Meta-Surface and Manufacturing Method for Redirecting Light

Abstract

To provide metasurfaces and fabrication methods for preferred light redirection. A display system includes a waveguide having a light incoupling or light outcoupling optical element formed from a metasurface. 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 from a 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 width of the protrusions and the spacing between the protrusions may be selected to diffract light, and the pitch of the protrusions may be between 10 and 600 nm.

Description

Technical Field

[0001] (Priority Application) This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 252,315, filed on November 6, 2015, entitled "METASURFACES FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING", and U.S. Provisional Patent Application No. 62 / 252,929, filed on November 9, 2015, entitled "METASURFACES FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING". The entireties of each of these priority applications are hereby incorporated by reference into this specification.

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

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

Background Art

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, where digitally reproduced images or portions thereof are presented to a user in a manner that appears or is perceived to be real. A virtual reality or "VR" scenario typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and an augmented reality or "AR" scenario typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world around the user. For example, referring to FIG. 1, an augmented reality scene 1 is depicted, where a user of AR technology can see a real-world park-like setting 1100 featuring people, trees, and buildings in the background, and a concrete platform 1120. In addition to these items, a user of AR technology also "sees" a robotic image 1110 standing on the real-world platform 1120 and an avatar character 1130 in the form of a flying cartoon that appears anthropomorphic like a honeybee, although these elements 1130, 1110 do not exist in the real world. The human visual perception system is complex, and the generation of VR or AR technology that promotes a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements is difficult.

[0005] The systems and methods disclosed herein address various issues related to VR or AR technology. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEMS

[0006] In some embodiments, a method for forming an optical waveguide includes providing an optically transmissive resist layer overlying an optically transmissive substrate. The resist is patterned in a pattern having protrusions and intervening gaps, and the protrusions have a pitch in the range of 10 nm to 600 nm. An optically transmissive material is deposited over 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 having a metasurface. The metasurface includes a plurality of spaced-apart protrusions formed from a first optically transparent material and a second optically transparent material extending across and between the spaced-apart protrusions. The waveguide may be optically coupled to an optical pipe.

[0008] In yet other embodiments, a display system includes a waveguide and an optical internal coupling optical element disposed on a surface of the waveguide. The optical internal coupling optical element includes a multi-level metasurface having a pitch and including a plurality of spaced-apart protrusions formed from a first optically transparent material and a second optically transparent material extending across and between the spaced-apart protrusions.

[0009] In some other embodiments, a display system includes a waveguide and an optical external coupling optical element disposed on a surface of the waveguide. The optical external coupling optical element includes a multi-level metasurface having a pitch and including a plurality of spaced-apart protrusions formed from a first optically transparent material and a second optically transparent material extending across and between the spaced-apart protrusions.

[0010] In yet other embodiments, a display system includes a waveguide and an optical internal coupling optical element disposed on a surface of the waveguide. The optical internal coupling optical element includes a metasurface including a plurality of spaced-apart protrusions formed from a first optically transparent material and an optically transparent resist between the spaced-apart protrusions.

[0011] In some other embodiments, a display system includes a waveguide and an optical external coupling optical element disposed on a surface of the waveguide. The optical external coupling optical element includes a metasurface including a plurality of spaced-apart protrusions formed from a first optically transparent material and an optically transparent 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, figures, and claims. The present invention provides, for example, the following. (Item 1) A method for forming an optical waveguide, the method comprising: forming a metasurface including the step of forming the metasurface includes: providing an optically transparent resist layer covering 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 including (Item 2) The method according to item 1, wherein the optically transparent material is amorphous. (Item 3) The method according to item 1, wherein the step of depositing the optically transparent material forms spaced flat regions of the optically transparent material above the protrusions. (Item 4) The method according to item 1, wherein the optically transparent material has a refractive index higher than that of either the patterned resist or the substrate. (Item 5) The method according to item 4, wherein the refractive index of the optically transparent material is higher than 1.7. (Item 6) The method according to item 4, wherein the optically transparent material is a resist. (Item 7) The method according to item 1, wherein the optically transparent substrate is a waveguide. (Item 8) The method according to item 1, wherein the step of patterning the resist includes imprinting the pattern into the resist. (Item 9) The method according to item 1, wherein the step of depositing the optically transparent material includes spin-coating the optically transparent material on the patterned resist. (Item 10) The method according to item 1, wherein the step of depositing the optically transparent material includes the step of performing conformal deposition or directional deposition of the optically transparent material. (Item 11) The method according to item 10, wherein the conformal deposition includes chemical vapor deposition or atomic layer deposition of the optically transparent material. (Item 12) The method according to item 10, wherein the directional deposition includes evaporation or sputtering of the optically transparent material. (Item 13) The method according to item 1, wherein the full width is in the range of 300 to 500 nm. (Item 14) The method according to item 1, wherein the step of depositing the optically transparent material deposits the optically transparent material to a thickness of 10 nm to 1 μm above the protrusion. (Item 15) The method according to item 1, wherein the protrusion includes steps at two levels. (Item 16) A display system, a waveguide, and an optical internal coupling optical element disposed on the surface of the waveguide, the optical internal coupling optical element comprising a multi-level metasurface, the multi-level metasurface having a certain pitch and including a plurality of spaced protrusions formed from a first optically transparent material, and a second optically transparent material covering and between the spaced protrusions and an optical internal coupling optical element comprising a display system. (Item 17) The display system according to item 16, wherein the pitch of the protrusions varies across the surface of the waveguide. (Item 18) The display system according to item 16, further comprising an image input device configured to input light carrying image information into the waveguide. (Item 19) The waveguide is one of a stack of waveguides, and each of the stacks of waveguides comprises an associated multi-level metasurface, the display system according to item 16. (Item 20) At least some of the associated multi-level metasurfaces of the waveguides are configured to redirect light in a wavelength range different from that of the other associated multi-level metasurfaces of the waveguides, the display system according to item 19. (Item 21) The first optically transparent material comprises a resist, the display system according to item 16. (Item 22) The space between each protrusion and the immediately adjacent protrusion defines an overall width of 10 to 600 nm, the display system according to item 16. (Item 23) The second optically transparent material forms the spaced-apart flat regions across the protrusions, the display system according to item 16. (Item 24) The first and second optically transparent materials are amorphous, the display system according to item 16. (Item 25) The second optically transparent material has a higher refractive index than either the first optically transparent material or the material forming the waveguide, the display system according to item 16. (Item 26) The second optically transparent material has a refractive index greater than 1.7, the display system according to item 25. (Item 27) The optically transparent material comprises a semiconductor, the display system according to item 25. (Item 28) The optically transparent material comprises silicon, the display system according to item 27. (Item 29) The optically transparent material comprises silicon nitride or silicon carbide, the display system according to item 28. (Item 30) The display system according to item 25, wherein the optically transparent material comprises an oxide. (Item 31) The display system according to item 25, wherein the optically transparent material comprises a metal oxide. (Item 32) The display system according to item 31, wherein the optically transparent material comprises titanium oxide, zirconium oxide, or zinc oxide. (Item 33) The display system according to item 16, wherein the metasurface is a bi-level metasurface. (Item 34) The display system according to item 16, wherein the metasurface is a tri-level or higher-level metasurface. (Item 35) A display system, a waveguide, and an optical external coupling optical element disposed on the surface of the waveguide, the optical external coupling optical element comprising a multi-level metasurface, the multi-level metasurface comprising a plurality of spaced-apart protrusions having a certain pitch and formed from a first optically transparent material, and a second optically transparent material extending across and between the spaced-apart protrusions and comprising an optical external coupling optical element and a display system comprising the same. (Item 36) The display system according to item 35, wherein the pitch of the protrusions varies across the surface of the waveguide. (Item 37) The display system according to item 35, further comprising an image input device configured to input light carrying image information into the waveguide. (Item 38) The display system according to item 35, wherein the waveguide is one of a stack of waveguides, each of the stack of waveguides comprising an associated multi-level metasurface. (Item 39) The display system according to item 38, wherein at least some of the associated multi-level metasurfaces of the waveguide are configured to redirect light in a wavelength range different from that of the other associated multi-level metasurfaces of the waveguide. (Item 40) The display system according to item 35, further comprising an optical internal coupling optical element disposed on the surface of the waveguide, wherein both the optical internal coupling optical element and the optical external coupling optical element comprise a multi-level metasurface. (Item 41) The display system according to item 35, wherein the space between each protrusion and the nearest protrusion defines an overall width of 200 to 500 nm. (Item 42) The display system according to item 35, wherein the second optically transparent material forms the spaced flat regions across the protrusions. (Item 43) The display system according to item 35, wherein the first and second optically transparent materials are amorphous. (Item 44) The display system according to item 35, wherein the first optically transparent material is a nanoimprint resist. (Item 45) The display system according to item 35, wherein the second optically transparent material has a refractive index higher than either the first optically transparent material or the material forming the waveguide. (Item 46) The display system according to item 45, wherein the second optically transparent material has a refractive index greater than 1.7. (Item 47) The display system according to item 46, wherein the optically transparent material comprises a semiconductor. (Item 48) The display system according to item 47, wherein the optically transparent material comprises silicon. (Item 49) The display system according to item 48, wherein the optically transparent material comprises silicon nitride or silicon carbide. (Item 50) The display system according to item 46, wherein the optically transmissive material comprises an oxide. (Item 51) The display system according to item 50, wherein the optically transmissive material comprises a metal oxide. (Item 52) The display system according to item 51, wherein the optically transmissive material comprises titanium oxide, zirconium oxide, or zinc oxide. (Item 53) The display system according to item 35, wherein the waveguide is formed of a material having a refractive index of 1.6 or higher. (Item 54) The display system according to item 35, wherein the protrusion has a single-level structure. (Item 55) The display system according to item 35, wherein the protrusion has a stepped multi-level structure.

Brief Description of the Drawings

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[0035] The drawings are provided to illustrate exemplary embodiments described in this specification and are not intended to limit the scope of the present disclosure. It should be understood that the drawings are schematic and not necessarily drawn to an exact scale.

DETAILED DESCRIPTION

[0036] The metasurface, which is a metamaterial of reduced dimensions, provides an opportunity to realize flat and aberration-free optics on a much smaller scale compared to geometric optics. Without being limited by theory, in some embodiments, the metasurface includes a high-density 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, metasurfaces are typically formed using very high refractive index materials, but their typical use is limited to infrared wavelengths due to their inherently high absorption rates in other cases. 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 a large amount of incident 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 about 2 are not considered to have a high enough refractive index to support the optical resonances desired for effectively manipulating the optical wavefront.

[0038] Metasurfaces also face challenges in their manufacturing. Assuming the size of the surface structures forming the metasurface and its characteristic features below the wavelength of the incident light, lithography and etching processes are typically used to process the surface. However, such processes and equipment used for these processes are prohibitively costly, especially when the metasurface extends across a large surface area where the metasurface can be thousands of times larger than the characteristic size of the metamaterial structure.

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

[0040] In some embodiments, the metasurface is a multilevel (e.g., bilayer) structure having a first level defined by spaced-apart protrusions formed from a first optically transparent material and a second optically transparent material between the protrusions. The metasurface also includes a second level formed by a second optically transparent material disposed on the upper surface of the protrusions. The first and second optically transparent materials may be formed on an optically transparent substrate, e.g., on a waveguide. The first and second optically transparent materials may be deposited on the substrate. In some embodiments, the first and second optically transparent 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, and the protrusions may take the form of steps, with the second optically transparent material accompanying both sides and the upper surface of the protrusions.

[0041] In some embodiments, the pitch of the protrusions is from 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 from 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 according to the wavelength of the light desired to be redirected and the angle of redirection. In some embodiments, the pitch is less than the wavelength of the light for which the metasurface is configured to redirect. In some embodiments, the second optically transparent material occupies the space between the protrusions, partially or completely, but does not extend above the protrusions. In some embodiments, in addition to the pitch and height of each level, the width of the protrusions may be selected based on the wavelength of the light desired for redirection and the angle of redirection. By way of example, the protrusions may have a width of from about 10 nm to 1 μm, including 10 - 250 nm.

[0042] As disclosed herein, the protrusions on the first level, i.e., the level below the upper level of a three or higher level structure, may in some embodiments be patterned by lithography and etching. More preferably, the protrusions may be patterned by nanoimprinting the first optically transparent material. The second optically transparent material may then be deposited (in some embodiments, across) between the patterned protrusions. The deposition may be accomplished by various processes including directed 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 the material sits between and on top of the protrusions, and the second optically transparent material forms a flat region of material across each of the protrusions, leaving a gap between the flat region on the upper level and the protrusions on the lower level. In some other embodiments, the deposition is advanced to the extent that the gaps between the protrusions are filled. In yet other embodiments, the deposition of the second optically transparent material is advanced 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 see-through display device or an eyepiece display device, and the waveguide is configured to receive input image information and generate an output image based on the input image information. These devices are wearable and, in some embodiments, may constitute eyewear. The input image information received by the waveguide can be encoded within a multiplexed light stream of different wavelengths (e.g., red, green, and blue light) that is internally coupled within one or more waveguides. The internally coupled light may propagate through the waveguide due to total internal reflection. The internally coupled light may be externally coupled (or output) from the waveguide by one or more external coupling optical elements.

[0044] Advantageously, the metasurface may be formed on the waveguide and may be an internal coupling and / or external coupling optical element. The compactness and planar nature of the metasurface enable not only a compact waveguide but also a stack of compact waveguides where multiple waveguides form a stack. Additionally, the high wavelength selectivity of the metasurface enables high precision of internally coupled and / or externally coupled light, which can provide high image quality in applications where light contains image information. For example, the high selectivity can reduce channel crosstalk in a configuration where a full-color image is formed by simultaneously outputting light of different colors or wavelengths.

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

[0046] Refer now to the drawings, where like reference numerals refer to like features throughout.

[0047] (Exemplary Display System) The various embodiments disclosed herein may generally be implemented as a display system. In some embodiments, the display system may take 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 a plurality of 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 the eyes of a user or viewer. In some embodiments, a plurality of waveguides, e.g., two stacks of one waveguide per viewer eye, may be utilized to provide different images to each eye.

[0048] FIG. 2 illustrates an embodiment 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 function of the display 62. The display 62 may constitute eyewear and be coupled to a frame 64, which is wearable by a display system user or viewer 60 and is configured to position the display 62 in front of the user 60's eyes. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user 60's external ear canal (in some embodiments, another speaker, not shown, is positioned adjacent to the other external ear canal of the user to provide stereo / formable sound control). In some embodiments, the display system also includes one or more microphones 67 or other devices and may detect sound. In some embodiments, the microphone is configured to enable the user to provide an input or command to the system 80 (e.g., selection of a voice menu command, natural language question, etc.) and / or enable audio communication with other persons (e.g., other users of a similar display system). In some embodiments, the display system may include one or more cameras (not shown) that are attached to the frame 64 or otherwise attachable to the user 60. The camera may be positioned and oriented to capture an image of the surrounding environment in which the user 60 is located.

[0049] Continuing to refer to FIG. 2, display 62 is operably coupled 68 to local data processing module 70, such as by wired leads or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to frame 64, fixedly attached to a helmet or hat worn by a user, embedded within headphones, or otherwise removably attached to user 60 (e.g., in a backpack-style configuration, a belt-coupled configuration). Local processing and data module 70 may comprise a hardware processor as well as digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. The data includes a) data captured from sensors such as an image capture device (e.g., a camera), microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, and / or gyroscope (e.g., operably coupled to frame 64 or otherwise attachable to user 60), and / or b) data obtained and / or processed using remote processing module 72 and / or remote data repository 74, possibly for passage to display 62 after such processing or retrieval. Local processing and data module 70 may be operably coupled to remote processing module 72 and remote data repository 74 by communication links 76, 78, such as via a wired or wireless communication link, such that these remote modules 72, 74 are operably coupled to each other and available as resources to local processing and data module 70. In some embodiments, local processing and data module 70 may include one or more than one of an image capture device, microphone, inertial measurement unit, accelerometer, compass, GPS unit, wireless device, and / or gyroscope. In some other embodiments, one or more than one of these sensors may be attached to frame 64 or may be of an independent construction that communicates with local processing and data module 70 via a wired or wireless communication path.

[0050] Continuing to refer to FIG. 2, in some embodiments, the remote processing module 72 may include one or more processors configured to analyze and process data and / or image information. In some embodiments, the remote data repository 74 may include a digital data storage facility that may be accessible through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, all data is stored and all computations are performed within the local processing and data module, enabling full autonomy from the remote module.

[0051] The perception of an image as “three-dimensional” or “3-D” can be achieved by providing slightly different presentations of the image to each eye of the 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. Images 5, 7 are separated from eyes 4, 6 by a distance 10 along an optical axis or z-axis parallel to the viewer's line of sight. Images 5, 7 are flat and eyes 4, 6 can be focused on the images by assuming a single focused state. Such a system relies on the human visual system to combine images 5, 7 and provide a perception of depth of the combined image.

[0052] However, it should be understood that the human visual system is more complex and it is more difficult to provide a realistic perception of depth. For example, many viewers of conventional "3-D" display systems find such systems uncomfortable or may not perceive any sense of depth at all. Although not limited by theory, it is thought that a viewer of an object can perceive the object as "three-dimensional" due to a combination of vergence and accommodation. The movement of the vergence of the two eyes relative to each other (i.e., the rolling movement of the pupils towards or away from each other to converge the lines of sight of the eyes and fix on the object) is closely associated with focusing 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 at a different distance to another object will automatically cause a corresponding change in vergence to the same distance under the relationship known as the "accommodation-vergence reflex". Similarly, a change in vergence will, under normal conditions, induce a corresponding change in accommodation. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and thus slightly different images) to each eye so that a three-dimensional viewpoint is perceived by the human visual system. However, such systems are uncomfortable for many viewers, especially because they simply provide different presentations of the scene and, when the eyes view the entire image information in a single accommodated state, they function against the "accommodation-vergence reflex". A display system that provides better alignment between accommodation and vergence can create a more realistic and comfortable simulation of a three-dimensional image.

[0053] FIG. 4 illustrates a side view of an approach for simulating a 3D image using multiple depth planes. Referring to FIG. 4, objects at various distances from eyes 4 and 6 on the z-axis are focused by eyes 4, 6 such that those objects are in focus. The eyes (4, 6) assume a particular focused state and focus on objects at different distances along the z-axis. As a result, a particular focused state can be said to be associated with a particular one of depth planes 14 having an associated focal length such that an object or a portion of an object in that particular depth plane is in focus when the eyes are in the focused state for that depth plane. In some embodiments, the 3D image may be simulated by providing different presentations of the image for each of eyes 4, 6 and also by providing different presentations of the image corresponding to each of the depth planes. It should be understood that, although shown separately for clarity of illustration, 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 contours of the depth planes may be curved in physical space such that all features within the depth plane are in focus with the eyes in a particular focused state.

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

[0055] Although not limited by theory, the human eye is thought to typically be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of images corresponding to each of these limited number of depth planes to the eye. The different presentations are separately focused by the viewer's eye, thereby based on the eye accommodation required to focus on different image features for scenes located on different depth planes and / or based on the observation of different out - of - focus image features on different depth planes, which can help provide depth cues to the user.

[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 a stacked waveguide assembly 178 that can be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 182, 184, 186, 188, 190. In some embodiments, display system 1000 is the system 80 of FIG. 2, and FIG. 6 shows some parts of that system 80 in more detail. For example, waveguide assembly 178 may be part of display 62 of FIG. 2.

[0057] Continuing to refer to FIG. 6, waveguide assembly 178 may also include a plurality of features 198, 196, 194, 192 between waveguides. In some embodiments, features 198, 196, 194, 192 may be lenses. Waveguides 182, 184, 186, 188, 190 and / or a plurality of 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 may be configured to output image information corresponding to that depth plane. Image input devices 200, 202, 204, 206, 208 may function as light sources for the waveguides and may be utilized to input image information into waveguides 182, 184, 186, 188, 190, each configured to disperse incident light across an individual waveguide for output toward eye 4 as described herein. Light exits from output surfaces 300, 302, 304, 306, 308 of image input devices 200, 202, 204, 206, 208 and is input into corresponding input surfaces 382, 384, 386, 388, 390 of waveguides 182, 184, 186, 188, 190. In some embodiments, input surfaces 382, 384, 386, 388, 390 may be the edges of the corresponding waveguides or may be a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly toward world 144 or viewer's eye 4). In some embodiments, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams, which are directed toward eye 4 at a particular angle (and amount of divergence) corresponding to a depth plane associated with a particular waveguide. In some embodiments, a single one of image input devices 200, 202, 204, 206, 208 may be associated with and input light into a plurality (e.g., three) of waveguides 182, 184, 186, 188, 190.

[0058] In some embodiments, the image input devices 200, 202, 204, 206, 208 are discrete displays, each generating image information for input into a respective waveguide 182, 184, 186, 188, 190. In some other embodiments, the image input devices 200, 202, 204, 206, 208 are the output ends of a single multiplexed display that can send image information, for example, via one or more optical waveguides (such as optical fiber cables) to each of the image input devices 200, 202, 204, 206, 208. It should be understood that the image information provided by the 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 input devices 200, 202, 204, 206, 208 may be the output ends of a scanning fiber display system, and the image input devices 200, 202, 204, 206, 208 move or scan across the surfaces of the corresponding input surfaces 382, 384, 386, 388, 390 of the waveguides 182, 184, 186, 188, 190 and input the 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, a plurality of the image input devices 200, 202, 204, 206, 208 may be replaced by scanning fibers.

[0060] Continuing to refer to FIG. 6, the controller 210 controls the operation of the stacked waveguide assemblies 178 and the image input devices 200, 202, 204, 206, 208. In some embodiments, the controller 210 is part of the local data processing module 70. The controller 210 includes programming (e.g., instructions in a non-transitory medium) that adjusts 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 monolithic device or a distributed system connected by wired or wireless communication channels. The controller 210 may be part of the processing module 70 or 72 (FIG. 1) in some embodiments.

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

[0062] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 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 input into such waveguide 182. The collimated light may represent an optically infinite focal plane. The next upper waveguide 184 may be configured to deliver collimated light that passes through a first lens 192 (e.g., a negative lens) before reaching the eye 4. Such a first lens 192 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 184 as originating from a first focal plane that is closer inwardly from the optically infinite towards 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 generate another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 186 as originating from a second focal plane that is even closer inwardly from the optically infinite, where the light from the next upper waveguide 184 originated, towards the person. Other ways of generating these perceived colors may also be considered as possibilities.

[0063] The other waveguide layers 188, 190 and lenses 196, 198 are similarly configured, and the top waveguide 190 in the stack sends its output through all of the lenses between it and the eye for the collective focusing power that represents the focal plane closest to the person. When viewing / interpreting light originating from the world 144 on the other side of the stacked waveguide assembly 178, a compensating lens layer 180 may be disposed on top of the stack to compensate for the stack of lenses 198, 196, 194, 192. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both or either of the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

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

[0065] Continuing to refer to FIG. 6, one or more external coupling optical elements 282, 284, 286, 288, 290 may be configured to both redirect light from its respective waveguide for a particular depth plane associated with the waveguide and output the light with an appropriate amount of divergence or collimation. As a result, waveguides having different associated depth planes may have different configurations of one or more external coupling 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., structures for forming cladding layers and / or air gaps).

[0066] In some embodiments, one or more external coupling 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 such that only a portion of the light of the beam is deflected toward the eye 4 using each intersection of the DOE while the remainder continues to travel through the waveguide via total internal reflection. The light carrying the image information is thus split into several associated output beams exiting the waveguide at various locations, resulting in a very uniform pattern of output emission toward the eye 4 with respect to this particular collimated beam bouncing within the waveguide.

[0067] In some embodiments, one or more DOEs may be switchable between an “on” state that actively diffracts and an “off” state that does not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which the microdroplets have a diffraction pattern in the 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 the 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 the incident light).

[0068] FIG. 7 shows an example of an output beam output by a waveguide. Although one waveguide is shown, it should be understood that other waveguides within the waveguide assembly 178 (FIG. 6) may function similarly, and the waveguide assembly 178 includes a plurality of waveguides. Light 400 is introduced into waveguide 182 at the 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 shown as being substantially parallel, but as discussed herein and depending on the depth plane associated with waveguide 182, it may be redirected to propagate to eye 4 at an angle (e.g., forming a diverging output beam). A waveguide with one or more external coupling optical elements that externally couple the light to form an image that appears to be set in a depth plane at a long distance (e.g., optical infinity) from eye 4 may be shown. It should be understood that other waveguides or other sets of external coupling optical elements may output a more diverging output beam pattern, which requires the eye 4 to focus at a closer distance and be interpreted by the brain as light from a distance closer to eye 4 than optical infinity.

[0069] FIG. 8 illustrates an embodiment of a stacked waveguide assembly, where each depth plane includes an image formed using a plurality of different primary colors. In some embodiments, a full-color image may be formed in each depth plane by overlaying an image on each of the primary colors, e.g., three or more primary colors. The illustrated embodiment shows depth planes 14a - 14f, although more or fewer depths may also be considered. Each depth plane may have three primary color images associated therewith, namely, a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are shown in the figure by different numbers associated with the diopters following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image.

[0070] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such embodiments, each box in the figure containing the letters G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images being provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of explanation, but it should be understood that in a physical device, all the waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, a plurality of primary colors may be output by the same waveguide, e.g., such that only a single waveguide is provided for each depth plane.

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

[0072] Throughout this disclosure, reference to the color of a given light is to be understood to encompass light of one or more wavelengths within the range of wavelengths of the light as perceived by a viewer as that given color. For example, red light may include light of one or more wavelengths within the range of approximately 620 to 780 nm, green light may include light of one or more wavelengths within the range of approximately 492 to 577 nm, and blue light may include light of one or more wavelengths within the range of approximately 435 to 493 nm.

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

[0074] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes an associated internal coupling optical element. For example, internal coupling optical element 1212 is disposed on a major surface (e.g., the bottom major surface) of waveguide 1210, internal coupling optical element 1224 is disposed on a major surface (e.g., the bottom major surface) of waveguide 1220, and internal coupling optical element 1232 is disposed on a major surface (e.g., the 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 upper major surface of the respective waveguide 1210, 1220, 1230 (in particular, one or more of the internal coupling optical elements are transmissive deflection optical elements). Preferably, the internal coupling optical elements 1212, 1222, 1232 are disposed on the bottom major surface (or the upper part of the next lower waveguide) of their respective waveguides 1210, 1220, 1230, and in particular, those internal coupling optical elements are reflective deflection 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 such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 1210, 1220, 1230, it should be understood that the internal coupling optical elements 1212, 1222, 1232 may be disposed within other areas of their respective waveguides 1210, 1220, 1230 in some embodiments.

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

[0076] Waveguides 1210, 1220, 1230 may be separated and isolated by a solid layer 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 immediate waveguides 1210, 1220, 1230). Preferably, the refractive index of the material forming layers 1218a, 1218b is less than the refractive index of the material forming waveguides 1210, 1220, 1230 by 0.05 or more, or by 0.10 or more. Advantageously, the lower refractive index layers 1218a, 1218b may function as cladding layers that promote total internal reflection (TIR) of light (e.g., TIR between the upper and bottom major surfaces of each waveguide) through waveguides 1210, 1220, 1230. In some embodiments, layers 1218a, 1218b are formed from air. It should be understood that although not shown, the upper and bottom of the illustrated set 1200 of waveguides may include immediate cladding layers.

[0077] Preferably, to facilitate manufacturing and other considerations, the materials forming waveguides 1210, 1220, 1230 are similar or identical, and the materials forming layers 1218a, 1218b are similar or identical. In some embodiments, the materials forming waveguides 1210, 1220, 1230 may be different between one or more waveguides and / or the materials forming layers 1218a, 1218b may still be different while maintaining the various refractive index relationships described above.

[0078] Continuing to refer to FIG. 9A, light rays 1240, 1242, 1244 are incident on a set 1200 of waveguides. It should be understood that light rays 1240, 1242, 1244 may be input into waveguides 1210, 1220, 1230 by one or more image input devices 200, 202, 204, 206, 208 (FIG. 6).

[0079] Preferably, light rays 1240, 1242, 1244 have different properties, such as different wavelengths or different wavelength ranges, which may correspond to different colors. In some embodiments, internal coupling optical elements 1212, 122, 1232 each selectively deflect light of one or more specific wavelengths while transmitting other wavelengths to underlying waveguides and associated internal coupling optical elements.

[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. The transmitted light ray 1242 then impinges on an internal coupling optical element 1222 that is configured to selectively deflect (e.g., reflect) light of the second wavelength or wavelength range, thereby being deflected. Light ray 1244 is transmitted by internal coupling optical element 1222 and impinges on an internal coupling optical element 1232 that is configured to selectively deflect (e.g., reflect) light of the third wavelength or wavelength range, thereby continuing to be deflected.

[0081] Continuing to refer to FIG. 9A, the deflected light rays 1240, 1242, 1244 are deflected to propagate through the corresponding waveguides 1210, 1220, 1230. That is, the internal coupling optical elements 1212, 1222, 1232 of each waveguide deflect the light into its corresponding waveguide 1210, 1220, 1230 and internally couple 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 individual waveguides 1210, 1220, 1230 by TIR.

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

[0083] Referring now to FIG. 9B, an embodiment of a perspective view of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 1240, 1242, 1244 are each deflected by the internal coupling optical elements 1212, 1222, 1232 and then propagate by TIR within the waveguides 1210, 1220, 1230, respectively. The light rays 1240, 1242, 1244 then each impinge on the light dispersing elements 1214, 1224, 1234, respectively. The light dispersing elements 1214, 1224, 1234 deflect the light rays 1240, 1242, 1244 to propagate toward the external coupling optical elements 1250, 1252, 1254, respectively.

[0084] In some embodiments, the light dispersing elements 1214, 1224, 1234 are orthogonal pupil expansion elements (OPEs). In some embodiments, the OPE performs both deflection and dispersion of light to the external coupling optical elements 1250, 1252, 1254, and increases the beam or spot size of the present light as it propagates to the external coupling optical elements. In some embodiments, for example, if the beam size is already at a desired size, the light dispersing elements 1214, 1224, 1234 may be omitted, and the internal coupling optical elements 1212, 1222, 1232 may be configured to directly deflect light to the external coupling optical elements 1250, 1252, 1254. For example, referring to FIG. 9A, in some embodiments, the light dispersing elements 1214, 1224, 1234 may each be replaced by the external coupling optical elements 1250, 1252, 1254. In some embodiments, the external coupling optical elements 1250, 1252, 1254 are exit pupils (EPs) or exit pupil expansion elements (EPEs) that direct light to the viewer's eye 4 (FIG. 7).

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

[0086] (Meta-Surface) FIG. 10A illustrates an example of a metasurface according to some embodiments. The substrate 2000 has a surface 2000a on which the metasurface 2010 is disposed. The metasurface 2010 includes multiple levels of optically transmissive material. As illustrated, in some embodiments, the metasurface is a bilayer structure having first and second levels 2012, 2014, respectively. The first level 2012 includes a plurality of protrusions 2020 formed from a first optically transmissive material and a mass 2030a of a second optically transmissive material between the protrusions. The second level 2014 includes a second-level mass 2030b of a second optically transmissive material formed on the protrusions (spaced apart and separated from the substrate by the first level). The protrusions 2020 may be ridges (or nanowires) that extend laterally in and out of the page and define trenches between adjacent protrusions. As illustrated, in the second level 2014, the mass 2030b of the second optically transmissive material may be localized on the surface of the protrusions 2020 to form a flat region of material spaced apart from other localized deposits (or flat regions) of the second optically transmissive material.

[0087] Preferably, the refractive index of the second optically transmissive material forming the masses 2030a, 2030b is higher than the refractive indices of both the first optically transmissive material forming the protrusions 2020 and the material forming the substrate 2000. In some embodiments, the refractive index of the first optically transmissive material is lower than or similar to the refractive index of the material forming the substrate 2000. The 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, for example, higher than 1.5, 1.6, 1.7, 1.8, or 1.9, which can increase the viewing field of a display that outputs light from the substrate 2000 and provide the advantage of forming an image. In some embodiments, the substrate 2000 is formed from glass (e.g., doped glass), lithium niobate, plastic, polymer, sapphire, or other optically transmissive materials. Preferably, the glass, plastic, polymer, sapphire, or other optically transmissive material has a high refractive index, for example, higher than 1.5, 1.6, 1.7, 1.8, or 1.9.

[0088] Continuing to refer to FIG. 10A, the first optically transparent material of the 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 the masses 2030a, 2030b has a higher refractive index than both the first optically transparent material of the protrusion 2020 and the material forming the 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 containing silicon, and oxides. 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 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 a wider range of surfaces than some crystalline materials. In some embodiments, the first and second optically transparent materials forming the features 2020, 2030a, 2030b may each be one of amorphous or crystalline semiconductor materials.

[0089] Continuing to refer to FIG. 10A, the protrusions have a pitch 2040. As used herein, pitch refers to the distance between two nearest structurally similar points. The similar points are understood to be similar in that they are in similar portions of the structure that are substantially the same (e.g., left or right edges). For example, the pitch of protrusion 2020 is equal to the total width defined by the protrusion 2020 and the nearest separation between the protrusion and the nearest similar protrusion 2020. In other words, the pitch can be understood to be the width of the repeating unit of the array of features formed by those protrusions 2020 (e.g., the sum of the widths of protrusion 2020 and block 2030a).

[0090] As shown, light of different wavelengths (corresponding to different colors) can impinge on the metasurface, and as discussed herein, the metasurface is highly selective when redirecting light of a specific wavelength. 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 protrusion 2020 is less than the wavelength of light desired for zero-order reflection light redirection in some embodiments. In some embodiments, the geometric size and periodicity increase as the wavelength gets longer, and the height or thickness of one or both of protrusion 2020 and blocks 2030a, 2030b also increases as the wavelength gets longer. The illustrated light rays 2050a, 2050b, and 2050c correspond to light of different wavelengths and colors in some embodiments. In the illustrated embodiment, the metasurface has a pitch that reflects light ray 2050b while light rays 2050a and 2050c propagate through substrate 2000 and metasurface 2010.

[0091] Advantageously, the multi-level metasurface is highly selective for a particular light wavelength. FIG. 10B shows a plot of the transmission and reflection spectra for a metasurface having the general structure shown in FIG. 10A. In this example, the protrusions 2020 have a width of 125 nm, a thickness of 25 nm, are formed from a resist, the masses of materials 2030a and 2030b have a thickness of 75 nm, are formed from silicon nitride, the pitch is 340 nm, and voids separate the masses 2030b. The horizontal axis indicates wavelength, and the vertical axis indicates transmittance (a scale of 0 to 1.00 from no reflection to total reflection). Notably, a sharp peak in reflection (517 nm) and an accompanying reduction in transmittance are observed for a narrow band of wavelengths, while other wavelengths are transmitted. Light is reflected when its wavelength matches the resonant wavelength (about 517 nm in this example). The protrusions 2020 and the upper structure 2030 are arranged with a sub-wavelength spacing, and only zero-order reflection and transmittance exist. As shown in FIG. 10B, the reflection spectrum shows a sharp peak across the visible wavelength region, which is characteristic of optical resonance.

[0092] It should be understood that the pitch of the metasurface structure (e.g., the pitch of the protrusions 2020 and the upper structure 2030) may be modified to change the light redirection 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 with respect to the surface of the substrate 2000) in response to incidence on the metasurface 2010. In some embodiments, when the substrate 2000 is a waveguide, the pitch of the metasurface structure may be selected such that light at the resonant wavelength is deflected at an angle such that it propagates through the waveguide by total internal reflection (TIR), while other wavelengths and colors are transmitted through the metasurface 2010. In such an arrangement, the metasurface 2010 can be said to be an internal coupling optical element that internally couples the deflected light. FIGS. 11A-11B show examples of cross-sectional side views of a metasurface that internally couples light into a waveguide.

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

[0094] It should be understood that the metasurface 2010 will also deflect the light impinging thereon out of the optical waveguide 2000. Utilizing this functionality, in some embodiments, the metasurfaces disclosed herein may be applied to form external coupling optical elements. FIGS. 12A-12B show examples of cross-sectional side views of a metasurface that externally couples light from a waveguide. FIG. 12A shows the external coupling of light of one wavelength, while FIG. 12B shows the external coupling of light of a different wavelength. As disclosed herein, the resonant wavelength of the metasurface 2010 can be engineered by varying the geometric size of its constituent structure, thereby providing wavelength selectivity. As an example, larger geometric sizes and periodicities (FIG. 12B) may be used to provide a metasurface that resonates at the wavelength of red light, while relatively smaller geometric sizes and periodicities may be used to provide a metasurface that resonates at the wavelength of green light (FIG. 12A). In some embodiments, the metasurface 2010 may form one or more than one of the 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 if different waveguides have different associated primary colors, the external coupling optical elements and / or internal coupling optical elements associated with each waveguide fabricated will have specific geometric sizes and / or periodicities for the wavelength or color of light configured to propagate in the waveguide. Thus, different waveguides may have metasurfaces with different geometric sizes and / or periodicities. As an example, metasurfaces for internally or externally coupling red, green, or blue light may have geometric sizes and / or periodicities (pitches) configured to redirect or diffract light at wavelengths of 638 nm, 520 nm, and 455 nm, respectively.

[0095] In some embodiments, the metasurface 2010 may have a geometric size and / or pitch that imparts optical power onto the diffracted light on the metasurface. For example, the metasurface may be configured to emit light from the metasurface in a diverging or converging direction. Different portions of the metasurface may have different pitches, for example, to deflect different light rays in different directions such that the light rays diverge or converge.

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

[0097] Referring to FIGS. 11A - 12B, as illustrated, the metasurface 2010 may deflect light in a "reflection mode" where the deflected light remains on the same side of the metasurface before and after impinging on 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 "transmission mode" where both the deflected and non - deflected light are transmitted across the thickness of the metasurface, the path of the deflected light is different after exiting the metasurface, while the path of the non - deflected light is substantially unchanged. It should be understood that the metasurface may have both transmission and reflection functionality. For example, in some embodiments, the metasurface may reflect a portion of the incident light while transmitting and deflecting another portion of that light.

[0098] Figures 13A - 13B illustrate an embodiment of a metasurface 2010 operating in transmission mode. Referring to FIG. 13A, light rays 1240, 1244 propagate through the metasurface without substantial deflection while light ray 1242 is deflected. Light ray 1242 may be at the resonant wavelength for the metasurface 2010, while light rays 1240, 1244 are not. In some embodiments, the deflection may be used to internally couple or externally couple light ray 1240. FIG. 13B illustrates an embodiment of a metasurface configured to operate in transmission mode for internal light coupling. In some embodiments, as illustrated, light rays 1240, 1242, 1244 each have a different wavelength (e.g., corresponding to different colors), and metasurfaces 1212, 1222, 1232 are each selective for deflecting a particular wavelength or wavelength range. For example, metasurface 1212 may selectively deflect light ray 1240 in transmission mode while transmitting light rays 1242 and 1244 without deflection. Similarly, as illustrated, metasurface 1222 may selectively deflect light ray 1242 in transmission mode while transmitting light ray 1244 without deflection, and metasurface 1232 may selectively deflect light ray 1244 in transmission mode. In some other embodiments, the transmission mode metasurface may also be applied as an external coupling optical element, such as one or more of external coupling optical elements 282, 284, 286, 288, 290 (FIG. 6) or 1250, 1252, 1254 (FIG. 9B).

[0099] A metasurface functioning in transmission mode can provide advantages in some applications, such as when utilized on a waveguide together with other transmission optical elements (e.g., some embodiments of the light dispersion elements 1214, 1224, 1234 and / or external coupling optical elements 1250, 1252, 1254 of FIG. 9B). Such a transmission mode metasurface may be formed on the same side as other optical elements of the substrate, which can have the advantage of facilitating the processing of the metasurface and the optical elements while reducing the possibility of damaging the metasurface or the optical elements (which can occur when processing is required on both sides of the substrate).

[0100] Figures 14A - 14D illustrate an example of a process flow for forming the metasurface 2010. Referring to Figure 14A, 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 transmissive and may be deposited, for example, by spin coating to form a layer of the resist. In some embodiments, the resist 2020a may be deposited by jet coating (e.g., inkjet printing), which may provide the advantage of forming a very thin layer and / or a layer with variable components and / or thickness. As shown, the resist 2020a may be delivered from a resist source 2022 to the substrate 2000.

[0101] Referring to Figure 14B, an imprint template or master 2024 is brought into contact with the resist 2020a to pattern the resist. It should be understood that the pattern in the 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 the resist on multiple substrates, thereby reducing the processing cost per unit for the ultimately formed metasurface.

[0102] After contact with 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 cured, for example, by exposure to light (such as UV light) and / or heat to immobilize the resist. The template 2024 is then removed, leaving the patterned resist 2020 as shown in Figure 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, silicon nitride, and silicon carbide, oxides including zirconium oxide, zinc oxide, and titanium oxide, and optically transmissive resists. As disclosed herein, the second material 2030 is preferably an optically transmissive material. The second material 2030 may be deposited by various processes including blanket deposition, directed deposition, and spin or jet coating. Examples of blanket deposition include chemical vapor deposition (CVD) where the resist is exposed to mutually reactive precursors that are simultaneously present within a deposition chamber containing the substrate 2000, and atomic layer deposition (ALD) where the resist is alternatively exposed to the precursors. ALD may provide the advantage of precisely controlling the thickness of the deposited layer when high precision is desired and when the deposited material is formed at low temperatures. Examples of directed deposition include evaporation and sputtering for delivering the second material to the resist 2020 and substrate 2000 that are nanoimprinted.

[0104] Referring now to FIG. 15, an enlarged cross-sectional view of the patterned material 2020 on the first level metasurface is shown. As illustrated, the patterned layer of material may have an unpatterned remaining layer thickness (RLT) 2021. Such remaining layer thicknesses are typical of nanoimprinting and may be present in various embodiments herein (not shown). It should be understood that when the protrusions 2020 are formed from the imprinted resist, the resist may be sensitive to high temperatures. Preferably, the deposition temperature for the second level material 2030 is within 30 to 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 to 4 (e.g., AR < 3 to 4). In some embodiments, the aspect ratio is about 1. In some embodiments, the refractive index of the resist is about 1.2 to 2.0.

[0105] Referring now to FIGS. 16A1 - 16C, it should be understood that various methods for depositing the second material 2030 may be utilized to provide different profiles for the metasurface 2010 by providing the second material 2030 at different locations, including different levels with respect to the protrusions 2030. FIGS. 16A1 and 16B - 16C illustrate examples of cross - sectional side views of metasurface structures, where the second material is deposited to different thicknesses across the underlying pattern of protrusions. In FIG. 16A1, the metasurface 2010 is defined by a bi - level structure with a gap between the protrusions 2020 and the masses 2030a and 2030b of the second material deposited on the protrusions. When the deposition is a directed deposition process, it should be understood that the second material is substantially localized on the upper surface of the protrusions and within the spaces between the protrusions 2020, with little or no material on the sides of the protrusions. When the deposition is a conformal blanket deposition, the second material 2030 is deposited on the upper part, between, and on the sides of the protrusions 2020. FIG. 16A1 illustrates a portion of the second material on the side of the protrusion 2020, although the material 2030 on the side 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, for example, by ALD.

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

[0107] FIG. 16B illustrates a metasurface defined by a bilayer structure without a gap between the protrusions 2020. The second material is deposited to such an extent that the gap between the protrusions 202 is completely filled by the mass 2030a. The deposition to achieve what is shown is a directional deposition, although conformal blanket deposition would also achieve a similar structure (with some widening of the flat region formed by the material 2030 on the upper level of the metasurface structure).

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

[0109] FIGS. 17A - 17C illustrate examples of cross - sectional side views of a metasurface structure, 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 the 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 the mass 2030a and a residue - free upper layer. In FIG. 16B, an amount of resist sufficient to fill the gap between the protrusions 2020 with the mass 2030a of resist is deposited, while no residue upper layer is present. In FIG. 16C, an amount of resist sufficient to fill the gap between the protrusions 2020 with the mass 2030a of resist is deposited, and also a continuous residue upper layer formed by the mass 2030b is formed.

[0110] In some embodiments, it takes the form of a bilayer structure, but it should be understood that the metasurfaces disclosed herein may include more than two levels. For example, the metasurface may include three or more levels. These three or higher level structures may be formed using stepped protrusions. The lower level (closest to the substrate) may include a portion of the protrusion formed from a first optically transmissive material and a mass of a second optically transmissive material on the side surface of the protrusion, and the highest level (farthest from the substrate) preferably contains only the second optically transmissive material deposited on the upper surface of the top step of the protrusion. Preferably, to form an n-level metasurface, n-1 level stepped protrusions are utilized, and the steps on each successive level have a smaller width than the steps on the level immediately below. In some embodiments, the steps are symmetric about an axis extending in the height of the protrusion as seen in a cross-sectional side view obtained in a direction transverse to the elongation axis of the protrusion. It is contemplated that these three or higher level metasurfaces may be applied in the same use as bilayer metasurfaces (e.g., as internal coupling and / or external coupling optical elements).

[0111] Figures 18A-18B illustrate examples of cross-sectional side views of a metasurface having more than two levels. Figure 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 with one step on each level, extending across two levels, and the width of the step on the second level is less than the width of the step on the first level. A mass 2030a of a second optically transmissive material is formed on the side surface of the protrusion 2020 on the first level 2012 and preferably extends continuously from one protrusion 2020 to the next adjacent protrusion 2020. A mass 2030b of a second optically transmissive material is formed on the side surface of the protrusion 2020 on the second level 2014. On the third level, a mass 2030c of a second optically transmissive material is formed on the upper surface of the protrusion 2020. As shown, the amount of the second optically transmissive material deposited, in conjunction with the height of the step of the protrusion 2020, is such that the second optically transmissive material does not have a thickness that occupies the full height of a given level. In a sense, voids exist at a given level within the space between adjacent protrusions 2020.

[0112] Figure 18B illustrates a metasurface similar to the metasurface of Figure 18A but with the side surfaces of the protrusions not exposed. It should be understood that the side surfaces of the protrusions 2020 may be coated by depositing a sufficient amount of the second optically transmissive material to completely fill the space between adjacent protrusions 2020 on each level.

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

[0114] Referring briefly to Fig. 19A, a first material 2020a, for example, a resist (such as a nano - imprint resist), is deposited on a substrate 2000. The resist 2020a is preferably optically transmissive and may be deposited as described above with respect to Fig. 14A.

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

[0116] Referring to FIG. 19D, a second material is subsequently 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, silicon nitride, silicon carbide, oxides including zirconium oxide, zinc oxide, and titanium oxide, and optically transmissive resists. The second material is preferably an optically transmissive material. The second material may be deposited by various processes including blanket deposition, directed deposition, and spin or jet coating, as previously described with respect to FIG. 14D.

[0117] Although not shown, it should be understood that by using an 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 three or higher levels of the metasurface. For example, the presence of voids between protrusions 2020 may be achieved by deposition that does not reach a particular level of total height. Alternatively, sufficient second optically transmissive material may be deposited to completely fill the metal surface at all levels such that a continuous layer of the second material extends across the top of protrusions 2020.

[0118] In some embodiments, a waveguide 2000 having a metasurface 2010 (as an internal coupling and / or external coupling optical element) may be used to form a display system such as the system 1000 (FIG. 6) disclosed herein. For example, after processing of the metasurface 2010, the waveguide 2000 may be optically coupled to an optical pipe such as an optical pipe for injecting image information into the waveguide. The optical pipe may be an optical fiber in some embodiments. Examples of optical pipes include image input devices 200, 202, 204, 206, 208 (FIG. 6) and scanning optical fibers. In some embodiments, a plurality of waveguides each having a metasurface 2010 may be provided, and each of these waveguides may be optically coupled to one or more than one image input device.

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

[0120] For example, advantageously, it is utilized with an AR display that provides an image across a plurality of depth planes, although the augmented reality content disclosed herein may also be displayed by a system that provides an image on a single depth plane. Further, although illustrated as being on a single surface of a substrate, it should be understood that the metasurface may be disposed on a plurality of 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, a plurality of metasurfaces, e.g., one active metasurface per color of light, may be provided on the waveguide. In some embodiments, the pitch or periodicity and / or geometric size of the protrusions forming the metasurface may vary across the metasurface. Such a metasurface may be active in redirecting light of different wavelengths depending on the geometric shape and pitch at the location where the light impinges on the metasurface. In some other embodiments, the geometric shape and pitch of the metasurface features are configured to vary such that the deflected light rays propagate from the metasurface at different angles even if they are of similar wavelengths. Also, a plurality of separated metasurfaces may be disposed across the substrate surface, and in some embodiments, the metasurfaces each have the same geometric shape and pitch, or in some other embodiments, at least some of the metasurfaces have a different geometric shape and / or pitch than other metasurfaces.

[0121] Also, advantageously, although applicable to displays such as wearable displays, the metasurface may be applied to various other devices where a compact thin light redirecting element is desired. For example, the metal surface may be applied to generally form the light redirecting portion of an optical plate (e.g., a glass plate), an optical fiber, a microscope, a sensor, a wristwatch, a camera, and an image projection device.

[0122] In addition, many modifications may be made to adapt a particular situation, material, composition, process, act or step of the process to the purposes, spirit, or scope of the invention. Further, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein has discrete components and features that can be readily separated from or combined with the features of any of several other embodiments without departing from the scope or spirit of the 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 can be performed using the device. The method may include the act of providing such a suitable device. Such providing may be performed by a user. In other words, the act of "providing" merely requires the user to obtain, access, approach, position, set, activate, power on, or otherwise act to provide the required device in the method. The methods described herein may be performed in any order of the described events that is logically possible, as well as in the order of the described events.

[0124] Exemplary aspects of the invention have been described above, along with details regarding material selection and manufacturing. Regarding other details of the invention, these are understood in relation to the above-referenced patents and publications and can generally be grasped or understood by those skilled in the art. The same can apply to the method-based aspects of the invention from the perspective of additional acts as generally or theoretically employed.

[0125] For ease of explanation, various words indicating the relative positions of features are used herein. For example, the various features may be described as being "above", "across", "on the side" of other features that are "higher" or "lower". Other words of relative position may also be used. It is to be understood that all such words of relative position assume that the set structure or system formed by the features as a whole is in an orientation as a reference point for purposes of explanation, but that in use, the structure may be positioned in a lateral, inverted, or any number of other orientations.

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

[0127] Also, it is contemplated that any optional features of the variations of the invention described herein may be described and claimed independently or in combination with any one or more of the features described herein. References to items in the singular include the possibility that there are multiple identical items. More specifically, as used herein and in the claims associated therewith, the singular forms "a," "an," "said," and "the" include plural referents unless specifically stated otherwise. In other words, the use of the articles is to enable "at least one" of the item in question in the above description as well as in the claims associated with this disclosure. Further, note that such claims may be drafted to exclude any optional elements. Accordingly, this description serves the purpose of acting as a preamble for the use of such exclusive terms as "only," "solely," and equivalents, such as in relation to the recitation of claim elements, or the use of "negative" limitations.

[0128] Without using such exclusive terms, the term "comprising" in the claims associated with this disclosure shall be taken to allow the inclusion of any additional elements, whether or not a given number of elements are recited in such claims or whether the addition of a feature can be regarded as transforming the nature of the elements recited in such claims. Unless otherwise specifically defined herein, all technical and scientific terms used herein shall be given the broadest possible generally understood meaning while maintaining the validity of the claims.

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

Claims

Claim 1 A method, the method comprising: Depositing a layer of a first optically transparent material on an optical waveguide; Generating a pattern within the layer of the first optically transparent material, the pattern comprising spaced-apart protrusions having a pitch within the range of 10 nm to 600 nm; Depositing a second optically transparent material on the pattern such that the second optically transparent material is conformally deposited as a conformal blanket layer on top of, between, and on the sides of the spaced-apart protrusions while maintaining voids between portions of the second optically transparent material across adjacent ones of the spaced-apart protrusions, thereby forming a multi-level metasurface comprising the patterned first optically transparent material and the second optically transparent material, wherein the second optically transparent material is deposited as the conformal blanket layer having a constant thickness over the entire surface of the spaced-apart protrusions including the sidewalls of the spaced-apart protrusions; Comprising; The multi-level metasurface is configured to redirect incident light at an angle such that the incident light propagates through the optical waveguide by total internal reflection; The second optically transparent material has a refractive index higher than both the first optically transparent material and the material forming the optical waveguide; The first optically transparent material has a refractive index lower than the material forming the optical waveguide. Claim 2 The method of claim 1, wherein the second optically transparent material is amorphous. Claim 3 The method of claim 1, wherein depositing the second optically transparent material comprises forming spaced-apart flat regions of the second optically transparent material above the spaced-apart protrusions. Claim 4 The method of claim 1, wherein the refractive index of the second optically transparent material is higher than 1.

7. Claim 5 The method of claim 1, wherein generating the pattern within the layer of the first optically transparent material comprises imprinting the pattern into the first optically transparent material. Claim 6 The method of claim 1, wherein depositing the second optically transparent material comprises spin-coating the second optically transparent material on the pattern. Claim 7 Depositing the second optically transparent material includes chemical vapor deposition or atomic layer deposition of the second optically transparent material, the method according to claim 1.

8. The pitch is in the range of 300 nm to 500 nm, the method according to claim 1.

9. The second optically transparent material is deposited to a thickness of 10 nm to 1 μm above the spaced-apart protrusions, the method according to claim 1.

10. The spaced-apart protrusions include steps at two levels, the method according to claim 1.

11. The second optically transparent material comprises a semiconductor, the method according to claim 1.

12. The second optically transparent material comprises silicon, the method according to claim 1.

13. The second optically transparent material comprises silicon nitride or silicon carbide, the method according to claim 1.

14. The second optically transparent material comprises an oxide, the method according to claim 1.

15. The second optically transparent material comprises a metal oxide, the method according to claim 1.

16. The second optically transparent material comprises titanium oxide, zirconium oxide, or zinc oxide, the method according to claim 1.

17. Depositing the second optically transparent material includes atomic layer deposition of the second optically transparent material, the method according to claim 1.

18. The conformal blanket layer has a constant thickness of 60 nm, the method according to claim 1.

19. The second optically transparent material comprises silicon nitride, the method according to claim 1.

20. The conformal blanket layer has a constant thickness of 60 nm, the method according to claim 19.

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