Air pocket structures for enhancing total internal reflection in waveguides.

Abstract

To provide favorable air pocket structures for promoting total internal reflection in a waveguide.SOLUTION: Recesses are formed on a front side and a rear side of a waveguide. A solid porogen material is spun onto the front side and the rear side and fills the recesses. First front and rear cap layers are then formed on raised formations of the waveguide and on the solid porogen material. The entire structure is then heated and the solid porogen material decomposes into a porogen gas. The first front and rear cap layers are porous to allow the porogen gas to escape and to allow air to enter into the recesses. The air maximizes a difference in refractive indices between a high-index transparent material of the waveguide and the air to promote reflection in the waveguide from interfaces between the waveguide and the air.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Provisional Patent Application No. 62 / 783,778, filed December 21, 2018, the entire contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates generally to optical systems and methods for manufacturing optical systems. [Background technology]

[0003] Modern computing and display technology has facilitated the development of so-called "virtual reality" viewing devices. Such viewing devices typically have a frame mountable on a user's head and frequently contain two waveguides, one in front of each of the viewer's eyes. The waveguides are transparent so that ambient light from an object can pass through them, making the object visible to the user. Each waveguide also serves to transmit projected light from a projector to a respective eye of the user. The projected light forms an image on the retina of the eye, which therefore receives the ambient light and the projected light. The user simultaneously sees the real object and the image generated by the projected light.

[0004] Projected light typically enters the waveguide on the edge of the waveguide, then reflects within the waveguide, and then exits the waveguide through the waveguide pupil towards the user's eye. Total internal reflection (TIR) ​​is the ideal situation where there is no loss of projected light out of the waveguide and 100 percent of the projected light reaches the user's eye. Summary of the Invention [Means for solving the problem]

[0005] The present invention provides a method of manufacturing an optical system that includes adhering a cap layer of selectively transparent material to a waveguide of high refractive index transparent material having a front side and a rear side, wherein a cavity is defined between the cap layer and the waveguide with an optical gas in the cavity such that when an ambient light source is located at the front side of the waveguide, a beam of ambient light is transmitted through the selectively transparent material of the cap layer, through the cavity holding an optical gas, and through the high refractive index transparent material of the waveguide.

[0006] The present invention also provides an optical system including a waveguide of a high refractive index transparent material having a front side and a rear side, a cap layer of a selectively transparent material affixed to the waveguide, a cavity being defined between the cap layer and the waveguide, and an optical gas in the cavity such that when an ambient light source is located at the front side of the waveguide, a beam of ambient light is transmitted through the selectively transparent material of the cap layer, through the cavity holding the optical gas, and through the high refractive index transparent material of the waveguide. The present specification also provides, for example, the following items: (Item 1) 1. A method of manufacturing an optical system, comprising: affixing a cap layer of selectively transparent material to a waveguide of high refractive index transparent material having a front side and a rear side, wherein a cavity is defined between the cap layer and the waveguide with an optical gas in the cavity such that when an ambient light source is located at the front side of the waveguide, a beam of ambient light is transmitted through the selectively transparent material of the cap layer, through the cavity holding an optical gas, and through the high refractive index transparent material of the waveguide; A method comprising: (Item 2) Item 10. The method of claim 1, wherein the cap layer is a front cap layer located between the ambient light source and a front side of the waveguide, and the beam of ambient light is transmitted sequentially through a selectively transparent material of the front cap layer, through the cavity holding the optical gas, and into a high refractive index transparent material of the waveguide. (Item 3) 3. The method of claim 2, wherein the selected transparent material of the front cap layer is an anti-reflective material that increases absorption of the ambient light by the front surface of the waveguide and reduces reflection of the ambient light by the front surface of the waveguide. (Item 4) Item 4. The method of item 3, wherein the high refractive index material is one of high refractive index glass, high refractive index lithium niobate, lithium tantalate, and silicon carbide. (Item 5) Item 4. The method of item 3, wherein the high refractive index material has a refractive index of at least 1.74. (Item 6) Item 10. The method of claim 1, wherein the optical gas has a refractive index of less than 1.3. (Item 7) Item 10. The method of claim 1, wherein the optical gas is air with a refractive index of 1. (Item 8) forming a stack including the waveguide, a solid porogen material, and the cap layer; replacing the porogen material with the optical gas; Item 1, the method of claim 1 further comprising: (Item 9) The porogen material is heating the porogen material to a decomposition temperature at which the porogen material is converted into a sacrificial gas; removing the sacrificial gas from the cavity; and Item 9. The method according to Item 8, wherein the oxidized layer is removed by carrying out the steps of: (Item 10) Item 10. The method of item 9, wherein the selected material of the cap layer is porous and the sacrificial gas outgasses through the selected material of the cap layer. (Item 11) Item 10. The method according to item 9, wherein the porogen material decomposes at a decomposition temperature of 120°C to 230°C. (Item 12) Item 11. The method of item 10, wherein the cap layer is made of SiOx having a thickness of at least 12 nm, where x is a variable. (Item 13) Item 10. The method of item 1, wherein a plurality of cavities are defined between the cap layer and the waveguide, and an optical gas is in each individual cavity. (Item 14) forming a front side of the waveguide to have a plurality of recesses and a plurality of raised formations, each raised formation being located between two of the recesses; supporting first portions of the cap layer with the ridge formations, with second portions of the cap layer located between the first portions of the cap layer positioned across the recesses, such that respective ones of the cavities are defined by respective ones of the second portions of the cap layer and respective ones of the recesses on the front side of the waveguide; Item 14. The method of item 13, further comprising: (Item 15) Item 15. The method of item 14, wherein each recess has a depth and a width, the width being less than 300 microns. (Item 16) Item 15. The method according to item 14, wherein the recesses are imprinted on the front side. (Item 17) forming a conformal layer on the front side of the waveguide, the conformal layer being made of a transparent material; Item 15. The method of item 14, further comprising: (Item 18) the cap layer is a front cap layer located between the ambient light source and the front side of the waveguide, and the cavity is a front cavity between the front cap layer and the front side of the waveguide; affixing a rear cap layer of selectively transparent material to the waveguide, wherein a rear cavity is defined between the rear cap layer and the rear face of the waveguide with an optical gas present in the rear cavity such that when an ambient light source is located at the front side of the waveguide, a beam of the ambient light is transmitted through the high refractive index transparent material of the waveguide, through the rear cavity holding the optical gas, and through the selectively transparent material of the rear cap layer; Item 1, the method of claim 1 further comprising: (Item 19) the cap layer is a first cap layer, and the selectively transparent material is a first selectively transparent material; bonding a second cap layer of a second selected transparent material to the first cap layer; Item 1, the method of claim 1 further comprising: (Item 20) 20. The method of claim 19, wherein the second cap layer is harder than the first cap layer. (Item 21) 20. The method of claim 19, wherein at least one of the selective transparent materials of the cap layer is an anti-reflective material that increases absorption of the ambient light by the front surface of the waveguide and reduces reflection of the ambient light by the front surface of the waveguide. (Item 22) Forming a stack of cap layers with refractive indices that vary in magnitude 22. The method of claim 21, further comprising: (Item 23) Item 23. The method according to item 22, wherein the cap layer is made of SiOx having a refractive index of 1.45 and TiOx having a refractive index of 2.2 to 2.3, where x is a variable. (Item 24) 1. An optical system comprising: a waveguide of high refractive index transparent material having a front side and a rear side; a cap layer of a selectively transparent material affixed to the waveguide, a cavity being defined between the cap layer and the waveguide; an optical gas in the cavity, wherein the optical gas in the cavity is such that when an ambient light source is located at a front side of the waveguide, a beam of the ambient light is transmitted through the selectively transparent material of the cap layer, through the cavity holding the optical gas, and through the high refractive index transparent material of the waveguide; An optical system comprising: [Brief explanation of the drawings]

[0007] The invention will now be further described, by way of example only, with reference to the accompanying drawings in which:

[0008] [Figure 1A] FIG. 1A is a cross-sectional side view of a waveguide of high refractive index transparent material.

[0009] [Figure 1B] FIG. 1B is a view similar to FIG. 1A after the waveguide has been patterned with multiple recesses and raised formations on the front and rear sides.

[0010] [Figure 1C] FIG. 1C is a view similar to FIG. 1B after the recesses have been filled with solid porogen material in a spin-on process.

[0011] [Figure 1D] FIG. 1D is a view similar to FIG. 1C after a first front cap layer has been formed on the front side and a first rear cap layer has been formed on the rear side.

[0012] [Figure 1E] FIG. 1E is a view similar to FIG. 1D after the structure has been heated to remove the solid porogen material and replace it with air.

[0013] [Figure 1F] FIG. 1F is a view similar to FIG. 1E after additional cap layers have been formed over the first front and first back cap layers to complete the fabrication of the optical system.

[0014] [Figure 1G] FIG. 1G is a view similar to FIG. 1F of the optical system, illustrating its function.

[0015] [Figure 1H] FIG. 1H is a cross-sectional side view of an optical system in accordance with an alternative embodiment of the present invention, in which the patterned layer is formed from a photoresist material.

[0016] [Figure 2]FIG. 2 is a cross-sectional side view of an optical system according to an alternative embodiment of the present invention having nanostructures to facilitate absorption of ambient light.

[0017] [Figure 3] FIG. 3 is a cross-sectional side view similar to FIG. 1F with nanostructures having variable feature heights or variable duty cycles.

[0018] [Figure 4] FIG. 4 is a cross-sectional side view similar to FIG. 2, with nanostructures with variable feature height or variable duty cycle.

[0019] [Figure 5] FIG. 5 is a cross-sectional side view of an optical system having air pockets in different layers.

[0020] [Figure 6A] FIG. 6A is a scanning electron microscope (SEM) image with a single coating.

[0021] [Figure 6B] FIG. 6B is an SEM image of an air pocket covered by a multilayer coating.

[0022] [Figure 7A] FIG. 7A is a cross-sectional side view of an air pocket that has been covered with a silicon oxide layer and then spin-coated with an optical polymer.

[0023] [Figure 7B] FIG. 7B is a view similar to FIG. 7A at a lower magnification level.

[0024] [Figure 8] FIG. 8 is a 0° transmission graph from an experimental measurement.

[0025] [Figure 9] Figure 9 is the model used for simulation purposes.

[0026] [Figure 10A] FIG. 10A is a side view of a waveguide without any coating for the simulation.

[0027] [Figure 10B] FIG. 10B is a side view of a waveguide with an optical polymer coating for the simulation.

[0028] [Figure 10C] FIG. 10C is a side view of a waveguide with an air pocket for the simulation.

[0029] [Figure 10D] FIG. 10D is a side view of a waveguide with polymer instead of an air gap for the simulation.

[0030] [Figure 11] FIG. 11 is a graph showing transmission data from the simulation.

[0031] [Figure 12] FIG. 12 is a graph showing the user-side diffraction efficiency from a simulation. DETAILED DESCRIPTION OF THE INVENTION

[0032] An optical system and a method for fabricating the optical system are described. Recesses are formed on the front and rear sides of a waveguide. A solid porogen material is spun on the front and rear sides, filling the recesses. First front and rear cap layers are then formed on the ridge formations of the waveguide and the solid porogen material. The entire structure is then heated, and the solid porogen material decomposes into porogen gas. The first front and rear cap layers are porous, allowing the porogen gas to escape and air to enter the recesses. The air maximizes the refractive index difference between the high-index transparent material of the waveguide and the air, promoting reflection within the waveguide from the interface between the waveguide and the air. Second front and rear cap layers are formed on the first front and rear cap layers, respectively, and additional front and rear cap layers are then formed on the second front and rear cap layers. The cap layer has a refractive index that facilitates absorption of ambient light through the cap layer and into the waveguide.

[0033] 1A-1F illustrate a method of manufacturing an optical system according to one embodiment of the present invention.

[0034] FIG. 1A illustrates a waveguide 20, which serves as a primary substrate for subsequent processing. The waveguide 20 is made from a high-index transparent material. Generally, the refractive index of the waveguide 20 is considered to be at least 1.5. In this embodiment, the waveguide 20 is made from a high-index glass, having a refractive index of 1.73. In other embodiments, the waveguide may be made from lithium niobate, lithium tantalate, or silicon carbide, which have a refractive index greater than 2.0. A high-index transparent material is preferred because it maximizes the field of view in the final product.

[0035] The waveguide 20 has front and back sides 22 and 24. The front and back sides 22 and 24 are spaced from each other by a thickness 26 of less than 3 mm. The front and back sides 22 and 24 each have a width 28 of 50-70 mm and a depth into the paper of 50-70 mm. The front and back sides 22 and 24 are planar surfaces that are planes parallel to each other. The material of the waveguide 20 is sufficiently soft to allow the front and back sides 22 and 24 to be formed at room temperature of 22° C. or at a moderately high temperature of 50° C. without the formation of microcracks or optical distortions in the material of the waveguide 20.

[0036] FIG. 1B illustrates the waveguide 20 after the front and rear sides 22 and 24 have been molded. The front side 22 is molded to have a plurality of recesses 30 and a plurality of raised formations 32, with each raised formation 32 located between two of the recesses 30. Sidewalls 34 of the recesses 30 form the sidewalls of the raised formations 32. The raised formations 32 have coplanar outer surfaces 36. The recesses 30 have coplanar groove surfaces 38 that are parallel to the plane of the outer surfaces 36. Each recess 30 has a width 40 that is between 10 nm and 500 nm. The rear side 24 is molded to have a plurality of recesses 44 and a plurality of raised formations 46, with each raised formation 46 located between two of the recesses 44. Sidewalls 48 of the recesses 44 form the sidewalls of the raised formations 46. The raised formations 46 have coplanar outer surfaces 50. The recesses 44 have coplanar groove surfaces 52 that are parallel to the plane of the outer surfaces 50. Each recess 44 has a width 54 that is between 10 nm and 500 nm.

[0037] The front and rear sides 22 and 24 are simultaneously formed using a tool that imprints the recesses 30 and 44 and the raised features 32 and 46. The tool has a front portion and a rear portion made of hardened metal. The front portion has a shape that is complementary to the contour created in the front side 22, and the rear portion has a shape that is complementary to the shape created in the rear side 24. The waveguide 20 is inserted between the front and rear portions, and an actuator moves the front and rear portions toward each other while a surface of the portion is used to apply pressure on the front and rear sides 22 and 24 of the waveguide 20. The waveguide 20 is then removed from the tool. The front and rear sides 22 and 24 are then etched. The etching process removes microscopic artifacts from the groove surfaces 38 and 52 and flattens the groove surfaces 38 and 52.

[0038] The thickness 58 of the waveguide 20, as measured between the outer surfaces 36 and 50, exceeds the thickness 26 of the substrate of FIG. 1A, and the thickness 60, as measured between the groove surfaces 38 and 52, is less than the thickness 26. The waveguide 20 has a thickness between 200 microns and 1 nm. Each recess 30 or 44 has a depth 62 between 10 nm and 500 nm.

[0039] 1C illustrates the waveguide 20 after a porogen (sacrificial) material has been deposited. The porogen material may be spin-coated on the front side 22 and the back side 24 of the waveguide 20. The porogen material fills the recesses 30 and 44. The porogen material forms a plurality of isolated porogen portions 64 within the recess 30 on the front side 22 and a plurality of isolated porogen portions 66 within the recess 44 on the back side 24. Each porogen portion 64 fills an individual recess 30 until an outer surface 68 of the porogen portion 64 is flush with the outer surface 36 of the ridge feature 32. The porogen portion 66 fills the recess 44 until an outer surface 70 of the porogen portion 66 is flush with the outer surface 50 of the ridge feature 46.

[0040] Figure ID illustrates the structure of Figure 1C after forming a first front cap layer 74 and a first back cap layer 76. The cap layers 74 and 76 may be formed, for example, in a chemical vapor deposition process.

[0041] The first front cap layer 74 is made of a selected solid transparent material. The first front cap layer 74 is formed directly on the outer surface 36 of the ridge formation 32 and the outer surface 68 of the porogen portion 64. The first front cap layer 74 also adheres to the outer surface 36 of the ridge formation 32 and is therefore secured to the waveguide 20.

[0042] The first front cap layer 74 is shown as final processed and is made from a relatively strong, solid material. However, during its fabrication, the first front cap layer 74 is initially a thin, unstable film. Such a thin film is brittle and would collapse without the support provided by the solid material of the porogen portion 64. The first front cap layer 74 grows thicker and eventually becomes more stable as it becomes thick enough that it no longer relies on the support provided by the porogen portion 64 for its structural integrity. The first front cap layer 74 has a plurality of first portions 80 formed on the ridge formations 32 and a plurality of second portions 82 formed on the porogen portion 64.

[0043] Similarly, the first rear cap layer 76 relies on the solid material of the porogen portion 66 for support during its initial processing, but does not require the support of the porogen portion 66 after it is finally processed and acquires a thickness suitable for supporting itself without requiring the porogen portion 66. The first rear cap layer 76 has a plurality of first portions 84 formed on the ridge formations 46 and a plurality of second portions 86 formed on the porogen portion 66.

[0044] 1E illustrates the structure of FIG. 1D after porogen portions 64 and 66 have been removed and exited from respective cavities 88 and 90. Each cavity 88 and 90 has the same dimensions as the respective porogen portion being removed. Each cavity 88 and 90 is filled with an optical gas in the form of air.

[0045] The solid porogen material of the porogen portions 64 and 66 is a thermally decomposable material or mixture of materials that can be decomposed at a temperature that does not cause damage to the waveguide 20, the first front cap layer 74, or the first rear cap layer 76. The entire structure of FIG. 1D is heated to a decomposition temperature, which converts the solid porogen material into a porogen gas. The materials of the first front cap layer 74 and the first rear cap layer 76 are sufficiently porous to allow the porogen gas to permeate through the first front cap layer 74 and the first rear cap layer 76 so that the porogen gas exits the cavities 88 and 90, and to allow air to permeate through the first front cap layer 74 and the first rear cap layer 76 into the cavities 88 and 90. For example, propylene carbonate (PPC) can be decomposed in an inert atmosphere or in air without leaving any appreciable residue. Generally, the decomposition temperature is considered to be between 120°C and 230°C. If a decomposition temperature of 200°C to 300°C is used, the porogen moieties 64 and 66 can be displaced by air within a short amount of time. If the decomposition temperature needs to be lowered, adding an additive or extending the firing time may be possible. A decomposition temperature of 120°C to 160°C is possible with a suitable combination of material, film thickness, and firing time. The firing temperature and temperature ramp rate need to be carefully controlled so that no significant residue is left behind and the rate of porogen gas release is controlled to avoid causing damage to the first front cap layer 74 and the first rear cap layer 76, such as rupture, loosening, and cracking.

[0046] When cavities 88 and 90 are finally formed, first portion 80 of first front cap layer 74 and first rear cap layer 76 are secured to and supported by ridge formations 32 and 46. Each one of cavities 88 is defined on three sides by the surfaces of respective ones of recesses 30 and on a fourth side by one of second portions 82 of first front cap layer 74. Similarly, each one of cavities 90 is defined on three sides by the surfaces of respective ones of recesses 44 and on a fourth side by one of second portions 86 of first rear cap layer 76. Note that second portions 82 and 86 of first front cap layer 74 and first rear cap layer 76 are no longer supported by porogen portions 64 and 66. However, the first front cap layer 74 and the first rear cap layer 76 are still supported by the ridge formations 32 and 46, and provided that the widths 40 and 54 of the cavities 88 and 90, respectively, are less than 500 nm, the structural integrity of the first front cap layer 74 and the first rear cap layer 76 can be preserved during and after outgassing of the solid porogen material.

[0047] 1F illustrates the structure of FIG. 1E after a second front cap layer 94 has been formed on the first front cap layer 74, and an additional front cap layer 96 has been formed, in turn, on the second front cap layer 94. The second front cap layer 94 provides additional strength to the first front cap layer 74. For better adhesion, an adhesion promoter such as Valmat® or TranSpin® can be used between the first and second front cap layers 74 and 94, and between the second front cap layer 94 and the additional front cap layer 96.

[0048] The second front cap layer 94 and the further front cap layer 96 are made from different selected transparent materials. One or more of the materials of the first, second, and further front cap layers 74, 94, and 96 are selected to have refractive indices that promote light absorption and reduce light reflection. In a practical example, the first front cap layer 74 is made from SiOx, which has a refractive index of 1.45, the second front cap layer 94 is made from TiOx, which has a refractive index of 2.2 to 2.3, the third front cap layer is made from SiOx, and the fourth front cap layer is made from TiOx (where "x" is a variable).

[0049] 1F also illustrates the structure of FIG. 1E after a second rear cap layer 98 has been formed on the first rear cap layer 76, and an additional rear cap layer 100 has been formed, in turn, on the second rear cap layer 98. The second rear cap layer 98 provides additional strength to the first rear cap layer 76. For better adhesion, an adhesion promoter such as Valmat® or TranSpin® can be used between the first and second rear cap layers 76 and 98, and between the second rear cap layer 98 and the additional rear cap layer 100.

[0050] The second rear cap layer 98 and the further rear cap layer 100 are made from different selected transparent materials. One or more of the materials of the first, second, and further rear cap layers 76, 98, and 100 are selected to have refractive indices that promote light absorption and reduce light reflection. In a practical example, the first rear cap layer 76 is made from SiOx, which has a refractive index of 1.45, the second rear cap layer 98 is made from TiOx, which has a refractive index of 2.2-2.3, the third rear cap layer is made from SiOx, and the fourth front rear layer is made from TiOx (where "x" is a variable).

[0051] FIG. 1G also shows an ambient light source 102 and a projector 106. The ambient light source 102 may be, for example, an object that reflects ambient light. The ambient light is represented by beams 104A and 104B. Each beam 104A and 104B transmits through ambient air and then passes sequentially through front cap layers 96, 94, and 74, through the waveguide 20, and through rear cap layers 76, 98, and 100. The refractive index between adjacent cap layers is minimized, minimizing reflection of ambient light and promoting absorption of the ambient light into the waveguide 20. Beam 104A also passes through air in one of the recesses 44 in the rear side 24 of the waveguide 20. Beam 104B passes through air in one of the recesses 30 in the front side 22 of the waveguide 20.

[0052] Projector 106 generates projection light, represented by beam 104C. Beam 104C is inserted into waveguide 20. Beam 104C may be inserted, for example, through rear cap layers 100, 98, and 76, whose refractive indices are selected to promote absorption of beam 104C and limit its reflection. Beam 104C is directed into one of the recesses 30 in front side 22. The difference between the refractive index of waveguide 20 and that of the air in recess 30 is maximized to promote reflection of beam 104C and limit transmission of beam 104C into the air in recess 30. Air may have a refractive index of 1, and waveguide 20 may have a refractive index of at least 1.74. The refractive indices therefore differ from each other by at least 0.74. In another embodiment, another optical gas may be used instead of air, provided that such optical gas has a refractive index less than 1.3. Ideally, the refractive index between the waveguide 20 material and the optical gas should be at least 0.50. Reflected from the air in one of the recesses 30, beam 104C subsequently transmits into one of the recesses 44 on the rear side 24 of the waveguide 20. From the air-to-recess 44 interface, beam 104C reflects toward another of the recesses 30 on the front side 22 of the waveguide 20. An alternative structure can be a direct imprint pattern using a Si-containing resist over a spin-coated paraben material that is then evaporated. The Si-containing resist can be plasma treated to form a SiOx polymer structure.

[0053] Air interface reflection significantly improves optical image quality by: 1) improving the overall transmission of world light through the "transparent" eyepiece, making world-side objects clearer and brighter; 2) maintaining the refractive index difference between the groove-to-grating height of the relief structure, allowing for high diffraction efficiency of the grating, forming a functional waveguide relief structure; 3) reducing after-image artifacts from light reflections exiting the eyepiece and reflecting back off different lenses or stacked waveguide interfaces; and 4) reducing extraneous light from diffraction into the user's eyebox, altering optical artifacts such as producing rainbow artifacts that would otherwise be much more intense without the nanofeatures and film stack architecture.

[0054] 1A-1G illustrate an example of creating an anti-reflective cap structure. Anti-reflective properties can also be fabricated using alternative methods. FIG. 1H illustrates an optical system in which front and rear patterned layers 120 and 122 are formed on the front and rear sides of a waveguide 20. Layers 120 and 122 may be patterned using conventional photolithography techniques or are made from a polymer or photoresist material suitable for patterning using photolithography. No additional etching steps are required. The layers are then coated with front and rear conformal layers 124 and 126, respectively. The conformal layers are made from inorganic SiOx and are formed using chemical vapor deposition. The conformal layers 124 and 126 define recesses 30 and 44, which are covered with front and rear cap layers 74 and 76.

[0055] Figure 2 illustrates an alternative structure in which nanopatterning 110 is performed on the exterior surface instead of multiple cap layers as illustrated in Figure 1F. The nanopatterning 110 reduces ambient light reflection and aids in ambient light absorption. Figure 2 has reference numbers similar to those used in Figure 1F, and like reference numbers indicate like or similar components.

[0056] Figures 3 and 4 are similar to Figures 1F and 2. The optical systems illustrated in Figures 3 and 4 have waveguides with variable heights or "duty cycles." Porogen material can be formed into such structures in a spin-coating operation as described above.

[0057] Figure 5 illustrates a further optical system having different layers of different three-dimensional nanostructure stacks. The three-dimensional nanostructure stacks can be designed differently for different waveguide purposes. The material composition, thickness, and nanopatterning, along with the various spatial and geometric configurations per cap layer, can be different or the same between layers.

[0058] Figure 6A illustrates a scanning electron microscope (SEM) image of an air pocket covered with a single layer of SiOx over an etched grating in high-index glass. Figure 6B shows an SEM image of an air pocket covered with a multilayer coating. The multilayer coating alternates between SiOx and TiOx, with different thicknesses for each layer. The composition and thickness of the layers on the grating, from bottom to top, are 20 nm porous SiOx, 15 nm TiOx, 65 nm SiOx, 34 nm TiOx, 18 nm SiOx, 59 nm TiOx, and 97 nm SiOx. The multilayer coating on top of the air pocket structure can be applied by chemical and / or physical vapor deposition, spin coating, or a combination of different coating techniques.

[0059] Figures 7A and 7B show a sample with air pockets that was first covered with a SiOx layer and then spin-coated with an optical polymer (Teflon AF1600 from Chemours Company) with a refractive index of 1.31. The air pockets reduced the effective refractive index of the nanostructured grating area, resulting in a gradual refractive index transition from the bulk substrate, to the surface grating area, to the SiOx cap layer, to the spin-coated optical polymer layer, and finally to air. This type of gradual refractive index transition is beneficial for anti-reflection purposes and can significantly improve the transmission of ambient light.

[0060] Figure 8 is a 0° transmission graph from an experimental measurement showing that transmission is significantly increased by the combination of the air pockets and coating of Figures 7A and 7B. The nanostructured substrate here is a high refractive index lithium niobate substrate that has been etched to form a surface grating.

[0061] FIG. 9 illustrates the model used for the purpose of simulating reflection properties. FIGS. 10A-10D show four different anti-reflection coating stacking configurations simulated within the structure of FIG. 9 . FIG. 10A is a side view of a waveguide without any coating for the simulation. FIG. 10B is a side view of a waveguide with an optical polymer coating for the simulation. FIG. 10C is a side view of a waveguide with an air pocket for the simulation. FIG. 10D is a side view of a waveguide with a polymer instead of an air gap for the simulation. FIG. 11 is a graph illustrating transmission data based on the simulation. FIG. 12 shows the user-side diffraction efficiency from a simulation using high-index lithium niobate for the waveguide. Regarding the simulated transmission data, it can be seen that a directly spun-on, low-index optical polymer (AF2400 from Chemours Company, refractive index 1.29) has a similar effect in improving transmission compared to the configuration with an air pocket. However, in terms of single-bounce diffraction efficiency, the air pocket configuration is significantly better than configurations with only a spin-on low-index polymer or a stack with PPC filling the grating grooves. Simulations show that the diffraction efficiency is significantly higher than when a low-index material fills the grooves, but still lower than when no anti-reflection coating is applied. To further increase the efficiency, the grating geometry needs to be modified accordingly.

[0062] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are illustrative only and do not limit the invention, and that the invention is not limited to the specific construction and arrangement shown and described, as modifications may occur to those skilled in the art.

Claims

1. 1. A method of manufacturing an optical system, comprising: forming a waveguide of a high refractive index transparent material having a front side and a rear side, the front side of the waveguide having a plurality of recesses and a plurality of raised formations, each raised formation being located between two of the recesses; affixing a cap layer of selectively transparent material to the waveguide, wherein a plurality of cavities are defined between the cap layer and the waveguide with a gas in each respective cavity, such that when an ambient light source is located at a front side of the waveguide, a beam of ambient light is transmitted through the selectively transparent material of the cap layer, through the cavities holding the gas, and through the high refractive index transparent material of the waveguide; supporting first portions of the cap layer with the ridge formations, with second portions of the cap layer located between the first portions of the cap layer across the recesses, such that respective ones of the cavities are defined by respective ones of the second portions of the cap layer and respective ones of the recesses on the front side of the waveguide; forming a stack including the waveguide, a solid porogen material, and the cap layer; replacing the solid porogen material with the gas; A method comprising:

2. 10. The method of claim 1, wherein the cap layer is a front cap layer located between the ambient light source and a front side of the waveguide, and the beam of ambient light is transmitted sequentially through a selectively transparent material of the front cap layer, through the cavity holding the gas, and into a high refractive index transparent material of the waveguide.

3. 3. The method of claim 2, wherein the selective transparent material of the front cap layer is an anti-reflective material that increases absorption of the ambient light by the front surface of the waveguide and reduces reflection of the ambient light by the front surface of the waveguide.

4. 4. The method of claim 3, wherein the high refractive index transparent material is one of high refractive index glass, high refractive index lithium niobate, lithium tantalate, and silicon carbide.

5. The method of claim 3 , wherein the high refractive index transparent material has a refractive index of at least 1.

74.

6. The method of claim 1 , wherein the gas has a refractive index less than 1.

3.

7. The method of claim 1 , wherein the gas is air with a refractive index of 1.

8. The solid porogen material is heating the solid porogen material to a decomposition temperature at which the solid porogen material is converted into a sacrificial gas; removing the sacrificial gas from the cavity; and The method of claim 1 , wherein the ion exchange layer is removed by

9. The method of claim 8 , wherein the selectively transparent material of the cap layer is porous and the sacrificial gas outgasses through the selectively transparent material of the cap layer.

10. The method of claim 8, wherein the solid porogen material decomposes at a decomposition temperature of 120°C to 230°C.

11. 10. The method of claim 9, wherein the cap layer is made of SiOx having a thickness of at least 12 nm, where x is a variable.

12. The method of claim 1 , wherein each recess has a depth and a width, the width being less than 300 microns.

13. The method of claim 1 , wherein the recesses are imprinted on the front side.

14. conformally depositing a transparent layer on the front side of said waveguide; The method of claim 1 further comprising:

15. the cap layer is a front cap layer located between the ambient light source and a front side of the waveguide, and the cavity is a front cavity between the front cap layer and the front side of the waveguide; affixing a rear cap layer of selectively transparent material to the waveguide, wherein a rear cavity is defined between the rear cap layer and the rear face of the waveguide with a gas present in the rear cavity such that when an ambient light source is located at the front side of the waveguide, a beam of ambient light is transmitted through the high refractive index transparent material of the waveguide, through the rear cavity holding a gas, and through the selectively transparent material of the rear cap layer; The method of claim 1 further comprising:

16. the cap layer is a first cap layer, and the selectively transparent material is a first selectively transparent material; bonding a second cap layer of a second selected transparent material to the first cap layer. The method of claim 1 further comprising:

17. The method of claim 16 , wherein the second cap layer is harder than the first cap layer.

18. 17. The method of claim 16, wherein at least one of the selective transparent materials of the cap layer is an anti-reflective material that increases absorption of the ambient light by the front surface of the waveguide and reduces reflection of the ambient light by the front surface of the waveguide.

19. Forming a stack of cap layers with refractive indices that vary in magnitude 20. The method of claim 18, further comprising:

20. 20. The method of claim 19, wherein the cap layer is made of SiOx having a refractive index of 1.45 and TiOx having a refractive index of 2.2-2.3, where x is a variable.

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