Optical waveguides for augmented reality displays

Abstract

This document discloses a solution for a light guide for an augmented reality display device. According to one aspect, the light guide comprises: a substrate, the substrate being arranged to guide an optical image inside the substrate from an entrance to an exit of the light guide via multiple reflections; a surface relief grating at the entrance or the exit of the light guide, the surface relief grating guiding the image in the light guide via diffraction and comprising multiple grooves; and a coating disposed on the surface relief grating, the coating at least partially filling at least one groove disposed on an edge of the surface relief grating, the coating having optical properties that converge with the optical properties of the substrate, the coating at least partially filling at least one groove disposed on an edge of the surface relief grating, the image coinciding with the at least one groove after a first reflection of the image inside the substrate.

Description

Technical Field

[0001] Embodiments of the present invention relate to the field of display devices used in augmented reality (AR) devices. In particular, the embodiments relate to improving the image quality in such devices.

Background Art

[0002] In an augmented reality display, such as eyewear or a head-mounted display, an image is sent from a projector to the user's eye(s) via an optical waveguide. The optical waveguide may include surface relief gratings at the entrance and the exit of the optical waveguide. The surface relief grating at the entrance diffracts and guides the incoming light (or image) from the projector towards the exit. Similarly, the surface relief grating at the exit directs the light from the optical waveguide towards the eye. Due to the dimensions, some components of the diffracted light may enter the optical waveguide through the surface relief grating at the entrance and then impinge on the surface relief grating. Such a situation may cause dispersion of the incident light and reduce the sharpness of the image.

[0003] Patent Document 1 discloses a technique for manufacturing a sloped surface relief structure. In some embodiments, a method for manufacturing a target sloped surface relief structure, such as a nanoimprint lithography (NIL) mold or a sloped surface relief grid, includes the steps of manufacturing a preliminary surface relief structure comprising a plurality of ridges, and modifying the parameters of the preliminary surface relief structure to manufacture the target sloped surface relief structure. The parameters include the width of each of the plurality of ridges, the height of each of the plurality of ridges, the surface energy of the preliminary surface relief structure, or the slope angle of the edges of the plurality of ridges. The step of modifying the parameters includes the steps of depositing a material layer on the preliminary surface relief structure and etching or surface treating the material layer.

[0004] Patent Document 2 discloses a waveguide configured for use with a near-eye display (NED) device. It may include a light-transmitting substrate configured to propagate light rays by internal total internal reflection, and a diffractive optical element (DOE) on the surface of the substrate configured to input light rays into the substrate and / or output light rays from the substrate. According to some embodiments, the DOE may include a diffraction grating made of a first material having a first refractive index, and a coating of a second material covering the diffraction grating, wherein the second material has a second refractive index not equal to the first refractive index.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

[0006] The present invention is defined by the subject matter of the independent claims.

[0007] Examples are defined in the dependent claims.

[0008] Examples and features described herein that do not fall within the scope of the independent claims should be interpreted as useful examples for understanding various embodiments of the invention, if any exist.

[0009] The present invention will be described in more detail below with reference to the accompanying drawings and preferred embodiments. [Brief explanation of the drawing]

[0010] [Figure 1] This figure illustrates an optical waveguide having a coated surface relief type grating according to one embodiment. [Figure 2] This figure illustrates a coating of a surface relief type grid according to one embodiment. [Figure 3] This figure illustrates non-uniform coating in the grooves of a surface relief type grid according to one embodiment. [Figure 4] This figure illustrates the uneven adhesion of a coating on a surface relief type grid according to one embodiment. [Figure 5] This figure illustrates an optical waveguide having a coated surface relief type grating according to another embodiment. [Figure 6] This figure illustrates a method for manufacturing an optical waveguide according to one embodiment. [Modes for carrying out the invention]

[0011] The following examples are illustrative. While this specification refers to “a certain,” “one,” or “several” examples in several places, this does not necessarily mean that each reference is made to the same example, or that only certain features apply to a single example. Single features from different examples may also be combined to provide other examples.

[0012] Figure 1 illustrates an optical waveguide for an augmented reality display device, such as augmented reality eyewear or a head-mounted display. The eyewear may have the appearance of, for example, glasses, spectacles, or goggles. The eyewear or head-mounted display may be connected to headwear such as a cap, hat, or helmet. An optical image is projected onto the inlet of the optical waveguide by a projector 110. The image may be a still image or a moving image. The image propagates through the optical waveguide from the inlet to the outlet via total internal reflection, as illustrated by the dashed arrows in Figure 1. The transmission of light or an image is therefore analogous to light propagating through an optical fiber. The optical waveguide comprises a substrate 100, which is arranged to guide an optical image inside the substrate from the inlet to the outlet of the optical waveguide via a plurality of (total) reflections; surface relief gratings (SRGs) 102, 104 at the inlet or outlet of the optical waveguide, which guide an image in the optical waveguide via diffraction and have a plurality of grooves; and a coating 106 which is arranged on the surface relief grating and at least partially fills at least one groove located at the edge of the surface relief grating, such that the image coincides with at least one groove after a first reflection of the image inside the substrate 100, and has optical properties that converge with the optical properties of the substrate 100.

[0013] As is well known in the art, a surface relief type lattice is a lattice that has alternating fine grooves and ridges to form a diffraction lattice that separates light incident on the lattice into multiple diffraction orders.

[0014] As described in the background art, the dimensions of the optical waveguide may be such that the light always coincides with the edge of the SRG. Typically, the first-order diffraction is arranged to propagate through the optical waveguide. Because the thickness or width of the substrate is very thin compared to the width of the SRG, the first-order light diffracts at a sufficiently high angle to avoid coincidence with the edge of the SRG. This is illustrated in Figure 1 by the leftmost dashed arrow, which extends upward and coincides with the groove at the edge of SRG102. Similarly, another reflected component coincides with the edge of SRG104 at the exit of the optical waveguide. There may be other reasons for the phenomenon that the light coincides with the groove after the light enters the substrate and / or before the light exits the substrate.

[0015] The coating provides a technical effect in which scattering of light incident on the groove after the first reflection can be reduced. This occurs because the optical properties of the coating and the substrate converge. Light traveling within the substrate and coinciding with the groove also occurs on the coating, and by converging its optical properties, such as the refractive index, the light can travel through the coating with substantially no scattering. Furthermore, since the coating effectively narrows the groove and, in some embodiments, even fills the groove, the light does not coincide with the optical barrier and is not dispersed, or at least its dispersion is reduced.

[0016] In one embodiment, the optical waveguide described herein is provided in augmented reality eyewear. The eyewear may include, in addition to the optical waveguide according to any embodiment described herein, a projector 110 configured to output an optical image, and a lens (not shown) configured to relay the optical image to the SRG at the inlet of the optical waveguide. The lens may be, for example, part of the projector.

[0017] The optical waveguide illustrated in FIG. 1 is a simplified illustration, and it should be recognized that certain features of the waveguide have been enlarged to illustrate the technical effects of the embodiments being described. For example, the thickness of the substrate may be substantially smaller than that illustrated. It should also be recognized that the dimensions and design of the SRG may be different from those illustrated. For example, some SRGs have sloped grooves, and the embodiments are directly applicable to such designs as well.

[0018] Converging the optical properties can be understood such that light incident on the groove and the coating therein acts as if it were optically similar to the coating with respect to the substrate, and the light from the substrate matches that of the coating. Since there is little or no “generation” of optical boundaries for the light, scattering can be reduced. Thus, the coating material can be designed from this concept. This is distinguished from other coatings that may be used to cover the optical waveguide, for example, anti-glare coatings, which have properties that vary and are not controlled with respect to optical convergence with the substrate.

[0019] In one embodiment, the optical properties, such as the refractive index of the coating, are the same as those of the substrate.

[0020] In one embodiment, the coating has at least one layer having a refractive index substantially equal to that of the substrate. The at least one layer having a refractive index substantially equal to that of the substrate may be in direct contact with the substrate. The coating may have another layer (on top of the at least one layer) having a different refractive index.

[0021] In yet another embodiment, at least one layer can include a plurality of layers, in which case none of the layers has a refractive index equal to that of the substrate, but the combined refractive index of the plurality of layers can be equal to the refractive index of the substrate. For example, the first layer disposed directly on the substrate can be tin dioxide TiO2 having a refractive index of 2.4. The second layer disposed on the first layer can be aluminum dioxide AlO2 having a refractive index of 1.7, and the combined refractive index of the first layer and the second layer can thus be 2.4 to 1.7, which can be adjusted according to the required optical properties. Such a multi-layer coating is not limited to the materials or layers described above and can be freely prepared from two or more materials. The materials and the properties of each layer can be designed such that, for example, the (combined) refractive index of the coating is substantially equal to the refractive index of the substrate, for example 2.0, so that convergence of the optical properties with the substrate is achieved.

[0022] In one embodiment, the coating includes a first coating material having a first refractive index and a second coating material having a second refractive index different from the first refractive index.

[0023] As illustrated in FIG. 1, at least one groove coated with the coating can be disposed at the edge of a surface relief grating where the first diffraction of the image coincides with at least one groove. The image can coincide with at least one groove that is the outermost edge of the SRG, either towards the exit (when the image is incident on the SRG at the entrance) or towards the entrance (when the image is incident on the SRG at the exit). Depending on the implementation, the image can coincide with a plurality of grooves at the edge of the SRG, and thus a plurality of grooves can be coated with the coating. In one embodiment, the entire SRG is coated with the coating. FIG. 2 illustrates an example of an embodiment in which the SRGs 102, 104 are coated with a coating that partially fills the grooves. The coating thus optically narrows the grooves, resulting in the above-described technical effects.

[0024] In one embodiment, the coating completely fills at least one groove, as illustrated in Figure 1 by coating 106.

[0025] In one embodiment, the thickness of the coating in the groove varies with the groove, as illustrated by coating 300 in Figure 3. When the coating is placed in the SRG and groove, the viscosity of the coating and other adhesion-related physical properties can affect how uniformly the coating fills the groove edges. It may be beneficial to select a coating that flows to the bottom of the groove, and thus form a thicker coating at the bottom of the groove than at the groove walls. Light incident in the groove will coincide at least with the bottom of the groove, and a thicker layer of coating at the bottom may result in less dispersion. In this embodiment, the coating partially fills the groove, including the outermost groove, so that the first diffraction of the image coincides with the outermost groove.

[0026] In one embodiment, a coating is used in conjunction with the dimensions of the grooves in the SRG to control dispersion. Dispersion can be reduced by gradually decreasing the groove dimensions from the center of the SRG towards the edges of the SRG. In other words, the groove dimensions at the edges of the SRG may be smaller than the groove dimensions at the center of the SRG. The width and / or depth of the grooves can be gradually reduced towards the edges of the SRG. This optically "thins" the edges of the SRG, and thus reduces the dispersion of light coinciding with the grooves after the first reflection within the substrate 100. The grooves may be fabricated using lithography, and there may be limitations on how narrow the grooves can be fabricated. Therefore, using a coating as a further means of controlling the effective dimensions of the grooves may help reduce scattering.

[0027] In one embodiment, the coating unevenly fills multiple grooves of a surface relief lattice. Figure 4 illustrates an embodiment in which the coating completely fills some of the grooves of the SRG and partially fills some of the grooves. Referring to Figure 4, the coating may completely fill at least the first groove 400 of the SRG and partially fill at least the second grooves 402 / 404 of the SRG, with the first groove 400 being closer to the edge of the SRG than the second grooves 402 / 404, and the second grooves 402 / 404 being wider than the first groove 400.

[0028] As illustrated in connection with Figure 1, the coating may be provided on the SRG at least at the inlet of the optical waveguide. In another embodiment, the coating is provided on the SRG at least at the outlet of the optical waveguide. In yet another embodiment, the coating is provided on both the inlet and outlet SRGs. Both SRGs induce an image in the optical waveguide via diffraction and have a plurality of grooves. The coating is arranged on both surface relief gratings and at least partially fills at least one groove located on the edge of the surface relief grating such that the image coincides with at least one groove after a first reflection of the image inside the substrate. Figure 5 illustrates such an embodiment.

[0029] Referring to Figure 5, the SRG502 at the inlet of the optical waveguide may be coated with coating material 106 according to any one of the embodiments described above. Similarly, the SRG504 at the outlet and along the waveguide from the inlet in the first direction may be coated with coating material 106 according to any one of the embodiments described above. In the embodiment of Figure 5, there is a further second outlet comprising an additional SRG506. The second outlet may be in the opposite direction from the inlet SRG502. At the inlet SRG502, the image is diffracted essentially in both opposite directions, as is known in optics. In the embodiment of Figure 1, diffraction in other directions deviating from the outlet is not used, but it is used in the embodiment of Figure 5, as illustrated by the arrows pointing from the inlet to both outlets. The SRG506 at the second outlet may also be coated according to any one of the embodiments described above.

[0030] It should be noted that if the coating is unevenly distributed on the SRG, the coating adhesion may be mirrored at the exit SRG with respect to the inlet SRG. In other words, the coating may be placed in grooves in which light is incident within the substrate 500 (see the highlighted grooves in Figure 5). Further grooves extending from the highlighted edges of the SRG towards the center of the SRG may also be coated as described above.

[0031] In other embodiments, one or more additional inlets and / or outlets, each having an SRG, may also be coated according to the principle described above.

[0032] Next, with reference to Figure 6, a method for manufacturing an optical waveguide according to one of the above embodiments will be described. According to one embodiment, such a manufacturing method includes forming a substrate (block 600) which is arranged to guide an optical image inside the substrate from the inlet to the outlet of an optical waveguide via multiple reflections; forming a surface relief grating (block 602) which has multiple grooves that guide an image to the substrate via diffraction at the inlet of the optical waveguide; and at least partially filling (block 604) at least one groove located at the edge of the surface relief grating, such that the image coincides with at least one groove after a first reflection of the image inside the optical waveguide, with a coating having a certain refractive index that optically narrows at least one groove and thus reduces scattering of the image incident on at least one groove after the first reflection.

[0033] In one embodiment, a surface relief type grid is formed by using lithography on the substrate.

[0034] The coating may be applied to block 604 by any of the most modern coating methods. Examples of possible coating methods include atomic layer deposition, spin coating, chemical vapor deposition, physical vapor deposition, and spray coating.

[0035] In one embodiment, the above satisfaction is achieved such that the coating completely fills at least one groove, as shown in the embodiment of Figure 1.

[0036] In one embodiment, satisfying the above is done such that the coating forms a thicker layer at the bottom of at least one groove than at the walls of at least one groove, as shown in the embodiment of Figure 3.

[0037] In one embodiment, forming the surface relief grid involves forming grooves in the surface relief grid such that the dimensions of the grooves gradually decrease toward the edges of the surface relief grid, and this fulfillment is carried out such that the coating non-uniformly fills the grooves of the surface relief grid, as illustrated, for example, in Figure 4.

[0038] In one embodiment, block 602 includes forming SRGs at multiple exits of the substrate, as illustrated in Figure 5, and filling the grooves of the inlet and outlet SRGs in block 604.

[0039] As technology advances, it will be apparent to those skilled in the art that the concept of the present invention can be implemented in various ways. The present invention and its embodiments are not limited to the examples described above and may vary within the scope of the claims.

Claims

1. An optical waveguide for an augmented reality display device, A substrate (100) is arranged such that an optical image is guided within the substrate from the inlet to the outlet of the optical waveguide via multiple reflections, The optical waveguide is used to guide the image through diffraction, and a surface relief type grating (102, 104) at the inlet or outlet of the optical waveguide has a plurality of grooves, A coating (106) is directly placed on the surface relief type grid and fills at least partially the grooves at least at the outermost edge of the surface relief type grid. Equipped with, The first-order diffraction of the image reflected from within the substrate is transmitted at least through the groove at the outermost edge, and the coating has the same optical properties as the substrate. An optical waveguide having optical groove widths such that the coating completely fills at least a first groove (400) of the surface relief grating and partially fills at least a second groove (402, 404) of the surface relief grating, the first groove is closer to the edge of the surface relief grating than the second groove, the second groove is wider than the first groove, and the coating causes the plurality of grooves of the surface relief grating to gradually narrow from the center to the edge of the surface relief grating.

2. The optical waveguide according to claim 1, wherein the coating comprises at least one layer having a refractive index equal to the refractive index of the substrate.

3. The optical waveguide according to claim 2, wherein the coating comprises a first coating material having a first refractive index and a second coating material having a second refractive index different from the first refractive index, and neither the first nor the second refractive index is equal to the refractive index of the substrate, but the first coating material together with the second coating material gives a refractive index equal to the refractive index of the substrate.

4. The optical waveguide according to claim 1 or 2, wherein the coating completely fills at least the groove at the outermost edge.

5. An optical waveguide according to any one of claims 1 to 4, comprising a surface relief grating (502, 504) at the inlet and outlet of the optical waveguide having a plurality of grooves, wherein the coating is disposed at least in the grooves at the outermost edge of the surface relief grating at the inlet and outlet, at least partially filling the grooves at the outermost edge of the surface relief grating, and the first diffraction of the image is transmitted through the grooves at the outermost edge.

6. The optical waveguide according to any one of claims 1 to 5, wherein the coating (106) is directly disposed on the surface relief type lattice at the inlet, and at least partially fills the grooves at least at the outermost edge of the surface relief type lattice at the inlet, and the first diffraction of the image is transmitted at least through the grooves at the outermost edge, with the edge toward the outlet.

7. The optical waveguide according to any one of claims 1 to 6, wherein the outlet is a first outlet, and the optical waveguide further comprises a second outlet in the opposite direction from the inlet to the first outlet, the second outlet also having a surface relief grating (506), the coating at least partially filling at least the outermost grooves at both edges of the surface relief grating at the inlet, and the first diffraction of the image at the inlet toward the first and second outlets is transmitted through the outermost grooves at both edges of the surface relief grating at the inlet.

8. An optical waveguide according to any one of claims 1 to 7, A projector (110) configured to output optical images, A lens configured to relay the optical image to the surface relief type grating at the entrance of the optical waveguide, Augmented reality eyewear equipped with [feature].

9. A method for manufacturing an optical waveguide, The process includes the step of forming a substrate (600) which is arranged to guide an optical image inside the substrate from the inlet to the outlet of the optical waveguide via multiple reflections, The steps (602) include: guiding the image to the substrate via diffraction at the inlet or outlet of the optical waveguide, and forming a surface relief type lattice having a plurality of grooves; The steps (604) include filling at least the grooves at the outermost edges of the surface relief type grid with a coating, and Includes, The first-order diffraction of the image reflected within the substrate is transmitted at least through the groove at the outermost edge, and the coating has a refractive index that optically narrows at least the groove at the outermost edge, and therefore reduces the scattering of the first-order diffraction of the image incident at least through the groove at the outermost edge. A method wherein the coating non-uniformly fills the plurality of grooves of the surface relief grid such that it completely fills at least a first groove (400) of the surface relief grid and partially fills at least a second groove (402, 404) of the surface relief grid, the first groove being closer to the edge of the surface relief grid than the second groove being wider than the first groove, and the coating gives the plurality of grooves of the surface relief grid an optical groove width such that it gradually narrows from the center of the surface relief grid toward the edge.

10. The method according to claim 9, wherein the surface relief type grid is formed by using lithography.

11. The method according to claim 9 or 10, wherein the satisfying step is performed such that the coating completely fills at least the grooves at the outermost edges.

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