Modulation-transfer-function preserving grating boundaries for surface relief grating waveguides

Abstract

Embodiments of the present disclosure generally relate to augmented reality waveguide combiners. More specifically, embodiments described herein relate to waveguide combiners with transitional grating boundary areas. In one or more embodiments, a waveguide includes an input coupler operable to receive a light and in-couple the light into the waveguide. A pupil expander is operable to receive the light from the input coupler. The pupil expander includes an expander boundary area. An output coupler is operable to receive the light from the pupil expander. The output coupler includes an output boundary area. The expander boundary area, and the output boundary area include a plurality of structures. The plurality of structures have a gradient depth, a gradient duty cycle, a gradient pitch, or a gradient refractive index.

Description

MODULATION-TRANSFER-FUNCTION PRESERVING GRATING BOUNDARIES FOR SURFACE RELIEF GRATING WAVEGUIDESBACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to augmented reality waveguide combiners. More specifically, embodiments described herein relate to waveguide combiners with transitional grating boundary areas.Description of the Related Art

[0002] Virtual reality is generally a computer generated simulated environment in which a user has an apparent physical presence. A virtual reality experience may be generated from a three-dimensional (3D) perspective and viewed with a headmounted display (HMD), such as glasses or other wearable display devices that have near-eye display panels as lenses to display a virtual reality environment that substantially replaces an actual environment.

[0003] Augmented reality (AR) enables an experience in which a user can still see through the display lenses of the glasses or other HMD device to view the surrounding environment, yet also see images of virtual objects that are generated for display and appear as part of the environment. Augmented reality can include any type of input, such as audio and haptic inputs, as well as virtual images, graphics, and video that enhances or augments the environment that the user experiences. As an emerging technology, there are many challenges and design constraints with augmented reality.

[0004] One such challenge is displaying a virtual image overlaid on an ambient environment. Waveguide combiners are used to assist in overlaying images. Generated light is in-coupled into a waveguide combiner, propagated through the augmented waveguide combiner, out-coupled from the augmented waveguide combiner, and overlaid on the ambient environment. Light is coupled into and out of augmented waveguide combiners using gratings. When light is coupled grating to another the image modulation transfer function (MTF) of the outcoupled image is degraded.

[0005] Accordingly, what is needed in the art are waveguide combiners having improved gratings that prevent degradation of the image modulation transfer function (MTF).SUMMARY

[0006] Embodiments of the present disclosure generally relate to augmented reality waveguide combiners. More specifically, embodiments described herein relate to waveguide combiners with transitional grating boundary areas.

[0007] In one or more embodiments, a waveguide includes an input coupler operable to receive a light and in-couple the light into the waveguide. A pupil expander is operable to receive the light from the input coupler. The pupil expander includes an expander boundary area. An output coupler is operable to receive the light from the pupil expander. The output coupler includes an output boundary area. The expander boundary area and the output boundary area include a plurality of structures. The plurality of structures have a gradient depth, a gradient duty cycle, a gradient pitch, or a gradient refractive index.

[0008] In one or more embodiments, a device, includes a substrate. A light engine is disposed above the substrate. Gratings are disposed over a surface of the substrate. The gratings include an input coupler operable to receive a light and incouple the light. A pupil expander is operable to receive the light from the input coupler. The pupil expander includes an expander boundary area. An output coupler is operable to receive the light from the pupil expander. The output coupler includes an output boundary area. The expander boundary area, and the output boundary area include a plurality of structures. The plurality of structures have a gradient depth, a gradient duty cycle, a gradient pitch, or a gradient refractive index.

[0009] In one or more embodiments, a waveguide includes an input coupler operable to receive a light and in-couple the light into the waveguide. A pupil expander is operable to receive the light from the input coupler, The pupil expander includes an expander boundary area disposed along at least a portion of an edge of the pupil expander. An output coupler is operable to receive the light from the pupil expander. The output coupler includes an output boundary area disposed along at least a portion of an edge of the output coupler. The expander boundary area and the outputboundary area include a plurality of structures, the plurality of structures having a gradient depth, a gradient duty cycle, a gradient pitch, or a gradient refractive index.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of scope, as the disclosure may admit to other equally effective embodiments.

[0011] Figure 1A is a perspective, frontal view of a waveguide, according to one or more embodiments.

[0012] Figure 1 B is a schematic, top view of the waveguide in operation, according to one or more embodiments.

[0013] Figure 2 is a schematic, top view of a waveguide, according to one or more embodiments.

[0014] Figures 3A - 3D are schematic cross sectional views along line A to A shown in Figure 2A, according to one or more embodiments.

[0015] Figures 4A - 4D are schematic cross sectional views along line B to B’ shown in Figure 2, according to one or more embodiments.

[0016] Figure 5A is a top view of a first grating shape, according to one or more embodiments.

[0017] Figure 5B is a top view of a second grating shape, according to one or more embodiments.

[0018] Figure 5C is a top down view of an additional view of the second grating shape, according to one or more embodiments.

[0019] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It iscontemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0020] Embodiments of the present disclosure generally relate to augmented reality waveguide combiners. More specifically, embodiments described herein relate to waveguide combiners with transitional grating boundary areas. The grating boundary areas maintain a high image modulation transfer function (MTF). As described herein, grating boundaries reduce the magnitude of the optical phase tear from the image crossing from one grating to another, and thereby preserving MTF.

[0021] Figure 1A is a perspective, frontal view of a waveguide 100, according to one or more embodiments. It is to be understood that the waveguide 100 described herein is an exemplary waveguide and that other waveguides may be used with or modified to accomplish aspects of the present disclosure. The waveguide 100 includes a plurality of structures 102. The structures 102 may be disposed over, under, or on a first surface 103 of a substrate 101 , or disposed in the substrate 101. The structures 102 are nanostructures have a sub-micron critical dimension, e.g., a width less than 1 micrometer. Regions of the structures 102 correspond to one or more gratings 104. Any of the grating 104 may be disposed over, under, or on the first surface 103 or over, under, or on a second surface opposing the first surface 103. In one embodiment, which can be combined with other embodiments described herein, the waveguide 100 includes at least an input coupler 104a corresponding to an input coupling grating (“input coupler”) and a output coupler 104c corresponding to an output coupling grating (“output coupler”). In another embodiment, which can be combined with other embodiments described herein, the waveguide 100 further includes a pupil expander 104b. The pupil expander 104b corresponds to a pupil expansion grating (“Pupil Expander”) or a fold grating.

[0022] Figure 1 B is a schematic, top view of the waveguide 100 in operation, according to one or more embodiments. The waveguide 100 includes a substrate 101 . An input coupler 104a, a pupil expander 104b, and an output coupler 104c are disposed in, on, or over the substrate 101. The input coupler 104a is aligned with a light engine 110. The light engine 110, in operation, projects incident beams (e.g., a virtual image) to the input coupler 104a. The incident beams are shown as the inputbeam 112. The input coupler 104a receives the input beam 1 12. The input beam 112 is incoupled by in the input coupler 104a such that the input beam 112 undergoes total-internal-reflection (TIR) through the substrate 101 until the input beam 1 12 comes in contact with the structures 102 of the pupil expander 104b. The reflected beams 114 undergo TIR in the pupil expander 104b until the reflected beams 114 contact the structures 102 of the output coupler 104c. The reflected beams 114 are reflected beams are reflected by within the output coupler 104c. The output coupler directs the reflected beams 114 towards a user’s eye 120 as out coupled beams 116. The outcoupled beams 116 are perceived by the user's eye 120 as a displayed image.

[0023] Figure 2 is a schematic, top view of a waveguide 200, according to one or more embodiments. The waveguide 200 is similar to the waveguide 100 shown in Figure 1 , and includes one or more aspects, features, components, operations, and / or properties thereof. The waveguide 200 includes an input coupler 104a, a pupil expander 104b, and an output coupler 104c. The input coupler 104a includes an input boundary area 204a. The pupil expander 104b includes an expander boundary area 204b. The output coupler 104c includes an output boundary area 204c.

[0024] The input coupler 104a has an outer edge 210. The input boundary area 204a is disposed along a portion of outer edge 210 facing disposed next to the pupil expander 104b. The pupil expander 104b includes a first edge 212, a second edge 213, a third edge 214, and a fourth edge 215. The first edge 212 of the pupil expander 104b is disposed next to the input coupler 104a. The second edge 213 of the pupil expander 104b is disposed next to the output coupler 104c. The expander boundary area 204b is disposed along at least a portion of the first edge 212 of the pupil expander 104b, at least a portion of the second edge 213 of the pupil expander 104b, or a combination thereof. The output coupler 104c includes a first edge 216, a second edge 217, a third edge 218, and a fourth edge 219. The first edge 212 of the output coupler 104c and the second edge 217 of the output coupler 104c are disposed next to the pupil expander 104b. The output boundary area 204c is disposed along at least a portion of the first edge 216 of the output coupler 104c, at least a portion of the second edge 217 of the output coupler 104c, or a combination thereof.

[0025] The boundary areas 204a, 204b, 204c are defined by regions of the gratings 104a, 104b, 104c where the material or the geometry of the structures 102 include agradual variation over a distance. The gradual variations to the material or the geometry of the structures 102 include gradual variations to a depth, a duty cycle, a phase, a coating, a refractive index, or combinations thereof. The gradual variation material or the geometry of the structures 102 reduces the magnitude of an optical phase tear of an incident beam crossing from one grating 104a, 104b, 104c to another grating 104a, 104b, 104c. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0026] Each boundary area 204a, 204b, 204c has a W1 . The width W1 is defined by the distance between a first structure 102 having a gradual variation to the material or the geometry and the edge of the respective boundary area’s 204a, 204b, 204c respective grating 104a, 104b, 104c. The width W1 is less than a pupil bounce length of the light beam reflected within the waveguide 200. The pupil bounce length is distance over which a light beam emitted into a grating 104 travels and reflects within the grating 104 before it is either coupled out of the grating 104 or continues its propagation within the grating 104. The pupil bounce length is less than 1 mm, such as less than 0.5 mm. The

[0027] Figures 3A - 3D are schematic cross sectional views along line A to A shown in Figure 2A, according to one or more embodiments. The cross sectional views of 3A-3D are also applicable along line B to B’. Figures 3A - 3D include the substrate 101 , the input coupler 104a, the input boundary area 204a, the pupil expander 104b, the expander boundary area 204b, and a transition area 302. Each zone is separated by a boundary line B in order to illustrate the boundary of each area. It should be understood that the boundary lines B are shown for illustrative purposes only and do not represent actual features of the waveguide 200. The input coupler 104a, the input boundary area 204a, the pupil expander 104b, the expander boundary area 204b each include a plurality of the structures 102.

[0028] The substrate 101 can be any substrate used in the art, and can be either opaque or transparent to a chosen wavelength of light, depending for the use of the substrate 101 as a substrate for a waveguide. Substrate selection may include substrates of any suitable material, including, but not limited to, amorphous dielectrics, non-amorphous dielectrics, crystalline dielectrics, polymers, or combinations thereof. In some embodiments, the substrate 101 includes, but is not limited to, a silicon-containing material, a silicon and oxygen containing compound, a germanium- containing material, a indium and phosphide containing compound, a gallium and arsenic containing compound, a gallium and nitrogen containing compound, a carbon- containing material, a silicon and carbon containing compound, a silicon, carbon, and oxygen containing compound, a silicon and nitrogen containing compound, a silicon, oxygen, and nitrogen containing compound, a niobium and oxygen containing compound, and lithium, niobium, and oxygen containing compound, an aluminum and oxygen containing compound, a indium, tin, and oxygen containing compound, a titanium and oxygen containing compound, a lanthanum and oxygen containing compound, a gadolinium and oxygen containing compound, a zinc and oxygen containing compound, a yttrium and oxygen containing compound, a tungsten and oxygen containing compound, a potassium, and oxygen containing compound, a phosphorous and oxygen containing compound, a barium and oxygen containing compound, a sodium and oxygen containing compound, or combinations thereof. In other embodiments, which can be combined with other embodiments described herein, the substrate 101 includes an oxide including one or more of gadolinium, silicon, sodium, barium, potassium, tungsten, phosphorus, zinc, calcium, titanium, tantalum, niobium, lanthanum, zirconium, lithium, or yttrium containing-materials. Example materials of the substrate 101 include silicon (Si), silicon monoxide (SiO), silicon dioxide (SiC>2), silicon carbide (SiC), fused silica, diamond, quartz germanium (Ge), silicon germanium (SiGe), indium phosphide (InP), gallium arsenide (GaAs), gallium nitride (GaN), sapphire, sapphire (AI2O3), lithium niobate (LiNbOs), indium tin oxide (ITO), lanthanum oxide (La20s), gadolinium oxide (Gd20s), zinc oxide (ZnO), yttrium oxide (Y2O3), tungsten oxide (WO3), titatium oxide (TiO2), zirconium oxide (ZrOs), sodium oxide (Na2O), niobium oxide (Nb20b), barium oxide (BaO), potassium oxide (K2O), phosphorus pentoxide (P2O5), calcium oxide (CaO), or combinations thereof.

[0029] The structures 102 are disposed on or over the substrate 101. The structures 102 are formed from a grating material. The grating material and the substrate 101 include a different material. The grating material includes, but is not limited to, one or more oxides, carbides, or nitrides of silicon, aluminum, zirconium, tin, tantalum, zirconium, barium, titanium, hafnium, lithium, lanthanum, cadmium, niobium, or combinations thereof. Example materials of the grating material includesilicon carbide, silicon oxycarbide, titanium oxide, silicon oxide, vanadium oxide, aluminum oxide, aluminum-doped zinc oxide, indium tin oxide, tin oxide, zinc oxide, tantalum oxide, silicon nitride, zirconium oxide, niobium oxide, cadmium stannate, silicon oxynitride, barium titanate, diamond like carbon, hafnium oxide, lithium niobate, silicon carbon-nitride, silver, cadmium selenide, mercury telluride, zinc selenide, silver-indium-gallium-sulfur, silver-indium-sulfur, indium phosphide, gallium phosphide, lead sulfide, lead selenide, zinc sulfide, molybdenum sulfide, tungsten sulfide, or combinations thereof. In one or more embodiments, the structures are coated with a metal. In one or more embodiments, the gratings are etched directly into the substrate. In one or more embodiments, the gratings are formed of a resist polymer material.

[0030] A gap g separates each structure 102 within the grating 104. A duty cycle may represent the ratio of a width w of a structure 102 to the period p of each structure 102 within the grating 104. In some cases, the grating 104 may have a plurality of structures 102 with varying duty cycles or a uniform duty cycle. Each structure 102 may have a height h of 20 nm to 300 nm. In certain aspects, the height h may vary or be uniform among the plurality of grating structures 102. Each gap g has a depth d. The depth d is defined by the distance between a top surface of the structures 102 and a bottom surface of the gap g.

[0031] The transition area 302 is an area on the substrate 101 between two gratings 104. For example in Figures 3A-3D, the transition area 302 is the area on the substrate 101 between the input boundary area 204a of the input coupler 104a and the expander boundary area 204b of the pupil expander 104b. The length of the transition zone is greater than or equal to about 100 pm. The transition area 302 includes the grating material disposed over the substrate 101. The transition zone does not include any structures 102 formed in the grating material.

[0032] During an image emitting process, the incident beams are emitted by the light engine 110 into the input coupler 104a. The incident beams are reflected and directed by the input coupler 104a in direction D1 from the input coupler 104a through the input boundary area 204a. The incident beams continue to travel from the input boundary area 204a, through the transition area 302, into the expander boundary area 204b, and into the pupil expander 104b.

[0033] Figure 3A is a schematic cross sectional view of the input boundary area 204a and the expander boundary area 204b having a gradient depth, according to one or more embodiments. In one or more embodiments, the gaps g between the structures 102 in the input coupler 104a and the pupil expander 104b have a consistent depth d. In the input boundary area 204a the depth d of each gap g decreases along the direction D1 until reaching the outer edge 210 of the input coupler 104a. The depth d of each gap within the expander boundary area 204b increases when moving from the first edge 212 of the pupil expander 104b along the direction D1 . The gradual variation of the depth d of each gap g within the input boundary area 204a and expander boundary area 204b forms a gradient depth. The gradient depth reduces the magnitude of an optical phase tear of incident beams crossing from the input coupler 104a to the pupil expander 104b. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0034] Figure 3B is a schematic cross sectional view of the input boundary area 204a and the expander boundary area 204b having a gradient duty cycle, according to one or more embodiments. In one or more embodiments, the structures 102 in the input coupler 104a and the pupil expander 104b have a consistent duty cycle. In the expander boundary area 204b the duty cycle of each structure 102 increases along the direction D1 until reaching the outer edge 210 of the input coupler 104a. The duty cycle of each structure 102 within the expander boundary area 204b decreases when moving from the first edge 212 of the pupil expander 104b along the direction D1. The gradual variation of the duty cycles of the structures 102 within the input boundary area 204a and expander boundary area 204b forms a gradient duty cycle. The gradient duty cycle reduces the magnitude of an optical phase tear of incident beams crossing from the input coupler 104a to the pupil expander 104b. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0035] Figure 3C is a schematic cross sectional view of the input boundary area 204a and the expander boundary area 204b having a gradient pitch p, according to one or more embodiments. In one or more embodiments, the structures 102 in the input coupler 104a and the pupil expander 104b have a consistent pitch p. In the input boundary area 204a the pitch in between each structure 102 decreases along thedirection D1 until reaching the outer edge 210 of the input coupler 104a. The pitch p in-between each structure 102 within the expander boundary area 204b increases when moving from the first edge 212 of the pupil expander 104b along the direction D1. The gradual variation of the pitch p in between the structures 102 within the input boundary area 204a and expander boundary area 204b forms a gradient pitch. The gradient pitch reduces the magnitude of an optical phase tear of incident beams crossing from the input coupler 104a to the pupil expander 104b. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0036] Figure 3D is a schematic cross sectional view of the input boundary area 204a and the expander boundary area 204b include a coating 320 deposited within the gap g in-between each structure 102, according to one or more embodiments. The coating 320 includes a gradient thickness t. The coating 320 is formed of a coating material. The coating material may include a noble metal, a non-noble metal, an oxide, a ceramic, a phase change material, a semiconductor, or any combination thereof, for example. The coating material may include amorphous silicon (aSi), silicon oxide (SiOx), silicon nitride (SiNx), titanium oxide (TiOx), tantalum oxide (TaOx), niobium oxide (NbOx), aluminum oxide (AIOx), chromium oxide (CrOx), magnesium oxide (MgOx), or a combination thereof. The thickness t of the coating 320 affects the refractive index of the coating 320. In the input boundary area 204a the thickness t of the coating 320 in between each structure 102 increases along the direction D1 until reaching the outer edge 210 of the input coupler 104a. In the expander boundary area 204b, the thickness t of the coating 320 in between each structure 102 decreases when moving from the first edge 212 of the pupil expander 104b along the direction D1 . The gradual variation of the thickness of the coating 320 in between the structures 102 within the input boundary area 204a and expander boundary area 204b forms a gradient refractive index. The gradient refractive index reduces the magnitude of an optical phase tear of incident beams crossing from the input coupler 104a to the pupil expander 104b. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0037] Figures 4A - 4D are schematic cross sectional views along line B to B’ shown in Figure 2, according to one or more embodiments. The cross sectional views of 4A-4D are also applicable along line A to . Figures 4A - 4D include the substrate101 , the pupil expander 104b, the expander boundary area 204b, the output coupler 104c, the output boundary area 204c, and a transition area 402. Each zone is separated by a boundary line B in order to illustrate the boundary of each area. It should be understood that the boundary lines B are shown for illustrative purposes only and do not represent actual features of the waveguide 200. The pupil expander 104b, the expander boundary area 204b, the output coupler 104c, and the output boundary area 204c each include a plurality of the structures 102.

[0038] The transition area 402 is an area on the substrate 101 between two gratings 104. For example in Figures 4A-4D, the transition area 402 is the area on the substrate 101 between the expander boundary area 204b of the pupil expander 104b and the output boundary area 204c of the output coupler 104c. The length of the transition zone is greater than or equal to about 100 pm. The transition area 402 includes the grating material disposed over the substrate 101. The transition zone does not include any structures 102 formed in the grating material.

[0039] During an image emitting process, the incident beams are emitted by the light engine 110 into the input coupler 104a. As described herein, the incident beams are reflected into the pupil expander 104b. The incident beams are reflected and directed by the pupil expander 104b in direction D2 from the pupil expander 104b through the expander boundary area 204b. The incident beams continue to travel from the input boundary area 204a, through the transition area 402, into the output boundary area 204c, and into the output coupler 104c.

[0040] Figure 4A is a schematic cross sectional view of the expander boundary area 204b and the output boundary area 204c having a gradient depth, according to one or more embodiments. In one or more embodiments, the gaps g between the structures 102 in the pupil expander 104b and the output coupler 104c have a consistent depth d. In the expander boundary area 204b the depth d of each gap decreases along the direction D2 until reaching the second edge 213 of the pupil expander 104b. The depth d of each gap g within the output boundary area 204c increases when moving from the second edge 217 of the output coupler 104c along the direction D2. The gradual variation of the depth d of each gap g within the expander boundary area 204b and output boundary area 204c forms a gradient depth. The gradient depth reduces the magnitude of an optical phase tear of incident beamscrossing from the pupil expander 104b to the output coupler 104c. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0041] Figure 4B is a schematic cross sectional view of the expander boundary area 204b and the output boundary area 204c having a gradient duty cycle, according to one or more embodiments. In one or more embodiments, the structures 102 in the pupil expander 104b and the output coupler 104c have a consistent duty cycle. In the expander boundary area 204b the duty cycle of each structure 102 increases along the direction D2 until reaching the second edge 213 of the pupil expander 104b. The duty cycle of each structure 102 within the output boundary area 204c decreases when moving from the second edge 217 of the output coupler 104c along the direction D2. The gradual variation of the duty cycles of the structures 102 within the expander boundary area 204b and the output boundary area 204c forms a gradient duty cycle. The gradient duty cycle reduces the magnitude of an optical phase tear of incident beams crossing from the pupil expander 104b to the output coupler 104c. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0042] Figure 4C is a schematic cross sectional view of the expander boundary area 204b and the output boundary area 204c having a gradient pitch p, according to one or more embodiments. In one or more embodiments, the structures 102 in the pupil expander 104b and the output coupler 104c have a consistent pitch p. In the expander boundary area 204b the pitch in between each structure 102 decreases along the direction D2 until reaching the second edge 213 of the pupil expander 104b. The pitch p in-between each structure 102 within the output boundary area 204c increases when moving from the second edge 217 of the output coupler 104c along the direction D2. The gradual variation of the pitch p in between the structures 102 within the expander boundary area 204b and the output boundary area 204c forms a gradient pitch. The gradient pitch reduces the magnitude of an optical phase tear of incident beams crossing from the pupil expander 104b to the output coupler 104c. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0043] Figure 4D is a schematic cross sectional view of the expander boundary area 204b and the output boundary area 204c include a coating 320 deposited within the gap g in-between each structure 102, according to one or more embodiments. The coating 320 includes a gradient thickness t. The coating 320 is formed of a coating material. The coating material may include a noble metal, a non-noble metal, an oxide, a ceramic, a phase change material, a semiconductor, or any combination thereof, for example. The coating material may include amorphous silicon (aSi), silicon oxide (SiOx), silicon nitride (SiNx), titanium oxide (TiOx), tantalum oxide (TaOx), niobium oxide (NbOx), aluminum oxide (AIOx), chromium oxide (CrOx), magnesium oxide (MgOx), or a combination thereof. The thickness t of the coating 320 affects the refractive index of the coating 320. In the expander boundary area 204b the thickness t of the coating 320 in between each structure 102 increases along the direction D2 until reaching the second edge 213 of the pupil expander 104b. In the output boundary area 204c, the thickness t of the coating 320 in between each structure 102 decreases when moving from the second edge 217 of the output coupler 104c along the direction D2. The gradual variation of the thickness t of the coating 320 in between the structures 102 within the expander boundary area 204b and the output boundary area 204c forms a gradient refractive index. The gradient refractive index reduces the magnitude of an optical phase tear of incident beams crossing from one the pupil expander 104b to the output coupler 104c. This reduction in optical tear helps preserve the image modulation transfer function (MTF) of the displayed image to the user’s eye 120.

[0044] Figure 5A is a top view of a first grating shape, according to one or more embodiments. The structures 102 having the first grating shape form lattice wherein the structures extend across a first direction. Figure 5B is a top view of a second grating shape, according to one or more embodiments. The structures 102 having the first grating shape form a plurality of three dimensional structures 102 wherein there is a gap between each structure in a first direction, and there is a gap between each structure in a second direction. Figure 5C is a top down view of an additional view of the second grating shape, according to one or more embodiments. Examples of varying the plurality of structures 102 may include binary gratings, slanted gratings, blazed gratings, or generalized gratings (e.g., gratings with an organic shape). The plurality of structures 102 direct light in the desired direction, as described above. Theplurality of structures 102 efficiency ranges may range from about 0% to about 15%, though other values are contemplated. Variable grating efficiency may be achieved through variable pitch, duty cycle, and / or depth of the plurality of structures 102.

[0045] Benefits of the present disclosure include a waveguide having gratings with an improved image modulation transfer function (MTF). The improved image MTF improves display performance and reduces the magnitude of the optical phase tear. The boundary areas allow for the manufacturing of thinner substrates. Further benefits include improved device performance, decreased costs, and decreased maintenance.

[0046] It is contemplated that one or more aspects disclosed herein may be combined. As an example, one or more aspects, features, components, operations and / or properties of the waveguide 100, the substrate 101 , the input coupler 104a, the pupil expander 104b, the output coupler 104c, the input boundary area 204a, the expander boundary area 204b, the output boundary area 204c, and / or the coating 320 may be combined. Moreover, it is contemplated that one or more aspects disclosed herein may include some or all of the aforementioned benefits.

[0047] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is:

1. A waveguide comprising: an input coupler operable to receive a light and in-couple the light into the waveguide; a pupil expander operable to receive the light from the input coupler, the pupil expander comprising an expander boundary area, the expander boundary area comprising a first plurality of structures, the first plurality of structures having a first gradient depth, a first gradient duty cycle, a first gradient pitch, or a first gradient refractive index; and an output coupler operable to receive the light from the pupil expander, the output coupler comprising an output boundary area, the output boundary area comprising a second plurality of structures, the second plurality of structures having a second gradient depth, a second gradient duty cycle, a second gradient pitch, or a second gradient refractive index.

2. The waveguide of claim 1 , wherein the input coupler is aligned under a light engine of an augmented reality (AR) device.

3. The waveguide of claim 1 , wherein the input coupler includes an input boundary area.

4. The waveguide of claim 1 , wherein the expander boundary area is disposed along at least a portion of an edge of the pupil expander.

5. The waveguide of claim 1 , wherein the output boundary area is disposed along at least a portion of an edge of the output coupler.

6. The waveguide of claim 1 , wherein the plurality of structures include a 1-D structure.

7. The waveguide of claim 1 , wherein the plurality of structures include a 2-D structure.

8. The waveguide of claim 1 , wherein the plurality of structures have coating deposited over the structures, wherein the coating has a gradient thickness.

9. The waveguide of claim 1 , wherein the expander boundary area and the output boundary area each have a width less than a pupil bounce length of the light.

10. The waveguide of claim 9, wherein the pupil bounce length is less than 1 mm.

11. A device, comprising: a substrate; a light engine disposed above the substrate; gratings disposed over a surface of the substrate, the gratings comprising: an input coupler operable to receive a light and in-couple the light; a pupil expander operable to receive the light from the input coupler, the pupil expander comprising an expander boundary area, the expander boundary area comprising a first plurality of structures, the first plurality of structures having a first gradient depth, a first gradient duty cycle, a first gradient pitch, or a first gradient refractive index; and an output coupler operable to receive the light from the pupil expander, the output coupler comprising an output boundary area, the output boundary area comprising a second plurality of structures, the second plurality of structures having a second gradient depth, a second gradient duty cycle, a second gradient pitch, or a second gradient refractive index.

12. The device of claim 11 , wherein the input coupler includes an input boundary area.

13. The device of claim 11 , wherein the expander boundary area is disposed along at least a portion of an edge of the pupil expander.

14. The device of claim 11 , wherein the output boundary area is disposed along at least a portion of an edge of the output coupler.

15. The device of claim 11 , wherein the plurality of structures include a 1-D structure.

16. The device of claim 11 , wherein the plurality of structures include a 2-D structure.

17. The device of claim 11 , wherein the plurality of structures have coating deposited over the gratings, wherein the coating has a gradient thickness.

18. The device of claim 11 , wherein the expander boundary area and the output boundary area each have a width less than a pupil bounce length of the light.

19. The device of claim 18, wherein the pupil bounce length is less than 1 mm.

20. A waveguide comprising: an input coupler operable to receive a light and in-couple the light into the waveguide; a pupil expander operable to receive the light from the input coupler, the pupil expander comprising an expander boundary area disposed along at least a portion of an edge of the pupil expander, the expander boundary area comprising a first plurality of structures, the first plurality of structures having a first gradient depth, a first gradient duty cycle, a first gradient pitch, or a first gradient refractive index; and an output coupler operable to receive the light from the pupil expander, the output coupler comprising an output boundary area disposed along at least a portion of an edge of the output coupler, the output boundary area comprising a second plurality of structures, the second plurality of structures having a second gradient depth, a second gradient duty cycle, a second gradient pitch, or a second gradient refractive index..

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