Global or local thickness variations for optical devices

Abstract

Embodiments of the present disclosure generally relate to a method for forming a waveguide. The method may include measuring a waveguide substrate, wherein the waveguide has a substrate thickness distribution, and depositing an index-matching layer on a face of the waveguide, the index-matching layer having a first face disposed on the waveguide substrate and a second face opposite the first face, wherein the index-matching layer is disposed on only a portion of the waveguide substrate, and wherein a device slope of the second face of the index-matching layer is substantially the same as a waveguide slope of the first face of the waveguide.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to substrates. More particularly, embodiments described herein provide for forming a substrate having a thickness distribution across the substrate in one or more eyepiece areas. [Background technology]

[0002] Virtual reality is generally considered to be a computer-generated simulated environment in which a user has an apparent physical presence. Virtual reality experiences are generated in 3D and may be viewed using a head-mounted display (HMD), such as glasses or other wearable display devices, that have a near-eye display panel as a base eyepiece for displaying the virtual reality environment that replaces the real environment.

[0003] However, augmented reality allows for an experience in which a user can still look through the substrate eyepieces of glasses or other HMD devices to view the surrounding environment and also see images of virtual objects that are generated for display and appear as part of that environment. Augmented reality can include any type of input, such as audio and haptic input, as well as virtual images, graphics, and video, that enhance or extend the environment the user experiences. As an emerging technology, there are many challenges and design constraints for augmented reality.

[0004] Therefore, what is needed in the art is a method for forming a substrate having a thickness distribution across the substrate in one or more eyepiece areas. Summary of the Invention

[0005] A waveguide is shown and described herein that may include a waveguide substrate, the waveguide having a substrate thickness profile, and an index-matched layer disposed on the waveguide substrate and having a first surface and a second surface opposite the first surface, the index-matching layer being disposed over a portion of the waveguide substrate, and a device slope of the second surface of the index-matching layer being substantially the same as the waveguide slope of the first surface of the waveguide.

[0006] A waveguide is shown and described herein that may include a waveguide substrate, the waveguide having a substrate thickness distribution, and an index-matching layer having a first surface and a second surface opposite the first surface disposed on the waveguide substrate, the index-matching layer being disposed over a portion of the waveguide substrate, and a device slope of the second surface of the index-matching layer having a slope value configured to vary the substrate thickness distribution across the index-matching layer.

[0007] A method for forming a waveguide is shown and described herein, which may include measuring a waveguide substrate, the waveguide having a substrate thickness distribution, and depositing an index-matching layer on a face of the waveguide, the index-matching layer having a first face disposed on the waveguide substrate and a second face opposite the first face, the index-matching layer being disposed on only a portion of the waveguide substrate, and a device slope of the second face of the index-matching layer being substantially the same as the waveguide slope of the first face of the waveguide.

[0008] So that the above-recited features of the present disclosure may be understood in detail, a more particular description of the present disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only exemplary embodiments and therefore should not be considered limiting of its scope, as other equally effective embodiments may be recognized. [Brief explanation of the drawings]

[0009] [Figure 1A-1B] 1 is a schematic plan view of a substrate, according to an embodiment. [Figure 2A] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 2B] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 2C] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 3A] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 3B] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 3C] 1 is a schematic cross-sectional view of a substrate having a substrate thickness distribution. [Figure 4] 1 is a flow diagram of a method for forming a waveguide. DETAILED DESCRIPTION OF THE INVENTION

[0010] For ease of understanding, where possible, like reference numerals have been used to designate like elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

[0011] The embodiments described herein relate to methods for forming a substrate having a thickness distribution across the substrate in one or more eyepiece areas, see attached appendix.

[0012] FIG. 1A is a schematic plan view of a substrate 100 according to embodiments described herein. The substrate 100 includes a plurality of waveguides 101. The waveguides 101 are areas on the substrate 100 in which the waveguides 101 will be formed. In some cases, the waveguides 101 may be substrate eyepieces. Although only nine of the waveguide areas 101 are shown in FIG. 1A, the substrate 100 is not limited in the number of waveguides 101 that will be formed thereon. FIG. 1B is a perspective front view of the substrate 100. It should be understood that the substrate 100 described herein is an exemplary substrate, and other substrates may be used with or modified to achieve aspects of the present disclosure.

[0013] The substrate 100 includes a plurality of substrate structures 102 disposed on a surface 103 of the waveguide 101. The substrate structures 102 may be nanostructures having submicron dimensions, e.g., nano-sized dimensions. Regions of the substrate structures 102 correspond to one or more gratings 104, such as a first grating 104a, a second grating 104b, and a third grating 104c, each having one or more index-matching layers 106. In one embodiment that may be combined with other embodiments described herein, the substrate 100 includes at least a first grating 104a corresponding to an input coupling grating including an index-matching layer 106A and a third grating 104c corresponding to an output coupling grating including an index-matching layer 106B. In one embodiment that may be combined with other embodiments described herein, the substrate 100 also includes a second grating 104b corresponding to an intermediate grating including an index-matching layer 106B. The substrate structures 102 may be angled or binary. The substrate structure 102 may have other shapes, including, but not limited to, circular, triangular, elliptical, regular polygonal, irregular polygonal, and / or irregularly shaped cross-sections.

[0014] In operation, the input-coupling grating receives an incident beam of light (a virtual image) having a certain intensity from the microdisplay. The incident beam is split by the substrate structure 102 into a T1 beam having all of the intensity of the incident beam to direct the virtual image to the intermediate grating (if utilized) or the output-coupling grating. In one embodiment, which may be combined with other embodiments described herein, the T1 beam undergoes total internal reflection (TIR) ​​through the substrate 100 until it contacts the intermediate grating substrate structure 102. The intermediate grating substrate structure 102 diffracts the T1 beam into a T-1 beam, which undergoes TIR through the substrate 100 to the output-coupling grating substrate structure 102. The output-coupling grating substrate structure 102 outcouples the T-1 beam to the user's eye, adjusting the field of view of the virtual image created from the microdisplay from the user's perspective and further increasing the viewing angle at which the user can view the virtual image. In another embodiment, which may be combined with other embodiments described herein, the T1 beam undergoes total internal reflection (TIR) ​​through the substrate 100 until the T1 beam contacts the substrate structure 102 of the output coupling grating and is output coupled to adjust the field of view of the virtual image produced from the microdisplay.

[0015] 2A, 2B, and 2C are schematic cross-sectional views of a substrate 200 having a first substrate thickness distribution 202 and a second substrate thickness distribution 204. The substrate 200 includes the waveguide 101 of FIG. 1 disposed across the substrate 200. Inactive areas 214 are disposed between the index-matching layers 106. The inactive areas 214 are areas of the substrate 200 over which one of the index-matching layers 106 will not be formed. The substrate 200 includes a base substrate 206 having a top surface 212 and a bottom surface 213.

[0016] The base substrate 206 may be formed from any suitable material, provided that the substrate 200 can adequately transmit light at the desired wavelength or wavelength range and can serve as sufficient support for the index-matching layer 106. The base substrate may be a material including, but not limited to, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, silicon oxides, polymers, and combinations thereof. In some embodiments, which may be combined with other embodiments described herein, the base substrate 206 comprises a transparent material. In one example, the base substrate 206 and / or the index-matching layer 208 comprises silicon (Si), silicon dioxide (SiO), fused silica, quartz, silicon carbide (SiC), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), sapphire, or a combination thereof.

[0017] At least the index-matching layer 106 of the substrate 200 includes one of a first target thickness distribution 202 or a second target thickness distribution 204. The first target thickness distribution 202 and the second target thickness distribution 204 are local thickness distributions determined to be replicated in each of the waveguides 101. The first target thickness distribution 202 and the second target thickness distribution 204 are defined by the distance between the top surface 212 and the bottom surface 213 of the substrate 200 across the waveguide 101. In FIG. 2A , the first target thickness distribution 202 and the second target thickness distribution 204 are determined by a device slope on the top surface 212 of the substrate, which is substantially the same as the waveguide slope on the bottom surface 213. The device slope can be achieved by depositing the index-matching layer 106 on at least a portion of the bottom surface 213. 2B and 2C, the first target thickness distribution 202 and the second target thickness distribution 204 are determined by a device slope on the bottom surface 213 of the substrate, which is substantially the same as the waveguide slope on the top surface 212. The device slope may be achieved by depositing an index-matching layer 106 on at least a portion of the top surface 212.

[0018] In FIG. 2A , the device tilt is the tilt of the bottom surface 216 of the index-matching layer 106 deposited to achieve at least one of the first target thickness distribution 202 or the second target thickness distribution 204. The waveguide tilt is the tilt of the top surface 212 of the base substrate 206. To achieve the first target thickness distribution 202 or the second target thickness distribution 204, the device tilt is matched to the waveguide tilt of the top surface 212 of the base substrate 206. Specifically, the device tilt at any given point on the bottom surface 216 is matched to the waveguide tilt at a point on the top surface 212 directly below the given point on the top surface 216. In FIGS. 2B and 2C , the device tilt is the tilt of the top surface 217 of the index-matching layer 106 deposited to achieve at least one of the first target thickness distribution 202 or the second target thickness distribution 204. The waveguide tilt is the tilt of the bottom surface 213 of the base substrate 206. To achieve the first target thickness distribution 202 or the second target thickness distribution 204, the device tilt is matched to the waveguide tilt of the bottom surface 213 of the base substrate 206. Specifically, the device tilt at any given point on the top surface 217 is matched to the waveguide tilt at a point on the bottom surface 213 directly below the given point on the top surface 217. By matching the device tilt of the index-matching layer 106 to the waveguide tilt of the base substrate surface disposed directly above or below the index-matching layer 106, the first target thickness distribution 202 or the second target thickness distribution 204 can be achieved uniformly.

[0019] The inactive areas 214 of the substrate 200 have an inactive thickness distribution 220, i.e., the inactive thickness distribution 220 does not substantially match the first target thickness distribution 202 or the second target thickness distribution 204. The inactive thickness distribution 220 is defined by the distance between the top surface 212 and the bottom surface 213 of the inactive areas 214 across the inactive areas 214. The first target thickness distribution 202 and the second target thickness distribution 204 are formed from the base substrate 206 of the substrate 200 in each index matching layer 106. In FIG. 2A , the first target thickness distribution 202 and the second target thickness distribution 204 are formed from the top surface 212 to the bottom surface 216 of the index matching layer 106. In FIGS. 2B and 2C , the first target thickness distribution 202 and the second target thickness distribution 204 are formed from the bottom surface 213 to the top surface 217 of the index matching layer 106.

[0020] The first target thickness distribution 202 and the second target thickness distribution 204 are designed to improve the performance of the substrate index-matching layer 106 to be formed thereon. The first target thickness distribution 202 and the second target thickness distribution 204 are the same in at least each waveguide 101 of the substrate 200. The methods and apparatus described herein provide the first target thickness distribution 202 and the second target thickness distribution 204 to be achieved in at least each waveguide 101. In one example, matching the device tilt to the corresponding wave tilt for depositing a given index-matching layer 106 can enable a substantially uniform target thickness distribution. The first target thickness distribution 202 and the second target thickness distribution 204 are not limited to the first target thickness distribution 202 and the second target thickness distribution 204 shown in FIGS. 2A-2C and can be any thickness distribution that is suitable and determined to improve the performance of the substrate index-matching layer 106.

[0021] At least the index matching layer 106 of the substrate 200 may include a grating structure 218. In FIG. 2A, at least one grating may be formed where the grating structure 218 is in the index matching layer 106. In FIG. 2B, at least one grating may be formed where the grating structure 218 is on the bottom surface 213 of the base substrate 206. In FIG. 2C, at least one grating may be formed where the grating structure 218 is disposed on the top surface 217 of the index matching layer 106. The grating structure 218 may be disposed vertically or diagonally. The grating structure 218 may form at least one grating, which may be a pupil expansion grating, an input coupler grating, an output coupler grating, etc.

[0022] Although Figures 2A-2C show a base substrate 206 in which the distance between the bottom surface 213 and the top surface 212 of the base substrate 206 varies across the base substrate 206, in other embodiments that may be combined with other embodiments described herein, the base substrate 206 is planar such that the distance between the bottom surface 213 and the top surface 212 of the base substrate 206 is constant across the base substrate 206.

[0023] 3A, 3B, and 3C are schematic cross-sectional views of a substrate 300 having a substrate thickness distribution 302. The substrate 300 includes the waveguide 101 of FIG. 1 disposed across the substrate 300. Inactive areas 314 are disposed between the index-matching layers 106. The inactive areas 314 are areas of the substrate 300 over which one of the index-matching layers 106 will not be formed. The substrate 300 includes a base substrate having a top surface 312 and a bottom surface 313.

[0024] The base substrate 306 may be formed from any suitable material, provided that the substrate 300 can adequately transmit light at the desired wavelength or range of wavelengths and can serve as sufficient support for the index-matching layer 106. The base substrate 306 may be made of materials including, but not limited to, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, silicon oxides, polymers, and combinations thereof. In some embodiments, which may be combined with other embodiments described herein, the base substrate 306 comprises a transparent material. In one example, the base substrate 306 and / or the index-matching layer 308 comprises silicon (Si), silicon dioxide (SiO), fused silica, quartz, silicon carbide (SiC), germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), sapphire, or a combination thereof.

[0025] At least the index matching layer 106 of the substrate 300 includes a target thickness distribution 302. The target thickness distribution 302 is a local thickness distribution determined to be replicated in each of the waveguides 101. The target thickness distribution 302 is defined by the distance between the top surface 312 and the bottom surface 313 of the substrate 300 across the waveguides 101. In FIG. 3A , the target thickness distribution 302 is determined by a device slope of the bottom surface 316 of the index matching layer 106. The slope can be a preconfigured value or a value determined based on the target thickness distribution 302. The device slope can be achieved by depositing the index matching layer 106 on at least a portion of the bottom surface 313 of the base substrate 306. In FIGS. 3B and 3C , the target thickness distribution 302 is determined by a device slope of the top surface 317 of the index matching layer 106. The slope can be a preconfigured value or a value determined based on the target thickness distribution 302. Device grading may be achieved by depositing an index-matching layer 106 on at least a portion of the top surface 312 of the base substrate 306 .

[0026] In FIG. 3A , the device tilt is the tilt of the bottom surface 216 of the deposited index-matching layer 106 to achieve at least one of the target thickness distributions 302. To achieve the target thickness distributions 302, the device tilt is matched to a desired tilt value for that index-matching layer 302. The device tilt of the second surface of the index-matching layer has a tilt value configured to vary the substrate thickness distribution across the index-matching layer. In some embodiments, the device tilt at any given point on the bottom surface 316 can be a linear tilt value capable of achieving the target thickness distribution 302, such that the target thickness distribution can increase or decrease laterally. In other embodiments, the device tilt at any given point on the bottom surface 316 can be a nonlinear tilt value capable of achieving the target thickness distribution 302, such that the target thickness distribution can increase or decrease laterally. In FIGS. 3B and 3C , the device tilt is the tilt of the top surface 317 of the deposited index-matching layer 106 to achieve at least one of the target thickness distributions 302. To achieve the target thickness distribution 302, the device tilt is matched to a desired tilt value for that index-matching layer 302. In particular, the device tilt at any given point on the top surface 317 can be a linear or non-linear tilt value capable of achieving the target thickness distribution 302, such that the target thickness distribution can increase or decrease laterally. By defining the device tilt as a target tilt value, the target thickness distribution 302 can be achieved uniformly.

[0027] The inactive areas 314 of the substrate 300 have an inactive thickness distribution 320, i.e., the inactive thickness distribution 320 does not substantially match the target thickness distribution 302. The inactive thickness distribution 320 is defined by the distance between the top surface 312 and the bottom surface 313 in the inactive areas 314 across the inactive areas 314. The target thickness distribution 302 is formed from the base substrate 306 of the substrate 300 in each index matching layer 106. In FIG. 3A , the target thickness distribution 302 is formed from the top surface 312 to the bottom surface 316 of the index matching layer 106. In FIGS. 3B and 3C , the target thickness distribution 302 is formed from the bottom surface 313 to the top surface 317 of the index matching layer 106.

[0028] The target thickness distribution 302 is designed to improve the performance of the substrate index-matching layer 106 to be formed thereon. The target thickness distribution 302 is the same in at least each waveguide 101 of the substrate 300. The methods described herein will provide a first target thickness distribution 302 and a second target thickness distribution 304 to be achieved in at least each waveguide 101. The first target thickness distribution 302 and the second target thickness distribution 304 are not limited to the first target thickness distribution 302 and the second target thickness distribution 304 shown in Figures 3A and 3B and can be any thickness distributions that are suitable and determined to improve the performance of the substrate index-matching layer 106.

[0029] At least the index matching layer 106 of the substrate 300 includes a grating structure 318 disposed within the index matching layer. The grating structure 318 may be disposed vertically or diagonally within the index matching layer 106. In FIG. 3A , the grating structure 318 may extend from a bottom surface 316 of the index matching layer 106 above a bottom surface 313 of the base substrate 306. A coating layer 308 may be disposed on a surface 316 of the grating structure 318. In FIG. 3B , the grating structure 318 may extend from a top surface 310 of the coating layer 308, through the index matching layer 106, and below a top surface 312 of the base substrate 306. In some cases, the coating layer 308 may optionally be disposed on a surface 317 of the grating structure 318. The grating structure 318 may be a two-dimensional grating, including a pupil expansion grating, an input coupler grating, an output coupler grating, etc.

[0030] Although Figures 3A and 3B show a base substrate 306 in which the distance between the bottom surface 313 and the top surface 312 of the base substrate 306 varies across the base substrate 306, in other embodiments that may be combined with other embodiments described herein, the base substrate 306 is planar such that the distance between the bottom surface 313 and the top surface 312 of the base substrate 306 is constant across the base substrate 306.

[0031] 4 is a flow diagram of a method 400 for forming substrates 100, 200, and / or 300 with the target thickness distributions 202, 203, or 302 shown in FIGS. 2A-3C. Method 400 may be utilized to form target thickness distributions 202, 203, and 302 in waveguide 101 and / or inactive areas 203, 304 (shown in FIGS. 2A-3B) of substrates 100, 200, and 300.

[0032] In step 402, the substrate 100, 200, or 300 is measured. In some embodiments, the base substrate thickness distribution of the base substrate 206, 306 is measured. The base substrate thickness distribution is defined by the distance between the bottom surface 213, 313 and the top surface 212, 312 of the base substrate 206, 306 across the waveguide 101. The base substrate thickness distribution is the measured thickness distribution of the base substrate 206, 306 prior to forming the target thickness distribution 202, 203, or 302.

[0033] In step 404, material for the index-matching layer 106 is disposed on the base substrate 206, 306. In some embodiments, the target thickness distribution 202, 203, or 302 is disposed according to a defined slope according to Figures 2A-3C. The target thickness distribution 202, 203, or 302 is the measured thickness distribution of the base substrate 206, 306 plus the index-matching layer 106 after forming the target thickness distribution 202, 203, or 302. The device layer 106 may be disposed on the upper surface 212, 312 of the base substrate 206, 306 and / or the bottom surface 213, 313 of the base substrate 206, 306 by one or more of PVD, CVD, PECVD, FCVD, ALD, spin-on coating processes, or inkjet printing processes.

[0034] Materials from which the index-matching layer can be formed can include any transparent substrate having a thickness from about 150 mm to about 50 mm, such as about 100 μm or less, to about 2 mm or more. Materials from which the index-matching layer can be formed can include any substrate whose refractive index is about 1.9, or from about 1.3 or less, such as about 1.8, or from about 1.8 or more, such as about 1.6. The refractive index of the index-matching layer can be within 5% of the refractive index of the substrate. Materials to be deposited on the substrate can include inkjet materials. For example, materials to be deposited on the substrate as part of the index-matching layer can have a refractive index from about 4.0 or less to about 0.2 or more, such as about 1.6. The materials to be deposited on the substrate are high refractive index nanoparticles, metal oxides (e.g., SiO2, TiO2, ZrO2, Nb2O5, HfO2, V2O5, Ta2O5, ZnO), metal sulfides, selenides, tellurides, nitrides, phosphides, etc., organic ligands, any core-shell structure with different compositions, acrylate-based monomers, oligomers, epoxy-based monomers, oligomers, polymers or oligomers, such as silicone, novolac, PS, PMMA, polyacrylate, polymethacrylate. The composition may include any one of ultraviolet (UV) or heat curable resins / binders, such as polymers or oligomers, such as polyvinyl alcohol, polystyrene, polyvinylpyrrolidone, polycarbonate, polyester, polyether, derivatives of the components described herein, copolymers of the components described herein, and solvents, such as ethers, esters, carbonates, silanes, and any solvents whose pressure is about 250°C or higher to about 350°C or lower, such as about 300°C, alone or in combination.

[0035] The target thickness change is utilized to determine a change in the base substrate thickness distribution that allows the target thickness distribution 202, 203, or 302 to be formed. Determining the target thickness change provides a process in step 404 that is adjusted accordingly to form the target thickness distribution 202, 203, or 302 as needed. Figures 2A-3C show the target thickness distributions 202, 203, and 302 formed in the base substrate 206, 306 of the substrate 200, 300. The substrates 200, 300 in Figures 2A-3C correspond to the waveguide 101 shown in Figure 1B. The substrates 200, 300 in Figures 2A-3C also correspond to the waveguide 101 and inactive areas 214, 314 shown in Figures 2A-3C.

[0036] 2A-3C are the result of utilizing the target thickness variation of method 400. A target thickness distribution 202, 203, or 302 may be formed in each waveguide 101. Thus, the target thickness distribution 202, 203, or 302 across the substrate 100 in each waveguide 101 is one or more uses of a configurable base associated with the waveguide 101. Each waveguide 101 having a target thickness distribution 202, 203, or 302 will enable reduced variability in devices to be formed thereon.

[0037] In optional step 406, a grating may be formed on the substrate 100, 200, 300. In some embodiments, the grating may include the grating structure 102 of FIG. 1 and the grating structures 218, 318 of FIGS. 2A-3C. The grating structures 102, 218, 316 may be formed vertically or diagonally in or on the substrate 100, 200, 300. The grating structures 102, 218, 318 may be disposed on the upper surface 212, 312 of the base substrate 206, 306, on the upper surface 217, 317 of the index-matching layer, on the bottom surface 216, 317 of the index-matching layer 106, and / or on the bottom surface 213, 313 of the base substrate 206. The grating structure 102, 218, 316 may be part of at least one grating, including a pupil expansion grating, an input coupler grating, an output coupler grating, or the like.

[0038] While the forgoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, which scope is determined by the following claims.

Claims

1. A waveguide, a waveguide substrate, the waveguide having a substrate thickness distribution; an index-matching layer disposed on the waveguide substrate and having a first surface and a second surface opposite the first surface; Equipped with the index-matching layer is disposed over a portion of the waveguide substrate; A waveguide wherein a device slope of the second surface of the index-matching layer is substantially the same as a waveguide slope of the first surface of the waveguide.

2. The waveguide of claim 1 , wherein the waveguide further comprises at least one grating having a grating structure in the index-matching layer.

3. The waveguide of claim 1 , wherein the waveguide further comprises at least one grating having a grating structure disposed on a bottom surface of the waveguide substrate.

4. The waveguide of claim 1 , wherein the waveguide further comprises at least one grating having a grating structure disposed on the index-matching layer.

5. 5. The waveguide of claim 4, wherein the at least one grating is a pupil-expanding grating.

6. 10. The waveguide of claim 1, wherein the refractive index of the index-matching layer is within 5% of the refractive index of the waveguide substrate.

7. 10. The waveguide of claim 1, wherein the refractive index is within about 5 percent of the refractive index of the waveguide substrate.

8. The waveguide of claim 1 , wherein the waveguide further comprises an inactive area disposed on the first surface of the waveguide substantially adjacent a grating.

9. A waveguide, a waveguide substrate, the waveguide having a substrate thickness distribution; an index-matching layer disposed on the waveguide substrate and having a first surface and a second surface opposite the first surface; Equipped with the index-matching layer is disposed over a portion of the waveguide substrate; A waveguide, wherein a device tilt of the second surface of the index-matching layer has a tilt value configured to vary the substrate thickness distribution across the index-matching layer.

10. 10. The waveguide of claim 9, wherein the waveguide further comprises at least one grating having a grating structure in the index-matching layer.

11. 10. The waveguide of claim 9, wherein the waveguide further comprises at least one grating having a grating structure disposed on a bottom surface of the waveguide substrate.

12. 10. The waveguide of claim 9, wherein the waveguide further comprises at least one grating having a grating structure disposed on the index-matching layer.

13. 13. The waveguide of claim 12, wherein the at least one grating is a pupil-expanding grating.

14. 10. The waveguide of claim 9, wherein the refractive index of the index-matching layer is within 5% of the refractive index of the waveguide substrate.

15. 10. The waveguide of claim 9, wherein the refractive index is within about 5 percent of the refractive index of the waveguide substrate.

16. The waveguide of claim 9 , wherein the waveguide further comprises an inactive area disposed on a first surface of the waveguide substantially adjacent a grating.

17. 1. A method for forming a waveguide, the method comprising: measuring a waveguide substrate, the waveguide having a substrate thickness distribution; depositing an index-matching layer on a surface of the waveguide, the index-matching layer having a first surface disposed on the waveguide substrate and a second surface opposite the first surface; Including, the index matching layer is disposed over only a portion of the waveguide substrate; The method wherein a device slope of the second surface of the index-matching layer is substantially the same as a waveguide slope of the first surface of the waveguide.

18. 20. The method of claim 17, wherein the method further comprises forming at least one grating having a grating structure in the index-matching layer.

19. 20. The waveguide of claim 17, wherein the method further comprises forming at least one grating having a grating structure disposed on a bottom surface of the waveguide substrate.

20. 10. The waveguide of claim 9, wherein the method further comprises forming at least one grating having a grating structure disposed on the index-matching layer.

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