Facebook Patent | Angular Selective Grating Coupler For Waveguide Display

Patent: Angular Selective Grating Coupler For Waveguide Display

Publication Number: 10598938

Publication Date: 20200324

Applicants: Facebook

Abstract

An optical coupler for a waveguide-based display includes a slanted surface-relief grating that includes a plurality of regions. Different regions of the plurality of regions of the slanted surface-relief grating have different angular selectivity characteristics for incident display light. Display light for different viewing angles is diffracted by different regions of the slanted surface-relief grating.

BACKGROUND

An artificial reality system, such as a head-mounted display (HMD) or heads-up display (HUD) system, generally includes a near-eye display (e.g., a headset or a pair of glasses) configured to present content to a user via an electronic or optic display within, for example, about 10-20 mm in front of the user’s eyes. The near-eye display may display virtual objects or combine images of real objects with virtual objects, as in virtual reality (VR), augmented reality (AR), or mixed reality (MR) applications. For example, in an AR system, a user may view both images of virtual objects (e.g., computer-generated images (CGIs)) and the surrounding environment by, for example, seeing through transparent display glasses or lenses (often referred to as optical see-through) or viewing displayed images of the surrounding environment captured by a camera (often referred to as video see-through).

One example optical see-through AR system may use a waveguide-based optical display, where light of projected images may be coupled into a waveguide (e.g., a substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations. In some implementations, the light may be coupled out of the waveguide using a diffractive optical element, such as a grating. As any other mobile electronic device, it is generally desirable that the efficiency of the waveguide-based optical display be as high as possible.

SUMMARY

This disclosure relates generally to techniques for artificial reality system, and more specifically, to a waveguide-based near-eye display system. According to certain embodiments, an optical coupler for a waveguide-based near-eye display may include a grating coupler (e.g., a slanted surface-relief grating) that includes multiple regions (e.g., with a width for each region in the range of about 10 micrometers to about 1 millimeter), where different regions of the grating coupler may have different angular selectivity characteristics (constructive interference conditions) for the incident display light such that, at any region of the waveguide-based near-eye display, diffraction light that would not eventually reach user’s eyes may be suppressed (i.e., may not be diffracted by the grating coupler so as to be coupled into or out of the waveguide), and only light that may eventually reach the user’s eyes may be diffracted by the grating coupler and be coupled into or out of the waveguide. In this way, the overall power efficiency of the near-eye display system may be significantly improved.

In some embodiments, an optical coupler for a waveguide-based display may include a slanted surface-relief grating that includes a plurality of regions, where different regions of the plurality of regions of the slanted surface-relief grating may have different angular selectivity characteristics for incident display light, and display light for different viewing angles may be diffracted by different regions of the slanted surface-relief grating. In some embodiments, different regions of the plurality of regions of the slanted surface-relief grating may have at least one of different grating duty cycles, different slant angles, or different refractive indexes.

In some embodiments, the slanted surface-relief grating may include an overcoat layer filling gaps in the slanted surface-relief grating, and different regions of the plurality of regions of the slanted surface-relief grating may have different refractive indexes in the overcoat layer. In some embodiments, the overcoat layer may include different materials or a same material with different doping at different regions of the slanted surface-relief grating. In some embodiments, a difference between a refractive index of the overcoat layer and a refractive index of the slanted surface-relief grating may be equal to or greater than 0.2.

In some embodiments, the slanted surface-relief grating may be configured to couple display light out of a waveguide of the waveguide-based display. The display light diffracted by different regions of the slanted surface-relief grating out of the waveguide may propagate at different directions towards an eyebox of the waveguide-based display. In some embodiments, an area of the eyebox may be less than one fifth of an output area of the waveguide-based display.

In some embodiments, each region of the plurality of regions of the slanted surface-relief grating may be configured to couple display light for a respective field of view into a waveguide of the waveguide-based display and prevent the coupled display light for other fields of view from being coupled out of the waveguide by the slanted surface-relief grating. The display light diffracted by different regions of the slanted surface-relief grating into the waveguide may propagate at different directions within the waveguide.

In some embodiments, the slanted surface-relief grating may be formed on a front or back surface of the waveguide-based display. In some embodiments, a width of each of the plurality of regions is between 10 micrometers and 1 millimeter. In some embodiments, the display light diffracted by each region of the slanted surface-relief grating may have an angular range greater than 10.degree.. In some embodiments, a slant angle of the slanted surface-relief grating may be greater than 30.degree..

According to certain embodiments, a waveguide-based near-eye display may include a substrate and an output coupler including a slanted surface-relief grating formed on a surface of the substrate. The slanted surface-relief grating may include a plurality of regions. Different regions of the plurality of regions of the slanted surface-relief grating may have different angular selectivity characteristics for incident display light. Display light diffracted by different regions of the slanted surface-relief grating may propagate at different directions towards an eyebox of the waveguide-based near-eye display.

In some embodiments of the waveguide-based near-eye display, different regions of the plurality of regions of the slanted surface-relief grating may have different grating duty cycles that range from 5% to 95%, and a depth of the slanted surface-relief grating may be greater than a threshold value. In some embodiments, the threshold may be greater than a half of a grating period of the slanted surface-relief grating.

In some embodiments, the slanted surface-relief grating may include an overcoat layer filling gaps in the slanted surface-relief grating. Different regions of the plurality of regions of the slanted surface-relief grating may have different refractive indexes in the overcoat layer. In some embodiments, a difference between a refractive index of the overcoat layer and a refractive index of the slanted surface-relief grating may be equal to or greater than 0.2.

In some embodiments, the display light diffracted by each region of the slanted surface-relief grating may have an angular range greater than 10.degree..

In some embodiments, the waveguide-based near-eye display may also include a light source, and an input coupler formed on the substrate and configured to couple display light from the light source into the substrate. The input coupler may include a plurality of regions having different angular selectivity characteristics. Each region of the input coupler may be configured to couple display light within a respective angular range into the substrate.

According to certain embodiments, a method of displaying images using a waveguide-based near-eye display may include diffracting, by a first region of a slanted grating coupler, only a first portion of display light out of a waveguide, where the first portion of display light may propagate at angles within a first angular range towards an eyebox of the waveguide-based near-eye display. The method may also include diffracting, by a second region of the slanted grating coupler, only a second portion of display light out of the waveguide, where the second portion of display light may propagate at angles within a second angular range towards the eyebox of the waveguide-based near-eye display, and the second angular range is different from the first angular range. In some embodiments, the first region and the second region of the slanted grating coupler have different duty cycles, slant angles, or refractive index modulations.

In some embodiments, an optical coupler for a waveguide-based display may include a slanted surface-relief grating that includes a plurality of regions, where different regions of the plurality of regions of the slanted surface-relief grating may have different angular selectivity characteristics for incident display light, and display light for different viewing angles may be diffracted by different regions of the slanted surface-relief grating. In some embodiments, different regions of the plurality of regions of the slanted surface-relief grating may have at least one of different grating duty cycles, different slant angles, or different refractive indexes.

In some embodiments, the slanted surface-relief grating may include an overcoat layer filling gaps in the slanted surface-relief grating, and different regions of the plurality of regions of the slanted surface-relief grating may have different refractive indexes in the overcoat layer. In some embodiments, the overcoat layer may include different materials or a same material with different doping at different regions of the slanted surface-relief grating. In some embodiments, a difference between a refractive index of the overcoat layer and a refractive index of the slanted surface-relief grating may be equal to or greater than 0.2.

In some embodiments, the slanted surface-relief grating may be configured to couple display light out of a waveguide of the waveguide-based display. The display light diffracted by different regions of the slanted surface-relief grating out of the waveguide may propagate at different directions towards an eyebox of the waveguide-based display. In some embodiments, an area of the eyebox may be less than one fifth of an output area of the waveguide-based display.

In some embodiments, each region of the plurality of regions of the slanted surface-relief grating may be configured to couple display light for a respective field of view into a waveguide of the waveguide-based display and prevent the coupled display light for other fields of view from being coupled out of the waveguide by the slanted surface-relief grating. The display light diffracted by different regions of the slanted surface-relief grating into the waveguide may propagate at different directions within the waveguide.

In some embodiments, the slanted surface-relief grating may be formed on a front or back surface of the waveguide-based display. In some embodiments, a width of each of the plurality of regions is between 10 micrometers and 1 millimeter. In some embodiments, the display light diffracted by each region of the slanted surface-relief grating may have an angular range greater than 10.degree.. In some embodiments, a slant angle of the slanted surface-relief grating may be greater than 30.degree..

According to certain embodiments, a waveguide-based near-eye display may include a substrate and an output coupler including a slanted surface-relief grating formed on a surface of the substrate. The slanted surface-relief grating may include a plurality of regions. Different regions of the plurality of regions of the slanted surface-relief grating may have different angular selectivity characteristics for incident display light. Display light diffracted by different regions of the slanted surface-relief grating may propagate at different directions towards an eyebox of the waveguide-based near-eye display.

In some embodiments of the waveguide-based near-eye display, different regions of the plurality of regions of the slanted surface-relief grating may have different grating duty cycles that range from 5% to 95%, and a depth of the slanted surface-relief grating may be greater than a threshold value. In some embodiments, the threshold may be greater than a half of a grating period of the slanted surface-relief grating.

In some embodiments, the slanted surface-relief grating may include an overcoat layer filling gaps in the slanted surface-relief grating. Different regions of the plurality of regions of the slanted surface-relief grating may have different refractive indexes in the overcoat layer. In some embodiments, a difference between a refractive index of the overcoat layer and a refractive index of the slanted surface-relief grating may be equal to or greater than 0.2.

In some embodiments, the display light diffracted by each region of the slanted surface-relief grating may have an angular range greater than 10.degree..

In some embodiments, the waveguide-based near-eye display may also include a light source, and an input coupler formed on the substrate and configured to couple display light from the light source into the substrate. The input coupler may include a plurality of regions having different angular selectivity characteristics. Each region of the input coupler may be configured to couple display light within a respective angular range into the substrate.

According to certain embodiments, a method of displaying images using a waveguide-based near-eye display may include diffracting, by a first region of a slanted grating coupler, only a first portion of display light out of a waveguide, where the first portion of display light may propagate at angles within a first angular range towards an eyebox of the waveguide-based near-eye display. The method may also include diffracting, by a second region of the slanted grating coupler, only a second portion of display light out of the waveguide, where the second portion of display light may propagate at angles within a second angular range towards the eyebox of the waveguide-based near-eye display, and the second angular range is different from the first angular range. In some embodiments, the first region and the second region of the slanted grating coupler have different duty cycles, slant angles, or refractive index modulations.

This summary is neither intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings, and each claim. The foregoing, together with other features and examples, will be described in more detail below in the following specification, claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference to the following figures.

FIG. 1 is a simplified block diagram of an example artificial reality system environment including a near-eye display according to certain embodiments.

FIG. 2 is a perspective view of an example near-eye display in the form of a head-mounted display (HMD) device for implementing some of the examples disclosed herein.

FIG. 3 is a perspective view of a simplified example near-eye display in the form of a pair of glasses for implementing some of the examples disclosed herein.

FIG. 4 illustrates an example optical see-through augmented reality system using a waveguide display according to certain embodiments.

FIG. 5 is a cross-sectional view of an example near-eye display according to certain embodiments.

FIG. 6A illustrates an example of a waveguide-based near-eye display where display light for all fields of view is uniformly output from different regions of the waveguide.

FIG. 6B illustrates an example of a waveguide-based near-eye display where display light is coupled out of the waveguide at different angles in different regions of the waveguide according to certain embodiments.

FIG. 7A illustrates an example of a waveguide-based near-eye display where display light is coupled out of the waveguide at a first angular range from a first region of the waveguide according to certain embodiments.

FIG. 7B illustrates an example of a waveguide-based near-eye display where display light is coupled out of the waveguide at a second angular range from a second region of the waveguide according to certain embodiments.

FIG. 7C illustrates an example of a waveguide-based near-eye display where display light is coupled out of the waveguide at a third angular range from a third region of the waveguide according to certain embodiments.

FIG. 8 illustrates light diffraction by an example of a slanted grating coupler on a front surface of a waveguide-based near-eye display according to certain embodiments.

FIG. 9 illustrates the angular selectivity of an example of a slanted grating coupler in a waveguide-based near-eye display according to certain embodiments.

FIG. 10 illustrates angular selectivity characteristics of different regions of an example of a slanted grating coupler in a waveguide-based near-eye display, where the slanted grating coupler has different duty cycles at different regions according to certain embodiments.

FIG. 11 illustrates the angular selectivity characteristics of different regions of an example of a slanted grating coupler in a waveguide-based near-eye display, where the slanted grating coupler has different refractive index modulations at different regions according to certain embodiments.

FIG. 12 illustrates light diffraction by an example of a slanted grating coupler on a back surface of a waveguide-based near-eye display according to certain embodiments.

FIG. 13 illustrates an example of a waveguide-based near-eye display where display light from different fields of view may be coupled into the waveguide at different angles in different regions of an input coupler according to certain embodiments.

FIG. 14 illustrates an example of a method of displaying images using a waveguide-based near-eye display according to certain embodiments.

FIG. 15 is a simplified block diagram of an example electronic system of an example near-eye display according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated may be employed without departing from the principles, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

DETAILED DESCRIPTION

Techniques disclosed herein relate generally to an artificial reality system, and more specifically, to a waveguide-based near-eye display system. In a waveguide-based near-eye display system, the output area of the waveguide is usually much larger than the size of the eyebox of the near-eye display system. Thus, if the display light for all fields of view is uniformly output from any region of the waveguide, the portion of light that may reach a user’s eyes may depend on the ratio between the size of the eyebox and the output area of the waveguide, which may be less than, for example 10% for a certain eye relief and field of view.

According to certain embodiments, an optical coupler for a waveguide-based display may include a grating coupler (e.g., a slanted surface-relief grating or other diffractive gratings) that may include multiple regions (e.g., with a width for each region in the range of about 10 micrometers to about 1 millimeter), where different regions of the grating coupler may have different angular selectivity characteristics (constructive interference conditions) for the incident display light such that diffraction light that would not eventually propagate towards the eyebox of the near-eye display system may be suppressed (i.e., may not be diffracted by the grating into or out of the waveguide). In this way, light from different fields of view (or viewing angles) may be coupled into or out of the waveguide at different regions of the waveguide, and, at any given region, only light that may eventually reach the eyebox may be coupled into or out of the waveguide, while other display light in the waveguide may continue to propagate within the waveguide until it is coupled out of the waveguide at a region of the grating coupler where the display light meets the corresponding angular selectivity condition at the region of the grating coupler. Therefore, most of the display light from different fields of view may reach the user’s eyes, and the efficiency of the waveguide-based display may thus be significantly improved.

The different angular selectivity characteristics of the grating coupler may be achieved by different grating configurations (and thus different effective optical path length over a grating period) of the grating coupler at different regions. The different configurations may include, for example, different duty cycles (a ratio between the width of a grating ridge and the grating period), different refractive indexes, different slant angles, different periods, or any combination thereof, at different regions of the slanted surface-relief grating. There may be many different ways to manufacture grating couplers with varying configurations (e.g., duty cycles or refractive index modulations) over the full region of the grating coupler. For example, a slanted surface-relief grating coupler with a varying duty cycle (e.g., from about 5% to about 95%) may be fabricated using various lithography and etching techniques, such as ion beam etch (IBE), reactive ion beam etch (RIBE), or chemically assisted ion beam etch (CAIBE) process, or other pattern transfer techniques. The different refractive index modulations can be achieved by, for example, varying the overcoat material for the slanted surface-relief grating or changing the doping in the overcoat layer at different regions of the grating coupler.

In grating couplers including slanted surface-relief gratings, a large refractive index variation (e.g., >0.2) between the grating ridge and grating groove region in a grating period can be achieved. Thus, a large angular bandwidth (e.g., >10.degree.) may be achieved to provide a sufficiently large eyebox for the waveguide-based display system. In addition, because of the large refractive index variation, the angular selectivity can be achieved by the constructive interference between a small number (e.g., two or more) of grating periods, and thus the depth of the slanted surface-relief grating can be small (e.g., a thinner grating).

The slanted surface-relief grating with a varying angular selectivity can be positioned on either the side of the waveguide closer to the user’s eyes or the side of the waveguide further from the user’s eyes. The same techniques can also be used for an optical input coupler in the waveguide-based display.

In the following description, for the purposes of explanation, specific details are set forth in order to provide a thorough understanding of examples of the disclosure. However, it will be apparent that various examples may be practiced without these specific details. For example, devices, systems, structures, assemblies, methods, and other components may be shown as components in block diagram form in order not to obscure the examples in unnecessary detail. In other instances, well-known devices, processes, systems, structures, and techniques may be shown without necessary detail in order to avoid obscuring the examples. The figures and description are not intended to be restrictive. The terms and expressions that have been employed in this disclosure are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. The word “example” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment or design described herein as “example” is not necessarily to be construed as preferred or advantageous over other embodiments or designs.

FIG. 1 is a simplified block diagram of an example artificial reality system environment 100 including a near-eye display 120 in accordance with certain embodiments. Artificial reality system environment 100 shown in FIG. 1 may include near-eye display 120, an optional external imaging device 150, and an optional input/output interface 140 that may each be coupled to an optional console 110. While FIG. 1 shows example artificial reality system environment 100 including one near-eye display 120, one external imaging device 150, and one input/output interface 140, any number of these components may be included in artificial reality system environment 100, or any of the components may be omitted. For example, there may be multiple near-eye displays 120 monitored by one or more external imaging devices 150 in communication with console 110. In some configurations, artificial reality system environment 100 may not include external imaging device 150, optional input/output interface 140, and optional console 110. In alternative configurations, different or additional components may be included in artificial reality system environment 100.

Near-eye display 120 may be a head-mounted display that presents content to a user. Examples of content presented by near-eye display 120 include one or more of images, videos, audios, or some combination thereof. In some embodiments, audios may be presented via an external device (e.g., speakers and/or headphones) that receives audio information from near-eye display 120, console 110, or both, and presents audio data based on the audio information. Near-eye display 120 may include one or more rigid bodies, which may be rigidly or non-rigidly coupled to each other. A rigid coupling between rigid bodies may cause the coupled rigid bodies to act as a single rigid entity. A non-rigid coupling between rigid bodies may allow the rigid bodies to move relative to each other. In various embodiments, near-eye display 120 may be implemented in any suitable form factor, including a pair of glasses. Some embodiments of near-eye display 120 are further described below with respect to FIGS. 2, 3, and 20. Additionally, in various embodiments, the functionality described herein may be used in a headset that combines images of an environment external to near-eye display 120 and artificial reality content (e.g., computer-generated images). Therefore, near-eye display 120 may augment images of a physical, real-world environment external to near-eye display 120 with generated content (e.g., images, video, sound, etc.) to present an augmented reality to a user.

In various embodiments, near-eye display 120 may include one or more of display electronics 122, display optics 124, and an eye-tracking unit 130. In some embodiments, near-eye display 120 may also include one or more locators 126, one or more position sensors 128, and an inertial measurement unit (IMU) 132. Near-eye display 120 may omit any of these elements or include additional elements in various embodiments. Additionally, in some embodiments, near-eye display 120 may include elements combining the function of various elements described in conjunction with FIG. 1.

Display electronics 122 may display or facilitate the display of images to the user according to data received from, for example, console 110. In various embodiments, display electronics 122 may include one or more display panels, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a micro light emitting diode (mLED) display, an active-matrix OLED display (AMOLED), a transparent OLED display (TOLED), or some other display. For example, in one implementation of near-eye display 120, display electronics 122 may include a front TOLED panel, a rear display panel, and an optical component (e.g., an attenuator, polarizer, or diffractive or spectral film) between the front and rear display panels. Display electronics 122 may include pixels to emit light of a predominant color such as red, green, blue, white, or yellow. In some implementations, display electronics 122 may display a three-dimensional (3D) image through stereo effects produced by two-dimensional panels to create a subjective perception of image depth. For example, display electronics 122 may include a left display and a right display positioned in front of a user’s left eye and right eye, respectively. The left and right displays may present copies of an image shifted horizontally relative to each other to create a stereoscopic effect (i.e., a perception of image depth by a user viewing the image).

In certain embodiments, display optics 124 may display image content optically (e.g., using optical waveguides and couplers) or magnify image light received from display electronics 122, correct optical errors associated with the image light, and present the corrected image light to a user of near-eye display 120. In various embodiments, display optics 124 may include one or more optical elements, such as, for example, a substrate, optical waveguides, an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical elements that may affect image light emitted from display electronics 122. Display optics 124 may include a combination of different optical elements as well as mechanical couplings to maintain relative spacing and orientation of the optical elements in the combination. One or more optical elements in display optics 124 may have an optical coating, such as an anti-reflective coating, a reflective coating, a filtering coating, or a combination of different optical coatings.

Magnification of the image light by display optics 124 may allow display electronics 122 to be physically smaller, weigh less, and consume less power than larger displays. Additionally, magnification may increase a field of view of the displayed content. The amount of magnification of image light by display optics 124 may be changed by adjusting, adding, or removing optical elements from display optics 124.

Display optics 124 may also be designed to correct one or more types of optical errors, such as two-dimensional optical errors, three-dimensional optical errors, or a combination thereof. Two-dimensional errors may include optical aberrations that occur in two dimensions. Example types of two-dimensional errors may include barrel distortion, pincushion distortion, longitudinal chromatic aberration, and transverse chromatic aberration. Three-dimensional errors may include optical errors that occur in three dimensions. Example types of three-dimensional errors may include spherical aberration, comatic aberration, field curvature, and astigmatism.