Diffractive optics elements, related systems, and methods for reducing re-bounce-induced light loss

Abstract

To provide diffractive optical elements, related systems, and methods that reduce re-bounce-induced light loss. [Solution] The display device includes a waveguide with an internally coupled optical element that reduces the re-bounce of internally coupled light and improves the overall internal coupling efficiency and / or uniformity. The waveguide includes an internally coupled optical element that receives light from a light source and / or projection optics, internally couples the received light, and propagates through the waveguide in the direction of propagation by total internal reflection. Once internally coupled in the waveguide, the light is subject to re-bounce, where the light is reflected from the waveguide surface, and after reflection, it may strike the internally coupled optical element. In response to striking the internally coupled optical element, the light is partially absorbed and / or externally coupled by the optical element, thereby substantially reducing the amount of internally coupled light propagating through the waveguide.

Description

Technical Field

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

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

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

Background Art

[0004] Modern computing and display technologies are driving the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or parts thereof are presented to the 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 imagery without transparency to other real-world visual inputs, while augmented reality, or "AR," scenarios typically involve the presentation of digital or virtual imagery as an extension of the user's visualization of the real world around them. Mixed reality, or "MR," scenarios, are a type of AR scenario that typically involves virtual objects integrated into and responding to the natural world. For example, an MR scenario may include AR imagery that appears blocked by, or is perceived to interact with, objects in the real world in a different way.

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

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

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

[0008] Some aspects include a waveguide comprising a first main surface, a second main surface, and an internally coupled diffractive optical element disposed on the second main surface, the internally coupled diffractive optical element having a diffraction region configured to internally couple incident light, wherein the width of the diffraction region parallel to the propagation direction is shorter than the length of the diffraction region perpendicular to the propagation direction.

[0009] The width of the diffraction region may be less than 80% of the length of the diffraction region. The diffraction region may be a high-efficiency diffraction region, and the internally coupled diffraction optical element further comprises a low-efficiency diffraction region positioned 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 and low-efficiency diffraction regions may partially form a metallized diffraction grating, where the diffraction grating is metallized in the high-efficiency diffraction region and non-metallized in the low-efficiency diffraction region. The internally coupled diffraction optical element may be sized and shaped to reduce the occurrence of re-bounce of internally coupled light compared to an internally coupled optical element having substantially equal length and width.

[0010] Some aspects include waveguide stacks for head-mounted display systems. The waveguide stack includes a first waveguide comprising a first main surface, a second main surface facing the first main surface, and a first internally coupled diffractive optical element disposed on the second main surface, comprising a first diffractive region configured to redirect incident light from a light source and propagate in the propagation direction within the first waveguide by total internal reflection; and a second waveguide comprising a second internally coupled diffractive optical element disposed on the second main surface of the second waveguide, comprising a second diffractive region configured to redirect incident light from a light source and propagate in the propagation direction within the second waveguide by total internal reflection. The width-to-length ratio of the second diffraction region is smaller than that of the first diffraction region.

[0011] The waveguide stack may be spaced away 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 internally coupled diffraction optical element may further include a low-efficiency diffraction region positioned directly adjacent to the high-efficiency diffraction region along the propagation direction. The high-efficiency diffraction region may include a metallized portion of the diffraction grating, and the low-efficiency diffraction region may include a non-metallized portion of the diffraction grating. The second internally coupled diffraction optical element may be sized and shaped to reduce the occurrence of re-bounce of internally coupled light compared to an internally coupled diffraction 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 for fabricating an optical waveguide structure having a reflective layer. The method includes the steps of providing an optical waveguide having a surface, wherein the surface comprises a region having a pattern of protrusions; depositing a liquid mixture on at least a portion of the region, wherein the liquid mixture comprises a metal salt; and forming a reflective layer by coating the region with the metal of the metal salt, wherein the coating step comprises depositing the metal on the region by dissociating the metal from the metal salt.

[0013] The step of dissociating the metal from the metal salt may include the step of reducing the metal salt by exposure to a reducing agent. The reducing agent may comprise at least one of a carbohydrate containing an alpha-hydroxyaldehyde or a carbohydrate containing an alpha-hydroxyketone. The liquid mixture may comprise the reducing agent. The method may further include the step of adding the reducing agent to the liquid mixture after the liquid mixture has been deposited. The step of forming the reflective layer may include the step of selectively forming the reflective layer on the region while leaving one or more areas around the region without metal. The surface of the waveguide may comprise a vertically extending wall that defines a volume within the region, and the step of depositing the liquid mixture comprises the step of depositing the deposited mixture into the volume. The projection may define a diffractive optical element, and the projection and the reflective layer form a reflective diffractive optical element. The diffractive optical element may be an internally coupled optical element configured to redirect incident light at an angle such that light propagates through the waveguide by total internal reflection. The projection may comprise a photoresist. The method may further include the steps of: forming an additional reflective layer on an additional optical waveguide by depositing a liquid mixture onto an additional region on the surface of the additional optical waveguide, wherein the additional reflective optical element is configured to reflect incident light; and attaching at least the additional waveguide to the surface of the waveguide to produce a stack of waveguides. The hydrophilicity of the region can 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 the step of depositing the liquid mixture. The step of pre-treating the region with plasma may include the step of 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 the step of selectively applying a catalyst to the region prior to the step of depositing the liquid mixture, wherein the catalyst is configured to promote the reduction of a silver salt. The liquid mixture may essentially consist of a metal salt, a reducing agent, and a base.The reflective layer may be pure or substantially pure metal. The liquid mixture may be deposited on the area by at least one of nano-dispensing, micro-dispensing, micro-piping, inkjet printing, and spraying. The method may further include a step of removing the residual liquid mixture material following the deposition of the metal. The step of removing the residual liquid crystal mixture may include a step of rinsing the optical waveguide. The method may further include a step of depositing a capping layer on the reflective layer. The reflective layer may be pinhole-free or substantially pinhole-free. The metal may be silver.

[0014] Some aspects include an optical device comprising a first waveguide having a reflective diffractive optical element. The reflective diffractive optical element comprises a projection on the surface of the first waveguide, an interface layer on the projection, 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 tin or palladium-containing composites. The reflective layer may be at least 95% metal. The reflective layer may be substantially pinhole-free. The reflective diffractive optical element may be an internally coupled optical element configured to redirect incident light at an angle such that light propagates through the first waveguide by total internal reflection. The reflective layer may reflect incident light with a reflectivity of at least 85%. The optical device may further comprise a second waveguide and a third waveguide, the second waveguide configured to output light in a different wavelength range than the third waveguide, and the first, second, and third waveguides each comprise a reflective diffractive optical element comprising a projection on the surface of the first waveguide, an interface layer on the projection, and a reflective layer on the interface layer. The first surface may comprise walls that define the boundaries of the reflective layer. The wall may include mechanical spacers configured to maintain space between the first waveguide and the other waveguide. The optical device may be a display system comprising a spatial light modulator, which is configured to output light containing image information onto a reflective diffractive optical element. The optical device may further include a capping layer on the reflective layer. The present invention provides, for example, the following: (Item 1) A display system for projecting an image onto a user's eyes, wherein the display system is A waveguide comprising a first main surface and a second main surface facing the first main surface, A projection optical system configured to project a beam of light toward the second main surface of the waveguide, An internal coupling optical element disposed on a second main surface of the waveguide, the internal coupling optical element comprising a diffraction region configured to internally couple light from the projection optical system, and the internal coupling optical element configured to redirect the light from the projection optical system to propagate in a first direction within the waveguide by total internal reflection, and Equipped with, A display system in which the diffraction region is sized and shaped such that a first portion of the light beam from the projection optical system is incident on the diffraction region, and a second portion of the light beam from the projection optical system does not incident on the diffraction region but collides with the waveguide. (Item 2) The 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 which is 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) The display system according to item 2, wherein the high-efficiency diffraction region is a reflective diffraction region comprising a metallized lattice portion, and the low-efficiency diffraction region comprises a non-metallized lattice portion. (Item 4) The display system according to item 1, wherein the second portion of the light beam propagates out of the waveguide through the second main surface without being internally coupled within the waveguide. (Item 5) The display system according to item 1, wherein the second portion of the light beam is internally coupled into the waveguide with less efficiency than the first portion of the light beam. (Item 6) The display system according to item 1, wherein the diffraction region is reflectively asymmetrical with respect to an axis of symmetry perpendicular to the propagation direction in the beam axis of the light beam from the projection optical system. (Item 7) The waveguide is part of a waveguide stack, and the waveguide stack is A second waveguide having a first main surface and a second main surface, A second internal coupling optical element disposed on the second main surface of the second waveguide, wherein the second internal coupling optical element comprises a second diffraction region that covers a larger proportion of the area defined by the second beam of light from the projection optical system than the proportion of the area defined by the diffraction region is covered by the beam of light. The display system according to item 1, further comprising (Item 8) The display system according to item 7, wherein the second diffraction region is configured to internally couple substantially all of the beam of the second light. (Item 9) The display system according to item 7, wherein the diffraction region of the first waveguide is reflection-asymmetric about a symmetry axis perpendicular to the propagation direction on the beam axis of the beam of light from the projection optical system, and the second diffraction region is reflection-symmetric about a second symmetry axis perpendicular to the propagation direction on the beam axis of the beam of the second light. (Item 10) The display system according to item 7, wherein the second waveguide is disposed between the waveguide and the projection optical system, and the waveguide is separated from the projection optical system by a distance exceeding the focal length of the projection optical system. (Item 11) A waveguide, comprising a first major surface, a second major surface, an internal coupling diffractive optical element disposed on the second major surface, the internal coupling optical element comprising a diffraction region configured to internally couple incident light, and a width of the diffraction region parallel to the propagation direction is shorter than a length of the diffraction region perpendicular to the propagation direction, the internal coupling diffractive optical element A waveguide comprising (Item 12) The waveguide according to item 11, wherein the width of the diffraction region is less than 80% of the length of the diffraction region. (Item 13) The waveguide according to item 11, wherein the diffraction region is a high-efficiency diffraction region, and the internal coupling diffractive optical element further comprises a low-efficiency diffraction region disposed adjacent to the high-efficiency diffraction region along the propagation direction. (Item 14) The waveguide according to item 13, wherein the high-efficiency diffraction region is a reflective diffraction region comprising a metallized diffraction grating portion, and the low-efficiency diffraction region comprises a non-metallized diffraction grating portion. (Item 15) The waveguide according to item 13, wherein the high-efficiency diffraction region and the low-efficiency diffraction region partially form a metallized diffraction grating, and the diffraction grating is metallized in the high-efficiency diffraction region and demetallized in the low-efficiency diffraction region. (Item 16) The waveguide according to item 11, wherein the internally coupled diffractive optical element is sized and shaped to reduce the occurrence of re-bounce of internally coupled light compared to an internally coupled optical element having substantially equal length and width. (Item 17) A waveguide stack for a head-mounted display system, wherein the waveguide stack comprises: A first waveguide comprising a first main surface, a second main surface facing the first main surface, and a first internally coupled diffracting optical element disposed on the second main surface, wherein the first internally coupled diffracting optical element comprises a first diffraction region configured to redirect incident light from a light source and propagate it in the propagation direction within the first waveguide by total internal reflection, A second waveguide comprising a first main surface, a second main surface opposite to the first main surface of the second waveguide, and a second internally coupled diffracting optical element disposed on the second main surface of the second waveguide, wherein the second internally coupled diffracting optical element comprises a second diffracting region configured to redirect incident light from the light source and propagate it through the second waveguide in the propagation direction by total internal reflection. Equipped with, A waveguide stack in which the width-to-length ratio of the second diffraction region is smaller than the width-to-length ratio of the first diffraction region. (Item 18) The waveguide stack according to item 17, wherein the waveguide stack is spaced away 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. (Item 19) The waveguide stack described in 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) The waveguide stack according to item 17, wherein the second diffraction region is a high-efficiency diffraction region, and the second internally coupled diffracting optical element further comprises a low-efficiency diffraction region located directly adjacent to the high-efficiency diffraction region along the propagation direction. (Item 21) The waveguide stack according to item 20, wherein the high-efficiency diffraction region comprises a metallized portion of the diffraction grating, and the low-efficiency diffraction region comprises a non-metallized portion of the diffraction grating. (Item 22) The waveguide stack according to item 17, wherein the second internally coupled diffractive optical element is sized and shaped to reduce the occurrence of re-bounce of the internally coupled light compared to an internally coupled diffractive optical element having a width-to-length ratio equal to the width-to-length ratio of the first diffractive region. (Item 23) A method for fabricating an optical waveguide structure having a reflective layer, wherein the method is: To provide an optical waveguide having a surface, wherein the surface includes a region having a pattern of protrusions, The method involves depositing a liquid mixture onto at least a portion of the said region, wherein the liquid mixture contains a metal salt. The reflective layer is formed by coating the region with the metal of the metal salt, and coating the region includes precipitation of the metal on the region by dissociating the metal from the metal salt. Methods that include... (Item 24) The method according to item 23, wherein dissociating a metal from the metal salt comprises reducing the metal salt by exposure to a reducing agent. (Item 25) The method according to item 24, wherein the reducing agent comprises at least one of a carbohydrate containing alpha-hydroxyaldehyde or a carbohydrate containing alpha-hydroxyketone. (Item 26) The liquid mixture comprises the reducing agent, as described in item 24. (Item 27) The method according to item 24, further comprising adding the reducing agent to the liquid mixture after depositing the liquid mixture. (Item 28) The method according to item 23, wherein forming the reflective layer comprises selectively forming the reflective layer on the region while leaving one or more areas around the region without metal. (Item 29) The method according to item 28, wherein the surface of the waveguide has a vertically extending wall that defines a volume within the region, and depositing the liquid mixture includes depositing the deposit mixture within the volume. (Item 30) The method according to item 23, wherein the protrusion defines a diffractive optical element, and the protrusion and reflective layer form a reflective diffractive optical element. (Item 31) The method according to item 30, wherein the diffractive optical element is an internally coupled optical element configured to redirect the incident light at an angle such that the light propagates through the waveguide by total internal reflection. (Item 32) The method according to item 23, wherein the protruding portion is provided with a photoresist. (Item 33) The method involves depositing the liquid mixture onto an additional region on the surface of the additional optical waveguide to form an additional reflective layer on the additional optical waveguide, wherein the additional reflective optical element is configured to reflect incident light. At least the additional waveguide is attached to the surface of the waveguide, thereby producing a stack of waveguides. The method described in item 23, further including the method described in item 23. (Item 34) The hydrophilicity of the region is increased by selectively pre-treating the region with one or more agents selected from the group consisting of plasma, surfactants, coatings, wet chemical etching solutions, and catalysts, prior to depositing the liquid mixture, according to the method of item 23. (Item 35) Pre-treating the region with plasma includes performing atmospheric plasma treatment. The aforementioned wet chemical etching agent contains chromic acid, The coating contains silica and / or The catalyst comprises tin or palladium. The method described in item 34, which is at least one of the following. (Item 36) The method according to item 23, further comprising selectively applying a catalyst to the region prior to depositing the liquid mixture, wherein the catalyst is configured to promote the reduction of the silver salt. (Item 37) The method according to item 23, wherein the liquid mixture essentially consists of the metal salt, reducing agent, and base. (Item 38) The method according to item 23, wherein the reflective layer is a pure metal or substantially a pure metal. (Item 39) The method according to item 23, wherein the liquid mixture is deposited on the area by at least one of nano-dispensing, micro-dispensing, micro-piping, inkjet printing, and spraying. (Item 40) The method according to item 23, further comprising removing the residual liquid mixture material following the deposition of the aforementioned metal. (Item 41) The method according to item 40, wherein removing the residual liquid crystal mixture includes rinsing the optical waveguide. (Item 42) The method according to item 23, further comprising depositing a capping layer on the reflective layer. (Item 43) The reflective layer is free from or substantially free from pinholes, as described in item 23. (Item 44) The method according to item 23, wherein the metal is silver. (Item 45) An optical device, A first waveguide comprising a reflective diffractive optical element, wherein the reflective diffractive optical element is The protrusion on the surface of the first waveguide, The interface layer on the protruding portion, The reflective layer on the interface layer and A first waveguide comprising An optical device equipped with the following features. (Item 46) The optical device according to item 45, wherein the interface layer comprises one or more of a plasma-treated surface, a surfactant layer, and a catalyst. (Item 47) The optical device according to item 46, wherein the catalyst comprises one or more tin or palladium-containing composites. (Item 48) The optical device according to item 45, wherein the reflective layer is at least 95% metal. (Item 49) The reflective layer is substantially free of pinholes, as described in item 45. (Item 50) The optical device according to item 45, wherein the reflective diffractive optical element is an internally coupled optical element configured to redirect the incident light at an angle such that the light propagates through the first waveguide by total internal reflection. (Item 51) The optical device according to item 50, wherein the reflective layer reflects the incident light with a reflectivity of at least 85%. (Item 52) The system further comprises a second waveguide and a third waveguide, wherein the second waveguide is configured to output light in a different wavelength range than the third waveguide. The first, second, and third waveguides each include a reflective diffractive optical element, and the reflective diffractive optical element is The protrusion on the surface of the first waveguide, The interface layer on the protruding portion, The reflective layer on the interface layer and An optical device as described in item 45, comprising: (Item 53) The optical device according to item 45, wherein the first surface comprises a wall defining the boundary of the reflective layer. (Item 54) The optical device according to item 53, wherein the wall comprises a mechanical spacer configured to maintain space between the first waveguide and the other waveguide. (Item 55) The optical device according to item 45, wherein the optical device is a display system comprising a spatial light modulator, the spatial light modulator is configured to output light containing image information onto the reflective diffractive optical element. (Item 56) The optical device according to item 45, further comprising a capping layer on the reflective layer. [Brief explanation of the drawing]

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

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

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

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

[0020] [Figure 4B]Figure 4B illustrates an example of different near and far accommodative states and convergence / divergence motion states of a pair of user eyes.

[0021] [Figure 4C] Figure 4C illustrates an example of how the upper and lower figures represent a user viewing content through a display system.

[0022] [Figure 4D] Figure 4D illustrates another embodiment of the representation of the upper and lower figures of a user viewing content through a display system.

[0023] [Figure 5] Figure 5 illustrates aspects of an approach to simulating a 3D image by correcting wavefront divergence.

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

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

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

[0027] [Figure 9A] Figure 9A shows a cross-sectional side view of an embodiment of a stacked waveguide set, each including an internally coupled optical element.

[0028] [Figure 9B] Figure 9B shows a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A.

[0029] [Figure 9C]Figure 9C shows top and bottom plan views of the embodiment of the multiple stacked waveguides shown in Figures 9A and 9B.

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

[0031] [Figure 10] Figure 10 illustrates an embodiment of a cross-sectional view of an optical projector system and waveguide for directing light towards the viewer.

[0032] [Figure 11A] Figures 11A and 11B illustrate embodiments of internal coupling of light into a waveguide at different incidence angles. [Figure 11B] Figures 11A and 11B illustrate embodiments of internal coupling of light into a waveguide at different incidence angles.

[0033] [Figure 12A] Figures 12A and 12B illustrate examples of the effects of re-bounce of internally coupled light within a waveguide. [Figure 12B] Figures 12A and 12B illustrate examples of the effects of re-bounce of internally coupled light within a waveguide.

[0034] [Figure 13] Figures 13A–13C illustrate embodiments of waveguide stacks and constituent waveguides, illustrating the distribution rate of re-bounces within waveguides positioned beyond the focal length of the corresponding projection optical system.

[0035] [Figure 14] Figures 14A-14B illustrate an example of truncation of an internally coupled optical element in an exemplary waveguide.

[0036] [Figure 15] Figure 15 shows top and bottom diagrams of an exemplary arrangement of internally coupled optical elements within a waveguide stack.

[0037] [Figure 16] Figures 16 and 17 illustrate examples of improved internal coupling efficiency due to truncation of internal coupling optical elements. [Figure 17] Figures 16 and 17 illustrate examples of improved internal coupling efficiency due to truncation of internal coupling optical elements.

[0038] [Figure 18] Figures 18A and 18B depict embodiments of waveguides and waveguide stacks having transparent internal coupling optical elements.

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

[0040] [Figure 19B] Figure 19B shows a schematic cross-sectional side view of a reflective layer deposited on a pattern of protrusions according to several other embodiments.

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

[0042] [Figure 20A] Figure 20A shows a schematic perspective view of the confined area for forming a reflective layer on a projection pattern from a reflective flowable material, according to several embodiments.

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

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

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

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

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

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

[0049] [Figure 22C] Figure 22C is an electron microscope image of a reflective layer formed using silver ion reduction according to several embodiments.

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

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

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

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

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

[0055] [Figure 25] Figure 25 is a flowchart illustrating a method for fabricating an optical waveguide structure as described herein. [Modes for carrying out the invention]

[0056] AR and / or VR systems can display virtual content to a user, i.e., a viewer. Preferably, this content is displayed on a head-mounted display, such as part of eyeglasses, which projects image information onto the user's eyes. In addition, if the system is an AR system, the display may also transmit light from the user's surrounding environment to the eyes, enabling a view of that surrounding environment. As used herein, “head-mounted” or “head-mountable” display should be understood as a display that can be mounted on the head of a viewer or user.

[0057] In some display systems, multiple waveguides constituting a stack of waveguides may be configured to form virtual images in multiple virtual depth planes (also referred to herein simply as “depth planes”) that are perceived as being at different distances from the user. In some embodiments, different waveguides in the stack of waveguides may have optical structures that provide different refractive powers, thereby simulating wavefront divergence of light propagating from objects at different distances from the user’s eye. In some embodiments, as an alternative to, or in addition to, the waveguide optical structures for providing refractive power, the display system may also include multiple lenses that provide, or in addition to, refractive power. Light from an image source may be directed toward the waveguides and internally coupled into the individual waveguides by internal coupling optical elements of each waveguide. The internal coupling optical elements may be diffractive optical elements such as gratings.

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

[0059] Some embodiments disclosed herein provide diffractive optical elements, which are also internally coupled optical elements and may be configured to mitigate optical losses resulting from the re-bounce of internally coupled light within a waveguide. Depending on the internal coupling of incident light, the diffractive optical element can generally redirect the light so that it propagates through the waveguide in the direction of propagation. In some cases, the re-bounce of internally coupled light occurs in the direction of propagation toward the side of the internally coupled optical element. For example, some incident light initially internally coupled near the opposite (opposite in the direction of propagation) side of the internally coupled optical element may re-bounce, i.e., be reflected from another surface of the waveguide and then strike the internally coupled optical element again. Although not limited by theory, depending on the impact with the internally coupled optical element, some of the incident light may again be undesirably externally coupled by the optical element and / or absorbed by the optical element (e.g., absorbed by a reflective coating on a diffraction grating if the internally coupled optical element is a reflective diffractive optical element).

[0060] In some embodiments, to mitigate optical loss due to re-bounce, the internally coupled optical element is truncated on the propagation direction side of the optical element. Advantageously, truncation can reduce the occurrence of optical loss caused by re-bounce by reducing the available area of ​​the internally coupled optical element where re-bounce is likely to result in undesirable optical loss. In some embodiments, the truncation may be a complete truncation of the entire structure of the internally coupled optical element, for example, the truncation may involve a reduction in the area of ​​the internally coupled optical element in the direction of light propagation. In some other embodiments, where the internally coupled optical element comprises a reflective coating (e.g., a reflective layer such as a metallic layer), a portion of the internally coupled optical element on the propagation direction side may not be coated such that the portion of the optical element on the propagation direction side absorbs little to no re-bounced light and / or externally couples the re-bounced light with lower efficiency. In some embodiments, as shown in the figures above and below, the diffraction region of the internally coupled optical element may have a width shorter than its length perpendicular to the propagation direction along the propagation direction, a smaller width-to-length ratio than that of the untruncated diffraction region, and / or may be sized and shaped such that a first portion of the beam of light from the projection optical system is incident on the diffraction region and a second portion of the beam of light does not occur on the diffraction region but collides on the waveguide (for example, portions of optical elements with high absorptivity and / or external coupling efficiency are 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 between waveguides across the stack of waveguides. For example, the width-to-length ratio of the internally coupled optical element in each waveguide may vary between different waveguides in the stack of waveguides.

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

[0062] Here, we refer to drawings where the same reference number refers to the same part throughout. Unless otherwise indicated, the drawings are schematic and not necessarily drawn to exact scale.

[0063] Exemplary display system Figure 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 and may form an image of the object in different locations on the retina of each eye. This may be called binocular parallax and can be used by the human visual system to provide a sense of depth. Conventional display systems simulate binocular parallax by presenting two distinctly different 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 that each eye would see as the virtual object would be the real object at a desired depth. These images provide binocular cues that the user's visual system interprets to derive a sense of depth.

[0064] Continuing with Figure 2, images 190 and 200 are spaced 230 units away from eyes 210 and 220 on the z-axis. The z-axis is parallel to the viewer's optical axis when the eyes are gazing at an object at optical infinity directly in front of the viewer. Images 190 and 200 are flat and at a fixed distance from eyes 210 and 220. Based on slightly different views of the virtual object in the images presented to eyes 210 and 220, respectively, the eyes may rotate so that the image of the object comes to the corresponding point on the respective retina of the eye, maintaining monobiocular vision. This rotation can converge the lines of sight of eyes 210 and 220 to a point in space where the virtual object is perceived to exist. As a result, the provision of three-dimensional images conventionally involves manipulating the convergence and divergence movements of the user's eyes 210 and 220 and providing binocular cues that the human visual system interprets to provide depth perception.

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

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

[0067] Referring here to Figure 4A, the representation of the accommodation-convergence-divergence response of the human visual system is illustrated. Eye movement to gaze at an object causes the eye to receive light from the object, and the light forms an image on each retina of the eye. The presence of retinal blur in the image formed on the retina can provide cues for accommodation, and the relative location of the image on the retina can provide cues for convergence-divergence movement. The cues for accommodation produce accommodation, resulting in the lens of the eye taking on a specific accommodative state in which a focused image of the object is formed on the retina of the eye (e.g., the fovea). On the other hand, the cues for convergence-divergence movement produce convergence-divergence movement (rotation of the eye) so that the image formed on each retina of each eye is at the corresponding retinal point that maintains monobiocular vision. At these positions, the eye can be said to be in a specific convergence-divergence state. Continuing to refer to Figure 4A, accommodation can be understood as the process by which the eye achieves a specific state of accommodation, and convergence / divergence can be understood as the process by which the eye achieves a specific state of convergence / divergence. As shown in Figure 4A, the state of accommodation and convergence / divergence 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] While not limited by theory, it is thought that an object viewer may perceive an object as "three-dimensional" due to a combination of convergence-divergence movements and accommodation. As mentioned earlier, convergence-divergence movements of two eyes relative to each other (e.g., eye rotations such as pupils moving toward or away from each other, converging the lines of sight and gazing at an object) are closely related to the accommodation of the eye's lens. Under normal conditions, changing the shape of the eye's lens and shifting focus from one object to another at a different distance will automatically produce a coherent change in convergence-divergence movements to the same distance, under a relationship known as the "accommodation-convergence-divergence reflex." Similarly, changes in convergence-divergence movements will, under normal conditions, trigger a coherent change in lens shape.

[0069] Referring now to Figure 4B, embodiments of different accommodation and convergence / divergence states of the eyes are illustrated. Pair of eyes 222a gaze at an object at optical infinity, while pair of eyes 222b gaze at an object 221 below optical infinity. Notably, the convergence / divergence states of each pair of eyes are different, with pair of eyes 222a pointing straight ahead, while pair of eyes 222 converges on the 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 the lenses 210a and 220a.

[0070] Unfortunately, many users of conventional "3-D" display systems find such systems uncomfortable or completely fail to perceive depth due to the mismatch between the accommodation and convergence / divergence states in these displays. As mentioned earlier, many stereoscopic or "3-D" display systems display scenes by providing slightly different images to each eye. Such systems are uncomfortable for many viewers because they, above all, simply provide different presentations of scenes and cause changes in the convergence / divergence states of the eyes, but without corresponding changes in the accommodation states of those eyes. Rather, the images are presented by the display at a fixed distance from the eyes so that the eyes perceive all image information in a single accommodation state. Such arrangements go against the "accommodation-convergence / divergence reflex" by causing changes in the convergence / divergence state without corresponding changes in the accommodation state. This mismatch is thought to cause viewer discomfort. A display system that provides better integration between distance accommodation and convergence / divergence motion can create a more realistic and comfortable simulation of three-dimensional images.

[0071] While not limited by theory, the human eye is typically thought to be capable of interpreting a finite number of depth planes and providing depth perception. Consequently, a highly realistic simulation of perceived depth can be achieved by providing the eye with different presentations of images corresponding to each of these limited number of depth planes. In some embodiments, the different presentations may provide both cues for convergence-divergence movements and matching cues for accommodation, thereby providing physiologically correct accommodation-convergence-divergence movement matching.

[0072] Continuing with Figure 4B, two depth planes 240 are illustrated, corresponding to different spatial distances from eyes 210 and 220. With respect to a given depth plane 240, condensation-divergence motion cues may be provided by displaying appropriately different viewpoint images for each eye 210 and 220. In addition, with respect to a given depth plane 240, the light forming the image provided to each eye 210 and 220 may have wavefront divergence corresponding to a light field generated by a point at a distance in that depth plane 240.

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

[0074] Referring here to Figures 4C and 4D, embodiments of aligned accommodation-convergence-divergence distance and misaligned accommodation-convergence-divergence distance are illustrated, respectively. As shown in Figure 4C, the display system may provide images of virtual objects to each eye 210, 220. The images can 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 images may be formed by light having a wavefront curvature corresponding to a real object in its depth plane 240. As a result, the eyes 210, 220 assume an accommodation state in which the images are in focus on the retinas of their eyes. Thus, the user can perceive the virtual object as being at point 15 on the depth plane 240.

[0075] It should be understood that the accommodation and convergence / divergence states of eyes 210 and 220 are each associated with a specific distance on the z-axis. For example, an object at a specific distance from eyes 210 and 220 will cause those eyes to assume a specific accommodation state based on the distance of the object. The distance associated with a specific accommodation state is the accommodation distance A. d It can be called a specific convergence-divergence distance V associated with the eye in a specific convergence-divergence movement state. d Alternatively, relative positions exist. When the near and far accommodation distance and the convergence / divergence distance are consistent, the relationship between near and far accommodation and convergence / divergence can be said to be physiologically correct. This is considered the most comfortable scenario for the viewer.

[0076] However, in stereoscopic displays, the accommodation distance and the convergence / divergence distance may not always be consistent. For example, as illustrated in Figure 4D, the images displayed to eyes 210 and 220 may be displayed with wavefront divergence corresponding to the depth plane 240, and eyes 210 and 220 may take on a specific accommodation state in which points 15a and 15b on their depth plane are in focus. However, the images displayed to eyes 210 and 220 may provide cues for convergence / divergence movements that cause eyes 210 and 220 to converge on point 15, which 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 eyes 210 and 220 to the depth plane 240, while the convergence / divergence distance corresponds to a larger distance from the exit pupils of eyes 210 and 220 to point 15. The accommodation distance is different from the convergence / divergence distance. As a result, there is a mismatch in accommodation-convergence / divergence motion. Such mismatches are considered undesirable and can cause discomfort to the user. The mismatch is due to distance (e.g., V d -A d Please understand that this corresponds to and can be characterized using diopters.

[0077] It should be understood that in some embodiments, reference points other than the exit pupils of eyes 210, 220 may be used to determine distances for determining accommodation distance and convergence / divergence mismatch, insofar as the same reference point is used for the near and far accommodation distance and convergence / divergence 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., the waveguide of a display device) to the depth plane, etc.

[0078] While not limited by theory, it is still conceivable that users can perceive physiologically correct accommodation-convergence-divergence mismatches of up to 0.25 diopters, up to 0.33 diopters, and up to approximately 0.5 diopters without the mismatch itself causing significant discomfort. In some embodiments, the display systems disclosed herein (e.g., display system 250, Figure 6) present the viewer with an image having accommodation-convergence-divergence mismatch of 0.5 diopters or less. In some other embodiments, the accommodation-convergence-divergence mismatch of the image provided by the display system is approximately 0.33 diopters or less. In yet another embodiment, the accommodation-convergence-divergence mismatch of the image provided by the display system is 0.25 diopters or less, including approximately 0.1 diopters or less.

[0079] Figure 5 illustrates an aspect of an approach to simulating a three-dimensional image by correcting wavefront divergence. The display system includes a waveguide 270 configured to receive light 770 encoded with image information and output the light to the user's eye 210. The waveguide 270 may output light 650 with a defined amount of wavefront divergence corresponding to the wavefront divergence of the light field generated by a point on a desired depth plane 240. In some embodiments, the same amount of wavefront divergence is provided for all objects presented on that depth plane. In addition, the user's other eye may be shown to be 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 one or a limited number of depth planes, and / or the waveguide may be configured to output light of a limited range of wavelengths. As a result, in some embodiments, multiple or stacked waveguides may be used to provide different wavefront divergences for different depth planes, and / or to output light of different ranges of wavelengths. As used herein, it will be understood that the depth plane may be a plane or follow the contour of a curved surface. One or more waveguides in a stack may comprise a reflective diffractive optical element having a reflective layer comprising, essentially, or consisting of, pure or substantially pure metal, as described herein.

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

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

[0083] Continuing with Figure 6, the waveguide assembly 260 may also include several features 320, 330, 340, and 350 between the waveguides. In some embodiments, features 320, 330, 340, and 350 may be one or more lenses. Waveguides 270, 280, 290, 300, and 310 and / or several lenses 320, 330, 340, and 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 specific depth plane and may be configured to output image information corresponding to that depth plane. Image input devices 360, 370, 380, 390, and 400 may function as light sources for the waveguides and may be used to input image information into waveguides 270, 280, 290, 300, and 310, and each may be configured to disperse incident light across each individual waveguide for output toward the eye 210, as described herein. The light exits from the output surfaces 410, 420, 430, 440, and 450 of image input devices 360, 370, 380, 390, and 400 and is input into the corresponding input surfaces 460, 470, 480, 490, and 500 of waveguides 270, 280, 290, 300, and 310. In some embodiments, the input surfaces 460, 470, 480, 490, and 500 may each be the edge of the corresponding waveguide or a portion of the main 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 injected into each waveguide to output a whole field of cloned collimated beams, which are directed toward the eye 210 at a specific angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, one of the image input devices 360, 370, 380, 390, and 400 may be associated with a plurality (e.g., three) of waveguides 270, 280, 290, 300, and 310 to injected light into them.

[0084] In some embodiments, the image input devices 360, 370, 380, 390, and 400 are discrete displays that generate image information for input into the corresponding waveguides 270, 280, 290, 300, and 310, respectively. In some other embodiments, the image input devices 360, 370, 380, 390, and 400 are output terminals of a single multiplexed display that can send image information to each of the image input devices 360, 370, 380, 390, and 400 via, for example, one or more optical conduits (such as optical fiber cables). It should be understood that the image information provided by the image input devices 360, 370, 380, 390, and 400 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0085] In some embodiments, the light introduced into waveguides 270, 280, 290, 300, and 310 is provided by an optical projector system 520, which comprises an optical module 530, which may include an optical emitter such as a light-emitting diode (LED). The light from the optical module 530 may be directed and modified by an optical modulator 540, such as a spatial light modulator, via a beam splitter 550. The optical modulator 540 may be configured to change the perceived intensity of the light introduced into waveguides 270, 280, 290, 300, and 310, thereby encoding the light with image information. Embodiments of the spatial light modulator include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. Image input devices 360, 370, 380, 390, and 400 are graphically illustrated, and it should be understood that in some embodiments, these image input devices may represent different optical paths and locations within a common projection system, configured to output light into associated waveguides 270, 280, 290, 300, and 310. In some embodiments, the waveguides of waveguide assembly 260 may function as ideal lenses, relaying the light input 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 the 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 scanning, helical scanning, Lissajous patterns, 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 input devices 360, 370, 380, 390, 400 may schematically represent a single scanning fiber or a bundle of scanning fibers configured to input light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image input devices 360, 370, 380, 390, 400 may schematically represent a plurality of scanning fibers or a plurality of bundles of scanning fibers, each configured to input light into one of the associated 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 multiple fibers and one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light emitted from the scanning fiber into one or more waveguides 270, 280, 290, 300, 310.

[0087] The controller 560 controls the operation of one or more of the stacked waveguide assemblies 260, including the operation of the image input devices 360, 370, 380, 390, 400, the light source 530, and the optical modulator 540. In some embodiments, the controller 560 is part of the local data processing module 140. The controller 560 includes programming (e.g., instructions in a non-transient medium) to coordinate the timing and provisioning of image information to the waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by wired or wireless communication channels. In some embodiments, the controller 560 may be part of the processing module 140 or 150 (Figure 9D).

[0088] Continuing with Figure 6, waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Waveguides 270, 280, 290, 300, and 310 may each be planar or have another shape (e.g., curved), with major upper and lower surfaces and edges extending between their major upper and lower surfaces. In the illustrated configuration, waveguides 270, 280, 290, 300, and 310 may each include external coupling optical elements 570, 580, 590, 600, and 610, respectively, configured to extract light from the waveguide by redirecting the light propagating within each individual waveguide and outputting image information to the eye 210. The extracted light may also be referred to as externally coupled light, and the external coupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light can be output by the waveguide at the point where light propagating within the waveguide strikes the light extraction optical element. The external coupling optical elements 570, 580, 590, 600, 610 may be gratings, for example, including diffractive optical features as further discussed herein. For ease of explanation and clarity of the drawings, they are shown positioned on the bottom main surfaces of the waveguides 270, 280, 290, 300, 310, but in some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be positioned on the top and / or bottom main surfaces, and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as further discussed herein. In some embodiments, the external coupling optical elements 570, 580, 590, 600, 610 may be mounted on a transparent substrate and formed within a layer of material that forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be monolithic components of the material, and the external coupling optical elements 570, 580, 590, 600, 610 may be formed on and / or inside the surface of that component of the material.

[0089] Continuing with reference to Figure 6, as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to emit light and form an image corresponding to a specific 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 the optical infinity focal plane. The next upper waveguide 280 may be configured to emit collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such a first lens 350 may generate some convex wavefront curvature so that the eye / brain interprets the light originating from the next upper waveguide 280 as originating from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to generate a different, gradually increasing wavefront curvature so that the eye / brain interprets the light originating from the third waveguide 290 as originating from a second focal plane that is closer inward toward the person from optical infinity than the light originating from the next upper waveguide 280.

[0090] Other waveguide layers 300, 310 and lenses 330, 320 are configured similarly, with the highest waveguide 310 in the stack emitting its output through all the lenses between it and the eye for a convergent focusing force representing the focal plane closest to the person. When viewing / interpreting light originating from the other side world 510 of the stacked waveguide assembly 260, a compensating lens layer 620 may be positioned on top of the stack to compensate for the convergent forces of the lower lens stacks 320, 330, 340, 350 to compensate for the stack of lenses 320, 330, 340, 350. Such a configuration provides the same number of perceived focal planes as there are available waveguide / lens pairs. Both the external coupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electroactive). In some alternative embodiments, one or both may be dynamic using electroactive features.

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

[0092] Continuing with Figure 6, the external coupling optical elements 570, 580, 590, 600, and 610 may be configured to redirect light from their respective waveguides for specific depth planes associated with the waveguides and to output the light with an appropriate amount of divergence or collimation. As a result, waveguides with different associated depth planes may have different configurations of the external coupling optical elements 570, 580, 590, 600, and 610, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light extraction optical elements 570, 580, 590, 600, and 610 may be volumetric or surface features, which may be configured to output light at specific angles. For example, the light extraction optical elements 570, 580, 590, 600, and 610 may be stereoscopic holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, and 350 may not be lenses. Rather, they may simply be spacers (e.g., structures for forming cladding layers and / or voids).

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

[0094] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal, in which microdroplets have a diffraction pattern in the host medium, and the refractive index of the microdroplets 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 light and infrared light cameras) may be provided to capture images of the eye 210 and / or the surrounding tissues, for example, to detect user input and / or monitor the user's physiological state. As used herein, the camera may be any image-capturing device. In some embodiments, the camera assembly 630 may include the image-capturing device and a light source that projects light (e.g., infrared light) onto the eye, which is then reflected by the eye and can be detected by the image-capturing device. In some embodiments, the camera assembly 630 may be mounted on a frame 80 (Figure 9D) and may communicate with processing modules 140 and / or 150 that can process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be used per eye to monitor each eye separately.

[0096] Referring here to Figure 7, an embodiment of an outgoing beam output by a waveguide is shown. Although one waveguide is illustrated, other waveguides within the waveguide assembly 260 (Figure 6) may function similarly, and it should be understood that the waveguide assembly 260 includes multiple waveguides. Light 640 is introduced into the waveguide 270 at the input surface 460 of the waveguide 270 and propagates through the waveguide 270 by TIR. At the point where the light 640 collides on the DOE 570, a portion of the light exits the waveguide as an outgoing beam 650. The outgoing beam 650 is illustrated as substantially parallel, but may be redirected to propagate to the eye 210 at a certain angle (e.g., divergent outgoing beam formation) depending on the depth plane associated with the waveguide 270, as discussed herein. It should be understood that a nearly parallel emitted beam may represent a waveguide with an external coupling optical element that externally couples the light to form an image that appears to be set in the depth plane at a distance from the eye 210 (e.g., optical infinity). Other waveguides or other sets of external coupling optical elements may output a more divergent emitted beam pattern, which would require the eye 210 to adjust to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0097] In some embodiments, a full-color image may be formed in each depth plane by overlaying an image onto each of primary colors, for example, three or more primary colors. Figure 8 illustrates an embodiment of a stacked waveguide assembly, where each depth plane includes an image formed using several different primary colors. The illustrated embodiment shows depth planes 240a–240f, but more or fewer depths are also conceivable. Each depth plane may have three or more associated primary color images, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are indicated in the figure by different numbers relating to diopters (dpt) following the letters G, R, and B. As merely an embodiment, the numbers following each of these letters indicate diopters (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the figure represents an individual primary color image. In some embodiments, the precise location of the depth plane for different primary colors may vary to account for differences in the focusing of light of different wavelengths in the eye. 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 arrangements may increase visual acuity and user comfort and / or reduce chromatic aberration.

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

[0099] Continuing to refer to Figure 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors 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] Throughout this disclosure, any reference to a given color of light should be understood as encompassing one or more wavelengths of light within a range of wavelengths that are perceived by the viewer as that given color. For example, red light may include one or more wavelengths of light in the range of approximately 620–780 nm, green light may include one or more wavelengths of light in the range of approximately 492–577 nm, and blue light may include one or more wavelengths of light in the range of approximately 435–493 nm.

[0101] In some embodiments, the light source 530 (Figure 6) may be configured to emit light of one or more wavelengths outside the viewer's visual perception range, such as infrared and / or ultraviolet wavelengths. In addition, internal coupling, external coupling, and other light redirection structures of the waveguide of the display 250 may be configured to direct and emit this light from the display toward the user's eye 210, for example, for imaging and / or user stimulation applications. In some embodiments, the internal coupling optical element and / or other light redirection structure comprises a reflective diffractive optical element having a reflective layer containing a metal deposited by wet chemical action as described herein. In some embodiments, the reflective layer may be formed from a metal essentially consisting of or comprising pure or substantially pure metal, formed by wet chemical action as described herein.

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

[0103] The illustrated set of stacked waveguides 660 includes waveguides 670, 680, and 690. Each waveguide includes associated internal coupling optical elements (which may also be referred to as optical input areas on the waveguide), for example, internal coupling optical element 700 is located on the main surface of waveguide 670 (e.g., the upper main surface), internal coupling optical element 710 is located on the main surface of waveguide 680 (e.g., the upper main surface), and internal coupling optical element 720 is located on the main surface of waveguide 690 (e.g., the upper main surface). In some embodiments, one or more of the internal coupling optical elements 700, 710, and 720 may be located on the bottom main surfaces of individual waveguides 670, 680, and 690 (in particular, one or more internal coupling optical elements are reflective deflection optical elements). As illustrated, the internally coupled optical elements 700, 710, and 720 may be located on the upper main surface of their respective waveguides 670, 680, and 690 (or on the upper part of the following lower waveguide), and in particular, these internally coupled optical elements are transmissive deflection optical elements. In some embodiments, the internally coupled optical elements 700, 710, and 720 may be located within the body of the respective waveguides 670, 680, and 690. In some embodiments, as discussed herein, the internally coupled optical elements 700, 710, and 720 are wavelength-selective, selectively redirecting one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 670, 680, and 690, it should be understood that in some embodiments, the internally coupled optical elements 700, 710, and 720 may be located within other areas of their respective waveguides 670, 680, and 690. In some embodiments, the internally coupled optical element and / or other optical redirection structure comprises a reflective diffractive optical element having a reflective layer comprising a metal formed by wet chemical action as described herein. In some embodiments, the reflective layer may consist of, or be composed of, a pure or substantially pure metal formed by wet chemical action as described herein.

[0104] As illustrated, the internally coupled optical elements 700, 710, and 720 may be offset laterally from one another. In some embodiments, each internally coupled optical element may be offset so that its light does not pass through another internally coupled optical element before receiving light. For example, each internally coupled optical element 700, 710, and 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in Figure 6, and may be separated from the other internally coupled optical elements 700, 710, and 720 (e.g., separated laterally) so that it does not substantially receive light from the other internally coupled optical elements 700, 710, and 720.

[0105] Each waveguide also includes associated optical dispersion elements, for example, optical dispersion element 730 is located on the main surface (e.g., upper main surface) of waveguide 670, optical dispersion element 740 is located on the main surface (e.g., upper main surface) of waveguide 680, and optical dispersion element 750 is located on the main surface (e.g., upper main surface) of waveguide 690. In some other embodiments, optical dispersion elements 730, 740, and 750 may be located on the bottom main surfaces of the associated waveguides 670, 680, and 690, respectively. In some other embodiments, optical dispersion elements 730, 740, and 750 may be located on both the top and bottom main surfaces of the associated waveguides 670, 680, and 690, respectively, or optical dispersion elements 730, 740, and 750 may be located on different top and bottom main surfaces within different associated waveguides 670, 680, and 690, respectively.

[0106] Waveguides 670, 680, and 690 may be separated and isolated by, for example, gaseous, 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 immediate vicinity of waveguides 670, 680, and 690). Preferably, the refractive index of the material forming layers 760a and 760b is 0.05 or greater than the refractive index of the material forming waveguides 670, 680, and 690, or 0.10 or less. 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 upper and lower main surfaces of each waveguide). In some embodiments, layers 760a, 760b are formed from air. It should be understood that, although not shown, the upper and lower parts of the illustrated set 660 waveguides may also include an immediate cladding layer.

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

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

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

[0110] For example, the internally coupled optical element 700 may be configured to transmit rays 780 and 790 having different second and third wavelengths or wavelength ranges, respectively, while deflecting a ray 770 having a first wavelength or wavelength range. The transmitted ray 780 collides with an internally coupled optical element 710 configured to selectively deflect light of the second wavelength or wavelength range, and is thereby deflected. The ray 790 is deflected by an internally coupled optical element 720 configured to selectively deflect light of the third wavelength or wavelength range.

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

[0112] Referring now to Figure 9B, a perspective view of an embodiment of the multiple stacked waveguides shown in Figure 9A is illustrated. As previously mentioned, the internally coupled rays 770, 780, and 790 are deflected by the internally coupled optical elements 700, 710, and 720, respectively, and then propagate by TIR within waveguides 670, 680, and 690, respectively. The rays 770, 780, and 790 then collide with the optical dispersion elements 730, 740, and 750, respectively. The optical dispersion elements 730, 740, and 750 deflect the rays 770, 780, and 790 so that they propagate toward the externally coupled optical elements 800, 810, and 820, respectively.

[0113] In some embodiments, the light dispersion elements 730, 740, and 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light to the external coupling optical elements 800, 810, and 820, and in some embodiments, they can also increase the beam or spot size of the light as it propagates to the external coupling optical elements. In some embodiments, the light dispersion elements 730, 740, and 750 may be omitted, and the internal coupling optical elements 700, 710, and 720 may be configured to deflect light directly to the external coupling optical elements 800, 810, and 820. For example, referring to Figure 9A, the light dispersion elements 730, 740, and 750 may be replaced by the external coupling optical elements 800, 810, and 820, respectively. In some embodiments, the external coupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light towards the viewer's eye 210 (Figure 7). It should be understood that the OPEs may be configured to increase the dimensions of the eyebox along at least one axis, and the EPEs may increase the eyebox along axes that intersect with the axes of the OPEs, for example, orthogonal axes. For example, each OPE may be configured to redirect a portion of the light impacting the OPE to an EPE in the same waveguide, while allowing the rest of the light to continue propagating along the waveguide. In response to the impact on the OPE, another portion of the remaining light is again redirected to the EPE, and the rest of that portion continues to propagate further along the waveguide, etc. Similarly, in response to the impact on the EPE, a portion of the impacting light is directed out of the waveguide towards the user, and the rest of that light continues to propagate through the waveguide until it impacts the EP again, at which point another portion of the impacting light is directed out of the waveguide, and so on. As a result, the internally coupled single beam of light is "duplicated" each time a portion of its light is redirected by the 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] Therefore, referring to Figures 9A and 9B, in some embodiments, the set of waveguides 660 includes, for each primary color, waveguides 670, 680, 690, internally coupled optical elements 700, 710, 720, optical dispersion elements (e.g., OPE) 730, 740, 750, and externally coupled optical elements (e.g., EP) 800, 810, 820. Waveguides 670, 680, 690 may be stacked with air gaps / cladding layers between each one. The internally coupled optical elements 700, 710, 720 redirect or deflect the incident light into their waveguides (using different internally coupled optical elements that receive light of different wavelengths). The light then propagates within the individual waveguides 670, 680, 690 at angles that will result in a TIR. In the embodiment shown, a ray 770 (e.g., blue light) is polarized by the first internal coupling optical element 700 in the manner described above, and then continues to bounce along the waveguide, interacting with the optical dispersion element (e.g., OPE) 730 and then the external coupling optical element (e.g., EP) 800. Rays 780 and 790 (e.g., green and red light, respectively) pass through waveguide 670, with ray 780 colliding with the internal coupling optical element 710, thereby being deflected. Ray 780 will then bounce along waveguide 680 via TIR, proceeding to its optical dispersion element (e.g., OPE) 740 and then the external coupling optical element (e.g., EP) 810. Finally, ray 790 (e.g., red light) passes through waveguide 690 and colliding with the optical internal coupling optical element 720 of waveguide 690. The internal optical coupling element 720 deflects the ray 790 so that it propagates by TIR to the optical dispersion element (e.g., OPE) 750, and then by TIR to the external coupling optical element (e.g., EP) 820. The external coupling optical element 820 then finally externally couples the ray 790 to the viewer, who also receives externally coupled light from the other waveguides 670, 680.

[0115] Figure 9C illustrates upper and lower plan views of embodiments of the multiple stacked waveguides shown in Figures 9A and 9B. As shown, waveguides 670, 680, and 690 may be vertically aligned with their associated optical dispersion elements 730, 740, and 750 and associated external coupling optical elements 800, 810, and 820. However, as discussed herein, the internal coupling optical elements 700, 710, and 720 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced, as seen in the upper and lower figures). As further discussed herein, this non-overlapping spatial arrangement facilitates the ingress of light from different resources into different waveguides on a one-to-one basis, thereby enabling a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrangements including non-overlapping, spatially separated internal coupling optical elements may be referred to as pupil-shifting systems, where the internal coupling optical elements in these arrangements may correspond to subpupils.

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

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

[0118] Continuing to refer to Figure 9D, the display 70 is operably coupled to the local data processing module 140 by a communication link 130, such as a wired cable or wireless connectivity, which may be mounted in various configurations, such as being fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded in headphones, or otherwise removable by the user 90 (e.g., in a backpack configuration, in a belt-mounted configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, such as a wired cable or wireless connectivity. The local processing and data module 140 may include a hardware processor and digital memory such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be used to assist in data processing, caching, and storage. Optionally, the 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 (image capture devices (such as cameras), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., operably coupled to frame 80 or otherwise attached to user 90), and / or b) data acquired and / or processed using the remote processing module 150 and / or remote data repository 160 (including data related to virtual content) for passing to display 70 after processing or reading, as possible. The local processing and data module 140 may be operably coupled to the remote processing module 150 and the remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, so that these remote modules 150, 160 are operably coupled to each other and available as resources to the local processing and data module 140.In some embodiments, the local processing and data module 140 may include one or more of the following: an image acquisition device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope. In some other embodiments, one or more of these sensors may be mounted on the frame 80 or may be a standalone structure communicating with the local processing and data module 140 via a wired or wireless communication path.

[0119] Continuing to refer to Figure 9D, in some embodiments, the 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, the 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, the remote data repository 160 may comprise one or more remote servers that provide information, for example, augmented reality content, for generating to the local processing and data modules 140 and / or the remote processing module 150. In some embodiments, all data is stored, and all calculations are performed within the local processing and data modules, enabling fully autonomous use from the remote modules. Optionally, an external system (e.g., one or more processors, one or more computer systems), including a CPU, GPU, etc., may perform at least part of the processing (e.g., generating image information, processing data) and provide information to modules 140, 150, and 160, and receive information from them, for example, via a wireless or wired connection.

[0120] Exemplary optical projector system and related structure Figure 10 illustrates an embodiment of a cross-sectional view of an optical projector system 2000 and an eyepiece 2010 for directing light towards the viewer's eye 210. As discussed herein, multiple optical emitters 2020 (e.g., multiple LEDs) may be used to illuminate a spatial light modulator (SLM) 2030. The optical emitters 2020 may be part of an optical module 2040. In some embodiments, a beam splitter (e.g., a polarizing beam splitter (PBS)) 2050 may be used to reflect light from the optical emitters 2020 to the spatial light modulator 2030, which reflects and modulates the light. The modulated light from the SLM 2030 can then propagate through the beam splitter 2050 to an eyepiece 2010, which may include one or more waveguides. In some embodiments, the eyepiece 2010 may correspond to a waveguide stack 260 (Figure 6) or 660 (Figures 9A-9C). The waveguide of the eyepiece 2010 relays or guides light and outputs it to the viewer's eye 210. Furthermore, it should be understood that the optical projector system 2000 may correspond to the optical projector system 520 (Figure 6). As shown, light propagating through the projection optical system can converge onto the area of ​​the eyepiece 2010. Also, as shown, due to this convergence, light also enters the converged area at different angles.

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

[0122] In some embodiments, the perception of a full-color image by a viewer may be achieved using time-division multiplexing. For example, different light emitters 2020 may be activated at different times to generate different primary color images. In such embodiments, the primary color images 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 higher than 60 Hz. It should be understood that a benefit of time-division multiplexing is that it can reduce the computational load on the processor (e.g., a graphics processor) used to form the displayed image. In some embodiments, where sufficient computational power is available, all primary color images forming a full-color image may be displayed simultaneously.

[0123] Continuing to refer to Figure 10, different color light emitters 2020 (e.g., red, green, and blue LEDs) may be positioned in different locations to illuminate the SLM 2030 and then used to image onto the eyepiece 2010 via a beam splitter 2050. In some embodiments, the SLM 2030 may be based on microelectromechanical technology (MEMS), liquid crystal technology, or other switching technology. In some embodiments, the images of the light emitters are spatially distinct on the eyepiece 2010, as the optical system of the optical projector system 2000 approximates the individual light sources within the eyepiece 2010.

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

[0125] Exemplary internally coupled optical elements As described above, after being internally coupled by an internally coupled optical element, light may be re-bounced, which undesirably can result in optical loss, for example, due to undesirable external coupling or absorption of light in the internally coupled optical element. Optical loss due to the re-bounce of internally coupled light can effectively reduce the net efficiency of the internally coupled optical element.

[0126] Figures 11A and 11B illustrate embodiments of light internally coupled into the waveguide 1110 at different angles of incidence in the outer portion of the internal coupling optical element 1100 (positioned away from the propagation direction of the internally coupled light). As described above, the different angles of incidence may result from the convergence of light from the optical projection system onto the waveguide 1110. Figure 11A depicts the path of the incident beam 11201 incident on the internal coupling optical element 1100 at a substantially inward angle (e.g., also called the "temple" angle, an angle toward the propagation direction 1112 within the waveguide). Figure 11B depicts the path of the incident beam 11202 incident on the waveguide at a substantially outward angle (e.g., also called the "nose" angle, an angle away from the propagation direction 1112 within the waveguide). During operation, the beam of light incident from the projection optical system into the waveguide 1110 can be a transformed or diverging beam containing an inwardly angled component and an outwardly angled component. That is, the beam can converge toward the focal point and then diverge. For example, the beam can diverge when the waveguide 1110 is positioned beyond the focal length of the projection optical system, as will be explained in more detail with reference to Figures 13A-13C.

[0127] Figures 11A and 11B each include a waveguide 1110 having a first main surface, a second main surface opposite the first main surface, and an internal coupling optical element 1100 positioned on the second main surface, the internal coupling optical element 1100 being a reflective optical element. Each beam 11201, 11202 enters the waveguide 1110 through the first main surface, and the internally coupled light propagates within the waveguide 1100 at an angle that supports total internal reflection (TIR), and is generally redirected by TIR to travel along the propagation direction 1112. The internally coupled light is described herein as propagating "along" the propagation direction, and its general aggregated propagation direction is parallel to the propagation direction. It should be understood that this propagation direction may involve multiple bounces of light from the main surfaces of the waveguide 1110. In other words, the propagation direction is the net propagation direction of the light after it has crossed multiple bounces.

[0128] Re-bounce can occur when light is internally coupled at the second primary surface of the waveguide 1110, internally reflected from the first primary surface, and incident on the internally coupled optical element 1100, or undergoes a second bounce there. As shown in Figure 11A, a beam 11201 incident on the internally coupled optical element 1100 at an inward angle typically experiences little to no re-bounce, as the inward angle can result in a relatively large bounce gap 11271, i.e., the distance between any two consecutive reflections on the second primary surface. In contrast, as shown in Figure 11B, a beam 11202 incident on the internally coupled optical element 1100 at an outward angle has a relatively smaller bounce gap 11272 and is therefore more likely to experience re-bounce.

[0129] While not limited by theory, it should be understood that diffractive optical elements can behave symmetrically; that is, they can 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 (e.g., depending on re-bounce) can also be externally coupled. In addition, or alternatively, reflection of light from a layer of material such as a metal can also involve partial absorption of the incident light, since the reflection may involve absorption and emission of light from the material. As a result, external coupling and / or absorption of light can undesirably lead to losses of internally coupled light, and re-bounced light can suffer significant losses compared to light that interacts with the internally coupled optical element only once.

[0130] Figures 12A and 12B further illustrate the optical losses. Figure 12B illustrates an example of the energy profile of the beam internally coupled within waveguide 1110 in Figure 12A at location 1115 along waveguide 1110. Beam 11201, incident inward or at a temple angle, is less likely to suffer a substantial amount of re-bounce, resulting in relatively efficient internal coupling and a substantially uniform beam profile. In contrast, beam 11202, incident outward or at a nose angle, is more likely to suffer a substantial amount of re-bounce, resulting in optical losses within the waveguide after initial internal coupling. In addition, as shown in Figure 12B, the inner or propagation-side portion of the outward-angled beam 11202 (e.g., the portion of beam 11202 closer to the propagation direction 1112) will experience little re-bounce, while the outer portion of beam 11202 further away from the propagation direction 1112 will experience more re-bounce, resulting in further optical loss and potentially causing inconsistent net internal coupling efficiency across the beam profile. If the internally coupled light is used to form an image or a portion of an image, the optical loss due to re-bounce can therefore irregularly reduce the brightness in some parts of the image formed using that light. Furthermore, if the display system includes individual waveguides and internal coupling gratings for red, green, and blue light, such reduced efficiency and / or non-uniformity within any of the waveguides can result in reduced color accuracy, including a 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 re-bounce may also depend, at least in part, on the distance between the waveguide and the incident light source. Figures 13A–13C depict an embodiment of a waveguide stack 1105 illustrating the distribution rate of re-bounce in waveguides positioned beyond the focal length of the corresponding projection optical system. As shown in Figure 13A, the waveguide stack 1105 includes waveguides 1110a, 1110b, and 1110c positioned at a certain distance from the projection optical system 2000. Each waveguide 1110a, 1110b, and 1110c includes internally coupled optical elements 100a, 1100b, and 1100c, respectively, positioned along the main surface of the waveguide 1110a, 1110b, and 1110c further from the projection optical system 2000. The internal coupling optical elements 1100a, 1100b, and 1100c internally couple light from the projection optical system 2000, which is then externally coupled as externally coupled light 1130 within the wearer's field of view.

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

[0133] Figures 13B and 13C are partial enlargements of the system in Figure 13A, illustrating the propagation of light from the display optics 2000 in waveguides 1110a (Figure 13C) and 1110c (Figure 13B). As shown in Figure 13C, re-bounce may not be a substantial concern in waveguides positioned closer to the focal length from the projection optics 2000. Since the light from the projection optics 2000 is still a converged beam before reaching the focal point, the outward-angled beam component 11202 is incident on the inner portion of the internal coupling optics element 1100a (e.g., the propagation direction side of the internal coupling optics element 1100a), while the inward-angled beam component 11201 is incident on the outer portion of the internal coupling optics element 1100a (e.g., the portion of the internal coupling optics element 1100a positioned opposite the propagation direction 1112). Therefore, the relatively short bounce spacing of the internally coupled outward-angled beam 11202 is still long enough for the internally coupled light to propagate along the propagation direction 1112 beyond the sides of the internally coupled optical element 1100a before its second incidence onto the second main surface of the waveguide 1100a. In addition, the bounce spacing of the internally coupled inward-angled beam 11201 is long enough to avoid any re-bounce of the inward-angled beam 11201.

[0134] In contrast, as shown in Figure 13B, re-bounces can be more significantly distributed within the waveguide 1110c, which is positioned beyond the focal length of the projection optical system 2000. Since the light from the projection optical system 2000 is a divergent beam after passing through the focal point, the outward-angled beam component 11202 is incident on the outer portion of the internally coupled optical element 1100c, while the inward-angled beam component 11201 is incident on the inner portion of the internally coupled optical element 1100c. Therefore, the internally coupled inward-angled beam component 11201 still experiences little to no re-bounce, while the internally coupled outward-angled beam component 11202 experiences one or more additional bounces 1135 along the length of the internally coupled optical element 1100c. Since energy can be lost along the length of the internally coupled optical element 1100c with each subsequent bounce, the internally coupled outward-angled beam component 11202 suffers a significant loss compared to the internally coupled inward-angled beam component 11201, which may result in a lower efficiency and / or inconsistent beam profile as described above with reference to Figure 12B. While the light of beam component 11201 is illustrated as not undergoing re-bounce for ease of explanation and illustration, it should be understood that beam component 11201 may undergo re-bounce in some embodiments. However, the number of bounces of beam component 11201 on the internally coupled optical element will be less than that of 11202. Since optical loss is proportional to the number of bounces, beam component 11201 will suffer less optical loss than beam component 11202.

[0135] Figures 14A and 14B illustrate an example of truncation of an internally coupled optical element to mitigate light loss due to re-bounce within an exemplary waveguide. Figures 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 internally coupled optical element 1100b, while waveguides 1110a and 1110b are omitted from Figures 14A and 14B for convenience. The configuration in Figure 14A is substantially identical to the configuration of waveguide 1110c and internally coupled optical element 1100c in Figure 13A. Figure 14B illustrates waveguide 1110c with a truncated internally coupled optical element 1100c.

[0136] Specifically, the truncated internal coupling optical element 1100c in Figure 14B is sized, shaped, and positioned such that at least the inner portion 11221 of the light from the projection optical system 2000 enters onto the waveguide 1110c but not onto the internal coupling optical element 1100c. In some embodiments, the beam of light from the projection optical system 2000 (e.g., represented by a combination of component beams 11201, 11202, and 11203) may define the light beam area on the second primary surface of the waveguide 1110c, and the diffraction region of the internal coupling optical element 1100c may occupy less than the entire light beam area. Generally, the truncated internal coupling optical element 1100c depicted in Figure 14B is asymmetrical with respect to the beam axis extending through the center of the central beam component 11203 of the light from the projection optical system 2000. For example, the truncated internal coupling optical element 1100c may be radially asymmetric and / or reflectivity asymmetric about an axis of symmetry perpendicular to the propagation direction 1112 in the beam axis. In some embodiments, the internal coupling optical element 1100c may be terminated at a location such that the inner portion 11221 of the inward-angled beam component 11201 passes through the second main surface of the waveguide 1110c without being internally coupled. In some other embodiments, such as embodiments in which the internal coupling optical element 1100c comprises an internal coupling grating with a metallized surface, the inner portion of the internal coupling optical element 1100c may not be metallized so that the re-bounce of internally coupled light in the inner portion will not be absorbed or externally coupled as easily as if the inner portion were metallized. Thus, by using the truncated internal coupling optical element 1100c, at least a portion of the inward-angled beam component 11201 can be internally coupled or, with lower efficiency, to the remainder of light from the projection optical system 2000. However, truncation of the internally coupled optical element 1100c also reduces the length, which may result in re-bounce along it with respect to the internally coupled outward-angled beam component 11202.Therefore, despite suffering some loss of internally coupled light at certain angles (i.e., some light from certain angles is not internally coupled, as shown in Figure 14B), the truncated internally coupled optical element 1100c can provide a net increase in internal coupling efficiency because the internally coupled light is not affected by, or is hardly affected by, re-bounce-related external coupling or absorption. As a result, the amount and uniformity of internally coupled light can be improved due to the reduction in re-bounce and associated light loss.

[0137] Figure 15 illustrates an exemplary arrangement of internally coupled optical elements in a waveguide stack, shown in upper and lower views. The configuration in Figure 15 is viewed in a direction along the central beam 11203 of Figure 13A perpendicular to the main surface of the waveguide, and each internally coupled optical element B1, B2, G1, G2, R1, and R2 is configured to internally couple incident light and propagate it along the propagation direction 1112 within its individual waveguide (not shown). Thus, each internally coupled optical element B1, B2, G1, G2, R1, and R2 has a distinctly different associated waveguide. Internally coupled optical elements B1, B2, G1, and G2 may be located on waveguides at or near the focal length of the projection optical system, while internally coupled optical elements R1 and R2 are located on waveguides beyond the focal length of the projection optical system. Thus, internally coupled optical elements R1 and R2 are truncated to reduce re-bounce, as described above. In some embodiments, the truncated regions 1140 of the internally coupled optical elements R1 and R2 may have open spaces that allow light incident on them to pass through the corresponding waveguide without being internally coupled. In other embodiments, the optical elements R1 and R2 may have a highly efficient internally coupled region 1145 (e.g., a portion coated with a reflective layer such as metallization or a metallic layer), while the truncated region 1140 is not metallized to reduce losses due to re-bounces occurring within the truncated region 1140.

[0138] Continuing with Figure 15, as described herein, the internally coupled optical elements B1, B2, G1, G2, R1, and R2 are each located on different associated waveguides. In some embodiments, light from the projection optical system may strike these optical elements from above, for example, normal to the page. Preferably, the optical elements are positioned so that they do not obstruct the propagation of light from the projection optical system to each individual optical element. For example, the optical elements are arranged so that the optical elements for waveguides ahead of the focus of the projection optical system are spaced laterally apart, as seen in the upper and lower figures (from the viewpoint of the projection optical system). Such an arrangement prevents the convergent beam of light from being blocked. The optical elements of waveguides behind the focus will receive the divergent beam of light. As a result, there may be some slight overlap with the optical elements ahead of these waveguides, so that the divergent beam of light expands after passing through the forward optical elements and is therefore not blocked by some overlap with those ahead of the optical elements.

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

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

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

[0142] The above description and Figures 11A-14B generally refer to the internal coupling of light using reflective diffractive optical elements, but it should be understood that the systems and methods described for mitigating optical loss due to re-bounce can equally be implemented in systems with transmissive diffractive optical elements. As shown in Figures 18A and 18B, re-bounce can also occur when light is internally coupled by a transmissive diffractive optical element 1100c' located on the first main surface of the waveguide 1110c. As shown in Figure 18B, an outward-angled beam 11202, which is redirected into the waveguide 1110c by the transmissive diffractive optical element 1100c' at the first main surface of the waveguide 1110c, may be reflected by the second main surface and return to strike the transmissive optical element 1100c' in one or more subsequent re-bounces 1135'. The transmissive diffractive optical element 1110c' does not have a reflective layer and is not susceptible to absorption losses caused by absorption by such a reflective layer, however, the transmissive diffractive optical element 1110c' may have external coupling losses. Therefore, optical losses due to re-bounce can be mitigated in the systems of Figures 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 the step of providing a high diffraction efficiency region having a truncation that has dimensions and relative width-to-length ratios as discussed herein and / or varies with distance from the waveguide focal point of the projection optical system 2000 as also discussed herein. In some embodiments, Figure 15 may be understood to show an upper and lower 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 a reflective layer to achieve desired light reflection. The reflective layer can conventionally be deposited using a metallization process, which includes the deposition of a metal layer. These conventional metallization processes can be time-consuming and involve numerous steps. For example, to direct the metallization to a desired location on the waveguide, the waveguide may need to be matched and covered 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, the deposition itself may require a vacuum, which would further complicate the metallization process and increase its duration 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 reflectivity than desired for certain applications, and may also exhibit non-uniform reflectivity across different wavelengths. For example, some metallic inks (such as silver ink) may contain organic or inorganic impurities, including metal composites and binders, which can inhibit reflectivity. These impurities can reduce optical reflectivity, particularly for shorter wavelengths of light, such as light 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). While not limited by theory, this poor diffraction efficiency is likely due to poor reflective properties resulting from one or more of the factors mentioned 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 devices and display devices having a reflective layer, and methods for fabricating optical waveguide structures and optical devices having a reflective layer. In some embodiments, the reflective layer may be formed on a substrate surface using wet chemical action. Wet chemical action may include a liquid-phase reaction for depositing a layer of reflective material onto the substrate surface from a 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 washing.

[0146] In some embodiments, the wet chemical reaction may involve the deposition of a metal from a liquid mixture. For example, the metal may be part of a metal composite, and the deposition may result from the dissociation of the metal from the composite in the liquid mixture. The metal composite may be an ionic composite, such as a metal salt. The ionic composite may dissociate after a chemical reaction with another reagent present in the liquid mixture or otherwise provided for contact with the ionic composite. For example, the chemical reaction may be metal ion reduction, for example, silver ion reduction, which results in the deposition of 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 a predetermined discrete region of the surface, but not the entire surface. Preferably, the deposition coats the discrete region on the surface of the waveguide. The discrete region of the surface may comprise projections, and the reflective layer may conformally deposit on the projections, for example, forming diffractive optical elements.

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

[0148] Advantageously, these reflective layers can exhibit superior optical and physical properties. The reflective layers may have high purity, as described herein. In addition, the reflective layers may be uniform at the nanoscale resolution such that they are free from or substantially free from features such as pinholes that can reduce reflectivity. Furthermore, unlike directional deposition such as PVD, the reflective layers can conformally coat the surfaces of protrusions, providing reflectivity to all of these surfaces. In addition, the reflective layers may be formed to a thickness that blocks light and prevents undesirable light leakage. While not limited by theory, these advantageous properties are assumed to provide the reflective layers 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. Generally, in addition to being lower, the reflectivity of layers formed using metal inks is even lower with respect to shorter wavelengths of light (blue light) within the visible light range.

[0149] Furthermore, in some embodiments, the metal of the reflective layer is stably bonded to the waveguide surface such that the reflective layer remains stably bonded to the waveguide surface, preferably 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 by metal coating the substrate without the need for post-coating treatments such as annealing. In some embodiments, the substrate surface is treated to facilitate adhesion of the metal species to its surface. In examples, the treatment may include the step of exposing the substrate surface to plasma. Other exemplary treatments include etching the substrate surface and forming an interface layer between the substrate and the metal to be deposited later.

[0150] In some embodiments, the reflective layer is formed over a projection, which is a diffractive optical element, such as a diffraction grating. The reflective layer and the projection together form a 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 internally coupled optical element configured to redirect incident ambient light at an angle so that light propagates through the waveguide by total internal reflection. In some embodiments, a reflective layer, such as those disclosed herein, can increase the optical performance of the reflective diffractive optical element by increasing the amount of light that is 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, e.g., diffractive optical elements or a portion of diffractive optical elements. In some embodiments, this confinement may be achieved using a physical structure (e.g., a wall or weir) for confining the diffusion of a flowable material. In some other embodiments, confinement may be achieved by treating a desired area of ​​the substrate surface such that the metal in the reflective layer is preferentially coated or retained within those desired areas (e.g., after washing). In yet another embodiment, a liquid mixture may be applied to a desired area and may have a composition such that they do not diffuse significantly away from those areas. It should be understood that one or more of these schemes for confining a liquid mixture may be utilized to form a particular reflective layer.

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

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

[0154] flowable material As discussed herein, flowable materials such as liquid mixtures may be used in various embodiments. The liquid mixture may contain metal salts. In some embodiments, the liquid mixture may also contain reducing agents. Examples of preferred metal salts include silver salts such as Ag(NH3)2. Preferred reducing agents include carbohydrates containing alpha-hydroxyaldehyde 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 Torrens reaction. In some embodiments, the liquid mixture is in a solution such as an aqueous solution. The liquid mixture may have a short shelf life, and therefore, in some embodiments, it is assumed that the compositions constituting the liquid mixture can be prepared immediately before or at the time of use. Several commercially available products may also provide suitable reactants for some embodiments, such as metal solutions sold by Peacock Laboratories (West Chester, PA) and byTransene Co, Inc. (Danvers, MA).

[0156] In some embodiments, the liquid mixture may include both a metal salt and a reducing agent, which are pre-mixed before the liquid mixture is deposited on the substrate. In some other embodiments, the metal salt and the reducing agent may be applied separately to a predetermined region of the waveguide and mixed in situ on that region.

[0157] In some embodiments, the liquid mixture further includes one or more of the following: pH modifiers, stabilizers, surfactants, catalysts, and viscosity modifiers. In some embodiments, the liquid mixture includes chemical species selected from the group consisting of metal salts, reducing agents, solvents (such as water), bases, pH modifiers, stabilizers, surfactants, catalysts, and viscosity modifiers, and includes combinations of two or more of the enumerated 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 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. Therefore, the liquid mixture may further contain a base. In some embodiments, the liquid mixture includes a pH range between any two of the listed values, or between any of the listed values ​​and 14, for example, 7-10, 7-12, 7-14, 8-10, 8-12, 8-14, 9-10, 9-12, 9-14, 10-12, 10-14, 11-12, 11-14, or 12-14. In some embodiments, the liquid mixture essentially consists of, or comprises, a metal salt, a reducing agent, and a base.

[0159] It should be understood that liquid mixtures of different viscosities can offer different advantages. For example, relatively viscous liquid mixtures may be suitable for remaining within the region where they are deposited with little further diffusion. On the other hand, relatively thin liquid mixtures may be suitable for forming a relatively thin and uniform reflective layer, allowing for easier flow between closely spaced features, but may require physical barriers such as walls or weirs to confine the liquid mixture to a given region of the waveguide surface. In some embodiments, once the deposited liquid mixture has reacted 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 In some embodiments of this specification, the reflective layer reflects at least one visible wavelength (e.g., light in the visible spectrum) of incident electromagnetic radiation. The reflective layer may be formed from a flowable material, such as a liquid mixture. The reflective layer preferably reflects at least about 30% of at least one visible wavelength of the incident electromagnetic radiation, for example, at least about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, 99.5%, or 99.9% of the incident electromagnetic radiation, and includes a range between any two of the listed values, for example, about 30% to 99%, 30% to 95%, 30% to 90%, 30% to 80%, 30% to 70%, 50% to 99%, 50% to 95%, 50% to 90%, 50% to 80%, 50% to 70%, 70% to 99%, 70% to 95%, 70% to 90%, or 70% to 80% of the incident electromagnetic radiation. In some embodiments, the incident electromagnetic radiation includes light in the visible spectrum. It should be understood that the reactants themselves (e.g., metal salts) do not necessarily possess the reflective properties shown prior to being reacted as described herein, but the reflective layer formed from the reactants (e.g., a metal layer) will have the reflective properties shown.

[0161] It should be understood that reflective layers 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 may contain pure or substantially pure metal. The term “substantially pure” as used herein has its usual and customary meaning as will be understood by those skilled in the art in light of this disclosure. It refers to a metal that contains only small trace amounts of other substances. Where additional numerical specificity is of interest, substantially pure metal may include at least 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% pure metal (w / w), and include a range between any two of the listed values, e.g., 95%~97%, 95%~99%, 95%~99.9%, 97%~99%, 97%~99.9%, 98%~99%, and 98%~99.9%. Therefore, the reflectivity of substantially pure metals is comparable to that of elemental ("pure") metals. In some embodiments, substantially pure metals have at least 95%, 96%, 97%, 98%, 99%, 99.5%, or 99.9% of the reflectivity of pure metals, and include a range between any two of the enumerated values.

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

[0163] As used herein, “projection,” “surface projection,” and variations thereof refer to a mass of material extending upward on or into a substrate, such as within an optical grating extending from the surface of a waveguide. In some embodiments, the projection may be formed by etching a substrate, which may include a deposited material (e.g., a photoresist deposited on the waveguide) or may be a substantially homogeneous structure (e.g., a waveguide). In some embodiments, the reflective layer 1010 is arranged across an optical grating 1020 (see, for example, Figures 19A–19C). In some embodiments, the reflective layer 1010 is arranged across an optical grating 1020 having a blazed configuration (see Figure 19B). In some embodiments, the reflective layer 1010 is arranged across an optical grating 1020 having a multilevel configuration (see Figure 19C). In some embodiments, the optical grating comprises a patterned photoresist.

[0164] It should be understood that the reflective layer is preferably used to provide reflection of light returning in and / or through the waveguide. As a result, the reflective layer preferably coats all surfaces of the protrusion. In some embodiments, the reflective layer is conformally arranged on the optical grating. It should be noted that when the material is “conformally” arranged, it will be substantially conformally arranged to the topology of the underlying surface. In some embodiments, the thickness of the reflective layer across the underlying surface (e.g., the linear thickness extending from the surface across the layer) varies by about ±20% or less across the entire reflective layer, such that the thickness is within ±20% of the mean, e.g., ±20%, ±15%, ±10%, ±5%, or ±1% of the mean. Preferably, the conformally reflective layer is arranged so that there is no or substantially no gap between the reflective layer and the surface of the substrate.

[0165] Furthermore, in some embodiments, a non-conformal reflective layer may also provide suitable reflectivity for the relevant interface (for example, although not limited by theory, as long as the surface of the reflective layer at the interface with the waveguide is sufficiently reflective and provides sufficient coverage, the opposing surface not facing the waveguide may not need to be conformal to the waveguide). Therefore, in some embodiments, the reflective layer is arranged non-conformally on the surface.

[0166] Preferably, the non-conformal layer is positioned so that there is no or substantially no gap between the reflective layer and the substrate surface. “Substantially no gap” between the reflective layer and the substrate has its usual and customary meaning as will be understood by those skilled in the art in light of this disclosure. Some gaps may exist, but they have been shown not to significantly reduce the reflectivity of the reflective optical elements formed by the reflective layer and the substrate compared to a gapless reflective layer. In some embodiments, the reflective layer is positioned so that at least 90% of the surface area of ​​the reflective layer at the waveguide surface interface, e.g., at least 90%, 95%, 97%, 98%, 99%, or 99.9%, is in direct contact with the waveguide surface, resulting in a substantially gapless configuration. In some embodiments, the ink is deposited to a thickness sufficient to completely or substantially completely fill the open volume or gap between the waveguide projections.

[0167] It should be understood that when metals are deposited by conventional means, e.g., 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 a nanoscale diameter, e.g., a diameter less than about 1 mm, e.g., in the range of about 1 nm to about 1000 nm. While not limited by theory, it is assumed that pinholes impede the reflectivity of the reflective layer. Furthermore, while not limited by theory, it is assumed that forming the reflective layer by metal ion reduction as described herein can, advantageously, minimize or avoid pinhole formation. In some embodiments, the reflective layer is pinhole-free or substantially pinhole-free. "Substantially pinhole-free" has its usual and customary meaning as will be understood by those skilled in the art in light of this disclosure. While some pinholes may exist, it has been confirmed that they do not significantly reduce the reflectivity of the reflective optical elements formed by the reflective layer and substrate compared to a pinhole-free reflective layer. In some embodiments, a substantially pinhole-free surface in some embodiments may contain pinholes in 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% or less of the surface, and include ranges between any two of the enumerated values, e.g., 1-5%, 1-7%, 1-10%, 2-5%, 2-7%, 2-10%, 5-7%, and 5-10%. It should be noted that a pinhole-free reflective layer will also be in a "substantially pinhole-free" state. In some embodiments, the surface of the reflective layer in interfacial contact with a projection on a waveguide is pinhole-free or substantially pinhole-free.

[0168] Advantageously, forming a reflective layer by metal ion reduction as described herein avoids the presence of particles such as metal particles (other than the metal itself) within the reflective layer. While not limited by theory, it is assumed that metal particles can partially scatter light, and therefore the reflectivity of a particle-containing reflective layer may be lower than that of a particle-free layer. For this reason, in some embodiments, the reflective layer is free of or substantially free of metal particles. "Substantially free" of particles (metal particles, etc.) has its usual and customary meaning as will be understood by those skilled in the art in light of this disclosure. Although trace amounts of particles such as metal particles (other than the metal itself) may be present, it has been confirmed that they do not significantly reduce the reflectivity of the reflective optical elements formed by the reflective layer and substrate compared to a reflective layer without such metal particles (other than the metal itself). In some embodiments, surfaces that are substantially free of particles of some embodiments (such as metal particles other than the metal itself) may contain more than 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, or 0.01% of metal particles (w / w), including a range between any two of the enumerated values, for example, 0.1–1%, 0.1–2%, 0.1–5%, 1–2%, 1–5%, 2–5%, or 3–5%.

[0169] In some embodiments, a reflective layer of a desired thickness is formed. In some embodiments, the reflective layer is 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, Having a thickness of 480, 490, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1000 nm, and a thickness in the range between any two of the listed values, for example, approximately 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 nm, 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 Includes thicknesses of ~900nm, 80nm~500nm, 80nm~450nm, 80nm~400nm, 80nm~350nm, 80nm~300nm, 80nm~250nm, 80nm~200nm, 80nm~150nm, 80nm~100nm, 100nm~900nm, 100nm~500nm, 100nm~450nm, 100nm~400nm, 100nm~350nm, 100nm~300nm, 100nm~250nm, 100nm~200nm, or 100nm~150nm.

[0170] In some embodiments, a single layer of 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 liquid mixture is applied in a first deposition cycle to allow at least partial reaction, and at least one subsequent layer of liquid mixture is applied on top of the first layer in a second deposition cycle. Optionally, by-products of the reaction can be removed between cycles of depositing layers of liquid mixture. The cycles of depositing the liquid mixture may be repeated until a reflective layer of the desired thickness is achieved. For example, at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 cycles of liquid mixture application may be carried out to form a reflective layer of the desired thickness (including a range 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 a liquid mixture behind a barrier, weir, or wall, as described herein. The barrier, weir, or wall can define at least a portion (or all) of a given area of ​​the waveguide surface, as described herein.

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

[0173] Pre-processing agent It is assumed that pre-treating the waveguide surface prior to the step of depositing the liquid mixture may improve the adhesion and formation of the reflective layer, as described herein. With respect to photoresist waveguides, it has been observed that pre-treatment may improve both the adhesion and reflectivity of the reflective layer (Example 3). Therefore, in some embodiments, waveguides comprising photoresist are pre-treated prior to the step of depositing the liquid mixture, as described herein. Furthermore, it is assumed that selectively pre-treating a certain area while leaving other areas of the waveguide surface untreated may facilitate the selective formation of the reflective layer in a desired predetermined area, as described herein.

[0174] While not limited by theory, it is assumed that pretreatment to increase the hydrophilicity of the waveguide surface (so that the waveguide surface is more hydrophilic than before pretreatment) can improve adhesion and reflectivity of the reflective layer. Therefore, in some embodiments, pretreatment increases the hydrophilicity of the waveguide surface. Pretreatment of a surface comprising a photoresist has been observed to substantially increase the adhesion and reflectivity of the reflective layer, as described herein. Therefore, in some embodiments where the waveguide surface comprises a photoresist, the surface is pretreated, for example, with a plasma to increase the surface hydrophilicity before depositing a liquid mixture onto the surface.

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

[0176] While not limited by theory, it is assumed that pretreatment to enhance the metal ion reduction reaction can be selectively applied to a predetermined region (other than other regions) of the waveguide surface, thereby improving the selectivity of reflective layer formation on that predetermined region (excluding other regions). Therefore, in some embodiments, a predetermined region of the waveguide surface, as described herein, is pretreated with a catalyst that enhances the metal ion reduction reaction (and reflective layer formation), as described herein.

[0177] Optical waveguide and method for fabricating the same In some embodiments, a method for fabricating an optical waveguide structure having a reflective layer is described. The method may include the step of providing an optical waveguide having a surface. The surface may include a predetermined region having a pattern of protrusions. For example, the predetermined region may define a nanopattern for the deposition of the reflective layer. The method may include the step of depositing a liquid mixture on 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 the step of allowing the metal salt to be reduced by the reducing agent in the liquid mixture to be deposited, thereby precipitating pure or substantially pure metal on the predetermined region of the surface. Thus, the 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 on protrusions within the predetermined region of the waveguide surface. In some embodiments, the method further includes a step of pre-treating a predetermined area of ​​the waveguide surface to increase the surface hydrophilicity, such as plasma treatment, as described herein. The pre-treating step may be performed 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 a step of die-cutting or dicing the substrate and the reflective layer into many different parts to form a plurality of reflective optical elements. In some embodiments, the optical waveguide comprising the reflective layer is part of an optical waveguide stack, and the method further includes a step of attaching one or more other optical waveguides to the optical waveguide to form a stack.In some embodiments, the optical waveguide, which has a reflective layer, is part of the display device, and therefore the method further includes the step of arranging the waveguide (or a stack comprising such waveguides) having a reflective layer within the display device. In some embodiments, a given region is defined with a resolution of ±50 microns, or a more precise (numerically smaller) resolution, for example, ±40, ±30, ±20, ±10, or ±5 microns.

[0178] Referring to Figure 23, in some embodiments, the method includes the step of providing an optical waveguide having a surface, the surface having a predetermined region having a pattern of protrusions 1600. The method may further include the step of increasing the hydrophilicity of a predetermined region 1610 of the surface, for example, if the surface has a photoresist. For example, hydrophilicity may be increased by pre-treating the predetermined region with plasma, as described herein. The method may further include the step of depositing a liquid mixture on a 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 the step of reducing the metal salt with the reducing agent so that pure or substantially pure metal is deposited on a predetermined region of the surface 1630. Thus, a reflective layer is formed on the optical waveguide structure 1640. The reflective layer contains, essentially consists of, or may consist of substantially pure metal (or the reflective layer contains, essentially consists of, or may consist of, pure metal). In some embodiments, the method further includes the step of removing the residue from the reflective layer 150, for example, by washing and / or drying, as described herein.

[0179] Advantageously, the reflective layer described herein is applied selectively to a predetermined region, as described herein, and not to other regions of the waveguide surface, and can form diffractive optical elements, such as internally coupled optical elements. In some embodiments, the waveguide surface further comprises a first region. The predetermined region, excluding the first region, is selectively contacted with the liquid mixture. Thus, a pure or substantially pure metal is deposited on the predetermined region, excluding the first region, and thus forms a reflective layer on the predetermined region but not on the first region of the optical waveguide surface. In some embodiments, the liquid mixture is applied selectively to only a predetermined region of the surface (excluding other regions) using selective plasma pretreatment, as described herein. Optionally, the selective plasma pretreatment can be selective using a mask that covers the substrate and exposes the predetermined region. In some embodiments, the liquid mixture is applied selectively using a physical structure such as a wall, weir, or well, as described herein. The physical structure defines at least a portion of a given area, preventing the liquid mixture from flowing from other areas of the waveguide surface (see, for example, Figures 20A–20B). The walls may be of stepped height, such that an inner wall 2002 defining the area for depositing the liquid mixture is lower than an outer wall 2004 surrounding the inner wall 2002. While not limited by theory, it is assumed that the degree of wall height progression may help prevent defects when filling the area defined by the inner wall, for example, by consistently confining the location of the liquid mixture to be deposited. Thus, in some embodiments, the walls act as a weir, mold, or well to contain the liquid mixture within a given area of ​​the substrate. In some embodiments, the walls may further act as spacers, separating the waveguides of a stack from each other. In some embodiments, the walls comprise a resist. According to some embodiments, the resist walls may extend across the substrate and then be deposited as layers, patterned, defining the walls.

[0180] Walls, weirs, or wells may be written in and / or removable. For example, walls, weirs, or wells may be removed by rinsing with water (or another liquid), peeling, removal, and / or vacuum. In some embodiments, walls, weirs, or wells are not removable and are rather retained as part of the final structure. In some embodiments, the liquid mixture is selectively applied using a mask. One or more openings in the mask can cover a given area, and the liquid mixture may be deposited within one or more openings. The mask may then be removed. In some embodiments, the liquid mixture is selectively applied by inkjet. An advantage of inkjet is that it can allow for the selective application of the deposition of the liquid mixture within a desired area.

[0181] As described herein, increasing the hydrophobicity of a substrate surface can improve the adhesion and reflectivity of a reflective layer deposited on the substrate. It should be noted that, with respect to the photoresist surface of a waveguide, the reflective layer can exhibit substantially superior adhesion and reflectivity when the hydrophobicity of the photoresist is increased prior to the step of depositing the liquid mixture (Example 3). Therefore, a pretreatment that selectively increases the hydrophilicity of a given area of ​​the waveguide surface (compared to the hydrophilicity of the given area before pretreatment) but not in other areas can facilitate the selective formation of a reflective layer on a given area of ​​the waveguide surface but not on other areas. In some embodiments, the method includes a step of increasing the hydrophilicity of a given area of ​​the surface prior to the step of depositing the liquid mixture. In some embodiments, the hydrophilicity is selectively increased on a given area of ​​the surface but not in a first area of ​​the surface. In some embodiments, the hydrophilicity of a given area of ​​the surface is increased by pretreatment of the given area of ​​the surface using a pretreatment agent selected from the group consisting of plasma, surfactants, coatings, wet chemical etching, and catalysts. In some embodiments, the method includes a step of pre-treating the surface using at least one of the following: plasma, wet etching with a wet chemical etchant containing chromic acid, a surfactant, a silica-containing coating, and / or a catalyst containing tin or palladium (such as tin chloride or palladium chloride). In some embodiments, a predetermined area of ​​the waveguide is not pre-treated with any pre-treatment reagent.

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

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

[0184] In some embodiments, a predetermined region of the waveguide surface, having a projection, is part of a grid. At least a portion of the reflective layer may be conformally or non-conformally arranged on the grid. The interface between the reflective layer and the surface may be substantially gapless. In some embodiments, at least a portion of the reflective layer is conformally arranged on the grid, and the interface between the reflective layer and the surface is substantially gapless. In some embodiments, the reflective layer is conformally arranged on the grid. In some embodiments, at least a portion of the reflective layer is non-conformally arranged on the grid, and the interface between the reflective layer and the surface is substantially gapless. In some embodiments, the reflective layer is configured to reflect incident electromagnetic radiation at the interface into the first waveguide.

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

[0186] In some embodiments, the waveguide is formed from an optically transparent material and configured to transmit light through total internal reflection. In some embodiments, the surface of a given waveguide includes, essentially consists of, or comprises a photoresist.

[0187] In some embodiments, optical waveguide stacks comprising a reflective layer are fabricated. The optical waveguide stack may comprise a first waveguide comprising a first surface and a reflective layer conformally arranged on a projection 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 of 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, projections on the surface of the first waveguide, on which the reflective layer is disposed, form 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 a reflective layer is formed on an 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 carried out), thus forming a stack of optical waveguides having a reflective layer.

[0188] The reduction of a metal salt to form a precipitated metal may be referred to herein as a “metal reduction” or “metal ion reduction” reaction. Examples of such reactions are schematically illustrated in Figure 21C. In some embodiments, the Torrens reaction reduces the metal salt to pure or substantially pure metal. In some embodiments, the reducing agent comprises, essentially, or consists of, a carbohydrate containing an alpha-hydroxyaldehyde and / or a carbohydrate containing an alpha-hydroxyketone. Exemplary reducing agents include sucrose, fructose, and combinations thereof. In some embodiments, the metal salt comprises, essentially, or consists of, Ag(NH3)2. In some embodiments, the liquid mixture comprises, essentially, a metal salt, a reducing agent, and a base in a solvent, e.g., water.

[0189] In some embodiments, the liquid mixture is incubated to facilitate the reduction of the metal salt. In some embodiments, incubation takes place at room temperature, e.g., about 20, 21, 22, 23, 24, or 25°C, and includes a range between any two of the enumerated 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 embodiments of this specification may be formulated to preferably take place at or below room temperature. On the other hand, the application of metal inks frequently involves firing / heating at high temperatures to produce purer metals, which can affect the waveguide's thermal budget (and potentially damage the waveguide, including damaging the resist structure) and prolong the process time. In addition, high-temperature firing may or may not be compatible with the 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, for example, at least about 1, 5, 10, 20, 30, 40, or 50 seconds, or at least about 1 minute, for example, at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 minutes, within a range between any two of the enumerated values, for example, 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 embodiments of the method, the pure or substantially pure metal is free from or substantially free from non-metallic particles as described herein.

[0192] It is assumed that metals may discolor and / or degrade, which can impair their reflective properties. Capping the reflective layer provides protection against discoloration or other degradation, and thus can extend the length of time that the reflective layer retains its desired reflective properties (Example 4). In some embodiments, the reflective layer is capped. In some embodiments, the reflective layer is capped with a capping layer that seals the reflective layer so that it is not directly exposed to air and / or humidity. In some embodiments, the capping layer contains, essentially consists of, or comprises a dielectric or a metal. In some embodiments, the capping is formed by vapor deposition of a dielectric or metallic 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 change of state. In some embodiments, the capping prevents direct exposure of the reflective surface of the reflective layer to air and / or humidity.

[0193] In some embodiments, the liquid mixture may have a short shelf life. Therefore, in the methods of some embodiments, the liquid mixture is prepared immediately before 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. The liquid mixture is therefore deposited when the different compositions are deposited on a predetermined area of ​​the waveguide surface. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited simultaneously on a predetermined area. For example, with respect to a coating process requiring that parts A and B react together, parts A and B can be deposited simultaneously on a predetermined surface. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are deposited sequentially on a predetermined area. For example, with respect to a coating process requiring that parts A and B react together, droplets or a number of droplets of part A can be applied first, and then droplets of part B can be applied thereon. In some embodiments, two or more different compositions comprising reactants for (collectively) forming a reflective layer are mixed and then deposited as a single composition on a given area.

[0194] Several preferred techniques can be used to deposit a liquid mixture onto a given area on the waveguide surface, according to the methods of some embodiments herein. For example, in some embodiments, the liquid mixture is deposited onto the given area via at least one of nano-dispensing, micro-dispensing, micropipette, inkjet, or spraying. In some embodiments, the liquid mixture is deposited onto the given area as a single or multiple droplets ranging from the picoliter to microliter range. In some embodiments, the liquid mixture is deposited using a single-droplet dispensing tool.

[0195] In some embodiments, after the reflective layer is formed, residues (e.g., oxidized carbohydrates and by-products of the reaction such as ammonia or excess reaction products) are removed from the reflective layer. The method in some embodiments further includes a step of removing residues from the metal ion reduction reaction. In the method in some embodiments, the reflective layer is rinsed after it has been formed. Residues remaining after the reaction can be removed by rinsing. Examples of preferred rinsing techniques include washing / spraying systems, circulating and / or stirring tanks, spin rinsing / drying systems, or combinations of two or more of the listed techniques. In some embodiments, rinsing is carried out with an aqueous solution, e.g., water. In some embodiments, the reflective layer is dried, for example, until the residue is completely dry or until the rinsed material is completely dry.

[0196] Furthermore, in some embodiments (for example, with respect to diffractive optical elements, internally coupled optical elements, or externally coupled optical elements as described herein), it is assumed that the relevant surface is at the interface of the reflective layer of the waveguide and therefore cannot 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, optical devices are described. The optical device may include a first waveguide having a first surface. The optical device may also include a reflective layer disposed on a region of the first surface, the reflective layer being pinhole-free or substantially pinhole-free. The layer contains, essentially, or may contain, a pure metal or substantially a pure metal. For example, the layer may contain at least 95% elemental metal. The reflective layer may be configured to reflect incident electromagnetic radiation at the interface into the first waveguide. In some embodiments of the optical device, the first waveguide is part of a stack of optical waveguides as described herein. In some embodiments of the optical device, two or more of the optical waveguides in the stack each include a reflective layer as described herein.

[0198] In some embodiments of optical devices, a region of the first surface comprises a projection, which, together with the reflective layer, is part of a reflective diffraction grating. Embodiments of the projection are depicted in Figures 19A–19C. In some embodiments, the reflective diffraction grating includes, essentially consists of, a reflective layer disposed on the projection. In some embodiments, the reflective diffraction grating includes, essentially consists of, a portion of the reflective layer disposed on the projection.

[0199] In some embodiments of optical devices, a reflective layer positioned on a projection is part of an internally coupled optical element configured to redirect incident ambient light at an angle such that the light propagates through a first waveguide. In one embodiment, light incident on a diffraction grating will be internally coupled to the waveguide so that it propagates away from the diffraction grating at an angle suitable for TIR within the waveguide. It should be understood that the internally coupled light propagates through the waveguide by TIR and may be reflected from the waveguide surface 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 be incident on the diffraction grating during early reflection in the TIR path and, undesirably, redirected out of the waveguide. For example, the diffraction grating may be on the surface of one waveguide, and incident light may be internally coupled and redirected to be reflected from the opposite surface of the waveguide. The reflected light may then be incident on the diffraction grating, which redirects the light out of the waveguide. In some embodiments, a reflective layer is deposited on the diffraction grating to prevent undesirable redirection of light out of the waveguide, the diffraction grating may be sized and shaped so that internally 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 embodiments of optical devices, the reflective layer reflects incident electromagnetic radiation (e.g., light in the visible spectrum) with a reflectivity (or reflectance) of at least 70%, for example, at least 70%, 75%, 80%, 85%, 90%, 95%, 97%, 99%, 99.9%, and includes a range between any two of the enumerated values, for example, 70% to 90%, 70% to 95%, 70% to 99.9%, 80% to 90%, 80% to 95%, 80% to 99.9%, 85% to 90%, 85% to 95%, 85% to 99.0%, 90% to 95%, or 90% to 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%. A predetermined area of ​​the waveguide surface may be sized and shaped as appropriate.

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

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

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

[0204] In some embodiments of optical devices, the reflective layer is free from or substantially free from non-metallic particles as described herein.

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

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

[0207] Display devices In some embodiments, a display device is provided. The display device may include a waveguide comprising a reflective diffractive optical element, in which a diffractive optical element is located on a region of the waveguide surface. The reflective layer may be substantially pinhole-free. The reflective layer may contain, essentially consist of, or consist of a pure metal or substantially pure metal. For example, the layer may contain at least 95% elemental metal. The reflective layer may be configured to reflect incident electromagnetic radiation at the interface into the first waveguide. In some embodiments, the first waveguide is part of a stack of optical waveguides as described herein. In some embodiments, two or more of the optical waveguides in the stack each 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 embodiments of the display device, the reflective diffractive optical elements form an internally coupled grating, configured to internally couple incident light into a waveguide, as described herein.

[0209] In some embodiments of the display device, the waveguide is one of a stack of waveguides, and each of the waveguide stacks comprises an internal coupling grating. In the upper and lower figures, the internal coupling gratings may be offset laterally from one another. For example, referring to Figure 9A, the internal coupling optical elements 700, 710, and 720 may be offset laterally from one another.

[0210] In some embodiments of the display device, the reflective layer is free from or substantially free from non-metallic particles as described herein.

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

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

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

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

[0215] How to fabricate a display device In some embodiments, a method for fabricating an optical device is described. The method may include the step of providing a waveguide having a surface. The method may include the step of depositing a liquid mixture onto a region of the surface. The liquid mixture may contain a metal salt. The liquid mixture may also contain a reducing agent at a basic pH. The method may include the step of incubating the liquid mixture on a predetermined region of the surface so that the metal salt is reduced by the reducing agent and pure or substantially pure metal deposition. 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 the step of pre-treating the surface to increase its hydrophilicity, as described herein. The pre-treating step may be performed before the liquid mixture is deposited onto a predetermined region of the surface.

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

[0217] Exemplary diffractive optical elements In some embodiments, the internally coupled optical elements (e.g., internally coupled optical elements 700, 710, 720) include a reflective diffractive optical element comprising a reflective layer that is essentially made of or composed of a pure or substantially pure metal, as described herein. [Examples]

[0218] (Example 1) Comparison of a reflective layer formed by metal ion reduction and silver-containing ink. Examples of different methods for forming a silver-containing layer 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 (Torens reaction) according to some embodiments herein (Figure 21C).

[0219] Methods for producing reflective layers via silver ion reduction, as described herein, were compared with other methods for producing reflective layers. The comparison was performed on internally bonded lattice (ICG) nanopatterned structures. Coating property evaluations using different methods are shown in Table 1. In some embodiments, silver-containing reflective layers were formed using a modified Torrence reaction. This reaction was carried out at room temperature and produced high-purity silver with good smoothness (no pinholes) at the nanoscale (Figure 22C, after rinsing). The coatings were also highly conformal around the ICG nanostructures. For comparison, inkjet-ready inks from NovaCentrix (Austine, Texas) (Figure 22A) and Electroinks (Figure 22B) formed nanoporous networks containing a substantial number of pinholes, which were highly conductive but associated with relatively low reflectivity. Adhesion of the reflective layers as described herein was also evaluated using tape peel tests. Compared to inkjet-compatible inks from NovaCentrix (Figure 22D) and Electroinks (Figure 22E) (silver tape peeling from glass), the reflective layers formed by using a modified Torrens reaction according to some embodiments of this specification (Figure 22F) exhibited substantially better adhesion. Note that, for tape peeling tests, the reflective layers in some embodiments were deposited on a 3nm SiOx coated ICG. These results are summarized in Tables 1A-B below. [Table 1-1] [Table 1-2] [Table 1-3]

[0220] Therefore, reflective layers according to some embodiments of this specification have been shown to have a smoother surface (without or substantially without pinholes) and exhibit better adhesion than layers formed from inkjet-readable metal-containing inks.

[0221] (Example 2) Comparison of reflective layer, vapor-deposited metal layer, and silver-containing ink. Plasma pretreatment of nanostructured photoresists resulted in superior adhesion. Reflectance and ICG diffraction efficiency were tested for a reflective layer containing silver produced on 385 resist treated with APPJ plasma by a modified Torrence reaction, and compared to a sputtered aluminum deposition layer on 385 resist and NovaCentrix inkjet-ready ink fired at 180°C for 15 minutes. The reflective layer containing silver produced by the modified Torrence reaction exhibited significantly higher reflectance than the tested commercial metal inks and also higher than the vapor-deposited aluminum coating (Figure 23). Furthermore, the reflective layer containing silver produced by the modified Torrence reaction exhibited higher reflectance for all wavelengths tested in the 400–700 nm range (Figure 23).

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

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

[0224] In addition, the reflective layer formed by silver ion deposition exhibited better 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] Thus, it can be concluded that for the methods and devices of some embodiments, the reflective layer exhibits better reflectivity and better diffraction efficiency compared to the layer formed from metal-containing ink and the Al layer formed by vapor deposition.

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

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

[0228] [[ID=:28]] The resist was cleaned with acetone in the imprinted area. This pretreatment resulted in a thin, translucent silver coating. The silver was thicker than in areas without acetone cleaning, but still very thin and unlikely to have sufficient reflectivity for many applications.

[0229] The resist was pre-treated with an ultrathin atmospheric pressure plasma jet (APPJ) coating. The plasma jet coating, using a SnCl2 catalyst, resulted in high reflectivity and acceptable adhesion.

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

[0231] The glass surface alone resulted in a silver coating of approximately 100 nm. This coating was highly reflective and exhibited better reflectivity than the aluminum layer formed by vapor deposition.

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

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

[0234] ICG diffraction efficiency was also measured for the reflective layer formed by silver ion reduction, both initially and after 360 hours at 100% humidity at 60°C. The results are shown in Table 4 below. Table 4 shows that the diffraction efficiency of the reflective layer in several embodiments remained substantially unchanged even after 360 hours at 100% humidity. [Table 4]

[0235] Various exemplary embodiments of the present invention are described herein. These embodiments are provided in a non-limiting sense to illustrate broader applicable aspects of the invention. Various modifications may be made to the described invention, and equivalents may be substituted without departing from the true spirit and scope of the invention.

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

[0237] In addition, numerous modifications may be made to adapt specific situations, materials, compositions, processes, actions, or steps of the process to the object, spirit, or scope of the present invention. Furthermore, as will be understood by those skilled in the art, each of the individual modifications described and illustrated herein has discrete components and features that can be readily separated from or combined with features of any of several other embodiments without departing from the scope or spirit of the present invention. All such modifications are intended to be within the scope of the claims associated with this disclosure.

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

[0239] Exemplary aspects of the present invention, along with details relating to material selection and manufacturing, are described above. Further details of the present invention are understood in connection with the above-referenced patents and publications and, generally, can be grasped or understood by those skilled in the art. The same may apply to the method-based aspects of the present invention in terms of additional actions that may be generally or logically adopted.

[0240] In addition, although the present invention has been described with reference to several embodiments that optionally incorporate various features, the present invention is not limited to those described or indicated to be considered with respect to each modification of the present invention. Various modifications may be made to the described invention, and equivalents may be substituted (whether described herein or not for the sake of some brevity) without departing from the true spirit and scope of the invention. In addition, if a range of values ​​is provided, it is understood that all intervening values ​​between the upper and lower limits of that range, and any other provisions or intervening values ​​within that defined range, are encompassed within the present invention.

[0241] Furthermore, it should be considered that any optional feature of a variation of the invention described herein may be described and claimed independently or in combination with one or more of the features described herein. References to singular items include the possibility of multiple identical items existing. More specifically, as used herein and in the claims associated therewith, the singular forms “a,” “an,” “said,” and “the” include multiple referents unless otherwise specifically stated. In other words, the use of articles allows for “at least one” of the subject items in the above description and in the claims associated with this disclosure. Furthermore, it should be noted that such claims may be drafted to exclude any optional elements. Thus, this statement is intended to function as an antecedent for the use of such exclusive terms, or “negative” restrictions, such as “only,” “only,” and “equivalents,” relating to the description of the claim elements.

[0242] Without using such exclusive terms, the term “equipped with” in the claims associated with this disclosure shall allow for the inclusion of any additional elements, whether a given number of elements are enumerated in such claims or whether the addition of features can be considered to transform the nature of the elements described in such claims. Unless otherwise specifically defined herein, all technical and scientific terms used herein are given the broadest possible generally understood meaning while maintaining the validity of the claims.

Claims

[Claim 1] The invention described herein.

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