Diffusion optical element involving reduction of re-bounce induced light loss and system and method related thereto

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] (Priority Claim) This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62 / 702,707, filed July 24, 2018, and 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 October 17, 2018, and entitled "WAVEGUIDES HAVING HIGHLY REFLECTIVE LAYERS AND METHODS FOR FORMING," both of which are incorporated herein by reference in their entireties for all purposes.

[0002] (Incorporated by reference) This application is incorporated by reference into the following patent applications: U.S. Patent Application No. 14 / 555,585, filed November 27, 2014, published July 23, 2015 as U.S. Patent Publication No. 2015 / 0205126; U.S. Patent Application No. 14 / 690,401, filed April 18, 2015, published October 22, 2015 as U.S. Patent Publication No. 2015 / 0302652; This application incorporates in its entirety each of U.S. Patent Application No. 14 / 212,961, filed on August 16, 2016, now U.S. Patent No. 9,417,452; U.S. Patent Application No. 14 / 331,218, filed on July 14, 2014, published on October 29, 2015 as U.S. Patent Publication No. 2015 / 0309263; and U.S. Patent Application No. 15 / 954,419, filed on April 16, 2018.

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

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

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

[0006] Some aspects include a display system for projecting an image to 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 including a diffractive region configured to internally couple light from the projection optical system and redirect the light from the projection optical system to propagate in a first direction within the waveguide 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 is incident on the diffractive region and a second portion of the beam of light from the projection optical system impinges on the waveguide without being incident on the diffractive region.

[0007] The diffraction region may be a high-efficiency diffraction region, and the internal coupling optical element further includes a low-efficiency diffraction region sized and shaped so 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 including a metallized grating portion, and the low-efficiency diffraction region may include 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 lower efficiency than the first portion of the beam of light. The diffraction region may be reflectively asymmetric about an axis of symmetry perpendicular to the propagation direction of the beam axis of the beam of light from the projection optical system. The waveguide may be part of a waveguide stack, the waveguide stack further comprising: a second waveguide having a first major surface and a second major surface; and a second in-coupling optical element disposed on the second major surface of the second waveguide, the second in-coupling optical element comprising a second diffraction region covering a larger proportion of an area defined by the second beam of light from the projection optical system than a proportion of the area defined by the beam of light covered by the diffraction region. The second diffraction region may be configured to in-couple substantially all of the second beam of light. The diffraction region of the first waveguide may be reflectively asymmetric about an axis of symmetry perpendicular to the propagation direction of the beam axis of the beam of light from the projection optical system, and the second diffraction region may be reflectively symmetric about a second axis of symmetry perpendicular to the propagation direction of the beam axis of the second beam of light. 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 comprising 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 diffractive region configured to internally couple incident light, wherein a width of the diffractive region parallel to the direction of propagation is less than a length of the diffractive region perpendicular to the direction of propagation.

[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 internal coupling diffractive optical element further comprises 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 comprising a metallized diffraction grating portion, and the low-efficiency diffraction region may comprise 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 in the high-efficiency diffraction region and non-metallized in the low-efficiency diffraction region. The internal coupling diffractive optical element may be sized and shaped to reduce the occurrence of re-bouncing of the internally coupled light compared to an internal coupling optical element having substantially equal length and width.

[0010] Some aspects include a waveguide stack for a head-mounted display system, the waveguide stack comprising: a first waveguide having a first major surface, a second major surface opposite the first major surface, and a first in-coupling diffractive optical element disposed on the second major surface, the first in-coupling diffractive optical element comprising a first diffractive region configured to redirect incident light from a light source and propagate within the first waveguide by total internal reflection in a propagation direction; and a second waveguide having a first major surface, a second major surface opposite the first major surface of the second waveguide, and a second in-coupling diffractive optical element disposed on the second major surface of the second waveguide, the second in-coupling diffractive optical element comprising a second diffractive region configured to redirect incident light from the light source and propagate within the second waveguide by total internal reflection in a propagation direction. 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 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 incoupling diffractive optical element may further comprise a low-efficiency diffraction region disposed immediately adjacent to the high-efficiency diffraction region along the propagation direction. The high-efficiency diffraction region may comprise a metallized portion of the diffraction grating, and the low-efficiency diffraction region may comprise a non-metallized portion of the diffraction grating. The second incoupling diffractive optical element may be sized and shaped to reduce the occurrence of re-bouncing of the incoupling light compared to an incoupling 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 making an optical waveguide structure with a reflective layer, the method including providing an optical waveguide with a surface, the surface including a region with a pattern of protrusions, depositing a liquid mixture over at least a portion of the region, the liquid mixture including a metal salt, and forming the reflective layer by coating the region with a metal of the metal salt, wherein coating the region includes precipitating 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 reducing the metal salt by exposing it to a reducing agent. The reducing agent may comprise at least one of an alpha-hydroxyaldehyde-containing carbohydrate or an alpha-hydroxyketone-containing carbohydrate. The liquid mixture may comprise a reducing agent. The method may further comprise adding the reducing agent to the liquid mixture after depositing the liquid mixture. The step of forming a reflective layer may include selectively forming the reflective layer on the region while leaving one or more areas around the region free of metal. The surface of the waveguide may comprise vertically extending walls defining a volume within the region, and depositing the liquid mixture includes depositing the deposition mixture within the volume. The protrusions may define a diffractive optical element, and the protrusions 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 protrusions may comprise photoresist. The method may further include forming an additional reflective layer on the additional optical waveguide by depositing the liquid mixture onto an additional region of the surface of the additional optical waveguide, the additional reflective optical element being configured to reflect incident light, and attaching at least the additional waveguide to the surface of the waveguide, thereby producing a waveguide stack. 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, surfactants, coatings, wet chemical etchants, and catalysts prior to depositing the liquid mixture. Pre-treating the region with plasma may include performing atmospheric plasma treatment. The wet chemical etchant may include chromic acid. The coating may include silica. The catalyst may include tin or palladium. The method may further include selectively applying a catalyst to the region prior to depositing the liquid mixture, the catalyst configured to promote 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 a pure or substantially pure metal. The liquid mixture may be deposited on the region by at least one of nanodispensing, microdispensing, micropiping, inkjet printing, and spraying. The method may further include removing residual liquid mixture material following deposition of the metal. Removing residual liquid crystal mixture may include rinsing the optical waveguide. The method may further include depositing a capping layer on the reflective layer. The reflective layer may be free or substantially free of pinholes. The metal may be silver.

[0014] Some aspects include an optical device comprising a first waveguide comprising a reflective diffractive optical element, the reflective diffractive optical element comprising a protrusion on a 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 comprise one or more of a tin- or palladium-containing compound. The reflective layer may be at least 95% metallic. The reflective layer may be substantially pinhole-free. 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 the first waveguide by total internal reflection. The reflective layer may reflect the incident light with at least 85% reflectivity. The optical device may further comprise a second waveguide and a third waveguide, the second waveguide configured to output light in a different wavelength range than the third waveguide, and the first, second, and third waveguides each comprising a reflective diffractive optical element comprising a protrusion on a 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 defining a boundary of the reflective layer. The wall may comprise a mechanical spacer configured to maintain a space between the first waveguide and the other waveguide. The optical device may be a display system comprising a spatial light modulator configured to output light containing image information onto a reflective diffractive optical element. The optical device may further comprise a capping layer on the reflective layer. The present invention provides, for example: (Item 1) 1. A display system for projecting an image to a user's eye, said display system comprising: a waveguide having a first major surface and a second major surface opposite the first major surface; projection optics configured to project a beam of light toward the second major surface of the waveguide; an internal coupling optical element disposed on a second major surface of the waveguide, the internal coupling optical element comprising a diffractive region configured to internally couple light from the projection optics, the internal coupling optical element configured to redirect light from the projection optics to propagate within the waveguide in a first direction by total internal reflection; and Equipped with a diffraction region sized and shaped such that a first portion of a 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 impinges on the waveguide without being incident on the diffraction region. (Item 2) Item 1, a display system according to item 1, wherein the diffraction region is a high-efficiency diffraction region, and the internal coupling optical element further comprises a low-efficiency diffraction region sized and shaped so that a second portion of the beam of light from the projection optical system is incident on the low-efficiency diffraction region. (Item 3) Item 3. The display system of item 2, wherein the high-efficiency diffractive regions are reflective diffractive regions comprising metallized grating portions, and the low-efficiency diffractive regions comprise non-metallized grating portions. (Item 4) Item 10. The display system of item 1, wherein a second portion of the beam of light propagates out of the waveguide through the second major surface without being internally coupled into the waveguide. (Item 5) Item 10. The display system of item 1, wherein the second portion of the beam of light is internally coupled into the waveguide with less efficiency than the first portion of the beam of light. (Item 6) Item 2. The display system of item 1, wherein the diffractive region is reflectively asymmetric about an axis of symmetry perpendicular to the propagation direction in the beam axis of the beam of light from the projection optical system. (Item 7) The waveguide is part of a waveguide stack, the waveguide stack comprising: a second waveguide having a first major surface and a second major surface; a second incoupling optical element disposed on a second major surface of the second waveguide, the second incoupling optical element comprising a second diffractive region covering a greater proportion of an area defined by a second beam of light from the projection optical system relative to a proportion of the area defined by the beam of light that is covered by a diffractive region; and Item 1. The display system of item 1, further comprising: (Item 8) Item 8. The display system of item 7, wherein the second diffractive region is configured to in-couple substantially all of the second beam of light. (Item 9) Item 8. A display system as described in Item 7, wherein the diffraction region of the first waveguide is reflectively asymmetric about a symmetry axis perpendicular to the propagation direction in the beam axis of the beam of light from the projection optical system, and the second diffraction region is reflectively symmetric about a second symmetry axis perpendicular to the propagation direction in the beam axis of the second beam of light. (Item 10) 8. The display system of claim 7, wherein the second waveguide is disposed between the waveguide and the projection optical system, and the waveguide is spaced from the projection optical system by a distance greater than the focal length of the projection optical system. (Item 11) A waveguide, a first major surface; a second major surface; and an in-coupling diffractive optical element disposed on the second major surface, the in-coupling optical element comprising a diffractive region configured to in-couple incident light, the diffractive region having a width parallel to the propagation direction that is less than a length perpendicular to the propagation direction; A waveguide comprising: (Item 12) Item 12. The waveguide of item 11, wherein the width of the diffraction region is less than 80% of the length of the diffraction region. (Item 13) Item 12. The waveguide of 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) Item 14. The waveguide of 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) Item 14. The waveguide of item 13, wherein the high-efficiency diffraction regions and the low-efficiency diffraction regions partially form a metallized diffraction grating, the diffraction grating being metallized in the high-efficiency diffraction regions and non-metallized in the low-efficiency diffraction regions. (Item 16) Item 12. The waveguide of item 11, wherein the internal coupling diffractive optical element is sized and shaped to reduce the occurrence of re-bouncing of the internally coupled light compared to an internal coupling optical element having a substantially equal length and width. (Item 17) 1. A waveguide stack for a head mounted display system, the waveguide stack comprising: a first waveguide comprising a first major surface, a second major surface opposite the first major surface, and a first in-coupling diffractive optical element disposed on the second major surface, the first in-coupling diffractive optical element comprising a first diffractive region configured to redirect incident light from a light source to propagate within the first waveguide in a propagation direction by total internal reflection; a second waveguide having a first major surface, a second major surface opposite the first major surface of the second waveguide, and a second in-coupling diffractive optical element disposed on the second major surface of the second waveguide, the second in-coupling diffractive optical element comprising a second diffractive region configured to redirect incident light from the light source to propagate within the second waveguide in the propagation direction by total internal reflection; Equipped with A waveguide stack, wherein the width-to-length ratio of the second diffraction region is less than the width-to-length ratio of the first diffraction region. (Item 18) Item 18. The waveguide stack of item 17, wherein the waveguide stack is spaced apart from the light source such that a distance between the light source and the first diffraction region is on a focal length of the light source and a distance between the light source and the second diffraction region is greater than the focal length. (Item 19) Item 18. The waveguide stack of item 17, wherein the width-to-length ratio of the first diffraction region is greater than 80% and the width-to-length ratio of the second diffraction region is less than 80%. (Item 20) Item 18. The waveguide stack of item 17, wherein 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 positioned immediately adjacent to the high-efficiency diffraction region along the propagation direction. (Item 21) 21. The waveguide stack of claim 20, wherein the high-efficiency diffraction regions comprise metallized portions of a diffraction grating and the low-efficiency diffraction regions comprise non-metallized portions of the diffraction grating. (Item 22) Item 18. The waveguide stack of item 17, wherein the second internal coupling diffractive optical element is sized and shaped to reduce the occurrence of re-bouncing of the internally coupled light compared to an internal coupling diffractive optical element having a width-to-length ratio equal to the width-to-length ratio of the first diffractive region. (Item 23) 1. A method of making an optical waveguide structure comprising a reflective layer, the method comprising: providing an optical waveguide comprising a surface, the surface comprising an area comprising a pattern 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, wherein coating the area includes precipitating the metal on the area by dissociating the metal from the metal salt; A method comprising: (Item 24) 24. The method of claim 23, wherein dissociating the metal from the metal salt comprises reducing the metal salt by exposure to a reducing agent. (Item 25) 25. The method of claim 24, wherein the reducing agent comprises at least one of an alpha-hydroxyaldehyde-containing carbohydrate or an alpha-hydroxyketone-containing carbohydrate. (Item 26) 25. The method according to claim 24, wherein the liquid mixture comprises the reducing agent. (Item 27) 25. The method of claim 24, further comprising adding the reducing agent to the liquid mixture after depositing the liquid mixture. (Item 28) 24. The method of claim 23, wherein forming the reflective layer comprises selectively forming the reflective layer on the metal-free region while leaving one or more areas around the metal-free region. (Item 29) 29. The method of claim 28, wherein the surface of the waveguide comprises a vertically extending wall defining a volume within the region, and depositing the liquid mixture comprises depositing the deposition mixture into the volume. (Item 30) Item 24. The method of item 23, wherein the protrusions define diffractive optical elements, and the protrusions and reflective layer form reflective diffractive optical elements. (Item 31) Item 31. The method of item 30, wherein 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. (Item 32) Item 24. The method of item 23, wherein the protrusion comprises photoresist. (Item 33) 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 optical element being configured to reflect incident light; attaching at least said additional waveguides to a surface of said waveguide, thereby producing a stack of waveguides; 24. The method of claim 23, further comprising: (Item 34) 24. The method of claim 23, wherein 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, surfactants, coatings, wet chemical etchants, and catalysts prior to depositing the liquid mixture. (Item 35) Pre-treating the region with plasma includes performing an atmospheric plasma treatment. The wet chemical etchant comprises chromic acid. the coating comprises silica, and / or The catalyst contains tin or palladium. Item 35. The method according to item 34, wherein the method is at least one of the following: (Item 36) 24. The method of claim 23, further comprising selectively applying a catalyst to the area prior to depositing the liquid mixture, the catalyst configured to promote the reduction of the silver salt. (Item 37) 24. The method of claim 23, wherein the liquid mixture consists essentially of the metal salt, a reducing agent, and a base. (Item 38) 24. The method of claim 23, wherein the reflective layer is a pure metal or a substantially pure metal. (Item 39) 24. The method of claim 23, wherein the liquid mixture is deposited on the region by at least one of nanodispensing, microdispensing, micropiping, inkjet printing, and spraying. (Item 40) 24. The method of claim 23, further comprising removing residual liquid mixture material following deposition of the metal. (Item 41) Item 41. The method of item 40, wherein removing the residual liquid crystal mixture comprises rinsing the optical waveguide. (Item 42) 24. The method of claim 23, further comprising depositing a capping layer on the reflective layer. (Item 43) 24. The method of claim 23, wherein the reflective layer is free or substantially free of pinholes. (Item 44) 24. The method of claim 23, wherein the metal is silver. (Item 45) 1. An optical device comprising: a first waveguide comprising a reflective diffractive optical element, the reflective diffractive optical element comprising: a protrusion on a surface of the first waveguide; an interface layer on the protrusion; a reflective layer on the interface layer; a first waveguide comprising: An optical device comprising: (Item 46) Item 46. The optical device of item 45, wherein the interfacial layer comprises one or more of a plasma-treated surface, a surfactant layer, and a catalyst. (Item 47) Item 47. The optical device of item 46, wherein the catalyst comprises one or more of a tin or palladium containing compound. (Item 48) Item 46. The optical device of item 45, wherein the reflective layer is at least 95% metal. (Item 49) Item 46. The optical device of item 45, wherein the reflective layer is substantially free of pinholes. (Item 50) Item 46. The optical device of 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) Item 51. The optical device of 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, the second waveguide configured to output light in a different wavelength range than the third waveguide; The first, second, and third waveguides each comprise a reflective diffractive optical element, the reflective diffractive optical element comprising: a protrusion on a surface of the first waveguide; an interface layer on the protrusion; a reflective layer on the interface layer; Item 46. The optical device according to item 45, comprising: (Item 53) Item 46. The optical device of item 45, wherein the first surface comprises a wall that defines a boundary of the reflective layer. (Item 54) Item 54. The optical device of item 53, wherein the wall comprises a mechanical spacer configured to maintain a space between the first waveguide and another waveguide. (Item 55) Item 46. The optical device of item 45, wherein the optical device is a display system comprising a spatial light modulator configured to output light containing image information onto the reflective diffractive optical element. (Item 56) Item 46. The optical device of item 45, further comprising a capping layer on the reflective layer. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0017] [Figure 2] FIG. 2 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0018] [Figure 3] 3A-3C illustrate the relationship between the radius of curvature and the radius of focus.

[0019] [Figure 4A] Figure 4A illustrates a representation of the accommodation-vergence response of the human visual system.

[0020] [Figure 4B]FIG. 4B illustrates an example of different accommodation and convergence states of a pair of a user's eyes.

[0021] [Figure 4C] FIG. 4C illustrates an example of a top-down view representation of a user viewing content through a display system.

[0022] [Figure 4D] FIG. 4D illustrates another example of a top-down view representation of a user viewing content through a display system.

[0023] [Figure 5] FIG. 5 illustrates aspects of an approach for simulating three-dimensional images by correcting for wavefront divergence.

[0024] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0025] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0026] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0027] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each including an internal coupling optical element.

[0028] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0029] [Figure 9C]FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0030] [Figure 9D] FIG. 9D illustrates an example of a wearable display system.

[0031] [Figure 10] FIG. 10 illustrates an example of a light projector system and a cross-sectional view of a waveguide for directing light to a viewer.

[0032] [Figure 11A] 11A and 11B illustrate examples of incoupling of light into a waveguide at different angles of incidence. [Figure 11B] 11A and 11B illustrate examples of incoupling of light into a waveguide at different angles of incidence.

[0033] [Figure 12A] 12A and 12B illustrate an example of the effect of rebouncing incoupling light within a waveguide. [Figure 12B] 12A and 12B illustrate an example of the effect of rebouncing incoupling light within a waveguide.

[0034] [Figure 13] 13A-13C depict examples of waveguide stacks and constituent waveguides illustrating the distribution of rebounces within waveguides positioned beyond the focal length of a corresponding projection optics system.

[0035] [Figure 14] 14A-14B illustrate a truncated embodiment of an internal coupling optical element within an exemplary waveguide.

[0036] [Figure 15] FIG. 15 illustrates a top-down view of an exemplary arrangement of internal coupling optical elements within a waveguide stack.

[0037] [Figure 16] 16 and 17 illustrate examples of improved incoupling efficiency due to truncation of the incoupling optical element. [Figure 17] 16 and 17 illustrate examples of improved incoupling efficiency due to truncation of the incoupling optical element.

[0038] [Figure 18] 18A and 18B depict examples of waveguides and waveguide stacks with transmissive incoupling optical elements.

[0039] [Figure 19A] FIG. 19A shows a schematic cross-sectional side view of a reflective layer deposited over a pattern of protrusions, according to some embodiments.

[0040] [Figure 19B] FIG. 19B shows a schematic cross-sectional side view of a reflective layer deposited over the pattern of protrusions, according to some other embodiments.

[0041] [Figure 19C] FIG. 19C shows a schematic cross-sectional side view of a reflective layer deposited over a pattern of protrusions according to yet another embodiment.

[0042] [Figure 20A] FIG. 20A shows a schematic perspective view of a confined area for forming a reflective layer from a reflective flowable material onto a pattern of protrusions, according to some embodiments.

[0043] [Figure 20B] FIG. 20B shows a schematic cross-sectional side view of the confined area of ​​FIG. 20A for forming a reflective layer from a reflective flowable material over a pattern of protrusions, according to some embodiments.

[0044] [Figure 21A-1] FIG. 21A is a schematic diagram of a "Type 1" reaction for forming a silver layer using a metallic ink. [Figure 21A-2] FIG. 21A is a schematic diagram of a "Type 1" reaction for forming a silver layer using a metallic ink.

[0045] [Figure 21B] FIG. 21B is a schematic diagram of a "Type 2" reaction for forming a silver layer using a metallic ink.

[0046] [Figure 21C] FIG. 21C is a schematic diagram of a "Type 3" reaction for forming a silver layer using silver ion reduction, according to some embodiments.

[0047] [Figure 22A] FIG. 22A is an electron microscope photograph of a silver layer formed by a metallic ink.

[0048] [Figure 22B] FIG. 22B is an electron microscope image of another silver layer formed by metallic ink.

[0049] [Figure 22C] FIG. 22C is an electron micrograph of a reflective layer formed using silver ion reduction, according to some embodiments.

[0050] [Figure 22D] FIG. 22D is an electron micrograph of a tape peel test of the silver layer formed by the metallic ink.

[0051] [Figure 22E] FIG. 22E is an electron micrograph of another tape peel test of a silver layer formed by a metallic ink.

[0052] [Figure 22F] FIG. 22F is an electron micrograph of a tape peel test of a silver layer formed using silver ion reduction, according to some embodiments.

[0053] [Figure 23] FIG. 23 is a graph showing the reflectivity (%) of a silver layer formed using silver ion reduction, an aluminum layer formed by vapor deposition, and a reflective layer formed from silver ink.

[0054] [Figure 24] FIG. 24 is a graph showing the stability of silver layers formed using silver ion reduction and aluminum layers formed by vapor deposition.

[0055] [Figure 25] FIG. 25 is a flow diagram illustrating a method of fabricating an optical waveguide structure as described herein. DETAILED DESCRIPTION OF THE INVENTION

[0056] An AR and / or VR system may display virtual content to a user, i.e., a viewer. Preferably, this content is displayed on a head-mounted display, e.g., as part of eyewear, that projects image information to the user's eyes. In addition, if the system is an AR system, the display may also transmit light from the user's surroundings to the eyes, allowing a view of the surroundings. As used herein, it should be understood that a "head-mounted" or "head-mountable" display is a display that can be mounted on the viewer's or user's head.

[0057] In some display systems, multiple waveguides making up a waveguide stack may be configured to form a virtual image at multiple virtual depth planes (also referred to herein simply as "depth planes") that are perceived as being at different distances away from the user. In some embodiments, different waveguides in a waveguide stack may have optical structures that provide different refractive powers, simulating 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, a waveguide optical structure to provide refractive power, the display system may also include multiple lenses that provide, or in addition to, refractive power. Light from an image source may be directed toward the waveguides and in-coupled into the individual waveguides by an in-coupling optical element in each waveguide. The in-coupling optical element may be a diffractive optical element, such as a grating.

[0058] In some embodiments, the systems and methods described herein include an internal coupling optical element configured to improve the internal coupling efficiency and / or uniformity of the internally coupled light by reducing the occurrence of light loss due to rebouncing of the internally coupled light. Rebouncing occurs when internally coupled light propagating along a waveguide strikes the internal coupling optical element a second or subsequent time after the initial internal coupling incident. As will be explained in more detail, rebouncing can result in some of the internally coupled light being undesirably outcoupled and / or absorbed by the material of the internal coupling optical element. The outcoupling and / or absorption can undesirably reduce the overall internal coupling efficiency and / or uniformity of the 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 light loss due to rebouncing of internally coupled light within a waveguide. In response to internal coupling of incident light, the diffractive optical element may redirect the light so that it generally propagates through the waveguide in the propagation direction. In some cases, rebouncing of internally coupled light occurs in the propagation direction toward a side of the internal coupling optical element. For example, some incident light that is initially internally coupled near the opposite side (opposite the propagation direction) of the internal coupling optical element may rebounce, i.e., strike the internal coupling optical element again after reflecting from another surface of the waveguide. Without being limited by theory, in response to striking the internal coupling optical element, some of the incident light may again be undesirably outcoupled by the optical element and / or absorbed by the optical element (e.g., absorbed by a reflective coating on the diffraction grating if the internal coupling optical element is a reflective diffractive optical element).

[0060] In some embodiments, the internal coupling optical element is truncated on the propagation direction side of the optical element to reduce light loss due to rebouncing. Advantageously, truncation can reduce the occurrence of light loss caused by rebouncing by reducing the available area of ​​the internal coupling optical element where rebouncing is likely to result in undesired light loss. In some embodiments, truncation can be complete truncation of all structures of the internal coupling optical element; for example, truncation can involve a reduction in the area of ​​the internal coupling optical element in the direction of light propagation. In some other embodiments where the internal coupling optical element comprises a reflective coating (e.g., a reflective layer such as a metal layer), a portion of the internal coupling optical element on the propagation direction side can be uncoated, such that the portion of the optical element on the propagation direction side absorbs little rebouncing light and / or outcouples it with lower efficiency. In some embodiments, as seen in the top and bottom views, the diffractive region of the in-coupling optical element may have a width along the propagation direction that is shorter than its length perpendicular to the propagation direction, may have a smaller width-to-length ratio relative to the non-truncated diffractive region, and / or may be sized and shaped so that a first portion of a beam of light from the projection optics is incident on the diffractive region and a second portion of the beam of light impinges on the waveguide without being incident on the diffractive region (e.g., a portion of the optical element with high absorption and / or out-coupling efficiency is preferably smaller in size than the area created by the incident beam of light on the waveguide). In some embodiments, the amount of truncation varies from waveguide to waveguide across a stack of waveguides. For example, the width-to-length ratio of the in-coupling optical element of each waveguide may vary between different waveguides of the stack of waveguides.

[0061] Waveguides may use optical elements to incouple external light and / or redirect light propagating within the waveguide in a desired direction. For example, optical elements may take the form of diffraction gratings and / or faceted features. Some optical elements may operate in a reflective mode, where light incident on the optical element from one or more angles is both reflected and redirected to propagate away from the optical element at a different desired angle. As disclosed herein, such waveguides may form part of display systems, such as augmented reality and virtual reality display systems. For example, waveguides may be configured to incouple light containing image information and then disperse and outcouple that light to a user. Exemplary waveguides and optical elements will be discussed in more detail herein. Reflective optical elements may include reflective layers formed by wet chemistry, which may advantageously provide greater 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 a user's eyes are spaced apart and viewing a real object in space, each eye may have a slightly different view of the object, forming an image of the object at a different location on each eye's retina. This may be referred to as binocular disparity and may be utilized by the human visual system to provide the perception of depth. Conventional display systems simulate binocular disparity by presenting two distinct images 190, 200, one for each eye 210, 220, with slightly different views of the same virtual object, corresponding to the view of the virtual object as it would appear by each eye as if it were a real object at a desired depth. These images provide binocular cues that the user's visual system interprets to derive the perception of depth.

[0064] Continuing with reference to FIG. 2 , the images 190, 200 are spaced from the eyes 210, 220 by a distance 230 on the z-axis. The z-axis is parallel to the optical axis of the viewer when the eyes are fixating on an object at optical infinity directly in front of the viewer. The images 190, 200 are flat and at a fixed distance from the eyes 210, 220. Based on slightly different views of the virtual object in the images presented to each eye 210, 220, the eyes may necessarily rotate so that the image of the object falls on a corresponding point on each eye's retina, maintaining single binocular vision. This rotation may cause the gaze of each eye 210, 220 to converge on a point in space where the virtual object is perceived to reside. As a result, providing three-dimensional images traditionally involves manipulating the convergence and divergence of the user's eyes 210, 220 and providing binocular cues that the human visual system interprets to provide the perception of depth.

[0065] However, creating a realistic and comfortable perception of depth is challenging. It should be understood that light from an object at different distances from the eye has a wavefront with different amounts of divergence. Figures 3A-3C illustrate the relationship between distance and light ray divergence. The distance between the object and the eye 210 is represented in the order of decreasing distances R1, R2, and R3. As shown in Figures 3A-3C, light rays become more divergent as the distance to the object decreases. Conversely, as the distance increases, light rays become more collimated. In other words, the light field generated by a point (an object or portion of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. While only a single eye 210 is illustrated in Figures 3A-3C and various other figures herein for clarity of illustration, the discussion regarding the eye 210 may apply to both eyes 210 and 220 of the viewer.

[0066] Continuing with reference to Figures 3A-3C, light from an object that a viewer's eyes are fixating may have different wavefront divergences. Due to the different wavefront divergences, the light may be focused differently by the eye's lens, which in turn may require the lens to assume a different shape to form a focused image on the eye's retina. If a focused image is not formed on the retina, the resulting retinal blur acts as an accommodative cue, causing the shape of the eye's lens to change until a focused image is formed on the retina. For example, the accommodative cue may trigger relaxation or contraction of the ciliary muscles surrounding the eye's lens, thereby modulating the force applied to the lower ligament that holds the lens, thus changing the shape of the eye's lens and forming a focused image of the fixated object on the eye's retina (e.g., fovea) until retinal blur of the fixated object is eliminated or minimized. 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 an object being gazed at on the eye's retina (e.g., the fovea) can be referred to as the state of accommodation.

[0067] Referring now to Figure 4A, a representation of the accommodation-vergence response of the human visual system is illustrated. Eye movements to gaze at an object cause the eye to receive light from the object, which forms an image on each of the eye's retinas. 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 vergence. Accommodative cues cause accommodation, resulting in the eye's lens adopting a specific accommodation state in which a focused image of the object is formed on the eye's retina (e.g., the fovea). Conversely, vergence cues cause vergence movements (eye rotations) so that the images formed on each retina of each eye are at corresponding retinal points, maintaining single binocular vision. In these positions, the eyes can be said to adopt a specific vergence state. Continuing with reference to FIG. 4A , accommodation can be understood as the process by which the eye achieves a particular accommodation state, and convergence can be understood as the process by which the eye achieves a particular convergence state. As shown in FIG. 4A , the accommodation and convergence states of the eye can change when the user gazes at a different object. For example, the accommodated state can change when the user gazes at a new object at a different depth on the z-axis.

[0068] Without being limited by theory, it is believed that a viewer of an object may perceive the object as "three-dimensional" due to a combination of convergence and accommodation. As previously mentioned, vergence movement of the two eyes relative to one another (e.g., rotation of the eyes such that the pupils move toward or away from one another, converging the eyes' lines of sight and fixating on an object) is closely linked to accommodation of the eye's lenses. Under normal conditions, changing the shape of the eye's lenses and shifting focus from one object to another at a different distance will automatically produce a corresponding change in vergence to the same distance, a relationship known as the "accommodation-vergence reflex." Similarly, a change in vergence will trigger a corresponding change in lens shape under normal conditions.

[0069] 4B, an example of different accommodation and convergence states of the eyes is illustrated. Paired eye 222a gazes at an object at optical infinity, while paired eye 222b gazes at object 221 at less than optical infinity. Notably, the convergence states of each pair of eyes are different: paired eye 222a is pointed straight ahead, while paired eye 222 converges on object 221. The accommodation states of the eyes forming each pair of eyes 222a and 222b are also different, as represented by the different shapes of lenses 210a, 220a.

[0070] Unfortunately, many users of conventional "3-D" display systems may find such systems uncomfortable or may not perceive any depth perception due to a mismatch between accommodation and convergence states in these displays. As previously mentioned, many stereoscopic or "3-D" display systems display a scene by providing a slightly different image to each eye. Such systems are uncomfortable for many viewers because, among other things, they simply provide different presentations of a scene, causing changes in the eyes' convergence states without corresponding changes in the eyes' accommodation states. Rather, images are presented by the display at a fixed distance from the eyes so that the eyes view all image information in a single accommodation state. Such an arrangement counters the "accommodation-vergence-divergence reflex" by causing changes in the convergence states without a corresponding change in the accommodation state. This mismatch is believed to cause viewer discomfort. Display systems that offer better alignment between accommodation and convergence-divergence movements may create a more realistic and comfortable simulation of three-dimensional images.

[0071] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth may be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both vergence cues and matching cues for accommodation, thereby providing physiologically correct accommodation-vergence divergence matching.

[0072] 4B , two depth planes 240 are illustrated, corresponding to different distances in space from the eyes 210, 220. For a given depth plane 240, vergence-divergence cues may be provided by displaying appropriately different perspective images for each eye 210, 220. Additionally, for a given depth plane 240, the light forming the image provided to each eye 210, 220 may have a wavefront divergence corresponding to the 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 meter. As used herein, distance or depth along the z-axis may be measured with a zero point located at the exit pupil of the user's eye. Thus, depth plane 240 located at a depth of 1 meter corresponds to a distance of 1 meter away from the exit pupil of the user's eye on the optical axis of the eye with the eye pointed toward optical infinity. As an approximation, the depth or distance along the z-axis may be measured from a display (e.g., the surface of a waveguide) in front of the user's eye, and a value for the distance between the device and the exit pupil of the user's eye may be added. That value may be referred to as pupil distance and may correspond to the distance between the exit pupil of the user's eye and a display worn by the user in front of the eye. In practice, the value for pupil distance may be a normalized value generally used for all viewers. For example, pupil distance may be assumed to be 20 mm, and the depth plane at a depth of 1 meter may be at a distance of 980 mm in front of the display.

[0074] 4C and 4D, examples of matched accommodation-vergence-divergence distances and mismatched accommodation-vergence-divergence distances are illustrated, respectively. As illustrated 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 convergence-divergence state in which the eyes converge on point 15 on the depth plane 240. In addition, the image may be formed by light having a wavefront curvature corresponding to the real object on that depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the image is focused on the retinas of those eyes. Thus, the user may perceive the virtual object as being at point 15 on the depth plane 240.

[0075] It should be understood that the accommodation and convergence 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 will cause those eyes to assume a particular accommodation state based on the distance of the object. The distance associated with a particular accommodation state is referred to as the accommodation distance A. d Similarly, a particular convergence-divergence distance V associated with the eyes in a particular convergence-divergence state can be d Or there exists a position relative to each other. When the accommodation distance and the convergence distance match, the relationship between accommodation and convergence is said to be physiologically correct. This is considered to be the most comfortable scenario for the viewer.

[0076] However, in a stereoscopic display, the accommodation distance and the convergence distance may not always be aligned. For example, as illustrated in FIG. 4D , images displayed to the eyes 210, 220 may be displayed with a wavefront divergence corresponding to the depth plane 240, and the eyes 210, 220 may be in a particular accommodation state in which points 15a, 15b on that depth plane are in focus. However, the images displayed to the eyes 210, 220 may provide convergence cues that cause the eyes 210, 220 to converge on a point 15 that is not located on the depth plane 240. As a result, in some embodiments, the accommodation distance corresponds to the distance from the exit pupils of the eyes 210, 220 to the depth plane 240, while the convergence distance corresponds to the greater distance from the exit pupils of the eyes 210, 220 to point 15. The accommodation distance is different from the convergence distance. As a result, there is an accommodation-vergence-divergence mismatch. Such a mismatch is considered undesirable and can cause discomfort to the user. The mismatch can be caused by distance (e.g., V d -A d ) and can be characterized in terms of diopters.

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

[0078] Without being limited by theory, it is believed that a user may still perceive physiologically correct accommodation-vergence-divergence mismatches of up to 0.25 diopters, up to 0.33 diopters, and up to about 0.5 diopters without the mismatch itself causing significant discomfort. In some embodiments, a display system disclosed herein (e.g., display system 250, FIG. 6 ) presents a viewer with images having an accommodation-vergence-divergence mismatch of 0.5 diopters or less. In some other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is about 0.33 diopters or less. In still other embodiments, the accommodation-vergence-divergence mismatch of images provided by the display system is 0.25 diopters or less, including about 0.1 diopters or less.

[0079] FIG. 5 illustrates aspects 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 a user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of a 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. In addition, the user's other eye will 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 wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light over a limited range of wavelengths. Consequently, in some embodiments, multiple or stacked waveguides may be utilized to provide different wavefront divergences for different depth planes and / or output light over different ranges of wavelengths. As used herein, it will be understood that a depth plane may be a planar surface or may follow the contours of a curved surface. One or more waveguides in the stack may comprise a reflective diffractive optical element, as described herein, comprising a reflective layer comprising, consisting essentially of, or consisting of a pure or substantially pure metal.

[0081] 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple 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 convergence and multiple discrete cues for accommodation. The cues for convergence may be provided by displaying different images to each of the user's eyes, and the cues for accommodation may be provided by outputting light forming images with selectable discrete amounts of wavefront divergence. In other words, display system 250 may be configured to output light with variable levels of wavefront divergence. In some embodiments, each discrete level of wavefront divergence corresponds to a particular depth plane and may be provided by a particular one of waveguides 270, 280, 290, 300, and 310.

[0083] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple 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 configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across each individual waveguide for output toward the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each input surface 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0084] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic 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, light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter such as a light emitting diode (LED). Light from the light module 530 may be directed and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically, and in some embodiments, these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of waveguide assembly 260 may function as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540, and the image may be an image on a depth plane.

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

[0087] Controller 560 controls the operation of one or more of stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 530, and light modulator 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 contains programming (e.g., instructions in a non-transitory medium) that coordinates 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 integrated device or a distributed system connected by wired or wireless communication channels. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 9D).

[0088] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). The waveguides 270, 280, 290, 300, and 310 may each be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, and 310 may each include outcoupling optical elements 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupling light, and the outcoupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as discussed further herein. While shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be monolithic pieces of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0089] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 280 as emerging from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as originating from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0090] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active 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, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0092] Continuing with reference to FIG. 6 , the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with that waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling 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-extracting optical elements 570, 580, 590, 600, 610 may be volume or surface features, which may be configured to output light at specific angles. For example, the light-extracting optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0093] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues traveling through the waveguide via TIR. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a fairly uniform pattern of output emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

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

[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 tissue surrounding the eye 210, for example, to detect user input and / or monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 (FIG. 9D) and may be in electrical communication with processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized per eye, monitoring each eye separately.

[0096] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 260 (FIG. 6) may function similarly, and that waveguide assembly 260 includes multiple waveguides. Light 640 is launched into waveguide 270 at input surface 460 of waveguide 270 and propagates within waveguide 270 by TIR. At the point where light 640 impinges on DOE 570, a portion of the light exits the waveguide as output beam 650. Output beam 650 is illustrated as being approximately parallel, but may be redirected to propagate to eye 210 at an angle (e.g., divergent output beam formation), as discussed herein, and depending on the depth plane associated with waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0097] In some embodiments, a full-color image may be formed at each depth plane by overlaying an image in each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for different primary colors may be varied to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberrations.

[0098] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, resulting in three primary color images per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

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

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

[0101] In some embodiments, the light source 530 ( FIG. 6 ) may be configured to emit light at one or more wavelengths outside the viewer's visual perception range, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide in-coupling, out-coupling, and other light redirecting structures of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications. In some embodiments, the in-coupling optical elements and / or other light redirecting structures comprise reflective diffractive optical elements comprising a reflective layer including a metal deposited by wet chemistry as described herein. In some embodiments, the reflective layer may be formed from a metal that consists essentially of, or consists of, pure or substantially pure metal formed by wet chemistry as described herein.

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

[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 light input area on the waveguide), for example, internal coupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more internal coupling optical elements are reflective polarizing optical elements). As shown, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguide 670, 680, 690 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the 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. While illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments. In some embodiments, the incoupling optical element and / or other light redirecting structure comprises a reflective diffractive optical element comprising a reflective layer comprising a metal formed by wet chemistry as described herein. In some embodiments, the reflective layer may consist essentially of or consist of a pure or substantially pure metal formed by wet chemistry as described herein.

[0104] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from a different image input device 360, 370, 380, 390, and 400, as shown in FIG. 6 , and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to substantially not receive light from others of the in-coupling optical elements 700, 710, 720.

[0105] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of associated waveguides 670, 680, 690, respectively. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of associated waveguides 670, 680, 690, respectively, or optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0106] Waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 760a may separate 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 immediately adjacent waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or greater, or 0.10 or less, than 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 through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0107] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. 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 differ while still maintaining the various refractive index relationships discussed above.

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

[0109] In some embodiments, light rays 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

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

[0111] 9A , the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the in-coupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690, in-coupling the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the waveguide's corresponding optical dispersive element 730, 740, 750.

[0112] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, in-coupled light rays 770, 780, 790 are deflected by in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within waveguides 670, 680, 690, respectively. Light rays 770, 780, 790 then impinge on optically dispersive elements 730, 740, 750, respectively. Optically dispersive elements 730, 740, 750 deflect light rays 770, 780, 790 to propagate toward out-coupling optical elements 800, 810, 820, respectively.

[0113] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light into the out-coupling optical elements 800, 810, 820, and in some embodiments, may also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted, and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly into the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A , the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light toward the viewer's eye 210 ( FIG. 7 ). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and that the EPE may increase the eyebox in an axis that intersects the axis of the OPE, e.g., orthogonal to the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE of the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. Upon striking the OPE, again, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further down the waveguide, etc. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide toward the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes an EP, at which point another portion of the impinging light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0114] 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optically dispersive elements (e.g., OPEs) 730, 740, 750, and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light into that waveguide (with different in-coupling optical elements receiving different wavelengths of light). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues bouncing down the waveguide, interacting with the optically dispersive element (e.g., OPE) 730 and then the out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through the waveguide 670, with light ray 780 impinging on and being deflected by the in-coupling optical element 710. Light ray 780 will then, via TIR, bounce down the waveguide 680, to its optically dispersive element (e.g., OPE) 740 and then the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through the waveguide 690 and impinges on the optically in-coupling optical element 720 of the waveguide 690. The light in-coupling optical element 720 deflects the light ray 790 so that it propagates by TIR to the light dispersive element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light ray 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0115] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned, along with each waveguide's associated optically dispersive elements 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted-pupil systems, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0116] 9D illustrates an example of a wearable display system 60 into which the various waveguide and associated systems disclosed herein may be integrated. In some embodiments, the display system 60 is the system 250 of FIG. 6, which diagrammatically illustrates some portions of the system 60 in greater detail. For example, the waveguide assembly 260 of FIG. 6 may be part of the display 70.

[0117] Continuing with reference to FIG. 9D , display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 directly in front of the user's 90's eye. The display 70, in some embodiments, may be considered an eyepiece. In some embodiments, a speaker 100 is coupled to frame 80 and configured to be positioned adjacent to the user's 90 ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). Display system 60 may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphones are configured to allow a user to provide input or commands to system 60 (e.g., voice menu command selections, natural language queries, etc.) and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include an ambient sensor 120a, which may be separate from the frame 80 and mounted on the body of the user 90 (e.g., the head, torso, limbs, etc. of the user 90). The ambient sensor 120a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 90. For example, the sensor 120a may be an electrode.

[0118] 9D , display 70 is operably coupled to local data processing module 140 by a communication link 130, such as wired or wireless connectivity, which may be mounted in a variety of configurations, such as fixedly attached to frame 80, fixedly attached to a helmet or hat worn by the user, embedded within headphones, or otherwise removably attached to user 90 (e.g., in a backpack-style configuration, in a belt-linked configuration). Similarly, sensor 120a may be operably coupled to local data processing module 140 by a communication link 120b, such as wired or wireless connectivity. Local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. Optionally, local processor and data module 140 may include one or more processing units (CPUs), graphics processing units (GPUs), dedicated processing hardware, etc. The data includes a) data captured from sensors (such as image capture devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (which may be operatively coupled to frame 80 or otherwise attached to user 90, for example) and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for passage to display 70 after processing or retrieval. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140.In some embodiments, local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on frame 80 or may be a freestanding structure that communicates with local processing and data module 140 by a wired or wireless communication path.

[0119] 9D , in some embodiments, remote processing module 150 may comprise 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, remote data repository 160 may comprise digital data storage facilities that may be available through the Internet or other networking configurations in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all computations are performed within the local processing and data module, allowing for fully autonomous use from the remote module. Optionally, an external system (e.g., one or more processors, one or more computer systems), 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, e.g., via a wireless or wired connection.

[0120] Exemplary Light Projector Systems 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 to a viewer's eye 210. As discussed herein, multiple light emitters 2020 (e.g., multiple LEDs) may be used to illuminate a spatial light modulator (SLM) 2030. The light emitters 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 emitters 2020 to the spatial light modulator 2030, which reflects and modulates the light. The modulated light 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 waveguide of the eyepiece 2010 relays or guides the light and outputs 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, light propagating through the projection optics may converge onto an 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 multiple light emitters 2020 that emit light in different wavelength ranges that correspond to different colors. Different sets of the multiple light emitters 2020 (e.g., light emitters 2020a, 2020b, 2020c) may emit light in different wavelength ranges, and a set of light emitters includes 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 to form a full-color image.

[0122] The perception of a full-color image by a viewer may be achieved in some embodiments 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 forming a single full-color image may be displayed quickly enough 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 displayed sequentially may be higher than the perceptual persistence of the human visual system. In some embodiments, different primary color images are displayed sequentially at a rate greater than 60 Hz. It should be appreciated 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 primary color images forming the full-color image may be displayed simultaneously.

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

[0124] As disclosed herein, the eyepiece 2010 may include multiple waveguides, one for each of multiple colors. Each waveguide may, in some embodiments, couple desired light from a corresponding light emitter in and relay it to the eye through the use of diffractive optics (e.g., a diffraction grating). In addition, the diffractive optics may direct light through the waveguides and also couple light out of the waveguides. The waveguides, as discussed herein, may have optical power that causes the light to appear to originate from a given depth or distance to the viewer upon relay to the eye (see, e.g., Figures 6-9C and related discussion).

[0125] Exemplary Incoupling Optical Elements As explained above, after being incoupling by an incoupling optical element, light may undergo rebouncing, which may undesirably result in light loss due to, for example, unwanted outcoupling or absorption of light in the incoupling optical element. Light loss due to rebouncing of incoupling light may effectively reduce the net efficiency of the incoupling optical element.

[0126] 11A and 11B illustrate examples of light being incoupling into the waveguide 1110 at different angles of incidence at the outer portion of the incoupling optical element 1100 (positioned away from the propagation direction of the incoupling light). As mentioned above, the different angles of incidence may result from the convergence of light from the light projection system onto the waveguide 1110. FIG. 11A depicts the path of an incident beam 11201 that enters the incoupling optical element 1100 at a generally inward angle (e.g., an angle toward the propagation direction 1112 in the waveguide, also referred to as a "temple" angle). FIG. 11B depicts the path of an incident beam 11202 that enters the waveguide at a generally outward angle (e.g., an angle away from the propagation direction 1112 in the waveguide, also referred to as a "nose" angle). In operation, a beam of light entering the waveguide 1110 from the projection optics may be a converted or diverging beam that includes an inwardly angled component and an outwardly angled component. That is, the beam may converge toward a focal point and then diverge. For example, the beam may diverge when the waveguide 1110 is positioned beyond the focal length of the projection optics, as will be described in more detail with reference to Figures 13A-13C.

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

[0128] Rebouncing can occur when light is incoupled at the second major surface of the waveguide 1110, internally reflected from the first major surface, and incident on the incoupling optical element 1100, or experiences a second bounce there. As shown in Figure 11A, a beam 11201 incident on the incoupling optical element 1100 at an inward angle typically experiences little or no rebouncing 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 Figure 11B, a beam 11202 incident on the incoupling optical element 1100 at an outward angle has a relatively smaller bounce spacing 11272 and therefore may be more likely to experience rebouncing.

[0129] Without being limited by theory, it should be understood that diffractive optical elements may behave symmetrically. That is, they may redirect incident light so that it propagates through the waveguide at a TIR angle. However, light incident on a diffractive optical element at a TIR angle (such as upon rebounce) may also be outcoupled. Additionally, or alternatively, it should be understood that reflection of light from a layer of material, such as metal, may also involve partial absorption of the incident light, since reflection may involve absorption and emission of light from the material. As a result, outcoupling and / or absorption of light may undesirably result in loss of incoupled light, and the rebounced light may suffer significant loss compared to light that interacts only once with the incoupling optical element.

[0130] 12A and 12B further illustrate this optical loss. FIG. 12B illustrates an example of the energy profile of a beam incoupling within waveguide 1110 of FIG. 12A at location 1115 along waveguide 1110. Beam 11201, incident at an inward or temple angle, is unlikely to experience a substantial amount of rebouncing, effectively resulting in a relatively high efficiency of incoupling and a substantially uniform beam profile. In contrast, beam 11202, incident at an outward or nasal angle, is likely to experience a substantial amount of rebouncing, resulting in optical loss within the waveguide after the initial incoupling. Additionally, as shown in FIG. 12B , inner or propagating portions of the outward angle beam 11202 (e.g., portions of the beam 11202 closer to the propagation direction 1112) may experience fewer rebouncings, while outer portions of the beam 11202 away from the propagation direction 1112 may experience more rebouncing, resulting in additional light loss and inconsistent net in-coupling efficiency across the beam profile. If the in-coupled light is used to form an image or part of an image, the light loss due to rebouncing may therefore irregularly reduce the brightness in some portions of the image formed using that light. Furthermore, if a display system includes individual waveguides and in-coupling gratings for red, green, and blue light, such reduced efficiency and / or non-uniformity within any of the waveguides may result in reduced color accuracy, including a reduced ability to reliably produce white light or other colors that require a combination of red, green, and / or blue light.

[0131] The occurrence of rebouncing can also depend, at least in part, on the distance between the waveguide and the incident light source. Figures 13A-13C depict an example of a waveguide stack 1105 illustrating the distribution of rebouncing within waveguides positioned beyond the focal length of the corresponding projection optics. As shown in Figure 13A, the waveguide stack 1105 includes waveguides 1110a, 1110b, and 1110c positioned a distance from the projection optics 2000. Each waveguide 1110a, 1110b, 1110c includes an internal coupling optical element 100a, 1100b, 1100c, respectively, positioned along a major surface of the waveguide 1110a, 1110b, 1110c that is farther from the projection optics 2000. The incoupling optical elements 1100a, 1100b, 1100c incoupling light from the projection optics 2000, which is outcoupled as outcoupled light 1130 within the wearer's field of view.

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

[0133] 13B and 13C are enlarged partial views of the system of FIG. 13A illustrating the propagation of light from the display optics 2000 in waveguide 1110a (FIG. 13C) and waveguide 1110c (FIG. 13B). As shown in FIG. 13C, rebouncing may not be a substantial concern with waveguides positioned closer to the focal length from the projection optics 2000. Because the light from the projection optics 2000 is still a converging beam before reaching the focal point, the outwardly angled beam 11202 component is incident on an inner portion of the internal coupling optical element 1100a (e.g., a portion of the internal coupling optical element 1100a on the side of the propagation direction 1112), while the inwardly angled beam component 11201 is incident on an outer portion of the internal coupling optical element 1100a (e.g., a portion of the internal coupling optical element 1100a positioned opposite the propagation direction 1112). Thus, the relatively short bounce interval of the incoupled outwardly angled beam 11202 is long enough for the incoupled light to still propagate past the side of the incoupling 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 incoupled inwardly angled beam 11201 is long enough to avoid any re-bouncing of the inwardly angled beam 11201.

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

[0135] 14A and 14B illustrate an example of truncating an internal coupling optical element to reduce light loss due to rebouncing within an exemplary waveguide. FIGS. 14A and 14B illustrate a single waveguide 1110c positioned beyond the focal length of the projection optical system 2000. The focal point is indicated by the internal coupling optical element 1100b, while the waveguides 1110a and 1110b are omitted from FIGS. 14A and 14B for convenience. The configuration of FIG. 14A is substantially identical to the configuration of the waveguide 1110c and internal coupling optical element 1100c in FIG. 13A. FIG. 14B illustrates the waveguide 1110c with a truncated internal coupling optical element 1100c.

[0136] 14B is sized, shaped, and positioned such that at least an inner portion 11221 of light from the projection optical system 2000 is incident on the waveguide 1110c but not on the in-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 diffractive region of the in-coupling optical element 1100c may occupy less than all of the light beam area. In general, the truncated in-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 light from the projection optical system 2000. For example, the truncated in-coupling optical element 1100c may be radially asymmetric and / or reflectively asymmetric about an axis of symmetry perpendicular to the propagation direction 1112 of the beam axis. In some embodiments, the in-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 in-coupled. In some other embodiments, such as embodiments in which the in-coupling optical element 1100c comprises an in-coupling grating with a metallized surface, the inner portion of the in-coupling optical element 1100c may not be metallized, so that re-bounces of the in-coupled light at the inner portion will not be absorbed or out-coupled as easily as if the inner portion were metallized. Thus, with the truncated in-coupling optical element 1100c, at least a portion of the inwardly angled beam component 11201 may not be in-coupled or may be in-coupled less efficiently relative to the rest of the light from the projection optical system 2000. However, the truncation of the incoupling optical element 1100 c also reduces the length along which re-bounce can occur for the incoupling outward angled beam component 11202 .Thus, despite experiencing some loss of some angles of incoupled light (i.e., some light from some angles is not incoupled, as shown in FIG. 14B), the truncated incoupling optical element 1100c may provide a net increase in incoupling efficiency because the incoupled light experiences no or little rebounce-related outcoupling or absorption. As a result, the amount and uniformity of incoupled light may be improved due to the reduction in rebounces and associated light loss.

[0137] FIG. 15 illustrates a top-down view of an example arrangement of internal coupling optical elements within a waveguide stack. The configuration of FIG. 15 is viewed in a direction along the central beam 11203 of FIG. 13A , which is perpendicular to the major surfaces of the waveguides, and each internal coupling 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 propagation direction 1112. Thus, each internal coupling optical element B1, B2, G1, G2, R1, and R2 has a distinct associated waveguide. The internal coupling optical elements B1, B2, G1, and G2 may be positioned on waveguides located at or near the focal length of the projection optics, while the internal coupling optical elements R1 and R2 are positioned on waveguides located beyond the focal length of the projection optics. Thus, the internal coupling optical elements R1 and R2 are truncated to reduce rebouncing, as described above. In some embodiments, the truncated regions 1140 of the in-coupling optical elements R1 and R2 may comprise open spaces that allow light incident thereon to pass through the corresponding waveguides without being in-coupling. In other embodiments, the optical elements R1 and R2 may comprise high-efficiency in-coupling regions 1145 (e.g., portions that are metalized or coated with a reflective layer such as a metal layer), while the truncated regions 1140 are not metallized to reduce losses due to re-bouncing that occurs within the truncated regions 1140.

[0138] Continuing with reference to FIG. 15 , as described herein, the internal coupling optical elements B1, B2, G1, G2, R1, and R2 are each positioned on a different associated waveguide. In some embodiments, light from the projection optics may strike these optical elements from above, e.g., normal to the page. Preferably, the optical elements are positioned so that they do not block the propagation of light from the projection optics to each individual optical element. For example, the optical elements are arranged so that the optical elements for the waveguides in front of the focal point of the projection optics are spaced laterally, as seen in a top-down view (from the perspective of the projection optics). Such an arrangement prevents the converging beam of light from being blocked. The optical elements for the waveguides behind the focal point will receive a 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 therefore may not be blocked by the slight overlap with the optical elements in front of them.

[0139] Additionally, it should be understood that outcoupling of light due to light leakage and / or rebouncing out of the waveguide can result in the leaked or outcoupled light impinging on other incoupling optical elements. For example, rebouncing light outcoupled from optical element G1 could potentially impinge on optical elements “downstream” of optical element G1 in the propagation direction 1112. For example, light leaked or outcoupled from optical element G1 could impinge on R1 and B1. It should be understood that crosstalk and image degradation could occur if R1 or B1 incoupled the outcoupled light of G1. Advantageously, the optical gratings may be configured to be selective with respect to the wavelength of light they incouple, such that R1 and B1 do not incouple incident light outcoupled from G1. However, G2 could incouple such light if it were downstream of G1. As a result, preferably the incoupling optical elements are arranged such that an optical element for incoupling light of a particular wavelength is not downstream of an optical element configured to incoupling 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 overall width of the in-coupling optical element. In some embodiments, the nominal (non-truncated) dimensions of the in-coupling optical element may be regular or approximately regular (e.g., the width of the in-coupling optical element parallel to the direction of propagation in the waveguide may be within 85%, 90%, 95%, 100%, 105%, etc., of the length of the in-coupling optical element perpendicular to the direction of propagation). Thus, a truncated in-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 in-coupling optical element, where the width extends parallel to the direction of propagation and the length is perpendicular to the direction of propagation. 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 be entirely removed, or may constitute a portion of the internal coupling optical element that 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, with the metal coating covering only the smaller, truncated dimension of the element, while the truncated portion remains unmetallized, i.e., less than the entire area of ​​the diffraction grating may be metallized in some embodiments.

[0141] 16 and 17 depict experimental results of truncating the in-coupling optical element in a configuration similar to FIG. 15 and illustrate the enhanced effective in-coupling efficiency due to the truncation of the in-coupling optical element. As explained above, truncating the inner portion of the in-coupling optical element beyond the focal length of the projection optical system can result in a net improvement in in-coupling efficiency because the increased efficiency due to reduced light loss due to re-bouncing can outweigh the loss in efficiency due to not in-coupling the innermost portion of light from the projection optical system (or in-coupling the innermost portion with lower efficiency). Thus, the amount of truncation may be selected to provide a desired balance between the reduced light loss due to re-bouncing and the initial in-coupling loss due to the truncation.

[0142] While the foregoing description and Figures 11A-14B generally refer to incoupling of light using a reflective diffractive optical element, it should be understood that the systems and methods described for mitigating light loss due to rebouncing can equally be implemented in systems involving transmissive diffractive optical elements. As shown in Figures 18A and 18B, rebouncing can also occur when light is incoupling by a transmissive diffractive optical element 1100c' disposed on a first major surface of a waveguide 1110c. As shown in Figure 18B, an outwardly angled beam 11202 that is redirected into the waveguide 1110c by the transmissive diffractive optical element 1100c' at the first major surface of the waveguide 1110c can be reflected by the second major surface and return to strike the transmissive optical element 1100c' in one or more subsequent rebounces 1135'. Although the transmissive diffractive optical element 1110c' does not have a reflective layer and may not suffer absorption losses caused by absorption by such a reflective layer, the transmissive diffractive optical element 1110c' may have outcoupling losses. Therefore, light loss due to rebouncing can be mitigated in the systems of FIGS. 18A and 18B by truncating the transmissive diffractive optical element 1100c' using any of the techniques disclosed herein, except for techniques using reflective coatings. For example, truncation may involve providing a high-diffraction efficiency region having dimensions and relative width and length ratios as discussed herein, and / or having truncations that vary with distance from the focal point of the waveguide from the projection optical system 2000, as also discussed herein. In some embodiments, FIG. 15 may be understood to show a top-down view of a truncated transmissive diffractive optical element, which may be understood to include optical elements R1 and R2.

[0143] Exemplary Waveguides and Optical Elements with Reflective Layers Reflective optical elements may utilize reflective layers to achieve the desired light reflection. Reflective layers may traditionally be deposited using metallization processes, including vapor deposition of a metal layer. These traditional metallization processes can be time-consuming and involve multiple steps. For example, to direct the metallization to the desired location on the waveguide, it may be necessary to align the waveguide and cover it with a mask to protect areas of the waveguide where metallization is not desired. However, the mask may become contaminated by the metallization and require frequent cleaning. In addition, vapor deposition itself may require a vacuum, which would further complicate and increase the duration of the metallization process by requiring the deposition chamber to be depressurized for deposition and then returned to atmospheric pressure for unloading.

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

[0145] Advantageously, according to some embodiments, reflective layers and structures incorporating such reflective layers (e.g., reflective diffractive optical elements) are provided with superior reflective properties. Some embodiments include optical and display devices having reflective layers, and methods of making optical waveguide structures and optical devices comprising reflective layers. In some embodiments, the reflective layer may be formed on the substrate surface using wet chemistry. The wet chemistry may include a liquid-phase reaction to deposit a layer of reflective material on the substrate surface from precursor species in a flowable material, such as a liquid mixture. In some embodiments, the deposition may leave a solid reflective coating on the substrate surface, with the liquid mixture covering the solid reflective coating. In some embodiments, the residual liquid mixture may be removed, for example, by rinsing.

[0146] In some embodiments, the wet chemistry may include deposition of a metal from a liquid mixture. For example, the metal may be part of a metal compound, and deposition may result from dissociation of the metal from the compound in the liquid mixture. The metal compound may be an ionic compound, such as a metal salt. The ionic compound may dissociate after a chemical reaction with another reagent that may be present in the liquid mixture or otherwise provided for contact with the ionic compound. As an example, the chemical reaction may be metal ion reduction, e.g., silver ion reduction, resulting in the deposition of a pure or substantially pure metal (e.g., silver) on the surface of the waveguide. In some embodiments, the metal deposition may form a reflective layer on predetermined discrete regions of the surface, but not the entire surface. Preferably, the deposition coats the discrete regions on the surface of the waveguide. The discrete regions 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 includes a metal salt (e.g., a silver salt) and a reducing agent that is reactive with the salt, e.g., at a basic pH. In the reaction, the reducing agent reduces the metal salt, causing the metal (e.g., silver) to precipitate and settle onto the substrate surface, forming a reflective layer on the surface of the substrate (e.g., on the surface of a waveguide). Thus, the reflective layer comprises, consists essentially of, or consists of a pure or substantially pure metal (e.g., pure silver or substantially pure silver).

[0148] Advantageously, these reflective layers may exhibit superior optical and physical properties. The reflective layer may have high purity, as described herein. Additionally, the reflective layer may be uniform at nanoscale resolution, such that the reflective layer is free or substantially free of features, such as pinholes, that can reduce reflectivity. Also, unlike directional deposition such as PVD, the reflective layer may conformally coat protruding surfaces, providing 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 contemplated that these advantageous properties, alone or in combination, may provide the reflective layer with reflectivity that exceeds that of layers deposited by other methods, such as PVD or the use of reflective inks. For example, as described herein, some inks exhibit lower reflectivity than reflective metal layers formed by ion reduction. In addition to being generally lower, the reflectivity of layers formed using metal inks is even lower for shorter wavelength light (blue light) in 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 preferably remains stably adhered to the surface of the waveguide without the need for adhesives or binders. In some embodiments, excellent adhesion of the metal is achieved during deposition. That is, excellent adhesion is provided upon metal coating of the substrate 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 a plasma. Another example treatment includes etching the substrate surface and forming an interfacial layer between the substrate and a subsequently deposited metal.

[0150] In some embodiments, a reflective layer is formed over the protrusions, which are diffractive optical elements, e.g., diffraction gratings. The reflective layer and the protrusions together form the reflective diffractive optical element. In some embodiments, the reflective diffractive optical element is part of a waveguide. For example, the reflective diffractive optical element may be an internal coupling optical element configured to angularly redirect incident ambient light such that the light propagates through the waveguide by total internal reflection. In some embodiments, a reflective layer as disclosed herein may 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 the location of a diffractive optical element or a portion of a diffractive optical element. In some embodiments, this confinement may be achieved using physical structures (e.g., walls or weirs) to confine the diffusion of the flowable material. In some other embodiments, confinement may be achieved by treating desired areas of the substrate surface such that the metal in the reflective layer preferentially coats or is retained in those desired areas (e.g., after rinsing). As yet another example, liquid mixtures may be applied to desired areas and may have compositions such that they do not significantly diffuse away from those areas. It should be understood that one or more of these schemes for confining liquid mixtures may be utilized to form a particular reflective layer.

[0152] In some embodiments, after coating a substrate with a metal from a liquid mixture as described herein, residual liquid mixture may be removed, which 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 to provide protection, for example, from chemical species present in the surrounding environment.

[0154] flowable material As discussed herein, a flowable material such as a liquid mixture 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, including alpha-hydroxyaldehydes and / or alpha-hydroxyketones. Examples of such carbohydrate reducing agents include glucose, fructose, or a combination of glucose and fructose.

[0155] In some embodiments, the metal salt and reducing agent of the liquid mixture are reactants for the Tollen 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; therefore, in some embodiments, it is contemplated that the compositions comprising the liquid mixture may be prepared immediately prior to or at the time of use. Some commercially available products may also provide suitable reactants for some embodiments, such as metal solutions sold by Peacock Laboratories (West Chester, PA) and Transene Co, Inc. (Danvers, MA).

[0156] In some embodiments, the liquid mixture may include both a metal salt and a reducing agent that are premixed before depositing the liquid mixture onto a substrate, hi 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 comprises one or more of a pH modifier, a stabilizer, a surfactant, a catalyst, and a viscosity adjusting component. In some embodiments, the liquid mixture comprises a 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, including 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 chemical species react with each other at a basic pH such that the reducing agent reduces the metal salt and precipitates the metal. Thus, the liquid mixture may further include a base. In some embodiments, the liquid mixture has a basic pH, e.g., a pH greater than 7, or greater than 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, including a pH range between any two of the recited values, or a range between any of the recited values ​​and 14, e.g., 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 may provide different advantages. For example, relatively viscous liquid mixtures may be suitable for remaining in the area where they are deposited with little further spreading. On the other hand, relatively thin liquid mixtures may be suitable for forming a relatively thin and uniform reflective layer, which may flow more easily between closely spaced features, but may require a physical barrier, such as a wall or weir, 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 a desired thickness, as described herein.

[0160] reflective layer The reflective layer, according to some embodiments herein, reflects at least one visible wavelength of incident electromagnetic radiation (e.g., light within the visible spectrum). The reflective layer may be formed from a flowable material, e.g., a liquid mixture. The reflective layer preferably reflects at least about 30% of at least one visible wavelength of 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, including 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 comprises light in the visible spectrum. It should be understood that the reactants themselves (e.g., metal salts) do not necessarily possess the reflective properties indicated prior to being reacted as described herein, but that the reflective layer (e.g., metal layer) formed from the reactants will have the reflective properties indicated.

[0161] It should be understood that the reflective layer may be structurally distinct from reflective layers formed by other means, such as vapor deposition or metal-containing inks. For example, in some embodiments, the reflective layer comprises a pure or substantially pure metal. As used herein, "substantially pure" metal has its ordinary and accustomed meaning as would be understood by one of ordinary skill in the art in light of this disclosure. It refers to a metal containing only trace amounts of other substances. When additional numerical specificities are noted, a substantially pure metal may comprise 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, e.g., 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 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 a pure metal, including ranges between any two of the recited values.

[0162] In some embodiments, the reflective layer is disposed on the waveguide and configured to redirect light propagating through the waveguide, e.g., as part of an optically dispersive element. In some embodiments, the reflective layer is disposed on the waveguide and configured to direct incident ambient light into the waveguide, e.g., as part of an incoupling optical element. 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 basic terms refer to a mass of material extending upward on or into a substrate, such as in an optical grating extending from the surface of a waveguide. In some embodiments, the protrusion may be formed by etching a substrate, which may include deposited material (e.g., photoresist deposited on a waveguide) or may be a substantially homogeneous structure (e.g., a waveguide). In some embodiments, a reflective layer 1010 is disposed over an optical grating 1020 (see, e.g., Figures 19A-19C). In some embodiments, the reflective layer 1010 is disposed over an optical grating 1020 having a blazed configuration (see Figure 19B). In some embodiments, the reflective layer 1010 is disposed over an optical grating 1020 having a multi-level configuration (see Figure 19C). In some embodiments, the optical grating comprises patterned photoresist.

[0164] It should be understood that the reflective layer is preferably utilized to provide reflection of light returning into and / or through the waveguide. As a result, the reflective layer preferably coats all surfaces of the protrusions. In some embodiments, the reflective layer is conformally disposed on the optical grating. It should be noted that when a material is "conformally" disposed, 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, such that the thickness across the entire reflective layer is within ±20% of the average value, e.g., within ±20%, ±15%, ±10%, ±5%, or ±1% of the average value. Preferably, the conformal reflective layer is disposed so that there is no or substantially no gap between the reflective layer and the surface of the substrate.

[0165] It is also envisioned that non-conformal reflective layers may, in some embodiments, provide suitable reflectivity at the relevant interface (e.g., without being limited by theory, the opposing surface not facing the waveguide may not need to conform to the waveguide, as long as the surface of the reflective layer at the interface with the waveguide is sufficiently reflective and provides sufficient coverage). 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. "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 this disclosure. While some gaps may be present, they have been determined not to significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and the substrate compared to a reflective layer without gaps. In some embodiments, the reflective layer is disposed substantially gap-free when at least 90% of the surface area of ​​the reflective layer at the interface with the waveguide surface, e.g., at least 90%, 95%, 97%, 98%, 99%, or 99.9%, is in direct contact with the waveguide surface. In some embodiments, the ink is deposited to a thickness sufficient to completely or substantially completely fill the open volumes or gaps between the waveguide protrusions.

[0167] It should be understood that when metals are deposited by conventional means, such as vapor deposition or metal-containing inks, the surface of the metal may be non-uniform, including nanoscale pinholes (see, e.g., Example 1 and Figures 22A-F). Pinholes refer to cavities, depressions, or extensions from the surface having nanoscale diameters, e.g., diameters less than about 1 mm, e.g., diameters in the range of about 1 nm to about 1000 nm. Without being limited by theory, it is believed that pinholes inhibit the reflectivity of the reflective layer. Without being limited by theory, it is further believed that forming the reflective layer by metal ion reduction as described herein may advantageously minimize or avoid the formation of pinholes. In some embodiments, the reflective layer is free or substantially free of pinholes. "Substantially free" of pinholes has its ordinary and accustomed meaning as would be understood by one of ordinary skill in the art in light of this disclosure. While some pinholes may be present, it has been determined that they do not significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and substrate compared to a reflective layer without pinholes. In some embodiments, the substantially pinhole-free surface of some embodiments may contain pinholes in 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% or less of the surface, including ranges between any two of the listed 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 "free" from pinholes would also be "substantially free" from pinholes. In some embodiments, the surface of the reflective layer that interfaces with the protrusion on the waveguide is free or substantially free of pinholes.

[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), in the reflective layer. Without being limited by theory, it is believed that metal particles may partially scatter light, and thus the reflectivity of a particle-containing reflective layer may be lower than that of a particle-free layer. Thus, 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 this disclosure. While particles, such as metal particles (other than the metal itself), may be present in trace amounts, it has been determined that they do not significantly reduce the reflectivity of a reflective optical element formed by the reflective layer and substrate compared to a reflective layer 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) of some embodiments may contain greater than 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or 0.01% metal particles (w / w), including ranges between any two of the listed values, e.g., 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, for example, 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 thick, including thicknesses in the range between any two of the listed values, e.g., 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 , 30nm~500nm, 30nm~450nm, 30nm~400nm, 30nm~350nm, 30nm~300nm, 30nm~250nm, 30nm~200nm, 30nm~150, 30nm~100nm, 30nm~50nm, 50 nm~900nm, 50nm~500nm, 50nm~450nm, 50nm~400nm, 50nm~350nm, 50nm~300nm, 50nm~250nm, 50nm~200nm, 50nm~150, 50nm~100nm, 80nm thicknesses including 100nm to 900nm, 80nm to 500nm, 80nm to 450nm, 80nm to 400nm, 80nm to 350nm, 80nm to 300nm, 80nm to 250nm, 80nm to 200nm, 80nm to 150, 80nm to 100nm, 100nm to 900nm, 100nm to 500nm, 100nm to 450nm, 100nm to 400nm, 100nm to 350nm, 100nm to 300nm, 100nm to 250nm, 100nm to 200nm, or 100nm to 150nm.

[0170] In some embodiments, a single layer of a 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 in a first deposition cycle and allowed to at least partially react, and at least one subsequent layer of the liquid mixture is applied on top of the first layer in a second deposition cycle. Optionally, reaction by-products can be removed between cycles of depositing layers of the liquid mixture. The cycle of depositing the liquid mixture can be repeated until a reflective layer of a 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 applying the liquid mixture can be performed to form a reflective layer of a desired thickness (including ranges between any two of the listed 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, which can define at least a portion (or all) of a predetermined area of ​​the surface of the waveguide.

[0172] It should be understood that the underlying protrusions may form diffractive optical elements (e.g., diffraction gratings), which in some embodiments may be utilized as internal coupling optical elements to internally couple light into a waveguide. As discussed herein, these protrusions may be metallized by PVD to form reflective diffractive optical elements. In some embodiments, metal may be deposited on the protrusions by wet chemistry instead of PVD metallization. For example, metal may be deposited to directly contact and conformally coat the surface of the protrusions, 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 the PVD metallization with a liquid metal reflective layer has been found to provide similar or better levels of optical performance. For example, reflective diffractive optical elements formed using reflective layers according to embodiments herein have been found to provide diffraction efficiencies that are similar to or superior to those otherwise 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% for light incident on the diffractive optical elements at an angle normal (perpendicular) to the diffractive optical elements. In some circumstances, the 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] Pre-processing Agent It is contemplated that pre-treating the surface of the waveguide prior to depositing the liquid mixture can improve adhesion and formation of a reflective layer, as described herein. With photoresist waveguides, it has been observed that pre-treatment can improve both adhesion and reflectivity of the reflective layer (Example 3). Thus, in some embodiments, the waveguide, including photoresist, is pre-treated prior to depositing the liquid mixture, as described herein. Furthermore, it is contemplated that selectively pre-treating predetermined areas, but not other areas of the surface of the waveguide, can facilitate selective formation of a reflective layer in desired predetermined areas, as described herein.

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

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

[0176] Without being limited by theory, it is envisioned that a pre-treatment that enhances the metal ion reduction reaction may be selectively applied to predetermined areas (and not other areas) of the surface of the waveguide, enhancing the selectivity of the formation of a reflective layer on the predetermined areas (and not other areas). Thus, in some embodiments, predetermined areas of the surface of a waveguide as described herein are pre-treated with a catalyst that enhances the metal ion reduction reaction (and reflective layer formation) as described herein.

[0177] Optical waveguide and method for making same In some embodiments, a method of fabricating an optical waveguide structure comprising a reflective layer is described. The method may include providing an optical waveguide comprising a surface. The surface may comprise a predetermined region comprising a pattern of protrusions. For example, the predetermined region may define a nanopattern for deposition of a reflective layer. The method may include depositing a liquid mixture onto 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 allowing the metal salt in the deposited liquid mixture to be reduced by the reducing agent, depositing pure or substantially pure metal onto the predetermined region of the surface. Thus, a reflective layer may be formed on the 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 onto the protrusions within the predetermined region of the surface of the waveguide. In some embodiments, the method further includes pre-treating a predetermined area of ​​the surface of the waveguide to increase the hydrophilicity of the surface, e.g., plasma treatment, as described herein. The pre-treating step may occur before the liquid mixture is deposited on the predetermined area 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 die-cutting or dicing the substrate and the reflective layer into multiple different pieces to form a plurality of reflective optical elements. In some embodiments, the optical waveguide including 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, the optical waveguide comprising the reflective layer is part of a display device, and thus the method further comprises disposing the waveguide comprising the reflective layer (or a stack comprising such a waveguide) within the display device. In some embodiments, the predetermined region is defined to a resolution of ±50 microns, or even finer (numerically smaller) resolution, for example, ±40, ±30, ±20, ±10, or ±5 microns.

[0178] Referring to FIG. 23 , in some embodiments, the method includes providing an optical waveguide comprising a surface, the surface comprising a predetermined region comprising a pattern of protrusions 1600. The method may further include increasing the hydrophilicity of the predetermined region 1610 of the surface, for example, if the surface comprises photoresist. For example, the hydrophilicity may be increased by pre-treating the predetermined region with a plasma, as described herein. The method may further include depositing a liquid mixture onto the predetermined 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 precipitates on the predetermined 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 residue from reflective layer 150, for example, by rinsing and / or drying, as described herein.

[0179] Advantageously, a reflective layer as described herein may be selectively applied to predetermined areas and not to other areas of the surface of the waveguide, for example, to form a diffractive optical element such as an incoupling optical element. In some embodiments, the surface of the waveguide further comprises a first region. The predetermined area, excluding the first region, is selectively contacted with the liquid mixture. Thus, a pure or substantially pure metal is deposited on the predetermined area, excluding the first region, thus forming a reflective layer on the predetermined area but not on the first region of the surface of the optical waveguide. In some embodiments, the liquid mixture is selectively applied only to the predetermined area (excluding other areas) 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 area. 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 area and prevents the liquid mixture from flowing from other areas of the surface of the waveguide (see, e.g., FIGS. 20A-20B). The walls may be of a graduated height, such that an inner wall 2002, which defines the area for depositing the liquid mixture, is lower than an outer wall 2004 that surrounds the inner wall 2002. Without being limited by theory, it is contemplated that the gradation in wall height may help prevent defects when filling the area defined by the inner wall, for example, by consistently confining the location of the deposited liquid mixture. Thus, in some embodiments, the walls act as weirs, molds, or wells to contain the liquid mixture within a predetermined area of ​​the substrate. In some embodiments, the walls may also act as spacers, separating the waveguides of the stack from one another. In some embodiments, the walls comprise resist. It is contemplated that resist walls, according to some embodiments, can be deposited as a layer that extends across the substrate and then patterned to define the walls.

[0180] The walls, weirs, or wells may be written and / or removable. For example, the walls, weirs, or wells may be removed by rinsing with water (or another liquid), peeling, dislodging, and / or vacuuming. In some embodiments, the walls, weirs, or wells are not removable, but rather are 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 predetermined areas, and the liquid mixture may be deposited in the one or more openings. The mask may then be removed. In some embodiments, the liquid mixture is selectively applied with an inkjet. An inkjet may advantageously allow for selective application of the liquid mixture deposit in desired areas.

[0181] As described herein, increasing the hydrophobicity of a 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 is noted that the reflective layer can exhibit substantially superior adhesion and reflectivity when the hydrophobicity of the photoresist is increased prior to depositing the liquid mixture (Example 3). Thus, a pretreatment that selectively increases the hydrophilicity of certain regions of the waveguide surface (compared to the hydrophilicity of the certain regions before the pretreatment) but not other regions can facilitate the selective formation of a reflective layer on certain regions of the waveguide surface but not other regions. In some embodiments, the method includes increasing the hydrophilicity of certain regions of the surface prior to depositing the liquid mixture. In some embodiments, the hydrophilicity is selectively increased on certain regions of the surface but not on a first region of the surface. In some embodiments, the hydrophilicity of certain regions of the surface is increased by pretreating the certain regions of the surface with a pretreatment agent selected from the group consisting of plasma, surfactants, coatings, wet chemical etching, and catalysts. In some embodiments, the method includes pre-treating the surface with at least one of a plasma, wet etching with a wet chemical etchant comprising chromic acid, a surfactant, a coating comprising silica, and / or a catalyst comprising tin or palladium (such as tin chloride or palladium chloride). In some embodiments, predetermined regions of the waveguide are not pre-treated with any pre-treatment reagents.

[0182] As described herein, using a catalyst to enhance metal ion reduction in predetermined regions of the surface of the waveguide (but not other regions) can also enhance selective deposition in the predetermined regions. In some embodiments, the method further includes selectively applying a catalyst to the predetermined regions of the surface prior to depositing the liquid mixture. The catalyst can be configured to promote reduction of metal salts, thereby depositing pure or substantially pure metal.

[0183] As described herein, in some embodiment methods, physical barriers, walls, weirs, and / or wells may also enhance the selective deposition of the reflective layer by confining the liquid mixture (and thus the deposited metal) to a predetermined region of the surface of the waveguide. In some embodiment methods, the surface of the waveguide comprises vertically extending walls that define at least a portion of the predetermined region onto which the liquid mixture is selectively deposited. The walls limit lateral movement of the liquid mixture into the first region. Examples of such walls, wells, or weirs are illustrated in Figures 20A-20B.

[0184] In some embodiment methods, the predetermined region of the waveguide surface comprising the protrusion 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 substantially gap-free. 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 gap-free. 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 gap-free. In some embodiments, the reflective layer is configured to reflect incident electromagnetic radiation at the interface into the first waveguide.

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

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

[0187] In some embodiment methods, 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 a protrusion of the first surface and bonded to 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 onto 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 bonded 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 optical waveguides are performed), thus forming a stack of optical waveguides with a reflective layer.

[0188] The reduction of a metal salt to form a deposited metal may be referred to herein as a "metal reduction" or "metal ion reduction" reaction. An example of such a reaction is illustrated diagrammatically in FIG. 21C. In some embodiment methods, a Tollens reaction reduces a metal salt to a pure or substantially pure metal. In some embodiments, the reducing agent comprises, consists essentially of, or consists of an alpha-hydroxyaldehyde-containing carbohydrate and / or an alpha-hydroxyketone-containing carbohydrate. Exemplary reducing agents include sucrose, fructose, and combinations thereof. In some embodiments, the metal salt comprises, consists essentially of, or consists of Ag(NH). In some embodiments, the liquid mixture consists essentially of a metal salt, a reducing agent, and a base in a solvent, e.g., water. In some embodiments, the liquid mixture consists of a metal salt, a reducing agent, and a base in a solvent, e.g., water.

[0189] In some embodiment methods, 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 listed 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 reactions described in some embodiment methods herein may be suitably formulated to occur at or below room temperature. On the other hand, application of metal inks frequently involves baking / heating at high temperatures to produce purer metals, which can affect the thermal budget of the waveguide (and may even damage the waveguide, including damaging the resist structure) and extend process time. Additionally, high temperature firing may or may not be compatible with materials used to fabricate nanostructures, such as protrusions, onto optical waveguides.

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

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

[0192] It is envisioned that metals may tarnish and / or deteriorate, impairing their reflective properties. Capping the reflective layer can provide protection against tarnish or other deterioration, thus extending the length of time the reflective layer retains 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 from direct exposure to air and / or moisture. In some embodiments, the capping layer comprises, consists essentially of, or consists of a dielectric or metal. In some embodiments, the capping is formed by vapor deposition of a dielectric or metal coating onto the reflective layer. In some embodiments, the protective layer may be liquid when applied and may be converted to a solid by a chemical reaction or physical state change. In some embodiments, the capping prevents direct exposure of air and / or moisture to the associated reflective surface of the reflective layer.

[0193] It is contemplated that the liquid mixture of some embodiments may have a short shelf life. Thus, in some embodiment methods, 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 onto a predetermined area of ​​the surface of the waveguide, the liquid mixture is thus deposited. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited onto a predetermined area simultaneously. For example, for a coating process requiring parts A and B to react together, parts A and B can be deposited onto a predetermined surface simultaneously. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited onto a predetermined area sequentially. For example, for a coating process requiring parts A and B to react together, a droplet or droplets of part A can be applied first, and then a droplet of part B can be applied thereon. In some embodiments, two or more different compositions comprising the reactants to (collectively) form the reflective layer are mixed and then deposited onto a predetermined area as a single composition.

[0194] Several suitable techniques can be used to deposit the liquid mixture onto a predetermined area of ​​a waveguide surface according to the methods of some embodiments herein. For example, in some embodiments, the liquid mixture is deposited onto the predetermined area via at least one of nanodispensing, microdispensing, micropipette, inkjet, or spraying. In some embodiments, the liquid mixture is deposited onto the predetermined area as a single droplet or multiple 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., by-products of the reaction, such as oxidized carbohydrates and ammonia or excess reactants) are removed from the reflective layer. The method of some embodiments further includes removing residues of the metal ion reduction reaction. In some embodiment methods, the reflective layer is rinsed after it is formed. Residues remaining after the reaction can be removed by rinsing. Examples of suitable rinsing techniques include a washing / spraying system, a liquid bath with circulation and / or agitation, a spin rinsing / drying system, or a combination of two or more of the listed techniques. In some embodiments, rinsing is performed with an aqueous solution, e.g., water. In some embodiments, the reflective layer is dried, for example, until the residues are completely dried or the rinsing is completely dried.

[0196] Furthermore, in some embodiments (e.g., with respect to a diffractive optical element, an incoupling optical element, or an outcoupling optical element as described herein), it is contemplated that the relevant surface is at the interface of a waveguide reflective layer and therefore may not 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 Devices In some embodiments, an optical device is described. The optical device may include a first waveguide having a first surface. The optical device may include a reflective layer disposed on a region of the first surface, wherein the reflective layer is pinhole-free or substantially pinhole-free. The layer may include, consist essentially of, or consist of 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 an interface. In some embodiment optical devices, the first waveguide is part of a stack of optical waveguides as described herein. In some embodiment optical devices, two or more of the optical waveguides of the stack each include a reflective layer as described herein.

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

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

[0200] In some optical device embodiments, the reflective layer reflects incident electromagnetic radiation (e.g., light in the visible spectrum) with a reflectivity (or degree of reflectivity) of at least 70%, e.g., at least 70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, or 99.9%, including ranges between any two of the listed values, e.g., 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 in the visible spectrum) with a reflectivity of at least 85%. The predetermined area of ​​the waveguide surface may be sized and shaped accordingly.

[0201] In some embodiment optical devices, the reflective layer maintains its ability to reflect incident electromagnetic radiation with at least 85%, e.g., at least 85%, 87%, or 90% reflectivity, for at least 500 hours. As shown in Example 4 and Figure 24, a reflective layer as described herein can maintain at least about 85% reflectivity (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 its ability to reflect incident electromagnetic radiation with at least 85% reflectivity, whether capped or not, for at least 500 hours.

[0202] As described herein, it may be advantageous to confine the reflective layer to a predetermined region of the surface of the waveguide. 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 the other waveguide.

[0203] In some embodiments, the optical device comprises, consists essentially of, or consists of an image projector, a display system configured to project light containing image information into the 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 metals as described herein.

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

[0206] The optical device of some embodiments further comprises a capping layer, as described herein, disposed on the reflective layer.

[0207] Display Device In some embodiments, a display device is provided. The display device may include a waveguide comprising a reflective diffractive optical element, wherein the diffractive optical element comprises a reflective layer disposed on a region of a surface of the waveguide. The reflective layer may be substantially pinhole-free. The reflective layer may comprise, consist essentially of, or consist of a pure metal or a substantially pure metal. For example, the layer may comprise at least 95% elemental metal. The reflective layer may be configured to reflect incident electromagnetic radiation into the first waveguide at an 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 of the stack each comprise a reflective layer as described herein. In some embodiments, the reflective layer does not cover the entire surface of the waveguide.

[0208] In some embodiment display devices, the reflective diffractive optical elements form an in-coupling grating configured to in-couple incident light into a waveguide, as described herein.

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

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

[0211] The display device of some embodiments further comprises 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 device of some embodiments further comprises a capping layer disposed on the reflective layer, as described herein. The capping layer may be positioned to prevent the interface of the reflective layer that is positioned to direct and / or propagate electromagnetic radiation from being directly exposed to air and humidity.

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

[0214] In some embodiment display devices, the reflective layer maintains its ability to reflect incident electromagnetic radiation with at least 85%, e.g., at least 85%, 87%, or 90% reflectivity, for at least 500 hours. In some embodiments, the reflective layer maintains its ability to reflect incident electromagnetic radiation with at least 85% reflectivity, whether capped or not, for at least 500 hours.

[0215] Method for making a display device In some embodiments, a method of fabricating an optical device is described. The method may include providing a waveguide comprising a surface. The method may include depositing a liquid mixture onto a region 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 the predetermined region of the surface such that the metal salt is reduced by the reducing agent and pure or substantially pure metal precipitates. Thus, a reflective layer is formed on the predetermined region 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 the hydrophilicity of the surface, as described herein. The pre-treating step may occur before the liquid mixture is deposited on the predetermined region of the surface.

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

[0217] Exemplary Diffractive Optical Elements In some embodiments, the internal coupling optical element (e.g., internal coupling optical element 700, 710, 720) comprises a reflective diffractive optical element comprising a reflective layer comprising, consisting essentially of, or consisting of a pure or substantially pure metal, as described herein. [Example]

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

[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 performed on internal coupling grating (ICG) nanopatterned structures. Coating quality ratings using different methods are shown in Table 1. Reflective layers containing silver according to some embodiments were formed using a modified Tollens reaction. The reaction was performed at room temperature and produced high-purity silver with good smoothness (no pinholes) at the nanoscale (Figure 22C, shown after rinsing). The coating was also highly conformal around the ICG nanostructures. In comparison, inkjet-compatible inks from NovaCentrix (Austine, Texas) (Figure 22A) and Electroinks (Figure 22B) contained a substantial number of pinholes and formed nanoporous networks that were highly conductive but associated with relatively low reflectivity. The adhesion of the reflective layer as described herein was also evaluated using a tape peel test. Compared to the NovaCentrix inkjet-enabled ink (FIG. 22D) and the Electroinks inkjet-enabled ink (FIG. 22E) (silver tape peeling from glass), the reflective layer formed by using the modified Tollens reaction according to some embodiments herein (FIG. 22F) exhibited substantially better adhesion. Note that for the tape peeling test, the reflective layer of some embodiments was deposited on a 3 nm SiOx-coated ICG. These results are summarized in Tables 1A-B below. [Table 1-1] [Table 1-2] [Table 1-3]

[0220] Thus, reflective layers according to some embodiments herein have been shown to possess smoother surfaces (free or substantially free of pinholes) and exhibit superior adhesion than layers formed from inkjettable metal-containing inks.

[0221] Example 2 Comparison of reflective layers with evaporated metal layers and silver-containing inks Plasma pretreatment of the nanostructured photoresist resulted in excellent adhesion. The reflectivity and ICG diffraction efficiency of a reflective layer containing silver produced by a modified Tollens reaction on APPJ plasma-treated 385 resist were compared with a sputtered aluminum layer on the 385 resist and a NovaCentrix inkjet ink baked at 180°C for 15 minutes. The reflective layer containing silver produced by the modified Tollens reaction exhibited significantly higher reflectivity than the commercial metallic inks tested and also higher than the evaporated aluminum coating (Figure 23). Furthermore, the reflective layer containing silver produced by the modified Tollens reaction exhibited higher reflectivity for all wavelengths tested within the 400-700 nm range (Figure 23).

[0222] The reflectivity and diffraction efficiency are summarized in Tables 2A-B below. [Table 2-1] [Table 2-2] [Table 2-3]

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

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

[0225] It can therefore be concluded that the reflective layers according to the methods and devices of some embodiments exhibit better reflectivity and better diffraction efficiency compared to layers formed from metal-containing inks and Al layers formed by vapor deposition.

[0226] Example 3 Surface treatment effects The effect of the surface treatment was evaluated on a reflective layer deposited by silver ion reduction as described herein.

[0227] As a control, the imprinted areas on the resist without pre-treatment exhibited a very thin Ag coating (only a slight residue after a light water rinse).

[0228] The resist was washed with acetone in the imprint areas. This pretreatment resulted in a thin, semi-transparent silver coating. Although the silver was thicker than in areas without the acetone wash, it was still very thin and unlikely to have sufficient reflectivity for many applications.

[0229] The resist was pre-treated with an ultra-thin atmospheric pressure plasma jet (APPJ) coating, which used a SnCl catalyst to provide high reflectivity and acceptable adhesion.

[0230] The resist was pre-treated with plasma, which resulted in high reflectivity and excellent adhesion.

[0231] The glass-only area received an approximately 100 nm silver coating, which was highly reflective and exhibited better reflectivity than the aluminum layer formed by vapor deposition.

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

[0233] Example 4 Reflective layer stability without capping The stability of reflective layers formed by silver ion reduction (which may also be referred to as "autogenous silver") as described herein was measured. The reflectance of reflective layers formed by silver ion reduction on 385M2 cured resist (without capping) was measured both initially and after 500 hours at 60°C and 100% humidity. The reflectance of aluminum layers formed by vapor deposition was also measured. As shown in FIG. 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 superior reflectance to the aluminum sample.

[0234] ICG diffraction efficiency was also measured for reflective layers 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 change substantially 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. Reference is made to these examples in a non-limiting sense. They are provided to illustrate the more broadly applicable aspects of the invention. Various modifications may be made to the invention described, and equivalents may be substituted without departing from the true spirit and scope of the invention.

[0236] For example, although advantageously utilized in conjunction with AR displays that provide images across multiple depth planes, the augmented reality content disclosed herein may also be displayed by systems that provide images on a single depth plane.

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

[0238] The present invention includes methods that may be carried out using the subject devices. The methods may include the act of providing such suitable devices. Such provision may be performed by a user. In other words, the act of "providing" merely requires the user to obtain, access, approach, position, configure, activate, power on, or otherwise act upon the requisite devices in the subject method, which is logically possible. Methods described herein may be carried out in any order of the recited events, and in the recited order of events.

[0239] Exemplary aspects of the invention, along with details regarding material selection and manufacturing, have been described above. As for other details of the invention, these may be understood in connection with the above-referenced patents and publications and may generally be known or understood by those skilled in the art. The same may be true with respect to method-based aspects of the invention in terms of additional acts as typically or logically adopted.

[0240] Additionally, while the present invention has been described with reference to several embodiments that optionally incorporate various features, the present invention is not limited to what has been described or indicated as being considered with respect to each variation of the invention. Various modifications may be made to the invention as described, and equivalents may be substituted (whether described herein or not included for purposes of brevity) without departing from the true spirit and scope of the invention. Additionally, when a range of values ​​is provided, it is understood that all intervening values ​​between the upper and lower limits of that range, and any other stated or intervening value within that stated range, are encompassed within the invention.

[0241] It is also contemplated that any optional features of the inventive variations described herein may be described and claimed independently or in combination with any one or more of the features described herein. Reference to a singular item includes the possibility that there are plural 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 articles in the above description and in the claims associated with this disclosure allows for "at least one" of the subject item. Furthermore, it should be noted that such claims may be drafted to exclude any optional element. Accordingly, this statement is intended to serve as a predicate for the use of such exclusive terminology, such as "only," "only," and the like, or the use of "negative" limitations, in connection with the recitation of claim elements.

[0242] Without using such exclusive language, the term "comprising" in the claims associated with this disclosure shall permit the inclusion of any additional elements, regardless of whether a given number of elements are recited in such claims or whether the addition of features can be considered as changing the nature of the elements recited in such claims. Except as specifically defined herein, all technical and scientific terms used herein shall be given the broadest possible commonly understood meaning while maintaining the validity of the claims.

Claims

[Claim 1] The invention described in this specification.

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