Waveguide having a reflective layer formed by a reflective flowable material - Patent Application 20070122997

Abstract

Providing a waveguide having a reflective layer formed from a reflective flowable material. In some embodiments, compositions and methods are described that include a reflective flowable material, e.g., a reflective liquid, including reflective ink and / or liquid metal. In some embodiments, a surface is contacted with the reflective flowable material, thereby forming a reflective layer on the surface. In some embodiments, the surface is a surface of a waveguide, e.g., a waveguide for a display device, and the flowable material coats the surface of protrusions on the surface, forming reflective diffractive optical elements. Some embodiments include a display device comprising a reflective layer of the reflective flowable material.

Description

[Technical Field]

[0001] (Priority Claim) This application claims priority to U.S. Provisional Application No. 62 / 486,873, filed April 18, 2017, the contents of which are incorporated herein by reference.

[0002] (Incorporated by reference) This application also incorporates by reference the entirety of each of the following patent applications: U.S. Patent Application No. 14 / 555,585 (filed November 27, 2014), U.S. Patent Application No. 14 / 690,401 (filed April 18, 2015), U.S. Patent Application No. 14 / 212,961 (filed March 14, 2014), and U.S. Patent Application No. 14 / 331,218 (filed July 14, 2014).

[0003] (background) (Field) FIELD OF THE DISCLOSURE The present disclosure relates to display systems. More particularly, some embodiments herein relate to methods and compositions, including, for example, reflective flowable materials for forming reflective layers on waveguides. [Background technology]

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

[0005] Referring to FIG. 1 , an augmented reality scene 1 is depicted. A user of AR technology views a real-world park-like setting 1100 featuring people, trees, a building in the background, and a concrete platform 1120. The user perceives that they also "see" "virtual content," such as a robotic figure 1110 standing on the real-world platform 1120 and a flying, cartoon-like avatar character 1130 that appears to be an anthropomorphic bumblebee. These elements 1130, 1110 are "virtual" in that they do not exist in the real world. The human visual perception system is highly complex, making it challenging to create AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

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

[0007] (summary) Some aspects include methods of fabricating an optical waveguide structure. The method may include forming a reflective optical element for the waveguide, where forming the reflective optical element includes providing a pattern of protrusions on a first surface of the waveguide and depositing a reflective ink on the surface of the protrusions. In some embodiments, the reflective ink is selectively deposited on predetermined areas of the first surface of the waveguide. In some embodiments, the depositing includes dispensing the reflective ink from an inkjet, a microdispenser, or an applicator rod. In some embodiments, the reflective ink comprises a particle-free ink. In some embodiments, the reflective ink comprises aluminum, silver, or a combination thereof. In some embodiments, the reflective ink further comprises a binder, the binder being present in the reflective optical element. In some embodiments, the reflective optical element further comprises a surface buildup. In some embodiments, the protrusions on the first surface comprise photoresist. In some embodiments, the first surface comprises walls defining at least a portion of the predetermined areas onto which the reflective ink is selectively deposited. In some embodiments, the wall comprises a mechanical spacer configured to maintain a space between the waveguide and the additional waveguide. In some embodiments, the protrusions on the first surface are part of a grating, and at least a portion of the reflective ink is non-conformally disposed on the grating, and the interface between the reflective ink and the first surface is substantially gap-free. In some embodiments, the reflective optical element is a diffractive optical element configured to redirect incident light at an angle such that the light propagates through the waveguide by total internal reflection. In some embodiments, the reflective optical element is configured to reflect incident electromagnetic radiation with at least 60% reflectivity. In some embodiments, the reflective optical element is part of an internal coupling optical element or a light distribution element configured to reflect electromagnetic radiation into the first waveguide. In some embodiments, the method further includes forming an additional reflective optical element on the additional waveguide by depositing reflective ink on the pattern of protrusions on the surface of the additional optical waveguide, the additional reflective optical element being configured to reflect incident electromagnetic radiation.The method may further comprise attaching at least additional waveguides to a surface of the waveguide, thus creating a stack of waveguides.

[0008] Some aspects include methods of making a display device. The method may include forming a reflective layer of reflective ink on a first surface of an optical waveguide, the first surface including protrusions that form a grating. The reflective layer may be disposed on the first surface, thus creating a reflective optical element. The method may include disposing the reflective optical element within the display device. In some embodiments, the reflective layer of reflective ink is non-conformally disposed on the first surface, and the interface between the reflective layer and the first surface is substantially gap-free. In some embodiments, the reflective layer and the protrusions form a diffractive optical element.

[0009] Some aspects include an optical waveguide structure. The optical waveguide structure may include a first waveguide including a first surface and a reflective layer of reflective ink disposed on the first surface. The reflective layer may include a binder. The reflective layer may be configured to reflect incident electromagnetic radiation into the first waveguide at an interface. In some embodiments, the reflective layer is substantially free of dispersed metal-containing particles. In some embodiments, the reflective layer includes a surface buildup. In some embodiments, the first surface, together with the reflective layer, forms protrusions that are part of a reflective diffraction grating. In some embodiments, the reflective layer reflects incident electromagnetic radiation with a reflectivity of at least 60%. In some embodiments, the reflective layer and the protrusions form an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through the first waveguide. In some embodiments, the optical waveguide structure further includes a second waveguide and a third waveguide, the second waveguide configured to output a different wavelength range than the third waveguide. The first waveguide may be in optical communication with at least one of the second and third waveguides. Each of the first, second, and third waveguides may include a reflective layer of reflective ink disposed on a surface including protrusions, thus forming a reflective grating, the reflective grating of each waveguide configured to redirect light of a different wavelength range. In some embodiments, the first surface includes walls defining boundaries of the reflective layer, the walls including mechanical spacers configured to maintain a space between the first waveguide and the other waveguides.

[0010] Some aspects include a display device comprising the optical waveguide structure described herein, for example, in the preceding paragraph. In some embodiments, the device comprises a spatial light modulator configured to inject image information into the first waveguide.

[0011] Some aspects include methods of fabricating a display device. The method may include fabricating an optical waveguide or stack of optical waveguides comprising, for example, the reflective optical element described herein in the preceding paragraph. The method may include disposing the optical waveguide or stack of optical waveguides within a display device.

[0012] Some aspects include a display device comprising a waveguide, the waveguide comprising a reflective diffractive optical element, the diffractive optical element comprising a plurality of protrusions on a surface of the waveguide, and a reflective layer on the surface of the protrusions, the reflective layer being formed from a reflective flowable material, examples of which include reflective ink and liquid metal.

[0013] Some aspects include a method of making an optical device, the method including providing a waveguide with a plurality of surface protrusions and depositing a reflective flowable material onto the surface protrusions to form a reflective layer on the surface protrusions, the surface protrusions and the reflective layer forming a reflective diffractive optical element.

[0014] Additional exemplary embodiments are provided below.

[0015] 1. A method of making an optical waveguide structure, the method comprising: forming a reflective optical element for the waveguide, the forming the reflective optical element comprising: providing a pattern of protrusions on a first surface of the waveguide; depositing reflective ink on the surface of the protrusion; A method comprising:

[0016] 2. The method of embodiment 1, wherein the reflective ink is selectively deposited on predetermined areas of the first surface of the waveguide.

[0017] 3. The method of embodiment 2, wherein depositing comprises dispensing the reflective ink from an inkjet, a microdispenser, or an applicator rod.

[0018] 4. The method of any one of embodiments 1-3, wherein the reflective ink comprises a particle-free ink.

[0019] 5. The method of any one of claims 1-4, wherein the reflective ink comprises aluminum, silver, or a combination thereof.

[0020] 6. The method of any one of embodiments 1-5, wherein the reflective ink further comprises a binder, the binder being present within the reflective optical element.

[0021] 7. The method of any one of embodiments 1-6, wherein the reflective optical element further comprises a surface deposit.

[0022] 8. The method of any one of embodiments 1-7, wherein the protrusions on the first surface comprise photoresist.

[0023] 9. The method of any one of embodiments 2-8, wherein the first surface comprises a wall defining at least a portion of a predetermined area onto which the reflective ink is selectively deposited.

[0024] 10. The method of embodiment 9, wherein the wall comprises a mechanical spacer configured to maintain a space between the waveguide and the additional waveguide.

[0025] 11. The method of any one of embodiments 1-10, wherein the protrusions on the first surface are part of a grating, at least a portion of the reflective ink is non-conformally disposed on the grating, and the interface between the reflective ink and the first surface is substantially free of gaps.

[0026] 12. The method of any one of embodiments 1-11, wherein the reflective optical element is a diffractive optical element configured to redirect incident light at an angle such that the light propagates through the waveguide by total internal reflection.

[0027] 13. The method of any one of embodiments 1-12, wherein the reflective optical element is configured to reflect incident electromagnetic radiation with a reflectivity of at least 60%.

[0028] 14. The method of any one of embodiments 1-13, wherein the reflective optical element is part of an internal coupling optical element or a light distribution element configured to reflect the electromagnetic radiation into the first waveguide.

[0029] 15. Forming an additional reflective optical element on the additional waveguide by depositing a reflective ink onto the pattern of protrusions on the surface of the additional optical waveguide, the additional reflective optical element being configured to reflect incident electromagnetic radiation; and attaching at least an additional waveguide to a surface of the waveguide; Thereby creating a stack of waveguides and 15. The method of any one of embodiments 1-14, further comprising:

[0030] 16. A method of making a display device, the method comprising: forming a reflective layer of reflective ink on a first surface of an optical waveguide, the first surface including protrusions forming a grating, the reflective layer disposed on the first surface, thereby creating a reflective optical element; disposing a reflective optical element within the display device; A method comprising:

[0031] 17. The method of embodiment 16, wherein the reflective layer of the reflective ink is non-conformally disposed on the first surface, and the interface between the reflective layer and the first surface is substantially free of gaps.

[0032] 18. The method of embodiment 16 or embodiment 17, wherein the reflective layer and the protrusions form a diffractive optical element.

[0033] 19. An optical waveguide structure, comprising: a first waveguide having a first surface; a reflective layer of reflective ink disposed on the first surface; Equipped with the reflective layer comprises a binder; An optical waveguide structure, wherein the reflective layer is configured to reflect incident electromagnetic radiation at the interface into the first waveguide.

[0034] 20. The optical waveguide structure of embodiment 19, wherein the reflective layer is substantially free of dispersed metal-containing particles.

[0035] 21. The optical waveguide structure of any one of embodiments 19-20, wherein the reflective layer comprises a surface buildup.

[0036] 22. An optical waveguide structure according to any one of embodiments 19-21, wherein the first surface, together with the reflective layer, constitutes a protrusion that is part of a reflective diffraction grating.

[0037] 23. The optical waveguide structure of any one of embodiments 19-22, wherein the reflective layer reflects incident electromagnetic radiation with a reflectivity of at least 60%.

[0038] 24. An optical waveguide structure described in any one of embodiments 22-23, wherein the reflective layer and the protrusion form an internal coupling optical element configured to redirect incident light at an angle such that the light propagates through the first waveguide.

[0039] 25. The optical waveguide structure further comprises a second waveguide and a third waveguide, the second waveguide configured to output a different range of wavelengths than the third waveguide, and the first waveguide in optical communication with at least one of the second and third waveguides; An optical waveguide structure described in any one of embodiments 19-24, wherein each of the first, second, and third waveguides is disposed on a surface having protrusions, thereby comprising a reflective layer of reflective ink that forms a reflective diffraction grating, and the reflective diffraction grating of each waveguide is configured to redirect light of a different wavelength range.

[0040] 26. An optical waveguide structure according to any one of embodiments 19-25, wherein the first surface comprises a wall defining a boundary of the reflective layer, the wall comprising a mechanical spacer configured to maintain a space between the first waveguide and the other waveguide.

[0041] 27. A display device comprising an optical waveguide structure according to any one of embodiments 19-26.

[0042] 28. The display device of embodiment 27, wherein the device comprises a spatial light modulator configured to inject image information into the first waveguide.

[0043] 29. A method of making a display device, the method comprising: Producing an optical waveguide or a stack of optical waveguides comprising a reflective optical element according to any of embodiments 1-13; disposing an optical waveguide or a stack of optical waveguides within a display device; A method comprising:

[0044] 30. A display device, comprising: a waveguide comprising a reflective diffractive optical element, the diffractive optical element comprising: a plurality of protrusions on a surface of the waveguide; a reflective layer on the surface of the protrusion, the reflective layer being formed from a flowable material; A waveguide display device comprising:

[0045] 31. The display device of embodiment 30, wherein the reflective diffractive optical element forms an incoupling grating configured to incoupling incident light into the waveguide.

[0046] 32. The waveguide is one of a stack of waveguides, each of the stacks of waveguides comprising an internal coupling grating; 32. A display device as described in embodiment 31, wherein, when viewed from above, the internal coupling gratings of different waveguides are laterally offset from each other.

[0047] 33. The display device of embodiment 30, wherein the flowable material comprises a reflective ink.

[0048] 34. The display device of embodiment 30, wherein the flowable material comprises a liquid metal.

[0049] 35. The display device of embodiment 30, wherein the liquid metal is selected from the group consisting of gallium; indium; mercury; gallium-indium eutectic; gallium-indium alloy; gallium indium tin alloy; Ga, In, Sn, and Zn alloy; Ga, In, and Sn alloy; sodium-potassium alloy; gallium, indium, and tin; gallium-indium-zinc-copper metal; and silver indium gallium. 36. The display of embodiment 32, wherein the reflective layer comprises an oxide of a component of the liquid metal.

[0050] 37. A method of making an optical device, the method comprising: providing a waveguide having a plurality of surface protrusions; forming a reflective layer on the surface protrusions by depositing a reflective flowable material on the surface protrusions; wherein the surface protrusions and the reflective layer form a reflective diffractive optical element.

[0051] 38. The method of embodiment 37, further comprising providing a spatial light modulator, the spatial light modulator positioned to output light onto a reflective diffractive optical element.

[0052] 39. The method of embodiment 37, wherein the flowable material comprises reflective ink.

[0053] 40. The method of embodiment 37, wherein the flowable material comprises a liquid metal. The present specification also provides, for example, the following items: (Item 1) 1. A method of making an optical waveguide structure, the method comprising forming a reflective optical element for the waveguide; forming the reflective optical element providing a pattern of protrusions on a first surface of the waveguide; depositing reflective ink onto the surface of said protrusions; A method comprising: (Item 2) Item 10. The method of item 1, wherein the reflective ink is selectively deposited on predetermined areas of the first surface of the waveguide. (Item 3) Item 3. The method of item 2, wherein the first surface comprises a vertically extending wall, the wall defining at least a portion of the predetermined area, the reflective ink being selectively deposited over the predetermined area, and the wall limiting lateral movement of the reflective ink. (Item 4) 3. The method of claim 2, wherein the depositing comprises dispensing the reflective ink from an inkjet, a microdispenser, or an applicator rod. (Item 5) forming an additional reflective optical element on the additional optical waveguide by depositing the reflective ink onto a pattern of protrusions on a surface of the additional optical waveguide, the additional reflective optical element being configured to reflect incident electromagnetic radiation; and attaching at least said additional waveguide to a surface of said waveguide; Thereby creating a stack of waveguides and Item 1, the method of claim 1 further comprising: (Item 6) Item 10. The method of item 1, wherein the reflective ink comprises a particle-free ink. (Item 7) Item 10. The method of item 1, wherein the reflective ink comprises aluminum, silver, or a combination thereof. (Item 8) Item 10. The method of item 1, wherein the reflective ink further comprises a binder, the binder being present within the reflective optical element. (Item 9) Item 10. The method of claim 1, wherein the reflective optical element further comprises a surface buildup. (Item 10) Item 10. The method of claim 1, wherein the protrusions on the first surface comprise photoresist. (Item 11) Item 11. The method of item 10, wherein the wall comprises a mechanical spacer configured to maintain a space between the waveguide and an additional waveguide in an upper layer. (Item 12) Item 10. The method of item 1, wherein the protrusions on the first surface are part of a grating, and wherein at least a portion of the reflective ink is non-conformally disposed on the grating, and wherein an interface between the reflective ink and the first surface is substantially free of gaps. (Item 13) Item 10. The method of item 1, wherein the reflective optical element is a diffractive optical element, and the diffractive optical element is configured to redirect the incident light at an angle such that the incident light propagates through the waveguide by total internal reflection. (Item 14) Item 10. The method of item 1, wherein the reflective optical element is configured to reflect incident electromagnetic radiation with a reflectivity of at least 60%. (Item 15) Item 10. The method of item 1, wherein the reflective optical element is part of an optical incoupling or distribution element configured to reflect electromagnetic radiation into the first waveguide. (Item 16) 1. A method of making a display device, said method comprising: forming a reflective layer of reflective ink on a first surface of an optical waveguide, the first surface including protrusions forming a grating, the reflective layer disposed on the first surface, thereby creating a reflective optical element; disposing said reflective optical element within a display device; A method comprising: (Item 17) Item 17. The method of item 16, wherein a reflective layer of the reflective ink is non-conformally disposed on the first surface, and an interface between the reflective layer and the first surface is substantially gap-free. (Item 18) Item 17. The method of item 16, wherein the reflective layer and protrusions form a diffractive optical element. (Item 19) An optical device, the optical device comprising: a first waveguide having a first surface; a reflective layer of reflective ink disposed on the first surface; Equipped with the reflective layer comprises a binder; The reflective layer is configured to reflect incident electromagnetic radiation into the first waveguide at an interface. (Item 20) 20. The optical device of claim 19, wherein the reflective layer is substantially free of dispersed metal-containing particles. (Item 21) 20. The optical device of claim 19, wherein the reflective layer comprises a surface buildup. (Item 22) 20. The optical device of claim 19, wherein the first surface comprises protrusions, the protrusions being, together with the reflective layer, part of a reflective diffraction grating. (Item 23) 20. The optical device of claim 19, wherein the reflective layer reflects the incident electromagnetic radiation with a reflectivity of at least 60%. (Item 24) Item 23. The optical device of item 22, wherein the reflective layer and the protrusion form an internal coupling optical element, the internal coupling optical element configured to redirect the incident light at an angle such that the incident light propagates through the first waveguide. (Item 25) the optical waveguide structure further comprises a second waveguide and a third waveguide, the second waveguide configured to output a different range of wavelengths than the third waveguide, the first waveguide in optical communication with at least one of the second and third waveguides; 20. The optical device of claim 19, wherein each of the first, second, and third waveguides comprises a reflective layer of reflective ink, the reflective ink being disposed on a surface having protrusions, thereby forming a reflective diffraction grating, the reflective diffraction grating of each waveguide being configured to redirect light of a different wavelength range. (Item 26) 20. The optical device of claim 19, wherein the first surface comprises a wall defining a boundary of the reflective layer, the wall comprising a mechanical spacer configured to maintain a space between the first waveguide and another waveguide. (Item 27) 20. The optical device of claim 19, wherein the optical device is a display system including a spatial light modulator, the spatial light modulator configured to output light containing image information into the first waveguide. (Item 28) 1. A display device comprising: a waveguide comprising a reflective diffractive optical element; The diffractive optical element is a plurality of protrusions on a surface of the waveguide; a reflective layer on the surface of the protrusion; Equipped with A display device wherein the reflective layer is formed from a reflective flowable material. (Item 29) Item 29. The display device of item 28, wherein the reflective diffractive optical element forms an internal coupling grating configured to internally couple incident light into the waveguide. (Item 30) the waveguide is one of a stack of waveguides, each of the stacks of waveguides comprising an internal coupling grating; 30. The display device of item 29, wherein when viewed from above, the internal bonding grates are laterally offset from each other. (Item 31) Item 29. The display device of item 28, wherein the flowable material comprises reflective ink. (Item 32) Item 29. The display device of item 28, wherein the flowable material comprises a liquid metal. (Item 33) 33. The display device of item 32, wherein the liquid metal is selected from the group consisting of gallium; indium; mercury; gallium-indium eutectic; gallium-indium alloy; gallium indium tin alloy; Ga, In, Sn, and Zn alloy; Ga, In, and Sn alloy; sodium-potassium alloy; gallium, indium, and tin; gallium-indium-zinc-copper metal; and silver indium gallium. (Item 34) Item 33. The display device of item 32, wherein the reflective layer comprises an oxide of a component of the liquid metal. (Item 35) 1. A method of making an optical device, the method comprising: providing a waveguide having a plurality of surface protrusions; forming a reflective layer on the surface protrusions by depositing a reflective flowable material on the surface protrusions; Including, The method, wherein the surface protrusions and the reflective layer form a reflective diffractive optical element. (Item 36) Item 36. The method of item 35, further comprising providing a spatial light modulator, the spatial light modulator positioned to output light onto the reflective diffractive optical element. (Item 37) Item 36. The method of item 35, wherein the flowable material comprises reflective ink. (Item 38) Item 36. The method of item 35, wherein the flowable material comprises a liquid metal. [Brief explanation of the drawings]

[0054] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0055] [Figure 2]FIG. 2 illustrates an example of a wearable display system.

[0056] [Figure 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0057] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0058] [Figure 5] 5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0059] [Figure 6] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user.

[0060] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0061] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly, where each depth plane contains an image formed using multiple different primary colors.

[0062] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example set of stacked waveguides, each containing an internal coupling optical element.

[0063] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide example of FIG. 9A.

[0064] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide example of FIGS. 9A and 9B.

[0065] [Figure 10A] FIG. 10A shows a schematic cross-sectional side view of a reflective layer deposited over a pattern of protrusions, according to some embodiments.

[0066] [Figure 10B] FIG. 10B shows a schematic cross-sectional side view of a reflective layer deposited over the pattern of protrusions, according to some other embodiments.

[0067] [Figure 10C] FIG. 10C shows a schematic cross-sectional side view of a reflective layer deposited over a pattern of protrusions according to yet another embodiment.

[0068] [Figure 11A] FIG. 11A shows a schematic perspective view of a confined area for forming a reflective layer from a reflective flowable material over a pattern of protrusions, according to some embodiments.

[0069] [Figure 11B] FIG. 11B shows a schematic cross-sectional side view of the confined area of ​​FIG. 11A for forming a reflective layer from a reflective flowable material over the pattern of protrusions, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0070] The drawings are provided to illustrate example embodiments and are not intended to limit the scope of the present disclosure.

[0071] (Detailed explanation) Waveguides may use optical elements to incouple 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 function in a reflective mode, where light incident on the optical element from one or more angles is reflected and redirected to propagate away from the optical element at a different desired angle. As disclosed herein, such waveguides may form part of a display system. For example, a waveguide may be configured to incouple light containing image information, distribute that light, and outcouple it to a user.

[0072] Reflective optical elements can utilize reflective layers to achieve the desired light reflection. Reflective layers are traditionally deposited using metallization processes, including vapor deposition of a metal layer. These traditional metallization processes can be time-consuming and involve multiple steps. For example, to direct the metallization to the desired location on the waveguide, it may be necessary to align and cover the waveguide 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 vapor deposition itself may require a vacuum, which further complicates the metallization process and increases its duration by requiring the deposition chamber to be depressurized for deposition and then returned to atmospheric pressure for unloading.

[0073] In some embodiments, the reflective layer is formed on the substrate surface using a reflective flowable material, such as a reflective ink and / or liquid metal. The flowable material may be deposited by flowing it from a dispenser onto the substrate surface. Preferably, the flowable material is flowable under standard conditions (e.g., atmospheric pressure and room temperature). In some embodiments, the reflective flowable material is in a liquid phase under deposition conditions (e.g., under standard conditions). In some embodiments, the flowable material may be heated to make it flowable. For example, the flowable material may be heated in a dispenser to maintain it in a flowable state (e.g., a liquid state).

[0074] The surface onto which the flowable material is deposited may include a pattern, such as a pattern comprising a plurality of protrusions and intervening recesses, which may form a grating structure (e.g., a diffractive optical grating), and a reflective layer may coat (e.g., conformally or non-conformally) the surface of the pattern. It should be understood that the protrusions and recesses may, in some embodiments, be part of the same structure. For example, adjacent protrusions may define recesses between them, and the reflective layer may coat both the protrusions and recesses. As a result, the structure may be described as having a recess-defined pattern and / or a protrusion-defined pattern. In some embodiments, the reflective flowable material may be located in separate regions of the substrate surface using partition walls extending perpendicularly onto the substrate surface. In some embodiments, the reflective flowable material may be applied using a dispenser (e.g., an inkjet or microdispenser) that outputs the flowable material to separate locations on the substrate surface. The substrate onto which the reflective flowable material is deposited may be a waveguide formed from an optically transmissive material and configured to propagate light therein by total internal reflection.

[0075] Such metallization of a diffractive optical grating can increase the efficiency of the grating by increasing the amount of light incoupling into the waveguide / substrate. For example, a diffraction grating may be designed to incoupling light into a waveguide over a given range of angles, but not all angles of light are incoupling with equal efficiency, which can lead to light uniformity or other aberrations across all angles. A reflective coating on the grating structure can improve the incoupling efficiency of one or more angles of light incident on the grating.

[0076] Advantageously, the reflective flowable material can be deposited directly onto a substrate surface, which can result in superior speed and throughput compared to conventional approaches involving vapor deposition. Preferably, the deposition does not require a vacuum and is carried out at atmospheric pressure, for example. It should be understood that conventional metallization processes can take several minutes, for example, about 5 to 30 minutes, to deposit a reflective layer. The methods of fabricating optical waveguides with reflective layers described herein can be performed more quickly. For example, the flowable material can be deposited onto a surface (e.g., a surface of a waveguide) in just a few seconds, for example, about 60 seconds or less, for example, about 60 seconds, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 9, 8, 7, 5, 6, 5, 4, 3, 2, 1, 0.5, or 0.1 seconds (including ranges between any two of the listed values). Furthermore, reflective layers formed from reflective flowable materials can provide performance characteristics comparable to or superior to those of reflective materials formed by vapor deposition. For example, reflective inks, including liquid metal or electronic ink, according to some embodiments have been found to provide reflectivity comparable to or superior to reference vapor-deposited aluminum on both flat glass and flat resist (see, e.g., Example 2 below). In some embodiments, the reflective layer is part of an optical element for a waveguide in a display device. In some embodiments, deposition of the reflective flowable material can be performed at room temperature or other relatively low temperatures. This can prevent damage to surface features on the substrate, where those surface features are formed by heat-sensitive materials (e.g., resist). Furthermore, depositing a reflective flowable material according to some embodiments herein can use materials more efficiently, leading to less waste and reducing manufacturing costs. For example, using conventional evaporation-based methods, a material such as Ag would be deposited over the entire surface. On the other hand, a reflective flowable material (e.g., reflective ink or liquid metal) can be easily deposited selectively only on desired areas.

[0077] (Reflective ink, liquid metal, and reflective layer) As used herein, "reflective ink" refers to a type of ink that is flowable when applied and then forms a solid reflective layer upon solidification (e.g., "curing" or "drying"). The reflective ink may include at least one constituent material, such as a metal, such as aluminum, silver, gold, platinum, chromium, or rhodium, that remains present after solidification to provide at least a portion of the reflectivity of the reflective layer. The reflective ink may further include other substances, such as a binder. Without being limited by theory, it is believed that metals such as aluminum and silver are highly reflective in the visible spectrum, making them highly suitable for reflective inks according to some embodiments. In some embodiments, the reflective ink includes a broadband reflector material, such as chromium, platinum, or rhodium.

[0078] Reflective inks according to some embodiments may be formulated as flowable materials, such as liquids or gels, that solidify to become less flowable, e.g., semi-solid or solid, to form a stable reflective layer. In some embodiments, the viscosity of the reflective ink may be selected (e.g., varied between a relatively thin liquid and a relatively viscous liquid) as needed to obtain a desired drying time, a desired uniformity of application, a desired concentration of reflective material, and / or a desired control over the orientation of the reflective layer. In some embodiments, the reflective ink is formulated as a gel, which solidifies to become a more viscous or solid reflective layer.

[0079] It will be appreciated that different levels of viscosity may provide different advantages. For example, a relatively viscous flowable material (e.g., a reflective ink) may be suitable for forming desired three-dimensional features such as walls (which may be useful, for example, in confining the location of subsequently deposited flowable material that is flowable), which may be suitable for solidification by air drying, avoiding the need for oven firing, thereby reducing the heat budget. On the other hand, a relatively thin ink may be suitable for forming a relatively thin and uniform reflective layer, which may flow more easily between closely spaced features, but solidification may involve a longer drying time or oven firing. In some embodiments, once deposited, the flowable material solidifies to form a reflective layer, and one or more additional layers of flowable material are applied and solidified as described herein to form a reflective layer of desired thickness.

[0080] In some embodiments, the reflective ink includes a binder, such as an organic or inorganic binder. The binder may modify the viscosity of the reflective ink, facilitate solidification of the reflective ink (e.g., reduce the temperature and / or time at which the reflective ink solidifies), and / or facilitate adhesion of a reflective layer formed by the reflective ink to a surface, such as that of a waveguide. In some embodiments, a reflective layer including a binder exhibits better adhesion to an underlying surface compared to a reflective layer of a similar material without a binder (e.g., a binder-containing layer formed from a reflective ink may be compared to a non-binder-containing layer deposited by vapor deposition).

[0081] In some embodiments, the reflective ink comprises silver. In some embodiments, the reflective ink comprises a compound of the formula |Ag(NH3)2| + |C2H3O2| - Such inks can be formulated as particle-free or substantially particle-free formulations and have been shown to result in materials with relatively high silver content upon application and drying (Walker et al., "Reactive Silver Inks for Patterning"). See, "High-Conductivity Features at Mild Temperatures," J. Am. Chem. Society 134:1419-1421, the entire contents of which are incorporated herein by reference with respect to reflective inks. Without being limited by theory, it is believed that increasing the metal content (such as silver content) of the reflective ink corresponds to increased reflectivity of the reflective layer.

[0082] In some embodiments, the reflective ink comprises silver-containing particles, such as silver-containing colloids or silver-containing nanoparticles. In some embodiments, the reflective ink comprises silver-containing nanocrystals. Such nanocrystal-containing reflective inks can be formed via a variety of approaches. For example, silver nanocrystals can be formed using a "bottom-up" approach, in which silver atoms are associated with nuclei, such as silver salts (e.g., silver nitrate, AgNO). For example, silver nanocrystals can be formed using a surfactant-assisted synthesis approach, in which silver crystals are grown from seeds and a surfactant is added to modify the growth rate along one or more crystal planes to control the shape of the silver-containing crystals. As another example, silver-containing particles and / or colloids can be formed with the assistance of ultraviolet radiation to control the shape and dimensions of the silver-containing particles, such as nanoparticles and / or colloids. Some approaches for synthesizing inks containing silver particles are described in "Silver nanoparticle ink technology: state of the art" Nanotechnol Sci. Appl. 2016;9:1-13 (incorporated herein by reference in its entirety).

[0083] In some embodiments, solidifying the flowable material can include drying and annealing. For example, particle-containing reflective inks can be deposited and then solidified by drying and annealing. Some particle-containing reflective inks can be annealed at temperatures well below the melting point of the metal in the reflective ink, which can also be useful for conserving heat budgets and minimizing heating and cooling times. For example, the melting point of silver is 960°C. In some embodiments, the reflective ink including metal-containing particles (e.g., silver-containing particles) is solidified, and solidifying can occur at temperatures below 960°C, such as at least about 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 450°C, 500°C, 550°C, 600°C, or 650°C. and annealing at a temperature ranging between any two of the listed values, e.g., about 150°C to 650°C, 150°C to 500°C, 150°C to 400°C, 150°C to 300°C, 150°C to 250°C, 150°C to 200°C, 200°C to 650°C, 200°C to 500°C, 200°C to 400°C, 200°C to 300°C, 200°C to 250°C, 250°C to 650°C, 250°C to 500°C, 250°C to 400°C, 250°C to 300°C, 300°C to 650°C, 300°C to 500°C, or 300°C to 400°C. In some embodiments, the reflective ink including metal-containing particles is solidified without annealing.

[0084] The reflective layer, according to some embodiments herein, reflects at least one visible wavelength of incident electromagnetic radiation (e.g., light within the visible spectrum). The reflective layer may be formed from a flowable material, for example, a flowable material that has been solidified through drying and / or annealing. The reflective layer preferably reflects at least about 30% of at least one visible wavelength of incident electromagnetic radiation, e.g., at least about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, 99.5%, or 99.9% of the incident electromagnetic radiation (including ranges between any two of the recited values, e.g., about 30%-99%, 30%-95%, 30%-90%, 30%-80%, 30%-70%, 50%-99%, 50%-95%, 50%-90%, 50%-80%, 50%-70%, 70%-99%, 70%-95%, 70%-90%, or 70%-80% of the incident electromagnetic radiation). In some embodiments, the incident electromagnetic radiation comprises light in the visible spectrum. It should be understood that the flowable material itself may not necessarily possess the reflective properties indicated prior to solidification, but upon solidification, the reflective layer formed from the flowable material will have the reflective properties indicated.

[0085] In some embodiments, a reflective layer formed from a reflective ink as described herein has the reflectivity, adhesion, and / or pattern as described herein, while being structurally different from conventional reflective materials. In some embodiments, the reflective layer comprises a structure, such as a binder and / or irregular accumulation of ink material as described herein, and has performance characteristics, such as reflectivity, pattern fidelity, and adhesion, suitable for forming waveguides and / or optical elements of display devices as described herein. Thus, in some embodiments, a reflective layer formed from a reflective ink as described herein offers patterning process advantages, such as superior patterning speed, throughput, and efficiency, over conventional deposition methods, such as evaporation (with or without a mask). In some embodiments, the reflective layer is on a waveguide that includes one or more surface protrusions that can form an optical grating as described herein. Additionally, the layer can have a reflectivity suitable for redirecting light for waveguides such as those in display devices as described herein.

[0086] It should be understood that the reflective layer may differ structurally from reflective layers formed by other means, such as vapor deposition. For example, in some embodiments, the reflective layer comprises a metal or combination of metals (e.g., aluminum, silver, or aluminum and silver) and at least one binder (e.g., an organic or inorganic binder), and the reflective layer has a reflective integrity of at least about 30%, e.g., at least about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, or more, that of the corresponding pure metal or combination of metals. or 99% (including ranges between any two of the listed values, e.g., about 30%-99%, 30%-95%, 30%-90%, 30%-80%, 40%-99%, 40%-95%, 40%-90%, 40%-80%, 50%-99%, 50%-95%, 50%-90%, 50%-80%, 60%-99%, 60%-95%, 60%-90%, 60%-80%, 70%-99%, 70%-95%, 70%-90%, or 70%-80%). In some embodiments, the reflective layer is disposed on the waveguide and configured to redirect light propagating through the waveguide, e.g., as part of a light distribution element. In some embodiments, the reflective layer can be disposed on the waveguide using a deposition process described herein. In some embodiments, the reflective layer is disposed on the waveguide and configured to direct light into the waveguide, e.g., as part of an incoupling optical element. In some embodiments, the waveguide is part of a display device.

[0087] As used herein, “surface buildup” refers to irregular accumulations of material formed from reflective ink (e.g., lines, “spaghetti-like” strands, or islands of ink material) that extend from the surface of a reflective layer as described herein as an artifact within the reflective layer due to the flowable and viscous nature of the reflective ink (e.g., see 1015 in FIG. 10A ). For ease of conceptualization only, surface buildup can be thought of as analogous to dried paint droplets that may be present when paint is applied thickly to a wall or canvas. The buildup, in some embodiments, may have nanometer-scale height, length, and diameter. The buildup is typically on a surface of the reflective layer that is not at the interface of another surface with the waveguide surface, or on the surface onto which the reflective layer is deposited. Thus, in some embodiments, a reflective layer formed from a reflective ink as described herein may comprise surface buildup yet maintain a high level of reflectivity.

[0088] As used herein, "protrusion," "surface protrusion," and variations of these basic terms refer to a mass of material extending upward on or within a substrate, such as an optical grating extending from the surface of a waveguide. In some embodiments, the protrusion may be formed by etching a substrate that may include deposited material (e.g., photoresist deposited on a waveguide) or may be a substantially homogeneous structure (e.g., a waveguide). In some embodiments, a reflective layer 1010 comprising surface buildup 1015 is disposed over an optical grating 1020 (see FIG. 10A). A patterned resist or grating 1020 may comprise the buildup 1015. In some embodiments, the reflective layer 1010 is disposed over an optical grating 1020 having a blazed configuration (see FIG. 10B). In some embodiments, the reflective layer 1010 is disposed over an optical grating 1020 having a multilevel configuration (see FIG. 10C). In some embodiments, the optical grating comprises photoresist.

[0089] It should be understood that the reflective layer is preferably utilized to provide reflection of light into and / or through the waveguide. As a result, the flowable material preferably coats all surfaces of the protrusions. In some embodiments, the reflective layer is conformally disposed over the optical grating. It should be noted that when a material is "conformally" disposed, it will substantially conform to the underlying surface.

[0090] In some embodiments, due to the liquid or semi-liquid properties of the reflective ink, the reflective layer may be slightly thinner nearer the top of the waveguide protrusion during solidification and may be slightly thicker nearer the bottom during solidification. Note that these slight variations are not expected to adversely affect the performance of the reflective layer. In some embodiments, the reflective layer is conformally deposited, such that the thickness of the reflective layer over the surface (e.g., the linear thickness extending from the surface across the layer) varies by no more than about ±20% across the reflective layer, such that the thickness is within ±20% of the average, e.g., within ±20%, ±15%, ±10%, ±5%, or ±1% of the average. Preferably, the conformal reflective layer is positioned so that there is no or substantially no gap between the reflective layer and the surface of the substrate. It is also believed that in some embodiments, a non-conformal reflective layer may provide suitable reflectivity at the relevant interface (e.g., without being limited by theory, as long as the surface of the reflective layer at the interface with the waveguide is sufficiently reflective and provides sufficient coverage, the opposing surface not facing the waveguide may not need to conform to the waveguide). Thus, in some embodiments, the reflective layer is non-conformally disposed on the substrate. Preferably, the non-conformal layer is disposed so that there are no or substantially no gaps between the reflective layer and the surface of the substrate. It should be understood that "substantially no" gaps between the reflective layer and the substrate mean that some gaps may exist, but they do not significantly reduce the reflectivity of the reflective optical element formed by the reflective layer and the substrate compared to a reflective layer without gaps. In some embodiments, the ink is deposited to a thickness sufficient to completely or substantially completely fill the open volumes or gaps between the waveguide protrusions.

[0091] In some embodiments, the reflective ink includes a binder, such as an organic or inorganic binder, which may provide one or more of the following: allowing the reflective ink to have sufficient viscosity to form high-fidelity patterns; allowing the reflective layer to solidify quickly and promote adhesion of deposited layers to surfaces such as waveguides; and allowing the reflective layer to be stably positioned over and remain adhered to a surface. Consequently, in some embodiments, a reflective layer comprising or consisting of a reflective ink as described herein includes a binder that, after solidification, can bond to the reflective layer or to a material in the surface on which the reflective layer is positioned. Relative adhesion can be measured, for example, using a scratch test, in which a deposited layer is cleaved or cut into a pattern, such as a crosshatched pattern, and contacted with an adhesive substrate, such as tape, which is then removed and the percentage of reflective layer units removed by the adhesive substrate is determined (e.g., the fewer reflective layer units removed, the stronger the adhesion). An exemplary scratch test is described in ATSM standard D3359-09, "Standard Test Methods for Measuring Adhesion," published in June 2009. by Tape Test,” which is incorporated herein by reference in its entirety.

[0092] In some embodiments, the reflective ink includes particles, such as metal-containing nanoparticles or microparticles. Without being limited by theory, it is believed that metal particles may partially scatter light, and thus the reflectivity of a particle-containing reflective layer may be lower than that of a particle-free layer. However, it is also believed that some reflective inks including particles may provide suitable reflectivity for waveguides and / or display devices as described herein. Thus, in some embodiments, the reflective layer includes particles, for example, metal-containing nanoparticles and / or metal-containing microparticles.

[0093] As noted above, without being limited by theory, particles present in reflective inks and layers can undesirably diffuse light. Thus, in some embodiments, the reflective ink is particle-free or substantially particle-free. Accordingly, in some embodiments, the reflective layer does not include particles as described herein (e.g., the reflective layer does not include either metal-containing microparticles or metal-containing nanoparticles). In some embodiments, the reflective ink is particle-free or substantially particle-free and includes non-metals, and therefore, the reflective layer formed from the reflective ink is particle-free or substantially particle-free and includes non-metals. In some embodiments, the particle-free ink comprises a silver-containing ink further comprising a metal and a ligand, e.g., a carbamate ligand, configured to bond to the metal to form the reflective layer upon solidification. In some embodiments, the particle-free ink comprises a silver-containing ink having the formula |Ag(NH3)2| + |C2H3O2| - In some embodiments, the reflective layer is free or substantially free of particles and further comprises a surface buildup as described herein.

[0094] In some embodiments, a reflective layer of a desired thickness is formed. Thus, in some embodiments, the reflective layer can be at least about 10 nm, e.g., at least about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460 , 470, 480, 490, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or 1,000 nm (thickness ranges between two of the listed values, e.g., about 10 nm to 900 nm, 10 nm to 500 nm, 10 nm to 410 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, 10 nm to 150 nm, 10 nm to 100 nm, 10 nm to 50 nm, 30 nm to 900 nm, 30 nm ~500nm, 30nm~450nm, 30nm~400nm, 30nm~350nm, 30nm~300nm, 30nm~250nm, 30nm~200nm, 30nm~150, 30nm~100nm, 30nm~50nm, 50nm~900 nm, 50nm~500nm, 50nm~450nm, 50nm~400nm, 50nm~350nm, 50nm~300nm, 50nm~250nm, 50nm~200nm, 50nm~150, 50nm~100nm, 80nm~900nm, In some embodiments, a single layer of flowable material is deposited with a suitable thickness and viscosity to form a reflective layer of desired thickness upon solidification.In some embodiments, a layer of flowable material is applied and at least partially solidified, and at least one subsequent layer of flowable material is applied on top of the solidified or partially solidified layer. The cycle of applying flowable material can 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 flowable material application can be performed to form a reflective layer of the desired thickness (including a range between any of the two recited values).

[0095] In some embodiments, liquid metal can be used to form the reflective layer as an alternative to or in addition to reflective ink. In some embodiments, the liquid metal can include gallium; indium; mercury; gallium-indium eutectic; gallium-indium alloy; gallium indium tin alloy; Ga, In, Sn, and Zn alloy; Ga, In, and Sn alloy; GALINSTAN® available from Geratherm Medical AG (Geschwenda, Germany); sodium-potassium alloy (NaK); gallium, indium, and tin; gallium-indium-zinc-copper metal; and silver indium gallium. Preferably, a sufficient amount of liquid metal is deposited to coat the exposed surfaces of the underlying protrusions. For example, the liquid metal can be dispensed onto the protrusions and flow into and fill the spaces between the protrusions. In some embodiments, the liquid metal can be deposited to a height greater than the protrusions.

[0096] It should be understood that the underlying protrusions can form diffractive optical elements (e.g., diffraction gratings), which can be utilized as internal coupling optical elements. As discussed herein, these protrusions can be metallized by PVD to form reflective diffractive optical elements. In some embodiments, liquid metal can be deposited on the protrusions in place of PVD metallization. For example, the liquid metal can be deposited to directly contact and coat the surface of the protrusions, thereby forming a reflective layer. Advantageously, replacing the PVD metallization with a liquid metal reflective layer has been found to provide similar levels of optical performance. For example, reflective diffractive optical elements formed using a liquid metal reflective layer have been found to provide similar diffraction efficiencies as otherwise similar diffractive optical elements formed using PVD metallization. In some embodiments, liquid metal-based diffractive optical elements have diffraction efficiencies of 2-4% or 2-3% for light incident on the diffractive optical elements at an angle normal (perpendicular) to the diffractive optical elements. In some circumstances, liquid metal-based diffractive optical elements are configured to redirect incident light for propagation through a substrate (eg, a waveguide) by total internal reflection.

[0097] In some embodiments, an optical waveguide stack is provided. The optical waveguide stack may include a first waveguide having a first surface, as described herein, and a reflective layer conformally disposed on a protrusion of the first surface and bonded to the first surface. The reflective layer may include an interface with the first surface configured to reflect incident electromagnetic radiation (e.g., light in the visible spectrum) into the first waveguide at the interface, as described herein. The optical waveguide stack may include at least one other optical waveguide, as described herein. In some embodiments, the protrusion of the surface of the first waveguide on which the reflective layer is disposed forms an optical grating, such as 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.

[0098] In some embodiments, the reflective layer may be positioned within a region of the surface of the waveguide using one or more walls. The one or more walls may extend vertically to a height above the surface protrusion on the substrate. In other words, the one or more walls may extend vertically from the bottom of the recess to or above the surface. In some embodiments, the reflective layer may partially or completely fill the volume enclosed by the walls. Advantageously, these walls and reflective layer function as spacers, providing gaps between the waveguides of the waveguide stack. In some embodiments, the gaps are air gaps, which promote total internal reflection within the waveguides by providing a low-index interface with the waveguides.

[0099] In some embodiments, the protrusion and reflective layer disposed on the first optical waveguide are each part of an internal coupling optical element or a light distribution element configured to reflect electromagnetic radiation (e.g., light in the visible spectrum) into the first waveguide or redirect light propagating within the waveguide, as described herein. The internal coupling optical element can facilitate the propagation of electromagnetic radiation (e.g., light in the visible spectrum) within the waveguide by total internal reflection by redirecting incident ambient light to propagate through the waveguide at an angle suitable for total internal reflection. In some embodiments, the reflective layer comprises an internal coupling optical element on the first optical waveguide. The first optical waveguide can be part of an optical waveguide stack further comprising a second optical waveguide. The second optical waveguide can be configured to allow electromagnetic radiation (e.g., light in the visible spectrum) to pass therethrough to the internal coupling optical element of the first optical waveguide. An internal coupling optical element of the first optical waveguide then redirects the electromagnetic radiation into the first optical waveguide.

[0100] In some embodiments, the optical waveguide stack comprises at least one additional waveguide, for example, at least 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 additional waveguides (including ranges between any two of the listed values). In some embodiments, the optical waveguide stack further comprises a third waveguide. The third waveguide may comprise an external coupling optical element configured to output a different wavelength range than the first and / or second optical waveguides. In some embodiments, the first waveguide is in optical communication with at least one of the second and third optical waveguides.

[0101] In some embodiments, a display device as described herein includes an optical waveguide stack. In some embodiments, a spatial light modulator may be optically coupled to the waveguide stack and configured to launch light into the waveguide stack. The light may be encoded with image information as described herein and directed through the waveguide stack for output to a user's eye.

[0102] It should be understood that a reflective layer formed from a flowable material may unintentionally reflect light out of the waveguide. As discussed herein, a reflective layer deposited on the surface of a pattern of protrusions may form a reflective grating on the waveguide. The grating may redirect incident light at an angle such that it propagates through the waveguide by total internal reflection. In one example, light incident on the grating may be internally coupled into the waveguide so that it propagates away from the grating at an angle suitable for TIR within the waveguide. It should be understood that internally coupled light may propagate through the waveguide by TIR and reflect off the surface of the waveguide at an angle similar to the angle at which it internally coupled. Depending on the geometry of the grating or the beam diameter of the light, some of this light may impinge on the grating during early reflections in the TIR path and be undesirably redirected out of the waveguide. For example, a grating may be on one surface of the waveguide, and incident light may be redirected so that it is internally coupled and reflects off the opposite surface of the waveguide. The reflected light may then impinge on a diffraction grating, which causes the light to be redirected out of the waveguide. In some embodiments, the diffraction grating, onto which a reflective layer is deposited to prevent undesired redirection of light out of the waveguide, may be sized and shaped, or the beam diameter adjusted, so that incoupled light reflected from the opposite surface of the waveguide does not strike the diffraction grating.

[0103] (Devices with Reflective Layers) In some embodiments, a reflective layer as described herein is disposed within a display device. In some embodiments, the reflective layer is disposed on a waveguide. The reflective layer can be, for example, part of an “internal coupling optical element” as described herein and / or a “light distribution element” as described herein, each of which is a type of “reflective optical element” (e.g., light distribution elements 1214, 1224, 1234 in FIG. 9A ) and can be disposed on a waveguide. In some embodiments, a first reflective layer is part of the “internal coupling optical element” and a second reflective layer comprises a “light distribution element,” and the first and second reflective layers are disposed on the same waveguide, e.g., at similar vertical levels. In some embodiments, a first portion of the reflective layer is part of the “internal coupling optical element,” and a second portion of the same reflective layer is part of the “light distribution element,” and the first and second portions of the reflective layer are disposed on the same waveguide. The waveguide can be part of a display device, such as a wearable display system as described herein. In some embodiments, the reflective layer may be disposed on the waveguide, for example, as a light distribution element to redirect light propagating internally within the waveguide, hi some embodiments, the reflective layer is part of a light distribution element that is a "pupil expander" that may increase the size of a relatively focused spot of light before directing the light onto the retina of a wearable display system wearer.

[0104] In some embodiments, the reflective layer is conformally disposed on an underlying surface, e.g., a waveguide. As discussed herein, the surface may comprise features such as protrusions, gratings (e.g., binary, blazed, metamaterial or metasurface, undercut, and / or multilevel gratings), which may be formed from a patterned material, such as a patterned resist. Thus, in some embodiments, the reflective layer 1010 is conformally deposited on a non-planar feature, such as a grating 1020, which may comprise a binary (see FIG. 10A), blazed (see FIG. 10B), or multilevel (see FIG. 10C) configuration. The feature 1020 may be disposed on a substrate 1030. Such features on the surface may be on the nanometer or micrometer scale. For example, nanometer-scale features may have heights, depths, and / or diameters in the nanometer-scale range, e.g., tens or hundreds of nanometers, e.g., heights, depths, and / or diameters in the range of about 20 nm to about 500 nm. In some embodiments, the reflective layer 1005 comprises a surface buildup 1015 .

[0105] In some embodiments, the reflective layer is adhered to an underlying substrate surface, e.g., a waveguide. In some embodiments, the reflective layer includes a bonding agent, which interacts with the underlying surface to contribute to adhesion of the reflective layer to the underlying surface.

[0106] Reference is now made to the drawings, wherein like reference numerals refer to like features throughout.

[0107] FIG. 2 illustrates an example of a wearable display system 80. The display system 80 includes a display 62 and various mechanical and electronic modules and systems to support the functionality of the display 62. The display 62 may be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 directly in front of the user's 60 eyes. The display 62 may, in some embodiments, be considered eyewear. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user's 60 ear canal (another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphones may be configured to allow a user to provide input or commands (e.g., voice menu command selections, natural language queries, etc.) to the system 80 and / or enable audio communication with others (e.g., other users of similar display systems).

[0108] 2, the display 62 is operatively coupled by a communications link 68, such as a wired lead or wireless connectivity, to a local data processing module 70, which may be mounted in a variety of configurations, such as fixedly attached to the frame 64, fixedly attached to a helmet or hat worn by the user, integrated into headphones, or otherwise removably attached to the user 60 (e.g., in a backpack configuration, in a belt-coupled configuration). The local processing and data module 70 may include a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data captured from sensors (such as 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., which may be operatively coupled to frame 64 or otherwise attached to user 60)) and / or b) data obtained and / or processed using remote processing module 72 and / or remote data repository 74 (including data related to virtual content), possibly for processing or readout and then passage to display 62. Local processing and data module 70 may be operatively coupled to remote processing module 72 and remote data repository 74 by communications links 76, 78, such as via wired or wireless communication links, such that these remote modules 72, 74 are operatively coupled to each other and available as resources to local processing and data module 70. In some embodiments, the local processing and data module 70 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope.In some other embodiments, one or more of these sensors may be mounted to the frame 64 or may be freestanding structures that communicate with the local processing and data module 70 by wired or wireless communication paths.

[0109] 2 , in some embodiments, remote processing module 72 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 74 may comprise a digital data storage facility and may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 74 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to local processing and data module 70 and / or remote processing module 72. In some embodiments, all data is stored and all calculations are performed in the local processing and data module, allowing for fully autonomous use from the remote module.

[0110] Referring now to FIG. 3, the perception of an image as "three-dimensional" or "3-D" can be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two different images 5, 7 are output to the user, one for each eye 4, 6. The images 5, 7 are spaced from the eyes 4, 6 by a distance 10 along the optical or z-axis parallel to the viewer's line of sight. The images 5, 7 are flat, and the eyes 4, 6 can focus on the images by assuming a single accommodative state. Such a system relies on the human visual system to combine the images 5, 7 and provide the perception of depth and / or scale of the combined image.

[0111] However, it should be understood that the human visual system is complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sensation of depth at all. Without being limited by theory, it is believed that a viewer of an object may perceive the object as “three-dimensional” due to a combination of vergence movement and accommodation. Vergence movement of the two eyes relative to each other (i.e., pupil rotation such that the pupils move toward or away from each other, converging the eyes’ lines of sight and fixating on the object) is closely linked to the focusing (or “accommodation”) of the eye’s lenses. Under normal conditions, a change in the focus of the eye’s lenses or accommodation of the eye to change focus from one object to another at a different distance will automatically produce a matching change in vergence at the same distance, a relationship known as the “accommodation-vergence reflex.” Similarly, changes in vergence will induce matching changes in accommodation in lens shape and pupil size under normal conditions. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems are uncomfortable for many viewers, particularly because they simply provide different presentations of the scene but work against the "accommodation-vergence reflex" when the eyes view all image information in a single, accommodated state. Display systems that provide better matching between accommodation and vergence can produce more realistic and comfortable simulations of three-dimensional images.

[0112] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. Referring to FIG. 4 , objects at various distances from the eyes 4, 6 on the z-axis are accommodated by the eyes 4, 6 so that the objects are in focus. The eyes (4 and 6) assume particular accommodation states to focus on objects at different distances along the z-axis. Consequently, a particular accommodation state may be said to be associated with a particular one of the depth planes 14 having an associated focal length such that an object or portion of an object at a particular depth plane is in focus when the eye is in an accommodated state relative to that depth plane. In some embodiments, a three-dimensional image may also be simulated by providing different presentations of images for each of the eyes 4, 6, thereby providing different presentations of images corresponding to each of the depth planes. While shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 4, 6 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it should be understood that the contours of the depth plane may be curved in physical space so that all features within the depth plane are in focus with the eye in a particular state of accommodation.

[0113] The distance between an object and the eye 4 or 6 can also change the amount of divergence of light from that object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between an object and the eye 210 is represented by decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 4 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the viewer's eye 4 decreases. While only a single eye 4 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 4 may apply to both eyes 4 and 6 of a viewer.

[0114] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations can be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on different depth planes and / or based on the observation of different image features on different depth planes that are out of focus.

[0115] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 1000 includes a stack of waveguides or stacked waveguide assembly 178 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 182, 184, 186, 188, 190. In some embodiments, display system 1000 is system 80 of FIG. 2 , and FIG. 6 diagrammatically illustrates some portions of system 80 in greater detail. For example, waveguide assembly 178 can be part of display 62 of FIG. 2 . It should be understood that display system 1000 can be considered a bright field display in some embodiments.

[0116] Continuing with reference to FIG. 6 , the waveguide assembly 178 may also include multiple features 198, 196, 194, 192 between the waveguides. In some embodiments, the features 198, 196, 194, 192 may be one or more lenses. The waveguides 182, 184, 186, 188, 190 and / or multiple lenses 198, 196, 194, 192 may be configured to transmit image information to the eye with various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. Image injection devices 200, 202, 204, 206, 208 may act as light sources for the waveguides and may be utilized to inject image information into waveguides 182, 184, 186, 188, 190, each of which may be configured as described herein to distribute incident light across each respective waveguide for output toward eye 4. Light exits output surfaces 300, 302, 304, 306, 308 of image injection devices 200, 202, 204, 206, 208 and is injected into corresponding input surfaces 382, ​​384, 386, 388, 390 of waveguides 182, 184, 186, 188, 190. In some embodiments, each of the input surfaces 382, ​​384, 386, 388, 390 may be an edge of the corresponding waveguide or may be a portion of a major surface of the corresponding waveguide (i.e., one or both of the waveguide surfaces directly facing the world 144 or the viewer's eye 4). In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams directed toward the eye 4 at a particular angle (and amount of divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 200, 202, 204, 206, 208 may be associated with and launch light into multiple (e.g., three) waveguides 182, 184, 186, 188, 190.

[0117] In some embodiments, image input devices 200, 202, 204, 206, 208 are separate displays that each generate image information for input into a respective corresponding waveguide 182, 184, 186, 188, 190. In some other embodiments, image input devices 200, 202, 204, 206, 208 are the output of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic cables) to each of image input devices 200, 202, 204, 206, 208. It should be understood that the image information provided by image input devices 200, 202, 204, 206, 208 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0118] In some embodiments, the light injected into the waveguides 182, 184, 186, 188, 190 is provided by a light projector system 2000, which includes a light module 2040, which may include a light emitter such as a light emitting diode (LED). Light from the light module 2040 may be directed via a beam splitter 2050 to and modified by a light modulator 2030, such as a spatial light modulator. The light modulator 2030 may be configured to change the perceived intensity of the light injected into the waveguides 182, 184, 186, 188, 190. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays.

[0119] In some embodiments, the display system 1000 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 182, 184, 186, 188, 190 and ultimately to the viewer's eye 4. In some embodiments, the illustrated image injection devices 200, 202, 204, 206, 208 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 182, 184, 186, 188, 190. In some other embodiments, the illustrated image injection devices 200, 202, 204, 206, 208 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 182, 184, 186, 188, 190. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 2040 to one or more waveguides 182, 184, 186, 188, 190. It should be understood that one or more intervening optical structures may be provided between the scanning fiber or fibers and one or more of the waveguides 182, 184, 186, 188, 190, for example, to redirect light exiting the scanning fiber into one or more of the waveguides 182, 184, 186, 188, 190.

[0120] The controller 210 controls the operation of one or more of the stacked waveguide assemblies 178, including the operation of the image input devices 200, 202, 204, 206, 208, the light source 2040, and the light module 2030. In some embodiments, the controller 210 is part of the local data processing module 70. The controller 210 includes programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provision of image information to the waveguides 182, 184, 186, 188, 190, 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 a wired or wireless communication channel. The controller 210 may be part of the processing module 70 or 72 (FIG. 1) in some embodiments.

[0121] Continuing with reference to FIG. 6 , the waveguides 182, 184, 186, 188, 190 may be configured to propagate light within each respective waveguide by total internal reflection (TIR). Each of the waveguides 182, 184, 186, 188, 190 may be planar with major top and bottom surfaces and edges extending between the major top and bottom surfaces, or may have another shape (e.g., curved). In the illustrated configuration, each of the waveguides 182, 184, 186, 188, 190 may include outcoupling optical elements 282, 284, 286, 288, 290 configured to extract light from the waveguide by redirecting the light to propagate within each respective waveguide and outputting image information from the waveguide to the eye 4. The extracted light may also be referred to as outcoupling light, and the outcoupling optical element light may also be referred to as light extraction optical elements. The extracted beams of light are output by the waveguides at locations where light propagating within the waveguides strikes the light-extraction optical elements. The outcoupling optical elements 282, 284, 286, 288, 290 may be, for example, gratings including diffractive optical features, as discussed further herein. While shown disposed on the bottom major surfaces of the waveguides 182, 184, 186, 188, 190 for ease of explanation and clarity of drawing, in some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 182, 184, 186, 188, 190, as discussed further herein. In some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 may be attached to a transparent substrate and formed within a layer of material that forms the waveguides 182, 184, 186, 188, 190. In some other embodiments, the waveguides 182, 184, 186, 188, 190 may be monolithic pieces of material, and the outcoupling optical elements 282, 284, 286, 288, 290 may be formed on and / or within the material pieces.

[0122] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 182, 184, 186, 188, 190 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 182 closest to the eye may be configured to deliver collimated light to the eye 4 when launched into such waveguide 182. The collimated light may represent an optical infinity focal plane. The next upper waveguide 184 may be configured to send collimated light that passes through a first lens 192 (e.g., a negative lens) before reaching the eye 4. Such first lens 192 may be configured to generate a slight convex wavefront curvature such that the eye / brain interprets light emerging from the next upper waveguide 184 as emerging from a first focal plane closer inward from optical infinity toward the eye 4. Similarly, the third upper waveguide 186 passes its output light through both the first lens 192 and the second lens 194 before reaching the eye 4. The combined refractive power of the first lens 192 and the second lens 194 may be configured to produce another, increasing amount of wavefront curvature so that the eye / brain interprets the light emerging from the third waveguide 186 as originating from a second focal plane closer inward toward the person from optical infinity, which was the light from the next upper waveguide 184.

[0123] The other waveguide layers 188, 190 and lenses 196, 198 are similarly configured, with the highest waveguide 190 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate the stack of lenses 198, 196, 194, 192 when viewing / interpreting light originating from the world 144 on the other side of the stacked waveguide assembly 178, a compensating lens layer 180 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 198, 196, 194, 192. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the outcoupling optical elements of the waveguides and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0124] In some embodiments, two or more of the waveguides 182, 184, 186, 188, 190 may have the same associated depth plane. For example, multiple waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same depth plane, or multiple subsets of the waveguides 182, 184, 186, 188, 190 may be configured to output images set at the same multiple depth planes, one set for each depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0125] Continuing with reference to FIG. 6 , the outcoupling optical elements 282, 284, 286, 288, 290 can be configured to both redirect light out of their respective waveguides and output this light with the appropriate amount of divergence or collimation for the particular depth plane associated with the waveguide. As a result, waveguides with different associated depth planes can have different configurations of the outcoupling optical elements 282, 284, 286, 288, 290, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extraction optical elements 282, 284, 286, 288, 290 can be volume or surface features, which can be configured to output light at specific angles. For example, the light-extraction optical elements 282, 284, 286, 288, 290 can be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 198, 196, 194, 192 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0126] In some embodiments, the outcoupling optical elements 282, 284, 286, 288, 290 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 4 with each intersection point of the DOE, while the remainder continues traveling through the waveguide via total internal reflection. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a very uniform pattern of output emission toward the eye 4 for this particular collimated beam bouncing within the waveguide.

[0127] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0128] In some embodiments, a camera assembly 500 (e.g., a digital camera including a visible light and infrared light camera) may be provided to capture images of the eye 4 and / or tissue surrounding the eye 4, for example, to detect user input. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 500 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 500 may be mounted to the frame 64 ( FIG. 2 ) and may be in electrical communication with processing modules 70 and / or 72 that may process image information from the camera assembly 500. In some embodiments, one camera assembly 500 may be utilized for each eye, monitoring each eye separately.

[0129] Referring now to FIG. 7 , an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 178 ( FIG. 6 ) may function similarly, and that waveguide assembly 178 includes multiple waveguides. Light 400 is launched into waveguide 182 at input surface 382 of waveguide 182 and propagates within waveguide 182 by TIR. At the point where light 400 impinges on DOE 282, a portion of the light exits the waveguide as output beam 402. While output beam 402 is illustrated as substantially parallel, as discussed herein, it may also be redirected to propagate to eye 4 at an angle (e.g., forming a diverging output beam) depending on the depth plane associated with waveguide 182. It should be understood that a substantially collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a long distance (e.g., optical infinity) from the eye 4. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 4 to accommodate to a closer distance and focus onto the retina, and would be interpreted by the brain as light from a distance closer to the eye 4 than optical infinity.

[0130] In some embodiments, a full-color image can be formed at each depth plane by overlaying an image on each of the primary colors, e.g., three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 14a-14f, but more or fewer depths are also contemplated. Each depth plane can have three primary color images associated with it, including a first image of a first color G, a second image of a second color R, and a third image of a third color B. Different depth planes are indicated in the diagram by different numbers for diopters (dpt) following the letters G, R, and B. By way of example only, the number following each of these letters indicates diopters (1 / m), i.e., the reciprocal of the distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for the different primary colors can be varied to account for differences in the eye's focusing of different wavelengths of light. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort.

[0131] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided for each depth plane, with three primary color images provided for each depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0132] 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.

[0133] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light within a range of about 620-780 nm, green light may include one or more wavelengths of light within a range of about 492-577 nm, and blue light may include one or more wavelengths of light within a range of about 435-493 nm.

[0134] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. In some embodiments, the incoupling element comprises a reflective layer, as described herein. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set of stacked waveguides 1200, each including an incoupling optical element. Each of the waveguides may be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 1200 may correspond to stack 178 (FIG. 6), and the illustrated waveguides of stack 1200 may correspond to portions of multiple waveguides 182, 184, 186, 188, 190, although it should be understood that light from one or more of image injection devices 200, 202, 204, 206, 208 is injected into the waveguides from a location requiring the light to be redirected for internal coupling.

[0135] The illustrated set 1200 of stacked waveguides includes waveguides 1210, 1220, and 1230. Each waveguide includes an associated internal coupling optical element (which may also be referred to as an optical input area on the waveguide), for example, internal coupling optical element 1212 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, internal coupling optical element 1224 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and internal coupling optical element 1232 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some embodiments, one or more of the internal coupling optical elements 1212, 1222, 1232 may be disposed on a bottom major surface of the respective waveguides 1210, 1220, 1230 (particularly, one or more of the internal coupling optical elements is a reflective polarizing optical element). As shown, the internal coupling optical elements 1212, 1222, 1232 may be disposed on the upper major surfaces of their respective waveguides 1210, 1220, 1230 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling optical elements 1212, 1222, 1232 may be disposed within the body of the respective waveguides 1210, 1220, 1230. In some embodiments, as discussed herein, the internal coupling optical elements 1212, 1222, 1232 are wavelength selective, such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. Although illustrated on one side or corner of their respective waveguides 1210, 1220, 1230, it should be understood that the internal coupling optical elements 1212, 1222, 1232 may be positioned in other areas of their respective waveguides 1210, 1220, 1230 in some embodiments.

[0136] As shown, the in-coupling optical elements 1212, 1222, 1232 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 1212, 1222, 1232 may be configured to receive light from a different image input device 1213, 1223, 1233 and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 1212, 1222, 1232 so as to receive substantially no light from others of the in-coupling optical elements 1212, 1222, 1232. Thus, a reflective layer may include laterally offset portions, and / or a waveguide may include two or more laterally offset reflective layers.

[0137] Each waveguide also includes an associated light distribution element, for example, light distribution element 1214 is disposed on a major surface (e.g., the top major surface) of waveguide 1210, light distribution element 1224 is disposed on a major surface (e.g., the top major surface) of waveguide 1220, and light distribution element 1234 is disposed on a major surface (e.g., the top major surface) of waveguide 1230. In some embodiments, the light distribution elements comprise a reflective layer as described herein. In some other embodiments, light distribution elements 1214, 1224, 1234 may be disposed on the bottom major surface of the associated waveguides 1210, 1220, 1230, respectively. In some other embodiments, the light distribution elements 1214, 1224, 1234 may be disposed on both the top and bottom major surfaces of the associated waveguides 1210, 1220, 1230, respectively, or the light distribution elements 1214, 1224, 1234 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 1210, 1220, 1230, respectively.

[0138] Waveguides 1210, 1220, 1230 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 1218a may separate waveguides 1210 and 1220, and layer 1218b may separate waveguides 1220 and 1230. In some embodiments, layers 1218a and 1218b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming immediately adjacent ones of waveguides 1210, 1220, 1230). Preferably, the refractive index of the material forming layers 1218a, 1218b is less than the refractive index of the material forming waveguides 1210, 1220, 1230 by 0.05 or more, or 0.10 or more. Advantageously, the lower refractive index layers 1218a, 1218b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 1210, 1220, 1230 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 1218a, 1218b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 1200 may include immediate cladding layers.

[0139] Preferably, for ease of manufacturing and other considerations, the materials forming the waveguides 1210, 1220, 1230 are similar or the same, and the materials forming the layers 1218a, 1218b are similar or the same. In some embodiments, the materials forming the waveguides 1210, 1220, 1230 may vary between one or more waveguides, and / or the materials forming the layers 1218a, 1218b may vary while still maintaining the various refractive index relationships discussed above.

[0140] 9A, light rays 1240, 1242, 1244 enter waveguide set 1200. It should be understood that light rays 1240, 1242, 1244 may be injected into waveguides 1210, 1220, 1230 by one or more image injection devices 200, 202, 204, 206, 208 (FIG. 6).

[0141] In some embodiments, the light rays 1240, 1242, 1244 have different characteristics, such as different wavelengths or different wavelength ranges, that may correspond to different colors. Each of the internal coupling optical elements 1212, 1222, 1232 deflects incident light so that the light propagates through a respective one of the waveguides 1210, 1220, 1230 by TIR. In some embodiments, each of the internal coupling optical elements 1212, 1222, 1232 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated internal coupling optical element. In some embodiments, each of the internal coupling optical elements 1212, 1222, 1232 includes a reflective layer, as described herein. The reflective layer may be configured to propagate the light rays through the respective waveguides 1210, 1220, 1230 by TIR. Thus, in some embodiments, the in-coupling optical elements 1212, 1222, 1232 comprise reflective layers with reflective surfaces at their interfaces with the corresponding waveguides to propagate light in the waveguides by TIR.

[0142] For example, internal coupling optical element 1212 may be configured to selectively deflect light beam 1240 having a first wavelength or wavelength range while transmitting light beams 1242 and 1244 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light beam 1242 then impinges on and is deflected by internal coupling optical element 1222, which is configured to selectively deflect light of the second wavelength or wavelength range. Light beam 1244 is transmitted by internal coupling optical element 1222 and subsequently impinges on and is deflected by internal coupling optical element 1232, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0143] 9A , the deflected light rays 1240, 1242, 1244 are deflected such that they propagate through their corresponding waveguides 1210, 1220, 1230. That is, the in-coupling optical element 1212, 1222, 1232 of each waveguide deflects the light into its corresponding waveguide 1210, 1220, 1230, in-coupling the light into its corresponding waveguide. The light rays 1240, 1242, 1244 are deflected at an angle that causes the light to propagate through their respective waveguides 1210, 1220, 1230 by TIR. The light rays 1240, 1242, 1244 propagate through their respective waveguides 1210, 1220, 1230 by TIR until they impinge on the waveguide's corresponding light distribution element 1214, 1224, 1234. In some embodiments, each of the light distribution elements 1214, 1224, 1234 comprises a reflective layer, as described herein. The reflective layer may be configured to propagate light through the respective waveguides 1210, 1220, 1230 by TIR. Thus, in some embodiments, the light distribution elements 1214, 1224, 1234 comprise a reflective layer having a reflective surface at an interface with the corresponding waveguide to redirect light propagating by TIR through the waveguide. In some embodiments, the internal coupling optical element 1212, 1222, 1232 for a given waveguide 1210, 1220, 1230 comprises a reflective layer, and a different portion of the same reflective layer comprises the light distribution element 1214, 1224, 1234 for the waveguide 1210, 1220, 1230. In some embodiments, the internal coupling optical element 1212, 1222, 1232 for a given waveguide 1210, 1220, 1230 comprises a first reflective layer, and the light distribution element 1214, 1224, 1234 for the waveguide 1210, 1220, 1230 comprises a second reflective layer that is different from the first reflective layer.

[0144] 9B, a perspective view of the example multiple stacked waveguides of FIG. 9A is illustrated. As previously described, the in-coupled light rays 1240, 1242, and 1244 are deflected by the in-coupling optical elements 1212, 1222, and 1232, respectively, and then propagate by TIR within the waveguides 1210, 1220, and 1230, respectively. The light rays 1240, 1242, and 1244 then impinge on the light distribution elements 1214, 1224, and 1234, respectively. The light distribution elements 1214, 1224, and 1234 deflect the light rays 1240, 1242, and 1244 to propagate toward the out-coupling optical elements 1250, 1252, and 1254, respectively. In some embodiments, the in-coupling optical elements 1212, 1222, 1232 comprise a reflective layer, as described herein. In some embodiments, the light distribution elements 1214, 1224, 1234 comprise a reflective layer, as described herein. In some embodiments, the in-coupling optical element 1212, 1222, 1232 for a given waveguide 1210, 1220, 1230 and the light distribution element 1214, 1224, 1234 for the same waveguide comprise different portions of the same reflective layer. In some embodiments, the in-coupling optical element 1212, 1222, 1232 for a given waveguide 1210, 1220, 1230 comprises a first reflective layer, and the light distribution element 1214, 1224, 1234 for the same waveguide comprises a second reflective layer that is different from the first reflective layer.

[0145] In some embodiments, the light distribution elements 1214, 1224, 1234 are orthogonal pupil expanders (OPEs). Thus, in some embodiments, the reflective layer is part of the OPE. In some embodiments, the OPEs deflect or distribute light to the out-coupling optical elements 1250, 1252, 1254, and the OPEs also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. For example, in some embodiments where the beam size is already the desired size, the light distribution elements 1214, 1224, 1234 can be omitted, and the in-coupling optical elements 1212, 1222, 1232 can be configured to deflect light directly into the out-coupling optical elements 1250, 1252, 1254. For example, with reference to FIG. 9A , the light distribution elements 1214, 1224, 1234 can be replaced with the out-coupling optical elements 1250, 1252, 1254, respectively. In some embodiments, the outcoupling optical elements 1250, 1252, 1254 are exit pupils (EP) or exit pupil expanders (EPE) that direct light to the viewer's eye 4 (FIG. 7).

[0146] 9A and 9B, in some embodiments, a waveguide set 1200 includes, for each primary color, waveguides 1210, 1220, 1230, in-coupling optical elements 1212, 1222, 1232, light distribution elements (e.g., OPEs) 1214, 1224, 1234, and out-coupling optical elements (e.g., EPs) 1250, 1252, 1254. The waveguides 1210, 1220, 1230 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 1212, 1222, 1232 redirect or deflect incident light into that waveguide (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the respective waveguide 1210, 1220, 1230. In the example shown, light ray 1240 (e.g., blue light) is deflected by the first in-coupling optical element 1212 in the manner described above, then continues bouncing back down the waveguide, interacting with the light distribution element (e.g., OPE) 1214 and then the out-coupling optical element (e.g., EP) 1250. Light rays 1242 and 1244 (e.g., green and red light, respectively) pass through the waveguide 1210, with light ray 1242 impinging on and being deflected by the in-coupling optical element 1222. Light ray 1242 will then bounce back down the waveguide 1220, via TIR, to its light distribution element (e.g., OPE) 1224 and then to the out-coupling optical element (e.g., EP) 1252. Finally, light ray 1244 (e.g., red light) passes through waveguide 1220 and impinges on light in-coupling optical element 1232 of waveguide 1230. Light in-coupling optical element 1232 deflects light ray 1244 such that it propagates by TIR to light distribution element (e.g., OPE) 1234 and then by TIR to out-coupling optical element (e.g., EP) 1254. Out-coupling optical element 1254 then finally out-couples light ray 1244 to a viewer, who also receives out-coupled light from the other waveguides 1210, 1220.

[0147] FIG. 9C illustrates a top-down plan view of the example of multiple stacked waveguides of FIGS. 9A and 9B. As shown, the waveguides 1210, 1220, 1230 may be vertically aligned, along with each waveguide's associated light distribution elements 1214, 1224, 1234 and associated external coupling optical elements 1250, 1252, 1254. However, as discussed herein, the internal coupling optical elements 1212, 1222, 1232 are not vertically aligned. Rather, the internal coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated internal coupling optical elements may be referred to as shifted pupil systems, and the internal coupling optical elements in these arrays may correspond to sub-pupils.

[0148] Optical Waveguides and Methods for Making Them In some embodiments, methods of fabricating optical waveguides are described. The methods may include dispensing a reflective flowable material as described herein directly onto a substrate, such as a waveguide. The reflective flowable material may be dispensed within predetermined areas of the substrate. The reflective flowable material, such as a reflective ink, may be solidified to form a reflective layer. In some embodiments, when the reflective layer of the reflective flowable material is formed over predetermined areas of the substrate, it forms a desired pattern. In some embodiments, the reflective layer of the reflective flowable material covers all or substantially all of the surface of the substrate. In some embodiments, the methods further include die-cutting or dicing the substrate and the reflective layer into many different elements 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 methods further include attaching one or more other optical waveguides to the optical waveguide to form a stack. In some embodiments, the optical waveguide comprising the reflective layer is part of a display device, and thus the method further includes disposing the waveguide comprising the reflective layer (or a stack comprising such a waveguide) within the display device. In some embodiments, the surfaces of one or more optical waveguides of the stack comprise walls that define an area onto which a reflective layer of reflective flowable material is deposited. The walls may be of a stepped height such that the inner wall defining the area for depositing the reflective flowable material is lower than the outer wall surrounding the inner wall. Without being limited by theory, it is envisioned that the stepped wall height may help prevent defects when filling the area defined by the inner wall, for example, by consistently confining the location of the reflective flowable material to be deposited. Thus, in some embodiments, the walls act as a dam or mold to contain the reflective flowable material within a predetermined area of ​​the substrate. In some embodiments, the walls may further act as spacers to separate the waveguides of the stack from one another. In some embodiments, the walls comprise resist.It is contemplated that the resist walls may be deposited as a layer that extends across the substrate and then patterned to define the walls, according to some embodiments.

[0149] In some embodiments, a method of fabricating an optical waveguide includes contacting a first surface of a first waveguide with a reflective flowable material as described herein. The method may further include allowing the reflective flowable material (e.g., a reflective ink) to solidify to form a reflective layer on the first surface of the first waveguide. The reflective layer may be configured to reflect incident electromagnetic radiation, such as light within the visible spectrum. For example, electromagnetic radiation may be reflected into the first waveguide at an angle depending on the pattern and dimensions of the underlying protrusions of the reflective layer. Thus, a reflective layer disposed on the waveguide may be formed, which may be part of fabricating a display device.

[0150] Several suitable reflective flowable materials can be used to form the reflective layer, including reflective inks and liquid metals as described herein, and combinations thereof. In some embodiments, the reflective ink comprises silver, aluminum, or a combination of silver and aluminum, and optionally a binder, as disclosed herein. In some circumstances, the flowable material is a liquid metal, examples of which are discussed above.

[0151] There are several non-limiting examples of suitable methods for depositing the reflective flowable material onto a substrate surface. In some embodiments, the reflective flowable material is applied using an inkjet printer. Several commercially available inkjet printers are suitable, such as the NSCRYPT MICRODISPENSER inkjet printer. In some embodiments, the inkjet printer is equipped with a movable head that can be used for automated dispensing of the reflective flowable material (e.g., reflective ink), or the substrate can be moved relative to a non-movable head. The reflective flowable material can be applied at ambient pressure and temperature. In some embodiments, the reflective flowable material is applied at a pressure of about 1 atm and a temperature of about 15-27°C or about 18-24°C, including 21°C. In some embodiments, the inkjet printer deposits the reflective flowable material over a predetermined portion of the surface of the substrate. In some embodiments, the inkjet printer deposits the reflective flowable material over the entire surface of the substrate.

[0152] In some embodiments, the reflective flowable material is deposited using a microdispenser. In some embodiments, the microdispenser includes microdroplet technology (see "Microdrop - Materials by Inkjet Technology," accessible on the World Wide Web at www.microdrop.com / microdrop.html). In microdroplet technology, the dispensing head may include a glass capillary tube surrounded by a piezoelectric actuator and having an opening at one end. The piezoelectric actuator may be configured to contract and propagate a pressure wave into the glass capillary tube, causing the liquid droplet to break up and form droplets that drip through the air. In this manner, the size and rate of droplet formation, e.g., picoliter-scale droplets, may be precisely controlled. The size of the droplets may depend on the size of the opening on the end of the glass capillary. For example, the opening may have a micrometer-scale diameter, e.g., about 30-100 micrometers, which may generate a droplet volume of 25-500 picoliters, corresponding to a droplet diameter of 35-100 micrometers. The reflective flowable material may be applied at ambient pressure and temperature. In some embodiments, the reflective flowable material is applied at a pressure of about 1 atm and a temperature of about 15-27°C or about 18-24°C, including 21°C. In some embodiments, the microdispenser deposits the reflective flowable material over a predetermined portion of the surface of the substrate. In some embodiments, the microdispenser deposits the reflective flowable material over the entire surface of the substrate.

[0153] In some embodiments, the reflective flowable material is applied using an applicator rod. The reflective flowable material can be applied at ambient pressure and temperature (e.g., 1 atmosphere and room temperature). In some embodiments, the reflective flowable material is applied at a pressure of about 1 atm and a temperature of about 15-27°C or about 18-24°C, including 21°C. In some embodiments, an applicator rod is used to deposit the reflective flowable material over a predetermined portion of the surface of the substrate. In some embodiments, an applicator rod is used to deposit the reflective flowable material over the entire surface of the substrate.

[0154] Preferably, as discussed herein, the flowable material is flowable under standard conditions. In some embodiments, the flowable material can be heated to change the material to a flowable or more flowable state. For example, various dispensers and applicators disclosed herein can include a heating element configured to heat the material so that it becomes flowable or more flowable reflective ink and / or liquid metal. For example, heating can change the material from a solid and / or highly viscous state to a liquid and / or less viscous state.

[0155] In some embodiments, the reflective flowable material has a thickness of at least about 10 nm, e.g., at least about 10 nm, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500, 510, 520, 530, 540, 550, 560, 570, 580, 590, 600, 610, 620, 630, 640, 650, 660, 670, 680, 690, 700, 710, 720, 730, 740, 750, 760, 770, 780, 790, 800, 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 910, 920, 930, 940, 950, 960, 970, 980 70, 480, 490, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, or about 1,000 nm (thickness ranges between two of the listed values, e.g., about 10 nm to 900 nm, 10 nm to 500 nm, 10 nm to 410 nm, 10 nm to 400 nm, 10 nm to 350 nm, 10 nm to 300 nm, 10 nm to 250 nm, 10 nm to 200 nm, 10 nm to 150 nm, 10 nm to 100 nm, 10 nm to 50 nm, 30 nm to 900 nm, 30 nm to 5 00nm, 30nm~450nm, 30nm~400nm, 30nm~350nm, 30nm~300nm, 30nm~250nm, 30nm~200nm, 30nm~150, 30nm~100nm, 30nm~50nm, 50nm~900nm , 50nm~500nm, 50nm~450nm, 50nm~400nm, 50nm~350nm, 50nm~300nm, 50nm~250nm, 50nm~200nm, 50nm~150, 50nm~100nm, 80nm~900nm, 80n Thicknesses up to about 100nm to 500nm, 80nm to 450nm, 80nm to 400nm, 80nm to 350nm, 80nm to 300nm, 80nm to 250nm, 80nm to 200nm, 80nm to 150, 80nm to 100nm, 100nm to 900nm, 100nm to 500nm, 100nm to 450nm, 100nm to 400nm, 100nm to 350nm, 100nm to 300nm, 100nm to 250nm, 100nm to 200nm, or thicknesses of about 100nm to 150nm may be applied.

[0156] In some embodiments, the thickness of the reflective layer formed by the flowable material can be varied. For example, the reflective layer can have a thickness that varies by 25% or more, 50% or more, or 100% or more between different portions of the layer (e.g., a layer can have one portion that is 10 nm thick and another portion that is 20 nm thick). This variable thickness can be achieved, for example, by depositing different amounts of material over different portions of the reflective layer. For example, the flowable material can be uniformly deposited over areas where the material can be stabilized by various processes disclosed herein (drying, annealing, etc.), and additional material can be deposited on selected portions of this area to increase the thickness in those areas, which can then also be stabilized. Preferably, the flowable material, at least for the extension material, is sufficiently viscous and / or has a sufficiently low wetting index to preserve the desired thickness differential by staying in place, for example, by limiting lateral diffusion over areas of the flowable material deposited earlier. In some embodiments, different flowable materials may be used to build desired portions of the reflective layer to a desired thickness.

[0157] In some embodiments, the flowable material may cover only a portion of the underlying grating. For example, the flowable material may be deposited onto only a portion of the grating, as discussed herein, and may have sufficient viscosity and / or low wettability to prevent flow onto other portions of the grating. As another example, as discussed herein, the surface of the substrate may include walls or barriers that limit the diffusion of the flowable material. In some embodiments, the walls or barriers may delineate an area that covers only a portion of the grating, such that the deposited flowable material extends only over the portion of the grating encompassed by the walls or barriers.

[0158] In some embodiments, the walls or barriers may be a permanent part of the final waveguide structure. In some embodiments, the walls or barriers may be removable mask structures that may be removed after the flowable material has solidified or stabilized (e.g., by exposure to atmospheric gases, by drying, and / or by annealing). For example, a photoresist layer may be deposited on the substrate and over the diffraction grating. The photoresist layer may then be patterned (e.g., by exposure to light propagating through a reticle) to leave openings where a reflective layer formed from the flowable material is desired. The reflective layer may then be solidified, and the photoresist mask may be removed (e.g., using an etch selective to the flowable material and the photoresist mask relative to the exposed substrate features).

[0159] Advantageously, selectively providing a reflective layer over the diffraction grating and / or providing different thicknesses for the reflective layer can allow the diffraction efficiency of the reflective diffraction grating formed with the reflective layer to be tailored. For example, portions of the diffraction grating that have a reflective layer can have a different effective diffraction efficiency than portions that do not have such a reflective layer. Similarly, thicker portions of the reflective layer can have a higher reflectivity and provide a different diffraction efficiency than portions of the diffraction grating that have thinner portions of the reflective layer.

[0160] Suitable conditions for allowing the flowable material to solidify can be readily ascertained based on the properties of the flowable material used, the particular application, the type of device being fabricated (including thermal budget considerations), and the layer thickness. For example, the flowable material can simply be allowed to solidify over time by reaction to environmental conditions. In some embodiments, the liquid metal can simply be allowed to react with oxygen in the ambient atmosphere and solidify (e.g., by forming an oxide such that the solidified liquid metal is comprised of an oxide of a component of the liquid metal, which can be a surface oxide). In some embodiments, the solidified liquid metal can include an oxide layer on its outer surface.

[0161] In some embodiments, for example, for reflective inks that are free or substantially free of metal-containing particles, the reflective ink may simply be allowed to dry (e.g., to remove solvent), and annealing may not be required. For example, the flowable material may be allowed to solidify for at least about 0.5 minutes, e.g., at least about 0.5 minutes, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 150, or about 180 minutes (including ranges between any of the recited values). In some embodiments, solidification occurs at ambient temperature, and the reflective ink is allowed to solidify without annealing.

[0162] In some embodiments, the flowable material may be annealed. For example, for a reflective ink that includes metal-containing particles, the reflective ink may be allowed to dry and then annealed. The annealing temperature may depend on the properties of the flowable material and may be at least about 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 450°C, 500°C, 550°C, 600°C, or about 650°C (any two of the listed values). The temperature may be in the range of, for example, about 150°C to 650°C, 150°C to 500°C, 150°C to 400°C, 150°C to 300°C, 150°C to 250°C, 150°C to 200°C, 200°C to 650°C, 200°C to 500°C, 200°C to 400°C, 200°C to 300°C, 200°C to 250°C, 250°C to 650°C, 250°C to 500°C, 250°C to 400°C, 250°C to 300°C, 300°C to 650°C, 300°C to 500°C, or about 300°C to 400°C.

[0163] In some embodiments, the method includes applying a reflective flowable material in a confined area onto the first surface of the first waveguide to position the reflective layer. For example, the first surface of the first waveguide may include walls (which may define a dam or mold) that may be filled with the reflective flowable material to obtain a reflective layer over a predetermined portion of the first surface of the first waveguide. In some embodiments, the walls include dummy or sacrificial material that is removed after the reflective layer is formed. Without being limited by any theory, it is believed that confining the reflective flowable material may enable precise control of the size and shape of the reflective layer and minimize spillage, particularly for relatively large and / or deep reflective layers. In some embodiments, for reflective layers having a thickness of at least 150 nm, confinement as described herein may be useful for controlling the shape of the reflective layer. Thus, in some embodiments, when the reflective layer has a thickness of at least 150 nm, e.g., at least 150 nm, 180, 200, 220, 250, 270, 300, 320, 350, 370, 400, 420, 450, 470, 500, 520, 550, 570, or 600 nm (including ranges between any of the recited values), the reflective flowable material is applied to a confined area defined by a wall (e.g., a dam, a mold, etc.) as described herein. In some embodiments, the confined area (e.g., a dam, mold, etc.) is defined by walls having a height of at least a desired height of the reflective layer, e.g., at least about 200 nm in height, e.g., 200 nm, 220, 250, 270, 300, 320, 350, 370, 400, 420, 450, 470, 500, 520, 550, 570, 600, 620, 650, 670, 700, 720, 750, or 800 nm in height. An exemplary confinement, according to some embodiments, is illustrated in Figures 11A-B. As shown in the diagrams of Figures 11A and 11B, a fill area 100 for the confinement of the reflective flowable material can be provided. The fill area can be disposed on a substrate 105, such as a waveguide. The waveguide can include protrusions 106. The protrusions 106 can form an optical grating.The fill area may include one or more walls 110, 111, 112, which may be the same height or different heights. The walls 110, 111, 112 may be taller than the desired height of the reflective layer 120. In some embodiments, the walls 110, 111, 112 may be of graduated height, with at least one wall 110, 111, 112 being taller than the reflective layer and defining a larger area. For example, if the reflective layer 120 has a height of approximately 150 nm, the walls 110, 111, 112 may have a height of 300 nm to 700 nm. For example, if the reflective layer 120 has a diameter of approximately 200 nm, the walls 110, 111, 112 may define a diameter of approximately 300 nm to 500 nm. In some embodiments, the walls are of a height such that they constitute mechanical spacers that maintain mechanical separation between the optical waveguides within the stack. As illustrated in FIG. 11B , such walls can define a transition confinement zone around a desired fill area for the reflective layer. The transition confinement zone can facilitate fill during fabrication of the reflective layer from the reflective flowable material. In some embodiments, walls 110, 111, and / or 112 further serve as spacers between substrate 105 and other substrates, such as additional waveguides, in the stack. For example, additional waveguides can be positioned on walls 110, 111, and / or 112 to space the additional waveguides from substrate 105.

[0164] In some embodiments, the reflective flowable material is deposited on a first surface, for example, a surface on a waveguide having multiple protrusions. In some embodiments, the reflective flowable material is conformally deposited on the protrusions. In some embodiments, the first surface has a non-planar configuration. In some embodiments, the first surface has a grating or faceted features, such as a diffraction grating. The grating can be in various configurations, for example, binary, blazed, multilayer, undercut, or a metamaterial or metasurface. In some embodiments, the reflective layer is conformally deposited, and the thickness of the reflective layer above the surface varies by about ±20% or less throughout the reflective layer, such that the thickness is within about ±20% of the average, for example, within about ±20%, ±15%, ±10%, ±5%, or ±1% of the average.

[0165] In some embodiments, the reflective layer is configured to reflect incident electromagnetic radiation (e.g., light in the visible spectrum). In some embodiments, the interface reflects at least about 40%, e.g., at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% of the reference (including ranges between any two of the listed values, e.g., about 30%-99%, 30%-95%, 30%-90%, 30%-80%, 40%-99%, 40%-95%, 40% The reflective layer is configured to reflect incident electromagnetic radiation (e.g., light within the visible spectrum) into the first waveguide at the interface with a reflectivity of 90%, 40% to 80%, 50% to 99%, 50% to 95%, 50% to 90%, 50% to 80%, 60% to 99%, 60% to 95%, 60% to 90%, 60% to 80%, 70% to 99%, 70% to 95%, 70% to 90%, or 70% to 80% (including). The percent reflectance of incident electromagnetic radiation (e.g., light in the visible spectrum) may, in some embodiments, be referenced to a material comprising only the metal of the reflective layer. The reference to the reflectivity may, in some embodiments, be aluminum.

[0166] In some embodiments, the reflective layer is formed on an optical waveguide that is part of a stack of optical waveguides, as described herein. In some embodiments, the reflective layer is formed on a first optical waveguide, and at least one optical waveguide is then attached to the first optical waveguide and / or each other to form a stack of optical waveguides. For example, forming the stack may include depositing additional optical waveguides. For example, forming the stack may include contacting the optical waveguides with each other. In some embodiments, the optical waveguides of the stack may be in optical communication with each other, as described herein.

[0167] Furthermore, the conventional processes described above may involve the additional step of creating a specific hard mask for each specific pattern of reflective layer to be applied. In contrast to such conventional processes, the methods described herein do not require creating a hard mask, and therefore, different patterns can be easily applied to different surfaces. Furthermore, the methods of creating optical waveguides with reflective layers described herein can be performed within the deposition chamber in which the waveguides are created, thus eliminating the need to move the waveguides in and / or out of the deposition chamber, thus increasing process flow efficiency.

[0168] To obtain a reflective layer of the desired thickness, in some embodiments, the method may include repeating the cycle of depositing and applying the reflective flowable material multiple times, for example, about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, or 50 times (including ranges between any two of the listed values).

[0169] (Method for making a display device) In some embodiments, a method of fabricating a display device is provided. The method may include fabricating an optical waveguide or optical waveguide structure (e.g., an optical waveguide structure comprising an optical waveguide stack) comprising a reflective optical element as described herein. The method may include disposing the optical waveguide or optical waveguide stack as described herein within a display device. In some embodiments, the method includes disposing an optical waveguide or optical waveguide stack within the display device, the optical waveguide or optical waveguide stack comprising a first waveguide comprising a reflective optical element as described herein. In some embodiments, the display device comprises an orthogonal pupil expander or exit pupil expander comprising a first optical waveguide comprising a reflective optical element, or a waveguide stack comprising a first optical waveguide comprising a reflective optical element.

[0170] In some embodiments, the method includes fabricating a waveguide comprising a reflective optical element according to a method as described herein and disposing the waveguide in a display device. In some embodiments, the method includes fabricating an optical waveguide stack comprising a first waveguide comprising a reflective optical element according to a method as described herein and disposing the optical waveguide stack in a display device.

[0171] Example 1: Making a reflective layer from a reflective ink A reflective ink containing aluminum was patterned onto a substrate using an applicator rod and allowed to solidify to form a reflective layer on the substrate. The reflectance of the reflective ink compared to a pure aluminum reflective layer (formed by evaporation) was compared and summarized in Table 1 below. [Table 1]

[0172] As shown in Table 1, many of the inks achieved at least 30% of the reflectance of evaporated aluminum, and some achieved substantially more than 30%. For example, the NG23 ink achieved more than 70% of the reflectance of evaporated Al. Without being limited by theory, it is believed that further refinement of ink selection, solidification or curing conditions, and cleanroom fabrication may achieve even higher reflectances than those shown below. In some embodiments, reflective inks containing silver have reflectances that match or exceed that of vacuum-deposited Al (see, e.g., Example 2 below).

[0173] Example 2: Reflectance of electronic ink A type of reflective ink, electronic ink containing silver in a species with the formula Ag(NH3)2|+|C2H3O2|-, was deposited onto a flat surface. This ink is described in Walker et al., "Reactive Silver Inks for Patterning High-Conductivity Features at Mild Surfaces." "Temperatures," J. Am. Chem. Society 134:1419-1421, the disclosure of which is incorporated herein by reference. For comparison, two different samples of evaporated aluminum (E1 and E2) were measured on resist and flat glass ("no resist"). The reflectance was measured. The reflectance of the electronic ink was measured at four random spots and compared to that of evaporated aluminum with (E2) or without (E1) resist. The results are shown in Table 2. [Table 2]

[0174] As shown in Table 2 above, the reflective ink ("EI Sample 2") consistently yielded 80-90% reflectance, which was similar to or higher than the evaporated aluminum standards (E1 and E2). Thus, the data demonstrates that the reflectance of reflective inks according to some embodiments herein is comparable to or superior to evaporated aluminum.

[0175] In the foregoing specification, various specific embodiments have been described. It will be apparent, however, that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0176] Indeed, it should be understood that each of the systems and methods of the present disclosure has several innovative aspects, no single one of which is solely responsible for or required to result in the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure.

[0177] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as operating in a combination and may even be initially claimed as such, one or more features from the claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination. No single feature or group of features is required or essential to every embodiment.

[0178] It should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, in particular, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to imply that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps should be included or performed in any particular embodiment, with or without authorial input or prompting. The terms "comprising," "including," "having," and the like, are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense); thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Additionally, the articles "a," "an," and "the," as used in this application and the appended claims, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, while operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order shown, or in sequential order, or that all of the depicted operations need not be performed to achieve desirable results. Furthermore, the figures may diagrammatically depict one or more exemplary processes in the form of a flowchart. However, other operations not depicted may be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, concurrently with, or during any of the depicted operations.Additionally, operations may be rearranged or reordered in other embodiments. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0179] Thus, the claims are not intended to be limited to the embodiments shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles and novel features disclosed herein.

Claims

1. 1. A display device, comprising: the display device comprises a waveguide comprising a reflective diffractive optical element; the reflective diffractive optical element comprises a reflective diffraction grating, the reflective diffraction grating including a plurality of protrusions on a surface of the waveguide and a reflective layer on a surface of the plurality of protrusions; the reflective layer having a variable thickness at different portions of the reflective layer; the reflective layer comprises a binder, the binder interacting with the underlying surface to contribute to adhesion of the reflective layer to the underlying surface; the reflectivity of the reflective diffraction grating has a first reflectivity for electromagnetic radiation of a first wavelength in a first region and a second reflectivity for electromagnetic radiation of the first wavelength in a second region, the second reflectivity being different from the first reflectivity; In the first region, the reflective layer has a first thickness; In the second region, the reflective layer has a second thickness different from the first thickness; a surface of the waveguide comprising a plurality of walls defining an area surrounding the reflective diffraction grating, the plurality of walls comprising an inner wall and an outer wall surrounding the inner wall; The height of the inner wall is less than the height of the outer wall; At least one of the walls maintains mechanical separation between the waveguide and another substrate.

2. The display device of claim 1 , wherein the reflective diffractive optical element forms an internal coupling element configured to couple electromagnetic radiation into the waveguide.

3. 10. The display device of claim 1, wherein the waveguide is part of an optical waveguide stack comprising a plurality of waveguides.

4. 10. The display device of claim 1, wherein the walls are spacers separating the waveguide from additional waveguides in an optical waveguide stack.

5. The display device of claim 1 , wherein the walls comprise a resist.

6. 10. The display device of claim 1, wherein a surface of the waveguide comprises a plurality of walls that delineate an area that covers only a portion of the reflective grating.

7. 10. The display device of claim 1, wherein the reflective diffraction grating is substantially free of dispersed metal-containing particles.

8. 10. The display device of claim 1, wherein the reflective grating comprises irregular buildups formed from a flowable reflective ink, the irregular buildups including spaghetti-like strands or islands.

9. 10. The display device of claim 1, wherein the reflective grating comprises a resist and a cured reflective ink.

10. 10. The display device of claim 1, wherein the reflective grating comprises a resist and a metal.

11. 10. The display device of claim 1, wherein in the first region, the reflective layer comprises a first reflective portion and in the second region, the reflective layer comprises a second reflective portion, the thickness of the first reflective portion being 25% or greater than the thickness of the second reflective portion.

12. 12. The display device of claim 11, wherein the thickness of the first reflective portion is greater than or equal to 50% of the thickness of the second reflective portion.

13. 13. The display device of claim 12, wherein the thickness of the first reflective portion is 100% or greater than the thickness of the second reflective portion.

14. 10. The display device of claim 1, wherein the first thickness is greater than the second thickness, and the first reflectivity in the first region is greater than the second reflectivity in the second region.

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