Air pocket structure to enhance total internal reflection within the waveguide

Abstract

To provide an air pocket structure that promotes optimal total internal reflection within a waveguide. [Solution] Recesses are formed on the front and rear sides of the waveguide. A solid porogen material is spun on the front and rear sides to fill the recesses. A first front and rear capping layer is then formed on the raised formations of the waveguide and on the solid porogen material. The entire structure is then heated and the solid porogen material decomposes into porogen gas. The first front and rear capping layer is porous, allowing the porogen gas to escape and air to enter the recesses. The air maximizes the difference in refractive index between the high refractive index transparent material of the waveguide and the air, promoting reflection within the waveguide from the interface between the waveguide and the air.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Patent Application No. 62 / 783,778, filed on December 21, 2018, which is hereby incorporated by reference in its entirety.

[0002] The present invention generally relates to optical systems and methods of manufacturing optical systems.

Background Art

[0003] Modern computing and display technologies have facilitated the development of so - called "virtual reality" viewing devices. Such viewing devices typically have a frame that can be mounted on a user's head and often include two waveguides, one in front of each eye of the viewer. The waveguides are transparent so that ambient light from an object can pass through the waveguide and the user can see the object. Each waveguide also serves to transmit light projected from a projector to the user's individual eye. The projected light forms an image on the retina of the eye. The retina of the eye thus receives both ambient light and the projected light. The user can see both the real object and the image generated by the projected light simultaneously.

[0004] The projected light typically enters the waveguide at the edge of the waveguide, then reflects within the waveguide, and then exits the waveguide through the pupil of the waveguide towards the user's eye. Total internal reflection (TIR) is an ideal situation where there is no loss of the 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 Problems

[0005] The present invention provides a method for manufacturing an optical system, comprising fixing a cap layer of a selective transparent material to a waveguide of a high refractive index transparent material having a front side and a rear side, wherein, when an ambient light source is located on the front side of the waveguide, a beam of ambient light is defined between the cap layer and the waveguide, with the light gas contained within the cavity, so that the ambient light beam passes through the selective transparent material of the cap layer, through the cavity holding the light gas, and through the high refractive index transparent material of the waveguide.

[0006] The present invention also provides an optical system comprising: a waveguide made of a high refractive index transparent material having a front side and a rear side; a cap layer made of a selective transparent material fixed to the waveguide, wherein a cavity is defined between the cap layer and the waveguide; and a light gas in a cavity such that, when an ambient light source is located on the front side of the waveguide, a beam of ambient light passes through the selective transparent material of the cap layer, through the cavity holding the light gas, and through the high refractive index transparent material of the waveguide. This specification also provides, for example, the following items: (Item 1) A method for manufacturing an optical system, The method involves fixing a cap layer of a selective transparent material to a waveguide of a high refractive index transparent material having a front side and a rear side, wherein, when an ambient light source is located on the front side of the waveguide, the ambient light beam is defined between the cap layer and the waveguide such that the cavity is located within the cavity and the light gas is contained within it, so that the ambient light beam passes through the selective transparent material of the cap layer, through the cavity holding the light gas, and through the high refractive index transparent material of the waveguide. Methods that include... (Item 2) The method according to item 1, wherein the cap layer is a front cap layer located between the ambient light source and the front side of the waveguide, and the beam of ambient light is transmitted sequentially through the selected transparent material of the front cap layer, through the cavity holding the light gas, and into the high refractive index transparent material of the waveguide. (Item 3) The method according to item 2, wherein the selected transparent material for the front cap layer is an anti-reflective material that increases the absorption of ambient light by the front surface of the waveguide and reduces the reflection of ambient light by the front surface of the waveguide. (Item 4) The method according to 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) The high refractive index material is the method according to item 3, having a refractive index of at least 1.74. (Item 6) The optical gas is the method according to item 1, having a refractive index of less than 1.3. (Item 7) The method according to item 1, wherein the light gas is air with a refractive index of 1. (Item 8) Forming a stack including the waveguide, the solid porogen material, and the cap layer, Replacing the aforementioned porogen material with the aforementioned photogas and The method described in item 1, further including the method described in item 1. (Item 9) The aforementioned porogen material is The pologen material is heated to a decomposition temperature at which the pologen material is converted into a sacrificial gas, To remove the sacrificial gas from the aforementioned cavity and The method described in item 8, which is removed by performing the following. (Item 10) The method according to item 9, wherein the selected material for the cap layer is porous, and the sacrificial gas is released through the selected material for the cap layer. (Item 11) The method described in item 9, wherein the aforementioned pologen material decomposes at a decomposition temperature of 120°C to 230°C. (Item 12) The cap layer is made of SiOx having a thickness of at least 12 nm, where x is a variable, according to the method of item 10. (Item 13) The method according to item 1, wherein multiple cavities are defined between the cap layer and the waveguide, and the optical gas is located in each individual cavity. (Item 14) The front side of the waveguide is formed to have a plurality of depressions and a plurality of raised formations, wherein each raised formation is located between two of the depressions. The first portion of the cap layer is supported by the raised formation such that the second portion of the cap layer, located between the first portions of the cap layer, is positioned across the recess, and each of the cavities is defined by each of the second portions of the cap layer and each of the recesses on the front side of the waveguide. The method described in item 13, further including the method described in item 13. (Item 15) The method according to item 14, wherein each recess has a depth and a width, the width being less than 300 microns. (Item 16) The recess is imprinted on the front side, as described in item 14. (Item 17) A conformal layer is formed on the front side of the waveguide, wherein the conformal layer is made from a transparent material. The method described in item 14, further including the method described in item 14. (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. The rear cap layer of a selective transparent material is fixed to the waveguide, and when the ambient light source is located on the front side of the waveguide, the beam of ambient light is defined between the rear cap layer and the rear surface of the waveguide, with the light gas located in the rear cavity, so that the light gas passes through the high refractive index transparent material of the waveguide, the rear cavity holding the light gas, and the selective transparent material of the rear cap layer. The method described in item 1, further including the method described in item 1. (Item 19) The cap layer is a first cap layer, and the selected transparent material is a first selected transparent material. Fixing a second cap layer of a second selected transparent material to the first cap layer The method according to item 1, further comprising. (Item 20) The method according to item 19, wherein the second cap layer is harder than the first cap layer. (Item 2:1) The method according to item 19, wherein at least one of the selected transparent materials of the cap layer is an antireflection material that increases the absorption of the ambient light by the front surface of the waveguide and reduces the reflection of the ambient light by the front surface of the waveguide. (Item 22) Forming a stack of cap layers having a refractive index that changes in size The method according to item 21, further comprising. (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, and x is a variable. (Item 24) An optical system, comprising: A waveguide of a high refractive index transparent material having a front side and a rear side; A cap layer of a selected transparent material fixed to the waveguide, a cavity being defined between the cap layer and the waveguide; An optical gas in the cavity, wherein when the ambient light source is located on the front side of the waveguide, the beam of the ambient light passes through the selected 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 optical system comprising.

Brief Description of the Drawings

[0007] The present invention will be further described by way of examples with reference to the accompanying drawings.

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

[0009] [Figure 1B] Figure 1B is a diagram similar to Figure 1A, showing the waveguide after it has been patterned to have multiple depressions and raised formations on its front and rear sides.

[0010] [Figure 1C] Figure 1C is similar to Figure 1B, showing the depression after it has been filled with solid porogen material in the spin process.

[0011] [Figure 1D] Figure 1D is similar to Figure 1C, showing the first front cap layer formed on the front side and the first rear cap layer formed on the rear side.

[0012] [Figure 1E] Figure 1E is similar to Figure 1D, but after the structure has been heated, the solid pologen material has been removed, and the solid pologen material has been replaced with air.

[0013] [Figure 1F] Figure 1F is similar to Figure 1E, after further capping layers have been formed on the first front and first rear capping layers, completing the fabrication of the optical system.

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

[0015] [Figure 1H] Figure 1H is a cross-sectional side view of an optical system according to an alternative embodiment of the present invention, in which patterned layers are formed from a photoresist material.

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

[0017] [Figure 3] Figure 3 is a cross-sectional side view similar to Figure 1F, showing a nanostructure with variable feature height or variable duty cycle.

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

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

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

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

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

[0023] [Figure 7B] Figure 7B is a similar figure to Figure 7A, but at a lower magnification level.

[0024] [Figure 8] Figure 8 shows the 0° transmission graph from the experimental measurements.

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

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

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

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

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

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

[0031] [Figure 12] Figure 12 is a graph showing the user side diffraction efficiency from the simulation. [Modes for carrying out the invention]

[0032] An optical system and a method for fabricating the optical system are described. A depression is formed on the front and rear sides of the waveguide. A solid porogen material is spun on the front and rear sides to fill the depression. A first front and rear capping layer is then formed on the raised 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 capping layer is porous, allowing the porogen gas to escape and air to enter the depression. The air maximizes the difference in refractive index between the high refractive index transparent material of the waveguide and the air, promoting reflection within the waveguide from the interface between the waveguide and the air. A second front and rear capping layer is formed on the first front and rear capping layer, respectively, and further front and rear capping layers are then formed on the second front and rear capping layer. The capping layer has a refractive index that enhances the absorption of ambient light into the waveguide through the capping layer.

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

[0034] Figure 1A illustrates a waveguide 20 that serves as a primary substrate for subsequent processing. The waveguide 20 is made from a high refractive 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 high refractive index glass having a refractive index of 1.73. In another embodiment, the waveguide may be made from lithium niobate, lithium tantalate, or silicon carbide, which have a refractive index greater than 2.0. High refractive index transparent materials are preferred to maximize the field of view in the final product.

[0035] The waveguide 20 has a front side and a rear side 22 and 24. The front side and the rear side 22 and 24 are spaced apart from each other by a thickness 26 of less than 3 mm. The front side and the rear side 22 and 24 each have a width 28 of 50 to 70 mm and a depth into the paper of 50 to 70 mm. The front side and the rear side 22 and 24 are planar surfaces, which are planes parallel to each other. The material of the waveguide 20 is soft enough to allow the front side and the rear side 22 and 24 to form at room temperature of 22°C or at a moderately high temperature of 50°C without the formation of microcracks or optical distortion within the material of the waveguide 20.

[0036] Figure 1B illustrates the waveguide 20 after the front and rear sides 22 and 24 have been formed. The front side 22 is formed to have a plurality of depressions 30 and a plurality of raised formations 32, with each raised formation 32 located between two of the depressions 30. The side walls 34 of the depressions 30 form the side walls of the raised formations 32. The raised formations 32 have an outer surface 36 that lies in the same plane. The depressions 30 have a groove surface 38 that lies in the same plane and is parallel to the plane of the outer surface 36. Each depression 30 has a width 40 of 10 nm to 500 nm. The rear side 24 is formed to have a plurality of depressions 44 and a plurality of raised formations 46, with each raised formation 46 located between two of the depressions 44. The side walls 48 of the depressions 44 form the side walls of the raised formations 46. The raised formation 46 has an outer surface 50 that lies in the same plane. The depression 44 has a groove surface 52 that lies in the same plane and is parallel to the plane of the outer surface 50. Each depression 44 has a width 54 of 10 nm to 500 nm.

[0037] The front and rear sections 22 and 24 are simultaneously formed using a tool that imprints the depressions 30 and 44 and the raised formations 32 and 46. The tool has a front section and a rear section, which are made from hardened metal. The front section has a shape complementary to the shape produced on the front section 22, and the rear section has a shape complementary to the shape produced on the rear section 24. The waveguide 20 is inserted between the front and rear sections, and an actuator is used to move the front and rear sections toward each other, while the surface of the actuator is used to apply pressure to the front and rear sections 22 and 24 of the waveguide 20. The waveguide 20 is then removed from the tool. The front and rear sections 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, is greater than the thickness 26 of the substrate in Figure 1A, while the thickness 60, as measured between the groove surfaces 38 and 52, is less than the thickness 26. The waveguide 20 has a thickness of 200 microns to 1 nm. Each recess 30 or 44 has a depth 62 of 10 nm to 500 nm.

[0039] Figure 1C illustrates the waveguide 20 after the deposition of porogen (sacrificial) material. The porogen material may be spin-coated on the front side 22 and the rear side 24 of the waveguide 20. The porogen material fills the depressions 30 and 44. The porogen material forms a plurality of separate porogen portions 64 in the depression 30 on the front side 22 and a plurality of separate porogen portions 66 in the depression 44 on the rear side 24. Each porogen portion 64 fills an individual depression 30 until its outer surface 68 is coplanar with the outer surface 36 of the raised formation 32. Each porogen portion 66 fills a depression 44 until its outer surface 70 is coplanar with the outer surface 50 of the raised formation 46.

[0040] Figure 1D illustrates the structure of Figure 1C after the first front cap layer 74 and the first rear cap layer 76 have been formed. The cap layers 74 and 76 may be formed, for example, by a chemical vapor deposition process.

[0041] The first front cap layer 74 is made from a selected solid transparent material. The first front cap layer 74 is formed directly on the outer surface 36 of the raised structure 32 and the outer surface 68 of the porogen portion 64. The first front cap layer 74 is also bonded to the outer surface 36 of the raised structure 32 and thus fixed to the waveguide 20.

[0042] The first front cap layer 74 is shown as the final processed portion and is made from a relatively strong solid material. However, during its manufacture, 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 becomes more stable as it grows thicker and eventually 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 raised formation 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 after it is finally processed and obtains a thickness suitable for supporting itself without requiring the porogen portion 66, it does not require support from the porogen portion 66. The first rear cap layer 76 has a plurality of first portions 84 formed on the raised formation 46 and a plurality of second portions 86 formed on the porogen portion 66.

[0044] Figure 1E illustrates the structure of Figure 1D after the pologen portions 64 and 66 have been removed and exited through the individual cavities 88 and 90. Each cavity 88 and 90 has the same dimensions as the individual pologen portions that have been removed. Each cavity 88 and 90 is filled with a light gas in the form of air.

[0045] The solid pologen materials of the pologen portions 64 and 66 are pyrolytic materials or material mixtures 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 Figure 1D is heated to a decomposition temperature that converts the solid pologen material into pologen gas. The materials of the first front cap layer 74 and the first rear cap layer 76 are sufficiently porous to allow pologen gas to permeate through the first front cap layer 74 and the first rear cap layer 76 so that the pologen gas can escape from the cavities 88 and 90, and 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 obvious residue. Generally, the decomposition temperature is considered to be between 120°C and 230°C. When a decomposition temperature of 200°C to 300°C is used, the pologen portions 64 and 66 can be replaced with air in a short amount of time. If the decomposition temperature needs to be lowered, the addition of additives or the extension of the firing time may be considered. A decomposition temperature of 120°C to 160°C is possible using a suitable combination of material, film thickness, and firing time. The firing temperature and temperature gradient must be carefully controlled so that no significant residue is left behind and the rate of pologen gas release does not cause damage such as rupture, loosening, and cracking to the first front cap layer 74 and the first rear cap layer 76.

[0046] Once the cavities 88 and 90 are finally formed, the first portion 80 of the first front cap layer 74 and the first rear cap layer 76 are fixed to and supported by the raised formations 32 and 46. Each of the cavities 88 is defined on three sides by the surfaces of the individual recesses 30 and on a fourth side by one of the second portions 82 of the first front cap layer 74. Similarly, each of the cavities 90 is defined on three sides by the surface of the recess 44 and on a fourth side by one of the second portions 86 of the first rear cap layer 76. Note that the first front cap layer 74 and the second portions 82 and 86 of the first rear cap layer 76 are not further supported by the porogen portions 64 and 66. However, provided that the first front cap layer 74 and the first rear cap layer 76 are still supported by the raised formations 32 and 46, and the widths 40 and 54 of the cavities 88 and 90 are less than 500 nm, respectively, the structural integrity of the first front cap layer 74 and the first rear cap layer 76 can be reserved during and after the gas release of the solid pologen material.

[0047] Figure 1F illustrates the structure of Figure 1E after a second front cap layer 94 is formed on the first front cap layer 74, and a further front cap layer 96 is subsequently formed 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(R) or TranSpin(R) can be used between the first and second front cap layers 74 and 94, and between the second front cap layer 94 and the further 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 a refractive index that enhances light absorption and reduces light reflection. In practical examples, the first front cap layer 74 is made from SiOx with a refractive index of 1.45, the second front cap layer 94 is made from TiOx with a refractive index of 2.2–2.3, 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] Figure 1F also illustrates the structure of Figure 1E after a second rear cap layer 98 is formed on the first rear cap layer 76, and a further rear cap layer 100 is subsequently formed 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(R) or TranSpin(R) can be used between the first and second rear cap layers 76 and 98, and between the second rear cap layer 98 and the further 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 for the first, second, and further rear cap layers 76, 98, and 100 are selected to have a refractive index that enhances light absorption and reduces light reflection. In practical embodiments, the first rear cap layer 76 is made from SiOx with a refractive index of 1.45, the second rear cap layer 98 is made from TiOx with 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] Figure 1G further 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 is transmitted through the ambient air and then, sequentially, through the front cap layers 96, 94, and 74, through the waveguide 20, and through the rear cap layers 76, 98, and 100. The refractive index between adjacent cap layers is minimized to minimize reflection of ambient light and promote absorption of ambient light into the waveguide 20. Beam 104A also passes through the air in one of the depressions 44 on the rear side 24 of the waveguide 20. Beam 104B passes through the air in one of the depressions 30 on the front side 22 of the waveguide 20.

[0052] The projector 106 generates projected light represented by beam 104C. Beam 104C is inserted into the waveguide 20. Beam 104C may also be inserted through, for example, rear cap layers 100, 98, and 76, whose refractive indices are selected to promote the absorption of beam 104C and limit its reflection. Beam 104C is directed towards one of the recesses 30 on the front side 22. The difference between the refractive index of the waveguide 20 and the refractive index of the air in the recess 30 is maximized to promote the reflection of beam 104C and limit the transmission of beam 104C into the air in the recess 30. The air has a refractive index of 1, and the waveguide 20 may have a refractive index of at least 1.74. The refractive indices are therefore at least 0.74 different from each other. In another embodiment, a different optical gas may be used instead of air, provided that such an optical gas has a refractive index of less than 1.3. Ideally, the refractive index between the waveguide material 20 and the optical gas should be at least 0.50. Reflected from the air in one of the depressions 30, the beam 104C then passes through one of the depressions 44 on the rear side 24 of the waveguide 20. The beam 104C is reflected from the interface between the air in the depression 44 toward the other of the depressions 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, which is then evaporated. The Si-containing resist can be plasma-treated to form an SiOx polymer structure.

[0053] Reflection at the air interface significantly improves optical image quality by altering optical artifacts, such as: 1) improving the overall transmission of world light through a "transparent" eyepiece, making world-side objects clearer and brighter; 2) maintaining the refractive index difference between groove and lattice height in the undulating structure, forming a functional waveguide undulating structure, enabling high diffraction efficiency of the lattice; 3) reducing afterimage artifacts from reflections of light that exit the eyepiece and reflect back from different lenses or stacked waveguide interfaces; and 4) reducing ambient light entering the user's eyebox from diffraction, which would otherwise be much stronger without nano-features and film stack architecture, such as generating rainbow defects.

[0054] Figures 1A-1G illustrate one embodiment of generating an anti-reflective cap structure. Anti-reflective properties can also be manufactured using alternative methods. Figure 1H illustrates an optical system in which front and rear patterned layers 120 and 122 are formed on the front and rear sides of the waveguide 20. Layers 120 and 122 may be patterned using conventional photolithography techniques or are made from polymer or photoresist materials 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 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 the nanopatterning 110 is performed on the outer surface instead of the multiple capping layers described in Figure 1F. The nanopatterning 110 reduces ambient light reflection and promotes ambient light absorption. Figure 2 has reference numbers similar to those used in Figure 1F, where similar reference numbers indicate similar or similar components.

[0056] Figures 3 and 4 are analogous to Figures 1F and 12. The optical systems illustrated in Figures 3 and 4 have waveguides with variable height or "duty cycle". Pologen materials can be formed into such structures in spin-coating operations 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, with various spatial and geometric configurations for each cap layer, can be different or identical between layers.

[0058] Figure 6A illustrates a scanning electron microscope (SEM) image of an air pocket covered with a single layer of SiOx across an etched lattice in high refractive 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 each layer having a different thickness. The composition and thickness of the layers on the lattice, 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 the air pocket structure can be applied by chemical and / or physical vapor deposition, or spin coating, or a combination of different coating techniques.

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

[0060] Figure 8 is a 0° transmission graph from experimental measurements, showing that transmission is significantly increased by the air pocket and coating combinations shown in Figures 7A and 7B. The nanostructured substrate here is a high refractive index lithium niobate substrate etched to form a surface lattice.

[0061] Figure 9 illustrates the model used for the purpose of simulating reflective properties. Figures 10A–10D show four different anti-reflective coating stacking configurations simulated within the structure in Figure 9. Figure 10A is a side view of the waveguide without any coating for simulation. Figure 10B is a side view of the waveguide with an optical polymer coating for simulation. Figure 10C is a side view of the waveguide with an air pocket for simulation. Figure 10D is a side view of the waveguide with polymer instead of air pocket for simulation. Figure 11 is a graph illustrating transmission data based on the simulation. Figure 12 shows the user side diffraction efficiency from the simulation using high refractive index lithium niobate for the waveguide. With respect to the simulated transmission data, it can be seen that directly spun-on, low refractive index optical polymer (AF2400, Chemors Company, refractive index 1.29) has a similar effect in improving transmission compared to the configuration with an air pocket. However, with respect to single bounce diffraction efficiency, the air pocket configuration is significantly better than configurations with only spin-on low refractive index polymers or configurations where stacks with PPCs fill the lattice grooves. Simulations show that diffraction efficiency is significantly higher than in the situation where low refractive index material fills the grooves, but still lower than in the situation where no anti-reflective coating is applied. To further improve efficiency, the lattice geometry needs to be modified accordingly.

[0062] While some exemplary embodiments are described and shown in the accompanying drawings, it should be understood that such embodiments are illustrative only and do not limit the invention, and that the invention is not limited to the specific structures and arrangements shown and described, as modifications can be conceived by those skilled in the art.

Claims

[Claim 1] The invention described herein.

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