Antireflection coatings for metasurfaces

Abstract

To provide favorable antireflection coatings for metasurfaces.SOLUTION: Antireflection coatings for metasurfaces are described herein. In some embodiments, the metasurface may include a substrate, a plurality of nanostructures thereon, and an antireflection coating disposed over the nanostructures. The antireflection coating may be a transparent polymer, for example a photoresist layer, and may have a refractive index lower than the refractive index of the nanostructures and higher than the refractive index of an overlying medium (e.g., air). Advantageously, the antireflection coatings may reduce or eliminate ghost images in an augmented reality display in which the metasurface is incorporated.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] This application claims the benefit of priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 62 / 451,587, filed January 27, 2017, the entire disclosure of which is incorporated herein by reference.

[0002] This application incorporates by reference each of the following patent applications in their entirety: U.S. Application No. 14 / 555,585, filed November 27, 2014; U.S. Application No. 14 / 690,401, filed April 18, 2015; U.S. Application No. 14 / 212,961, filed March 14, 2014; U.S. Application No. 14 / 331,218, filed July 14, 2014; U.S. Application No. 15 / 342,033, filed November 2, 2016 (Attorney Docket No. MLEAP.027A); U.S. Provisional Application No. 62 / 333,067, filed May 6, 2016 (Attorney Docket No. MLEAP.066PR); U.S. Provisional Application No. 62 / 451,608, entitled "DIFFRACTION GRATINGS FORMED BY No. 62 / 451,615, entitled “DIFFRACTION GRATINGS BASED ON METASURFACES HAVING ASYMMETRIC OPTICAL- ELEMENTS,” filed January 27, 2017 (Attorney Docket No. MLEAP.103PR).

[0003] The present disclosure relates to optical systems, such as display systems, including augmented reality systems. [Background technology]

[0004] Modern computing and display technologies have facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or may be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual 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. Mixed reality or "MR" scenarios are a type of AR scenario that typically involve virtual objects that are integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is otherwise perceived to interact with objects in the real world.

[0005] Referring to FIG. 1, an augmented reality scene 10 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user also perceives that they are "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying cartoon-like avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The human visual perception system is complex, making it difficult to create AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0007] According to some embodiments, an optical system is presented herein. In some embodiments, the optical system may comprise an optically transmissive substrate, a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures, and an antireflective coating comprising an optically transparent material conformally disposed over the nanostructures of the metasurface, the optically transparent material having a refractive index less than that of the nanostructures.

[0008] According to some embodiments, the antireflective coating is an interference coating. In some embodiments, the metasurface comprises a diffraction grating. In some embodiments, the metasurface comprises an asymmetric diffraction grating. In some embodiments, the metasurface comprises a Pancharatnam Berry Phase Optical Element (PBOE). In some embodiments, the metasurface comprises a multi-stage nanostructure. In some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, the optically transparent material has a refractive index of about 1.2 to about 2. In some embodiments, the distance from the top surface of the nanostructures to the top surface of the antireflective coating is about 10 nm to about 1 micron. In some embodiments, the distance from the top surface of the nanostructures to the top surface of the antireflective coating is about 30 nm to about 250 nm. In some embodiments, the antireflective coating forms a planarizing layer that extends between and across the nanostructures.

[0009] According to some other embodiments, presented herein is an optical system comprising an antireflective coating for an optical element comprising a metasurface, the antireflective coating comprising a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of a material comprising the metasurface, the layer of polymeric material being conformally disposed over the metasurface.

[0010] According to some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, the optically transparent material has a refractive index of about 1.2 to about 2. In some embodiments, the distance from the top surface of the metasurface to the top surface of the antireflective coating is about 10 nm to about 1 micron. In some embodiments, the antireflective coating reduces the amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface that does not include an antireflective coating. In some embodiments, the incident light has an angle of incidence of about -50° to 50°.

[0011] According to yet other embodiments, a method is provided for forming an antireflective coating on a metasurface. In some embodiments, the method may include providing an optically transmissive substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures, and depositing a layer of optically transparent material over the plurality of nanostructures, the layer of optically transparent material forming the antireflective coating.

[0012] According to some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, a distance from a top surface of the nanostructures to a top surface of the formed anti-reflective coating is between about 10 nm and about 1 micron. In some embodiments, conformally depositing the optically transparent material comprises spin-coating the optically transparent material over the nanostructures. In some embodiments, conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process.

[0013] Various additional embodiments are provided below.

[0014] 1. An optical system comprising: an optically transmissive substrate; a metasurface overlying a substrate, the metasurface comprising a plurality of nanostructures; an antireflective coating comprising an optically transparent material conformally disposed over the nanostructures of the metasurface, the optically transparent material having a refractive index less than the refractive index of the nanostructures; An optical system comprising:

[0015] 2. The optical system of embodiment 1, wherein the anti-reflective coating is an interference coating.

[0016] 3. The optical system of embodiment 1, wherein the metasurface comprises a diffraction grating.

[0017] 4. The optical system of embodiment 3, wherein the metasurface comprises an asymmetric diffraction grating.

[0018] 5. The optical system of any one of embodiments 1-3, wherein the metasurface comprises a Pancharatnam Berry phase optical element (PBOE).

[0019] 6. The optical system of embodiment 1, wherein the metasurface comprises a multi-stage nanostructure.

[0020] 7. The optical system of any one of embodiments 1-6, wherein the optically transparent material comprises a polymer.

[0021] 8. The optical system of embodiment 7, wherein the optically transparent material comprises a photoresist.

[0022] 9. The optical system of any one of embodiments 1-8, wherein the optically transparent material has a refractive index of about 1.2 to about 2.

[0023] 10. The optical system of any one of embodiments 1-9, wherein the distance from the top surface of the nanostructure to the top surface of the antireflective coating is from about 10 nm to about 1 micron.

[0024] 11. The optical system of embodiment 10, wherein the distance from the top surface of the nanostructure to the top surface of the antireflective coating is between about 30 nm and about 250 nm.

[0025] 12. The optical system of any one of embodiments 1-11, wherein the anti-reflective coating forms a planarizing layer that extends between and across the nanostructures.

[0026] 13. An optical system comprising: 1. An anti-reflective coating for an optical element comprising a metasurface, the anti-reflective coating comprising: a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of the material that constitutes the metasurface; A layer of polymeric material is conformally disposed over the metasurface. Anti-reflective coating An optical system comprising:

[0027] 14. The antireflective coating of embodiment 13, wherein the optically transparent material comprises a polymer.

[0028] 15. The antireflective coating of embodiment 14, wherein the optically transparent material comprises a photoresist.

[0029] 16. The antireflective coating of any one of embodiments 13-15, wherein the optically transparent material has a refractive index of about 1.2 to about 2.

[0030] 17. An antireflective coating according to any one of embodiments 13-16, wherein the distance from the top surface of the metasurface to the top surface of the antireflective coating is from about 10 nm to about 1 micron.

[0031] 18. An antireflective coating according to any one of embodiments 13-17, wherein the antireflective coating reduces the amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface without the antireflective coating.

[0032] 19. The antireflective coating of embodiment 18, wherein the incident light has an angle of incidence of about -20° to 20°.

[0033] 20. A method for forming an anti-reflective coating on a metasurface, the method comprising: providing an optically transmissive substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures; depositing a layer of optically transparent material over the plurality of nanostructures; Including, The layer of optically transparent material forms an anti-reflective coating.

[0034] 21. The method of embodiment 20, wherein the optically transparent material comprises a polymer.

[0035] 22. The method of embodiment 21, wherein the optically transparent material comprises a photoresist.

[0036] 23. The method of any one of embodiments 20-22, wherein the distance from the top surface of the nanostructure to the top surface of the antireflective coating formed is from about 10 nm to about 1 micron.

[0037] 24. The method of any one of embodiments 20-23, wherein conformally depositing the optically transparent material comprises spin-coating the optically transparent material over the nanostructures.

[0038] 25. The method of any one of embodiments 20-23, wherein conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process. The present invention provides, for example, the following: (Item 1) 1. An optical system comprising: an optically transmissive substrate; a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures; an antireflective coating comprising an optically transparent material conformally disposed over the nanostructures of the metasurface, the optically transparent material having a refractive index less than the refractive index of the nanostructures; An optical system comprising: (Item 2) Item 10. The optical system of item 0, wherein the anti-reflective coating is an interference coating. (Item 3) Item 10. The optical system of item 0, wherein the metasurface comprises a diffraction grating. (Item 4) Item 10. The optical system of item 0, wherein the metasurface comprises an asymmetric diffraction grating. (Item 5) Item 10. The optical system of item 0, wherein the metasurface comprises a Pancharatnam Berry phase optical element (PBOE). (Item 6) Item 10. The optical system of item 0, wherein the metasurface comprises a multi-stage nanostructure. (Item 7) Item 10. The optical system of item 0, wherein the optically transparent material comprises a polymer. (Item 8) Item 10. The optical system of item 0, wherein the optically transparent material comprises a photoresist. (Item 9) 10. The optical system according to claim 0, wherein the optically transparent material has a refractive index of about 1.2 to about 2. (Item 10) 13. The optical system of claim 0, wherein the distance from the top surface of the nanostructure to the top surface of the anti-reflective coating is from about 10 nm to about 1 micron. (Item 11) 10. The optical system of claim 0, wherein the distance from the top surface of the nanostructure to the top surface of the anti-reflective coating is about 30 nm to about 250 nm. (Item 12) Item 11. The optical system of any one of items 0-0, wherein the anti-reflective coating forms a planarizing layer extending between and across the nanostructures. (Item 13) 1. An optical system comprising: 1. An anti-reflective coating for an optical element comprising a metasurface, the anti-reflective coating comprising: a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of a material comprising said metasurface; a layer of polymeric material is conformally disposed over the metasurface; Anti-reflective coating An optical system comprising: (Item 14) Item 11. The anti-reflective coating of item 0, wherein the optically transparent material comprises a polymer. (Item 15) Item 10. The antireflective coating of item 0, wherein the optically transparent material comprises a photoresist. (Item 16) 10. The antireflective coating of claim 0, wherein the optically transparent material has a refractive index of about 1.2 to about 2. (Item 17) 10. The antireflective coating according to claim 0, wherein the distance from the top surface of the metasurface to the top surface of the antireflective coating is from about 10 nm to about 1 micron. (Item 18) 13. The antireflective coating of claim 0, wherein the antireflective coating reduces an amount of incident light reflected by the metasurface by more than about 50% as compared to the amount of incident light reflected by a substantially similar metasurface that does not include the antireflective coating. (Item 19) Item 19. The anti-reflective coating according to item 18, wherein the incident light has an incident angle of about -20° to 20°. (Item 20) 1. A method for forming an anti-reflective coating on a metasurface, the method comprising: providing an optically transmissive substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures; depositing a layer of optically transparent material over the plurality of nanostructures; Including, The layer of optically transparent material forms the anti-reflective coating. (Item 21) Item 10. The method of item 0, wherein the optically transparent material comprises a polymer. (Item 22) Item 1. The method of item 0, wherein the optically transparent material comprises a photoresist. (Item 23) The method of any one of items 0-0, wherein the distance from the top surface of the nanostructure to the top surface of the formed antireflective coating is from about 10 nm to about 1 micron. (Item 24) 13. The method of claim 0, wherein conformally depositing the optically transparent material comprises spin coating the optically transparent material over the nanostructures. (Item 25) Item 10. The method of item 0, wherein conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process. [Brief description of the drawings]

[0039] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0040] [Diagram 2] FIG. 2 illustrates an example of a wearable display system.

[0041] [Diagram 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0042] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0043] [Diagram 5]5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0044] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0045] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0046] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0047] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an embodiment of a set of stacked waveguides, each of which includes an incoupling optical element.

[0048] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0049] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0050] [Figure 10] FIG. 10 illustrates a cross-sectional side view of an example optical structure including a metasurface and an anti-reflective coating.

[0051] [Figure 11A] FIG. 11A illustrates a top-down view of an example metasurface comprising an asymmetric Pancharatnam Berry phase optical element (PBOE).

[0052] [Figure 11B]FIG. 11B illustrates a perspective view of the metasurface of FIG. 11A with a top antireflective coating.

[0053] [Figure 11C] FIG. 11C is a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in FIGS. 11A-11B.

[0054] [Figure 12A] FIG. 12A illustrates a cross-sectional perspective view of an example metasurface comprising an asymmetric diffraction grating and an anti-reflective coating.

[0055] [Figure 12B] FIG. 12B illustrates a cross-sectional side view of the example metasurface and antireflective coating of FIG.

[0056] [Figure 12C] FIG. 12C is a plot of the transmission and reflectance spectra for the optical structure of FIGS. 12A-12B.

[0057] [Figure 13] 13A-13D are cross-sectional views of intermediate structures at various stages of fabrication of an example optical structure comprising a metasurface, according to some embodiments.

[0058] [Figure 14] 14A-14D are cross-sectional views of intermediate structures at various stages of fabrication of an example optical structure comprising a metasurface, according to some embodiments.

[0059] [Figure 15] FIG. 15 illustrates a cross-sectional side view of a metasurface with a conformal antireflective coating. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Metasurfaces, also referred to as metamaterial surfaces, offer the opportunity to achieve virtually flat, aberration-free optics at a much smaller scale compared to geometric optics. Without being limited by theory, in some embodiments, metasurfaces include a dense array of surface structures or nanostructures that act as resonant optical antennas. The resonant nature of the interaction of light with the surface structures provides the ability to manipulate the optical wavefront. In some cases, metasurfaces may allow for the replacement of bulky or difficult to manufacture optical components with thin, planar elements formed by simple patterning processes.

[0061] It should be understood that optical elements formed from metasurfaces can function in reflection and / or transmission modes. In reflection mode, the metasurface can reflect light at a desired angle. In transmission mode, the metasurface can transmit light through the body of the metasurface while also deflecting the light at a desired angle. Undesirably, metasurfaces operating in transmission mode can also reflect incident light, for example, due to Fresnel reflections at interfaces with other materials. Additionally, for metasurfaces operating in reflection mode, the angle at which the metasurface is configured to reflect light can differ from the angle at which the light is reflected from the interface.

[0062] Undesirably, unintended reflections by the metasurface can cause optical artifacts. For example, in a display device in which the metasurface is used as an optical element to direct light encoded with image content (e.g., light modified by a spatial light modulator), reflections can cause residual images due to round-trip reflections of a portion of the light along the optical path before reaching the user. For example, the metasurface may form an internal coupling optical element configured to internally couple light into a waveguide and thus output the image content to the user. If some of this light is reflected rather than internally coupled into the waveguide, the reflected light may propagate back to the light projector or light source, which may then reflect the light back to the metasurface for internal coupling into the waveguide and ultimately output to the user. Due to this round-trip reflection, light from a previous video image frame may be provided to the waveguide along with light encoding the current image frame. The light encoding the previous image frame may be visible to the user as a residual image that reduces the image quality of the display device.

[0063] In some embodiments, an antireflective coating may reduce or eliminate reflection of light from the metasurface. The antireflective coating may be formed from an optically transparent layer of material, such as a polymer layer, e.g., a layer of photoresist. In some embodiments, no air or other material may be present between the metasurface and the antireflective coating. That is, the antireflective coating may directly contact the metasurface. The material forming the antireflective coating may have a refractive index lower than the refractive index of the nanostructures of the metasurface, but higher than the refractive index of the material or medium (e.g., air) that forms the interface between the metasurface and the opposing antireflective coating.

[0064] In some embodiments, the antireflective coating may be an interference coating, where the thickness of the layer of material is selected to provide destructive interference between light reflecting from the top and bottom surfaces of the layer. Preferably, the thickness of the layer is selected to provide this interference for light in the visible wavelengths. In some embodiments, the metasurface may be part of a color display that utilizes multiple primary colors. As a result, a particular metasurface may be exposed only to light of an associated limited range of wavelengths that corresponds to a particular primary color, and the antireflective coating may have a thickness selected to provide interference for light having this associated limited range of wavelengths.

[0065] In some embodiments, the antireflective coating may be a planar layer that extends across and between the nanostructures forming the metasurface, forming a planar surface of the nanostructures. Such a planar layer may advantageously provide antireflective properties over a wide range of incident angles of light. In some embodiments, the antireflective coating may be a conformal layer that is disposed on the surface of the nanostructures forming the metasurface. The conformal layer may be continuous, extending across and between multiple nanostructures, or may be isolated on individual ones of the nanostructures.

[0066] Advantageously, the reduction in reflection may reduce or eliminate optical effects such as residual images, thereby enabling a display device to output images with higher perceived quality. In some embodiments, the antireflective coating may reduce the amount of light reflected by the metasurface by about 50%, 75%, 85%, 90%, 95%, 99%, or more compared to the same structure without the antireflective coating. Antireflective coatings may be particularly advantageously applied to metasurfaces operating in a transmissive mode, where reflection is not part of the metasurface's design.

[0067] Reference is now made to the drawings, in which like reference numbers refer to like parts throughout.

[0068] In some embodiments, metasurfaces may be advantageously applied to form optical elements in display devices, such as display devices for AR or VR display systems. These display systems may display virtual content to a user or viewer, and AR systems may also allow users to see the world around them by transmitting light from the surrounding environment to the user's eyes. Preferably, this virtual content is displayed on a wearable head-mounted display, for example as part of eyewear that projects image information to the user's eyes. As used herein, it should be understood that a "head-mounted" display is a display that may be mounted on the viewer's head.

[0069] FIG. 2 illustrates an example of a wearable display system 80. The display system 80 includes a head mounted display 62 and various mechanical and electronic modules and systems to support the functionality of the display 62. The display 62 may be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 in front of the user's 60 eyes. The display 62 may be considered eyewear in some embodiments. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the ear canal of the user 60 (in some embodiments, another speaker, not shown, is positioned adjacent to the user's other ear canal to provide stereo / adjustable 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 (e.g., voice menu command selections, natural language questions, etc.) to the system 80 and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as an ambient sensor to continuously collect audio data (e.g., to passively collect from the user and / or the environment). Such audio data may include user sounds, such as heavy breathing, or environmental sounds, such as commotion, indicative of a nearby event. The display system may also include an ambient sensor 30a, which may be separate from the frame 64 and attached to the body of the user 60 (e.g., on the head, torso, limbs, etc. of the user 60). The ambient sensor 30a may be configured to obtain data characterizing a physiological state of the user 60 in some embodiments, as described further herein. For example, the sensor 30a may be an electrode.

[0070] FIG. 2 illustrates an example of a wearable display system 60. The display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 in front of the eye of the user 90. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the ear canal of the user 90 (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone may be configured to allow the user to provide input or commands to the system 60 (e.g., voice menu command selection, natural language questions, etc.) and / or audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and attached to the body of the user 90 (e.g., on the head, torso, limbs, etc. of the user 90). The ambient sensor 120a may be configured in some embodiments to obtain data characterizing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0071] 2, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as wired or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded within headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-type configuration, belt-type configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, such as wired or wireless connectivity. The local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data captured from sensors (such as image capture devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., which may be operatively coupled to the frame 80 or otherwise attached to the user 90)) and / or b) data acquired and / or processed using a remote processing module 150 and / or a remote data repository 160 (including data related to virtual content), possibly for passing to the display 70 after processing or retrieval. The local processing and data module 140 may be operatively coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to the local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope.In some other embodiments, one or more of these sensors may be mounted on the frame 80 or may be free-standing structures that communicate with the local processing and data module 140 via wired or wireless communication paths.

[0072] 2, in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 160 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, remote data repository 160 may include one or more remote servers that provide information, such as information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all calculations are performed within the local processing and data module, allowing for fully autonomous use from the remote modules.

[0073] Referring now to FIG. 3, the perception of an image as "three-dimensional" or "3-D" may be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 190, 200, one for each eye 210, 220, are output to the user. The images 190, 200 are spaced apart from the eyes 210, 220 by a distance 230 along an optical axis or z-axis parallel to the viewer's line of sight. The images 190, 200 are flat and the eyes 210, 220 may focus on the images by assuming a single accommodated state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide a perception of depth and / or scale of the combined image.

[0074] However, it should be appreciated that the human visual system is more complex and more difficult to provide a realistic perception of depth. For example, many viewers of conventional "3-D" display systems may find such systems uncomfortable or may not perceive any sensation of depth at all. Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of vergence and accommodation. The vergence movement of the two eyes relative to each other (i.e., eye rotation, in which the pupils move toward or away from each other to converge the gaze of the eyes and fixate on an object) is closely linked to the focusing (or "accommodation") of the eye's lenses and pupils. Under normal conditions, changing the focus of the eye's lens, or accommodating the eye and changing focus from one object to another at a different distance, will automatically produce a matching change in vergence to the same distance, under a relationship known as the "accommodation-vergence reflex" and pupil dilation or constriction. Similarly, a change in vergence will induce a matching change in accommodation of lens shape and pupil size under normal conditions. As described herein, many stereoscopic or "3-D" display systems display a scene using a slightly different presentation (and therefore a slightly different image) to each eye such that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers because, among other things, they simply provide a different presentation of the scene, but work against the "accommodation-vergence reflex" when the eyes view the entire image information in a single accommodated state. Display systems that provide better matching between accommodation and vergence may produce a more realistic and comfortable simulation of a three-dimensional image.

[0075] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 4, objects at various distances from the eyes 210, 220 on the z-axis are accommodated by the eyes 210, 220 such that the objects are in focus. The eyes 210, 220 assume a particular accommodated state and focus on objects at different distances along the z-axis. As a result, a particular accommodated state may be said to be associated with a particular one of the depth planes 240 having an associated focal length such that an object or part of an object at a particular depth plane is in focus when the eye is in an accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image to each eye 210, 220 and by providing a different presentation of an image corresponding to each of the depth planes. Although shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 210, 220 may overlap, for example, as the distance along the z-axis increases. Additionally, while shown as flat for ease of illustration, it should be understood that the contour of the depth plane may be curved in physical space, for example, so that all features in the depth plane are in focus with the eye in a particular accommodated state.

[0076] The distance between an object and the eye 210 or 220 may also change the amount of divergence of light from that object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, the light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) may be said to have a spherical wavefront curvature that is a function of the distance the point is away from the user's eye. The curvature increases with decreasing distance between the object and the eye 210. As a result, at different depth planes, the divergence of the light rays is also different, and the divergence increases with decreasing distance between the depth plane and the viewer's eye 210. Although only a monocular 210 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a viewer.

[0077] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. The different presentations may be focused separately by the viewer's eye, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on the different depth planes and / or based on the observation of different image features on the different depth planes that are out of focus.

[0078] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. The display system 250 includes a stack of waveguides or a stacked waveguide assembly 260 that may be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, the display system 250 is the system 60 of FIG. 2, of which FIG. 6 illustrates several portions in more detail. For example, the waveguide assembly 260 may be part of the display 70 of FIG. 2. It should be understood that the display system 250 may be considered a light field display in some embodiments.

[0079] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light of a limited range of wavelengths. As a result, in some embodiments, multiple waveguides or stacks of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light of different ranges of wavelengths. As used herein, it should be understood that a depth plane may follow the contour of a flat or curved surface. In some embodiments, advantageously and for convenience, a depth plane may follow the contour of a flat surface.

[0080] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include a number of features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or the number of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye with various levels of wavefront curvature or light beam divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. The image input devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to input image information into the waveguides 270, 280, 290, 300, 310, each of which may be configured to disperse incident light across each individual waveguide for output towards the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each of the input surfaces 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). It should be understood that the major surface of the waveguide corresponds to the relatively large area surface of the waveguide between which the thickness of the waveguide extends. In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams, which are directed towards the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0081] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information to each of the image input devices 360, 370, 380, 390, 400 via one or more optical conduits (such as fiber optic cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors as discussed herein).

[0082] In some embodiments, the light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter such as a light emitting diode (LED). The light from the light module 530 may be directed and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically and in some embodiments these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may act as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540 and the image may be an image on a depth plane.

[0083] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between one or more of the scanning fibers and one or more of the waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0084] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the light module 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) that coordinates the timing and provisioning of image information to the waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. The controller 560 may be part of the processing module 140 or 150 (FIG. 2) in some embodiments.

[0085] Continuing with reference to FIG. 6, the waveguides 270, 280, 290, 300, 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, each of the waveguides 270, 280, 290, 300, 310 may include out-coupling optical elements 570, 580, 590, 600, 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as out-coupled light, and the out-coupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at the location where the light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as further discussed herein. Although shown disposed on the bottom major surface of the waveguide 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top major surface and / or bottom major surface and / or directly within the volume of the waveguide 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguide 270, 280, 290, 300, 310. In some other embodiments, the waveguide 270, 280, 290, 300, 310 may be a monolithic piece of material and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0086] With continued reference to FIG. 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before it can reach the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive powers of the first lens 350 and the second lens 340 may be configured to produce another incremental amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as emerging from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0087] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for an aggregate focal power that represents the focal plane closest to the person. To compensate the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the aggregate power of the lens stacks 320, 330, 340, 350 below. Such a configuration provides as many perceived focal planes as there are waveguide / lens pairs available. Both the outcoupling 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.

[0088] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0089] Continuing with reference to FIG. 6, the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610 that output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, 610 may be volumetric or surface features that may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0090] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency such that only a portion of the light in the beam is deflected towards the eye 210 at each intersection of the DOE, while the remainder continues to travel through the waveguide via TIR. The light carrying the image information is thus split into several related exit beams that exit the waveguide at various locations, resulting in a very uniform pattern of exit emission towards the eye 210 for this particular collimated beam bouncing within the waveguide.

[0091] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0092] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor a physiological condition of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye that may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 2) and may be in electrical communication with the processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye to monitor each eye separately.

[0093] 7, an example of an output beam output by a waveguide is shown. Although one waveguide is shown, it should be understood that other waveguides in the waveguide assembly 260 (FIG. 6) may function similarly and that the waveguide assembly 260 includes multiple waveguides. Light 640 is launched into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates within the waveguide 270 by TIR. At the point where the light 640 impinges on the DOE 570, a portion of the light exits the waveguide as an output beam 650. The output beam 650 is shown as approximately parallel, but may be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging output beam) as discussed herein and depending on the depth plane associated with the waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output an exit beam pattern that is more divergent, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0094] In some embodiments, a full color image may be formed at each depth plane by overlaying images in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, where each depth plane includes an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or less depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. The different depth planes are indicated in the diagram by different numbers for diopters following the letters G, R, and B. By way of example only, the numbers following each of these letters indicate the diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact location of the depth planes for the different primary colors may be varied to account for differences in the eye's focusing of different wavelengths of light. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0095] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the figure containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, with three primary color images provided per depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, but it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0096] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or in place of one or more of the red, green, or blue colors.

[0097] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0098] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of visual perception of a viewer, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0099] 9A, in some embodiments, light impinging on a waveguide may need to be redirected to in-couple the light into the waveguide. An in-coupling optical element may be used to redirect and in-couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an in-coupling optical element. Each of the waveguides may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. The stack 660 may correspond to the stack 260 (FIG. 6), and the illustrated waveguides of the stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of the image input devices 360, 370, 380, 390, 400 is launched into the waveguide from a position that requires the light to be redirected for in-coupling.

[0100] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated incoupling optical element (which may also be referred to as the light input area on the waveguide), for example, incoupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, incoupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and incoupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of the incoupling optical elements 700, 710, 720 may be disposed on a bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more of the incoupling optical elements are reflective polarizing optical elements). As shown, the incoupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguide 670, 680, 690 (or on top of the next lower waveguide), and in particular, the incoupling optical elements are transmissive deflecting optical elements. In some embodiments, the incoupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the incoupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the incoupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments.

[0101] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400 as shown in FIG. 6 and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to not substantially receive light from others of the in-coupling optical elements 700, 710, 720.

[0102] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0103] The waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid and / or solid layers of material. For example, as shown, layer 760a may separate the waveguides 670 and 680, and layer 760b may separate the waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediate neighbors of the waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more or 0.10 or less compared to the refractive index of the material forming the waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may act as cladding layers to promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0104] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 670, 680, 690 are similar or the same, and the materials forming the layers 760a, 760b are similar or the same. In some embodiments, the materials forming the waveguides 670, 680, 690 may differ between one or more of the waveguides, and / or the materials forming the layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0105] 9A, light rays 770, 780, 790 are incident on the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0106] In some embodiments, the light beams 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects the incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0107] For example, incoupling optical element 700 may be configured to selectively deflect light beam 770 having a first wavelength or wavelength range while transmitting light beams 1242 and 1244 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light beam 780 impinges on and is deflected by incoupling optical element 710, which is configured to selectively deflect light of the second wavelength or wavelength range. Light beam 790 is deflected by incoupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0108] 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the incoupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690 and incouplings the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the corresponding optical dispersive element 730, 740, 750 of the waveguide.

[0109] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, the in-coupled light rays 770, 780, 790 are deflected by the in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within the waveguides 670, 680, 690, respectively. The light rays 770, 780, 790 then impinge on the optically dispersive elements 730, 740, 750, respectively. The optically dispersive elements 730, 740, 750 deflect the light rays 770, 780, 790 to propagate towards the out-coupling optical elements 800, 810, 820, respectively.

[0110] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse the light to the out-coupling optical elements 800, 810, 820, and in some embodiments may also increase the beam or spot size of this light as it propagates to the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted and the in-coupling optical elements 700, 710, 720 may be configured to deflect the light directly to the out-coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light to the viewer's eye 210 (FIG. 7). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and an EPE may increase the eyebox in an axis that intersects (e.g., perpendicular to) the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. In response to striking the OPE, again, another portion of the remaining light is redirected to the EPE, which continues to propagate further down the waveguide, and so on. Similarly, in response to striking the EPE, a portion of the striking light is directed out of the waveguide towards the user, and the remaining portion of the light continues to propagate through the waveguide until it strikes the EP again, at which point another portion of the striking light is directed out of the waveguide, and so on. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0111] Thus, referring to Figures 9A and 9B, in some embodiments, a set of waveguides 660 includes, for each primary color, a waveguide 670, 680, 690, an in-coupling optical element 700, 710, 720, an optically dispersive element (e.g., OPE) 730, 740, 750, and an out-coupling optical element (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical element 700, 710, 720 redirects or deflects the incoming light into its waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated embodiment, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues to bounce back down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, with light ray 780 incident on the in-coupling optical element 710 and being deflected thereby. Light ray 780 will then proceed via TIR back down the waveguide 680, to its optically dispersive element (e.g., OPE) 740 and then to the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light beam 790 such that it propagates by TIR to a light dispersive element (e.g., OPE) 750 and then by TIR to an out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light beam 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0112] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 670, 680, 690 may be vertically aligned with each waveguide's associated light dispersive element 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an arrangement including non-overlapping spatially separated in-coupling optical elements may be referred to as a shifted pupil system, and the in-coupling optical elements in these arrangements may correspond to sub-pupils.

[0113] 10 , a cross-sectional side view of an example optical structure 1400 is illustrated comprising a metasurface 1418 formed by a plurality of nanostructures 1420 and an antireflective coating 1430 disposed directly over the nanostructures 1420, according to some embodiments. The metasurface 1418 and the antireflective coating 1430 may be disposed on an optically transmissive substrate 1410. In some embodiments, as shown, the antireflective coating 1430 fills the spaces between the nanostructures 1420 such that no air or other material is disposed between the nanostructures 1420 and the antireflective coating 1430, at least over a majority of the extent of the metasurface 1418. The antireflective coating 1430 may be optically transmissive or substantially transmissive to light.

[0114] In some embodiments, the antireflective coating 1430 has a substantially planar upper surface 1430a. The antireflective coating 1430 may act as a planarizing layer for the underlying non-uniform topology of the nanostructures 1420. In some embodiments, the upper surface 1430a of the antireflective coating 1430 may be substantially parallel to a substantially horizontal plane defined by the upper surfaces 1420a of the nanostructures 1420.

[0115] The thickness 1422 of the antireflective coating 1430 may be defined as the distance from the top surface 1420a of the nanostructures 1420 to the top surface of the antireflective coating 1430. In some embodiments, the thickness 1422 may be in the range of about 10 nm to about 2 microns. In some embodiments, the thickness 1422 may be about 20 nm to about 1 micron. In some embodiments, the thickness 1422 may be about 25 nm to about 500 nm, about 30 nm to about 250 nm, about 40 nm to about 100 nm, and about 45 nm to about 55 nm. In some embodiments, the thickness 1422 may be about 50 nm. In some embodiments, the thickness 1422 may be greater than the height of the nanostructures 1420, where the height of the nanostructures 1420 is the distance from the bottom of the nanostructures 1420 to the top surface 1420a.

[0116] Without being bound by theory, it is believed that the antireflective coating 1430 may provide an impedance match between the overlying medium (e.g., air) and one or both of the nanostructures 1420 and the substrate 1410, reducing the occurrence of reflections. It is also believed that the antireflective coating 1430 may cause destructive interference between light reflected from the top surface 1430a of the antireflective coating and the bottom surface 1430b of the antireflective coating and / or light backscattered from the surface of the nanostructures 1420 and / or the surface of the substrate 1410. It is believed that this interference leads to a reduction or elimination in the amount of light perceived as reflected from the optical structure 1400. In some embodiments, the ability of the antireflective coating 1430 to reduce or eliminate light reflected from the optical structure 1400 may depend on the thickness of the antireflective coating 1430 and the wavelength of light impinging on the antireflective coating 1430. Preferably, thickness 1422 is selected relative to the refractive index and dimensions of nanostructures 1420 and the wavelength of light for which destructive interference is desired, as described above, to provide destructive interference.

[0117] The antireflective coating 1430 may include an optically transmissive material having a refractive index lower than the refractive index of the nanostructures 1420, but higher than the refractive index of the medium or material directly covering and interfacing with the antireflective coating 1430. For example, the medium covering and interfacing with the antireflective coating 1430 may be air. In some embodiments, the antireflective coating 1430 may have a refractive index of about 1.2 to about 2.0, about 1.2 to about 1.7, about 1.3 to about 1.6, or about 1.4 to about 1.5. In some embodiments, the antireflective coating 1430 may have a refractive index of about 1.45. In some embodiments, the refractive index of the antireflective coating 1430 may also be lower than the refractive index of the substrate 1410. It should be appreciated that in some embodiments, the lower refractive index of the antireflective coating 1430 compared to the substrate 1410 facilitates TIR of light within the substrate 1410, and the higher refractive index of the antireflective coating 1430 compared to the medium covering the coating 1430 facilitates passage of light to the metasurface 1418 for internal coupling into the substrate 1410.

[0118] 10 , to reduce potential reflections caused by interfaces between additional materials, the antireflective coating 1430 may follow the contours of the nanostructures 1420 such that substantially no air or other material is present between the nanostructures 1420 and the antireflective coating 1430 over all or substantially all of the area over which the metasurface is disposed. In some embodiments, as shown, the antireflective coating 1430 is disposed directly on the optical structure 1400 such that the antireflective coating 1430 encapsulates the nanostructures 1420 above the surface of the substrate 1410.

[0119] As discussed herein, the antireflective coating 1430 preferably comprises an optically transmissive material. By way of example, the optically transmissive material may be an optically transmissive organic material, such as a transparent polymer. In some embodiments, the antireflective coating 1430 may comprise a resist material, such as a photoresist material. Non-limiting examples of photoresists include positive resists and negative resists. In some embodiments, the antireflective coating 1430 may comprise a UV photoresist, an EUV photoresist, or a DUV photoresist.

[0120] It should be understood that the antireflective coating 1430 may be formed on the nanostructures 1420 by a variety of deposition processes. In some embodiments, the antireflective coating 1430 may be applied to the nanostructures 1420 as a liquid, whereby the liquid forms the antireflective coating 1430. For example, the antireflective coating 1430 may be deposited on the nanostructures 1420 as a liquid by spin coating. In some embodiments, the antireflective coating 1430 may be deposited on the nanostructures 1420 using gas phase precursors in a vapor deposition process, such as a chemical vapor deposition (CVD) process and atomic layer deposition (ALD).

[0121] In some embodiments, the anti-reflective coating 1430 may reduce the amount of incident light reflected by the optical structure 1400 operating in a transmissive mode by about 50%, 75%, 85%, 90%, 95%, 99%, or more, as compared to a substantially similar optical structure without the anti-reflective coating 1430. In some embodiments, the anti-reflective coating may achieve such reduction in reflected light over a range of angles of incidence of -10° to 10°, -20° to 20°, -30° to 30°, -40° to 40°, -50° to 50°, or more.

[0122] The metasurface 1418, comprising a plurality of nanostructures 1420, may be configured to manipulate light, such as for beam steering, wavefront shaping, wavelength and / or polarization separation, and combination of different wavelengths and / or polarizations. Preferably, the light is visible light, having a wavelength in the range of 350 nm to 800 nm. In some embodiments, the metasurface on which the anti-reflective coating is disposed may comprise nanostructures having a size and periodicity less than the wavelength of visible light. It should be appreciated that in some embodiments, the metasurface 1418 selectively redirects some wavelengths of light while allowing other wavelengths of light to pass without being redirected. While such properties are typically engineered with structures on the micron scale (e.g., photonic crystal fibers or distributed Bragg reflectors), various embodiments herein include nanoscale (e.g., 10-100 times smaller scale) geometries to provide selective redirection of light within the visible portion of the electromagnetic spectrum.

[0123] As an example, the metasurface 1418 may operate in a transmission mode where light enters the metasurface from a first side of the metasurface 1418, propagates through the body of the metasurface 1418, and then propagates away from the metasurface 1418 on the opposite side of the metasurface 1418. The light propagates away from the metasurface 1418 in a direction different than the direction of incidence of the light on the first side. In some embodiments, the antireflective coating 1430 may reduce or eliminate the amount of light reflected from the metasurface 1418 compared to a metasurface 1418 without the antireflective coating 1430. In some embodiments, the antireflective coating 1430 may not substantially reduce or have no effect on the amount of light propagating through and away from the metasurface 1418 compared to a metasurface 1418 without the antireflective coating 1430.

[0124] In some embodiments, the substrate 1410 supporting the metasurface 1418 on which the anti-reflective coating 1430 is disposed may be a waveguide, and the waveguide may be used to form a direct-view or eyepiece display device configured to receive input image information and generate an output image in the form of light encoded with image information based on the input image information. These devices may be wearable and, in some embodiments, may constitute eyewear or may be a display device as described herein with respect to Figures 1-9C. In some embodiments, the input image information received by the waveguide may be encoded into multiplexed light streams of different wavelengths (e.g., red light, green light, and blue light) that are incoupling into one or more waveguides. The incoupling light may propagate through the waveguide due to total internal reflection. The incoupling light may be outcoupling (or output) from the waveguide by one or more outcoupling optical elements as described above with respect to Figures 9A-9C.

[0125] In some embodiments, the metasurface 1418, on which the anti-reflective coating 1430 is conformally disposed, may be the in-coupling optical element, the out-coupling optical element, and / or the light dispersing element of the waveguide. The compactness and planarity of the metasurface 1418 and the anti-reflective coating 1430 allow for compact waveguides and compact stacks of waveguides, where multiple waveguides form a stack. Additionally, the metasurface 1418 may be configured to provide high precision when in-coupling and / or out-coupling light, which may provide high image quality. For example, the high selectivity may reduce channel crosstalk in configurations where a full color image is formed by simultaneously outputting light of different colors or wavelengths, while the anti-reflective coating 1430 may reduce residual images.

[0126] It should be appreciated that the nanostructures 1420 may have different sizes and be arranged in different orientations relative to one another to form the metasurface 1418 for different applications. For example, the nanostructures 1420 may be arranged to form a grating, such as an asymmetric or asymmetric grating, as discussed herein. In some embodiments, the metasurface 1418 may be formed from nanostructures 1420 that are multi-level or multi-stage. For example, the nanostructures 1420 may be relatively wide on a first level and relatively narrow on a second level. In some embodiments, the metasurface 1418 may be formed on a single level and have a substantially constant width on that level. Examples of metasurfaces that may be utilized as metasurface 1418 are described in U.S. patent application Ser. No. 15 / 342,033, filed Nov. 2, 2016 (Attorney Docket No. MLEAP.027A), U.S. Provisional Application No. 62 / 333,067, filed May 6, 2016 (Attorney Docket No. MLEAP.066PR), entitled “DIFFRACTION GRATINGS FORMED BY METASURFACES HAVING DIFFERENTLY ORIENTED NANOBEAMS,” filed Jan. 27, 2017 (Attorney Docket No. MLEAP.092PR), and U.S. Provisional Application No. 62 / 451,608, filed Jan. 27, 2017 (Attorney Docket No. MLEAP.092PR), entitled “DIFFRACTION GRATINGS FORMED BY METASURFACES HAVING DIFFERENTLY ORIENTED NANOBEAMS,” and U.S. Provisional Application No. 62 / 451,608, filed Jan. 27, 2017 (Attorney Docket No. MLEAP.092PR), and entitled “DIFFRACTION GRATINGS BASED ON METASURFACES HAVING ASYMMETRIC OPTICAL No. 62 / 451,615, entitled "META-BASED SURFACE ELEMENTS" filed Jan. 27, 2017 (Attorney Docket No. MLEAP.103PR), each of which is incorporated herein by reference. It should be understood that the nanostructures 1420 disclosed herein may correspond to the protrusions, nanobeams, etc. described in these applications. In some embodiments, the optical structure 1400 may be any metasurface comprising a plurality of nanostructures known in the art or developed in the future.

[0127] Examples of different configurations of nanostructure 1420 are described below. It should be understood that for clarity of description, the nanostructures discussed below may have different reference numbers than 1420. However, it should be understood that the various nanostructures (1520, 1620) described below correspond to nanostructure 1420 of FIG.

[0128] 11A , a top-down view of an example optical structure 1500 comprising a metasurface 1518 comprising nanostructures 1520 forming an asymmetric Pancharatnam Berry phase optical element (PBOE), which may be advantageous for, among other things, light steering, according to some embodiments. A substrate 1410 underlies the nanostructures 1520. In some embodiments, the substrate 1410 may be an optically transmissive substrate, such as a waveguide.

[0129] 11B, a perspective view of an example optical element 1500 comprising an asymmetric Pancharatnam Berry phase optical element (PBOE) and including an antireflective coating 1430 is illustrated, according to some embodiments. As described herein, the antireflective coating 1430 follows the contours of the nanostructures 1520 such that substantially no air or other material is present between the nanostructures 1520 and the antireflective coating 1430. Furthermore, as described herein, the antireflective coating 1430 may have a substantially flat top surface 1430a. The antireflective coating 1430 may function as a planarizing layer for the underlying non-uniform topology of the nanostructures 1520. In some embodiments, the top surface 1430a of the antireflective coating 1430 may be substantially parallel to a substantially horizontal plane defined by the top surfaces (not shown) of the nanostructures 1520. The thickness 1522 of the antireflective coating 1430 may be defined as the distance from the top surface of the nanostructures 1520 to the top surface 1430a of the antireflective coating 1430. In some embodiments, the thickness 1522 may be in a range of about 10 nm to about 2 microns. In some embodiments, the thickness 1522 may be about 20 nm to about 1 micron. In some embodiments, the thickness 1522 may be about 25 nm to about 500 nm, about 30 nm to about 250 nm, about 40 nm to about 100 nm, and about 45 nm to about 55 nm. In some embodiments, the thickness 1522 may be about 50 nm. In some embodiments, the thickness 1522 may be selected based on the wavelength of light that the metasurface is configured to redirect and is therefore expected to impinge on the antireflective coating 1430. Preferably, thickness 1522 is selected to provide destructive interference between light reflected from the top and bottom surfaces of antireflective coating 1430, respectively, the bottom surface (not shown) being the surface of the antireflective coating that forms an interface with the top surface of nanostructure 1520.

[0130] FIG. 11C is a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure described with reference to FIGS. 11A-11B. The various orders of diffracted transmitted light are indicated by "T" and the reflected light is indicated by "R". In this example, the antireflective coating 1430 is an optically transmissive photoresist having a refractive index of about 1.45, which is lower than the refractive index of the nanostructures 1520 and lower than the refractive index of the substrate 1410, which is formed from polysilicon, which is about 1.77. The thickness 1522 of the antireflective coating 1430 is about 50 nm, and air forms an interface with the top surface of the antireflective coating 1430.

[0131] As can be seen from the plot, the percentage of incident light reflected from the optical structure 1500 remains below about 2% over a wide range of angles of incidence from greater than -20° to greater than 20°. In comparison, the percentage of light reflected from a substantially similar metasurface 1518 without an antireflective coating was determined to be about 10% (not shown) over the same range of angles of incidence. Thus, in this embodiment, the antireflective coating 1430 provides about an 80% reduction in the amount of light reflected from the metasurface 1518 as compared to a substantially similar metasurface 1518 without the antireflective coating 1430.

[0132] On the other hand, the percentage of light incident on metasurface 1518 with antireflective coating 1430 that undergoes first order diffraction for angles suitable for TIR (T1) is about 42% for an angle of incidence of 0° and remains at approximately this level over angles of incidence from about -10° to about 10°. Advantageously, the amount of incident light diffracted at angles suitable for TIR is substantially the same as for a substantially similar metasurface 1518 without antireflective coating 1430. Thus, metasurface 1518 with antireflective coating 1430 may be used as an optical element 1500 as described herein, e.g., an incoupling optical element, while reducing the amount of light reflected without a substantial reduction in the amount of incoupling light, thereby reducing or eliminating potential residual images in a display device in which the optical element is incorporated.

[0133] 12A, a cross-sectional perspective view of an example optical element 1600 comprising a metasurface 1618 and an antireflective coating 1430 is illustrated. The metasurface 1618 comprises an asymmetric diffraction grating formed by nanostructures 1620 having different widths. FIG. 12B illustrates a cross-sectional side view of the optical element 1600 of FIG. 12A. In this example, the substrate 1410 comprises sapphire, having a refractive index of about 1.77. The nanostructures 1620 comprise amorphous silicon. The antireflective coating 1430 may comprise an optically transmissive photoresist, having a material refractive index of about 1.45, and in some embodiments may be conformally applied to the asymmetric diffraction grating 1618 by spin coating. The thickness 1622 of the antireflective coating 1430, which is the distance from the top surface 1620a of the nanostructures 1620 to the top surface 1430a of the antireflective coating 1430, is about 50 nm.

[0134] 12C is a plot of the transmission and reflection spectra for an optical element having the general structure shown in FIGs. 12A-12B. As can be seen from the plot, the percentage of incident light reflected from the optical element 1600 with the anti-reflective coating 1430 remains below about 2% over a wide range of angles of incidence from greater than -30° to greater than 30°. The percentage of light reflected from the optical element 1600 with the anti-reflective coating 1430 is about 0 over angles of incidence from about -15° to about 15°.

[0135] In comparison, the percentage of light reflected from a substantially similar optical element 1600 without the anti-reflective coating 1430 is about 15% (not shown) over the same range of angles of incidence. Thus, in this embodiment, the anti-reflective coating 1430 provides about an 87% reduction in the amount of light reflected from the optical element 1600 as compared to a substantially similar optical element 1600 without the anti-reflective coating 1430.

[0136] On the other hand, the percentage of light incident on the optical element 1600 with the anti-reflective coating 1430 that undergoes first order diffraction for TIR (T1) is greater than about 30% over angles of incidence from about -30° to about 20°. Advantageously, the amount of incident light diffracted for TIR for the optical element 1600 with the anti-reflective coating 1430 is substantially identical to the amount of light diffracted for TIR for a substantially similar optical element 1600 without the anti-reflective coating 1430. Thus, the optical element 1600 with the anti-reflective coating 1430 may be used as an optical element as described herein, e.g., an in-coupling optical element, without a substantial reduction in the amount of in-coupling light, while reducing the amount of light reflected, thereby reducing or eliminating potential residual images, as discussed herein.

[0137] It should be understood that the metal surfaces and nanostructures disclosed herein may be formed by patterning, such as patterning by lithography and etching. In some embodiments, the metasurfaces and nanostructures may be patterned using nanoimprinting, thereby avoiding costly lithography and etching processes. Once the nanostructures are patterned, any mask material may be removed, in some embodiments, and an antireflective coating 1430 may be applied to, deposited over, or formed on the metasurface as described herein. In some other embodiments, the mask material itself may be utilized as the antireflective coating. Figures 13A-13D and Figures 14A-14D illustrate examples of process flows for forming optical structures with antireflective coatings.

[0138] 13A-13D respectively illustrate cross-sectional views of intermediate structures 1700A-1700D at various stages of fabrication of optical elements 1400, 1500, 1600 having metasurfaces 1418, 1518, 1618 using lithography and etching according to some embodiments. Referring to intermediate structure 1700A of FIG. 13A, the method includes providing a substrate 1410 having a surface 1410S suitable for forming metasurfaces 1418, 1518, 1618 thereon. Substrate 1410 includes an optically transmissive material having a refractive index n2 and various other material attributes as described above with reference to FIG. 10. The method additionally includes providing a substrate 1410 having a surface 1410S suitable for forming metasurfaces 1418, 1518, 1618 thereon. 1bulkThe method includes forming a high refractive index layer 1411 having a thickness of 100 nm to 150 nm, the high refractive index layer 1411 being suitable for forming one or more nanostructures 1420, 1520, 1620 when patterned as described above with reference to FIGS. 10-12. The high refractive index layer 1411 may be deposited using any suitable technique, such as chemical vapor deposition (CVD), including plasma-based CVD processes such as plasma-enhanced chemical vapor deposition (PECVD) and thermal-based CVD processes such as low-pressure chemical vapor deposition (LPCVD), according to some embodiments. The high refractive index layer 1411 may also be deposited using physical vapor deposition (PVD), evaporation, and atomic layer deposition, among other techniques. The method additionally includes forming a mask layer 1431A on the high refractive index layer 1411. The mask layer 1431A may be formed from or include one or more layers of a material suitable for providing a template for subsequent etching of the underlying high refractive index layer 1411. In some embodiments, the mask layer 1431A may be a photoresist, which may be spin-coated followed by a post-bake. In some other embodiments, the mask layer 1431A may include multiple layers, including a hard mask layer formed on the high refractive index layer 1411 and a photoresist layer formed on the hard mask layer. The hard mask layer may be included, for example, when the photoresist layer may not provide sufficient etch selectivity during the subsequent etch pattern transfer to the underlying high refractive index layer 1411. The hard mask layer may also act as an anti-reflective coating to minimize reflections during the subsequent exposure process. In some embodiments, the hard mask layer may be a film deposited by either a spin-coated polymer or deposition technique for depositing the high refractive index layer 1411. When included, the hard mask layer may provide better etch selectivity than the overlying photoresist layer. In some embodiments, the photoresist may be a positive photoresist or a negative photoresist.A positive photoresist is a type of photoresist in which the portions of the photoresist exposed to light become soluble in a photoresist developer, while a negative resist is a type of photoresist in which the portions of the photoresist exposed to light become insoluble in a photoresist developer.

[0139] In some embodiments, the photoresist and / or hard mask layer may be formed from a silicon or silicon oxide containing material that may have sufficient etch selectivity to the high index layer 1411 such that the photoresist and / or hard mask layer remains relatively intact through etching of the underlying high index layer 1411. In these embodiments, the silicon or silicon oxide containing photoresist and / or hard mask layer may remain on top of the one or more nanostructures 1420, 1520, 1620 after patterning, as described above with reference to Figures 10-12.

[0140] Referring to intermediate structure 1700B of FIG. 13B, after deposition and post-deposition bake, the method includes patterning the photoresist layer of the mask layer 1431 by selectively exposing portions of the photoresist to a pattern of light. Exposure to light, e.g., coherent UV light or an electron beam, creates chemical changes, e.g., polymer cross-linking, in the photoresist, which allows the exposed portions of the photoresist to be selectively removed by a developer solution for a positive photoresist, or the unexposed portions of the photoresist to be selectively removed by a developer solution for a negative photoresist. Upon selective removal, the resulting patterned mask photoresist remains on the high index layer 1411, thereby serving as a template for subsequent patterning, e.g., by etching, of the underlying hard mask layer, when included. The resulting intermediate structure 1700C shows the patterned mask layer 1411, which includes the patterned photoresist and, optionally, the patterned hard mask layer, when included.

[0141] Referring to intermediate structure 1700C of FIG. 13C, patterned mask layer 1431 may be used as a template to etch underlying high index layer 1411 into one or more nanostructures 1420, 1520, 1620. It should be understood that nanostructures 1420, 1520, 1620 may be configured as desired based on the desired properties of the resulting metasurface. In some embodiments, nanostructures 1420, 1520, 1620 may include features extending in a first lateral direction (e.g., y-direction) and a plurality of second nanostructures 1420, 1520, 1620 extending in a second direction (e.g., x-direction), as described in more detail above with reference to FIGS. 10-12. In various embodiments, high index layer 1411 may be etched, e.g., anisotropically dry etched. The etching process employed may have suitable selectivity to mask layer 1431 and / or substrate 1410 such that portions of high index layer 1411 are removed without prematurely removing mask layer 1431 and / or undesirably damaging exposed portions of substrate 1410.

[0142] Referring to intermediate structure 1700D, in some embodiments, the mask layer 1431 on one or more of the nanostructures 1420, 1520, 1620 is removed therefrom. The resist portion of the mask layer 1431 may be removed, for example, by using a liquid resist stripper or an oxygen-based plasma, in a process referred to as ashing. If desired, the underlying hard mask layer, when included, may then be removed using a wet or dry etching process that selectively removes the hard mask while not substantially affecting the one or more of the nanostructures 1420, 1520, 1620 or the substrate 1410. An anti-reflective coating may then be deposited on or on the sides of the nanostructures 1420, 1520, 1620, for example, by spin coating or by chemical vapor deposition and subsequent planarization of the deposited layer.

[0143] In some other embodiments, such as those described above with reference to Figures 10-12, the mask layer 1431, e.g., a photoresist / hard mask or a hard mask, may be left in place rather than being removed. In these embodiments, the mask layer 1431 may comprise an anti-reflective coating 1430, as described herein with reference to Figures 10-12.

[0144] 14A-14D illustrate cross-sectional views of intermediate structures 1800A-1800D at various stages of fabrication of optical elements 1400, 1500, 1600 having metasurfaces 1418, 1518, 1618, respectively, according to some embodiments. In some embodiments, the method of forming intermediate structures 1800A, 1800C, and 1800D of FIGS. 14A, 14C, and 14D, respectively, is similar to the method of forming intermediate structures 1700A, 1700C, and 1700D of FIGS. 13A, 13C, and 13D, respectively. However, the method of forming intermediate structure 1800B of FIG. 14B differs from the method of forming intermediate structure 1700B of FIG. 13B, and the differences are described below.

[0145] With reference to intermediate structure 1800B in FIG. 14B, unlike the method described above with reference to FIG. 13B, instead of patterning a photoresist layer by selectively exposing and removing portions of the photoresist using light or an electron beam, in the illustrated embodiment, a nanoimprint template 1432 or nanoimprint mold having a predetermined topological pattern according to the formation of one or more nanostructures 1420, 1520, 1620 is brought into contact with the imprint resist of mask layer 1431A. In some embodiments, the template 1432 is pressed into the imprint resist, which is formed from a thermoplastic polymer, at a temperature, for example, higher than the glass transition temperature of the imprint resist, thereby transferring the pattern of the template 1432 to the softened imprint resist. After cooling, the template 1432 is separated from the imprint resist, and the patterned resist is left on the high refractive index layer 1411. In some other embodiments, after being pressed into the imprint resist, the imprint resist is hardened by cross-linking under UV light.

[0146] 15, according to some embodiments, after removal of the mask layer 1431 from one or more nanostructures 1420, 1520, 1620 as described above with respect to Figures 13D and 14D, an antireflective coating 1430 may be conformally deposited on the nanostructures 1420, 1520, 1620 by a deposition process, such as, for example, a chemical vapor deposition process or an atomic layer deposition process. Thus, in some embodiments, the deposited antireflective coating 1430 may be a conformal layer that covers the nanostructures 1420, 1520, 1620 and follows the contours of the nanostructures 1420, 1520, 1620 without completely filling the volumes separating those nanostructures.

[0147] In the foregoing specification, various specific embodiments have been described. It will be apparent, however, that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0148] Indeed, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, none of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure.

[0149] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, although features may be described above as acting in a combination and may even be initially claimed as such, one or more features from the claimed combination may in some cases be deleted from the combination, and the claimed combination may be directed to a subcombination or variation of the subcombination. No single feature or group of features is required or essential to every embodiment.

[0150] In particular, it should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, are generally intended to convey that certain embodiments include certain features, elements, and / or steps while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to suggest that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether or not those features, elements, and / or steps are included or should be performed in any particular embodiment, with or without authorial input or prompting. The terms "comprising," "including," "having," and the like, are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense), thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. In addition, the articles "a," "an," and "the," as used in this application and the appended claims, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, although operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order or sequential order depicted, or that all of the depicted operations need not be performed, to achieve desirable results. Additionally, the figures may diagrammatically depict one or more exemplary processes in the form of a flow chart. However, other operations not depicted may also be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, simultaneously with, or during any of the depicted operations.In addition, operations may be rearranged or reordered in other embodiments. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve desirable results.

[0151] Thus, the claims are not intended to be limited to the implementations shown in the specification but are to be accorded the widest scope consistent with the disclosure, the principles and novel features disclosed herein.

Claims

[Claim 1] A system, method, etc. as depicted in the drawings.

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