Waveguides with high index materials and methods of fabrication thereof

BACKGROUND
Field

The present disclosure relates to optical systems, including augmented reality imaging and visualization systems.

Description of the Related Art

Modern computing and display technologies have 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 wherein they seem to be, or may be perceived as, real. A virtual reality, or “VR”, scenario typically involves the presentation of digital or virtual image information without transparency to other actual real-world visual input; an augmented reality, or “AR”, scenario typically involves presentation of digital or virtual image information as an augmentation to visualization of the actual world around the user. A mixed reality, or “MR”, scenario is a type of AR scenario and typically involves virtual objects that are integrated into, and responsive to, the natural world. For example, an MR scenario may include AR image content that appears to be blocked by or is otherwise perceived to interact with objects in the real world.

Referring to FIG. 1, an augmented reality scene 10 is depicted. The user of an AR technology sees a real-world park-like setting 20 featuring people, trees, buildings in the background, and a concrete platform 30. The user also perceives that he/she “sees” “virtual content” such as a robot statue 40 standing upon the real-world platform 30, and a flying cartoon-like avatar character 50 which seems to be a personification of a bumble bee. These elements 50, 40 are “virtual” in that they do not exist in the real world. Because the human visual perception system is complex, it is challenging to produce AR technology that facilitates a comfortable, natural-feeling, rich presentation of virtual image elements amongst other virtual or real-world imagery elements.

Systems and methods disclosed herein address various challenges related to AR and VR technology.

SUMMARY

A head mounted display system may be configured to project light to an eye of a user to display augmented reality image content in a vision field of the user. The head-mounted display system may include a frame that is configured to be supported on a head of the user. The head-mounted display system may also include an eyepiece disposed on the frame. At least a portion of the eyepiece may be transparent and/or disposed at a location in front of the user's eye when the user wears the head-mounted display such that the transparent portion transmits light from the environment in front of the user to the user's eye to provide a view of that environment in front of the user. The eyepiece may include one or more waveguides disposed to direct light into the user's eye to form augmented reality image content.

Various embodiments of the head mounted display system comprise a projector having at least one pupil or sub-pupil that outputs light (e.g., image light) having a plurality of colors or ranges of wavelengths (e.g., two or three colors or ranges of wavelengths) within the at least one pupil or sub-pupil. Different colors or wavelengths in the plurality of ranges of wavelengths may include one or more colors or wavelengths. In some embodiments, the head mounted display system comprises a waveguide assembly comprising a plurality of waveguides stacked over each other and configured to receive light having a plurality of colors or ranges of wavelengths outputted from at least one pupil of the projector. Different waveguides in the plurality of waveguides may comprise an in-coupling optical element configured to in-couple light of one of the colors or plurality of ranges of wavelengths from the light outputted from the pupil of the projector. One or more waveguides comprising materials with relatively high refractive index (e.g., refractive index greater than refractive index of glass and/or refractive index greater than or equal to about 1.8) can advantageously enlarge the field of view as compared to waveguides comprising glass and/or materials with refractive index less than about 1.8. Additionally, in various embodiments of display devices, different colors or wavelengths of light (e.g., red, green and/or blue wavelengths of light) can be in-coupled into a single waveguide comprising materials with relatively high refractive index (e.g., refractive index greater than refractive index of glass and/or refractive index greater than or equal to about 1.8). In one or more embodiments, two or more colors (e.g., two or three colors) can be coupled into and propagate within a single waveguide comprising materials with relatively high refractive index and maintain a high field of view (e.g., refractive index greater than or equal to about 1.8). Accordingly, various embodiments of display devices contemplated in this application include one or more waveguides comprising materials with refractive index greater than refractive index of glass. For example, one or more waveguides in various embodiments of display devices contemplated in this application can comprise Lithium Niobate (LiNbO₃), Lithium Tantalate (LiTaO₃), Diamond, Silicon Carbide (SiC), and other similar materials having refractive index greater than or equal to about 1.8 and absorption coefficient less than 0.001. In various embodiments, one or more waveguides in various embodiments of display devices contemplated in this application can comprise materials that are transparent to visible light and have a refractive index greater than refractive index of glass. This application also describes systems and methods of fabricating gratings on one or more surfaces of a waveguide comprising a material that are transparent to visible light and have a refractive index greater than refractive index of glass, such as, for example Lithium Niobate (LiNbO₃), Silicon Carbide (SiC), Diamond, and other similar materials. Waveguides comprising materials such as Diamond and SiC having a hardness factor (e.g., approximately 9-10 Mohs) can have additional advantages of being scratch resistant and/or harder to break. In some implementations, the waveguide and grating formed therein comprises x-cut lithium niobate.

The systems, methods and devices disclosed herein each have several innovative aspects, no single one of which is solely responsible for the desirable attributes disclosed herein. A variety of example systems and methods are provided below.

Part I

Example 1: A method of manufacturing a diffractive optical element, the method comprising:

- providing a substrate comprising material having a refractive index greater than 2.0 that is transparent to visible light;
- disposing a patternable layer over a surface of the substrate;
- forming a pattern on the patternable layer, the pattern comprising a plurality of surface relief features with different heights; and
- etching the surface of the substrate through the patternable layer to fabricate structures on the surface of the substrate, wherein said structure comprise diffractive features configured to diffract visible light.

Example 2: The method of Example 1, wherein the transparent material comprises at least one of LiNbO₃, LiTaO₃, or BaTiO₃.

Example 3: The method of Example 2, wherein the transparent material comprises an X-cut LiNbO₃wafer.

Example 4: The method of any of the Examples above, further comprising disposing over the substrate a layer between the substrate and the patternable layer.

Example 5: The method of Example 4, wherein the layer between the substrate and the patternable layer comprises a dielectric layer.

Example 6: The method of Example 4, wherein the layer between the substrate and the patternable layer comprises a conducting layer.

Example 7: The method of Examples 4, 5 or 6, wherein the layer between the substrate and the patternable layer comprises a transparent oxide.

Example 8: The method of Examples 4 or 6, wherein the layer between the substrate and the patternable layer comprises a conductive oxide.

Example 9: The method of Example 4, wherein the layer between the substrate and the patternable layer comprises at least one of SiC, TiO₂, ZrO₂, Si₃N₄, or SiO₂.

Example 10: The method of any of Examples 4 to 9, wherein the layer between the substrate and the patternable layer comprises a material having a refractive index between 1.45 and 3.5.

Example 11: The method of any of Examples 4 to 9, wherein the layer between the substrate and the patternable layer comprises a material having a refractive index greater than or equal to 2.0.

Example 12: The method of any of Examples 4, 6, 8, 10, or 11, wherein the layer between the substrate and the patternable layer comprises a material configured to dissipate static charge.

Example 13: The method of any of the Examples above, further comprising disposing an adhesion promoter layer over the substrate prior to disposing the patternable layer.

Example 14: The method of Example 13, wherein the adhesion promoter layer has a thickness less than or equal to 10 nm.

Example 15: The method of Examples 13 or 14, wherein the adhesion promoter layer is configured to covalently bond with the patternable layer.

Example 16: The method of Examples 13 or 14, wherein the adhesion promoter layer is configured to cross-link with the substrate.

Example 17: The method of any of the Examples above, wherein the patternable layer has a refractive index less than 2.0.

Example 18: The method of any of the Examples above, further comprising exposing the surface of the substrate to an ionizer prior to disposing the patternable layer.

Example 19: The method of Example 18, wherein the ionizer comprises bipolar clean air ionization.

Example 20: The method of Example 18, wherein the ionizer comprises positive or negative ions.

Example 21: The method of any of the Examples above, further comprising bringing a charged surface close to or in contact with the surface of the substrate thereby dissipating surface charges.

Example 22: The method of any of the Examples above, further comprising mounting the substrate on an electrically grounded mount thereby dissipating surface charges.

Example 23: The method of any of the Examples above, further comprising depositing a metal layer over the substrate thereby dissipating surface charges.

Example 24: The method of Example 23, wherein the metal layer comprises iridium, chromium or nickel.

Example 25: The method of any of the Examples above, wherein depositing the patternable layer comprises jet depositing the patternable layer over the surface.

Example 26: The method of any of the Examples above, wherein the patternable layer is deposited non-uniformly across the surface, regions of surface where the patternable layer is thicker producing higher surface relief features than regions of surface where the patternable layer is thinner.

Example 27: The method of any of the Examples above, wherein etching the surface of the substrate comprises:

exposing the patternable layer to a first etchant that is configured to etch the patternable layer.

Example 28: The method of Example 27, further comprising exposing the surface of the substrate to a second etchant, the second etchant configured to etch the substrate.

Example 29: The method of Example 27, further comprising exposing a layer of dielectric material disposed on the substrate to the second etchant configured to etch a layer of dielectric material.

Example 30: The method of Example 29, further comprising exposing the surface of the substrate to a third etchant configured to etch the material of the substrate.

Example 31: The method of any of the Examples above, wherein said forming a pattern on said patternable layer comprises imprinting a pattern in said patternable layer.

Example 32: The method of Example 31, wherein imprinting a pattern on the patternable layer of comprising contacting the patternable layer with a patterned template.

Example 33: The method of any of the Examples above, wherein said forming a pattern on said patternable layer comprises patterning using photolithograrphy.

Example 34: The method of any of the Examples above, wherein said substrate comprises a dielectric.

Example 35: The method of any of the Examples above, wherein said patternable layer comprise polymer.

Example 36: The method of any of the Examples above, wherein said patternable layer comprise resist.

Example 37: The method of Example 36, wherein said patternable layer comprise photoresist.

Example 38: The method of any of the Examples above, further comprising integrating the diffractive optical element in a head mounted display.

Example 39: A method of manufacturing a diffractive optical element, the method comprising:

providing a substrate comprising a material having a refractive index greater than 2.0 that is an transparent to visible light;

disposing different amounts of a patternable material over different regions on a surface of the substrate; and

etching the surface of the substrate through the patternable material to fabricate structures having different heights on the surface of the substrate thereby forming diffractive features.

Example 40: The method of Example 39, wherein regions of surface having more patternable material produce higher surface relief features than regions of surface having less patternable material.

Example 41: A method of manufacturing a diffractive optical element, the method comprising:

- providing a substrate comprising a material having a refractive index greater than 2.0 that is an transparent to visible light;
- disposing different compositions of a patternable material over different laterally spaced regions on a surface of the substrate, the different compositions of the patternable material having different etch rates to an etchant; and
- etching the surface of the substrate through the patternable material with the etchant to fabricate structures having different heights on the surface of the substrate thereby forming diffractive features.

Example 42: A display device comprising:

- a waveguide stack comprising a plurality of waveguides, at least one of the plurality of waveguides comprising a material having a refractive index greater than 2.0 that is that is transparent to visible light,
- wherein said at least one of the plurality of waveguides comprises a first major surface, a second major surface, and a plurality of thinner edges, wherein the first major surface comprises a plurality of diffractive features having different heights.

Example 43: The display device of Example 42, wherein the second major surface comprises a plurality of diffractive features offset from the plurality of diffractive features of the first major surface.

Example 44: The display device of Examples 42 or 43, wherein the transparent material comprises one or more of LiNbO₃, LiTaO₃, SiC, or TiO₂.

Example 45: The display device of any of Examples 42 to 44, further comprising:

- a frame configured to be supported on the head of the user; and
- an eyepiece comprising the waveguide stack disposed on the frame.

Example 46: The display device comprises a head mounted display.

Example 47: A method of manufacturing a diffractive optical element, the method comprising:

- providing a substrate comprising material having a refractive index greater than 1.79 that is transparent to visible light;
- disposing a patternable layer over a surface of the substrate;
- patterning the patternable layer, the pattern comprising a plurality of features; and
- etching the surface of the substrate through the patternable layer to fabricate structures on the surface of the substrate, wherein the structures comprise diffractive features configured to diffract visible light.

Example 48: The method of Example 47, wherein the transparent material comprises LiNbO₃or silicon carbide.

Example 49: The method of Examples 47 or 48, wherein patterning the patternable layer comprises imprinting the patternable layer with an imprint template comprising a plurality of features.

Example 50: The method of any of Examples 47-49, further comprising curing the patterned patternable layer.

Example 51: The method of any of Examples 47-50, wherein disposing the patternable layer over the surface of the substrate comprises jet-depositing the patternable layer over the surface of the substrate.

Example 52: The method of any of Examples 47-51, wherein the surface of the substrate is discharged prior to disposing the patternable layer by at least one of (i) exposing the surface to a plasma; (ii) using an ionizer; (iii) bringing a secondary charged surface or a grounded surface near the surface; or (iv) providing a transparent metal or other conductive coating.

Example 53: The method of any of Examples 47-52, wherein the patternable layer comprises a resist or a polymer.

Example 54: The method of any of Examples 47-53, further comprising disposing an adhesion promoter layer over the surface of the substrate prior to disposing the patternable layer.

Example 55: The method of any of Examples 47-54, further comprising disposing a layer of a high refractive index material having a refractive index greater than 1.79 over the surface of the substrate prior to disposing the patternable layer, the layer of the high refractive index material comprising a material different from the material of the substrate.

Example 56: The method of Example 55, wherein the layer of the high refractive index material comprises at least one of titanium dioxide, zirconium dioxide, silicon nitride or silicon carbide.

Example 57: The method of any of Examples 47-56, wherein etching the surface of the substrate comprises:

- etching the patterned patternable layer using a first etch process to expose the surface of the substrate between the plurality of features of the patternable layer; and
- etching the plurality of the features and the exposed surface of the substrate using a second etch process to fabricate a plurality of features on the surface of the substrate.

Example 58: The method of Example 57, wherein the first etch process comprises etching in the presence of at least one of Argon, oxygen and Helium, and wherein the second etch process comprises etching in the presence of at least one of Fluorine, Bromine, Argon or methane.

Example 59: The method of any of Example 47-58, wherein disposing the patternable layer over the surface of the substrate comprises disposing a plurality of droplets of a patternable material over the substrate.

Example 60: The method of Example 59, wherein the volume of the plurality of droplets of the patternable material varies across the surface of the substrate.

Example 61: The method of Example 60, wherein the plurality of features of the patterned patternable layer have different heights.

Example 62: The method of Example 60, wherein a base of the cured patterned patternable layer is sloped.

Example 63: The method of Example 60, wherein a spacing between the plurality of features of the patterned patternable layer varies across the surface of the substrate.

Example 64: The method of any of Examples 59-63, wherein the plurality of structures formed on the surface of the substrate have different heights.

Example 65: The method of Example 59, wherein the volume of the plurality of droplets of the patternable material is constant.

Example 66: The method of Example 65, wherein the plurality of features of the cured patternable layer have approximately a same height.

Example 67: The method of any of Examples 65-66, wherein the plurality of structures formed on the surface of the substrate have approximately a constant height.

Example 68: A method of manufacturing a diffractive optical element, the method comprising:

- providing a substrate comprising material having a refractive index greater than 1.79 that is transparent to visible light;
- disposing a patternable layer over a surface of the substrate; and
- patterning the patternable layer to form a pattern comprising a plurality of features,
- wherein the plurality of features of the patterned patternable layer comprise diffractive features configured to diffract visible light into the substrate to be guided therein or to diffract visible light guided within the substrate out of the substrate.

Example 69: The method of Example 68, wherein the transparent material comprises LiNbO₃or silicon carbide.

Example 70: The method of Examples 68 or 69, wherein patterning the patternable layer comprises imprinting the patternable layer with an imprint template comprising a plurality of features.

Example 71: The method of any of Examples 68-71, further comprising curing the patterned patternable layer.

Example 72: The method of any of Examples 68-71, wherein disposing the patternable layer over the surface of the substrate comprises jet-depositing the patternable layer over the surface of the substrate.

Example 73: The method of any of Examples 68-72, wherein the surface of the substrate is discharged prior to disposing the patternable layer using at least one of (i) exposing the surface a plasma; (ii) an ionizer; (iii) bringing a secondary charged surface or a grounded surface near the surface; or (iv) providing a transparent metal or other conductive coating.

Example 74: The method of any of Examples 68-73, wherein the patternable layer comprises a resist or a polymer.

Example 75: The method of any of Examples 68-74, further comprising disposing an adhesion promoter layer over the surface of the substrate prior to disposing the patternable layer.

Example 76: The method of any of Examples 68-75, further comprising disposing a layer of a high refractive index material having a refractive index greater than 1.79 over the surface of the substrate prior to disposing the patternable layer, the layer of the high refractive index material comprising a material different from the material of the substrate.

Example 77: The method of Example 76, wherein the layer of the high refractive index material comprises at least one of titanium dioxide, zirconium dioxide, silicon nitride or silicon carbide.

Example 78: The method of any of Example 68-75, wherein the disposing the patternable layer over the surface of the substrate comprises disposing a plurality of droplets of a patternable material over the substrate.

Example 79: The method of Example 78, wherein the volume of the plurality of droplets of the patternable material varies across the surface of the substrate.

Example 80: The method of Example 79, wherein the plurality of features of the patterned patternable layer have different heights.

Example 81: The method of Example 80, wherein the base of the patterned patternable layer is sloped.

Example 82: The method of Example 80, wherein a spacing between the plurality of features of the patterned patternable layer varies across the surface of the substrate.

Example 83: The method of Example 78, wherein the volume of the plurality of droplets of the patternable material is constant.

Example 84: The method of Example 83, wherein the plurality of features of the patterned patternable layer have approximately a same height.

Example 85: A method of manufacturing a diffractive optical element, the method comprising:

- providing a substrate comprising material having a refractive index greater than 1.79 that is transparent to visible light;
- jet-depositing the patternable layer over a surface of the substrate; and
- patterning the patternable layer to form a pattern comprising a plurality of features.

Example 86: The method of Example 85, wherein the transparent material comprises LiNbO₃or silicon carbide.

Example 87: The method of Examples 85 or 86, wherein patterning the patternable layer comprises using imprinting the patternable layer with an imprint template comprising a plurality of features.

Example 88: The method of any of Examples 85-87, further comprising curing the patterned patternable layer.

Example 89: The method of Examples 85 or 88, wherein the surface of the substrate is discharged prior to disposing the patternable layer using at least one of (i) exposing the surface a plasma; (ii) an ionizer; (iii) bringing a secondary charged surface or a grounded surface near the surface; or (iv) providing a transparent metal or other conductive coating.

Example 90: The method of any of Examples 85-89, wherein the patternable layer comprises a resist or a polymer.

Example 91: The method of any of Examples 85-90, further comprising disposing an adhesion promoter layer over the substrate prior to disposing the patternable layer.

Example 92: The method of any of Examples 85-91, further comprising disposing a layer of a high refractive index material having a refractive index greater than 1.79 over the surface of the substrate prior to disposing the patternable layer, the layer of the high refractive index material comprising a material different from the material of the substrate.

Example 93: The method of Example 92, wherein the layer of the high refractive index material comprises at least one of titanium dioxide, zirconium dioxide, silicon nitride or silicon carbide.

Example 94: The method of any of Example 85-93, wherein jet-depositing the patternable layer over the substrate comprises jet-depositing a plurality of droplets of a patternable material over the substrate.

Example 95: The method of Example 94, wherein the volume of the plurality of droplets of the patternable material varies across the surface of the substrate.

Example 96: The method of Example 95, wherein the plurality of features of the patterned patternable layer have different heights.

Example 97: The method of Example 95, wherein the base of the patterned patternable layer is sloped.

Example 98: The method of Example 97, wherein a spacing between the plurality of features of the patterned patternable layer varies across the surface of the substrate.

Example 99: The method of Example 94, wherein the volume of the plurality of droplets of the patternable material is constant.

Example 100: The method of Example 99, wherein the plurality of features of the cured patternable layer have approximately a same height.

Example 101: The method of Example 48, wherein the transparent material comprises LiNbO₃.

Example 102: The method of Example 48, wherein the transparent material comprises silicon carbide.

Example 103: The method of Example 52, wherein the surface of the substrate is discharged prior to disposing the patternable layer by exposing the surface to a plasma.

Example 104: The method of Example 52, wherein the surface of the substrate is discharged prior to disposing the patternable layer using an ionizer.

Example 105: The method of Example 52, wherein the surface of the substrate is discharged prior to disposing the patternable layer by bringing a secondary charged surface or a grounded surface near the surface.

Example 106: The method of Example 52, wherein the surface of the substrate is discharged prior to disposing the patternable layer by providing a transparent metal or other conductive coating.

Example 107: The method of Example 57, wherein the first etch process does not etch the substrate.

Example 108: The method of Example 57, wherein the first etch process etches the substrate at a lower etch rate than the second etch process.

Example 109: The method of any of Examples 1-41 and 47-108, further including an optical component over said diffractive optical element.

Example 110: The method of Example 109, wherein said optical component is in contact with said diffractive features.

Example 111: The method of Example 109, further including a planarization layer between said optical component and said diffractive features.

Example 112: The method of Example 109, further including a structural stability providing layer between said optical component and said substrate.

Example 113: The method of Example 109, further including a planarization layer between said optical component and said substrate.

Example 114: The method of any of Example 109 to 113, wherein said optical component is at least 1 centimeter (cm) in spatial extent.

Example 115: The method of any of Example 109 to 113, wherein said optical component is at least a plurality of centimeters in spatial extent.

Example 116: The method of any of Example 109 to 115, wherein said optical component comprises a refractive optical component.

Example 117: The method of any of Example 109 to 115, wherein said optical component comprises a diffractive optical component.

Example 118: The method of any of Example 109 to 117, wherein said optical component comprises a lens.

Example 119: The method of Example 118, wherein said lens is at least 1 centimeter (cm) in spatial extent.

Example 120: The method of Example 118, wherein said lens is at least a plurality of centimeters in spatial extent.

Example 121: The method of any of Example 118 to 120, wherein said lens comprises a convex lens.

Example 122: The method of any of Example 118 to 120, wherein said lens comprises a concave lens.

Example 123: The method of any of Example 118 to 122, wherein said lens comprises a Fresnel lens.

Example 124: The method of any of Examples 1-41 and 47-108, further including disposing a first layer over the surface of the substrate prior to disposing the patternable layer, the first layer comprising a material different from the material of the substrate.

Example 125: The method of any of Example 124, wherein said first layer comprises a dielectric layer.

Example 126: The method of any of Examples 124 or 125, wherein said first layer comprises a high refractive index material having a refractive index greater than 1.79.

Example 127: The method of any of Examples 124 to 126, wherein the first layer comprises at least one of titanium dioxide, zirconium dioxide, silicon nitride or silicon carbide.

Example 128: The method of any of Examples 124 to 126, wherein the first layer comprises a layer of titanium dioxide.

Example 129: The method of any of Examples 124 to 128, further including an adhesion promotor layer between said first layer and said patternable layer.

Example 130: The method of any of Examples 124 to 129, wherein said first layer reduces reflection from the substrate.

Example 131: The method of any of Examples 124 to 130, further including a second layer between the first layer and the patternable material.

Example 132: The method of Example 131, wherein said second layer comprises dielectric material.

Example 133: The method of Examples 131 or 132, wherein the first layer has an index of refraction between that of the substrate and the said second layer.

Example 134: The method of any of Examples 131 to 133, further including a third layer between the second layer and the patternable material.

Example 135: The method of Example 134, wherein said third layer between the second layer and the patternable material comprises dielectric material.

Example 136: The method of Examples 134 or 135, wherein the second layer has an index of refraction between that of the first layer and the third layer.

Example 137: The method of any of Examples 131 to 136, wherein the first layer comprises titanium dioxide.

Example 138: The method of any of Examples 131 to 137, wherein the second layer comprises silicon nitride.

Example 139: The method of any of Examples 134 to 138, wherein the third layer comprises silicon dioxide.

Example 140: The method of any of Examples 131 to 139, wherein the first layer and the second layer reduce reflection from the substrate.

Example 141: The method of any of Examples 133 to 139, wherein the first layer, the second layer and the second layer reduce reflection from the substrate.

Example 142: The method of any of Examples 124 to 141, further comprising removing said patternable material and retaining said the first layer as a least part of diffractive features.

Example 143: The method of any of Examples 131 to 141, further comprising removing said patternable material and retaining said the first layer and said second layer as a least part of diffractive features.

Example 144: The method of any of Examples 134 to 141, further comprising removing said patternable material and retaining said the first layer, said second layer, and said third layer as a least part of diffractive features.

Example 145: The method of any of Examples 124 to 141, further comprising removing said patternable material and retaining said the first layer as diffractive features on said substrate, said substrate not including corresponding diffractive features etched therein.

Example 146: The method of any of Examples 131 to 141, further comprising removing said patternable material and retaining said the first layer and the second layer as diffractive features on said substrate, said substrate not including corresponding diffractive features etched therein.

Example 147: The method of any of Examples 134 to 141, further comprising removing said patternable material and retaining said the first layer, said second layer, and said third layer as diffractive features on said substrate, said substrate not including corresponding diffractive features etched therein.

Example 148: The method of any of the Examples above, wherein said diffractive features have the same height with respect to the substrate.

Example 149: The method of any of the Examples above, wherein said different of said diffractive features have the different heights with respect to the substrate.

Example 150: The method of Example 149, wherein said different of said diffractive features have different height with respect to the substrate such that the height increases progressively with lateral position along said substrate.

Example 151: The method of any of Examples 1-41 and 47-108, further including a plurality of layers over the surface of the substrate prior to disposing the patternable layer, the plurality of layers comprising a material different from the material of the substrate.

Example 152: The method of Example 151, wherein said plurality of layers comprise dielectric material.

Example 152: The method of Example 151, wherein said plurality of layers comprise at least one layer of titanium dioxide.

Example 153: The method of any of Examples 151 to 152, wherein said plurality of layers comprise at least one layer of silicon dioxide.

Example 154: The method of any of Examples 151 to 153, wherein said plurality of layers comprise at least one layer of magnesium fluoride.

Example 155: The method of any of Examples 151 to 154, wherein said plurality of layers comprise a plurality of layers of titanium dioxide.

Example 156: The method of any of Examples 151 to 155, wherein said plurality of layers comprise a plurality of layers of silicon dioxide.

Example 157: The method of any of Examples 151 to 156, wherein said plurality of layers comprise a plurality of layers of magnesium fluoride.

Example 158: The method of any of Examples 151 to 157, wherein said plurality of layers comprise alternating layers of material.

Example 159: The method of any of Examples 151 to 158, wherein said plurality of layers comprise repeating layers of material.

Example 160: The method of any of Examples 151 to 159, wherein said plurality of layers reduce reflection from said substrate.

Example 161: The method of any of Examples 151 to 160, further comprising removing said patternable material and retaining said plurality of layers as a least part of diffractive features.

Example 162: The method of any of Examples 150 to 159, further comprising removing said patternable material and retaining said plurality of layers as diffractive features on said substrate, said substrate not including corresponding diffractive features etched therein.

Example 163: The method of Example 161 or 162, wherein said diffractive features have the same height with respect to the substrate.

Example 164: The method of Example 161 or 162, wherein said different of said diffractive features have the different heights with respect to the substrate.

Example 165: The method of Example 164, wherein said different of said diffractive features have different heights with respect to the substrate such that the height increases progressively with lateral position along said substrate.

Example 166: The method of any of Examples 1-41 and 47-108, further including a first layer comprising material having a refractive index less than 1.8 over the substrate.

Example 167: The method of Example 166, wherein said first layer comprises resist.

Example 168: The method of Example 166 or 167, further including a second layer comprising material having a refractive index at least 1.8 over the first layer.

Example 169: The method of Example 168, wherein said second layer comprises TiO₂.

Example 170: The method of Example 168, wherein said second layer comprises ZrO₂.

Example 171: The method of Example 168, wherein said second layer comprises Si₃N₄.

Example 172: The method of Example 168, wherein said second layer comprises SiC.

Example 173: The method of any of Example 168 to 172, wherein said second layer is deposited using glancing angle deposition.

Example 174: The method of any of Example 168 to 173, wherein said second layer is primarily over surfaces parallel to said substrate.

Example 175: The method of any of Example 168 to 173, wherein the material of said second layer on sidewalls of said first layer is negligible.

Example 176: The method of any of Example 168 to 172, wherein said material of said second layer is on both horizontal and vertical surfaces.

Example 175: The method of any of Example 168 to 173, wherein the material of said second layer is more on a first side of features of the first layer than on a second side of features of the first layer.

Example 176: The method of any of Examples 1-41 and 47-108, further including one or more reflection mitigating layers over the diffractive optical element.

Example 177: The method of Example 176, wherein the one or more reflection mitigating layers comprises material having a refractive index less than the refractive index of the material of the waveguide.

Example 178: The method of Example 176, wherein the one or more reflection mitigating layers comprises material having a refractive index between 1.2 and 1.7.

Example 179: The method of Example 176, wherein the one or more reflection mitigating layers comprises magnesium fluoride.

Example 180: The method of Example 176 or 179, wherein the one or more reflection mitigating layers comprises silicon dioxide.

Example 181: The method of any of Example 176, 179, or 180, wherein the one or more reflection mitigating layers comprises resist.

Example 182: The method of any of Examples 176 to 181, wherein a plurality of reflection mitigating layers are disposed over the diffractive optical element.

Example 183: The method of Example 182, wherein one of the reflection mitigating layers farther away from the substrate has lower refractive index than one of the reflection mitigation layers closer to the substrate.

Example 184: The method of Example 182, wherein a reflection mitigating layer farthest from the substrate has a lower index of refraction than a reflection mitigating layer closest to the waveguide and one or more reflection mitigating layers between the reflection mitigating layer farthest from the substrate and the reflection mitigating layer closest to the substrate has an index of refraction between that of the reflection mitigating layer farthest from the substrate and the reflection mitigating layer closest to the substrate.

Example 185: The method of any of Examples 176 to 184, wherein the one or more reflection mitigating layers is deposited using glazing angle deposition.

Example 186: The method of any of Examples 176 to 185, wherein sidewalls and trenches of the diffractive optical element comprise negligible amounts of material of the one or more reflection mitigating layer.

Example 187: The method of any of Examples 176 to 184, wherein material of the reflection mitigating layer is deposited on top surfaces of the plurality of diffractive features of the diffractive optical element that are parallel to the surface of the substrate and the surfaces of trenches of the diffractive optical element, and wherein sidewalls of the diffractive optical element comprise negligible amounts of material of the reflection mitigating layers.

Example 188: The method of any of Examples 176 to 184, wherein material of the reflection mitigating layer is deposited both on horizontal and vertical exposed surfaces of the plurality of features of the optical element.

Example 189: The method of any of Examples 176 to 188, wherein the reflection mitigating layer on the diffractive optical element is planarized.

Example 190: The method of any of Examples 176 to 189, further including a structural stability providing layer disposed over the one or more reflection mitigating layer to increase structural stability.

Example 191: The method of Example 190, wherein the structural stability providing layer comprises glass.

Example 192: The method of Example 190, wherein the structural stability providing layer comprises glass having an anti-reflective coating thereon.

Example 193: The method of Example 192, wherein the anti-reflective coating on the glass comprises alternating layers.

Example 194: The method of Example 193, wherein anti-reflective coating on the glass comprises alternating layers of TiO₂and SiO₂.

Example 195: The method of any of Examples 176 to 194, further including an additional layer between the reflection mitigating layer and the diffractive features of the diffractive optical element.

Example 196: The method of any of Examples 1-41 and 47-108, further including an anti-reflective structure disposed over the diffractive optical element, the anti-reflective structure comprising nano-structure configured to reduce reflection.

Example 197: The method of Example 196, wherein the nano-structure is directly on the diffractive optical element.

Example 198: The method of Example 196, wherein the nano-structure is formed in a coating disposed over the diffractive optical element.

Example 199: The method of Examples 198, wherein the coating has a refractive index lower than that of the substrate.

Example 200: The method of Example 198 or 199, wherein the coating comprises photoresist.

Example 201: The method of any of Examples 1-41 and 47-108, further including reflective gratings disposed at an edge of the substrate to receive light propagating to the edge of the substrate by total internal reflection within the substrate.

Example 202: The method of Example 201, wherein the reflective gratings are configured to redirect light back away from the edge.

Example 203: The method of Example 201 or 202, wherein the reflective gratings are configured to direct light back toward an exit pupil expander configured to couple light out of the substrate to a user.

Example 204: The method of Example 203, wherein the exit pupil expander comprises a diffractive optical element having a pitch and the reflective gratings have a pitch that is about half the pitch of the exit pupil expander.

Example 205: The method of any of Examples 201-204, wherein the reflective gratings are metalized.

Example 206: The method of any of Examples 1-41 and 47-108, further including light extracting features disposed at an edge of the substrate to receive light propagating to the edge of the substrate by total internal reflection within the substrate.

Example 207: The method of Example 206, wherein the light extracting features are configured to extract light out from the edge.

Example 208: The method of Example 206 or 207, wherein the light extracting features comprise diffractive features.

Example 209: The method of any of Examples 206 to 208, further including an absorbing element disposed about said edge to receive light extracted by said light extracting features.

Example 210: The method of Example 209, wherein said absorbing element comprises a cuff, collar, cup, or sleeve.

Example 211: The method of Example 209 or 210, wherein said absorbing element comprises carbon black.

Example 212: The method of any of Example 206 to 208, further comprising comprise an absorbing coating on said light extracting features.

Example 213: The method of any of Examples 1-41 and 47-108, further including at least one structural support layer with said substrate to provide increased structural strength.

Example 214: The method of Examples 213, wherein said at least one structural support layer comprises material having a refractive index of less than or equal to 1.7.

Example 215: The method of Examples 213 or 214, wherein at least one said structural support layer comprises glass.

Example 216: The method of Examples 215, wherein at least one said structural support layer comprises glass having an anti-reflective coating thereon.

Example 217: The method of any of Examples 213 to 216, wherein the at least said structural support layer is directly adjacent the substrate.

Example 218: The method of any of Examples 213 to 217, wherein the at least one said structural support layer fills in spaces between the plurality of diffractive features of the diffractive optical element.

Example 219: The method of any of Examples 213 to 216, further including air between said at least one structural support layer and said substrate.

Example 220: The method of any of Examples 213 to 216 and 219, further including air between said at least one structural support layer and said plurality of diffractive features.

Example 221: The method any of Examples 213 to 216 and 219 and 220, further including spacers between said at least one structural support layer and said substrate to provide air gaps between said at least one structural support layer and said substrate.

Example 222: The method of any of Examples 213 to 216 and 219 to 221, further including forming air gaps comprises evaporating a polymer layer.

Example 223: The method of any of Examples 213 to 222, wherein at least one said structural support layer provides anti-scratch functionality.

Example 224: The method of any of Examples 213 to 223, wherein at least one said structural support layer comprises a low index coating.

Example 225: The method of any of Examples 213 to 224, wherein at least one said structural support layer comprises an anti-reflective glass.

Example 226: The method of any of Examples 213 to 225, wherein at least one said structural support layer is disposed on one side of said substrate.

Example 227: The method of any of Examples 213 to 226, wherein said structural support layers comprises at least two structural support layers.

Example 228: The method of Examples 227, wherein said at least two structural support layers are disposed on opposite sides of said substrate.

Example 229: The method of any of Examples above, wherein said diffractive features are between 10 and 50 nm in height.

Example 230: The method of any of Examples above, wherein said diffractive features comprise material having an index of at least 1.8, said material being different from the material of said substrate.

Example 231: The method of any of Examples above, further including a planarization layer over said diffractive features.

Example 232: The method of Examples 231, wherein the planarization layer has an index of refraction less than 1.6.

Example 233: The method of any of Examples above, further including an anti-reflective coating on the opposite side of the substrate as the diffractive optical element.

Example 234: The method of any of Examples above, wherein said substrate is tinted.

Example 235: The method of any of Examples above, wherein first and second diffractive optical elements are disposed on first and second opposite faces of the waveguide.

Example 236: The method of Example 235, wherein the plurality of diffractive features of the first diffractive optical element are offset from the plurality of diffractive features of the second diffractive optical element.

Example 237: The method of any of Examples above, wherein said diffractive features have varying height.

Example 238: The method of any of Examples above, wherein said diffractive features have height that varies progressively with lateral position across said substrate.

Example 239: The method of any of Examples above, wherein said substrate comprises a waveguide.

Example 240: The method of Example 239, wherein said waveguide in included in an eyepiece for a head mounted display.

Example 241: The method of Example 239, wherein said waveguide in included in a stack of waveguides in an eyepiece for a head mounted display.

Example 242: The method of Example 240 or 241, wherein said eyepiece is transparent to provide the user a view of the environment in front of the user and the head mounted display.

Example 243: The method of Example 240, 241 or 242, wherein said eyepiece is configured to receive light from an image projector and to direct at least a portion of said light to an eye of the user to direct image content to said eye of the user.

Example 244: The method of Example 240, 241, 242 or 243, wherein said eyepiece is mounted on a frame configured to be worn on the head of a user.

Example 245: A device formed by any of the methods in any of Examples above.

Example 246: A device of Example 245, wherein the plurality of diffractive features or features form a diffraction grating and said diffracting grating is a blazed grating.

Example 247: The optical device of any of the Examples above, wherein the plurality of diffractive features or features are asymmetrical so as to provide for a blazed grating.

Example 248: The optical device of any of the Examples above, wherein the plurality of diffractive features or features have material asymmetrically deposited thereon so as to provide for a blazed grating.

Example 249: The optical device of any of the Examples above, wherein said substrate includes first and second sides and only said first side of said substrate includes a diffraction grating.

Example 250: The optical device of any of the Examples above, wherein the diffractive features or features are arranged in a 1D array.

Example 251: The optical device of any of the Examples above, wherein the diffractive features or features are arranged in a 2D array.

Example 252: The optical device of Example 251, wherein the 2D array comprises a square array.

Example 253: The optical device of any of the Examples above, wherein said at least part of an etching mask remains on said diffractive features.

Example 254: The optical device of any of the Examples above, wherein said polymer remains on said diffractive features thereby increasing the height of said diffractive features.

Example 255: The optical device of any of the Examples above, wherein resist remains on said diffractive features.

Example 256: The method of any of the Examples above, further comprising leaving at least a portion of the patternable material on said diffractive features.

Example 257: The method of any of the Examples above, further comprising leaving at least part of an etching mask on said diffractive features.

Example 258: The method of any of the Examples above, further comprising leaving polymer on said diffractive features thereby increasing the height of the diffractive features.

Example 259: The method of any of the Examples above, further comprising leaving resist on said diffractive features thereby increasing the height of the diffractive features.

Example 260: The method of any of the Examples above, wherein the diffractive features are formed in a 1D array.

Example 261: The method of any of the Examples above, wherein the diffractive features are formed in a 2D array.

Example 262: The optical device of Example 261, wherein the 2D array comprises a square array.

Example 263: The method of any of the Examples above, wherein the diffractive features form a 1D diffraction grating.

Example 264: The method of any of the Examples above, wherein the diffractive features are formed in a 2D diffraction grating.

Example 265: The method of any of the Examples above, wherein the diffractive features are blazed.

Example 266: The method of any of the Examples above, wherein the diffractive features are asymmetrical so as to provide for a blazed grating.

Example 267: The method of any of the Examples above, wherein the plurality of diffractive features have material asymmetrically deposited thereon so as to provide for a blazed grating.

Example 268: The optical device of any of the Examples above, wherein said substrate includes first and second sides and only said first side of said substrate includes a diffraction grating.

Example 269: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an in-coupling optical element disposed so as to receive light from an image source and couple said light into said substrate to be guided therein.

Example 270: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and direct said light to an out-coupling optical elements to be coupled out of said substrate.

Example 271: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and spread said light within said waveguide out to increase beam size or eye box size.

Example 272: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate and couple said light out of said substrate.

Example 273: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in a combined light distributing/out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate, spread said light out in at least two directions and couple said light out of said substrate.

Example 274: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in a combined pupil expander-extractor disposed so as to receive light from an image source that is guided in said substrate, spread said light out and couple said light out of said substrate.

Example 275: The optical device of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating configured to direct light preferentially in at least two directions.

Example 276: The optical device of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating blazed in two directions.

Example 277: The method of any of the Examples above, wherein said plurality of diffractive features are included in an in-coupling optical element disposed so as to receive light from an image source and couple said light into said substrate to be guided therein.

Example 278: The method of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and direct said light to an out-coupling optical elements to be coupled out of said substrate.

Example 279: The method of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and spread said light within said waveguide out to increase beam size or eye box size.

Example 280: The method of any of the Examples above, wherein said plurality of diffractive features are included in an out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate and couple said light out of said substrate.

Example 281: The method of any of the Examples above, wherein said plurality of diffractive features are included in a combined light distributing/out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate, spread said light out in at least two directions and couple said light out of said substrate.

Example 282: The method of any of the Examples above, wherein said plurality of diffractive features are included in a combined pupil expander-extractor disposed so as to receive light from an image source that is guided in said substrate, spread said light out and couple said light out of said substrate.

Example 283: The method of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating configured to direct light preferentially in at least two directions.

Example 284: The method of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating blazed in two directions.

Part II

Example 1: An optical device comprising:

- a substrate comprising a material having a refractive index greater than 2.0 that is a transparent to visible light, said substrate comprising a waveguide;
- a plurality of diffractive features formed in said substrate; and
- a layer of material disposed over said diffractive features.

Example 2: The optical device of Example 1, wherein said substrate material comprises lithium niobate or silicon carbide.

Example 3: The optical device of any of the Examples above, wherein said substrate material has an index of refraction that is at least 2.1.

Example 4: The optical device of any of the Examples above, wherein said substrate material has an index of refraction that is at least 2.2.

Example 5: The optical device of any of the Examples above, wherein said substrate material has an index of refraction that is at least 2.3.

Example 6: The optical device of any of the Examples above, wherein said layer of material has an index of refraction that is less than 1.8.

Example 7: The optical device of any of the Examples above, wherein said layer of material comprises photoresist.

Example 8: The optical device of any of the Examples above, wherein said diffractive features are separated by spaces and said spaces comprise exposed regions of said substrate material.

Example 9: The optical device of any of the Examples above, wherein said diffractive features are separated by spaces and said spaces between said diffractive features not covered by said layer of material.

Example 10: The optical device of any of the Examples above, wherein said diffractive features are separated by spaces and said spaces between said diffractive features comprise exposed regions of said substrate material.

Example 11: The optical device of any of the Examples above, wherein said plurality of diffractive features comprise first, second, and third diffractive features laterally displaced with respect to each other, said second diffractive feature disposed between the first and the third diffractive features.

Example 12: The optical device of Example 11, wherein said layer of material has a different thickness over each of said first, second, and third diffractive features.

Example 13: The optical device of Example 11 or 12, wherein the thickness of said layer of material over said third diffractive feature is higher than the thickness of said layer of material over said second diffractive feature, and the thickness of said layer of material over said second diffractive feature is higher than the thickness of said layer of material over said first diffractive feature.

Example 14: The optical device of Example 11, wherein said layer of material has the same thickness over said first, second, and third diffractive features.

Example 15: The optical device of any of the Examples 11-14, wherein the height of the of said third diffractive feature is higher than the height of said second diffractive feature, and the height of said second diffractive feature is higher than the height of said first diffractive feature.

Example 16: The optical device of any of the Examples above, wherein the height of the diffractive features progressively increases with lateral position.

Example 17: The optical device of any of the Examples above, wherein said layer of material has a thickness that progressively increases with lateral position.

Example 18: The optical device of any of the Examples above, wherein the thickness of said substrate is graded.

Example 19: The optical device of any of the Examples above, wherein the thickness of said layer of material is graded.

Example 20: The optical device of any of the Examples above, wherein the thickness of said substrate progressively increases with lateral position.

Example 21: The optical device of any of the Examples above, wherein the height of the diffractive features is substantially constant with lateral position.

Example 22: The optical device of any of the Examples above, wherein the height of said first, second, and third diffractive feature are the same.

Example 23: The optical device of any of the Examples above, wherein said layer of material has a thickness that is substantially constant with lateral position.

Example 24: The optical device of any of the Examples above, wherein said layer of material has the same thickness over said first, second, and third diffractive features.

Example 25: The optical device of any of the Examples above, wherein at least some of the diffractive features have sloping sidewalls.

Example 26: The optical device of any of the Examples above, wherein at least some of the diffractive features have a trapezoidal cross-section.

Example 27: The optical device of any of the Examples above, wherein said waveguide in included in an eyepiece for a head mounted display.

Example 28: The optical device of any of the Examples above, wherein said waveguide in included in a stack of waveguides in an eyepiece for a head mounted display.

Example 29: The optical device of Example 27 or 28, wherein said eyepiece is transparent to provide the user a view of the environment in front of the user and the head mounted display.

Example 30: The optical device of any of Examples 27-29, wherein said eyepiece is configured to receive light from an image projector and to direct at least a portion of said light to an eye of the user to direct image content to said eye of the user.

Example 31: The optical device of any of Examples 27-30, wherein said eyepiece is mounted on a frame configured to be worn on the head of a user.

Example 32: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an in-coupling optical element disposed so as to receive light from an image source and couple said light into said substrate to be guided therein.

Example 33: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate and couple said light out of said substrate to an eye of a user wearing said head mounted display.

Example 34: The optical device of any of Examples 27-33, wherein said plurality of diffractive features comprise first, second, and third diffractive features, said second diffractive feature disposed between the first and the third diffractive features.

Example 35: The optical device of Example 35, wherein the height of the of said third diffractive feature is higher than the height of said second diffractive feature, and the height of said second diffractive feature is higher than the height of said first diffractive feature.

Example 36: The optical device of Examples 34 or 35, further comprising a projector disposed with respect to the substrate to direct light into the substrate, said projector positioned closer to said first diffractive features than said second diffractive features.

Example 37: The optical device of any of the Examples above, wherein the height of the diffractive features progressively increases with lateral position.

Example 38: The optical device of Example 37, further comprising a projector disposed with respect to the substrate to direct light into the substrate, said projector positioned closer to said diffractive features with lower heights that to said diffractive features with higher heights.

Example 39: The optical device of any of Examples 34-38, wherein the thickness of said layer of material on said third diffractive feature is higher than the thickness of said layer of material on said second diffractive feature, and the thickness of said layer of material on said second diffractive feature is higher than the thickness of said layer of material on said first diffractive feature.

Example 40: The optical device of Example 39, further comprising a projector disposed with respect to the substrate to direct light into the substrate, said projector positioned closer to said first diffractive features than said second diffractive features.

Example 41: The optical device of any of the Examples above, wherein said layer of material has a thickness that progressively increases with lateral position.

Example 42: The optical device of any of the Examples above, further comprising a projector disposed with respect to the substrate to direct light into the substrate, said projector positioned closer to said diffractive features wherein said layer of material is thinner than to said diffractive features wherein said layer of material is thicker.

Example 43: The optical device of any of the Examples above, wherein said substrate comprises opposite first and second sides.

Example 44: The optical device of Example 43, wherein said optical device is integrated in a head mounted display, and said second side is disposed closer to a wearer's eye when said head mounted display is worn than said first side.

Example 45: The optical device of Example 43 or 44, wherein said plurality of diffractive feature are disposed on said first side of said substrate.

Example 46: The optical device of any of Examples 43-45, further comprising an additional plurality of diffractive features formed in said substrate on the second opposite side of said substrate.

Example 47: The optical device of Example 46, wherein said additional plurality of diffractive features are separated by spaces, said optical device further comprising an additional layer of material disposed over said plurality of additional diffractive features.

Example 48: An optical device comprising:

- a substrate comprising a material having a refractive index greater than 2.0 that is transparent to visible light, said substrate comprising a waveguide;
- a plurality of diffractive features formed on said substrate, said diffractive features formed of a different material having an index of refraction less than the material of said substrate; and
- higher index material disposed over said diffractive features, said higher index material having a higher index than said material forming said diffractive features.

Example 49: The optical device of Example 48, wherein said substrate material comprises lithium niobate or silicon carbide.

Example 50: The optical device of Example 48 or 49, wherein said material comprising said substrate has an index of refraction that of at least 2.1.

Example 51: The optical device of any of the Examples 48-50, wherein said material comprising said substrate has an index of refraction that of at least 2.2.

Example 52: The optical device of any of the Examples 48-50, wherein said material comprising said substrate has an index of refraction that of at least 2.3.

Example 53: The optical device of any of the Examples 48-52, wherein said plurality of diffractive features comprises photoresist.

Example 54: The optical device of any of the Examples 48-53, wherein said plurality of diffractive features have an index of refraction that is less than 1.8.

Example 55: The optical device of any of the Examples 48-54, wherein said plurality of diffractive features have an index of refraction of about 1.5.

Example 56: The optical device of any of the Examples 48-55, wherein said plurality of diffractive features have an index of refraction of between 1.7 and 1.8.

Example 57: The optical device of any of the Examples 48-56, wherein said higher index material disposed over said diffractive features has an index of refraction of at least 2.1.

Example 58: The optical device of any of the Examples 48-57, wherein said higher index material disposed over said diffractive features has an index of refraction of at least 2.2.

Example 59: The optical device of any of the Examples 48-58, wherein said higher index material disposed over said diffractive features has an index of refraction of at least 2.3.

Example 60: The optical device of any of the Examples 48-59, wherein said higher index material disposed over said diffractive features comprises lithium niobate.

Example 61: The optical device of any of the Examples 48-59, wherein said higher index material disposed over said diffractive features comprises silicon carbide.

Example 62: The optical device of any of the Examples 48-61, wherein said plurality of diffractive features comprises a blazed diffractive grating.

Example 63: The optical device of any of the Examples 48-62, wherein said plurality of diffractive features are asymmetrically shaped.

Example 64: The optical device of any of the Examples 48-63, wherein more of said high index material is on a first sidewall of diffractive features than on a second sidewall of the diffractive features.

Example 65: The optical device of any of the Examples 48-64, wherein more of said high index material is on a first side of diffractive features than on a second side of the diffractive features.

Example 66: The optical device of any of the Examples 48-64, wherein at least one of said diffractive features has said high index material on a first side of diffractive features while said second side of the diffractive features are exposed.

Example 67: The optical device of any of the Examples above, wherein the diffractive features are arranged in a 1D array.

Example 68: The optical device of any of the Examples above, wherein the diffractive features are arranged in a 2D array.

Example 69: The optical device any of Examples 1-47, wherein the diffractive features have a top surface and sidewalls disposed about said top surface, and wherein the layer of material is on said top surface of said diffractive features.

Example 70: The optical device of Example 47, wherein said additional plurality of diffractive features have a top surface and sidewalls disposed about said top surface, and wherein said additional layer of material is on said top surface of said plurality of additional diffractive features.

Example 71: The optical device of any of Examples 48-68, wherein said diffractive features have a top surface and sidewalls disposed about said top surface, and wherein said higher index material is on said top surface of said diffractive features.

Example 72: The optical device of any of Examples 48-68, wherein said waveguide in included in an eyepiece for a head mounted display.

Example 73: The optical device of any of Examples 48-68, wherein said waveguide in included in a stack of waveguides in an eyepiece for a head mounted display.

Example 74: The optical device of Example 72 or 73, wherein said eyepiece is transparent to provide the user a view of the environment in front of the user and the head mounted display.

Example 75: The optical device of any of Examples 72-74, wherein said eyepiece is configured to receive light from an image projector and to direct at least a portion of said light to an eye of the user to direct image content to said eye of the user.

Example 76: The optical device of any of Examples 72-75, wherein said eyepiece is mounted on a frame configured to be worn on the head of a user.

Example 77: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an in-coupling optical element disposed so as to receive light from an image source and couple said light into said substrate to be guided therein.

Example 78: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate out of said substrate to an eye of a user wearing said head mounted display.

Example 79: The optical device of any of the Examples 1-47, wherein said layer of material comprises polymer.

Example 80: The optical device of any of the Examples 1-47, wherein said layer of material comprises resist.

Example 81: The optical device of any of the Examples 1-47, wherein said layer of material comprises at least part of an etching mask.

Example 82: The optical device of any of the Examples 1-47, wherein said layer of material reduces reflection.

Example 83: The optical device of any of the Examples 1-82, wherein the plurality of diffractive features form a diffraction grating and said diffracting grating is a blazed grating.

Example 84: The optical device of any of the Examples above, wherein the plurality of diffractive features are asymmetrical so as to provide for a blazed grating.

Example 85: The optical device of any of the Examples above, wherein the plurality of diffractive features have material asymmetrically deposited thereon so as to provide for a blazed grating.

Example 86: The optical device of any of the Examples above, wherein said substrate includes first and second sides and only said first side of said substrate includes a diffraction grating.

Example 87: The optical device of any of the Examples 1-86, wherein the diffractive features are arranged in a 1D array.

Example 88: The optical device of any of the Examples 1-86, wherein the diffractive features are arranged in a 2D array.

Example 89: The optical device of Example 88, wherein the 2D array comprises a square array.

Example 90: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an in-coupling optical element disposed so as to receive light from an image source and couple said light into said substrate to be guided therein.

Example 91: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and direct said light to an out-coupling optical elements to be coupled out of said substrate.

Example 92: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an light distributing optical element disposed so as to receive light from an image source that is guided in said substrate and spread said light within said waveguide out to increase beam size or eye box size.

Example 93: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in an out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate and couple said light out of said substrate.

Example 94: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in a combined light distributing/out-coupling optical element disposed so as to receive light from an image source that is guided in said substrate, spread said light out in at least two directions and couple said light out of said substrate.

Example 95: The optical device of any of the Examples above, wherein said plurality of diffractive features are included in a combined pupil expander-extractor disposed so as to receive light from an image source that is guided in said substrate, spread said light out and couple said light out of said substrate to an eye of a user wearing said head mounted display.

Example 96: The optical device of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating configured to direct light preferentially in at least two directions.

Example 97: The method of any of the Examples above, wherein said plurality of diffractive features comprise a blazed diffraction grating blazed in two directions.

Part III