US-20260126656-A1 - WAVEGUIDE FOR AN AUGMENTED REALITY OR VIRTUAL REALITY DISPLAY

US20260126656A1US 20260126656 A1US20260126656 A1US 20260126656A1US-20260126656-A1

Abstract

A planar slab waveguide for use in an augmented reality or virtual reality display is disclosed. The planar slab waveguide comprises a diffractive element comprising optical structures having a different refractive index to a surrounding waveguide medium. The optical structures are arranged in an array parallel to a first major surface and a second major surface of the waveguide. The array is configured to diffract a first portion of the light to provide 2D expansion across the plane of the waveguide and to diffract a second portion of the light out of the plane of the waveguide. At least one of the optical structures has a height that varies along a direction parallel to the plane of the waveguide, thereby causing the second portion of light to be diffracted preferentially from the first major surface of the waveguide, compared to the second major surface of the waveguide.

Inventors

Tom Vidar Michalsen
Mohmed Salim Valera

Assignees

SNAP INC.

Dates

Publication Date: 20260507
Application Date: 20251229
Priority Date: 20200403

Claims (20)

1 . A planar slab waveguide for use in an augmented reality or virtual reality display, comprising: a diffractive element comprising a plurality of optical structures having a different refractive index to a surrounding waveguide medium; wherein the plurality of optical structures are arranged in a planar array of the planar slab waveguide parallel to a first major surface of the planar slab waveguide and a second major surface of the planar slab waveguide, the planar array configured to: diffract a first portion of received light into an angle relative to an input light path to provide 2D expansion across a plane of the planar slab waveguide that is parallel to the planar array, the first major surface, and the second major surface; and diffract a second portion of the received light out of the plane of the planar slab waveguide, wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide.
2 . The planar slab waveguide of claim 1 , wherein the height of the at least one of the optical structures of the plurality of optical structures varies continuously along the one or more directions parallel to the plane of the planar slab waveguide.
3 . The planar slab waveguide of claim 1 , wherein the at least one of the plurality of optical structures has a discontinuity in its height.
4 . The planar slab waveguide of claim 3 , wherein the at least one of the plurality of optical structures comprises a plurality of discontinuities.
5 . The planar slab waveguide according to claim 1 , wherein a variation in height of at least some of the plurality of optical structures is different to the variation in height of others of the plurality of optical structures.
6 . The planar slab waveguide according to claim 5 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures different from the first variation in height, and the first region being displaced from the second region along the plane of the planar slab waveguide.
7 . The planar slab waveguide according to claim 5 , wherein the input light path defines a first axis in the plane of the planar slab waveguide, and the one or more directions through which the optical structures vary in height is at an angle to the input light path.
8 . The planar slab waveguide according to claim 7 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures, wherein the direction through which the first subset of optical structures vary in height is at a first angle to the input light path and the direction through which the second subset of optical structures vary in height is at a second angle to the input light path, wherein the first region and the second region are separated by a line formed along the input light path extending from a point at which light is incident at the diffractive element.
9 . The planar slab waveguide according to claim 1 , wherein at least one of the plurality of optical structures is arranged such that the height of the at least one optical structure has a negative gradient in a direction away from a point at which the light is incident on the at least one optical structure.
10 . The planar slab waveguide according to claim 1 , wherein at least one of the plurality of optical structures is arranged such that the height of the at least one optical structure has a positive gradient in a direction away from a point at which the light is incident on the at least one optical structure.
11 . The planar slab waveguide of claim 1 , wherein the plurality of optical structures, respectively, have a shape, when viewed in the plane of the planar slab waveguide, comprising a plurality of substantially straight sides having respective normal vectors at different angles.
12 . An augmented reality or virtual reality display, comprising: a planar slab waveguide comprising: a diffractive element including a plurality of optical structures having a different refractive index to a surrounding waveguide medium; wherein the plurality of optical structures are arranged in a planar array of the planar slab waveguide parallel to a first major surface of the planar slab waveguide and a second major surface of the planar waveguide, the planar array configured to: diffract a first portion of received light into an angle relative to an input light path to provide 2D expansion across a plane of the planar slab waveguide that is parallel to the planar array, the first major surface, and the second major surface, and diffract a second portion of the received light out of the plane of the planar slab waveguide; wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide.
13 . The augmented reality or virtual reality display of claim 12 , wherein the height of the at least one of the optical structures of the plurality of optical structures varies continuously along the one or more directions parallel to the plane of the planar slab waveguide.
14 . The augmented reality or virtual reality display of claim 12 , wherein the at least one of the plurality of optical structures has a discontinuity in its height.
15 . The augmented reality or virtual reality display of claim 14 , wherein the at least one of the plurality of optical structures comprises a plurality of discontinuities.
16 . The augmented reality or virtual reality display of claim 12 , wherein a variation in height of at least some of the plurality of optical structures is different to the variation in height of others of the plurality of optical structures.
17 . The augmented reality or virtual reality display according to claim 16 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures different from the first variation in height, and the first region being displaced from the second region along the plane of the planar slab waveguide.
18 . The augmented reality or virtual reality display according to claim 15 , wherein the input light path defines a first axis in the plane of the planar slab waveguide, and the one or more directions through which the optical structures vary in height is at an angle to the input light path.
19 . The augmented reality or virtual reality display according to claim 18 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures, wherein the direction through which the first subset of optical structures vary in height is at a first angle to the input light path and the direction through which the second subset of optical structures vary in height is at a second angle to the input light path, wherein the first region and the second region are separated by a line formed along the input light path extending from a point at which light is incident at the diffractive element.
20 . A method of manufacture of a planar slab waveguide for an augmented reality or virtual reality display, the method comprising: providing a planar slab waveguide comprising a diffractive element comprising a plurality of optical structures, wherein the optical structures have a different refractive index to a surrounding waveguide medium; and arranging the plurality of optical structures, wherein the planar slab waveguide comprises a first major surface of the waveguide, and a second major surface of the waveguide, the second major surface parallel to the first major surface, wherein light propagates through the planar slab waveguide along an input light path towards the diffractive element by undergoing total internal reflection between the first and second major surfaces; wherein the plurality of optical structures are arranged in a plane of the planar slab waveguide parallel to the first major surface and the second major surface in an array which is configured to: diffract a first portion of the light into an angle relative to the input light path to provide 2D expansion across the plane of the planar slab waveguide; and diffract a second portion of the light out of the plane of the planar slab waveguide, wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of the light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide.

Description

CLAIM OF PRIORITY This application is a continuation of U.S. patent application Ser. No. 17/995,372, filed on Oct. 3, 2022, which is a U.S. national-phase application filed under 35 U.S.C. § 371 from International Application Serial No. PCT/EP2021/057311, filed on Mar. 22, 2021, and published as WO 2021/197907 on Oct. 7, 2021, which claims the benefit of priority to EP Patent Application Serial No. 20168055.0, filed on Apr. 3, 2020, each of which are incorporated herein by reference in their entireties. TECHNICAL FIELD The present invention relates to a waveguide for use in an augmented reality or virtual reality display. In particular, the invention relates to a waveguide in which input light is expanded in two orthogonal directions in an output element and is coupled out of a waveguide towards a viewer in a preferential direction. This can allow physical expansion of the eyebox in an augmented reality display whilst ensuring improved efficiency of the system. BACKGROUND An augmented reality display allows a user to view their surroundings as well as projected images. In military or transportation applications the projected images can be overlaid on the real world perceived by the user. Other applications for these displays include video games and wearable devices, such as glasses. In a normal augmented reality set-up a transparent display screen is provided in front of a user so that they can continue to see the physical world. The display screen is typically a glass waveguide, and a projector is provided to one side. Light from the projector is coupled into the waveguide by a diffraction grating. The projected light is totally internally reflected within the waveguide. The light is then coupled out of the waveguide by another diffraction grating so that it can be viewed by a user. The projector can provide information and/or images that augment a user's view of the physical world. An optical device is disclosed in WO 2016/020643 for expanding input light in two dimensions in an augmented reality display. An input diffractive optical element is provided for coupling input light from a projector into a waveguide. The optical device also includes an output element having two diffractive optical elements overlaid on one another in the waveguide so that each of the two diffractive optical elements can receive light from the input diffractive optical element and couple it towards the other diffractive optical element in the pair, which can then act as an output diffractive optical element which couples light out of the waveguide towards a viewer. In one embodiment the two diffractive optical elements overlaid on one another are provided in a photonic crystal. This is achieved by having an array of pillars arranged within or on the surfaces the waveguide, having a refractive index change relative to the surrounding waveguide medium. The pillars in WO 2016/020643 are described as having a circular cross-sectional shape when viewed in the plane of the waveguide, from the perspective of a viewer. This arrangement has been found to be very effective at simultaneously expanding light in two dimensions and coupling light out of the waveguide. Advantageously this can improve the use of space on the waveguide which can decrease the cost of manufacture. An optical device having pillars which have a diamond cross-sectional shape is disclosed in WO2018/178626. A modified diamond cross-sectional shape is also shown, the modified diamond having notches. Pillars having these shapes, rather than circular cross section, have been shown to reduce the occurrence of a central strip in the output element having a higher relative brightness than other parts, reducing the undesirable “striping” effect somewhat in the output image. Other shapes have also been proposed. One drawback of these types of waveguides is that when the light is incident on the output element diffraction orders which couple light out of the waveguide may extend in opposite directions. This may include orders that are transmitted through the grating and out to the viewer, and orders that are reflected by the grating and out to the viewer. Typically waveguide systems are designed such that the viewer views only a single one of these out-coupled orders. This leads to a decrease in efficiency of the waveguide as a portion of the light that could be used to form an image for the viewer is wasted in this unwanted outcoupling direction. In addition, the unwanted coupling order also forms an image which could cause privacy concerns by allowing external observers to see what the wearer is viewing. SUMMARY OF INVENTION According to an aspect of the invention there is provided a waveguide for use in an augmented reality or virtual reality display, comprising: an output diffractive element comprising a plurality of optical structures in a photonic crystal; wherein the plurality of optical structures are arranged in a plane of the waveguide in an array which is configured