Diffractive optical elements, related systems, and methods with reduced recirculation bounce-induced optical losses

Abstract

To provide a diffusion optical element involving reduction of re-bounce induced light loss, and a system and a method related to the diffusion optical element.SOLUTION: A display device includes a waveguide tube having an internal combining optical element which reduces re-bounce of internally combined light and improves the total internal combination efficiency and / or the uniformity. The waveguide tube includes an internal combining optical element which receives light from a light source and / or a projection optical system, internally combines the received light, and propagates in the waveguide tube in a propagation direction by a total inside reflection. Once the optical element is internally combined in the waveguide tube, light receives re-bounce that light reflects from a surface of the waveguide tube, and can hit against the internal combination optical element after the reflection. The light is partially absorbed and / or is externally combined by the optical element according to hitting against the internal combination optical element. In that way, it becomes possible to virtually reduce the amount of internally combined light propagating through the waveguide tube.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] (Claim of Priority) This application claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62 / 702,707, filed Jul. 24, 2018, entitled “DIFFRACTIVE OPTICAL ELEMENTS WITH MITIGATION OF REBOUNCE-INDUCED LIGHT LOSS AND DISPLAY DEVICES CONTAINING THE SAME,” and U.S. Provisional Application No. 62 / 747,032, filed Oct. 17, 2018, entitled “WAVEGUIDES HAVING HIGHLY REFLECTIVE LAYERS AND METHODS FOR FORMING,” which are hereby incorporated by reference in their entireties for all purposes.

[0002] (Incorporation by Reference) This application incorporates by reference in their entireties the following patent applications: U.S. Patent Application No. 14 / 555,585, filed Nov. 27, 2014, and published as U.S. Patent Publication No. 2015 / 0205126 on Jul. 23, 2015; U.S. Patent Application No. 14 / 690,401, filed Apr. 18, 2015, and published as U.S. Patent Publication No. 2015 / 0302652 on Oct. 22, 2015; U.S. Patent Application No. 14 / 212,961, filed Mar. 14, 2014, and issued as U.S. Patent No. 9,417,452 on Aug. 16, 2016; U.S. Patent Application No. 14 / 331,218, filed Jul. 14, 2014, and published as U.S. Patent Publication No. 2015 / 0309263 on Oct. 29, 2015; and U.S. Patent Application No. 15 / 954,419, filed Apr. 16, 2018.

[0003] The present disclosure relates to display systems, and more particularly to augmented and virtual reality display systems.

Background Art

[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 can be perceived as being real. A virtual reality, i.e., a "VR" scenario, typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual inputs, and an augmented reality, i.e., an "AR" scenario, typically involves the presentation of digital or virtual image information as an augmentation to the visualization of the actual world around the user. A mixed reality or "MR" scenario is a type of AR scenario that typically involves virtual objects integrated into and responsive to the natural world. For example, an MR scenario may include AR image content that appears to be blocked by or otherwise interact with objects within the real world.

[0005] Referring to FIG. 1, an augmented reality scene 10 is depicted. To a user of AR technology, a real-world park-like setting 20 is visible, featuring people, trees, buildings in the background, and a concrete platform 30. The user also "sees" "virtual content" such as a robot figure 40 standing on the real-world platform 30 and an avatar character 50 in the form of a flying cartoon that appears anthropomorphic like a bumblebee. These elements 50, 40 are "virtual" in that they do not exist within the real world. Due to the complexity of the human visual perception system, the generation of AR technology that facilitates a comfortable, natural, and rich presentation of virtual image elements among other virtual or real-world image elements is difficult. SUMMARY OF THE INVENTION MEANS FOR SOLVING THE PROBLEM

[0006] Some aspects include a display system for projecting an image onto a user's eye. The display system includes a waveguide having a first major surface and a second major surface opposite the first major surface, a projection optical system configured to project a beam of light toward the second major surface of the waveguide, and an internal coupling optical element disposed on the second major surface of the waveguide, the internal coupling optical element comprising a diffractive region configured to internally couple light from the projection optical system and configured to redirect light from the projection optical system to propagate within the waveguide in a first direction by total internal reflection. The diffractive region is sized and shaped such that a first portion of the beam of light from the projection optical system impinges on the diffractive region and a second portion of the beam of light from the projection optical system impinges on the waveguide without impinging on the diffractive region.

[0007] The diffraction region may be a high-efficiency diffraction region, and the internal coupling optical element further comprises a low-efficiency diffraction region sized and shaped such that a second portion of the beam of light from the projection optical system is incident on the low-efficiency diffraction region. The high-efficiency diffraction region may be a reflective diffraction region comprising a metallized grating portion, and the low-efficiency diffraction region may comprise a non-metallized grating portion. The second portion of the beam of light may propagate out of the waveguide through the second major surface without being internally coupled into the waveguide. The second portion of the beam of light may be internally coupled into the waveguide with a lower efficiency than the first portion of the beam of light. The diffraction region may be reflection-asymmetric about a symmetry axis perpendicular to the propagation direction of the beam of light from the projection optical system at the beam axis. The waveguide may be part of a waveguide stack, and the waveguide stack further comprises a second waveguide having a first major surface and a second major surface, and a second internal coupling optical element disposed on the second major surface of the second waveguide, the second internal coupling optical element comprising a second diffraction region that covers a larger proportion of the area defined by the second beam of light from the projection optical system than the proportion of the area defined by the diffraction region of the area covered by the beam of light, the second diffraction region being configured to internally couple substantially all of the second beam of light. The diffraction region of the first waveguide may be reflection-asymmetric about a symmetry axis perpendicular to the propagation direction of the beam of light from the projection optical system at the beam axis, and the second diffraction region may be reflection-symmetric about a second symmetry axis perpendicular to the propagation direction of the second beam of light at the beam axis. The second waveguide may be disposed between the waveguide and the projection optical system, and the waveguide may be spaced from the projection optical system by a distance greater than the focal length of the projection optical system.

[0008] Some aspects include a waveguide including a first major surface, a second major surface, and an internal coupling diffractive optical element disposed on the second major surface, the internal coupling optical element comprising a diffraction region configured to internally couple incident light, the width of the diffraction region parallel to the propagation direction being shorter than the length of the diffraction region perpendicular to the propagation direction.

[0009] The width of the diffraction region may be less than 80% of the length of the diffraction region. The diffraction region may be a high-efficiency diffraction region, and the internally coupled diffractive optical element further includes a low-efficiency diffraction region disposed adjacent to the high-efficiency diffraction region along the propagation direction. The high-efficiency diffraction region may be a reflective diffraction region including a metallized diffraction grating portion, and the low-efficiency diffraction region may include a non-metallized diffraction grating portion. The high-efficiency diffraction region and the low-efficiency diffraction region may partially form a metallized diffraction grating, and the diffraction grating is metallized within the high-efficiency diffraction region and non-metallized within the low-efficiency diffraction region. The internally coupled diffractive optical element may be sized and shaped to reduce the occurrence of re-bounces of internally coupled light compared to an internally coupled optical element having substantially equal length and width.

[0010] Some aspects include a waveguide stack for a head-mounted display system. The waveguide stack includes a first waveguide having a first major surface, a second major surface opposing the first major surface, and a first internally coupled diffractive optical element disposed on the second major surface and configured to re-direct incident light from a light source to propagate in a propagation direction within the first waveguide by total internal reflection, the first internally coupled diffractive optical element including a first diffraction region; and a second waveguide having a first major surface, a second major surface opposing the first major surface of the second waveguide, and a second internally coupled diffractive optical element disposed on the second major surface of the second waveguide and configured to re-direct incident light from a light source to propagate in a propagation direction within the second waveguide by total internal reflection, the second internally coupled diffractive optical element including a second diffraction region. The width-to-length ratio of the second diffraction region is smaller than the width-to-length ratio of the first diffraction region.

[0011] The waveguide stack may be spaced apart from the light source such that the distance between the light source and the first diffraction region is on the focal length of the light source and the distance between the light source and the second diffraction region is greater than the focal length. The width-to-length ratio of the first diffraction region may be greater than 80%, and the width-to-length ratio of the second diffraction region may be less than 80%. The second diffraction region may be a high-efficiency diffraction region, and the second internal coupling diffractive optical element may further include a low-efficiency diffraction region disposed directly adjacent to the high-efficiency diffraction region along the propagation direction. The high-efficiency diffraction region may include a metallized portion of the diffraction grating, and the low-efficiency diffraction region may include a non-metallized portion of the diffraction grating. The second internal coupling diffractive optical element may be sized and shaped to reduce the occurrence of re-bounces of internally coupled light as compared to an internal coupling diffractive optical element having a width-to-length ratio equal to the width-to-length ratio of the first diffraction region.

[0012] Some aspects include a method of fabricating an optical waveguide structure having a reflective layer. The method includes providing an optical waveguide having a surface, the surface including a region having a pattern of protrusions, depositing a liquid mixture on at least a portion of the region, the liquid mixture including a metal salt, and forming a reflective layer by coating the region with the metal of the metal salt, the coating step including depositing the metal on the region by dissociating the metal from the metal salt.

[0013] The step of dissociating the metal from the metal salt may include the step of reducing the metal salt by exposing it to a reducing agent. The reducing agent may comprise at least one of a carbohydrate containing an alpha-hydroxyaldehyde or a carbohydrate containing an alpha-hydroxyketone. The liquid mixture may comprise the reducing agent. The method may further include the step of adding a reducing agent to the liquid mixture after depositing the liquid mixture. The step of forming the reflective layer may include selectively forming the reflective layer over the region while leaving one or more areas around the metal-free regions. The surface of the waveguide may comprise a vertically extending wall that defines a volume within the region, and the step of depositing the liquid mixture may include depositing the deposited mixture into the volume. The protrusion may define a diffractive optical element, and the protrusion and the reflective layer form a reflective diffractive optical element. The diffractive optical element may be an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through the waveguide by total internal reflection. The protrusion may comprise a photoresist. The method may further include forming an additional reflective layer on the additional optical waveguide by depositing the liquid mixture on an additional region of the surface of the additional optical waveguide, wherein the additional reflective optical element is configured to reflect incident light, and attaching at least the additional waveguide to the surface of the waveguide, thereby producing a stack of waveguides. The hydrophilicity of the region may be increased by selectively pre-treating the region with one or more agents selected from the group consisting of plasma, surfactant, coating, wet chemical etching solution, and catalyst prior to the step of depositing the liquid mixture. The step of pre-treating the region with plasma may include performing an atmospheric plasma treatment. The wet chemical etching agent may comprise chromic acid. The coating may comprise silica. The catalyst may comprise tin or palladium. The method may further include selectively applying a catalyst to the region prior to the step of depositing the liquid mixture, wherein the catalyst is configured to facilitate the reduction of the silver salt. The liquid mixture may consist essentially of a metal salt, a reducing agent, and a base.The reflective layer may be pure or substantially pure metal. The liquid mixture may be deposited onto the region by at least one of nano-dispensing, micro-dispensing, micro-pipetting, inkjet printing, and spraying. The method may further include a step of removing the residual liquid mixture material following the deposition of the metal. The step of removing the residual liquid crystal mixture may include a step of flushing the optical waveguide. The method may further include a step of depositing a capping layer onto the reflective layer. The reflective layer may be in a state without or substantially without pinholes. The metal may be silver.

[0014] Some aspects include an optical device comprising a first waveguide with a reflective diffractive optical element. The reflective diffractive optical element comprises a protrusion on the surface of the first waveguide, an interface layer on the protrusion, and a reflective layer on the interface layer.

[0015] The interface layer may comprise one or more of a plasma-treated surface, a surfactant layer, and a catalyst. The catalyst may include one or more of a tin or palladium-containing composite. The reflective layer may be at least 95% metal. The reflective layer may be in a state substantially free of pinholes. The reflective diffractive optical element may be an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through a first waveguide by total internal reflection. The reflective layer may reflect incident light with a reflectivity of at least 85%. The optical device may further comprise a second waveguide and a third waveguide, the second waveguide being configured to output light in a wavelength range different from that of the third waveguide, and the first, second, and third waveguides each comprising a reflective diffractive optical element comprising a protrusion on the surface of the first waveguide, an interface layer on the protrusion, and a reflective layer on the interface layer. The first surface may comprise a wall that defines a boundary of the reflective layer. The wall may comprise a mechanical spacer configured to maintain a space between the first waveguide and other waveguides. The optical device may be a display system comprising a spatial light modulator, the spatial light modulator being configured to output light containing image information onto the reflective diffractive optical element. The optical device may further comprise a capping layer on the reflective layer. The present invention provides, for example, the following. (Item 1) A display system for projecting an image onto a user's eye, the display system comprising: a waveguide comprising a first major surface and a second major surface opposite the first major surface; a projection optical system configured to project a beam of light towards the second major surface of the waveguide; an internal coupling optical element disposed on the second major surface of the waveguide, the internal coupling optical element comprising a diffractive region configured to internally couple light from the projection optical system, the internal coupling optical element being configured to redirect light from the projection optical system to propagate in a first direction within the waveguide by total internal reflection; and The diffraction region is sized and shaped such that a first portion of the beam of light from the projection optical system is incident on the diffraction region and a second portion of the beam of light from the projection optical system collides with the waveguide without being incident on the diffraction region, a display system. (Item 2) The diffraction region is a high-efficiency diffraction region, and the internal coupling optical element further includes a low-efficiency diffraction region sized and shaped such that a second portion of the beam of light from the projection optical system is incident on the low-efficiency diffraction region, the display system according to item 1. (Item 3) The high-efficiency diffraction region is a reflective diffraction region including a metallized grating portion, and the low-efficiency diffraction region is non-metallized, the display system according to item 2. (Item 4) The second portion of the beam of light propagates out of the waveguide through the second major surface without being internally coupled into the waveguide, the display system according to item 1. (Item 5) The second portion of the beam of light is internally coupled into the waveguide with lower efficiency than the first portion of the beam of light, the display system according to item 1. (Item 6) The diffraction region is reflection-asymmetric about a symmetry axis perpendicular to the propagation direction on the beam axis of the beam of light from the projection optical system, the display system according to item 1. (Item 7) The waveguide is part of a waveguide stack, and the waveguide stack a second waveguide having a first major surface and a second major surface, a second internal coupling optical element disposed on the second major surface of the second waveguide, the second internal coupling optical element including a second diffraction region that covers a larger proportion of the area defined by the second beam of light from the projection optical system than the proportion of the area defined by the diffraction region of the area defined by the beam of light, a second internal coupling optical element The display system according to item 1, further comprising (Item 8) The display system according to item 7, wherein the second diffraction region is configured to internally couple substantially all of the beam of the second light. (Item 9) The display system according to item 7, wherein the diffraction region of the first waveguide is reflection-asymmetric about a symmetry axis perpendicular to the propagation direction on the beam axis of the beam of light from the projection optical system, and the second diffraction region is reflection-symmetric about a second symmetry axis perpendicular to the propagation direction on the beam axis of the beam of the second light. (Item 10) The display system according to item 7, wherein the second waveguide is disposed between the waveguide and the projection optical system, and the waveguide is separated from the projection optical system by a distance exceeding the focal length of the projection optical system. (Item 11) A waveguide, comprising a first major surface, a second major surface, an internal coupling diffractive optical element disposed on the second major surface, the internal coupling optical element comprising a diffraction region configured to internally couple incident light, and a width of the diffraction region parallel to the propagation direction being shorter than a length of the diffraction region perpendicular to the propagation direction, and the internal coupling diffractive optical element A waveguide comprising (Item 12) The waveguide according to item 11, wherein the width of the diffraction region is less than 80% of the length of the diffraction region. (Item 13) The waveguide according to item 11, wherein the diffraction region is a high-efficiency diffraction region, and the internal coupling diffractive optical element further comprises a low-efficiency diffraction region disposed adjacent to the high-efficiency diffraction region along the propagation direction. (Item 14) The waveguide according to item 13, wherein the high-efficiency diffraction region is a reflective diffraction region comprising a metallized diffraction grating portion, and the low-efficiency diffraction region comprises a non-metallized diffraction grating portion. (Item 15) The high-efficiency diffraction region and the low-efficiency diffraction region partially form a metallized diffraction grating, and the diffraction grating is metallized within the high-efficiency diffraction region and non-metallized within the low-efficiency diffraction region, for the waveguide according to item 13. (Item 16) The internally coupled diffractive optical element is sized and shaped to reduce the occurrence of re-bounces of internally coupled light as compared to an internally coupled optical element having substantially equal length and width, for the waveguide according to item 11. (Item 17) A waveguide stack for a head-mounted display system, the waveguide stack comprising A first waveguide, the first waveguide comprising a first major surface, a second major surface facing the first major surface, and a first internally coupled diffractive optical element disposed on the second major surface, the first internally coupled diffractive optical element comprising a first diffraction region configured to re-direct incident light from a light source and propagate in a propagation direction within the first waveguide by total internal reflection, a first waveguide; A second waveguide, the second waveguide comprising a first major surface, a second major surface facing the first major surface of the second waveguide, and a second internally coupled diffractive optical element disposed on the second major surface of the second waveguide, the second internally coupled diffractive optical element comprising a second diffraction region configured to re-direct incident light from the light source and propagate in the propagation direction within the second waveguide by total internal reflection, a second waveguide comprising The waveguide stack, wherein a width-to-length ratio of the second diffraction region is smaller than a width-to-length ratio of the first diffraction region. (Item 18) The waveguide stack according to item 17, wherein the distance between the light source and the first diffraction region is at the focal length of the light source, and the distance between the light source and the second diffraction region is greater than the focal length, and the waveguide stack is spaced apart from the light source. (Item 19) The width-to-length ratio of the first diffraction region exceeds 80%, and the width-to-length ratio of the second diffraction region is less than 80%, the waveguide stack according to item 17. (Item 20) The second diffraction region is a high-efficiency diffraction region, and the second internally coupled diffractive optical element further comprises a low-efficiency diffraction region disposed directly adjacent to the high-efficiency diffraction region along the propagation direction, the waveguide stack according to item 17. (Item 21) The high-efficiency diffraction region comprises a metallized portion of the diffraction grating, and the low-efficiency diffraction region comprises a non-metallized portion of the diffraction grating, the waveguide stack according to item 20. (Item 22) The second internally coupled diffractive optical element is sized and shaped to reduce the occurrence of re-bounce of the internally coupled light as compared to an internally coupled diffractive optical element having a width-to-length ratio equal to the width-to-length ratio of the first diffraction region, the waveguide stack according to item 17. (Item 23) A method of fabricating an optical waveguide structure comprising a reflective layer, the method comprising: providing an optical waveguide having a surface, the surface comprising a region having a pattern of protrusions; depositing a liquid mixture on at least a portion of the region, the liquid mixture comprising a metal salt; forming the reflective layer by coating the region with the metal of the metal salt, coating the region comprising depositing the metal on the region by dissociating the metal from the metal salt; comprising, a method. (Item 24) Dissociating the metal from the metal salt comprises reducing the metal salt by exposure to a reducing agent, the method according to item 23. (Item 25) The reducing agent comprises at least one of a carbohydrate containing an alpha-hydroxyaldehyde or a carbohydrate containing an alpha-hydroxyketone, the method according to item 24. (Item 26) The liquid mixture contains the reducing agent, and the method according to item 24. (Item 27) After depositing the liquid mixture, further including adding the reducing agent to the liquid mixture, and the method according to item 24. (Item 28) Forming the reflective layer includes selectively forming the reflective layer on the region while leaving one or more areas around the region without the metal, and the method according to item 23. (Item 29) The surface of the waveguide has a vertically extending wall that defines a volume within the region, and depositing the liquid mixture includes depositing the deposited mixture into the volume, and the method according to item 28. (Item 30) The protrusion defines a diffractive optical element, and the protrusion and the reflective layer form a reflective diffractive optical element, and the method according to item 23. (Item 31) The diffractive optical element is an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through the waveguide by total internal reflection, and the method according to item 30. (Item 32) The protrusion includes a photoresist, and the method according to item 23. (Item 33) Forming an additional reflective layer on the additional optical waveguide by depositing the liquid mixture on an additional region of the surface of the additional optical waveguide, wherein the additional reflective optical element is configured to reflect incident light, and attaching at least the additional waveguide to the surface of the waveguide, thereby producing a stack of waveguides and further including the method according to item 23. (Item 34) The hydrophilicity of the region is increased by selectively pre-treating the region with one or more agents selected from the group consisting of plasma, surfactant, coating, wet chemical etching solution, and catalyst prior to depositing the liquid mixture, the method according to item 23. (Item 35) Pre-treating the region with plasma includes performing atmospheric plasma treatment. The wet chemical etching agent includes chromic acid. The coating includes silica and / or The catalyst includes tin or palladium. The method according to item 34, wherein it is at least one of the above. (Item 36) The method according to item 23, further including selectively applying a catalyst to the region prior to depositing the liquid mixture, the catalyst being configured to promote the reduction of the silver salt. (Item 37) The liquid mixture consists essentially of the metal salt, reducing agent, and base, the method according to item 23. (Item 38) The reflective layer is a pure metal or substantially pure metal, the method according to item 23. (Item 39) The liquid mixture is deposited on the region by at least one of nano-dispensing, micro-dispensing, micro-pipetting, inkjet printing, and spraying, the method according to item 23. (Item 40) The method according to item 23, further including removing the residual liquid mixture material following the deposition of the metal. (Item 41) Removing the residual liquid crystal mixture includes rinsing the optical waveguide, the method according to item 40. (Item 42) The method according to item 23, further including depositing a capping layer on the reflective layer. (Item 43) The method according to item 23, wherein the reflective layer has no or substantially no pinholes. (Item 44) The method according to item 23, wherein the metal is silver. (Item 45) An optical device, A first waveguide comprising a reflective diffractive optical element, wherein the reflective diffractive optical element protrusions on the surface of the first waveguide, an interface layer on the protrusions, and a reflective layer on the interface layer and comprises a first waveguide and comprises an optical device. (Item 46) The optical device according to item 45, wherein the interface layer comprises one or more of a plasma-treated surface, a surfactant layer, and a catalyst. (Item 47) The optical device according to item 46, wherein the catalyst comprises one or more of tin or a palladium-containing composite. (Item 48) The optical device according to item 45, wherein the reflective layer is at least 95% metal. (Item 49) The optical device according to item 45, wherein the reflective layer has substantially no pinholes. (Item 50) The optical device according to item 45, wherein the reflective diffractive optical element is an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through the first waveguide by total internal reflection. (Item 51) The optical device according to item 50, wherein the reflective layer reflects the incident light with a reflectivity of at least 85%. (Item 52) Further comprising a second waveguide and a third waveguide, wherein the second waveguide is configured to output light in a wavelength range different from that of the third waveguide, the first, second, and third waveguides each comprise a reflective diffractive optical element, and the reflective diffractive optical element The protrusion on the surface of the first waveguide, the interface layer on the protrusion, and the reflective layer on the interface layer The optical device according to item 45, comprising: (Item 53) The optical device according to item 45, wherein the first surface comprises a wall that defines the boundary of the reflective layer. (Item 54) The optical device according to item 53, wherein the wall comprises a mechanical spacer configured to maintain a space between the first waveguide and other waveguides. (Item 55) The optical device according to item 45, wherein the optical device is a display system comprising a spatial light modulator, and the spatial light modulator is configured to output light containing image information onto the reflective diffractive optical element. (Item 56) The optical device according to item 45, further comprising a capping layer on the reflective layer.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0056] An AR and / or VR system can display virtual content to a user, i.e., a viewer. Preferably, this content is displayed on a head-mounted display as part of glasses, which projects, for example, image information onto the user's eyes. Additionally, if the system is an AR system, the display can also transmit light from the user's surrounding environment to the eyes, enabling a view of that surrounding environment. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the head of a viewer or user.

[0057] In some display systems, a plurality of waveguides that make up a stack of waveguides can be configured to form virtual images on a plurality of virtual depth planes (also simply referred to herein as "depth planes") that are perceived to be at different distances from the user. In some embodiments, different waveguides of the stack of waveguides can have optical structures that provide different refractive powers and can simulate the wavefront divergence of light propagating from objects at different distances from the user's eyes. In some embodiments, as an alternative to or in addition to the waveguide optical structures for providing refractive power, the display system may also include a plurality of lenses that provide or additionally provide refractive power. Light from an image source can be directed towards the waveguides and internally coupled into the individual waveguides by internal coupling optical elements of each waveguide. The internal coupling optical element may be a diffractive optical element such as a grating.

[0058] In some embodiments, the systems and methods described herein include internal coupling optical elements configured to improve internal coupling efficiency and / or the uniformity of internally coupled light by reducing the occurrence of light loss due to the rebounce of internally coupled light. Rebounce occurs when internally coupled light propagating along a waveguide strikes the internal coupling optical element a second or subsequent time after an initial internal coupling incidence. As will be described in more detail, rebounce can result in a portion of the internally coupled light being undesirably externally coupled and / or absorbed by the material of the internal coupling optical element. External coupling and / or absorption can undesirably result in a reduction in overall internal coupling efficiency and / or the uniformity of internally coupled light.

[0059] Some embodiments disclosed herein provide a diffractive optical element, which may also be an internal coupling optical element configured to reduce optical losses due to the rebounce of internally coupled light within a waveguide. In response to internally coupling incident light, the diffractive optical element may generally redirect the light to propagate in a propagation direction through the waveguide. In some cases, the rebounce of the internally coupled light occurs in the propagation direction towards the side surface of the internal coupling optical element. For example, initially, some of the incident light internally coupled in the vicinity of the opposite (opposite to the propagation direction) side of the internal coupling optical element may rebounce, i.e., after reflection from another surface of the waveguide, it may strike the internal coupling optical element again. Without being limited by theory, in response to striking the internal coupling optical element, again, a portion of the incident light may undesirably be externally coupled by the optical element and / or absorbed by the optical element (e.g., when the internal coupling optical element is a reflective diffractive optical element, it is absorbed by the reflective coating on the diffraction grating).

[0060] In some embodiments, to reduce optical losses due to rebounce, the internally coupled optical element is truncated on the propagation direction side of the optical element. Advantageously, the truncation can reduce the occurrence of optical losses caused by rebounce by reducing the available area of the internally coupled optical element where rebounce is likely to result in undesirable optical losses. In some embodiments, the truncation may be a complete truncation of all structures of the internally coupled optical element. For example, the truncation may involve a reduction in the area of the internally coupled optical element in the direction of optical propagation. In some other embodiments where the internally coupled optical element comprises a reflective coating (e.g., a reflective layer such as a metal layer), a portion of the internally coupled optical element on the propagation direction side may not be coated such that the portion of the optical element on the propagation direction side hardly absorbs the rebounce light and / or externally couples the rebounce light with lower efficiency. In some embodiments, as seen in the figures above and below, the diffractive region of the internally coupled optical element may have a smaller width-to-length ratio than the non-truncated diffractive region, may have a width shorter than its length perpendicular to the propagation direction along the propagation direction, and / or may be sized and shaped such that a first portion of the beam of light from the projection optical system impinges on the diffractive region and a second portion of the beam of light impinges on the waveguide without impinging on the diffractive region (e.g., the portion of the optical element having a high absorption rate and / or external coupling efficiency is preferably smaller in size than the area created by the incident beam of light on the waveguide). In some embodiments, across the stack of waveguides, the amount of truncation varies between waveguides. For example, the width-to-length ratio of the internally coupled optical element of each waveguide may vary between different waveguides in the stack of waveguides.

[0061] The waveguide may use optical elements to internally couple external light and / or redirect the light propagating within the waveguide in a desired direction. For example, the optical elements may take the form of diffraction gratings and / or facet features. Some optical elements may operate in a reflective mode, performing both reflection and redirection such that light incident on the optical element from one or more angles propagates away from the optical element at different desired angles. As disclosed herein, such waveguides may form part of a display system such as an augmented reality and virtual reality display system. For example, the waveguide may be configured to internally couple light containing image information and externally couple and distribute that light to the user. Exemplary waveguides and optical elements will be discussed in more detail herein. The reflective optical element may include a reflective layer formed by wet chemical action, which may advantageously provide better diffraction efficiency as discussed herein.

[0062] Reference is now made to the drawings, in which like reference numerals refer to like parts throughout. Unless otherwise indicated, the drawings are schematic and are not necessarily drawn to scale.

[0063] Exemplary display system FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user. It should be understood that when the user's eyes are spaced apart and looking at a real object in space, each eye has a slightly different view of the object and can form an image of the object at different locations on the retina of each eye. This may be referred to as binocular disparity and can be utilized by the human visual system to provide a perception of depth. The conventional display system simulates binocular disparity by presenting two distinct different images 190, 200 with slightly different views of the same virtual object, one for each eye 210, 220, corresponding to views of the virtual object that would appear to each eye as if the virtual object were a real object at the desired depth. These images provide binocular cues that the user's visual system interprets to derive a perception of depth.

[0064] Continuing to refer to FIG. 2, images 190, 200 are separated from eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer in a state where the eyes are gazing at an object at optical infinity directly in front of the viewer. Images 190, 200 are flat and at a fixed distance from eyes 210, 220. Based on slightly different views of the virtual object in the images presented to eyes 210, 220 respectively, the eyes can necessarily rotate so that the image of the object comes to corresponding points on the respective retinas of the eyes and single binocular vision is maintained. This rotation can converge the respective lines of sight of eyes 210, 220 onto a point in the space where the virtual object is perceived to exist. As a result, providing a three-dimensional image has conventionally involved providing binocular cues that can manipulate the convergence / divergence movement of the user's eyes 210, 220 and are interpreted such that the human visual system provides depth perception.

[0065] However, generating a realistic and comfortable perception of depth is difficult. It should be understood that light from objects at different distances from the eyes has wavefronts with different amounts of divergence. FIGS. 3A - 3C illustrate the relationship between distance and the divergence of light rays. The distances between the object and eye 210 are represented in the order of decreasing distances R1, R2, and R3. As shown in FIGS. 3A - 3C, the light rays diverge more as the distance to the object decreases. Conversely, as the distance increases, the light rays become more collimated. In other words, it can be said that the light field generated by a point (object or part of an object) has a spherical wavefront curvature that is a function of the distance the point is away from the user's eyes. The curvature increases as the distance between the object and eye 210 decreases. Only monocular 210 is illustrated in FIGS. 3A - 3C and various other figures in this specification for clarity of illustration, but the discussion regarding eye 210 can be applied to both eyes 210 and 220 of the viewer.

[0066] Continuing to refer to FIGS. 3A - 3C, light from an object on which a viewer's eye is fixated can have different wavefront divergences. Due to the different amounts of wavefront divergence, the light can be focused differently by the eye's lens, which in turn can require the lens to take on different shapes to form a focused image on the eye's retina. If the focused image is not formed on the retina, the resulting retinal blur acts as a cue for accommodation, causing a change in the shape of the eye's lens until the focused image is formed on the retina. For example, the cue for accommodation can trigger the relaxation or contraction of the ciliary muscle surrounding the eye's lens, thereby modulating the force applied to the zonular fibers that hold the lens, and thus changing the shape of the eye's lens until the retinal blur of the fixated object is eliminated or minimized, thereby forming a focused image of the fixated object on the eye's retina (e.g., the fovea). The process by which the eye's lens changes shape can be referred to as accommodation, and the shape of the eye's lens required to form a focused image of the fixated object on the eye's retina (e.g., the fovea) can be referred to as the accommodative state.

[0067] Referring now to FIG. 4A, the representation of the accommodation-convergence / divergence movement response of the human visual system is illustrated. Eye movements to fixate an object cause the eye to receive light from the object, and the light forms an image on each of the retinas of the eye. The presence of retinal blur in the image formed on the retina can provide a cue for accommodation, and the relative location of the image on the retina can provide a cue for convergence / divergence movement. The cue for accommodation results in accommodation occurring and the eye's lens assuming a particular accommodation state that forms a focused image of the object on the retina of the eye (e.g., the fovea). On the other hand, the cue for convergence / divergence movement causes a convergence / divergence movement (rotation of the eye) such that the images formed on each retina of each eye are at corresponding retinal points that maintain single binocular vision. At these positions, it can be said that the eye is in a particular convergence / divergence movement state. Continuing to refer to FIG. 4A, accommodation can be understood as the process by which the eye achieves a particular accommodation state, and convergence / divergence movement can be understood as the process by which the eye achieves a particular convergence / divergence movement state. As shown in FIG. 4A, the accommodation and convergence / divergence movement states of the eye can change when the user fixates on another object. For example, the accommodated state can change when the user fixates on a new object at a different depth on the z-axis.

[0068] Without being limited by theory, it is believed that the viewer of an object can perceive the object as "three-dimensional" due to the combination of convergence / divergence movement and accommodation. As described above, the convergence / divergence movement of the two eyes relative to each other (e.g., the rotation of the eyes such that the pupils move towards or away from each other, converging the lines of sight of the eyes to fixate on an object) is closely associated with the accommodation of the eye's lens. Under normal conditions, changing the shape of the eye's lens to change focus from one object to another at a different distance will automatically cause a corresponding change in convergence / divergence movement to the same distance under a relationship known as the "accommodation-convergence / divergence reflex". Similarly, a change in convergence / divergence movement will, under normal conditions, trigger a corresponding change in the shape of the lens.

[0069] Referring now to FIG. 4B, examples of different accommodation and convergence / divergence states of the eyes are illustrated. The pair of eyes 222a is gazing at an object at optical infinity, while the pair of eyes 222b is gazing at an object 221 that is less than optical infinity. It should be noted that the convergence / divergence states of each pair of eyes are different, with the pair of eyes 222a being directed straight ahead, while the pair of eyes 222 converges onto the object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b also differ, as represented by the different shapes of the lenses 210a, 220a.

[0070] Unfortunately, many users of conventional "3-D" display systems find such conventional systems uncomfortable or perceive no sense of depth due to the mismatch between accommodation and convergence / divergence states in these displays. As described above, many stereoscopic or "3-D" display systems present a scene by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they merely provide different presentations of the scene, causing a change in the convergence / divergence state of the eyes without a corresponding change in the accommodation state of those eyes. Rather, the images are presented at a fixed distance from the eyes by the display such that the eyes view all the image information in a single accommodation state. Such an arrangement goes against the "accommodation-convergence / divergence reflex" by causing a change in the convergence / divergence state without a matching change in the accommodation state. This mismatch is thought to cause viewer discomfort. A display system that provides better matching between accommodation and convergence / divergence can result in a more realistic and comfortable simulation of three-dimensional images.

[0071] Although not limited by theory, the human eye is typically thought to be able to interpret a finite number of depth planes and provide depth perception. As a result, a highly realistic simulation of the perceived depth can be achieved by providing different presentations of an image corresponding to each of these limited number of depth planes to the eye. In some embodiments, the different presentations may provide both cues for convergence / divergence motion and matching cues for focusing, thereby providing physiologically correct focusing-convergence / divergence motion matching.

[0072] Continuing to refer to FIG. 4B, two depth planes 240 corresponding to different distances in space from eyes 210, 220 are illustrated. For a given depth plane 240, convergence / divergence motion cues may be provided by appropriately displaying images of different viewpoints for each of eyes 210, 220. Additionally, for a given depth plane 240, the light forming the images provided to each eye 210, 220 may have wavefront divergence corresponding to a light field generated by a point at the distance of that depth plane 240.

[0073] In the illustrated embodiment, the distance along the z-axis of depth plane 240 containing point 221 is 1 m. As used herein, the distance or depth along the z-axis may be measured using a zero point located at the exit pupil of the user's eye. Thus, the depth plane 240 located at a depth of 1 m corresponds to a distance 1 m away from the exit pupil of the user's eye on the optical axis of those eyes with the eyes directed towards optical infinity. As an approximation, the depth or distance along the z-axis may be measured from the front of the user's eye (e.g., the surface of a waveguide), and a value related to the distance between the device and the exit pupil of the user's eye may be added. That value is referred to as the pupil distance and may correspond to the distance between the exit pupil of the user's eye and the display worn by the user in front of the eye. In practice, the value for the pupil distance may generally be a normalized value used for all viewers. For example, the pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 m may be at a distance of 980 mm in front of the display.

[0074] Referring now to FIGS. 4C and 4D, examples of consistent vergence-accommodation movement distances and inconsistent vergence-accommodation movement distances are illustrated, respectively. As shown in FIG. 4C, the display system may provide an image of a virtual object to each eye 210, 220. The image may cause the eyes 210, 220 to assume a vergence-accommodation state in which the eyes converge on a point 15 on the depth plane 240. Additionally, the image may be formed by light having a wavefront curvature corresponding to an actual object in the depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is in focus on their retinas. Thus, the user may perceive the virtual object as being at the point 15 on the depth plane 240.

[0075] It should be understood that the accommodation and vergence-accommodation states of the eyes 210, 220 are each associated with a particular distance on the z-axis. For example, an object at a particular distance from the eyes 210, 220 causes the eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state may be referred to as the accommodation distance A d Similarly, there exists a particular vergence distance V d or relative position to each other associated with the eyes in a particular vergence-accommodation state. When the accommodation distance and the vergence distance are consistent, the relationship between accommodation and vergence is said to be physiologically correct. This is considered the most comfortable scenario for the viewer.

[0076] However, in a stereoscopic display, the focusing adjustment distance and the vergence / accommodation movement distance may not always match. For example, as shown in FIG. 4D, the images displayed on eyes 210, 220 may be displayed with wavefront divergence corresponding to depth plane 240, and eyes 210, 220 may take a specific focusing adjustment state in which points 15a, 15b on that depth plane are in focus. However, the images displayed on eyes 210, 220 may provide a cue for vergence / accommodation movement that converges eyes 210, 220 on point 15 not located on depth plane 240. As a result, in some embodiments, the focusing adjustment distance corresponds to the distance from the exit pupils of eyes 210, 220 to depth plane 240, while the vergence / accommodation movement distance corresponds to a greater distance from the exit pupils of eyes 210, 220 to point 15. The focusing adjustment distance is different from the vergence / accommodation movement distance. As a result, there is a focusing adjustment - vergence / accommodation movement mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch corresponds to a distance (e.g., V d -A d ) and it should be understood that it can be characterized using diopters.

[0077] It should be understood that in some embodiments, as long as the same reference point is used for the focusing adjustment distance and the vergence / accommodation movement distance, a reference point other than the exit pupils of eyes 210, 220 may be used to determine the distance for determining the focusing adjustment distance and the vergence / accommodation movement mismatch. For example, the distance can be measured from the cornea to the depth plane, from the retina to the depth plane, from the eyepiece (e.g., the waveguide of the display device) to the depth plane, etc.

[0078] Although not limited by theory, it is believed that the user can still perceive accommodation-convergence / divergence motion mismatches of up to 0.25 diopters, up to 0.33 diopters, and up to about 0.5 diopters, which are physiologically correct, without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6) presents an image having an accommodation-convergence / divergence motion mismatch of 0.5 diopters or less to a viewer. In some other embodiments, the accommodation-convergence / divergence motion mismatch of the image provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-convergence / divergence motion mismatch of the image provided by the display system is 0.25 diopters or less, including about 0.1 diopters or less.

[0079] FIG. 5 illustrates a side view of an approach for simulating a three-dimensional image by modifying wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. Additionally, the user's other eye would be illustrated as being provided with image information from a similar waveguide.

[0080] 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 within a limited range of wavelengths. As a result, in some embodiments, multiple or a stack of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or to output light within different ranges of wavelengths. As used herein, it will be understood that a depth plane may be planar or may follow the contour of a curved surface. One or more waveguides of the stack may comprise, consist essentially of, or consist of a reflective diffractive optical element with a reflective layer that comprises, consists essentially of, or consists of pure or substantially pure metal, as described herein.

[0081] FIG. 6 illustrates an example of a stack of waveguides for outputting image information to a user. Display system 250 includes a stack or stacked waveguide assembly 260 of waveguides that can be utilized to provide three-dimensional perception to the eye / brain using a plurality of waveguides 270, 280, 290, 300, 310. It should be understood that display system 250 may be considered a light field display in some embodiments. Additionally, waveguide assembly 260 may also be referred to as an eyepiece.

[0082] In some embodiments, display system 250 may be configured to provide a substantially continuous cue for convergent / divergent motion and a plurality of discrete cues for depth adjustment. The cue for convergent / divergent motion may be provided by displaying different images to each of the user's eyes, and the cue for depth adjustment may be provided by outputting light that forms an image with a selectable discrete amount of wavefront divergence. In other words, display system 250 may be configured to output light with a variable level of wavefront divergence. In some embodiments, each discrete level of wavefront divergence may correspond to a particular depth plane and may be provided by a particular one of waveguides 270, 280, 290, 300, 310.

[0083] Continuing to refer to FIG. 6, waveguide assembly 260 may also include a plurality of features 320, 330, 340, 350 between waveguides. In some embodiments, features 320, 330, 340, 350 may be one or more lenses. Waveguides 270, 280, 290, 300, 310 and / or a plurality of lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, 400 may function as light sources for the waveguides and may be utilized to input image information into waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across an individual waveguide for output toward eye 210 as described herein. Light exits from output surfaces 410, 420, 430, 440, 450 of image input devices 360, 370, 380, 390, 400 and is input into corresponding input surfaces 460, 470, 480, 490, 500 of waveguides 270, 280, 290, 300, 310. In some embodiments, input surfaces 460, 470, 480, 490, 500 may each be an edge of the corresponding waveguide or a portion of the major surface of the corresponding waveguide (i.e., one of the waveguide surfaces facing directly the world 510 or viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be input into each waveguide and output an entire field of cloned collimated beams, which are directed toward eye 210 at a particular angle (and amount of divergence) corresponding to a depth plane associated with a particular waveguide. In some embodiments, a single one of image input devices 360, 370, 380, 390, 400 may be associated with and input light into a plurality (e.g., three) of waveguides 270, 280, 290, 300, 310.

[0084] In some embodiments, the image input devices 360, 370, 380, 390, 400 are each discrete displays that generate image information for input into their respective waveguides 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output ends of a single multiplexed display that can send image information, for example, via one or more optical waveguides (such as optical fiber cables) to each of the image input devices 360, 370, 380, 390, 400. 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).

[0085] In some embodiments, the light input into the waveguides 270, 280, 290, 300, 310 is provided by an optical projector system 520, which includes an optical module 530 that may include a light emitter such as a light emitting diode (LED). The light from the optical module 530 may be directed and modified by a beam splitter 550 and an optical modulator 540, such as a spatial light modulator. The optical modulator 540 may be configured to vary the perceived intensity of the light input into the waveguides 270, 280, 290, 300, 310 and to encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs) and liquid crystal on silicon (LCOS) displays. The image input devices 360, 370, 380, 390, 400 are shown schematically, and in some embodiments, these image input devices may represent different optical paths and locations within a common projection system that are configured to output light into their associated waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of the waveguide assembly 260 may function as an ideal lens while relaying the light input into the waveguide to the user's eye. In this concept, the object may be the spatial light modulator 540, and the image may be an image on a depth plane.

[0086] 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, helical scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately into the viewer's eye 210. In some embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input 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 waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and the one or more waveguides 270, 280, 290, 300, 310 and may, for example, redirect light exiting the scanning fiber into one or more of the waveguides 270, 280, 290, 300, 310.

[0087] 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 modulator 540. In some embodiments, controller 560 is part of the local data processing module 140. Controller 560 includes programming (e.g., instructions in a non-transitory medium) that adjusts the timing and provisioning of image information to 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 monolithic device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some embodiments, also be part of processing module 140 or 150 (FIG. 9D).

[0088] Continuing to refer 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). The waveguides 270, 280, 290, 300, 310 may each be planar, or have another shape (e.g., curved), with a major top and bottom surface and an edge extending between those major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, 310 each include external 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 the image information to the eye 210. The extracted light may also be referred to as external coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The beam of extracted light may be output by the waveguide at the location where the light propagating within the waveguide impinges on the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, the external coupling optical elements 570, 580, 590, 600, 610 are shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310, but in some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces, and / or directly disposed within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be attached to a transparent substrate and formed within a layer of material forming the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be monolithic parts of material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or within the surface of that part of the material.

[0089] Continuing to refer to FIG. 6, as discussed herein, each of the waveguides 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 (input into such waveguide 270) to the eye 210. The collimated light may represent an optically infinite focal plane. The next upper waveguide 280 may be configured to output collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may be configured to generate a somewhat 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 that is closer inwardly toward the eye 210 from the optically infinite. 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 power of the first lens 350 and the second lens 340 may be configured to generate another incremental amount of wavefront curvature such that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is closer inwardly toward the person from the optically infinite than the light from the next upper waveguide 280 was.

[0090] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, and the top waveguide 310 in the stack sends its output through all of the lenses between it and the eye for the converging focusing power representing the focal plane closest to the person. 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 disposed on top of the stack to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

[0091] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, a plurality of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same depth plane, or a plurality of subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set to the same plurality of depth planes, with one set per depth plane. This can provide the advantage of forming a tiled image to provide an extended field of view in those depth planes.

[0092] Continuing to refer to FIG. 6, the external coupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from their respective waveguides for a particular depth plane associated with the waveguide and output the light with an appropriate amount of divergence or collimation. As a result, waveguides having different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, 610, which 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 volume or surface features, which may be configured to output light at a specific angle. For example, the light extraction optical elements 570, 580, 590, 600, 610 may be a volume hologram, a surface hologram, and / or a diffraction grating. In some embodiments, the features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., structures for forming a cladding layer and / or voids).

[0093] In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 are diffraction features or “diffractive optical elements” (also referred to herein as “DOEs”) that form a diffraction pattern. Preferably, the DOE has a sufficiently low diffraction efficiency such that only a portion of the light of 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 associated output beams exiting the waveguide at various locations, resulting in a very uniform pattern of output emission towards the eye 210 with respect to this particular collimated beam bouncing within the waveguide.

[0094] In some embodiments, one or more DOEs may be switchable between an “on” state where they actively diffract and an “off” state where they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer dispersed liquid crystal, in which microdroplets have a diffraction pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match that of the host material (in which case the pattern does not significantly diffract the 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 the incident light).

[0095] 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 the tissue surrounding the eye 210, e.g., to detect user input and / or monitor the user's physiological state. 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 (e.g., infrared light) that projects light onto the eye and is then reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be attached to the frame 80 (FIG. 9D) and may communicate electrically with a processing module 140 and / or 150 that can process the image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye to monitor each eye separately.

[0096] Referring now to FIG. 7, an embodiment of an output beam output by a waveguide is shown. Although one waveguide is illustrated, it should be understood that other waveguides within the waveguide assembly 260 (FIG. 6) may function similarly, and the waveguide assembly 260 includes a plurality of waveguides. Light 640 is input into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates through 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 the output beam 650. The output beam 650 is illustrated as being substantially parallel, but as discussed herein, it may also be redirected to propagate to the eye 210 at an angle (e.g., forming a diverging output beam) depending on the depth plane associated with the waveguide 270. It should be understood that a waveguide with an external coupling optical element that externally couples light to form an image that appears to be set in a depth plane at a long distance (e.g., optically infinite) from the eye 210 may be shown for the substantially parallel output beam. Other waveguides or other sets of external coupling optical elements may output a more divergent output beam pattern, which would require the eye 210 to focus at a closer distance and would be interpreted by the brain as light from a distance closer to the eye 210 than optically infinite.

[0097] In some embodiments, a full-color image may be formed in each depth plane by overlaying the image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, and each depth plane includes an image formed using a plurality of different primary colors. The illustrated embodiment shows depth planes 240a-240f, although more or fewer depths are also envisioned. Each depth plane may have three or more primary color images associated therewith, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are shown in the figure by different numbers associated with the diopter (dpt) following the letters G, R, and B. As a mere example, the numbers following each of these letters indicate the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the exact location of the depth planes for different primary colors may vary to account for differences in the focusing of light of different wavelengths by the eye. For example, the different primary color images for a given depth plane may be disposed on a depth plane corresponding to a different distance from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0098] In some embodiments, the light of each primary color may be output by a single dedicated waveguide, and as a result, each depth plane may have a plurality of waveguides associated therewith. In such embodiments, each box in the figure, including those containing the letters G, R, or B, may be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images being provided for each depth plane. The waveguides associated with each depth plane are shown adjacent to each other in this figure for ease of explanation, but it should be understood that in a physical device, all of the waveguides may be arranged in a stack with one waveguide per level. In some other embodiments, a plurality of primary colors may be output by the same waveguide, e.g., such that only a single waveguide is provided for each depth plane.

[0099] Continuing to refer to FIG. 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may also be used in addition to or in place of one or more of red, green, or blue.

[0100] It is to be understood that references throughout this disclosure to the color of a given light include light of one or more wavelengths within the range of wavelengths of the light as perceived by a viewer as that given color. For example, red light may include light of one or more wavelengths within the range of about 620 - 780 nm, green light may include light of one or more wavelengths within the range of about 492 - 577 nm, and blue light may include light of one or more wavelengths within the range of about 435 - 493 nm.

[0101] In some embodiments, the light source 530 (FIG. 6) may be configured to emit light of one or more wavelengths outside the visual perception range of the viewer, such as infrared and / or ultraviolet wavelengths. Additionally, the internal coupling, external coupling, and other light redirection structures of the waveguide of the display 250 may be configured to direct and emit this light from the display towards the user's eye 210, for example, for imaging and / or user stimulation applications. In some embodiments, the internal coupling optical elements and / or other light redirection structures comprise reflective diffraction optical elements comprising a reflective layer that includes a metal deposited by a wet chemical action as described herein. In some embodiments, the reflective layer may be formed from a metal that consists essentially of, or consists of, a pure or substantially pure metal formed by a wet chemical action as described herein.

[0102] Referring now to FIG. 9A, in some embodiments, light impinging on the waveguide may need to be redirected to internally couple the light into the waveguide. An internal coupling optical element may be used to redirect and internally couple the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a stack 660 of multiple or a set of waveguides, each including an internal coupling optical element. Each waveguide may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 (FIG. 6), and the illustrated waveguides of stack 660 may correspond to a portion of the plurality of waveguides 270, 280, 290, 300, 310, but it should be understood that light from one or more of the image input devices 360, 370, 380, 390, 400 is input into the waveguide from a position where the light is required to be redirected for internal coupling.

[0103] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the optical input area on the waveguide). For example, internal coupling optical element 700 is disposed on the major surface (e.g., the upper major surface) of waveguide 670, internal coupling optical element 710 is disposed on the major surface (e.g., the upper major surface) of waveguide 680, and internal coupling optical element 720 is disposed on the major surface (e.g., the upper major surface) of waveguide 690. In some embodiments, one or more of the internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of the individual waveguides 670, 680, 690 (in particular, one or more of the internal coupling optical elements are reflective deflecting optical elements). As illustrated, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface of their respective waveguides 670, 680, 690 (or the upper portion of the next lower waveguide), and in particular, those internal coupling optical elements are transmissive deflecting optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the individual waveguides 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may, in some embodiments, be disposed within other areas of their respective waveguides 670, 680, 690. In some embodiments, the internal coupling optical elements and / or other light redirecting structures include a reflective layer comprising a metal formed by a wet chemical action as described herein, a reflective diffractive optical element, or a reflective diffraction optical element. In some embodiments, the reflective layer may consist essentially of, or consist of, a pure or substantially pure metal formed by a wet chemical action as described herein.

[0104] As shown, the internal coupling optical elements 700, 710, 720 may be laterally offset from each other. In some embodiments, each internal coupling optical element may be offset such that its light is received without passing through another internal coupling optical element. For example, each internal 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 other internal coupling optical elements 700, 710, 720 such that it substantially does not receive light from other internal coupling optical elements 700, 710, 720.

[0105] Each waveguide also includes an associated light dispersing element. For example, the light dispersing element 730 is disposed on a major surface (e.g., the upper major surface) of the waveguide 670, the light dispersing element 740 is disposed on a major surface (e.g., the upper major surface) of the waveguide 680, and the light dispersing element 750 is disposed on a major surface (e.g., the upper major surface) of the waveguide 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on the bottom major surface of the associated waveguides 670, 680, 690. In some other embodiments, the light dispersing elements 730, 740, 750 may each be disposed on both the upper and bottom major surfaces of the associated waveguides 670, 680, 690, or the light dispersing elements 730, 740, 750 may each be disposed on different ones of the upper and bottom major surfaces within different associated waveguides 670, 680, 690.

[0106] Waveguides 670, 680, 690 may be separated and isolated, for example, by a gas, liquid, and / or solid layer of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate 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 waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more above, or 0.10 or less below, the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) of light (e.g., TIR between the top and bottom major surfaces of each waveguide) through waveguides 670, 680, 690. In some embodiments, layers 760a, 760b are formed from air. It should be understood that although not shown, the top and bottom of the illustrated set 660 of waveguides may include an immediate cladding layer.

[0107] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or identical, and the materials forming layers 760a, 760b are similar or identical. In some embodiments, the materials forming waveguides 670, 680, 690 may differ between one or more waveguides, and / or the materials forming layers 760a, 760b may still differ while maintaining the various refractive index relationships described above.

[0108] Continuing to refer to FIG. 9A, light rays 770, 780, 790 are incident on the set 660 of waveguides. It should be understood that light rays 770, 780, 790 may be input into waveguides 670, 680, 690 by one or more image input devices 360, 370, 380, 390, 400 (FIG. 6).

[0109] In some embodiments, the light rays 770, 780, 790 may have different properties, such as different wavelengths or different wavelength ranges, corresponding to different colors. The internal coupling optical elements 700, 710, 720 each deflect the incident light so that light propagates through an individual one of the waveguides 670, 680, 690 by TIR. In some embodiments, the internal coupling optical elements 700, 710, 720 each selectively deflect one or more specific wavelengths of light while transmitting other wavelengths to the underlying waveguide and the associated internal coupling optical element.

[0110] For example, the internal coupling optical element 700 may be configured to deflect the light ray 770 having the first wavelength or wavelength range while transmitting the light rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively. The transmitted light ray 780 impinges on the internal coupling optical element 710 configured to selectively deflect the light of the second wavelength or wavelength range, and is thereby deflected. The light ray 790 is deflected by the internal coupling optical element 720 configured to selectively deflect the light of the third wavelength or wavelength range.

[0111] Continuing to refer to FIG. 9A, the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the internal coupling optical elements 700, 710, 720 of each waveguide deflect the light into its corresponding waveguide 670, 680, 690 and internally couple 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 individual waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the individual waveguides 670, 680, 690 by TIR until they impinge on the corresponding light dispersion elements 730, 740, 750 of the waveguide.

[0112] Referring now to FIG. 9B, a perspective view of an embodiment of the plurality of stacked waveguides of FIG. 9A is illustrated. As described above, the internally coupled light rays 770, 780, 790 are each deflected by the internally coupled optical elements 700, 710, 720 and then each propagate by TIR within waveguides 670, 680, 690. The light rays 770, 780, 790 then each impinge on the light dispersing elements 730, 740, 750. The light dispersing elements 730, 740, 750 each deflect the light rays 770, 780, 790 so as to propagate towards the externally coupled optical elements 800, 810, 820.

[0113] In some embodiments, the light dispersing elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light to the external coupling optical elements 800, 810, 820, and in some embodiments, also increase the beam or spot size of the present light as it propagates to the external coupling optical elements. In some embodiments, the light dispersing elements 730, 740, 750 may be omitted, and the internal coupling optical elements 700, 710, 720 may be configured to deflect light directly to the external coupling optical elements 800, 810, 820. For example, referring to FIG. 9A, the light dispersing elements 730, 740, 750 may each be replaced with the external coupling optical elements 800, 810, 820. In some embodiments, the external coupling 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 the OPE may be configured to increase the size of the eyebox in at least one axis, and the EPE may increase the eyebox in an axis that intersects, for example, is orthogonal to, the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light impinging on the OPE to the EPE of the same waveguide while allowing the remaining portion of the light to continue to propagate along the waveguide. In response to a collision with the OPE, again, another portion of the remaining light is redirected to the EPE, and the remaining portion of that portion continues to propagate further along the waveguide or the like. Similarly, in response to a collision with the EPE, a portion of the colliding light is directed from the waveguide towards the user, and the remaining portion of that light continues to propagate through the waveguide until it impinges again on the EP, at which point another portion of the colliding light is directed from the waveguide, etc. As a result, a single beam of internally coupled light is "replicated" each time a portion of that light is redirected by the OPE or EPE, thereby forming a beam field of cloned light as shown in FIG. 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0114] Thus, referring to FIGS. 9A and 9B, in some embodiments, the waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, internal coupling optical elements 700, 710, 720, light dispersion elements (e.g., OPE) 730, 740, 750, and external coupling optical elements (e.g., EP) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with a gap / cladding layer between each one. The internal coupling optical elements 700, 710, 720 redirect or deflect the incident light into their respective waveguides (using different internal coupling optical elements for receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the illustrated example, the light ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, then bounces along the waveguide and interacts with the light dispersion element (e.g., OPE) 730, then the external coupling optical element (e.g., EP) 800. The light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, and the light ray 780 impinges on the internal coupling optical element 710 and is thereby deflected. The light ray 780 then bounces along the waveguide 680 via TIR and will proceed to its light dispersion element (e.g., OPE) 740, then the external coupling optical element (e.g., EP) 810. Finally, the light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the internal coupling optical element 720 of the waveguide 690. The internal coupling optical element 720 deflects the light ray 790 such that the light ray propagates by TIR to the light dispersion element (e.g., OPE) 750, then by TIR to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the light ray 790 to the viewer, who also receives the externally coupled light from the other waveguides 670, 680.

[0115] FIG. 9C illustrates a top and bottom plan view of an embodiment of the plurality of stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned with their associated optical dispersion elements 730, 740, 750 and associated external coupling optical elements 800, 810, 820. However, as discussed herein, the internal coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced as seen in the top and bottom views). As further discussed herein, this non-overlapping spatial arrangement facilitates the injection of light from different resources into different waveguides on a one-to-one basis, thereby enabling a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, an array comprising non-overlapping spatially separated internal coupling optical elements may be referred to as a pupil-offset system, and the internal coupling optical elements within these arrays may correspond to sub-pupils.

[0116] FIG. 9D illustrates an embodiment of a wearable display system 60 in which various waveguides and related systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which schematically shows some parts of that system 60 in more detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0117] Continuing to refer to FIG. 9D, the display system 60 includes a display 70 and various mechanical and electronic modules and systems for supporting the functions 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 is configured to position the display 70 in front of the user's 90 eyes. The display 70 may be considered an eyepiece in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user's 90 outer ear canal (in some embodiments, another speaker, not shown, may also be optionally positioned adjacent to the user's other outer ear canal to provide stereo / formable sound control). The display system 60 may also include one or more microphones 110 or other devices that may detect sound. In some embodiments, the microphone is configured to enable the user to provide an input or command to the system 60 (e.g., selection of a voice menu command, natural language question, etc.) and / or enable audio communication with other persons (e.g., other users of a similar display system). The microphone may further be configured as a peripheral sensor to collect audio data (e.g., sound from the user and / or the environment). In some embodiments, the display system may also include a peripheral sensor 120a, which is separate from the frame 80 and may be attached on the user's 90 body (e.g., the user's 90 head, torso, limbs, etc.). The peripheral sensor 120a may be configured to obtain data characterizing the physiological state of the user 90 in some embodiments. For example, the sensor 120a may be an electrode.

[0118] Continuing to refer to FIG. 9D, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as a wired conductor 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 removably attached to the user 90 in another manner (e.g., in a backpack configuration, in a belt attachment configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, such as a wired conductor or wireless connectivity. The local processing and data module 140 may include digital memory, such as a hardware processor and non-volatile memory (e.g., flash memory or hard disk drive), both of which may be utilized to assist in the processing, caching, and storage of data. Optionally, the local processor and data module 140 may include one or more processing units (CPUs), a graphics processing unit (GPU), dedicated processing hardware, etc. The data includes a) data captured from sensors (image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., operably coupled to the frame 80 or otherwise attachable to the user 90)) and / or b) data obtained and / or processed using the remote processing module 150 and / or the remote data repository 160 (including data related to virtual content) potentially for passage to the display 70 after processing or retrieval. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via a wired or wireless communication link, such that these remote modules 150, 160 are operably 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 attached to the frame 80 or may be an independent structure that communicates with the local processing and data module 140 via a wired or wireless communication path.

[0119] Continuing to refer to FIG. 9D, in some embodiments, the remote processing module 150 may include one or more processors configured to analyze and process data and / or image information, including, for example, one or more central processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. In some embodiments, the remote data repository 160 may include a digital data storage facility that may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, the remote data repository 160 may include one or more remote servers that provide information, such as information for generating augmented reality content, to the local processing and data module 140 and / or the remote processing module 150. In some embodiments, all data is stored and all calculations are performed within the local processing and data module, enabling fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, a system of one or more computers) including a CPU, GPU, etc. may perform at least a portion of the processing (e.g., generating image information, processing data) and provide information to and receive information from modules 140, 150, 160, for example, via a wireless or wired connection.

[0120] Exemplary Optical Projector System and Related Structures FIG. 10 illustrates an example of a cross-sectional view of a light projector system 2000 and an eyepiece 2010 for directing light towards a viewer's eye 210. As discussed herein, a plurality of light emitters 2020 (e.g., a plurality of LEDs) may be used to illuminate a spatial light modulator (SLM) 2030. The light emitter 2020 may be part of a light module 2040. In some embodiments, a beam splitter (e.g., a polarizing beam splitter (PBS)) 2050 may be used to reflect light from the light emitter 2020 to the spatial light modulator 2030 that reflects and modulates the light. The light modulated from the SLM 2030 may then propagate through the beam splitter 2050 to the eyepiece 2010, which may include one or more waveguides. In some embodiments, the eyepiece 2010 may correspond to a waveguide stack 260 (FIG. 6) or 660 (FIGS. 9A-9C). The waveguides of the eyepiece 2010 relay or guide the light and output it to the viewer's eye 210. Additionally, it should be understood that the light projector system 2000 may correspond to the light projector system 520 (FIG. 6). As shown, the light propagating through the projection optics may converge onto the area of the eyepiece 2010. Also, as shown, due to this convergence, the light also enters the convergence area at different angles.

[0121] The light module 2040 may include a plurality of light emitters 2020 that emit light in different wavelength ranges corresponding to different colors. Different sets of the plurality of light emitters 2020 (e.g., light emitters 2020a, 2020b, 2020c) may emit light in different wavelength ranges, and a set of light emitters may include one or more light emitters 2020. In some embodiments, the total number of sets of light emitters 2020 may correspond to the total number of primary colors used by the display system and may form a full-color image.

[0122] In some embodiments, the perception of a full-color image by a viewer may be achieved using time-division multiplexing. For example, different light emitters 2020 may be activated at different times to generate different primary color images. In such embodiments, the primary color images that form a single full-color image may be displayed quickly enough so that the human visual system does not perceive the primary color images as being displayed at different times. For example, the rate at which the primary color images are sequentially displayed may be higher than the persistence of perception of the human visual system. In some embodiments, different primary color images are sequentially displayed at a rate higher than 60 Hz. It should be understood that time-division multiplexing may advantageously reduce the computational load on a processor (e.g., a graphics processor) utilized to form the displayed image. In some embodiments where sufficient computational power is available, all the primary color images that form a full-color image may be displayed simultaneously.

[0123] Continuing to refer to FIG. 10, different color light emitters 2020 (e.g., red, green, and blue LEDs) may be located at different locations, illuminate the SLM 2030, and then be used to be imaged onto the eyepiece lens 2010 through the beam splitter 2050. In some embodiments, the SLM 2030 may be based on microelectromechanical technology (MEMS) or liquid crystal technology or other switching technologies. In some embodiments, the optical system of the optical projector system 2000 approximately images the individual light sources into the eyepiece lens 2010, so the images of the light emitters are spatially distinct on the eyepiece lens 2010.

[0124] As disclosed herein, the eyepiece 2010 may include a plurality of waveguides for each of a plurality of colors. In some embodiments, the individual waveguides may internally couple desired light from a corresponding light emitter using diffractive optics (e.g., a diffraction grating) and relay it to the eye. Additionally, the diffractive optics may direct light through the waveguide and may also couple light out of the waveguide. The waveguide may have a refractive power that causes the light to appear to originate from a given depth or distance from the viewer when relayed to the eye (see, for example, FIGS. 6-9C and related discussion).

[0125] Exemplary internally-coupling optical element As described above, after being internally coupled by the internally-coupling optical element, the light may undergo re-bounces, which can undesirably cause light loss, for example, due to unwanted external coupling or absorption of the light in the internally-coupling optical element. The light loss due to re-bounces of the internally-coupled light can effectively reduce the net efficiency of the internally-coupling optical element.

[0126] Figures 11A and 11B illustrate examples of light internally coupled into waveguide 1110 at different angles of incidence in an outer portion of internal coupling optical element 1100 (arranged away from the propagation direction of the internally coupled light). As described above, the different angles of incidence can be due to the focusing of light from the light projection system onto waveguide 1110. FIG. 11A depicts the path of incident beam 11201 incident on internal coupling optical element 1100 at a generally inward angle (e.g., an angle toward propagation direction 1112 within the waveguide, also referred to as the "cheek" angle). FIG. 11B depicts the path of incident beam 11202 incident on the waveguide at a generally outward angle (e.g., an angle away from propagation direction 1112 within the waveguide, also referred to as the "nose" angle). During operation, the beam of light incident on waveguide 1110 from the projection optics can be a converted or divergent beam that includes a component with an inward angle and a component with an outward angle. That is, the beam can converge toward a focus and then diverge. For example, the beam can diverge when waveguide 1110 is placed beyond the focal length of the projection optics, as will be described in more detail with reference to FIGS. 13A - 13C.

[0127] Each of FIGS. 11A and 11B includes waveguide 1110 having a first major surface, a second major surface opposite the first major surface, and internal coupling optical element 1100 disposed on the second major surface, where internal coupling optical element 1100 is a reflective optical element. Each beam 11201, 11202 enters waveguide 1110 through the first major surface, and internal coupling optical element 1100 causes the internally coupled light to propagate within waveguide 1100 at an angle that aids total internal reflection (TIR) and is generally redirected by TIR to travel along propagation direction 1112. The internally coupled light is described herein as propagating "along" the propagation direction, and its general aggregate propagation direction is parallel to the propagation direction. It should be understood that this propagation direction can involve multiple bounces of the light from the major surface of waveguide 1110. That is, the propagation direction is the net propagation direction of the light across those multiple bounces of the light.

[0128] A second bounce can occur when light is internally coupled at the second major surface of waveguide 1110, internally reflected from the first major surface, and incident on or undergoes a second bounce at internal coupling optical element 1100. As shown in FIG. 11A, a beam 11201 incident on internal coupling optical element 1100 at an inward angle typically experiences little or no second bounce because the inward angle can result in a relatively large bounce spacing 11271, i.e., the distance between any two consecutive reflections at the second major surface. In contrast, as shown in FIG. 11B, a beam 11202 incident on internal coupling optical element 1100 at an outward angle has a relatively smaller bounce spacing 11272 and thus may be more likely to undergo a second bounce.

[0129] Although not limited by theory, it should be understood that diffractive optical elements can behave symmetrically. That is, they can redirect incident light such that the incident light propagates at the TIR angle through the waveguide. However, light incident on the diffractive optical element at the TIR angle (such as in response to a second bounce) can also be externally coupled. Additionally, or alternatively, reflection of light from a layer of material such as metal can also involve partial absorption of the incident light because the reflection can involve absorption and emission of light from the material. As a result, external coupling and / or absorption of light can undesirably result in loss of internally coupled light, and light that has undergone a second bounce can experience significant loss compared to light that interacts with the internal coupling optical element only once.

[0130] Figures 12A and 12B further illustrate this optical loss. FIG. 12B illustrates an example of the energy profile of a beam internally coupled within waveguide 1110 of FIG. 12A at location 1115 along waveguide 1110. Beam 11201, which is incident at an inward or cheek angle, experiences a relatively low amount of substantial bounce and thus results in a relatively high efficiency of internal coupling and a substantially uniform beam profile. In contrast, beam 11202, which is incident at an outward or nose angle, is likely to experience a substantial amount of bounce, resulting in optical loss within the waveguide after initial internal coupling. In addition, as shown in FIG. 12B, the inner or propagation side portion of the outward angle beam 11202 (e.g., the portion of beam 11202 closer to propagation direction 1112) is unlikely to experience much bounce, while the outer portion of beam 11202 away from propagation direction 1112 experiences more bounce, further resulting in optical loss and producing a non-uniform net internal coupling efficiency across the beam profile. When the internally coupled light is used to form an image or a portion of an image, the optical loss due to bounce can thus irregularly reduce the brightness in some portions of the image formed using that light. Further, if the display system includes individual waveguides and internal coupling gratings for red, green, and blue light, such reduced efficiency and / or non-uniformity within any of the waveguides can result in reduced color accuracy, including a reduction in the ability to reliably produce white light or other colors that require a combination of red, green, and / or blue light.

[0131] The occurrence of re-bounces may also depend, at least in part, on the distance between the waveguide and the incident light source. FIGS. 13A-13C depict an embodiment of a waveguide stack 1105 that illustrates the distribution rate of re-bounces within a waveguide disposed beyond the focal length of the corresponding projection optical system. As shown in FIG. 13A, the waveguide stack 1105 includes waveguides 1110a, 1110b, and 1110c disposed at a distance from the projection optical system 2000. Each of the waveguides 1110a, 1110b, 1110c includes internal coupling optical elements 1100a, 1100b, 1100c disposed along the major surfaces of the waveguides 1110a, 1110b, 1110c that are further from the projection optical system 2000. The internal coupling optical elements 1100a, 1100b, 1100c internally couple the light from the projection optical system 2000, which is externally coupled as externally coupled light 1130 within the wearer's field of view.

[0132] The projection optical system 2000 may output a converging beam. In FIG. 13A, the range of angles present within the converging beam is represented by an inwardly angled beam 11201, an outwardly angled beam 11202, and a central beam 11203. The waveguide 1110b is disposed at the focal length of the projection optical system 2000 corresponding to the distance from the projection optical system 2000 at which the beams 11201, 11202, 11203 converge at a focus. Beyond the focal length, the light from the projection optical system 2000 becomes a diverging beam. As shown in FIG. 13A, in various embodiments, one or more waveguides (e.g., waveguide 1110c) within the waveguide stack 1105 may be disposed beyond the focal length, while other waveguides within the waveguide stack 1105 may be disposed closer to the focal length (e.g., waveguide 1110b) or the projection optical system 2000 (e.g., waveguide 1110a).

[0133] Figures 13B and 13C are partial enlarged views of the system of Figure 13A, illustrating the propagation of light from the display optical system 2000 within waveguide 1110a (Figure 13C) and waveguide 1110c (Figure 13B). As shown in Figure 13C, the re-bounce can be of substantially no concern in waveguides positioned closer to the focal length from the projection optical system 2000. Since the light from the projection optical system 2000 is still a converging beam before reaching the focus, the beam 11202 component with an outward angle is incident on the inner portion of the internal coupling optical element 1100a (e.g., the propagation direction side portion of the internal coupling optical element 1100a), while the beam component 11201 with an inward angle is incident on the outer portion of the internal coupling optical element 1100a (e.g., the portion of the internal coupling optical element 1100a arranged opposite to the propagation direction 1112). Therefore, the relatively short bounce interval of the internally coupled beam 11202 with an outward angle is still long enough for the internally coupled light to propagate beyond the side surface of the internal coupling optical element 1100a along the propagation direction 1112 before its second incidence on the second major surface of the waveguide 1100a. In addition, the bounce interval of the internally coupled beam 11201 with an inward angle is long enough to avoid any re-bounce of the beam 11201 with an inward angle.

[0134] In contrast, as shown in FIG. 13B, the re-bounces can be significantly distributed within the waveguide 1110c disposed beyond the focal length of the projection optical system 2000. Since the light from the projection optical system 2000 is a diverging beam after passing through the focal point, the outwardly angled beam component 11202 is incident on the outer portion of the internal coupling optical element 1100c, while the inwardly angled beam component 11201 is incident on the inner portion of the internal coupling optical element 1100c. Thus, the internally coupled inwardly angled beam component 11201 still experiences little or no re-bounce, while the internally coupled outwardly angled beam component 11202 experiences one or more additional bounces 1135 along the length of the internal coupling optical element 1100c. Since energy can be lost at each subsequent bounce along the length of the internal coupling optical element 1100c, the internally coupled outwardly angled beam component 11202 experiences significant loss relative to the internally coupled inwardly angled beam component 11201, resulting in a lower efficiency and / or non-uniform beam profile as described above with reference to FIG. 12B. The light of the beam component 11201 is illustrated as not experiencing re-bounce for ease of explanation and illustration, but it should be understood that the beam component 11201 can experience re-bounce in some embodiments. However, the number of bounces of the beam component 11201 on the internal coupling optical element will be less than that for 11202. Since the light loss is proportional to the number of bounces, the beam component 11201 will experience less light loss than the beam component 11202

[0135] Figures 14A and 14B illustrate an example of the truncation of an internal coupling optical element for reducing light loss due to re-bounce within an exemplary waveguide. Figures 14A and 14B illustrate a single waveguide 1110c disposed beyond the focal length of the projection optical system 2000. The location of the focus is indicated by the internal coupling optical element 1100b, while waveguides 1110a and 1110b are omitted from Figures 14A and 14B for the sake of simplicity. The configuration of Figure 14A is substantially the same as the configuration of waveguide 1110c and internal coupling optical element 1100c in Figure 13A. Figure 14B illustrates waveguide 1110c with a truncated internal coupling optical element 1100c.

[0136] Specifically, the truncated internal coupling optical element 1100c of FIG. 14B is sized, shaped, and positioned such that at least the inner portion 11221 of the light from the projection optical system 2000 is incident on the waveguide 1110c but not on the internal coupling optical element 1100c. In some embodiments, the beam of light from the projection optical system 2000 (e.g., as represented by the combination of component beams 11201, 11202, and 11203) may define a light beam area on the second major surface of the waveguide 1110c, and the diffraction region of the internal coupling optical element 1100c may occupy less than all of the light beam area. Generally, the truncated internal coupling optical element 1100c depicted in FIG. 14B is asymmetric about a beam axis extending through the center of the central beam component 11203 of the light from the projection optical system 2000. For example, the truncated internal coupling optical element 1100c may be radially asymmetric and / or reflection asymmetric about a symmetry axis perpendicular to the propagation direction 1112 at the beam axis. In some embodiments, the internal coupling optical element 1100c may terminate at a location such that the inner portion 11221 of the inwardly angled beam component 11201 passes through the second major surface of the waveguide 1110c without being internally coupled. In some other embodiments, such as embodiments with an internal coupling grating with a metallized surface of the internal coupling optical element 1100c, the inner portion of the internal coupling optical element 1100c may not be metallized such that the re-bounce of the internally coupled light in the inner portion is not as readily absorbed or externally coupled as would be the case if the inner portion were metallized. Thus, by using the truncated internal coupling optical element of 1100c, at least a portion of the inwardly angled beam component 11201 may not be internally coupled or may be internally coupled with a lower efficiency relative to the rest of the light from the projection optical system 2000. However, the truncation of the internal coupling optical element 1100c also reduces the length that can occur with respect to the outwardly angled beam component 11202 with internally coupled re-bounce along it.Thus, even though the truncated internally coupled optical element 1100c suffers some loss of light at certain angles of the internally coupled light (i.e., a portion of the light from some angles is not internally coupled, as shown in FIG. 14B), it can provide a net increase in internal coupling efficiency because the internally coupled light does not, or hardly, suffer re-bounce related external coupling or absorption. As a result, the amount and uniformity of the internally coupled light can be improved due to the reduction of re-bounce and associated light losses.

[0137] FIG. 15 illustrates top and bottom views of an exemplary arrangement of internally coupled optical elements within a waveguide stack. The configuration of FIG. 15 is viewed in a direction along the central beam 11203 of FIG. 13A perpendicular to the major surface of the waveguide, and each internally coupled optical element B1, B2, G1, G2, R1, and R2 is configured to internally couple incident light and propagate it within its respective waveguide (not shown) along the propagation direction 1112. Thus, each internally coupled optical element B1, B2, G1, G2, R1, and R2 has a distinct associated waveguide. The internally coupled optical elements B1, B2, G1, and G2 may be disposed on waveguides that are located at or closer to the focal length of the projection optical system, while the internally coupled optical elements R1 and R2 are disposed on waveguides that are located beyond the focal length of the projection optical system. Thus, the internally coupled optical elements R1 and R2 are truncated to reduce re-bounce as described above. In some embodiments, the truncated regions 1140 of the internally coupled optical elements R1 and R2 may include open spaces that allow the light incident thereon to pass through the corresponding waveguides without being internally coupled. In other embodiments, the optical elements R1 and R2 may include highly efficient internal coupling regions 1145 (e.g., portions coated with a reflective layer such as a metallization or metal layer), while the truncated regions 1140 are not metallized to reduce losses resulting from re-bounce occurring within the truncated regions 1140.

[0138] Continuing to refer to FIG. 15, as described herein, the internal coupling optical elements B1, B2, G1, G2, R1, and R2 are each disposed on different associated waveguides. In some embodiments, the light from the projection optical system can impinge on these optical elements from above, for example, normal to the page. Preferably, the optical elements are positioned such that they do not block the propagation of light from the projection optical system to each individual optical element. For example, the optical elements are arranged such that the optical elements for the waveguides in front of the focus of the projection optical system are laterally spaced apart as seen in the top and bottom views (from the perspective of the projection optical system). Such an arrangement prevents the converging beam of light from being blocked. The optical elements of the waveguides behind the focus will receive the diverging beam of light. As a result, there may be some slight overlap with the optical elements in front of these waveguides because the diverging beam of light expands after passing through the front optical elements and thus cannot be blocked by some overlap with those in front of the optical elements.

[0139] In addition, it should be understood that external coupling of light due to light leakage out of the waveguide and / or re - bounce can result in the leaked or externally coupled light colliding with other internal coupling optical elements. For example, it is possible that the re - bounced light externally coupled from the optical element G1 can collide with an optical element that is "downstream" of the optical element G1 in the propagation direction 1112. For example, the light leaked or externally coupled from the optical element G1 can collide with R1 and B1. It should be understood that crosstalk and image degradation can occur if R1 or B1 internally couples the light externally coupled from G1. Advantageously, the optical grating may be configured to be selective with respect to the wavelength of the light they internally couple such that R1 and B1 do not internally couple the incident light externally coupled from G1. However, if G2 is downstream of G1, it can internally couple such light. As a result, preferably, the internal coupling optical elements are arranged such that the optical elements for internally coupling light of a particular wavelength are not downstream of the optical elements configured to internally couple light of a similar wavelength.

[0140] In some embodiments, the truncation may be, for example, up to 5%, 10%, 15%, 20%, 25%, 30%, 35%, or more of the full width of the internal coupling optical element. In some embodiments, the nominal (non-truncated) dimensions of the internal coupling optical element may be regular or substantially regular (e.g., the width of the internal coupling optical element parallel to the propagation direction in the waveguide may be within the range of 85%, 90%, 95%, 100%, 105%, etc. of the length of the internal coupling optical element perpendicular to the propagation direction). Thus, a truncated internal coupling optical element as described herein may have a width that is less than 55%, 60%, 65%, 70%, 75%, 80%, etc. of the length of the internal coupling optical element, the width extends parallel to the propagation direction, and the length is perpendicular to the propagation direction. In one non-limiting exemplary embodiment, an internal coupling optical element having a length of 1.71 mm and a nominal (non-truncated) width of 1.56 mm may have its width truncated by a distance within the range of 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or more. In another non-limiting exemplary embodiment, an internal coupling optical element having a length of 1.83 mm and a nominal (non-truncated) width of 1.63 mm may have its width truncated by a distance within the range of 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, or more. In each of the examples described above, the truncated portion may constitute part of the internal coupling optical element that is entirely removed, or is not a diffractive region, or is a less efficient diffractive region relative to the non-truncated portion. For example, the internal coupling optical element may comprise a reflective diffraction grating of full nominal dimensions, and the metal coating covers only the smaller truncated dimensions of the element while the truncated portion remains unmetallized. That is, less than the entire area of the diffraction grating may be metallized in some embodiments.

[0141] Figures 16 and 17 depict the experimental results of the truncation of the internal coupling optical element in a configuration similar to that of FIG. 15, and illustrate the improved effective internal coupling efficiency resulting from the truncation of the internal coupling optical element. As explained above, the truncation of the inner portion of the internal coupling optical element beyond the focal length of the projection optical system can result in a net improvement in the internal coupling efficiency because the increase in efficiency due to the reduced optical loss caused by the re-bounce exceeds the loss in efficiency caused by not internally coupling (or internally coupling with a lower efficiency) the innermost portion of the light from the projection optical system. Therefore, the amount of truncation may be selected to provide a desirable balance between the reduction in optical loss due to the re-bounce and the loss of the initial internal coupling due to the truncation.

[0142] The foregoing description and FIGS. 11A-14B generally refer to internal coupling of light using reflective diffractive optical elements, but it should be understood that the systems and methods described for reducing optical loss due to rebounce can equally be implemented within systems with transmissive diffractive optical elements. As shown in FIGS. 18A and 18B, rebounce can similarly occur when light is internally coupled by a transmissive diffractive optical element 1100c' disposed on the first major surface of waveguide 1110c. As shown in FIG. 18B, an outwardly angled beam 11202 redirected into waveguide 1110c by transmissive diffractive optical element 1100c' at the first major surface of waveguide 1110c can be reflected by the second major surface and return to impinge on transmissive optical element 1100c' at one or more subsequent rebounces 1135'. Transmissive diffractive optical element 1110c' does not have a reflective layer and cannot suffer absorption losses caused by absorption by such a reflective layer, but transmissive diffractive optical element 1110c' can have external coupling losses. Thus, optical loss due to rebounce can be reduced in the systems of FIGS. 18A and 18B by apodizing transmissive diffractive optical element 1100c' using any of the techniques disclosed herein, except for techniques using a reflective coating. For example, apodization may involve providing a high diffraction efficiency region having an apodization that has dimensions and relative widths and length ratios as discussed herein and / or that varies with the distance from the focus of the waveguide from projection optical system 2000 as also discussed herein. In some embodiments, FIG. 15 can be understood to show a top and bottom view of an apodized transmissive diffractive optical element, which can be understood to include optical elements R1 and R2.

[0143] Exemplary Waveguides and Optical Elements with Reflective Layers Reflective optical elements may utilize a reflective layer to achieve the desired light reflection. The reflective layer may conventionally be deposited using a metallization process that includes the deposition of a metal layer. These conventional metallization processes can be time-consuming and can include a number of steps. For example, in order to direct the metallization to a desired location on a waveguide, it may be necessary to align and mask the waveguide to protect the areas of the waveguide where metallization is not desired. However, the mask can be contaminated by the metallization and may require frequent cleaning. In addition, the deposition itself may require a vacuum, which will further complicate the metallization process and increase its duration by requiring that the deposition chamber be evacuated for deposition and then returned to atmospheric pressure for load-unload.

[0144] As an alternative to vapor-based metallization processes, metal-containing flowable materials such as reflective inks have been proposed for forming the reflective layer. It has been found that some layers formed from reflective inks can have a lower reflectivity than desired for some applications and can have a non-uniform reflectivity across different wavelengths. For example, some metal inks (such as silver ink) can contain organic or inorganic impurities, such as metal complexes and binders, that can inhibit the reflectivity. These impurities can reduce the optical reflectivity, particularly for light of shorter wavelengths, such as light with wavelengths in the blue region. In addition, some reflective inks have been found to form layers with non-uniform thicknesses or pinholes, which can further adversely affect the reflection of light from these layers. Reflective diffractive optical elements formed using some metal inks have been found to have a worse diffraction efficiency than similar diffractive elements formed using reflective layers formed by physical vapor deposition (PVD). Without being limited by theory, this poor diffraction efficiency is thought to be due to the poor reflective properties caused by one or more of the above factors.

[0145] Advantageously, according to some embodiments, a reflective layer and a structure incorporating such a reflective layer (e.g., a reflective diffractive optical element) provide superior reflective properties. Some embodiments include optical devices and display devices having a reflective layer, and methods of making an optical waveguide structure comprising a reflective layer and methods of making an optical device. In some embodiments, the reflective layer may be formed on a substrate surface using wet chemical action. Wet chemical action may include a liquid phase reaction for depositing a layer of a reflective material from precursor species in a flowable material such as a liquid mixture onto the substrate surface. In some embodiments, the deposition may leave a solid reflective coating on the substrate surface and the liquid mixture may cover the solid reflective coating. In some embodiments, the residual liquid mixture may be removed, for example, by rinsing.

[0146] In some embodiments, wet chemical action may include the precipitation of a metal from a liquid mixture. For example, the metal may be part of a metal complex and the precipitation may result from the dissociation of the metal from the complex in the liquid mixture. The metal complex may be an ionic complex such as a metal salt. The ionic complex may dissociate after a chemical reaction with another reagent that is present in the liquid mixture or otherwise provided for contact with the ionic complex. As an example, the chemical reaction may be a metal ion reduction, e.g., a silver ion reduction, which results in the deposition of pure or substantially pure metal (e.g., silver) onto the surface of the waveguide. In some embodiments, the metal precipitation may form a reflective layer on a predetermined discrete region of the surface but not over the entire surface. Preferably, the precipitation coats the discrete region on the surface of the waveguide. The discrete region of the surface may comprise protrusions and the reflective layer may conformally deposit on the protrusions to form, for example, a diffractive optical element.

[0147] In some embodiments, the liquid mixture comprises a metal salt (e.g., a silver salt) and a reducing agent that is reactive with the salt, for example, at basic pH. In the reaction, the reducing agent reduces the metal salt, precipitates a metal (e.g., silver), deposits it on the substrate surface, and forms a reflective layer on the surface of the substrate (e.g., on the surface of a waveguide). Thus, the reflective layer consists essentially of or consists of a pure metal or substantially pure metal (e.g., pure silver or substantially pure silver).

[0148] Advantageously, these reflective layers can exhibit better optical and physical properties. The reflective layer can have a high purity, as described herein. Additionally, the reflective layer can be uniform at the nanoscale resolution such that features such as pinholes, which can reduce the reflectivity, are absent or substantially absent. Also, unlike directed deposition such as PVD, the reflective layer can conformally coat the surface of the protrusion and provide reflectivity on all of these surfaces. Additionally, the reflective layer may be formed to a thickness that blocks light and prevents unwanted light leakage. Without being limited by theory, it is envisioned that these advantageous properties, alone or in combination, can provide a reflectivity to the reflective layer that exceeds that of layers deposited by other methods such as the use of PVD or reflective inks. For example, as described herein, some inks exhibit a lower reflectivity than the reflective metal layers formed by ion reduction. Generally, in addition to being lower, the reflectivity of layers formed using metal inks is even lower for shorter wavelength light (blue light) within the visible light range.

[0149] Furthermore, in some embodiments, the metal of the reflective layer is stably bonded to the surface of the waveguide such that the reflective layer remains stably adhered to the surface of the waveguide, preferably without the need for an adhesive or binder. In some embodiments, excellent adhesion of the metal is achieved during deposition. That is, excellent adhesion is provided in response to coating the substrate with the metal without the need for post-coating treatments such as annealing. In some embodiments, the substrate surface is treated to promote adhesion of metal species onto the surface. As an example, the treatment may include exposing the substrate surface to plasma. Other example treatments include etching of the substrate surface and formation of an interfacial layer between the substrate and the metal to be deposited later.

[0150] In some embodiments, the reflective layer is formed over the protrusions, which are diffractive optical elements, for example, diffraction gratings. Both the reflective layer and the protrusions form a reflective diffractive optical element. In some embodiments, the reflective diffractive optical element is part of the waveguide. For example, the reflective diffractive optical element may be an internal coupling optical element configured to redirect incident ambient light at an angle such that light propagates through the waveguide by total internal reflection. In some embodiments, a reflective layer as disclosed herein can increase the optical performance of the reflective diffractive optical element by increasing the amount of light redirected (e.g., internally coupled) by the diffractive optical element.

[0151] As discussed herein, in some embodiments, the reflective layer may be confined to discrete locations, such as at or in a diffractive optical element or a portion of a diffractive optical element. In some embodiments, this confinement may be achieved using a physical structure (e.g., a wall or a weir) to confine the diffusion of a flowable material. In some other embodiments, the confinement may be achieved by treating a desired area of the substrate surface such that the metal within the reflective layer preferentially coats or remains within those desired areas (e.g., after rinsing). As yet another example, a liquid mixture may be applied to a desired area and have a composition such that they do not significantly diffuse away from their areas. It should be understood that one or more of these schemes for confining the liquid mixture may be utilized to form a particular reflective layer.

[0152] In some embodiments, as described herein, after coating the substrate with metal from a liquid mixture, the residual liquid mixture may be removed. This may be accomplished, for example, by rinsing the substrate with a liquid.

[0153] In some embodiments, a capping layer may be formed over the reflective layer, for example, to provide protection from chemical species present in the ambient environment.

[0154] Flowable material As discussed herein, flowable materials such as liquid mixtures may be utilized in various embodiments. The liquid mixture may include a metal salt. In some embodiments, the liquid mixture may also include a reducing agent. Examples of suitable metal salts include silver salts such as Ag(NH3)2. Suitable reducing agents include carbohydrates that include alpha-hydroxy aldehydes and / or alpha-hydroxy ketones. Examples of such carbohydrate reducing agents include glucose, fructose, or a combination of glucose and fructose.

[0155] In some embodiments, the metal salt and the reducing agent of the liquid mixture are reactants for the trans reaction. In some embodiments, the liquid mixture is in a solution such as an aqueous solution. The liquid mixture may have a short shelf life, and thus, in some embodiments, it is envisioned that the compositions constituting the liquid mixture can be prepared immediately before use or at the time of use. Some commercially available products may also provide suitable reactants for some embodiments, for example, metal solutions sold by Peacock Laboratories (West Chester, PA) and byTransene Co, Inc. (Danvers, MA).

[0156] In some embodiments, the liquid mixture may contain both the metal salt and the reducing agent, which are premixed before depositing the liquid mixture onto the substrate. In some other embodiments, the metal salt and the reducing agent may be applied separately to a predetermined region of the waveguide and mixed in situ on the predetermined region.

[0157] In some embodiments, the liquid mixture further contains one or more of a pH modifier, a stabilizer, a surfactant, a catalyst, and a viscosity adjusting component. In some embodiments, the liquid mixture contains chemical species selected from the group consisting of a metal salt, a reducing agent, a solvent (such as water), a base, a pH modifier, a stabilizer, a surfactant, a catalyst, and a viscosity adjusting component, and includes combinations of two or more of the listed items. It should be understood that the relative concentrations of the chemical species may be adjusted to improve the purity of the metal in the reflective layer, inhibit pinholes on the reflective layer, improve the reaction rate of the metal salt and the reducing agent, improve the stability of the chemical species, improve the stability of the coating, etc.

[0158] In some embodiments, the species react with each other at basic pH such that the reducing agent reduces the metal salt and deposits the metal. Thus, the liquid mixture may further contain a base. In some embodiments, the liquid mixture is at a basic pH, for example, above 7, or above or equal to 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, or 13.9, and is within a pH range between any two of the recited values, or a range between any of the recited values and 14, for example, 7-10, 7-12, 7-14, 8-10, 8-12, 8-14, 9-10, 9-12, 9-14, 10-12, 10-14, 11-12, 11-14, or 12-14. In some embodiments, the liquid mixture consists essentially of, or consists of, a metal salt, a reducing agent, and a base.

[0159] It should be understood that liquid mixtures of different levels of viscosity can provide different advantages. For example, relatively viscous liquid mixtures may be suitable for staying in the areas where they are deposited with little further diffusion. On the other hand, relatively thin liquid mixtures may be suitable for forming a relatively thin and uniform reflective layer and can flow more easily between closely spaced features, but may require physical barriers such as walls or dams to confine the liquid mixture to a predetermined area of the waveguide surface. In some embodiments, once the deposited liquid mixture reacts to form a reflective layer, one or more additional layers of the liquid mixture may be applied to sequentially form a reflective layer of the desired thickness as described herein.

[0160] Reflective layer According to some embodiments of the present specification, the reflective layer reflects at least one visible wavelength of the incident electromagnetic radiation (e.g., light within the visible spectrum). The reflective layer may be formed from a flowable material, such as a liquid mixture. The reflective layer preferably reflects at least about 30% of at least one visible wavelength of the incident electromagnetic radiation, e.g., at least about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, 99.5%, or 99.9% of the incident electromagnetic radiation, and ranges between any two of the recited values, e.g., about 30% - 99%, 30% - 95%, 30% - 90%, 30% - 80%, 30% - 70%, 50% - 99%, 50% - 95%, 50% - 90%, 50% - 80%, 50% - 70%, 70% - 99%, 70% - 95%, 70% - 90%, or 70% - 80% of the incident electromagnetic radiation. In some embodiments, the incident electromagnetic radiation includes light in the visible spectrum. It should be understood that the reactants themselves (e.g., metal salts) do not necessarily possess the indicated reflective properties prior to being reacted as described herein, but the reflective layer (e.g., metal layer) formed from the reactants has the indicated reflective properties.

[0161] It should be understood that the reflective layer can be structurally distinct from a reflective layer formed by vapor deposition or other means such as a metal-containing ink. For example, in some embodiments, the reflective layer comprises a pure or substantially pure metal. A "substantially pure" metal as used herein has its ordinary and customary meaning as would be understood by one of ordinary skill in the art in light of the present disclosure. This refers to a metal that contains a minor amount of other substances. When additional numerical specificities are of interest, a substantially pure metal can contain at least 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% pure metal (w / w), including ranges between any two of the recited values, such as 95% - 97%, 95% - 99%, 95% - 99.9%, 97% - 99%, 97% - 99.9%, 98% - 99%, and 98% - 99.9%. Thus, the reflective properties of a substantially pure metal are comparable to those of the elemental ("pure") metal. In some embodiments, a substantially pure metal has at least 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% of the reflectivity of the pure metal, including ranges between any two of the recited values.

[0162] In some embodiments, the reflective layer is disposed on a waveguide and configured, for example, as part of a light dispersing element, to redirect light propagating through the waveguide. In some embodiments, the reflective layer is disposed on a waveguide and configured, for example, as part of an internal coupling optical element, to direct incident ambient light into the waveguide. In some embodiments, the waveguide is part of a display device such as an augmented or virtual reality display device.

[0163] As used herein, "protrusion", "surface protrusion", and variations of these base terms refer to a mass of material that extends upwardly on or within a substrate, such as within an optical grating that extends from the surface of a waveguide. In some embodiments, the protrusion may comprise a material to be deposited (e.g., a photoresist deposited on a waveguide) or may be formed by etching a substrate that may be a substantially homogeneous structure (e.g., a waveguide). In some embodiments, the reflective layer 1010 is disposed across the optical grating 1020 (see, e.g., FIGS. 19A - 19C). In some embodiments, the reflective layer 1010 is disposed across the optical grating 1020 having a blazed configuration (see FIG. 19B). In some embodiments, the reflective layer 1010 is disposed across the optical grating 1020 having a multi - level configuration (see FIG. 19C). In some embodiments, the optical grating comprises a patterned photoresist.

[0164] It should be understood that the reflective layer is preferably utilized to provide reflection of light within and / or back through the waveguide. As a result, the reflective layer preferably coats all surfaces of the protrusion. In some embodiments, the reflective layer is conformally disposed on the optical grating. Note that when a material is disposed "conformally", it will substantially conform to the topology of the underlying surface. In some embodiments, the thickness of the reflective layer across the underlying surface (e.g., the linear thickness extending from the surface across the layer) varies by about ±20% or less across the reflective layer such that the thickness is within ±20%, ±15%, ±10%, ±5%, or ±1% of an average value. Preferably, the conformal reflective layer is disposed such that there is no or substantially no gap between the reflective layer and the surface of the substrate.

[0165] Also, in some embodiments, the non-conformal reflective layer is assumed to be able to provide a suitable reflectivity at the relevant interface (for example, without being limited by theory, as long as the surface of the reflective layer at the interface with the waveguide is sufficiently reflective and provides sufficient coverage, the opposing surface not facing the waveguide may not need to be conformal to the waveguide). Thus, in some embodiments, the reflective layer is non-conformally disposed on the surface.

[0166] Preferably, the non-conformal layer is disposed such that there is no or substantially no gap between the reflective layer and the surface of the substrate. The phrase "substantially no" gap between the reflective layer and the substrate has its ordinary and customary meaning as would be understood by one of ordinary skill in the art in light of the present disclosure. Some degree of gap may exist, but it has been confirmed that they do not significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and the substrate compared to a reflective layer with no gap. In some embodiments, the reflective layer is disposed in a state where there is substantially no gap when at least 90%, for example, at least 90%, 95%, 97%, 98%, 99%, or 99.9% of the surface area of the reflective layer at the interface with the waveguide surface is in direct contact with the waveguide surface. In some embodiments, the ink is deposited to a sufficient thickness to completely or substantially completely fill the open volume or gap between the waveguide protrusions.

[0167] It is to be understood that when a metal is deposited by conventional means, such as evaporation, or a metal-containing ink, the surface of the metal can be non-uniform, including nanoscale pinholes (see, for example, Example 1 and FIGS. 22A-F). A pinhole refers to a cavity, depression, or extension from the surface having a nanoscale diameter, for example, a diameter of less than about 1 mm, for example, in the range of about 1 nm to about 1000 nm. Without being limited by theory, it is assumed that pinholes inhibit the reflectivity of the reflective layer. Without being limited by theory, further, forming a reflective layer by metal ion reduction as described herein is advantageously assumed to minimize or avoid the formation of pinholes. In some embodiments, the reflective layer is pinhole-free or substantially pinhole-free. "Substantially pinhole-free" has its ordinary and customary meaning as would be understood by one of ordinary skill in the art in light of the present disclosure. Some degree of pinholes may be present, but they have been confirmed not to significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and the substrate as compared to a pinhole-free reflective layer. In some embodiments, the surface of the reflective layer in interface contact with the protrusion on the waveguide is pinhole-free or substantially pinhole-free. The surface of the reflective layer in interface contact with the protrusion on the waveguide may include pinholes at 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% or less of the surface, and ranges between any two of the recited values, such as 1-5%, 1-7%, 1-10%, 2-5%, 2-7%, 2-10%, 5-7%, and 5-10%. Note that a reflective layer that is "pinhole-free" will also be in a state where the pinholes are "substantially pinhole-free".

[0168] Advantageously, forming a reflective layer by metal ion reduction as described herein can avoid the presence of particles such as metal particles (other than the metal itself) within the reflective layer. Without being limited by theory, it is assumed that metal particles can, in part, scatter light, and thus the reflectivity of a particle-containing reflective layer can be lower than that of a particle-free layer. Accordingly, in some embodiments, the reflective layer is free or substantially free of metal particles. "Substantially free" of particles (such as metal particles) has its ordinary and customary meaning as would be understood by one of ordinary skill in the art in light of the present disclosure. Particles such as metal particles (other than the metal itself) may be present in trace amounts, but it has been confirmed that they do not significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and the substrate as compared to a reflective layer that is free of such metal particles (other than the metal itself). In some embodiments, a surface that is substantially free of particles (such as metal particles other than the metal itself) in some embodiments may contain metal particles (w / w) in excess of 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or 0.01%, including ranges between any two of the recited values, for example, 0.1-1%, 0.1-2%, 0.1-5%, 1-2%, 1-5%, 2-5%, or 3-5%.

[0169] In some embodiments, a reflective layer of a desired thickness is formed. In some embodiments, the reflective layer has a thickness of at least about 10 nm, such as at least about 10 nm, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nm, and includes a thickness in the range between any two of the recited values, such as about 10 nm to 900 nm, 10 nm to 500 nm, 10 nm to 410 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, 10 nm to 150, 10 nm to 100 nm, 10 nm to 50 nm, 30 nm to 900 nm, 30 nm to 500 nm, 30 nm to 450 nm, 30 nm to 400 nm, 30 nm to 350 nm, 30 nm to 300 nm, 30 nm to 250 nm, 30 nm to 200 nm, 30 nm to 150, 30 nm to 100 nm, 30 nm to 50 nm, 50 nm to 900 nm, 50 nm to 500 nm, 50 nm to 450 nm, 50 nm to 400 nm, 50 nm to 350 nm, 50 nm to 300 nm, 50 nm to 250 nm, 50 nm to 200 nm, 50 nm to 150, 50 nm to 100 nm, 80 nm to 900 nm, 80 nm to 500 nm, 80 nm to 450 nm, 80 nm to 400 nm, 80 nm to 350 nm, 80 nm to 300 nm, 80 nm to 250 nm, 80 nm to 200 nm, 80 nm to 150, 80 nm to 100 nm, 100 nm to 900 nm, 100 nm to 500 nm, 100 nm to 450 nm, 100 nm to 400 nm, 100 nm to 350 nm, 100 nm to 300 nm, 100 nm to 250 nm, 100 nm to 200 nm, or 100 nm to 150 nm.

[0170] In some embodiments, a single layer of the liquid mixture is deposited with a suitable reactant content and viscosity to form a reflective layer of a desired thickness in response to a metal ion reduction reaction, as described herein. In some embodiments, a layer of the liquid mixture is applied and allowed to react at least partially in a first deposition cycle, and at least one subsequent layer of the liquid mixture is applied on top of the first layer in a second deposition cycle. Optionally, by-products of the reaction can be removed between cycles of depositing layers of the liquid mixture. The cycles of depositing the liquid mixture may be repeated until a reflective layer of the desired thickness is achieved. For example, at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 cycles of liquid mixture application may be carried out to form a reflective layer of the desired thickness (including the range between any two of the recited values).

[0171] In some embodiments, a reflective layer of a desired thickness is formed by confining a suitable amount of the liquid mixture behind a barrier, weir, or wall, as described herein. The barrier, weir, or wall can define at least a portion (or all) of a predetermined region of the surface of the waveguide, as described herein.

[0172] The lower protrusions may form a diffractive optical element (e.g., a diffraction grating), which, in some embodiments, may be utilized as an internal coupling optical element to internally couple light into the waveguide. As discussed herein, these protrusions may be metallized by PVD to form a reflective diffractive optical element. In some embodiments, the metal may be deposited on the protrusions by wet chemical action instead of PVD metallization. For example, the metal may be deposited in direct contact with the surface of the protrusion to conformally coat it, thereby forming a reflective layer. It should be understood that PVD metallization may not provide a conformal layer due to the directionality of the path of the metal species delivered to the substrate by PVD. Advantageously, replacing PVD metallization with a liquid metal reflective layer has been found to provide a similar or better level of optical performance. For example, reflective diffractive optical elements formed using a reflective layer according to embodiments herein have been found to provide similar diffraction efficiencies that are similar or superior to those of diffractive optical elements formed using PVD metallization (see Example 2, Tables 2A - B). In some embodiments, liquid metal-based diffractive optical elements have a diffraction efficiency of 20%, 30%, or 40% with respect to light incident on the diffractive optical element at an angle normal (perpendicular) to those diffractive optical elements. In some environments, liquid metal-based diffractive optical elements are configured to redirect incident light to propagate through a substrate (e.g., a waveguide) by total internal reflection.

[0173] Pretreatment agent Prior to the step of depositing the liquid mixture, it is contemplated that pre-treating the surface of the waveguide, as described herein, can improve the adhesion and formation of the reflective layer. With respect to a photoresist waveguide, it has been observed that the pre-treatment can improve both the adhesion and the reflectivity of the reflective layer (Example 3). Thus, in some embodiments, a waveguide comprising a photoresist is pre-treated prior to the step of depositing the liquid mixture, as described herein. Further, it is contemplated that selectively pre-treating a predetermined region and not treating other regions of the surface of the waveguide can facilitate the selective formation of the reflective layer within the desired predetermined region, as described herein.

[0174] Without being bound by theory, it is contemplated that a pre-treatment that increases the hydrophilicity of the waveguide surface (such that the waveguide surface is more hydrophilic than prior to the pre-treatment) can improve the adhesion and the reflectivity of the reflective layer. Thus, in some embodiments, the pre-treatment increases the hydrophilicity of the waveguide surface. Pre-treating the surface of a waveguide comprising a photoresist has been observed to substantially increase the adhesion and the reflectivity of the reflective layer, as described herein. Thus, in some embodiments where the waveguide surface comprises a photoresist, the surface is pre-treated, for example, with plasma to increase the hydrophilicity of the surface prior to depositing the liquid mixture thereon.

[0175] In some embodiments, the pre-treatment consists essentially of, or consists of, applying a pre-treatment agent to the surface of the waveguide, e.g., to a predetermined region, as described herein. Exemplary pre-treatment agents include, but are not limited to, plasma (which can be applied by, e.g., an atmospheric pressure plasma jet "APPJ"), surfactants, coatings (e.g., silica), wet chemical etching (e.g., chromic acid), and catalysts (tin or palladium, e.g., tin chloride or palladium chloride, etc.). In some embodiments, the step of pre-treating the surface with plasma includes atmospheric plasma treatment, the wet chemical etching agent includes chromic acid, the coating includes silica, and / or the catalyst includes tin or palladium, or combinations thereof. In some embodiments, the surface of the waveguide comprises a photoresist and the surface is pre-treated with a pre-treatment agent. In some embodiments, the surface of the waveguide comprises a photoresist and the surface is pre-treated with plasma. The plasma treatment can be instantaneous, e.g., about 10, 9, 8, 7, 6, 5, 3, 2, 1 seconds, or less. In some embodiments, the plasma treatment lasts for about 1 second or less.

[0176] Without being bound by theory, the pre-treatment that improves the metal ion reduction reaction can be selectively applied to a predetermined region (other than other regions) of the surface of the waveguide, and it is envisioned that it can improve the selectivity of the formation of the reflective layer on the predetermined region (excluding other regions). Thus, in some embodiments, a predetermined region of the surface of the waveguide as described herein is pre-treated with a catalyst that improves the metal ion reduction reaction (and reflective layer formation) as described herein.

[0177] Optical Waveguide and Method of Fabricating the Same In some embodiments, a method of fabricating an optical waveguide structure with a reflective layer is described. The method may include providing an optical waveguide having a surface. The surface may include a predetermined region having a pattern of protrusions. For example, the predetermined region may define a nanopattern for deposition of the reflective layer. The method may include depositing a liquid mixture over the predetermined region of the surface. The liquid mixture may include a metal salt and a reducing agent and may be at a basic pH. The method may include enabling the metal salt to be reduced by the reducing agent in the deposited liquid mixture to deposit pure or substantially pure metal over the predetermined region of the surface. Thus, the reflective layer may be formed over a predetermined region of the optical waveguide structure. The resulting reflective layer may be pinhole-free or substantially pinhole-free as described herein. In some embodiments, the predetermined region is less than the entire surface of the waveguide. In some embodiments, the reflective layer is conformally deposited over the protrusions within a predetermined region of the surface of the waveguide. In some embodiments, the method further includes pre-treating a predetermined region of the surface of the waveguide to increase the hydrophilicity of the surface, such as by plasma treatment, as described herein. The pre-treatment step may be performed before the liquid mixture is deposited over the predetermined region of the surface. In some embodiments, the method is an electroless plating and / or electroless deposition method. In some embodiments, the reflective layer does not cover the entire surface of the substrate. In some embodiments, the reflective layer covers all or substantially all of the surface of the substrate. In some embodiments, the method further includes dicing or singulating the substrate and the reflective layer into multiple different components to form a plurality of reflective optical elements. In some embodiments, the optical waveguide with the reflective layer is part of an optical waveguide stack, and the method further includes attaching one or more other optical waveguides to the optical waveguide to form a stack.In some embodiments, an optical waveguide comprising a reflective layer is part of a display device, and thus the method further includes placing a waveguide (or a stack comprising such a waveguide) comprising a reflective layer within the display device. In some embodiments, a given region is defined with a resolution of ±50 microns, or an even more precise (numerically smaller) resolution, e.g., ±40, ±30, ±20, ±10, or ±5 microns.

[0178] Referring to FIG. 23, in some embodiments, the method includes providing an optical waveguide having a surface, the surface comprising a given region comprising a pattern 1600 of protrusions. The method may further include increasing the hydrophilicity of a given region 1610 of the surface, e.g., if the surface comprises a photoresist. For example, the hydrophilicity may be increased by pre-treating the given region with plasma as described herein. The method may further include depositing a liquid mixture on the given region of the surface, the liquid mixture comprising a metal salt and a reducing agent at a basic pH 1620. The method may further include reducing the metal salt with the reducing agent such that a pure or substantially pure metal deposits on the given region of the surface 1630. Thus, a reflective layer is formed on the optical waveguide structure 1640. The reflective layer may comprise, consist essentially of, or consist of a substantially pure metal (or the reflective layer may comprise, consist essentially of, or consist of a pure metal). In some embodiments, the method further includes removing residues from the reflective layer 150, e.g., by rinsing and / or drying, as described herein.

[0179] Advantageously, a reflective layer as described herein is selectively applied to a predetermined region and not to other regions of the surface of the waveguide, and can form diffractive optical elements such as internal coupling optical elements, for example, as described herein. In some embodiments, the surface of the waveguide further comprises a first region. The predetermined region, excluding the first region, is selectively contacted with a liquid mixture. Thus, pure or substantially pure metal deposits on the predetermined region, excluding the first region, and thus forms a reflective layer on the predetermined region but not on the first region of the surface of the optical waveguide. In some embodiments, the liquid mixture is selectively applied only to a predetermined region (excluding other regions) of the surface using selective plasma pretreatment as described herein. Optionally, the selective plasma pretreatment can be selective using a mask that covers the substrate and exposes the predetermined region. In some embodiments, the liquid mixture is selectively applied using a physical structure such as a wall, weir, or well as described herein. The physical structure defines at least a portion of the predetermined region and prevents the liquid mixture from flowing from other regions of the surface of the waveguide (see, e.g., FIGS. 20A - 20B). The wall may be stepped such that the inner wall 2002 that defines the area for depositing the liquid mixture is lower than the outer wall 2004 that surrounds the inner wall 2002. Without being limited by theory, it is envisioned that the gradualness of the wall height may help prevent defects when filling the region defined by the inner wall, for example, by consistently confining the location of the deposited liquid mixture. Thus, in some embodiments, the wall serves as a weir or mold or well to contain the liquid mixture within a predetermined region of the substrate. In some embodiments, the wall further serves as a spacer and can separate stacked waveguides from each other. In some embodiments, the wall comprises a resist. The resist wall is envisioned to be deposited as a layer that extends across the substrate and is then patterned to define the wall, according to some embodiments.

[0180] The wall, weir, or well may be written and / or removable. For example, the wall, weir, or well may be removed by rinsing, peeling, taking out with water (or another liquid), and / or by vacuum. In some embodiments, the wall, weir, or well is not removable, but rather retained as part of the final structure. In some embodiments, the liquid mixture is selectively applied using a mask. One or more openings in the mask can cover a predetermined area, and the liquid mixture may be deposited within the one or more openings. The mask may subsequently be removed. In some embodiments, the liquid mixture is selectively applied by an inkjet. The inkjet can advantageously enable selective application of the deposition of the liquid mixture into a desired area.

[0181] As described herein, increasing the hydrophobicity of the surface of a substrate can improve the adhesion and reflectivity of a reflective layer deposited on the substrate. With respect to the photoresist surface of a waveguide, it has been noted that the reflective layer can exhibit substantially excellent adhesion and reflectivity when the hydrophobicity of the photoresist is increased prior to the step of depositing the liquid mixture (Example 3). Thus, a pretreatment that selectively increases the hydrophilicity of a predetermined region of the surface of the waveguide (compared to the hydrophilicity of the predetermined region before pretreatment) but not in other regions can facilitate the selective formation of a reflective layer on the predetermined region of the waveguide surface but not on other regions. In some embodiments, the method includes the step of increasing the hydrophilicity of a predetermined region of the surface prior to the step of depositing the liquid mixture. In some embodiments, the hydrophilicity is selectively increased on a predetermined region of the surface but not in a first region of the surface. In some embodiments, the hydrophilicity of a predetermined region of the surface is increased by pre-treating the predetermined region of the surface with a pretreatment agent selected from the group consisting of plasma, surfactant, coating, wet chemical etching, and catalyst. In some embodiments, the method includes the step of pre-treating the surface with at least one of plasma, wet etching with a wet chemical etching agent containing chromic acid, surfactant, coating containing silica, and / or catalyst containing tin or palladium (such as stannous chloride or palladium chloride). In some embodiments, a predetermined region of the waveguide is not pre-treated with any pretreatment reagent.

[0182] As described herein, using a catalyst to improve the reduction of metal ions within a predetermined region (excluding other regions) of the surface of a waveguide can also improve the selective deposition within the predetermined region. In some embodiments, the method further includes the step of selectively applying a catalyst to a predetermined region of the surface prior to the step of depositing the liquid mixture. The catalyst can be configured to promote the reduction of a metal salt, thereby promoting the deposition of pure or substantially pure metal.

[0183] As described herein, in some embodiments of the method, physical barriers, walls, dams, and / or wells may also improve the selective deposition of the reflective layer by confining the liquid mixture (and thus the deposited metal) to a predetermined region of the waveguide surface. In some embodiments of the method, the surface of the waveguide comprises a vertically extending wall that defines at least a portion of a predetermined region on which the liquid mixture is selectively deposited. The wall restricts the lateral movement of the liquid mixture into the first region. Examples of such walls, wells, or dams are illustrated in FIGS. 20A-20B.

[0184] In some embodiments of the method, a predetermined region of the waveguide surface comprising protrusions is part of a grating. At least a portion of the reflective layer may be conformally or non-conformally disposed on the grating. The interface between the reflective layer and the surface may be in a state where there is substantially no gap. In some embodiments, at least a portion of the reflective layer is conformally disposed on the grating and the interface between the reflective layer and the surface is substantially gapless. In some embodiments, the reflective layer is conformally disposed on the grating. In some embodiments, at least a portion of the reflective layer is non-conformally disposed on the grating and the interface between the reflective layer and the surface is substantially gapless. In some embodiments, the reflective layer is configured to reflect incident electromagnetic radiation into the first waveguide at the interface.

[0185] In some embodiments of the method, the reflective layer on the optical waveguide structure is a diffractive optical element or a part thereof. The optical element may be configured to redirect the incident light at an angle such that the light propagates through the waveguide by total internal reflection. In some embodiments of the method, a predetermined region of the surface comprises an internal coupling optical element or a part thereof, on which the reflective layer is formed.

[0186] In some embodiments of the method, the waveguide is formed from an optically transmissive material and is configured to propagate light therein by total internal reflection. In some embodiments, the surface of a predetermined waveguide comprises, consists essentially of, or consists of a photoresist.

[0187] In some embodiments of the method, an optical waveguide stack comprising a reflective layer is fabricated. The optical waveguide stack may comprise a first waveguide comprising a first surface and a reflective layer conformally disposed on and adhered to a protrusion of the first surface, as described herein. The reflective layer may comprise an interface with the first surface configured to reflect incident electromagnetic radiation (e.g., light in the visible spectrum) into the first waveguide at the interface, as described herein. The optical waveguide stack may comprise at least one other optical waveguide, as described herein. In some embodiments, the protrusion of the surface of the first waveguide on which the reflective layer is disposed forms an optical grating, e.g., a binary grating, a blazed grating, a multilevel grating, an undercut grating, or a metamaterial or metasurface grating, as described herein. In some embodiments, the optical grating comprises a patterned photoresist. In some embodiments, after the reflective layer is formed on the optical waveguide structure, the optical waveguide structure is adhered to one or more other optical waveguides and / or another optical waveguide is deposited on the surface of the optical waveguide (or several cycles of depositing the optical waveguide are performed), thus forming a stack of optical waveguides comprising the reflective layer.

[0188] The reduction of metal salts to form the deposited metal may be referred to herein as a "metal reduction" or "metal ion reduction" reaction. An example of such a reaction is schematically illustrated in FIG. 21C. In some embodiments of the method, the trence reaction reduces the metal salt to pure or substantially pure metal. In some embodiments, the reducing agent consists essentially of or consists of carbohydrates containing alpha-hydroxy aldehydes and / or carbohydrates containing alpha-hydroxy ketones. Exemplary reducing agents include sucrose, fructose, and combinations thereof. In some embodiments, the metal salt consists essentially of or consists of Ag(NH3)2. In some embodiments, the liquid mixture consists essentially of a solvent, e.g., a metal salt, a reducing agent, and a base in water. In some embodiments, the liquid mixture consists of a solvent, e.g., a metal salt, a reducing agent, and a base in water.

[0189] In some embodiments of the method, the liquid mixture is incubated to promote the reduction of the metal salt. In some embodiments, the incubation occurs at room temperature, e.g., about 20, 21, 22, 23, 24, or 25 °C, including ranges between any two of the recited values, e.g., 20 - 25 °C. In some embodiments, the liquid mixture is incubated slightly below or slightly above room temperature, e.g., 15 - 20 °C or 25 - 30 °C. In some embodiments, the liquid mixture is incubated at about 15 - 30 °C. For example, the metal ion reduction reaction described in some embodiments of the methods herein may be suitably formulated to be carried out at or below room temperature. On the other hand, the application of metal ink often involves firing / heating at high temperatures to produce a purer metal, which can affect the thermal budget of the waveguide (and even damage the waveguide, including damaging the resist structure) and can extend the process time. In addition, high-temperature firing may or may not be compatible with the materials used to fabricate nanostructures such as protrusions on the optical waveguide.

[0190] In some embodiments, the liquid mixture is incubated for at least about 1 second, such as at least about 1, 5, 10, 20, 30, 40, or 50 seconds, or at least about 1 minute, such as at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 minutes, including ranges between any two of the recited values, such as 1 second to 1 minute, 1 second to 2 minutes, 1 second to 5 minutes, 10 seconds to 1 minute, 10 seconds to 2 minutes, 10 seconds to 5 minutes, 1 - 5 minutes, 1 - 10 minutes, 2 - 5 minutes, 2 - 10 minutes, or 5 - 10 minutes.

[0191] In the methods of some embodiments, the pure or substantially pure metal is free or substantially free of metal particles other than the metals as described herein.

[0192] It is contemplated that the metal may discolor and / or deteriorate, inhibiting its reflective properties. Capping the reflective layer provides protection against discoloration or other deterioration and thus may extend the length of time that the reflective layer retains its desired reflective properties (Example 4). In some embodiments, the reflective layer is capped. In some embodiments, the reflective layer is capped with a capping layer that seals the reflective layer so that the reflective layer is not directly exposed to air and / or humidity. In some embodiments, the capping layer comprises, consists essentially of, or consists of a dielectric or a metal. In some embodiments, the capping is formed by deposition of a dielectric coating or a metal coating onto the reflective layer. In some embodiments, the protective layer may be a liquid when applied and may be converted to a solid by a chemical reaction or a physical state change. In some embodiments, the capping prevents direct exposure of air and / or humidity to the associated reflective surface of the reflective layer.

[0193] The liquid mixtures of some embodiments are assumed to have a short shelf life. Thus, in the methods of some embodiments, the liquid mixture is prepared immediately prior to deposition. In some embodiments, the liquid mixture is in a single composition. In some embodiments, the liquid mixture is provided in two or more different compositions. When the different compositions are deposited on a predetermined region of the waveguide surface, the liquid mixture is thus deposited. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited simultaneously on a predetermined region. For example, with respect to a coating process that requires both part A and part B to react, part A and part B can be deposited simultaneously on a predetermined surface. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited sequentially on a predetermined region. For example, with respect to a coating process that requires both part A and part B to react, droplets or a plurality of droplets of part A can be applied first, and then droplets of part B can be applied thereon. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are mixed and then deposited as a single composition on a predetermined region.

[0194] Several suitable techniques can be used to deposit a liquid mixture on a predetermined region of the waveguide surface in accordance with the methods of some embodiments herein. For example, in some embodiments, the liquid mixture is deposited on the predetermined region via at least one of nanodispensing, microdispensing, micropipetting, inkjet, or spraying. In some embodiments, the liquid mixture is deposited on the predetermined region as a single droplet or a plurality of droplets ranging from the picoliter range to the microliter range. In some embodiments, the liquid mixture is deposited using a single-droplet dispensing tool.

[0195] In some embodiments, after the reflective layer is formed, residues (e.g., oxidized carbohydrates and by-products of reactants such as ammonia or excess reactants) are removed from the reflective layer. The method of some embodiments further includes the step of removing residues of the metal ion reduction reaction. In the method of some embodiments, the reflective layer is rinsed after being formed. Residues remaining after the reaction can be removed by rinsing. Examples of suitable rinsing techniques include a wash / spray system, a tank with circulation and / or agitation, a spin rinse / dry system, or a combination of two or more of the listed techniques. In some embodiments, the rinsing is performed with an aqueous solution, such as water. In some embodiments, the reflective layer is dried, for example, until the residues are completely dried or until the rinsed material is completely dried.

[0196] Furthermore, in some embodiments, (e.g., with respect to diffractive optical elements, internal coupling optical elements, or external coupling optical elements as described herein), the relevant surface is at the interface of the reflective layer of the waveguide and is thus assumed not to be directly exposed to air. Thus, in some embodiments, for example, if the relevant reflective surface is not exposed to air, the reflective layer is not capped.

[0197] Optical device In some embodiments, an optical device is described. The optical device may comprise a first waveguide having a first surface. The optical device may comprise a reflective layer disposed over an area of the first surface, wherein the reflective layer has no or substantially no pinholes. The layer may consist essentially of or consist of a pure metal or substantially pure metal. For example, the layer may contain at least 95% elemental metal. The reflective layer may be configured to reflect incident electromagnetic radiation into the first waveguide at the interface. In the optical device of some embodiments, the first waveguide is part of a stack of optical waveguides as described herein. In the optical device of some embodiments, two or more of the optical waveguides in the stack each comprise a reflective layer as described herein.

[0198] In some embodiments of the optical device, the region of the first surface comprises protrusions that, together with the reflective layer, are part of a reflective diffraction grating. Examples of the protrusions are depicted in FIGS. 19A - 19C. In some embodiments, the reflective diffraction grating consists essentially of or consists of a reflective layer disposed on the protrusions. In some embodiments, the reflective diffraction grating consists essentially of or consists of a portion of the reflective layer disposed on the protrusions.

[0199] In some embodiments of the optical device, the reflective layer disposed on the protrusions is part of an internal coupling optical element configured to redirect incident ambient light at an angle such that light propagates through the first waveguide. In one example, light incident on the diffraction grating will be internally coupled to the waveguide such that it propagates away from the diffraction grating at an angle suitable for TIR within the waveguide. It should be understood that the internally coupled light can propagate through the waveguide by TIR and reflect from the surface of the waveguide at an angle similar to the angle at internal coupling. Depending on the geometry of the diffraction grating or the beam diameter of the light, a portion of this light can be incident on the diffraction grating during an early reflection within the TIR path and, undesirably, will be redirected out of the waveguide. For example, the diffraction grating can be on the surface of one waveguide and the incident light can be internally coupled and redirected to reflect from the opposing surface of the waveguide. The reflected light can then be incident on the diffraction grating, which redirects the light out of the waveguide. In some embodiments, to prevent the undesired redirecting of light out of the waveguide, the diffraction grating, on which the reflective layer is deposited, may be sized and shaped such that internally coupled light reflected from the opposing surface of the waveguide does not impinge on the diffraction grating, or the beam diameter may be adjusted.

[0200] In some embodiments of the optical device, the reflective layer reflects incident electromagnetic radiation (e.g., light within the visible spectrum) with a reflectivity (or reflectance) of at least 70%, for example, at least 70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, 99.9%, and includes ranges between any two of the recited values, such as 70% - 90%, 70% - 95%, 70% - 99.9%, 80% - 90%, 80% - 95%, 80% - 99.9%, 85% - 90%, 85% - 95%, 85% - 99.0%, 90% - 95%, or 90% - 99.9%. In some embodiments, the reflective layer reflects incident electromagnetic radiation (e.g., light within the visible spectrum) with a reflectivity of at least 85%. The predetermined region of the waveguide surface may be sized and shaped as appropriate.

[0201] In some embodiments of the optical device, the reflective layer maintains the ability to reflect incident electromagnetic radiation with a reflectivity of at least 85%, for example, at least 85%, 87%, or 90% over at least 500 hours. As shown in Example 4 and FIG. 24, the reflective layer as described herein can maintain a reflectivity of at least about 85% (across the 400 - 700 nm light spectrum) without capping even after 500 hours at 60 °C and 100% humidity. Thus, in some embodiments, the reflective layer maintains the ability to reflect incident electromagnetic radiation with a reflectivity of at least 85% over at least 500 hours, whether or not it is capped.

[0202] As described herein, it can be advantageous to confine the reflective layer to a predetermined region of the waveguide surface. Thus, in some embodiments, the first surface comprises a wall that defines the boundary of the reflective layer. The wall may comprise, consist essentially of, or consist of a mechanical spacer configured to maintain a space between the first waveguide and other waveguides.

[0203] In some embodiments, the optical device comprises, consists essentially of, or consists of a display system that includes an image projector configured to project light containing image information into a first waveguide. For example, the display system may be a wearable display system or a component of a wearable display system as described herein.

[0204] In some embodiments of the optical device, the reflective layer is free or substantially free of metal particles other than the metals described herein.

[0205] Some embodiments of the optical device may further include an interface layer that includes at least one of a surfactant, a catalyst, or a coating disposed at the interface between the reflective layer and the first surface. As described herein, the surfactant, catalyst, and / or coating may facilitate the selective deposition of the reflective layer and may improve the adhesion and optical performance of the reflective layer. In some embodiments, some embodiments of the optical device further include at least one of a surfactant or a catalyst disposed at the interface between the reflective layer and the first surface. In some embodiments, some embodiments of the optical device further include at least one of a catalyst or a coating disposed at the interface between the reflective layer and the first surface. In some embodiments, some embodiments of the optical device further include at least one of a surfactant or a coating disposed at the interface between the reflective layer and the first surface.

[0206] Some embodiments of the optical device further include a capping layer disposed on the reflective layer as described herein.

[0207] Display device In some embodiments, a display device is provided. The display device may include a waveguide having a reflective diffractive optical element, where a diffractive optical element is disposed on a region of the surface of the waveguide. The reflective layer may be in a state where there are substantially no pinholes. The reflective layer may consist essentially of, consist of, or include a pure metal or a substantially pure metal. For example, the layer may include at least 95% elemental metal. The reflective layer may be configured to reflect incident electromagnetic radiation into the first waveguide at the interface. In some embodiments, the first waveguide is part of a stack of optical waveguides as described herein. In some embodiments, two or more of the optical waveguides in the stack each include a reflective layer as described herein. In some embodiments, the reflective layer does not cover the entire surface of the waveguide.

[0208] In some embodiments of the display device, the reflective diffractive optical element forms an internal coupling grating configured to internally couple incident light into the waveguide as described herein.

[0209] In some embodiments of the display device, the waveguide is one of a stack of waveguides, and each of the stack of waveguides includes an internal coupling grating. In the top and bottom views, the internal coupling gratings may be laterally offset from each other. For example, referring to FIG. 9A, the internal coupling optical elements 700, 710, 720 may be laterally offset from each other.

[0210] In some embodiments of the display device, the reflective layer is free of or substantially free of metal particles other than the metals as described herein.

[0211] The display devices of some embodiments further comprise at least one of a surfactant, a catalyst, or a coating disposed at the interface of the reflective layer and the surface, as described herein. In some embodiments, the display device further comprises at least one of a surfactant or a coating disposed at the interface of the reflective layer and the surface, as described herein. In some embodiments, the display device further comprises at least one of a catalyst or a coating disposed at the interface of the reflective layer and the surface, as described herein. In some embodiments, the display device further comprises at least one of a surfactant or a catalyst disposed at the interface of the reflective layer and the surface, as described herein.

[0212] The display devices of some embodiments further comprise a capping layer disposed on the reflective layer, as described herein. The capping layer may be disposed such that the interface of the reflective layer, which is arranged to direct / propagate electromagnetic radiation, is not directly exposed to air and humidity.

[0213] In some embodiments of the display device, the reflective layer reflects incident electromagnetic radiation (e.g., light within the visible spectrum) with a reflectivity (or reflectance) of at least 70%, such as at least 70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, 99.9%, including ranges between any two of the recited values, such as 70% - 90%, 70% - 95%, 70% - 99.9%, 80% - 90%, 80% - 95%, 80% - 99.9%, 85% - 90%, 85% - 95%, 85% - 99.0%, 90% - 95%, or 90% - 99.9%. In some embodiments, the reflective layer reflects incident electromagnetic radiation (e.g., light within the visible spectrum) with a reflectivity of at least 85%.

[0214] In some embodiments of the display device, the reflective layer maintains the ability to reflect incident electromagnetic radiation with a reflectivity of at least 85%, for example, at least 85%, 87%, or 90% over at least 500 hours. In some embodiments, the reflective layer maintains the ability to reflect incident electromagnetic radiation with a reflectivity of at least 85% over at least 500 hours, whether or not it is capped.

[0215] Method of manufacturing a display device In some embodiments, a method of manufacturing an optical device is described. The method may include providing a waveguide having a surface. The method may include depositing a liquid mixture on an area of the surface. The liquid mixture may include a metal salt. The liquid mixture may also include a reducing agent at a basic pH. The method may include incubating the liquid mixture on a predetermined area of the surface such that the metal salt is reduced by the reducing agent and pure or substantially pure metal deposition occurs. Accordingly, a reflective layer is formed on a predetermined area of the surface. The reflective layer on the surface may form a reflective diffractive optical element. In some embodiments, the method further includes pre-treating the surface to increase its hydrophilicity as described herein. The pre-treating step may be performed before the liquid mixture is deposited on a predetermined area of the surface.

[0216] In some embodiments, the method further includes providing an image projector positioned to output light onto the reflective diffractive optical element.

[0217] Exemplary diffractive optical element In some embodiments, an internally coupled optical element (e.g., internally coupled optical elements 700, 710, 720) comprises a reflective diffractive optical element comprising a reflective layer comprising, consisting essentially of, or consisting of pure or substantially pure metal as described herein.

Examples

[0218] (Example 1) Comparison between a reflective layer formed by metal ion reduction and silver-containing ink Examples of different methods for forming silver-containing layers are shown in FIGS. 21A-C, including "Type 1" high silver composite loading (FIG. 21A), "Type 2" inorganic aqueous silver ion thermal deposition (FIG. 21B), and "Type 3" wet chemical silver ion reduction (Trench reaction) according to some embodiments herein (FIG. 21C).

[0219] The method of fabricating a reflective layer via silver ion reduction as described herein was compared with other methods of fabricating a reflective layer. The comparison was carried out on an internal connection grating (ICG) nanostructured surface. The coating property evaluations using different methods are shown in Table 1. According to some embodiments, a reflective layer containing silver was formed using a modified Trench reaction. This reaction was carried out at room temperature and produced high-purity silver with good smoothness at the nanoscale (without pinholes) (FIG. 22C, the one after rinsing is shown). The coating was also highly conformal around the ICG nanostructure. For comparison, the inkjetable inks from NovaCentrix (Austine, Texas) (FIG. 22A) and Electroinks (FIG. 22B) formed a nanoporous network that contained a substantial number of pinholes, was highly conductive, but was associated with a relatively low reflectivity. The adhesion of the reflective layer as described herein was also evaluated using a tape peel test. The reflective layer formed by using a modified Trench reaction according to some embodiments herein (FIG. 22F) exhibited substantially better adhesion compared to the inkjetable inks from NovaCentrix (FIG. 22D) and Electroinks (FIG. 22E) (silver tape peel from glass). It should be noted that for the tape peel test, the reflective layers of some embodiments were deposited on 3 nm SiOx-coated ICGs. These results are summarized in Tables 1A-B below.

Table 1-1

Table 1-2

Table 1-3

[0220] Thus, the reflective layer according to some embodiments of the present specification has a smoother surface (no or substantially no pinholes) and has been shown to exhibit better adhesion than a layer formed from an inkjetable metal-containing ink.

[0221] (Example 2) Comparison of Reflective Layer with Evaporated Metal Layer and Silver-Containing Ink Pretreatment of the nanostructured photoresist by plasma resulted in excellent adhesion. Reflectivity and ICG diffraction efficiency were tested for the reflective layer containing silver generated on the 385 resist processed with APPJ plasma by a modified Trance reaction and compared with a sputtered aluminum deposition layer on the 385 resist and an inkjetable ink from NovaCentrix fired at 180 °C for 15 minutes. The reflective layer containing silver generated by the modified Trance reaction exhibited a reflectivity that was clearly higher than that of the tested commercial metal inks and also higher than that of the aluminum coating by evaporation (Figure 23). Furthermore, the reflective layer containing silver generated by the modified Trance reaction exhibited a higher reflectivity for all wavelengths tested in the range of 400 - 700 nm (Figure 23).

[0222] Reflectance and diffraction efficiency are summarized in Table 2A - B below.

Table 2-1

Table 2-2

Table 2-3

[0223] Advantageously, the reflective layer formed by silver ion precipitation was highly smooth, exhibited high reflectivity, excellent adhesion, and could be formed at room temperature. The aluminum vapor deposition layer was stable but exhibited lower reflectivity and diffraction efficiency and was hampered by issues associated with stencil use. The metal-containing inks from NovaCentrix and Electroinks exhibited lower reflectivity and diffraction efficiency and required a firing step, which would extend production time and affect the thermal budget for some waveguides.

[0224] In addition, the reflective layer formed by silver ion precipitation exhibited better eyepiece efficiency compared to sputtered aluminum. The D55 green efficiency for the reflective layer formed by silver ion precipitation was 4.5 - 4.9% (for 4 - 5 eyepieces) compared to approximately 3.9% for sputtered aluminum.

[0225] Thus, it can be concluded that for the methods and devices of some embodiments, the reflective layer exhibits better reflectivity and better diffraction efficiency compared to layers formed from metal-containing inks and Al layers formed by vapor deposition.

[0226] (Example 3) Effect of surface treatment The effect of surface treatment was evaluated for the reflective layer deposited by silver ion reduction as described herein.

[0227] As a control, the imprint area on the resist without pretreatment exhibited a very thin Ag coating (only slight residue after light water washing).

[0228] The resist was cleaned with acetone in the imprint area. This pretreatment resulted in a thin, semi-transparent silver coating. The silver was thicker than the area without acetone cleaning, but was still very thin and had a low likelihood of having sufficient reflectivity for many applications.

[0229] The resist was pretreated with an ultra-thin atmospheric pressure plasma jet (APPJ) coating. The plasma jet coating provided high reflectivity and acceptable adhesion using an SnCl2 catalyst.

[0230] The resist was pretreated with plasma. This pretreatment provided high reflectivity and excellent adhesion.

[0231] The glass-only area resulted in a ~100 nm silver coating. This coating was highly reflective and exhibited better reflectivity than an aluminum layer formed by evaporation.

[0232] The results of these pretreatments are summarized in Table 3 below.

Table 3

[0233] (Example 4) Stability of the Reflective Layer without Capping As described herein, the stability of a reflective layer formed by silver ion reduction (which may also be referred to as "self-silver") was measured. The reflectance of a reflective layer formed by silver ion reduction on a 385M2 cured resist (without capping) was measured both initially and after 500 hours at 60 °C and 100% humidity. The reflectance of an aluminum layer formed by vapor deposition was also measured. As shown in Figure 24, the reflective layer formed by silver ion reduction exhibited excellent stability, with little change in reflectance across all tested wavelengths (400 - 700 nm) between the initial sample and the sample after 500 hours at 60 °C and 100% humidity. Both the initial reflective layer formed by silver ion reduction (according to some embodiments herein) and the reflective layer after 500 hours at 60 °C and 100% humidity exhibited better reflectance than the aluminum sample.

[0234] The ICG diffraction efficiency was also measured for the reflective layer formed by silver ion reduction, both initially and after 360 hours at 60 °C and 100% humidity. The results are shown in Table 4 below. Table 4 shows that the diffraction efficiency did not substantially change even after the reflective layers of some embodiments were at 100% humidity for 360 hours.

Table 4

[0235] Various exemplary embodiments of the present invention are described herein. By way of non-limiting example, reference is made to these embodiments. They are provided to illustrate more broadly applicable aspects of the present invention. Various changes may be made to the invention as described, and equivalents may be substituted without departing from the true spirit and scope of the invention.

[0236] For example, advantageously, it is utilized with an AR display that provides images across multiple depth planes, although the augmented reality content disclosed herein may also be displayed by a system that provides images on a single depth plane.

[0237] In addition, many modifications may be made to adapt a particular situation, material, composition, process, act of a process, or step to the purpose, spirit, or scope of the present invention. Further, as will be understood by those skilled in the art, each of the individual variations described and illustrated herein can be readily separated from or combined with features of any of the other several embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

[0238] The present invention includes methods that can be performed using the device. The method may include the act of providing such a suitable device. Such provision may be performed by a user. In other words, the act of "providing" simply requires that the user obtain, access, approach, position, configure, activate, power on, or otherwise act so as to provide the essential device in the subject method. The methods described herein may be performed in any order of the described events that is logically possible and in the order of the described events.

[0239] Exemplary aspects of the present invention have been described above, along with details regarding material selection and manufacture. Regarding other details of the present invention, these are understood in relation to the above-referenced patents and publications and can generally be grasped or understood by those skilled in the art. The same may apply to the method-based aspects of the present invention from the perspective of additional acts that are commonly or logically employed.

[0240] In addition, although the present invention has been described with reference to several embodiments incorporating various features optionally, the present invention is not limited to what is described or indicated as being contemplated with respect to each variation of the present invention. Various modifications may be made to the invention described herein, and equivalents may be substituted (whether or not described herein or not included for sake of brevity) without departing from the true spirit and scope of the present invention. In addition, when ranges of values are provided, it is understood that all intervening values between the upper and lower limits of that range, as well as any other defined or intervening values within that defined range, are included within the present invention.

[0241] Also contemplated is that any optional feature of a variation of the invention described herein may be described and claimed independently or in combination with any one or more of the features described herein. Reference to items in the singular includes the possibility that there are a plurality of the same items. More specifically, as used herein and in the claims associated therewith, the singular forms "a", "an", "said", and "the" include plural referents unless specifically stated otherwise. In other words, the use of the articles enables "at least one" of the item in question in the above description and the claims associated with this disclosure. Further, note that such claims may be drafted to exclude any optional element. Accordingly, this description serves the purpose of acting as a precedent for the use of such exclusive terms as "only", "solely", and equivalents thereof, in relation to the recitation of claim elements, or the use of "negative" limitations.

[0242] Without using such exclusive terms, the term "comprising" in the claims associated with the present disclosure shall be construed to allow the inclusion of any additional elements, whether or not a given number of elements are recited in such claims or whether the addition of features can be regarded as transforming the nature of the elements recited in such claims. Unless otherwise specifically defined herein, all technical and scientific terms used herein shall be given the broadest possible generally understood meaning while maintaining the validity of the claims.

Claims

1. 1. A method of making an optical waveguide structure comprising a reflective layer, the method comprising:

1. An optical waveguide comprising a surface, the surface comprising an area comprising a pattern of a plurality of protrusions; depositing a liquid mixture onto at least a portion of the region, the liquid mixture including a metal salt; forming the reflective layer by coating the area with a metal of the metal salt, where coating the area includes precipitating the metal on the area by dissociating the metal from the metal salt; removing residual liquid mixture material following depositing said metal; A method comprising:

2. The method of claim 1 , wherein dissociating a metal from the metal salt comprises reducing the metal salt by exposure to a reducing agent.

3. 3. The method of claim 2, wherein the reducing agent comprises at least one of an alpha-hydroxyaldehyde-containing carbohydrate or an alpha-hydroxyketone-containing carbohydrate.

4. The method of claim 2 , wherein the liquid mixture includes the reducing agent.

5. The method of claim 2 , wherein the method further comprises adding the reducing agent to the liquid mixture after depositing the liquid mixture.

6. The method of claim 1 , wherein forming the reflective layer comprises selectively forming the reflective layer over the regions while leaving one or more areas around the metal-free regions.

7. 7. The method of claim 6, wherein a surface of the optical waveguide comprises vertically extending walls defining a volume within the region, and depositing the liquid mixture comprises depositing the liquid mixture into the volume.

8. The method of claim 1 , wherein the plurality of protrusions defines a diffractive optical element, and the plurality of protrusions and the reflective layer form a reflective diffractive optical element.

9. The method of claim 8 , wherein the diffractive optical element is an internal coupling optical element configured to redirect the incident light at an angle such that the incident light propagates through the optical waveguide by total internal reflection.

10. The method of claim 1 , wherein the plurality of protrusions comprises photoresist.

11. The method comprises: forming an additional reflective layer on the additional optical waveguide by depositing the liquid mixture onto an additional area of ​​a surface of the additional optical waveguide, the additional reflective layer being configured to reflect incident light; attaching at least said additional optical waveguides to a surface of said optical waveguide, thereby producing a stack of waveguides. The method of claim 1 further comprising:

12. 10. The method of claim 1, wherein the hydrophilicity of the regions is increased by selectively pre-treating the regions with one or more agents selected from the group consisting of plasmas, surfactants, coatings, wet chemical etchants, and catalysts prior to depositing the liquid mixture.

13. moreover, When the one or more agents include the plasma, pre-treating the area with plasma includes performing an atmospheric pressure plasma treatment; When the one or more agents include the wet chemical etchant, the wet chemical etchant includes chromic acid; When the one or more agents comprise a coating, the coating comprises silica; and / or The method of claim 12, wherein when the one or more agents include the catalyst, the catalyst comprises tin or palladium.

14. 10. The method of claim 1, wherein the method further comprises selectively applying a catalyst to the area prior to depositing the liquid mixture, the catalyst configured to promote reduction of the metal salt.

15. The method of claim 1 , wherein the liquid mixture consists essentially of the metal salt and a reducing agent and a base.

16. The method of claim 1 , wherein the reflective layer is a pure or substantially pure metal.

17. The method of claim 1 , wherein the liquid mixture is deposited on the region by at least one of nanodispensing, microdispensing, micropipetting, inkjet printing, and spraying.

18. The method of claim 1 , wherein removing the residual liquid mixture material comprises rinsing the optical waveguide.

19. The method of claim 1 further comprising depositing a capping layer on the reflective layer.

2. The method according to claim 1.

20. The method of claim 1 , wherein the reflective layer is pinhole-free or substantially pinhole-free.

21. The method of claim 1 , wherein the metal is silver.

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