to the eye 4. The extracted light may also be referred to as out-coupled light, and one or more light-outcoupling optical elements may also be referred to as light-extracting optical elements. The extracted light beam is output by the waveguide where light propagating within the waveguide strikes the light-extracting optical element. Some or all of the one or more out-coupling optical elements 282, 284, 286, 288, 290 may be, for example, one or more gratings including diffractive optical features as discussed further herein. Although shown disposed on the bottom major surfaces of the waveguides 182, 184, 186, 188, 190 for ease of explanation and clarity of the drawings, in some embodiments, the one or more outcoupling optical elements 282, 284, 286, 288, 290 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 182, 184, 186, 188, 190, as discussed further herein. In some embodiments, the one or more outcoupling optical elements 282, 284, 286, 288, 290 may be attached to a transparent substrate and formed within a layer of material that forms the waveguides 182, 184, 186, 188, 190. In some other embodiments, the waveguides 182, 184, 186, 188, 190 may be a monolithic piece of material, and one or more outcoupling optical elements 282, 284, 286, 288, 290 may be formed on a surface of and / or within that piece of material.

[0062] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 182, 184, 186, 188, 190 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 182 closest to the eye may be configured to deliver collimated light to the eye 4 as it is launched into such waveguide 182. The collimated light may represent an optical infinity focal plane. The next upper waveguide 184 may be configured to send collimated light that passes through a first lens 192 (e.g., a negative lens) before reaching the eye 4. Such first lens 192 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 184 as emerging from a first focal plane closer inward from optical infinity toward the eye 4. Similarly, the third upper waveguide 186 passes its output light through both the first lens 192 and the second lens 194 before reaching the eye 4. The combined refractive power of the first lens 192 and the second lens 194 may be configured to produce another, increasing amount of wavefront curvature so that the eye / brain interprets the light emerging from the third waveguide 186 as emerging from a second focal plane closer inward toward the person from optical infinity, which was the light from the next upper waveguide 184. Other methods of producing these perceived colors are also possible.

[0063] The other waveguide layers 188, 190 and lenses 196, 198 are similarly configured, with the highest waveguide 190 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 198, 196, 194, 192 when viewing / interpreting light originating from the world 144 on the other side of the stacked waveguide assembly 178, a compensating lens layer 180 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 198, 196, 194, 192. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Either or both of the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, either or both may be dynamic using electro-active features.

[0064] In some embodiments, two or more of the waveguides 182, 184, 186, 188, 190 may have the same associated depth plane. For example, multiple waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same multiple depth planes, with one set per depth plane. This can provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0065] 6 , one or more outcoupling optical elements 282, 284, 286, 288, 290 may be configured to both redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with that waveguide. As a result, waveguides with different associated depth planes may have different configurations of one or more outcoupling optical elements 282, 284, 286, 288, 290, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, features 198, 196, 194, 192 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0066] In some embodiments, one or more outcoupling optical elements 282, 284, 286, 288, 290 are diffractive features that form a diffraction pattern or "diffractive optical element" (also referred to herein as a "DOE"). Preferably, the DOE has a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 4 with each intersection point of the DOE, while the remainder continues traveling through the waveguide via total internal reflection. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a very uniform pattern of output emission toward the eye 4 for this particular collimated beam bouncing within the waveguide.

[0067] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets can be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets can be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0068] FIG. 7 shows an example of an output beam output by a waveguide. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 178 (FIG. 6) may function similarly, and that waveguide assembly 178 includes multiple waveguides. Light 400 is launched into waveguide 182 at input surface 382 of waveguide 182 and propagates within waveguide 182 by TIR. At the point where light 400 impinges on DOE 282, a portion of the light exits the waveguide as output beam 402. Output beam 402 is illustrated as being approximately parallel, but may be redirected to propagate to eye 4 at an angle (e.g., forming a diverging output beam), as discussed herein and depending on the depth plane associated with waveguide 182. It should be understood that a substantially collimated exit beam may refer to a waveguide with one or more outcoupling optical elements that outcouple light to form an image that appears to be set at a depth plane at a long distance (e.g., optical infinity) from the eye 4. Other waveguides or other sets of outcoupling optical elements may output a more divergent exit beam pattern, which would require the eye 4 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 4 than optical infinity.

[0069] FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. In some embodiments, a full-color image may be formed at each depth plane by overlaying an image in each of the primary colors, for example, three or more primary colors. The illustrated embodiment shows depth planes 14a-14f, but more or fewer depths are also contemplated. Each depth plane may have three primary color images associated with it: a first image in a first color G, a second image in a second color R, and a third image in a third color B. The different depth planes are indicated in the diagram by different numbers for diopters following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image.

[0070] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, resulting in three primary color images per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0071] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors, including magenta and cyan, may be used in addition to or may replace one or more of the red, green, or blue colors.

[0072] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0073] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates an example of a cross-sectional side view of a plurality or set 1200 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. While stack 1200 may correspond to stack 178 ( FIG. 6 ), and the illustrated waveguides of stack 1200 may correspond to a portion of multiple waveguides 182, 184, 186, 188, 190, it should be understood that light from one or more of image injection devices 200, 202, 204, 206, 208 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0074] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes an associated internal coupling optical element, e.g., internal coupling optical element 1212 is disposed on a major surface (e.g., bottom major surface) of waveguide 1210, internal coupling optical element 1224 is disposed on a major surface (e.g., bottom major surface) of waveguide 1220, and internal coupling optical element 1232 is disposed on a major surface (e.g., bottom major surface) of waveguide 1230. In some embodiments, one or more of the internal coupling optical elements 1212, 1222, 1232 may be disposed on the top major surface of the respective waveguides 1210, 1220, 1230 (particularly, one or more internal coupling optical elements are transmissive deflecting optical elements). Preferably, the internal coupling optical elements 1212, 1222, 1232 are disposed on the bottom major surface of their respective waveguides 1210, 1220, 1230 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are reflective polarizing optical elements. In some embodiments, the internal coupling optical elements 1212, 1222, 1232 may be disposed within the body of the respective waveguides 1210, 1220, 1230. In some embodiments, as discussed herein, the internal coupling optical elements 1212, 1222, 1232 are wavelength selective so as to selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of the respective waveguides 1210, 1220, 1230, it should be understood that the internal coupling optical elements 1212, 1222, 1232 may be located within other areas of the respective waveguides 1210, 1220, 1230 in some embodiments.

[0075] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 1214 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, optically dispersive element 1224 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and optically dispersive element 1234 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some other embodiments, optically dispersive elements 1214, 1224, 1234 may be disposed on the bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively. In some other embodiments, the optically dispersive elements 1214, 1224, 1234 may be disposed on both the top and bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively, or the optically dispersive elements 1214, 1224, 1234 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 1210, 1220, 1230, respectively.

[0076] The waveguides 1210, 1220, 1230 may be spaced apart and separated by solid layers of gas and / or material. For example, as shown, layer 1218a may separate waveguides 1210 and 1220, and layer 1218b may separate waveguides 1220 and 1230. In some embodiments, layers 1218a and 1218b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent ones of waveguides 1210, 1220, 1230). Preferably, the refractive index of the material forming layers 1218a, 1218b is 0.05 or more, or 0.10 or more, less than the refractive index of the material forming waveguides 1210, 1220, 1230. Advantageously, the lower refractive index layers 1218a, 1218b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 1210, 1220, 1230 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 1218a, 1218b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 1200 may include immediate cladding layers.

[0077] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 1210, 1220, 1230 are similar or the same, and the materials forming the layers 1218a, 1218b are similar or the same. In some embodiments, the materials forming the waveguides 1210, 1220, 1230 may differ between one or more waveguides, and / or the materials forming the layers 1218a, 1218b may differ while still maintaining the various refractive index relationships discussed above.

[0078] 9A, light rays 1240, 1242, 1244 enter waveguide set 1200. It should be understood that light rays 1240, 1242, 1244 may be injected into waveguides 1210, 1220, 1230 by one or more image injection devices 200, 202, 204, 206, 208 (FIG. 6).

[0079] Preferably, light beams 1240, 1242, 1244 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. In some embodiments, incoupling optical elements 1212, 122, 1232 each selectively deflect one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0080] For example, internal coupling optical element 1212 may be configured to selectively deflect (e.g., reflect) light ray 1240 having a first wavelength or wavelength range while transmitting light rays 1242 and 1244 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light ray 1242 then impinges on and is deflected by internal coupling optical element 1222, which is configured to selectively deflect (e.g., reflect) light of the second wavelength or wavelength range. Light ray 1244 is transmitted by internal coupling optical element 1222 and continues to be deflected by impinging on and being deflected by internal coupling optical element 1232, which is configured to selectively deflect (e.g., reflect) light of the third wavelength or wavelength range.

[0081] 9A , the deflected light rays 1240, 1242, 1244 are deflected to propagate through the corresponding waveguides 1210, 1220, 1230. That is, the in-coupling optical element 1212, 1222, 1232 of each waveguide deflects the light into its corresponding waveguide 1210, 1220, 1230, in-coupling the light into the corresponding waveguide. The light rays 1240, 1242, 1244 are deflected at an angle that causes the light to propagate through the respective waveguides 1210, 1220, 1230 by TIR.

[0082] Continuing with reference to FIG. 9A, light rays 1240, 1242, 1244 propagate through the respective waveguides 1210, 1220, 1230 by TIR until they impinge on the corresponding optically dispersive elements 1214, 1224, 1234 of the waveguides.

[0083] 9B, an example of a perspective view of the multiple stacked waveguides of FIG. 9A is illustrated. As previously described, the in-coupled light rays 1240, 1242, and 1244 are deflected by the in-coupling optical elements 1212, 1222, and 1232, respectively, and then propagate by TIR within the waveguides 1210, 1220, and 1230, respectively. The light rays 1240, 1242, and 1244 then impinge on the optically dispersive elements 1214, 1224, and 1234, respectively. The optically dispersive elements 1214, 1224, and 1234 deflect the light rays 1240, 1242, and 1244 to propagate toward the out-coupling optical elements 1250, 1252, and 1254, respectively.

[0084] In some embodiments, the optically dispersive elements 1214, 1224, 1234 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs both deflect or disperse light into the out-coupling optical elements 1250, 1252, 1254 and also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, for example, if the beam size is already the desired size, the optically dispersive elements 1214, 1224, 1234 may be omitted and the in-coupling optical elements 1212, 1222, 1232 may be configured to deflect light directly into the out-coupling optical elements 1250, 1252, 1254. For example, with reference to FIG. 9A , the optically dispersive elements 1214, 1224, 1234 may be replaced with the out-coupling optical elements 1250, 1252, 1254, respectively, in some embodiments. In some embodiments, the outcoupling optical elements 1250, 1252, 1254 are exit pupils (EP) or exit pupil expanders (EPE) that direct light to the viewer's eye 4 (FIG. 7).

[0085] 9A and 9B, in some embodiments, a waveguide set 1200 includes, for each primary color, waveguides 1210, 1220, 1230, in-coupling optical elements 1212, 1222, 1232, optically dispersive elements (e.g., OPEs) 1214, 1224, 1234, and out-coupling optical elements (e.g., EPs) 1250, 1252, 1254. The waveguides 1210, 1220, 1230 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 1212, 1222, 1232 redirect or deflect the desired color into its appropriate waveguide while transmitting light of other colors. The light then propagates at an angle that will result in TIR within the individual waveguides 1210, 1220, 1230. In the example shown, light ray 1242 (e.g., green light) would reflect from the first in-coupling optical element (e.g., color filter) 1212, then continue bouncing back down the waveguide, interacting with the light-dispersive element (e.g., OPE) 1214 and then the out-coupling optical element (e.g., EP) 1250, in the manner described above. Light rays 1242 and 1244 (e.g., blue and red light) would pass through the in-coupling optical element (e.g., color filter) 1212 into the next waveguide 1220. Light ray 1242 would reflect from the next in-coupling optical element (e.g., color filter) 1222, then, via TIR, bounce back down the waveguide 1220, proceeding to its light-dispersive element (e.g., OPE) 1224 and then the out-coupling optical element (e.g., EP) 1252. Finally, light ray 1244 (e.g., red light) will pass through the internal coupling optical element (e.g., color filter) 1232 into that waveguide 1230, where it will propagate to its optical dispersion element (e.g., OPE) 1234, then to the external coupling optical element (e.g., EP) 1254, and finally be externally coupled to the viewer along with light from the other waveguides 1210, 1220.

[0086] (Metasurface) FIG. 10A illustrates an example of a metasurface, according to some embodiments. A substrate 2000 has a surface 2000a on which a metasurface 2010 is disposed. The metasurface 2010 includes multiple levels of optically transparent material. As shown, in some embodiments, the metasurface is a bi-level structure having first and second levels 2012, 2014, respectively. The first level 2012 includes multiple protrusions 2020 formed from the first optically transparent material and masses 2030a of the second optically transparent material between the protrusions. The second level 2014 is located on the protrusions (spaced and separated from the substrate by the first level) and includes second-level masses 2030b of the second optically transparent material formed on the protrusions 2020. The protrusions 2020 may be ridges (or nanowires) that extend laterally into and out of the page, defining trenches between neighboring protrusions. As shown, at the second level 2014, the mass 2030b of the second optically transmissive material may be localized on the surface of the protrusion 2020, forming a plateau of material spaced apart from other localized deposits (or plateaus) of the second optically transmissive material.

[0087] Preferably, the refractive index of the second optically transparent material forming masses 2030a, 2030b is higher than the refractive index of both the first optically transparent material forming protrusions 2020 and the material forming substrate 2000. In some embodiments, the refractive index of the first optically transparent material is lower than or similar to the refractive index of the material forming substrate 2000. It should be understood that substrate 2000 may be a waveguide and may correspond to waveguides 182, 184, 186, 188, 190 (FIG. 6) and / or waveguides 1210, 1220, and 1230 (FIG. 9A). In such applications, the substrate preferably has a relatively high refractive index, e.g., greater than 1.5, 1.6, 1.7, 1.8, or 1.9, which can provide advantages in increasing the field of view and forming images in a display outputting light from that substrate 2000. In some embodiments, the substrate 2000 is formed from glass (e.g., doped glass), lithium niobate, plastic, polymer, sapphire, or other optically transmissive material. Preferably, the glass, plastic, polymer, sapphire, or other optically transmissive material has a high refractive index, for example, greater than 1.5, 1.6, 1.7, 1.8, or 1.9.

[0088] Continuing with reference to FIG. 10A , the first optically transparent material of protrusion 2020 is preferably a material that can be patterned, for example, by lithography and etching processes. More preferably, the first optically transparent material is a nanoimprint resist that can be patterned by nanoimprinting. As discussed herein, the second optically transparent material forming masses 2030a, 2030b has a refractive index higher than both the first optically transparent material of protrusion 2020 and the material forming substrate 2000. In some embodiments, the refractive index of the second optically transparent material is higher than 1.6, 1.7, 1.8, or 1.9. Examples of materials for the second optically transparent material include semiconductor materials and oxides, including silicon-containing materials. Examples of silicon-containing materials include silicon nitride and silicon carbide. Examples of oxides include titanium oxide, zirconium oxide, and zinc oxide. In some embodiments, the second optically transparent material may have a lower optical transparency. For example, the second optically transparent material may be silicon or a derivative thereof. In some embodiments, the first and second optically transparent materials 2020, 2030 are amorphous solid-state materials or crystalline solid-state materials. Without being limited by theory, amorphous materials may be desirable in some applications because they can be formed at lower temperatures and over larger surfaces than some crystalline materials. In some embodiments, the first and second optically transparent materials forming features 2020, 2030a, 2030b may each be one of amorphous or crystalline semiconductor materials.

[0089] 10A , the protrusions have a pitch 2040. As used herein, pitch refers to the distance between two immediately adjacent structural similarities. Similarities should be understood to be similar in that they are located in similar portions of the structure (e.g., left or right edges) that are substantially the same. For example, the pitch of a protrusion 2020 is equal to the overall width defined by the protrusion 2020 and the immediate separation between the protrusion and its immediately similar protrusions 2020. In other words, the pitch can be understood to be the width of a repeating unit of the array of features formed by those protrusions 2020 (e.g., the sum of the widths of the protrusions 2020 and the chunks 2030a).

[0090] As shown, different wavelengths (corresponding to different colors) of light can impinge on the metasurface, and as discussed herein, the metasurface is highly selective in redirecting light of specific wavelengths. This selectivity may be achieved based on the pitch and physical parameters of the features of the first and second levels 2012, 2014, as discussed herein. The pitch of the protrusions 2020, in some embodiments, is less than the wavelength of light desired for zero-order reflection light redirection. In some embodiments, the geometric size and periodicity increase with longer wavelengths, and the height or thickness of one or both of the protrusions 2020 and the masses 2030a, 2030b also increase with longer wavelengths. The illustrated light rays 2050a, 2050b, and 2050c, in some embodiments, correspond to light of different wavelengths and colors. In the illustrated embodiment, the metasurface has a pitch that causes light ray 2050b to be reflected while light rays 2050a and 2050c propagate through substrate 2000 and metasurface 2010.

[0091] Advantageously, multilevel metasurfaces are highly selective for specific wavelengths of light. Figure 10B shows plots of transmission and reflection spectra for a metasurface having the general structure shown in Figure 10A. In this example, protrusions 2020 are 125 nm wide, 25 nm thick, and formed from resist; chunks of material 2030a and 2030b are 75 nm thick and formed from silicon nitride; the pitch is 340 nm; and an air gap separates chunks 2030b. The horizontal axis represents wavelength, while the horizontal axis represents transmittance (on a scale of 0 to 1.00, from no reflection to total reflection). Notably, a sharp peak in reflectance (517 nm) and a concomitant decrease in transmittance are observed for a narrow band of wavelengths, while other wavelengths are transmitted. Light is reflected when the wavelength matches the resonant wavelength (approximately 517 nm in this example). The protrusions 2020 and superstrate 2030 are arranged with subwavelength spacing, and only zero-order reflection and transmittance are present. As shown in Figure 10B, the reflection spectrum exhibits a sharp peak across the visible wavelength range, which is characteristic of optical resonance.

[0092] It should be understood that the pitch of the metasurface structures (e.g., the pitch of the protrusions 2020 and the overlying structure 2030) may be modified to change the light redirecting properties of the metasurface. For example, when the pitch is larger, light at the resonant wavelength will be diffracted (or deflected at a non-normal angle, e.g., less than 90 degrees relative to the surface of the substrate 2000) upon incidence on the metasurface 2010. In some embodiments, when the substrate 2000 is a waveguide, the pitch of the metasurface structures may be selected so that light at the resonant wavelength propagates through the waveguide by total internal reflection (TIR), while other wavelengths and colors are deflected at an angle such that they will be transmitted through the metasurface 2010. In such an arrangement, the metasurface 2010 may be said to be an internal coupling optical element, incoupling the deflected light. FIGS. 11A-11B show examples of cross-sectional side views of a metasurface incoupling light into a waveguide.

[0093] FIG. 11A shows one wavelength of light being internally coupled, while FIG. 11B shows a different wavelength of light being internally coupled. The resonant wavelength of metasurface 2010 can be engineered by varying the geometric size of its constituent structures. For example, a metasurface resonating at red wavelengths (FIG. 11B) has a larger geometric size and periodicity than a metasurface resonating at green wavelengths (FIG. 11A). In some embodiments, the pitch of protrusions 2020 is about 10 nm to 1 μm, 10 to 600 nm, about 200 to 500 nm, or about 300 to 500 nm, and the height of each level is about 10 nm to 1 μm, about 10 to 500 nm, about 50 to 500 nm, or about 100 to 500 nm. In some embodiments, the height of second level 2014 is different from that of the first level. For example, the height of the second level 2014 may be about 10 nm to 1 μm or about 10 to 300 nm, and the height of the first level may be about 10 nm to 1 μm or 10 to 500 nm. In some embodiments, the metasurface 2010 may form one or more of the internal coupling optical elements 1212, 1222, 1232 (FIG. 9A) as shown and may receive light rays 1240, 1242, 1244.

[0094] It should be understood that metasurface 2010 will also deflect light impinging on it from within optical waveguide 2000. Taking advantage of this functionality, in some embodiments, the metasurfaces disclosed herein may be applied to form outcoupling optical elements. FIGS. 12A-12B show examples of cross-sectional side views of metasurfaces outcoupling light from a waveguide. FIG. 12A shows the outcoupling of light of one wavelength, while FIG. 12B shows the outcoupling of light of a different wavelength. As disclosed herein, the resonant wavelength of metasurface 2010 can be engineered by varying the geometric size of its constituent structures, thereby providing wavelength selectivity. As an example, a larger geometric size and periodicity ( FIG. 12B ) may be used to provide a metasurface that resonates at wavelengths of red light, while a relatively smaller geometric size and periodicity may be used to provide a metasurface that resonates at wavelengths of green light ( FIG. 12A ). In some embodiments, metasurface 2010 may form one or more of external coupling optical elements 282, 284, 286, 288, 290 (FIG. 6) or 1250, 1252, 1254 (FIG. 9B) instead of or in addition to forming internal coupling optical elements. It should be understood that when different waveguides have different associated primary colors, the external coupling optical element and / or internal coupling optical element associated with each waveguide that is fabricated will have a specific geometric size and / or periodicity for the wavelength or color of light that the waveguide is configured to propagate. Thus, different waveguides may have metasurfaces with different geometric sizes and / or periodicities. As an example, a metasurface for internally or externally coupling red, green, or blue light may have a geometric size and / or periodicity (pitch) configured to redirect or diffract light at wavelengths of 638 nm, 520 nm, and 455 nm, respectively.

[0095] In some embodiments, the metasurface 2010 may have a geometric size and / or pitch that causes the metasurface to impart optical power to the diffracted light. For example, the metasurface may be configured to cause light to exit the metasurface in a diverging or converging direction. Different portions of the metasurface may have different pitches that deflect different light rays in different directions, e.g., so that the light rays diverge or converge.

[0096] In some other embodiments, the metasurface may deflect light such that it propagates from the metasurface as collimated rays of light. For example, if collimated light impinges on the metasurface at a similar angle, the metasurface may have a consistent geometric size and consistent pitch across the entire metasurface and deflect the light at a similar angle.

[0097] 11A-12B, as shown, the metasurface 2010 may deflect light in a "reflective mode," in which polarized light remains on the same side of the metasurface before and after striking the metasurface, while light of wavelengths that are not reflected is transmitted across the thickness of the metasurface. In some embodiments, the metasurface may deflect light in a "transmissive mode," in which both polarized and unpolarized light are transmitted across the thickness of the metasurface, with the path of polarized light being different after exiting the metasurface, while the path of unpolarized light is substantially unchanged. It should be understood that a metasurface may have both transmissive and reflective functionality; for example, in some embodiments, the metasurface may reflect a portion of incident light while transmitting and deflecting another portion of that light.

[0098] 13A-13B show an example of metasurface 2010 operating in a transmission mode. Referring to FIG. 13A, light rays 1240 and 1244 propagate through the metasurface substantially undeflected while light ray 1242 is deflected. Light ray 1242 may be at a resonant wavelength for metasurface 2010, while light rays 1240 and 1244 are not. In some embodiments, the deflection may be used to incouple or outcouple light ray 1240. FIG. 13B shows an example of a metasurface configured to operate in a transmission mode for optical incoupling. In some embodiments, as shown, light rays 1240, 1242, and 1244 each have a different wavelength (e.g., corresponding to a different color), and metasurfaces 1212, 1222, and 1232 are each selective for deflecting a particular wavelength or range of wavelengths. For example, metasurface 1212 may selectively deflect light ray 1240 in a transmission mode while transmitting light rays 1242 and 1244 without deflection. Similarly, as shown, metasurface 1222 may selectively deflect light ray 1242 in a transmission mode while transmitting light ray 1244 without deflection, and metasurface 1232 may selectively deflect light ray 1244 in a transmission mode. In some other embodiments, transmission-mode metasurfaces may also be applied as outcoupling optical elements, such as one or more of outcoupling optical elements 282, 284, 286, 288, 290 ( FIG. 6 ) or 1250, 1252, 1254 ( FIG. 9B ).

[0099] Metasurfaces that function in transmission mode may offer advantages in some applications, such as when utilized on a waveguide in conjunction with other transmission optical elements (such as some embodiments of optically dispersive elements 1214, 1224, 1234 and / or outcoupling optical elements 1250, 1252, 1254 in FIG. 9B). Such transmission-mode metasurfaces may be formed on the same side of the substrate as the other optical elements, which may have the advantage of facilitating processing of the metasurface and optical elements while reducing the likelihood of damaging the metasurface or optical elements (as may occur when processing is required on two sides of the substrate).

[0100] 14A-14D illustrate an example process flow for forming metasurface 2010. Referring to FIG. 14A, a first material 2020a, e.g., a resist (such as a nanoimprint resist), is deposited on substrate 2000. Resist 2020a is preferably optically transparent and may be deposited by, for example, spin coating to form a layer of resist. In some embodiments, resist 2020a may be deposited by jet coating (e.g., inkjet printing), which may offer the advantage of forming very thin layers, as well as layers with variable composition and / or thickness. As shown, resist 2020a may be delivered to substrate 2000 from a resist source 2022.

[0101] 14B, an imprint template or master 2024 is brought into contact with resist 2020a to pattern the resist. It should be understood that the pattern in imprint template 2024 may be formed by lithography, including, for example, electron beam lithography or EUV lithography. However, the same template may be reused to pattern resist on multiple substrates, thereby reducing the per-unit processing cost for the ultimately formed metasurface.

[0102] After contacting the imprint template 2024, the resist 2020a takes on the pattern defined by the openings in the template 2024. In some embodiments, the resist 2020a may be hardened, for example by exposure to light (such as UV light) and / or heat, to immobilize the resist. The template 2024 may then be removed, leaving behind the patterned resist 2020, as shown in FIG. 14C.

[0103] Referring to FIG. 14D , a second material 2030 is subsequently deposited on the patterned resist 2020. Examples of materials for the second material 2030 include semiconductor materials, including silicon-containing materials such as silicon nitride and silicon carbide; oxides, including zirconium oxide, zinc oxide, and titanium oxide; and optically transparent resists. As disclosed herein, the second material 2030 is preferably an optically transparent material. The second material 2030 may be deposited by various processes, including blanket deposition, directional deposition, and spin or jet coating. Examples of blanket deposition include chemical vapor deposition (CVD), in which the resist is exposed to mutually reactive precursors simultaneously present in a deposition chamber containing the substrate 2000, and atomic layer deposition (ALD), in which the resist is alternately exposed to precursors. ALD may offer the advantage of precisely controlling the thickness of the deposited layer when high precision is desired and when forming the deposited material at low temperatures. Examples of directional deposition include evaporation and sputtering to deliver the second material to the resist 2020 and substrate 2000 to be nanoimprinted.

[0104] Referring now to FIG. 15, an enlarged cross-sectional view of patterned material 2020 on a first level metasurface is shown. As shown, the patterned layer of material may have a residual layer thickness (RLT) 2021 that remains unpatterned. Such residual layer thickness is typical of nanoimprinting and may be present in various embodiments herein (not shown). It should be understood that if protrusions 2020 are formed from imprinted resist, the resist may be sensitive to high temperatures. Preferably, the deposition temperature for second level material 2030 is within 30-50 degrees Celsius of the glass transition temperature (Tg) of the resist. More preferably, the deposition temperature is below Tg. In some embodiments, the aspect ratio (AR, h:w) of each protrusion is less than about 3-4 (e.g., AR<3-4). In some embodiments, the aspect ratio is about 1. In some embodiments, the refractive index of the resist is about 1.2-2.0.

[0105] 16A1-16C, it should be understood that various methods for depositing second material 2030 may be utilized to provide different profiles for metasurface 2010 by providing second material 2030 in different locations, including different levels relative to protrusions 2030. FIGS. 16A1 and 16B-16C illustrate examples of cross-sectional side views of metasurface structures in which the second material is deposited to different thicknesses across an underlying pattern of protrusions. In FIG. 16A1, metasurface 2010 is defined by a bi-level structure with voids between protrusions 2020 and the masses of second material 2030a and 2030b deposited on the protrusions. It should be understood that if the deposition is a directional deposition process, the second material is substantially localized on the top surfaces of the protrusions and in the spaces between the protrusions 2020, with no or only minimal material on the sides of the protrusions. If the deposition is a conformal blanket deposition, the second material 2030 is deposited on top of, between, and on the sides of the protrusions 2020. While FIG. 16A1 illustrates a portion of the second material on the sides of the protrusions 2020, this material 2030 on the sides is not necessarily to scale. In some embodiments, the material 2030 forms a blanket layer having a substantially constant thickness across all surfaces, including the sidewalls of the protrusions 2020. As discussed herein, such a blanket layer may be deposited by, for example, ALD.

[0106] FIG. 16A2 shows plots of transmission and reflection spectra for a metasurface having the general structure shown in FIG. 16A1. The horizontal axis represents the angle of incidence of light, and the horizontal axis represents transmittance (on a scale of 0 to 1). In this example, protrusions 2020 are formed from resist and have a thickness of 100 nm and a width of 130 nm, and overlying material 2030 is a conformal blanket layer of silicon nitride having a substantially constant thickness of 60 nm, with a pitch of 382 nm, and voids separating the nodules 2030b. As can be seen in FIG. 16A2, the metasurface advantageously has a wide range of incident angles over which it reflects light. For example, the metasurface is highly light reflective with angles of about ±0.25 radians relative to the metasurface normal (e.g., relative to the thickness axis of the metasurface).

[0107] 16B illustrates a metasurface defined by a bilevel structure with no gaps between the protrusions 2020. The second material has been deposited to the extent that the gaps between the protrusions 2020 are completely filled with blobs 2030a. The deposition to achieve what is shown is directional deposition, but conformal blanket deposition would also achieve a similar structure (albeit with some broadening of the plateau formed by the material 2030 on the upper levels of the metasurface structure).

[0108] 16C illustrates a metasurface defined by a bi-level structure with a thick, continuous upper-level layer 2030b. In some embodiments, such a layer 2030b may be achieved using conformal blanket deposition, completely filling the gaps between the protrusions 2020 and then continuing to the extent that the mass 2030b forms a continuous layer across the protrusions 2020.

[0109] 17A-17C illustrate examples of cross-sectional side views of metasurface structures, where the second material is a resist deposited by spin or jet coating. Preferably, the resist is a high-refractive index resist with a refractive index higher than 1.6, 1.7, 1.8, or 1.9. Advantageously, varying the viscosity of the resist and coating conditions allows different structures to be created. In FIG. 17A, the resist is deposited on the protrusions 2020 but has a low enough viscosity to settle into the gaps between the protrusions, thereby forming a metasurface with globs 2030a and no residual top layer. In FIG. 16B, a sufficient amount of resist is deposited so that the gaps between the protrusions 2020 are filled with globs 2030a of resist, while no residual top layer is present. In FIG. 16C, a sufficient amount of resist is deposited so that the gaps between the protrusions 2020 are filled with globs 2030a, while also forming a continuous residual top layer formed by globs 2030b.

[0110] While some embodiments take the form of a bilevel structure, it should be understood that the metasurfaces disclosed herein may include more than two levels. For example, a metasurface may include three or more levels. These three or higher level structures may be formed using stepped protrusions. The lower levels (closest to the substrate) may include portions of the protrusion formed from a first optically transparent material and a mass of a second optically transparent material on the sides of the protrusion, while the highest level (farthest from the substrate) preferably contains only the second optically transparent material deposited on the top surface of the highest step of the protrusion. Preferably, n-1 levels of stepped protrusions are utilized to form an n-level metasurface, with the step on each successive level having a smaller width than the step on the level immediately below. In some embodiments, the steps are symmetric about an axis extending the height of the protrusion, as seen in a cross-sectional side view taken transverse to the axis of extension of the protrusion. It is contemplated that these three or higher level metasurfaces may be applied in the same application (eg, as incoupling and / or outcoupling optical elements) as a bi-level metasurface.

[0111] 18A-18B illustrate examples of cross-sectional side views of metasurfaces having more than two levels. FIG. 18A illustrates a metasurface 2010 having first, second, and third levels 2012, 2014, and 2016, respectively. The tri-level metasurface 2010 is formed using stepped protrusions 2020, each extending across two levels, one step on each level, with the width of the step on the second level being less than the width of the step on the first level. A second mass of optically transmissive material 2030a is formed on the side of the protrusion 2020 on the first level 2012, preferably extending continuously from one protrusion 2020 to the nearest protrusion 2020. A second mass of optically transmissive material 2030b is formed on the side of the protrusion 2020 on the second level 2014. On the third level, globs 2030c of second optically transmissive material are formed on the top surfaces of protrusions 2020. As shown, the amount of second optically transmissive material deposited, in conjunction with the step height of protrusions 2020, is such that the second optically transmissive material does not have a thickness that occupies the entire height of a given level. In a sense, voids exist at a given level in the spaces between adjacent protrusions 2020.

[0112] 18B illustrates a metasurface similar to that of FIG. 18A, but in which the sides of the protrusions 2020 are not exposed. It should be understood that the sides of the protrusions 2020 may be covered by depositing a second optically transparent material on each level in an amount sufficient to completely fill the spaces between the nearest protrusions 2020.

[0113] 19A-19D illustrate example process flows for forming metasurfaces having more than two levels. In some embodiments, the process flow may proceed using processes similar to those of FIGS. 14A-14D , but the imprint template 2026 is a multilevel structure configured for imprinting multilevel protrusions. Such a multilevel imprint template 2026 may be formed by multiple-exposure lithography, including, for example, multiple-exposure electron-beam lithography or multiple-exposure EUV lithography. In some embodiments, each exposure may be used to pattern a negative step or level for the multilevel protrusions.

[0114] 19A, a first material 2020a, for example, a resist (such as a nanoimprint resist), is deposited on a substrate 2000. The resist 2020a is preferably optically transparent and may be deposited as described above with respect to FIG.

[0115] Referring to Figure 19B, an imprint template or master 2026 is brought into contact with the resist 2020a to pattern the resist. After contacting the imprint template 2026, the resist 2020a takes on a pattern containing stepped protrusions 2020. As described herein, the resist may be cured to immobilize it before removing the template 2026. The resulting stepped multi-level protrusions are shown in Figure 19C.

[0116] Referring to Figure 19D, a second material is then deposited on the patterned resist. As described herein, examples of materials for the second material include semiconductor materials, including silicon-containing materials such as silicon nitride and silicon carbide; oxides, including zirconium oxide, zinc oxide, and titanium oxide; and optically transparent resists. The second material is preferably an optically transparent material. The second material may be deposited by a variety of processes, including blanket deposition, directional deposition, and spin- or jet-coating, as described above with respect to Figure 14D.

[0117] Although not shown, it should be understood that by using appropriate selection of deposition process, deposition time, and / or deposition conditions, the physical structure of the metasurface may be varied as illustrated in FIGS. 16A1 and 16B-17C. The deposition described with respect to any of those FIGS. 16A1 and 16B-17C may be applied to a three- or higher-level metasurface. For example, the presence of voids between protrusions 2020 may be achieved by a deposition that does not reach the full height of a particular level. Alternatively, enough second optically transparent material may be deposited to completely fill the metal surface of all levels, such that a continuous layer of the second material extends over the top of the protrusions 2020.

[0118] In some embodiments, waveguide 2000 having metasurface 2010 (as an incoupling and / or outcoupling optical element) may be used to form a display system, such as system 1000 ( FIG. 6 ), disclosed herein. For example, after fabrication of metasurface 2010, 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, in some embodiments, be an optical fiber. Examples of light pipes include image injection devices 200, 202, 204, 206, 208 ( FIG. 6 ) and scanning optical fibers. In some embodiments, multiple waveguides, each having metasurface 2010, may be provided, and each of these waveguides may be optically coupled to one or more image injection devices.

[0119] Various exemplary embodiments of the present invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate the more broadly applicable aspects of the invention. Various modifications may be made to the invention described, and equivalents may be substituted without departing from the true spirit and scope of the invention.

[0120] For example, while advantageously utilized with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by a system that provides images on a single depth plane. Furthermore, while illustrated as being on a single surface of a substrate, it should be understood that metasurfaces may be disposed on multiple substrate surfaces (e.g., opposing major surfaces of a waveguide). In some embodiments where multiplexed image information (e.g., light of different colors) is directed into the waveguide, multiple metasurfaces may be provided on the waveguide, e.g., one active metasurface per color of light. In some embodiments, the pitch or periodicity and / or geometric size of the protrusions forming the metasurface may vary across the metasurface. Such metasurfaces may be active in redirecting light of different wavelengths depending on the geometry and pitch at which the light strikes the metasurface. In some other embodiments, the geometry and pitch of the metasurface features are configured to vary so that deflected light rays, even of similar wavelengths, propagate from the metasurface at different angles. It should also be understood that multiple separated metasurfaces may be disposed across the substrate surface, and in some embodiments, the metasurfaces each have the same geometry and pitch, or in some other embodiments, at least some of the metasurfaces have a different geometry and / or pitch than the other metasurfaces.

[0121] Although advantageously applied to displays such as wearable displays, metasurfaces may also be applied to a variety of other devices where a compact, thin light redirecting element is desired. For example, metallic surfaces may generally be applied to form the light redirecting portions of optical plates (e.g., glass plates), optical fibers, microscopes, sensors, watches, cameras, and image projection devices.

[0122] In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process acts or steps, to the objective, spirit, or scope of the present invention. Moreover, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein has discrete components and features that can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

[0123] The present invention includes methods that may be performed using the present device. The method may include the act of providing such a suitable device. Such provision may be performed by a user. In other words, the act of "providing" merely requires the user to obtain, access, approach, locate, configure, activate, power on, or otherwise act to provide the required device in the method. The methods described herein may be carried out in any order of the recited events that is logically possible, as well as the recited order of events.

[0124] Exemplary aspects of the invention, along with details regarding material selection and manufacturing, have been described above. As for other details of the invention, these may be understood in conjunction with the above-referenced patents and publications and may generally be understood or understood by those skilled in the art. The same may be true with respect to method-based aspects of the invention in terms of additional acts as generally or theoretically employed.

[0125] For ease of description, various words are used herein to indicate the relative location of features. For example, various features may be described as being "higher" or "lower" than other features, "above," "over," or "to the side of." Other words of relative location may also be used. All such words of relative location assume that the collective structure or system formed by the features as a whole is in a certain orientation as a reference point for purposes of description, but it should be understood that when used, the structure may be positioned laterally, inverted, or in any number of other orientations.

[0126] Additionally, while the present invention has been described with reference to several embodiments that optionally incorporate various features, the present invention is not limited to what has been described or indicated as being considered with respect to each variation of the invention. Various modifications may be made to the invention as described, and equivalents may be substituted (whether described herein or not included for purposes of brevity) without departing from the true spirit and scope of the invention. Additionally, when a range of values ​​is provided, it is understood that all intervening values ​​between the upper and lower limits of that range, and any other stated or intervening value within that stated range, are encompassed within the invention.

[0127] It is also contemplated that any optional features of the inventive variations described herein may be described and claimed independently or in combination with any one or more of the features described herein. Reference to a singular item includes the possibility that plurals of the same items are present. More specifically, as used herein and in the claims associated therewith, the singular forms "a," "an," "said," and "the" include plural referents unless specifically stated otherwise. In other words, the use of articles in the above description and in the claims associated with this disclosure allows for "at least one" of the subject item. Furthermore, it should be noted that such claims may be drafted to exclude any optional element. Accordingly, this statement is intended to serve as a predicate for the use of such exclusive terminology, such as "only," "only," and the like, or the use of "negative" limitations, in connection with the recitation of claim elements.

[0128] Without using such exclusive language, the term "comprising" in the claims associated with this disclosure shall permit the inclusion of any additional elements, regardless of whether a given number of elements are recited in such claims or whether the addition of features can be considered as changing the nature of the elements recited in such claims. Except as specifically defined herein, all technical and scientific terms used herein shall be given the broadest possible commonly understood meaning while maintaining the validity of the claims.

[0129] The scope of the present invention is not intended to be limited to the examples provided and / or this specification, but rather is intended to be limited only by the scope of the claims associated with this disclosure.

Claims

[Claim 1] Metasurfaces for redirecting light, methods of manufacture, etc.

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