Optical waveguides for augmented reality displays

Abstract

This paper discloses a solution for an optical waveguide for an augmented reality display device. According to one aspect, the optical waveguide includes: a substrate arranged to guide an optical image within the substrate from an entrance to an exit of the optical waveguide via multiple reflections; a surface relief grating at the entrance or exit of the optical waveguide, the surface relief grating guiding the image within the optical waveguide via diffraction and comprising a plurality of grooves; and a coating disposed on the surface relief grating and at least partially filling at least one groove disposed at an edge of the surface relief grating, wherein the image coincides with the at least one groove after a first reflection within the substrate, and the coating having optical properties that converge with the optical properties of 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, embodiments relate to improving image quality in such devices. Background Art

[0002] In an augmented reality display (e.g., glasses or a head-mounted display), an image is delivered from a projector to one (or both) eyes of a user via an optical waveguide. The optical waveguide may include surface relief gratings at the entrance and exit of the optical waveguide. The surface relief grating at the entrance guides the incident light (or image) from the projector toward the exit by diffraction. Similarly, the surface relief grating at the exit guides the light from the optical waveguide toward the eye. Due to size reasons, some components of the diffracted light may be incident on the surface relief grating after entering the optical waveguide via the surface relief grating at the entrance. Such incidence may cause dispersion of the incident light and reduce the sharpness of the image. US2020 / 018875 discloses a technique for manufacturing an inclined surface relief structure. In some embodiments, a method for manufacturing a target inclined surface relief structure (such as a nanoimprint lithography (NIL) mold or an inclined surface relief grating) includes manufacturing a preliminary surface relief structure comprising a plurality of ridges and modifying the parameters of the preliminary surface relief structure to manufacture a target inclined 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 tilt angle of the edges of the plurality of ridges. Modifying the parameters includes depositing a material layer on the preliminary surface relief structure and etching or surface treating the material layer. US2017 / 307886 discloses a waveguide configured for use with a near-eye display (NED) device. It may include a light-transmitting substrate configured to propagate light by total internal reflection and a diffractive optical element (DOE) on the surface of the substrate, the DOE being configured to input light to and / or output light 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 above the diffraction grating, the second material having a second refractive index that is not equal to the first refractive index. Summary of the Invention

[0003] The invention is defined by the subject-matter of the independent claims.

[0004] Embodiments are defined in the dependent claims.

[0005] The embodiments and features described in this specification that do not fall within the scope of the independent claims, if any, should be interpreted as examples useful for understanding the various embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The present invention will be described in more detail below by way of preferred embodiments with reference to the accompanying drawings, in which:

[0007] Figure 1 An optical waveguide coated with a surface relief grating according to an embodiment is shown;

[0008] Figure 2 shows the coating of a surface relief grating according to an embodiment;

[0009] Figure 3 shows a non-uniform coating in the grooves of a surface relief grating according to an embodiment;

[0010] Figure 4 shows non-uniform deposition of a coating on a surface relief grating according to an embodiment;

[0011] Figure 5 An optical waveguide coated with a surface relief grating according to another embodiment is shown;

[0012] Figure 6 A method for producing an optical waveguide according to an embodiment is shown. DETAILED DESCRIPTION

[0013] The following embodiments are exemplary. Although the specification may refer to "one," "an," or "some" embodiments in several places throughout the text, this does not necessarily mean that each reference is to the same embodiment, or that a particular feature applies only to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments.

[0014] Figure 1 An optical waveguide for an augmented reality display device, such as augmented reality glasses or a head-mounted display, is shown. For example, the glasses may look like glasses, spectacles, or goggles. For example, the glasses or head-mounted display may be connected to headgear, such as a cap, hat, or helmet. An optical image is projected by a projector 110 into an inlet of the optical waveguide. The image may be a still image or a video. The image propagates within the optical waveguide via total internal reflection from the inlet to the outlet, as shown in FIG. Figure 1As shown by the dashed arrows in . Therefore, the propagation of light or an image is similar to that of light propagating in an optical fiber. The optical waveguide comprises: a substrate 100, which is arranged to guide an optical image in the substrate from an entrance to an exit of the optical waveguide via multiple (total) reflections; a surface relief grating (SRG) 102, 104, which is at the entrance or exit of the optical waveguide, the surface relief grating guiding the image in the optical waveguide via diffraction and comprising a plurality of grooves; and a coating 106, which is disposed on the surface relief grating and at least partially fills at least one groove disposed at an edge of the surface relief grating, wherein the image coincides with the at least one groove after a first reflection in the substrate 100, and the coating 106 has optical properties that converge with the optical properties of the substrate 100.

[0015] As is known in the art, a surface relief grating is a grating having alternating microscopic grooves and ridges to form a diffraction grating that separates light incident on the grating into multiple diffraction orders.

[0016] As mentioned in the background, the dimensions of the optical waveguide can be such that the light is constrained to coincide with the edge of the SRG. Typically, the first order diffraction is arranged to travel through the optical waveguide. The thickness or width of the substrate can be thin relative to the width of the SRG so that the first order light is diffracted at a sufficiently high angle to avoid coinciding with the edge of the SRG. This is particularly important in Figure 1 104. This is shown by the leftmost dashed arrow traveling upward and coinciding with a groove at the edge of SRG 102. Similarly, another reflected component coincides with the edge of SRG 104 at the exit of the optical waveguide. There may be other reasons for the light coinciding with the groove after entering the substrate and / or before exiting the substrate.

[0017] The coating provides a technical effect of reducing the scattering of light incident on the groove after the first reflection. This leverages the convergent optical properties of the coating and substrate. Light propagating within the substrate and coinciding with the groove also strikes the coating, and due to the convergent optical properties (e.g., refractive index), the light can travel through the coating substantially without scattering. Furthermore, because the coating effectively narrows or even fills the groove in some embodiments, the light does not coincide with the optical barrier and is not scattered, or at least has reduced scattering.

[0018] In one embodiment, the optical waveguide described herein is included in augmented reality glasses. In addition to the optical waveguide according to any embodiment described herein, the glasses may also include 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 entrance of the optical waveguide. For example, the lens may be part of the projector.

[0019] It should be understood that Figure 1The optical waveguide shown in FIG is a simplified illustration, and certain features of the waveguide have been exaggerated to illustrate the technical effects of the described embodiments. For example, the thickness of the substrate can be substantially less than that shown. It should also be understood that the size and design of the SRG can vary from that shown. For example, some SRGs have angled grooves, and the embodiments are directly applicable to such SRGs.

[0020] Converging optical properties can be understood as light incident on the grooves and the coating therein being optically similar to the substrate, while light emitted from the substrate coincides with the coating. Since light sees no or minimal optical boundaries, scattering is reduced. Therefore, coating materials can be designed with this in mind. This differs from other coatings that may be used to cover optical waveguides, such as anti-glare coatings, which have variable, uncontrolled properties regarding light convergence with the substrate.

[0021] In one embodiment, the optical properties, such as the refractive index of the coating, are consistent with the optical properties of the substrate.

[0022] 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 include another layer (on top of the at least one layer) having another refractive index.

[0023] In yet another embodiment, at least one layer may comprise a plurality of layers, none of which has a refractive index equal to that of the substrate, but the combined refractive index of the plurality of layers may be equal to that of the substrate. For example, a first layer disposed directly on top of the substrate may be tin dioxide TiO2 having a refractive index of 2.4. A second layer disposed on top of the first layer may be aluminum oxide AlO2 having a refractive index of 1.7, and thus the combined refractive index of the first and second layers may be between 2.4 and 1.7 and may be customized according to the desired optical properties. Such a multilayer coating is not limited to the materials or layers described, but may be freely customized from two or more materials. The properties of the materials and the corresponding layers may be designed such that convergence of the optical properties with the substrate is achieved, for example such that the (combined) refractive index of the coating is substantially equal to the refractive index of the substrate, for example 2.0.

[0024] 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.

[0025] like Figure 1As shown, at least one groove coated with the coating can be positioned at an edge of the surface relief grating, wherein the first order diffraction of the image coincides with the at least one groove. The image can coincide with at least the outermost groove of the SRG facing toward the exit (when the image is incident on the SRG at the entrance) or toward the entrance (when the image is incident on the SRG at the exit). Depending on the embodiment, the image can coincide with multiple grooves at the edge of the SRG, and thus, multiple grooves can be coated. In one embodiment, the entire SRG is coated. Figure 2 An embodiment is shown in which the SRGs 102, 104 are coated with a coating that partially fills the grooves. Thus, the coating optically narrows the grooves, leading to the technical effect described above.

[0026] In one embodiment, the coating completely fills at least one groove, e.g. Figure 1 As shown in the coating 106.

[0027] In one embodiment, the thickness of the coating in the groove varies within the groove, e.g. Figure 3 300 in FIG. When a coating is applied over an SRG and grooves, the coating's viscosity and other deposition-related physical properties can affect how evenly the coating fills the edges of the grooves. It can be beneficial to select a coating that slots toward the bottom of the grooves, resulting in a thicker coating at the bottom than at the groove walls. Light incident on the grooves at least coincides with the bottom of the grooves, and a thicker coating at the bottom can reduce dispersion. In this embodiment, the coating thus only partially fills the grooves, including the outermost grooves where the first order diffraction of the image coincides with the outermost grooves.

[0028] In one embodiment, dispersion is controlled using a coating and the size of the grooves of the SRG. Scattering can be reduced by gradually decreasing the size of the grooves from the center of the SRG toward the edge of the SRG. In other words, the size of the grooves at the edge of the SRG can be smaller than the size of the grooves at the center of the SRG. The width and / or depth of the grooves can gradually decrease toward the edge of the SRG. This optically attenuates the edge of the SRG, thereby reducing dispersion of light that coincides with the grooves after a first reflection within the substrate 100. Grooves can be created using photolithography, but there may be limitations on how narrow the grooves can be. Therefore, using a coating as another tool to control the effective size of the grooves can help reduce scattering.

[0029] In one embodiment, the coating fills the plurality of grooves of the surface relief grating unevenly. Figure 4 An embodiment is shown in which the coating completely fills some grooves of the SRG, while some grooves are only partially filled. Figure 4, the coating may completely fill at least a first groove 400 of the SRG and partially fill at least a second groove 402 , 404 of the SRG, wherein the first groove 400 is closer to an edge of the SRG than the second grooves 402 , 404 , and wherein the second grooves 402 , 404 are wider than the first groove 400 .

[0030] If combined Figure 1 As described above, the coating may be provided on the SRG at least at the entrance of the optical waveguide. According to another aspect, the coating is provided on the SRG at least at the exit of the optical waveguide. According to yet another aspect, the coating is provided on both the entrance SRG and the exit SRG. The two SRGs guide an image in the optical waveguide via diffraction and include a plurality of grooves. The coating is provided on both surface relief gratings and at least partially fills at least one groove provided at an edge of the surface relief grating, wherein the image coincides with the at least one groove after a first reflection within the substrate. Figure 5 Such an embodiment is shown.

[0031] refer to Figure 5 , the SRG 502 at the entrance of the optical waveguide can be coated with the coating material 106 described in any of the above embodiments. In a similar manner, the SRG 504 at the exit and along the waveguide from the entrance toward the first direction can be coated with the coating material 106 described in any of the above embodiments. Figure 5 In an embodiment, there is also a second outlet comprising another SRG 506. The second outlet may be in an opposite direction to the entrance SRG 502. In the entrance SRG 502, the image is inherently diffracted into two opposite directions as is known in optics. Figure 1 In the embodiment, diffraction in another direction away from the exit is not used, but Figure 5 This diffraction is employed in the embodiment of (as shown by the arrows from the entrance towards the two exits). The SRG 506 at the second exit can also be coated by any of the above embodiments.

[0032] It will be appreciated that when the coating is not uniformly disposed on the SRG, the deposition of the coating may be mirrored at the exit SRG relative to the entry SRG. In other words, the coating may be disposed at least within the grooves where light is incident upon the grooves in the substrate 500 (see FIG. Figure 5 As mentioned above, grooves can also be coated from the highlighted edge of the SRG towards the center of the SRG.

[0033] It will also be appreciated that in other embodiments, one or more additional inlets and / or outlets with corresponding SRGs may be present and may also be coated according to the principles described above.

[0034] Then let's refer to Figure 6A method for manufacturing an optical waveguide as described in any of the preceding embodiments is described. According to an embodiment, the manufacturing method includes: forming (block 600) a substrate arranged to guide an optical image within the substrate from an entrance to an exit of the optical waveguide via a plurality of reflections; forming (block 602) a surface relief grating at the entrance of the optical waveguide, the surface relief grating guiding the image to the substrate via diffraction and comprising a plurality of grooves; and at least partially filling (block 604) at least one groove disposed at an edge of the surface relief grating with a coating, wherein the image coincides with the at least one groove after a first reflection within the optical waveguide, the coating having a refractive index that optically narrows the at least one groove and thereby reduces scattering of the image incident on the at least one groove after the first reflection.

[0035] In one embodiment, the surface relief grating is formed on the substrate using photolithography.

[0036] In block 604, a coating may be provided according to any known coating method. Examples of possible coating methods include atomic layer deposition, spin coating, chemical vapor deposition, physical vapor deposition, and spray coating.

[0037] In one embodiment, according to Figure 1 In an embodiment, the filling is performed such that the coating completely fills the at least one groove.

[0038] In one embodiment, the filling is performed so that the coating forms a thicker layer on the bottom of the at least one groove than on the walls of the at least one groove, e.g. Figure 3 As shown in the implementation method.

[0039] In one embodiment, forming the surface relief grating comprises forming grooves of the surface relief grating such that the size of the grooves gradually decreases toward the edge of the surface relief grating, and wherein filling is performed such that the coating fills the grooves of the surface relief grating unevenly, e.g. Figure 4 shown.

[0040] In one embodiment, block 602 includes forming SRGs at a plurality of outlets on a substrate, and filling the grooves of the inlet SRGs and outlet SRGs in block 604, such as Figure 5 shown.

[0041] It is obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above, but may vary within the scope of the claims.

Claims

1. An optical waveguide for an augmented reality display device, comprising: a substrate (100) arranged to guide an optical image within the substrate from an entrance to an exit of the optical waveguide via a plurality of reflections; a surface relief grating (102, 104) at the entrance or the exit of the optical waveguide, the surface relief grating guiding the image in the optical waveguide via diffraction and comprising a plurality of grooves; A coating (106) is directly disposed on the surface relief grating and at least partially fills at least the outermost grooves of the surface relief grating, wherein a first order diffraction of the image coincides with the at least outermost grooves, the coating having a refractive index consistent with the refractive index of the substrate, wherein the coating fills the plurality of grooves of the surface relief grating unevenly 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, wherein the first groove is closer to an edge of the surface relief grating than the second groove, and wherein the second groove is wider than the first groove, wherein the coating together with the groove width of the surface relief grating provides the grooves of the surface relief grating with an optical groove width that gradually narrows toward the edge of the surface relief grating.

2. The optical waveguide according to claim 1, wherein The coating has one layer whose refractive index is substantially equal to that of the substrate; or the coating has multiple layers whose combined refractive index is substantially equal to that of the substrate.

3. The optical waveguide according to claim 2, wherein 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, wherein neither the first refractive index nor the second refractive index is substantially equal to the refractive index of the substrate, but the first coating material and the second coating material together provide a refractive index substantially equal to the refractive index of the substrate.

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

5. The optical waveguide according to claim 1 , comprising surface relief gratings ( 502 , 504 ) at the entrance and the exit of the optical waveguide, the two surface relief gratings guiding the image in the optical waveguide via diffraction and comprising a plurality of grooves, wherein the coating is provided on at least the outermost grooves of the two surface relief gratings and at least partially fills the outermost grooves of the surface relief gratings, wherein the first diffraction order of the image coincides with the outermost grooves.

6. An optical waveguide according to any one of the preceding claims, wherein The coating (106) is directly disposed on the surface relief grating at the entrance and at least partially fills at least one groove disposed at the outermost groove of the entrance surface relief grating, wherein the first order diffraction of the image coincides with the at least one groove and the edge faces the exit.

7. An optical waveguide according to any one of the preceding claims, wherein The outlet is a first outlet, and the optical waveguide further comprises a second outlet opposite to the inlet in a direction opposite to the first outlet, the second outlet further being provided with a surface relief grating (506), wherein the coating at least partially fills the edgemost grooves at both edges of the surface relief grating at the inlet, wherein the first order diffraction of the image at the inlet toward the first outlet and the second outlet coincides with the edgemost grooves at the edge of the inlet surface relief grating.

8. Augmented reality glasses, comprising: An optical waveguide as claimed in any preceding claim; a projector (110) configured to output an optical image; A lens is configured to relay the optical image to the surface relief grating at an entrance to the optical waveguide.

9. A method for manufacturing an optical waveguide, comprising: forming (600) a substrate arranged to direct an optical image within the substrate from an entrance to an exit of the optical waveguide via a plurality of reflections; forming (602) a surface relief grating at the inlet or the outlet of the optical waveguide, the surface relief grating directing the image to the substrate via diffraction and comprising a plurality of grooves; At least the outermost grooves of the surface relief grating are at least partially filled (604) with a coating, wherein a first order diffraction of the image coincides with at least one groove, the coating having a refractive index that optically narrows the at least outermost groove and thereby reduces scattering of an image incident on the at least outermost groove with a first order diffraction, wherein the coating fills the plurality of grooves of the surface relief grating unevenly 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, wherein the first groove is closer to an edge of the surface relief grating than the second groove, and wherein the second groove is wider than the first groove, wherein the coating together with the groove width of the surface relief grating provides the grooves of the surface relief grating with an optical groove width that gradually narrows toward the edge of the surface relief grating.

10. The method according to claim 9, wherein: The surface relief grating is formed using photolithography.

11. The method according to claim 9 or 10, wherein: The filling is performed such that the coating completely fills the at least edgemost groove.

Images