Metasurfaces and manufacturing methods for redirecting light

Abstract

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

Description

Technical Field

[0001] (Priority Application) This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 252,315, filed Nov. 6, 2015, entitled “METASURFACES FOR REDIRECTING LIGHT AND METHODS FOR FABRICATING” and U.S. Provisional Patent Application No. 62 / 252,929, filed Nov. 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 their entireties U.S. Application No. 14 / 331,218 (Magic Leap Control No. 20020.00), U.S. Application No. 14 / 641,376 (Magic Leap Control No. 20014.00), U.S. Provisional Application No. 62 / 012,273 (Magic Leap Control No. 30019.00), and U.S. Provisional Application No. 62 / 005,807 (Magic Leap Control No. 30016.00).

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

Background Art

[0004] Modern computing and display technologies are driving the development of systems for so-called "virtual reality" or "augmented reality" experiences, where digitally reproduced images or parts thereof are presented to the user in a manner that appears to be real, or can be perceived as such. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other real-world visual inputs, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an extension to the visualization of the real world around the user. For example, referring to Figure 1, an augmented reality scene 1 is depicted, in which a user of AR technology sees 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, the user of AR technology also perceives "seeing" a robot statue 1110 standing on the real-world platform 1120 and a flying cartoonish avatar character 1130 that appears to be a personification of a bumblebee, although these elements 1130 and 1110 do not exist in the real world. The human visual perception system is complex, making it difficult to create VR or AR technologies that facilitate a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0005] The systems and methods disclosed herein address various challenges related to VR or AR technologies. [Overview of the project] [Means for solving the problem]

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

[0007] In some other embodiments, a method for fabricating a display device includes the step of providing a waveguide having a metasurface. The metasurface comprises a plurality of spaced projections formed from a first optically transparent material, and a second optically transparent material extending across and between the spaced projections. The waveguide may be optically coupled to an optical pipe.

[0008] In yet another embodiment, the display system comprises a waveguide and an optically coupled optical element disposed on the surface of the waveguide. The optically coupled optical element comprises a multilevel metasurface having a plurality of spaced projections having a certain pitch and formed from a first optically transparent material, and a second optically transparent material extending across and between the spaced projections.

[0009] In some other embodiments, the display system comprises a waveguide and an optical external coupling optical element disposed on the surface of the waveguide. The optical external coupling optical element comprises a multilevel metasurface having a plurality of spaced projections having a certain pitch and formed from a first optically transparent material, and a second optically transparent material extending across and between the spaced projections.

[0010] In yet another embodiment, the display system comprises a waveguide and an optically coupled optical element disposed on the surface of the waveguide. The optically coupled optical element comprises a metasurface formed from a first optically transparent material, having a plurality of spaced-apart protrusions and optically transparent resists between the spaced-apart protrusions.

[0011] In some other embodiments, the display system comprises a waveguide and an optically externally coupled optical element disposed on the surface of the waveguide. The optically externally coupled optical element comprises a metasurface formed from a first optically transparent material, having a plurality of spaced-apart projections and optically transparent resists between the spaced-apart projections.

[0012] Additional and other purposes, features, and advantages of the present invention are described in the detailed description, figures, and claims. The present invention provides, for example, the following: (Item 1) A method for forming an optical waveguide, wherein the method is Steps to form a metasurface Includes, The step of forming the metasurface is, The steps include: covering an optically transparent substrate to provide an optically transparent resist layer, A step of patterning the resist with a pattern comprising protrusions and intervening gaps, wherein the protrusions have a pitch in the range of 10 nm to 600 nm, The steps include depositing an optically transparent material on the protrusions and in the gaps between the protrusions, Methods that include... (Item 2) The optically transparent material is amorphous, as described in item 1. (Item 3) The method according to item 1, wherein the step of depositing the optically transparent material is to form 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 higher refractive index than 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 optically transparent material is a resist, as described in item 4. (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 the step of imprinting the pattern into the resist. (Item 9) The method according to item 1, wherein the step of depositing the optically transparent material includes the step of spin-coating the optically transparent material onto 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 directed 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 directed deposition includes evaporation or sputtering of the optically transparent material. (Item 13) The method according to item 1, wherein the full width is within 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, An internal optical coupling optical element disposed on the surface of the waveguide, the internal optical 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, A second optically transparent material covering and between the spaced protrusions And an internal optical coupling optical element comprising A display system comprising. (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 display system according to item 16, wherein the waveguide is one of a stack of waveguides, and each of the stack of waveguides comprises an associated multilevel metasurface. (Item 20) The display system according to item 19, wherein at least some associated multilevel metasurfaces of the waveguide are configured to redirect light in a different wavelength range from other associated multilevel metasurfaces of the waveguide. (Item 21) The display system according to item 16, wherein the first optically transparent material comprises a resist. (Item 22) The display system as described in item 16, wherein the space between each protrusion and the nearest protrusion defines a total width of 10 to 600 nm. (Item 23) The display system according to item 16, wherein the second optically transparent material forms the spaced-apart flat regions across the protrusions. (Item 24) The display system according to item 16, wherein the first and second optically transparent materials are amorphous. (Item 25) The display system according to item 16, wherein the second optically transparent material has a higher refractive index than either the first optically transparent material or the material forming the waveguide. (Item 26) The display system according to item 25, wherein the second optically transparent material has a refractive index greater than 1.7. (Item 27) The optically transparent material comprises a semiconductor, as described in item 25. (Item 28) The optically transparent material comprises silicon, as described in item 27. (Item 29) The display system according to item 28, wherein the optically transparent material comprises silicon nitride or silicon carbide. (Item 30) The optically transparent material comprises an oxide, as described in item 25, for the display system. (Item 31) The optically transparent material comprises a metal oxide, as described in item 25, for the display system. (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 bilevel metasurface. (Item 34) The display system according to item 16, wherein the metasurface is a tri-level or higher level metasurface. (Item 35) It is a display system, Waveguide and An optical external coupling element disposed on the surface of the waveguide, wherein the optical external coupling element comprises a multilevel metasurface, and the multilevel metasurface is A plurality of spaced projections having a certain pitch and formed from a first optically transparent material, A second optically transparent material extends across and between the spaced-apart protrusions. An optical external coupling element comprising A display system equipped with the following features. (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 introduce light containing image information into the waveguide. (Item 38) The display system according to item 35, wherein the waveguide is one of a stack of waveguides, and each of the stack of waveguides comprises an associated multilevel metasurface. (Item 39) The display system according to item 38, wherein at least some associated multilevel metasurfaces of the waveguide are configured to redirect light in a different wavelength range from other associated multilevel 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 have multilevel metasurfaces. (Item 41) The display system as described in item 35, wherein the space between each protrusion and the nearest protrusion defines a total width of 200 to 500 nm. (Item 42) The display system according to item 35, wherein the second optically transparent material forms the spaced-apart 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 higher refractive index 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 optically transparent material comprises a semiconductor, as described in item 46. (Item 48) The optically transparent material comprises silicon, as described in item 47. (Item 49) The display system according to item 48, wherein the optically transparent material comprises silicon nitride or silicon carbide. (Item 50) The optically transparent material comprises an oxide, as described in item 46, for the display system. (Item 51) The optically transparent material comprises a metal oxide, as described in item 50, for the display system. (Item 52) The display system according to item 51, wherein the optically transparent material comprises titanium oxide, zirconium oxide, or zinc oxide. (Item 53) The display system according to item 35, wherein the waveguide is formed from a material having a refractive index of 1.6 or higher. (Item 54) The display system according to item 35, wherein the projection is a single-level structure. (Item 55) The display system according to item 35, wherein the protrusion has a stepped multi-level structure. [Brief explanation of the drawing]

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

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

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

[0016] [Figure 4] Figure 4 illustrates aspects of an approach to simulating a 3D image using multiple depth planes.

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

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

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

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

[0021] [Figure 9A] Figure 9A illustrates an embodiment of a cross-sectional side view of a stacked set of waveguides, each including an internally coupled optical element.

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

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

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

[0025] [Figure 11] Figures 11A-11B show an example of a cross-sectional side view of a metasurface that internally couples light into a waveguide.

[0026] [Figure 12] Figures 12A-12B show an example of a cross-sectional side view of a metasurface that externally couples light from a waveguide.

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

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

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

[0030] [Figure 16-1] Figures 16A1 and 16B-16C illustrate an example of a cross-sectional side view of the metasurface structure, in which the second material is deposited to different thicknesses across the underlying pattern of the protrusion.

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

[0032] [Figure 17] Figures 17A-17C illustrate an example of a cross-sectional side view of a metasurface structure, where the second material is a resist deposited by spin or jet coating.

[0033] [Figure 18] Figures 18A-18B illustrate an example of a cross-sectional side view of a metasurface having more than two levels.

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

[0035] The drawings are provided to illustrate exemplary embodiments described herein and are not intended to limit the scope of this disclosure. It should be understood that the drawings are schematic and not necessarily drawn to exact scale. [Modes for carrying out the invention]

[0036] Metasurfaces, which are metamaterials at reduced dimensions, offer the opportunity to achieve flat and aberration-free optics at a much smaller scale compared to geometric optics. While not limited by theory, in some embodiments, metasurfaces include 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 optical wavefronts.

[0037] However, while metasurfaces are typically formed using very high refractive index materials, their typical applications are, in other cases, limited to infrared wavelengths due to their inherently high absorptivity. 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 impact 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 sufficiently high refractive index to support the optical resonances desired for effectively manipulating the optical wavefront.

[0038] Metasurfaces also face challenges in their manufacturing. Given the size of the surface structure forming the metasurface and its characteristic features that are below the wavelength of incident light, lithography and etching processes are typically used to process the surface. However, such processes and equipment used in these processes are prohibitively expensive, 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, multilevel metasurfaces allow the use of relatively low refractive index materials while providing highly wavelength-selective redirection of light, including light in the visible portion of the optical spectrum. Preferably, the metasurface selectively redirects certain wavelengths of light while transmitting other wavelengths of light. While such properties are typically fabricated using micron-scale structures (e.g., in crystalline fibers or dispersed Bragg reflectors), various embodiments herein involve nanoscale (e.g., scales smaller than 10 to 100 times) multilevel geometric shapes to provide 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-functionality layers. Furthermore, metasurface structures can be formed by patterning using nanoimprint, thereby avoiding costly lithography and etching processes.

[0040] In some embodiments, the metasurface is a multi-level (e.g., bi-level) structure having a first level defined by spaced-out protrusions formed from a first optically transparent material between protrusions and a second optically transparent material. The metasurface also includes a second level formed by a second optically transparent material located on the upper surface of the protrusions. The first and second optically transparent materials may be formed on an optically transparent substrate, e.g., 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, for example, by diffraction. In some embodiments, the metasurface may be a three-level or higher structure, where the protrusions take the form of steps, with the second optically transparent material on both sides and on the upper surface of the protrusions.

[0041] In some embodiments, the pitch of the protrusions is about 10 nm to 1 μm, 10 to 600 nm, about 200 to 500 nm, or about 300 to 500 nm, and the height of each level is about 10 nm to 1 μm, about 10 to 500 nm, about 50 to 500 nm, or about 100 to 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 light desired for re-direction and the angle of re-direction. In some embodiments, the pitch is less than the wavelength of light to which the metasurface is configured to re-direct. In some embodiments, the second optically transparent material partially or completely occupies the space between the protrusions but does not extend above the protrusions. In some embodiments, in addition to the pitch and height of each level, the width of the protrusions may be selected based on the wavelength of light desired for re-direction and the angle of re-direction. As an example, the protrusions may have a width of about 10 nm to 1 μm, including 10 to 250 nm.

[0042] As disclosed herein, projections on a first level, i.e., a level below the upper level of a three or higher level structure, may be patterned by lithography and etching in some embodiments. More preferably, the projections may be patterned by nanoimprinting a first optically transparent material. A second optically transparent material may then be deposited between (and, in some embodiments, across) the patterned projections. The deposition may be carried out by a variety of processes, including directional deposition, blanket deposition (e.g., conformal deposition), and spin or jet coating. In some embodiments, the second optically transparent material is deposited to a thickness such that the material settles between and over the projections, and the second optically transparent material forms a flat area of ​​material across each projection, leaving a gap between the flat area on the upper level and the projections on the lower level. In some other embodiments, the deposition is advanced to the extent that the gaps between the projections are filled. In yet another embodiment, 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 direct-view 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 in a multiplexed optical 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 externally coupled optical elements.

[0044] Advantageously, the metasurface may be formed on a waveguide and may be an internally coupled and / or externally coupled optical element. The compactness and planarity of the metasurface enable not only compact waveguides but also stacking of compact waveguides where multiple waveguides form a stack. In addition, 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, high selectivity can reduce channel crosstalk in configurations where a full-color image is formed by simultaneously outputting light of different colors or wavelengths.

[0045] It should be understood that, in some embodiments, metasurfaces may selectively redirect light by reflection or diffraction. For example, a 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 light redirected by reflection or diffraction. In some other embodiments, a metasurface may function in a “transmission mode,” selectively redirecting light of one or more wavelengths while also transmitting light of other wavelengths, without substantially altering the path of light of those other wavelengths.

[0046] Here, we refer to a figure where the same reference number indicates the same feature throughout.

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

[0048] Figure 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 functions 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 ear canal (in some embodiments, another speaker, not shown, is positioned adjacent to the user's other ear canal to provide stereo / shapeable sound control). In some embodiments, the display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphones may be configured to allow the user to provide input or commands to the system 80 (e.g., selection of voice menu commands, natural language questions, 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 mounted on the frame 64 or otherwise mounted on the user 60. The cameras may be positioned and oriented to capture images of the surrounding environment in which the user 60 is located.

[0049] Continuing to refer to Figure 2, the display 62 is operably coupled to the local data processing module 70 by wired connections or wireless connectivity, etc. 68, which may be mounted in various configurations, such as being fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removable by the user 60 (e.g., in a backpack configuration, a belt-mounted configuration). The local processing and data module 70 may include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be used to assist in data processing, caching, and storage. The data includes a) data captured from sensors such as an image capture device (e.g., a camera), a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope (e.g., operably coupled to frame 64 or otherwise attached to user 60), and / or b) data acquired and / or processed using a remote processing module 72 and / or remote data repository 74 for passage to display 62 after such processing or reading, as possible. The local processing and data module 70 may be operably coupled to the remote processing module 72 and the remote data repository 74 by communication links 76, 78, such as via wired or wireless communication links, so that these remote modules 72, 74 are operably coupled to each other and available as resources for the local processing and data module 70. In some embodiments, the local processing and data module 70 may include one or more of the image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on the frame 64 or may be independent structures communicating with the location processing and data module 70 via a wired or wireless communication path.

[0050] Continuing to refer to Figure 2, in some embodiments, the remote processing module 72 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, the remote data repository 74 may comprise digital data storage facilities that may be available through the internet or other networking configurations in a “cloud” resource configuration. In some embodiments, all data is stored, and all calculations are performed within the local processing and data module, enabling fully autonomous use 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. Figure 3 illustrates a conventional display system for simulating a three-dimensional image with respect to a user. Two distinctly different images 5,7 are output to the user, one for each eye 4,6. Images 5,7 are spaced 10 units apart from eyes 4,6 along the optical axis or z-axis parallel to the viewer's line of sight. Images 5,7 are flat, and eyes 4,6 can focus on the image by taking a single, focused state. Such a system relies on the human visual system, combines images 5,7, and provides a perception of depth in the combined image.

[0052] However, it should be understood that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional "3-D" display systems may find such systems uncomfortable or may not perceive any sense of depth at all. While not limited by theory, it is thought that viewers of objects may perceive them as "three-dimensional" due to a combination of vergence and accommodation. The movement of vergence and divergence of two eyes relative to each other (i.e., the rolling movement of pupils toward or away from each other to converge the lines of sight of the eyes and fix them on an object) is closely related to focusing the lens of the eye (or "accommodation"). Under normal conditions, changing the focus of the lens of the eye, or accommodating the eye to change focus from one object to another at different distances, will automatically produce a consistent change in vergence and divergence up to the same distance, under a relationship known as the "accommodation-vergence-divergence reflex". Similarly, changes in convergence and divergence movements will, under normal conditions, induce corresponding changes in accommodation. As described herein, many stereoscopic or "3-D" display systems display scenes using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional viewpoint is perceived by the human visual system. However, such systems, above all, simply provide different presentations of scenes, but are uncomfortable for many viewers because they act against the "accommodation-convergence / divergence reflex" when the eyes view all image information in a single accommodated state. Display systems that provide better coordination between accommodation and convergence / divergence movements can form a more realistic and comfortable simulation of three-dimensional images.

[0053] Figure 4 illustrates aspects of an approach to simulating a three-dimensional image using multiple depth planes. Referring to Figure 4, objects at various distances from eyes 4 and 6 on the z-axis are accommodated by eyes 4 and 6 so that those objects are in focus. Eyes (4 and 6) take on specific accommodated states to focus on objects at different distances along the z-axis. As a result, a specific accommodated state can be associated with one of the depth planes 14, each having an associated focal length such that an object or part of an object in a particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, the three-dimensional image may be simulated by providing a different presentation of the image for each eye 4 and 6, and by providing a different presentation of the image corresponding to each depth plane. For the sake of clarity in the illustration, it should be understood that the fields of view of eyes 4 and 6 may overlap, for example, as the distance along the z-axis increases, although they are shown as separate. Furthermore, for the sake of illustration, although shown as flat, it should be understood that the contour of the depth plane can be curved in physical space so that all features within the depth plane are in focus with the eye in a particular state of perspective adjustment.

[0054] The distance between an object and eye 4 or 6 can also change the amount of light diverging from that object as it is visible to that eye. Figures 5A-5C illustrate the relationship between distance and ray divergence. The distances between the object and eye 4 are expressed in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, rays diverge more as the distance to the object decreases. As the distance increases, rays become more collimated. In other words, the light field produced by a point (object or part of an object) can be said to have a spherical wavefront curvature, which is a function of the distance the point is from the user's eye. The curvature increases with decreasing distance between the object and eye 4. Consequently, in different depth planes, the ray divergence is also different, and the divergence increases with decreasing distance between the depth plane and the viewer's eye 4. Only monocular eye 4 is illustrated in Figures 5A–5C and various other figures herein for the sake of clarity in the illustration, but it should be understood that the discussion relating to eye 4 may apply to both eyes 4 and 6 of the viewer.

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

[0056] Figure 6 illustrates an embodiment of a waveguide stack for outputting image information to a user. The display system 1000 includes a waveguide stack or a stacked waveguide assembly 178, which may be used to provide three-dimensional perception to the eyes / brain using a plurality of waveguides 182, 184, 186, 188, 190. In some embodiments, the display system 1000 is the system 80 of Figure 2, and Figure 6 shows some parts of that system 80 in more detail. For example, the waveguide assembly 178 may be part of the display 62 of Figure 2.

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

[0058] In some embodiments, the image input devices 200, 202, 204, 206, and 208 are discrete displays that generate image information for input into the corresponding waveguides 182, 184, 186, 188, and 190, respectively. In some other embodiments, the image input devices 200, 202, 204, 206, and 208 are output terminals of a single multiplexed display that can send image information to each of the image input devices 200, 202, 204, 206, and 208 via, for example, one or more optical conduits (such as optical fiber cables). It should be understood that the image information provided by the image input devices 200, 202, 204, 206, and 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, and 208 may also be the output terminals of a scanning fiber display system, and the image input devices 200, 202, 204, 206, and 208 move or scan across the corresponding input surfaces 382, ​​384, 386, 388, and 390 of waveguides 182, 184, 186, 188, and 190 to input image information into those waveguides. An embodiment of such a scanning fiber system is disclosed in U.S. Patent Application No. 14 / 641,376 and is incorporated herein by reference. In some embodiments, several of the image input devices 200, 202, 204, 206, and 208 may be replaced by scanning fibers.

[0060] Continuing with Figure 6, the controller 210 controls the operation of the stacked waveguide assembly 178 and the image input devices 200, 202, 204, 206, and 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-transient medium) to coordinate the timing and provisioning of image information to the waveguides 182, 184, 186, 188, and 190, for example, according to one of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. In some embodiments, the controller 210 may be part of the processing module 70 or 72 (Figure 1).

[0061] Continuing with Figure 6, the waveguides 182, 184, 186, 188, and 190 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each waveguide 182, 184, 186, 188, and 190 may be planar or have another shape (e.g., curved), with major upper and lower surfaces and edges extending between their major upper and lower surfaces. In the illustrated configuration, each waveguide 182, 184, 186, 188, and 190 may include one or more externally coupled optical elements 282, 284, 286, 288, and 290 configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide and outputting image information to the eye 4. The extracted light may also be referred to as externally coupled light, and the optical elements that externally couple one or more lights may also be referred to as light extraction optical elements. The beam of extracted light is output by a waveguide at the point where the light propagating within the waveguide strikes the light extraction optical element. Some or all of the one or more externally coupled optical elements 282, 284, 286, 288, 290 may 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, 188, 190 are shown positioned on the bottom main surface, but in some embodiments, one or more external coupling optical elements 282, 284, 286, 288, 290 may be positioned on the top and / or bottom main surface, as further discussed herein, and / or directly within the volume of the waveguides 182, 184, 186, 188, 190. In some embodiments, one or more external coupling optical elements 282, 284, 286, 288, 290 may be mounted on a transparent substrate and formed within a layer of material forming the waveguides 182, 184, 186, 188, 190. In some other embodiments, the waveguides 182, 184, 186, 188, 190 may be monolithic components of the material, and one or more externally coupled optical elements 282, 284, 286, 288, 290 may be formed on and / or inside the surface of that component of the material.

[0062] Continuing with reference to Figure 6, as discussed herein, each waveguide 182, 184, 186, 188, 190 is configured to emit 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 introduced into such waveguide 182. The collimated light may represent the optical infinity focal plane. The next upper waveguide 184 may be configured to emit collimated light that passes through a first lens 192 (e.g., a negative lens) before it can reach the eye 4. Such a first lens 192 may be configured to generate some convex wavefront curvature so that the eye / brain interprets the light originating from the next upper waveguide 184 as originating from a first focal plane closer inward from optical infinity toward the eye 4. Similarly, the third upper waveguide 186 passes its output light through both the first lens 192 and the second lens 194 before reaching the eye 4. The combined refractive power of the first lens 192 and the second lens 194 may be configured to produce another gradually increasing wavefront curvature so that the eye / brain interprets the light emanating from the third waveguide 186 as emanating from a second focal plane even closer, inward toward the person from optical infinity, which was the light from the next upper waveguide 184. Other methods for producing these perceived colors may also be considered as possibilities.

[0063] Other waveguide layers 188, 190 and lenses 196, 198 are configured similarly, with the highest waveguide 190 in the stack emitting its output through all the lenses between it and the eye for a convergent focusing force representing the focal plane closest to the person. When viewing / interpreting light originating from the other side world 144 of the stacked waveguide assembly 178, a compensating lens layer 180 may be positioned on top of the stack to compensate for the stack of lenses 198, 196, 194, 192 and to compensate for the convergent force of the lower lens stacks 198, 196, 194, 192. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both or one 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, and 190 may have the same associated depth plane. For example, a plurality of waveguides 182, 184, 186, 188, and 190 may be configured to output images set in the same depth plane, or a plurality of subsets of waveguides 182, 184, 186, 188, and 190 may be configured to output images set in the same plurality of depth planes, with one set for each 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 Figure 6, one or more external coupling optical elements 282, 284, 286, 288, 290 may be configured to both redirect light from its individual waveguide and output this light with an appropriate amount of divergence or collimation for a specific depth plane associated with the waveguide. As a result, waveguides with 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 voids).

[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 “DOE”). Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the beam light is deflected toward the eye 4 through 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 therefore split into several associated outgoing beams that exit the waveguide at various locations, resulting in a very uniform pattern of outgoing 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 in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal, in which microdroplets 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 incident light), or the microdroplets can be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0068] Figure 7 shows an embodiment of an outgoing beam output by a waveguide. Although one waveguide is shown, other waveguides within the waveguide assembly 178 (Figure 6) may function similarly, and it should be understood that the waveguide assembly 178 includes multiple waveguides. Light 400 is introduced into the waveguide 182 at the input surface 382 of the waveguide 182 and propagates through the waveguide 182 by TIR. At the point where the light 400 collides on the DOE 282, a portion of the light exits the waveguide as an outgoing beam 402. The outgoing beam 402 is shown as substantially parallel, but may be redirected to propagate to eye 4 at a certain angle (e.g., forming a divergent outgoing beam), depending on the depth plane associated with the waveguide 182, as discussed herein. It should be understood that a nearly parallel emitted beam may represent a waveguide with one or more externally coupled optical elements that externally couple the light to form an image that appears to be set in the depth plane at a distance from eye 4 (e.g., optical infinity). Other waveguides or other sets of externally coupled optical elements may output a more divergent emitted beam pattern, which would require eye 4 to adjust to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to eye 4 than optical infinity.

[0069] Figure 8 illustrates an embodiment of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors. In some embodiments, a full-color image may be formed in each depth plane by overlaying an image onto each of the primary colors, e.g., three or more primary colors. The illustrated embodiment shows depth planes 14a–14f, but more or fewer depths may also be considered. Each depth plane may have three primary color images associated with it, 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 indicated in the figure by different numbers relating to diopters following the letters G, R, and B. As merely an embodiment, the numbers following each of these letters indicate diopters (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, each primary color light may be output by a single dedicated waveguide, and as a result, each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure, including the letters G, R, or B, can be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, and three primary color images are 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 waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, for example, so that only a single waveguide may be provided for each depth plane.

[0071] Continuing to refer to Figure 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, or may replace one or more of red, green, or blue.

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

[0073] Referring here to Figure 9A, in some embodiments, light impacting a waveguide may need to be redirected to internally couple that light into the waveguide. Internal coupling optical elements may be used to redirect and internally couple the light into its corresponding waveguide. Figure 9A illustrates embodiments of cross-sectional side views of multiple or set 1200 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 (Figure 6), and the illustrated waveguides of stack 1200 may correspond to some of the multiple waveguides 182, 184, 186, 188, 190, but it should be understood that light from one or more of the 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 located on the main surface (e.g., bottom main surface) of waveguide 1210, internal coupling optical element 1224 is located on the main surface (e.g., bottom main surface) of waveguide 1220, and internal coupling optical element 1232 is located on the main surface (e.g., bottom main surface) of waveguide 1230. In some embodiments, one or more of the internal coupling optical elements 1212, 1222, 1232 may be located on the upper main surfaces of the individual waveguides 1210, 1220, 1230 (in particular, one or more internal coupling optical elements are transmissive deflection optical elements). Preferably, the internally coupled optical elements 1212, 1222, 1232 are located on the bottom main surface of their respective waveguides 1210, 1220, 1230 (or on the top of the next lower waveguide), and in particular, their internally coupled optical elements are reflective deflection optical elements. In some embodiments, the internally coupled optical elements 1212, 1222, 1232 may be located within the bodies of the respective waveguides 1210, 1220, 1230. In some embodiments, as discussed herein, the internally coupled optical elements 1212, 1222, 1232 are wavelength-selective to selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although the internal coupling optical elements 1212, 1222, 1232 are shown on one side or corner of the individual waveguides 1210, 1220, 1230, it should be understood that in some embodiments, they may be located within other areas of the individual waveguides 1210, 1220, 1230.

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

[0076] Waveguides 1210, 1220, and 1230 may be separated and isolated by solid layers of gas and / or material. For example, as shown, layer 1218a may separate waveguides 1210 and 1220, and layer 1218b may separate waveguides 1220 and 1230. In some embodiments, layers 1218a and 1218b are formed from low refractive index material (i.e., material having a lower refractive index than the material forming the immediate vicinity of waveguides 1210, 1220, and 1230). Preferably, the refractive index of the material forming layers 1218a and 1218b is 0.05 or greater, or 0.10 or greater than greater, than the refractive index of the material forming waveguides 1210, 1220, and 1230. Advantageously, layers 1218a and 1218b with lower refractive indices may function as cladding layers that promote total internal reflection (TIR) ​​of light through waveguides 1210, 1220, and 1230 (e.g., TIR between the upper and lower main surfaces of each waveguide). In some embodiments, layers 1218a and 1218b are formed from air. It should be understood that the upper and lower parts of the illustrated set of waveguides 1200 may also include an immediate cladding layer, although these are not shown.

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

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

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

[0080] For example, the internally coupled optical element 1212 may be configured to selectively deflect (e.g., reflect) a ray 1240 having a first wavelength or wavelength range, while transmitting rays 1242 and 1244 having different second and third wavelengths or wavelength ranges, respectively. The transmitted ray 1242 then collides with an internally coupled optical element 1222, which is configured to selectively deflect (e.g., reflect) light of the second wavelength or wavelength range, and is deflected by it. The ray 1244 is transmitted by the internally coupled optical element 1222 and collides with an internally coupled optical element 1232, which is configured to selectively deflect (e.g., reflect) light of the third wavelength or wavelength range, and continues to be deflected by it.

[0081] Continuing with Figure 9A, the deflected rays 1240, 1242, and 1244 are deflected so that they propagate through the corresponding waveguides 1210, 1220, and 1230. That is, the internal coupling optical elements 1212, 1222, and 1232 of each waveguide deflect the light into their corresponding waveguides 1210, 1220, and 1230, and internally couple the light into the corresponding waveguides. The rays 1240, 1242, and 1244 are deflected at an angle that causes the light to propagate through the individual waveguides 1210, 1220, and 1230 by TIR.

[0082] Continuing to refer to Figure 9A, rays 1240, 1242, and 1244 propagate through the individual waveguides 1210, 1220, and 1230 by TIR until they collide with the corresponding optical dispersion elements 1214, 1224, and 1234 of the waveguides.

[0083] Referring now to Figure 9B, an embodiment of the perspective view of multiple stacked waveguides in Figure 9A is illustrated. As previously mentioned, the internally coupled rays 1240, 1242, and 1244 are deflected by the internally coupled optical elements 1212, 1222, and 1232, respectively, and then propagate by TIR within waveguides 1210, 1220, and 1230, respectively. The rays 1240, 1242, and 1244 then collide with the optical dispersion elements 1214, 1224, and 1234, respectively. The optical dispersion elements 1214, 1224, and 1234 deflect the rays 1240, 1242, and 1244 so that they propagate toward the externally coupled optical elements 1250, 1252, and 1254, respectively.

[0084] In some embodiments, the optical dispersion elements 1214, 1224, and 1234 are orthogonal pupil magnification elements (OPEs). In some embodiments, the OPEs both deflect or disperse light to the external coupling optical elements 1250, 1252, and 1254, and increase the beam or spot size of the light as it propagates to the external coupling optical elements. In some embodiments, for example, if the beam size is already of a desired size, the optical dispersion elements 1214, 1224, and 1234 may be omitted, and the internal coupling optical elements 1212, 1222, and 1232 may be configured to deflect light directly to the external coupling optical elements 1250, 1252, and 1254. Referring to Figure 9A, for example, in some embodiments, the optical dispersion elements 1214, 1224, and 1234 may be replaced by the external coupling optical elements 1250, 1252, and 1254, respectively. In some embodiments, the external coupling optical elements 1250, 1252, and 1254 are exit pupils (EPs) or exit pupil enlargement elements (EPEs) that direct light towards the viewer's eye 4 (Figure 7).

[0085] Therefore, referring to Figures 9A and 9B, in some embodiments, the set of waveguides 1200 includes, for each primary color, waveguides 1210, 1220, 1230, internal coupling optical elements 1212, 1222, 1232, optical dispersion elements (e.g., OPE) 1214, 1224, 1234, and external coupling optical elements (e.g., EP) 1250, 1252, 1254. Waveguides 1210, 1220, 1230 may be stacked with air gaps / cladding layers between each one. The internal coupling optical elements 1212, 1222, 1232 redirect or deflect the desired color into its appropriate waveguide while transmitting light of other colors. The light then propagates within the individual waveguides 1210, 1220, 1230 at an angle that will result in a TIR. In the embodiment shown, a ray 1242 (e.g., green light) will be reflected from the first internally coupled optical element (e.g., color filter) 1212 in the manner described above, and will then continue to bounce along the waveguide, interacting with the optical dispersion element (e.g., OPE) 1214, and then with the externally coupled optical element (e.g., EP) 1250. Rays 1242 and 1244 (e.g., blue and red light) will pass through the internally coupled optical element (e.g., color filter) 1212 into the next waveguide 1220. Ray 1242 will be reflected from the next internally coupled optical element (e.g., color filter) 1222, and will then bounce along the waveguide 1220 via TIR, proceeding to its optical dispersion element (e.g., OPE) 1224, and then with the externally coupled optical element (e.g., EP) 1252. Finally, the light 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, then to the external coupling optical element (e.g., EP) 1254, and finally, together with the light from the other waveguides 1210, 1220, it will be externally coupled to the viewer.

[0086] (Meta-surface) Figure 10A illustrates an embodiment of a metasurface according to several embodiments. The substrate 2000 has a surface 2000a on which the metasurface 2010 is placed. The metasurface 2010 comprises multiple levels of optically transparent material. As shown, in some embodiments, the metasurface is a bilevel structure having first and second levels 2012 and 2014, respectively. The first level 2012 comprises multiple protrusions 2020 formed from the first optically transparent material and clumps 2030a of the second optically transparent material between the protrusions. The second level 2014 is located on the protrusions (separated and separated from the substrate by the first level) and comprises clumps 2030b of the second level of the second optically transparent material formed on the protrusions 2020. The protrusions 2020 may be ridges (or nanowires) that extend laterally in and out of the page, defining trenches between neighboring protrusions. As shown in the figure, at the second level 2014, the chunks 2030b of the second optically transparent material may be localized on the surface of the projection 2020, forming a flat region of material separated from other localized deposits (or flat regions) of the second optically transparent material.

[0087] Preferably, the refractive index of the second optically transparent material forming the blocks 2030a and 2030b is higher than the refractive index of both the first optically transparent material forming the protrusion 2020 and the material forming the substrate 2000. In some embodiments, the refractive index of the first optically transparent material is lower than or similar to the refractive index of the material forming the substrate 2000. It should be understood that the substrate 2000 may also be a waveguide, and may correspond to waveguides 182, 184, 186, 188, 190 (Figure 6) and / or waveguides 1210, 1220, and 1230 (Figure 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 provide the advantage of increasing the field of view of a display that emits light from its substrate 2000 and 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 transparent material. Preferably, the glass, plastic, polymer, sapphire, or other optically transparent material has a high refractive index, for example, higher than 1.5, 1.6, 1.7, 1.8, or 1.9.

[0088] Continuing with Figure 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 blocks 2030a and 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 and oxides, including silicon-containing materials. Examples of silicon-containing materials include silicon nitride and silicon carbide. Examples of oxides include titanium oxide, zirconium oxide, and zinc oxide. In some embodiments, the second optically transparent material may have 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. Although not limited by theory, amorphous materials may be preferred in some applications because they can be formed at lower temperatures and over a wider surface area than some crystalline materials. In some embodiments, the first and second optically transparent materials forming features 2020, 2030a, 2030b may each be one of amorphous or crystalline semiconductor materials.

[0089] Continuing with Figure 10A, the projection has a pitch of 2040. As used herein, pitch refers to the distance between similar points on two nearest structures. Similar points should be understood as being located on similar parts (e.g., left or right edge) of structures that are substantially identical. For example, the pitch of projection 2020 is equal to the total width defined by projection 2020 and the nearest separation between projection 2020 and its nearest similar projection 2020. In other words, pitch can be understood as the width of the repeating units of the array of features formed by those projections 2020 (e.g., the sum of the widths of projection 2020 and block 2030a).

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

[0091] Advantageously, multilevel metasurfaces are highly selective for specific wavelengths of light. Figure 10B shows plots of transmission and reflection spectra for a metasurface having the general structure shown in Figure 10A. In this embodiment, the protrusion 2020 has a width of 125 nm and a thickness of 25 nm and is formed from resist, while the blocks of material 2030a and 2030b have a thickness of 75 nm and are formed from silicon nitride, with a pitch of 340 nm and voids separating block 2030b. The horizontal axis represents wavelength, and the horizontal axis represents transmittance (scale from 0 to 1.00 from no reflection to total reflection). Notably, a sharp peak in reflection (517 nm) and a corresponding reduction in transmittance are observed for narrowband wavelengths, while other wavelengths are transmitted. Light is reflected when its wavelength matches the resonant wavelength (approximately 517 nm in this embodiment). The protrusions 2020 and the upper structure 2030 are arranged with subwavelength spacing, and only zero-order reflectance and transmittance exist. As shown in Figure 10B, the reflectance spectrum shows a steep 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 protrusion 2020 and the upper structure 2030) may be modified to alter the optical redirectivity of the metasurface. For example, when the pitch is larger, light at the resonant wavelength will be diffracted (or deflected at an off-normal angle, e.g., less than 90 degrees with respect to the surface of the substrate 2000) upon incidence onto the metasurface 2010. In some embodiments, if the substrate 2000 is a waveguide, the pitch of the metasurface structure may be selected such that light at the resonant wavelength propagates through the waveguide by total internal reflection (TIR), while other wavelengths and colors will be 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. Figures 11A-11B show an embodiment of a cross-sectional side view of a metasurface that internally couples light into a waveguide.

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

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

[0095] In some embodiments, the metasurface 2010 may have a geometric size and / or pitch that imparts optical power to the diffracted light on the metasurface. For example, the metasurface may be configured to cause light to radiate out of the metasurface in a divergent or convergent direction. Different portions of the metasurface may have different pitches that deflect different rays in different directions, for example, so that the rays diverge or converge.

[0096] In some other embodiments, the metasurface may deflect light so that it propagates from the metasurface as collimated rays of light. For example, if collimated light strikes the metasurface at similar angles, the metasurface may have a consistent geometric size and consistent pitch across its entire surface, deflecting the light at similar angles.

[0097] Referring to Figures 11A-12B, as illustrated, the metasurface 2010 may deflect light in a "reflection mode," where deflected light remains on the same side of the metasurface before and after impacting it, 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 deflected and undeflected light are transmitted across the thickness of the metasurface, and the path of the deflected light differs after exiting the metasurface, while the path of the undeflected light remains substantially unchanged. It should be understood that the metasurface may have both transmission and reflection capabilities; for example, in some embodiments, the metasurface may reflect some of the incident light while transmitting and deflecting other parts of it.

[0098] Figures 13A-13B show embodiments of the metasurface 2010 operating in transmission mode. Referring to Figure 13A, rays 1240 and 1244 propagate through the metasurface substantially unblinded while ray 1242 is deflected. Ray 1242 may be at the resonant wavelength for the metasurface 2010, while rays 1240 and 1244 are not. In some embodiments, deflection may be used to internally or externally couple ray 1240. Figure 13B shows an embodiment of the metasurface configured to operate in transmission mode for optical internal coupling. In some embodiments, as illustrated, rays 1240, 1242, and 1244 each have different wavelengths (e.g., corresponding to different colors), and metasurfaces 1212, 1222, and 1232 each are selective for deflecting specific wavelengths or wavelength ranges. For example, the metasurface 1212 may selectively deflect ray 1240 in transmission mode while transmitting rays 1242 and 1244 without deflection. Similarly, as shown, the metasurface 1222 may selectively deflect ray 1242 in transmission mode while transmitting ray 1244 without deflection, and the metasurface 1232 may selectively deflect 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 the external coupling optical elements 282, 284, 286, 288, 290 (Figure 6) or 1250, 1252, 1254 (Figure 9B).

[0099] Metasurfaces that function in transmission mode can offer advantages in several applications, such as when used on a waveguide in conjunction with other transmission optical elements (e.g., several embodiments of the optical dispersion elements 1214, 1224, 1234 and / or externally coupled optical elements 1250, 1252, 1254 in Figure 9B). Such transmission mode metasurfaces may be formed on the same side of the substrate as the other optical elements, which can have the advantage of facilitating the processing of the metasurface and optical elements while reducing the possibility of damaging the metasurface or optical elements (which can occur when processing is required on two sides of the substrate).

[0100] Figures 14A-14D illustrate an example of a process flow for forming a 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 transparent and may be deposited, for example, by spin coating to form a layer of resist. In some embodiments, the resist 2020a may be deposited by jet coating (e.g., inkjet printing), which may offer the advantage of forming a very thin layer, and also 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, the imprint template or master 2024 is brought into contact with the resist 2020a to pattern the resist. It should be understood that the pattern within 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 a 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 may then be removed, leaving the patterned resist 2020 as shown in Figure 14C.

[0103] Referring to Figure 14D, the 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 transparent resists. As disclosed herein, the second material 2030 is preferably an optically transparent material. The second material 2030 may be deposited by various processes, including blanket deposition, directional deposition, and spin or jet coating. Examples of blanket deposition include chemical vapor deposition (CVD), in which the resist is exposed to mutually reactive precursors simultaneously present in a deposition chamber containing the substrate 2000, and atomic layer deposition (ALD), in which the resist is exposed to precursors as an alternative. ALD may offer the advantage of precise control of the thickness of the deposited layer when high precision is desired and when the deposited material is formed at low temperatures. An example of directional deposition involves evaporation and sputtering to deliver a second material to a resist 2020 and substrate 2000 to be nanoimprinted.

[0104] Referring here to Figure 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 residual layer thickness (RLT) 2021. Such residual layer thicknesses are typical of nanoimprints and may be present in various embodiments of this specification (not shown). If the protrusions 2020 are formed from an imprinted resist, it should be understood that 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 about 3 to less than 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 here to Figures 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 in different locations, including different levels relative to the protrusion 2030. Figures 16A1 and 16B-16C illustrate embodiments of cross-sectional side views of metasurface structures, where the second material is deposited to different thicknesses across the underlying pattern of the protrusion. In Figure 16A1, the metasurface 2010 is defined by a bilevel structure with a void between the protrusion 2020 and the lumps 2030a and 2030b of the second material deposited on the protrusion. If the deposition is a directed deposition process, it should be understood that the second material is substantially localized on the upper surface of the protrusion and within the space between the protrusions 2020, with little to no material accompanying the sides of the protrusion. If the deposition is conformal blanket deposition, the second material 2030 is deposited on the top, between, and sides of the projection 2020. Figure 16A1 illustrates a portion of the second material on the side of the projection 2020, although the material 2030 on the side is not necessarily to an exact scale. In some embodiments, the material 2030 forms a blanket layer having substantially constant thickness over all surfaces, including the sidewalls of the projection 2020. As discussed herein, such a blanket layer may be deposited, for example, by ALD.

[0106] Figure 16A2 shows plots of transmission and reflection spectra for a metasurface having the general structure shown in Figure 16A1. The horizontal axis represents the angle of incidence of light, and the horizontal axis represents the transmittance (scale from 0 to 1). In this embodiment, the protrusion 2020 is formed from a resist and has 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 with a substantially constant thickness of 60 nm and a pitch of 382 nm, with voids separating the mass 2030b. As seen in Figure 16A2, the metasurface has a wide range of angles of incidence, which is advantageous as it reflects light. For example, the metasurface is highly light reflective when it has an angle of about ±0.25 radians with respect to the normal to the metasurface (e.g., with respect to the thickness axis of the metasurface).

[0107] Figure 16B illustrates a metasurface defined by a bilevel structure with no gaps between the protrusions 2020. The second material is deposited to such an extent that the gaps between the protrusions 2020 are completely filled by the mass 2030a. The deposition required to achieve the illustrated structure is directional deposition, but conformal blanket deposition would also achieve a similar structure (with some widening of the flat area formed by the material 2030 on the upper level of the metasurface structure).

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

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

[0110] In some embodiments, the structure takes the form of a bilevel structure, but it should be understood that the metasurfaces disclosed herein may include more than two levels. For example, a metasurface may include three or more levels. These three or higher level structures may be formed using stepped projections. The lower levels (closest to the substrate) may include portions of the projection formed from a first optically transparent material and chunks of the second optically transparent material on the sides of the projection, while the highest level (farthest from the substrate) preferably contains only the second optically transparent material deposited on the upper surface of the highest step of the projection. Preferably, n-1 levels of stepped projections are utilized to form n levels of metasurfaces, with each step on a continuous level having a smaller width than the step on the level directly below it. In some embodiments, the steps are symmetrical with respect to an axis extending to the height of the projection, as seen in a cross-sectional side view obtained laterally with respect to the extension axis of the projection. These three or higher levels of metasurfaces may be considered as bilevel metasurfaces in the same application (e.g., as internally coupled and / or externally coupled optical elements).

[0111] Figures 18A-18B illustrate embodiments of cross-sectional side views of metasurfaces having more than two levels. Figure 18A illustrates a metasurface 2010 having first, second, and third levels, 2012, 2014, and 2016, respectively. The trilevel metasurface 2010 is formed using stepped projections 2020, each extending across two levels with one step on each level, the width of the step on the second level being less than the width of the step on the first level. A second block of optically transparent material 2030a is formed on the side of the projection 2020 on the first level 2012, preferably extending continuously from one projection 2020 to the nearest projection 2020. A second block of optically transparent material 2030b is formed on the side of the projection 2020 on the second level 2014. On the third level, the mass 2030c of the second optically transparent material is formed on the upper surface of the projection 2020. As shown in the figure, the amount of the second optically transparent material deposited is such that, together with the height of the step of the projection 2020, the second optically transparent material does not have a thickness that occupies the entire height of the given level. In a sense, a void exists at the given level in the space between the nearest projections 2020.

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

[0113] Figures 19A–19D illustrate an example of a process flow for forming a metasurface having two or more levels. In some embodiments, the process flow may proceed using a process similar to the process flow in Figures 14A–14D, but the imprint template 2026 is a multilevel structure configured for imprinting multilevel protrusions. Such a multilevel imprint template 2026 may be formed by 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 multilevel protrusions.

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

[0115] Referring to Figure 19B, the 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 multilevel protrusions are shown in Figure 19C.

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

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

[0118] In some embodiments, a waveguide 2000 having a metasurface 2010 (as an internally coupled and / or externally coupled optical element) may be used to form a display system such as system 1000 (Figure 6) disclosed herein. For example, after processing the metasurface 2010, the waveguide 2000 may be optically coupled to an optical pipe, such as an optical pipe for loading image information into the waveguide. In some embodiments, the optical pipe may be an optical fiber. Examples of optical pipes include image loading devices 200, 202, 204, 206, 208 (Figure 6) and a scanning optical fiber. 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 image loading devices.

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

[0120] For example, advantageously, it is used with an AR display that provides images across multiple depth planes, but the augmented reality content disclosed herein may also be displayed by a system that provides images on a single depth plane. Furthermore, although illustrated as being on a single surface of a substrate, it should be understood that metasurfaces may be located on multiple substrate surfaces (e.g., opposing primary surfaces of a waveguide). In some embodiments, where multiplexed image information (e.g., light of different colors) is directed into the waveguide, multiple metasurfaces, e.g., one active metasurface for each color of light, may be provided on the waveguide. In some embodiments, the pitch or periodicity and / or geometric size of the projections forming the metasurface may vary across the metasurface. Such metasurfaces may be active in redirecting light of different wavelengths depending on the geometry and pitch at the point where light strikes the metasurface. In some other embodiments, the geometry and pitch of the metasurface features are configured to vary so that the deflected rays propagate from the metasurface at different angles, even if they are of similar wavelengths. Furthermore, multiple separate metasurfaces may be arranged across the substrate surface, and in some embodiments, each metasurface may have the same geometric shape and pitch, or in some other embodiments, at least some of the metasurfaces may have a different geometric shape and / or pitch from the others.

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

[0122] In addition, numerous modifications may be made to adapt specific situations, materials, compositions, processes, actions or steps of a process to the object, spirit, or scope of the present invention. Furthermore, as will be understood by those skilled in the art, each of the individual modifications described and illustrated herein has discrete components and features that can be readily separated from or combined with features of any of several other embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

[0123] The present invention includes methods that may be performed using the device. The methods may include the act of providing such a suitable device. Such provision may be performed by a user. In other words, the act of “providing” is merely requiring the user to acquire, access, approach, position, configure, activate, power on, or otherwise operate in order to provide the necessary device in the method. The methods described herein may be performed in any logically possible order of the described events, as well as in the order in which the events are described.

[0124] Exemplary aspects of the present invention, along with details relating to material selection and manufacturing, are described above. Other details of the present invention are understood in connection with the above-referenced patents and publications and, generally, can be grasped or understood by those skilled in the art. The same may apply to the method-based aspects of the present invention in terms of additional actions that may be adopted generally or theoretically.

[0125] To facilitate explanation, various words indicating the relative position of features are used herein. For example, different features may be described as being "higher" or "lower" than other features, "on top of," "across," or "on the side of." Other words for relative position may also be used. All such words for relative position assume, for explanatory purposes, that the collective structure or system formed by the features as a whole is in a certain orientation, which serves as a reference point. However, it should be understood that, when used, the structure may be positioned laterally, inverted, or in any number of other orientations.

[0126] In addition, although the present invention has been described with reference to several embodiments that optionally incorporate various features, the present invention is not limited to those described or indicated to be considered with respect to each modification of the present invention. Various modifications may be made to the described invention, and equivalents may be substituted (whether described herein or not for the sake of some brevity) without departing from the true spirit and scope of the invention. In addition, if a range of values ​​is provided, it is understood that all intervening values ​​between the upper and lower limits of that range, and any other provisions or intervening values ​​within that defined range, are encompassed within the present invention.

[0127] Furthermore, it should be considered that any optional feature of a variation of the invention described herein may be described and claimed independently or in combination with any one or more features of those described herein. References to singular items include the possibility of multiple identical items existing. More specifically, as used herein and in the claims associated therewith, the singular forms “a, an,” “said,” and “the” include multiple referents unless otherwise specifically stated. In other words, the use of articles allows for “at least one” of the subject items in the above description and in the claims associated with this disclosure. Furthermore, it should be noted that such claims may be drafted to exclude any optional elements. Thus, this statement is intended to function as an antecedent for the use of such exclusive terms, or “negative” restrictions, such as “only,” “only,” and “equivalents,” relating to the description of the claim elements.

[0128] Without using such exclusive terms, the term “equipped with” in the claims associated with this disclosure shall allow for the inclusion of any additional elements, whether a given number of elements are enumerated in such claims or whether the addition of features can be considered to transform the nature of the elements described in such claims. Unless otherwise specifically defined herein, all technical and scientific terms used herein are 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 this specification, but rather is limited only to the claims associated with this disclosure.

Claims

1. A display system, A waveguide configured to propagate and output light that transmits image information, An optical element placed on the surface of the waveguide and Equipped with, The optical element is configured to redirect the light, and the redirection includes at least one of internally coupling the light into the waveguide or externally coupling the light out of the waveguide. The optical element comprises a multilevel metasurface, The aforementioned multilevel metasurface is A plurality of spaced projections projecting outward from the surface of the waveguide, wherein the plurality of spaced projections have a certain pitch, are formed from a first optically transparent material, and each of the spaced projections includes at least two steps, A second optically transparent material located between the spaced protrusions, wherein the second optically transparent material at least partially fills the space between the protrusions. Equipped with, A display system in which the first optically transparent material has a different refractive index from the second optically transparent material, the second optically transparent material has a higher refractive index than the first optically transparent material, and the second optically transparent material has a higher refractive index than the material forming the waveguide.

2. The display system according to claim 1, wherein the surface of the second optically transparent material between the spaced projections is substantially at the same level as the first step of the spaced projections.

3. The display system according to claim 1, wherein the surface of the second optically transparent material between the spaced projections is not at substantially the same level as the first step of the spaced projections.

4. The display system according to claim 1, further comprising a layer of resist beneath the plurality of spaced-apart protrusions.

5. The display system according to claim 1, wherein the pitch of the protrusions varies across the surface of the waveguide.

6. The display system according to claim 1, further comprising an image input device configured to input light containing the image information into the waveguide.

7. The display system according to claim 6, wherein the optical element is an internally coupled optical element, and the image input device is configured to input light into the waveguide through the internally coupled optical element.

8. The display system according to claim 1, wherein the waveguide is one of a stack of waveguides, and each of the stack of waveguides comprises an associated multilevel metasurface.

9. The display system according to claim 8, wherein at least some associated multilevel metasurfaces of the waveguide are configured to redirect light in a different wavelength range from other associated multilevel metasurfaces of the waveguide.

10. The display system according to claim 1, wherein the pitch is in the range of 10 to 600 nm.

11. The display system according to claim 1, wherein the pitch is less than the wavelength of the redirected light.

12. The display system according to claim 1, wherein the multilevel metasurface further comprises a mass of the second optically transparent material on at least one of the steps of each of the plurality of spaced-apart protrusions.

13. The display system according to claim 1, wherein the multilevel metasurface further comprises a mass of the second optically transparent material on each of the steps of each of the plurality of spaced-apart protrusions.

14. The display system according to claim 1, wherein each of the spaced-apart projections includes a first step at a first level and a second step at a second level, the first step being wider than the second step.

15. The display system according to claim 1, wherein the second optically transparent material located between the spaced-apart protrusions extends continuously between neighboring protrusions among the spaced-apart protrusions.

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