Patent Description:
Light transmitted from a microdisplay to a user's eye in an eyewear display device generally undergoes multiple reflections, refractions, diffractions, and/or changes in polarization that can result in stray light within the system. Stray light within an eyewear display device reduces image contrast and can create haziness and ghost images in the field of view. Minimizing stray light in eyewear display devices provides a user with a more enjoyable viewing experience while also reducing eye fatigue.

<CIT> discloses an image display device to be used in a wearable electronic eyewear device, said display device comprising a microdisplay, a curved lightguide, an incoupler for directing light from the microdisplay into the lightguide and an outcoupler for directing a portion of the light out of the lightguide toward a user's eye, said outcoupler being arranged to receive a single interaction of the light at the side of the outcoupler facing the user's eye.

The present disclosure describes embodiments of an eyewear display having an expanded eyebox and techniques for mitigating artifacts. The proposed solution relates to an eyewear display device of claim <NUM> and a method of claim <NUM>.

The population of potential eyewear display users exhibits a large range of facial geometries characterized by a distribution of nose geometries, a distribution of distances from ear apex to ear apex, and a distribution of interpupillary distances (i.e., a distance between centers of the user's pupils). A single eyewear display device design is not likely to provide an optimal experience for all users while meeting all the physical and geometric constraints of a wearable device. For example, a user only sees the entirety of the image displayed by the eyewear display device if the user's pupils fall within an "eyebox" produced by the optical system implemented in the device. However, a conventional eyewear display device produces a relatively small eyebox that does not encompass pupil locations throughout the entire distribution of facial geometries. Consequently, not all users are able to view the image displayed by the eyewear display.

The term "eyebox" refers to a three-dimensional (3D) volume in space within which the pupil of an eye is positioned in order to satisfy one or more viewing experience criteria. One example of a viewing experience criterion is that the user sees four edges of a magnified virtual image. In that case, the eyebox is the 3D volume in space within which the user's pupil is positioned to see the four edges of the magnified virtual image. In some embodiments, the volume of the eyebox produced by an electronic eyewear device is evaluated based on pupil diameter, an angular extent of an emission cone produced by the electronic eyewear device, a set of criteria, and thresholds for the criteria. Thus, increasing the pupil diameter increases the eyebox of an eyewear display, meaning the eyewear display can be used by a larger population of potential users with differing facial sizes and geometries.

Current flat waveguide architectures have optics, manufacturing, thickness, and prescription lens constraints. For example, optics are limited by battery life, image quality challenges such as resolution and color uniformity, and cost. In addition, optics are constrained by light leakage, lens back reflections, diffractive artifacts, and visible structures from within the lenses. Previous curved lightguide designs targeted optics efficiency of approximately <NUM>%, implying an optical combiner tilt angle designed such that all light rays undergo total internal reflection (TIR). However, a tilt angle that results in TIR for all light rays geometrically limits the eyebox to the lightguide thickness. As light sources achieve higher luminance (on the order of one million nits), the percentage of light rays for which TIR is targeted can be relaxed.

<FIG> illustrate thin, curved lightguides that employ at least one incoupler that is thicker than the curved lightguide as well as an outcoupler disposed at an angle with respect to the curved lightguide to receive at least two interactions of display light before coupling the display light out of the curved lightguide toward a user's eye to achieve a relatively large pupil diameter (i.e., eyebox). In some embodiments, the curved lightguide is approximately <NUM> thick. The curved lightguides can be implemented in a variety of eyewear display devices, including those with an eyeglass form factor. In general, the terms "incoupler" and "outcoupler" refer to certain types of optical structures, including, but not limited to, transmissive gratings (e.g., a transmissive diffraction grating or a transmissive holographic grating) that causes the incoupler or outcoupler to transmit light and to apply designed optical function(s) to the light during the transmission. In some embodiments, a given incoupler or outcoupler is a reflective grating (e.g., a reflective diffraction grating or a reflective holographic grating) that causes the incoupler or outcoupler to reflect light and to apply designed optical function(s) to the light during the reflection. In some embodiments, the outcoupler is a freeform mirror.

The outcoupler (also sometimes referred to as an optical combiner) combines two light sources, such as environmental light from outside of the combiner and light transmitted from a microdisplay that is directed to the combiner via a waveguide (also referred to as a lightguide). Optical combiners in eyewear display devices, sometimes referred to as near-eye displays, allow a user to view computer-generated content such as text, images, or video content, superimposed over a user's environment viewed through the eyewear display, creating an augmented reality (AR) or mixed reality (MR) experience.

The thicker incoupler couples more display light into the curved lightguide than would be possible with an incoupler that is the same thickness as the curved lightguide. The additional incoupled display light and the outcoupler tilted to receive two bounces of display light result in a larger eyebox, but also allow additional artifact light to be transmitted through the curved lightguide. For example, extraneous side images are produced by light emitted at high angles from the microdisplay in an eyewear display. High-angle light rays that are coupled into the lightguide of the eyewear display create side images in addition to the main image. Depending on the number of bounces, given N bounces for the main image, N+<NUM> and N-<NUM> bounces create artifact images (also referred to as side images). The side images interfere with a user's view of the world and detract from the experience of using the eyewear display.

The thicker incoupler allows more display light that includes both main image light and side image light into the curved lightguide and enlarges the footprints of both main image light and side image light. While the respective footprints of the main image light and side image light overlap in some areas, in other areas the footprints do not overlap. To dim the side images, a surface of the curved lightguide is coated with a low-index coating in areas that experience interactions (i.e., bounces) of main image light, and is not coated with the low-index coating in areas that experience interactions of side image light. Thus, the main image light reflects off the low-index coating and remains within the curved lightguide, but the side image light is transmitted through the gap in the low-index coating out of the curved lightguide. The lens of the display system is coated with a polarizing or light-absorbing coating (i.e., a sunglass coating), which absorbs the side image light that escapes the curved lightguide through the gap in the low-index coating.

Some embodiments described herein relate to techniques for dimming side images in a curved lightguide by utilizing a polarized light source combined with a half-wave plate (HWP). Light rays traveling through the lightguide to generate a main image undergo an even number of interactions (bounces) within the lightguide, whereas light rays traveling through the lightguide to generate side images undergo an odd number of bounces within the lightguide. The HWP flips the input polarization for the main image to the orthogonal polarization and preserves the linear polarization for the side images due to the even number of bounces of main image light and the odd number of bounces of side image light. In some embodiments, the HWP is a curved HWP placed on the eye-side or the world-side of the lightguide. Once the polarization of the main image has been flipped, the display light is directed to a dielectric mirror, which acts as a weak analyzer to dim the side images by an order of magnitude. The main image polarization is aligned to s- for higher luminance and p-for the side images to dim them.

<FIG> illustrates an example eyewear display system <NUM> including an incoupler and outcoupler configured to produce an enlarged eyebox in accordance with some embodiments. The eyewear display system <NUM> has a support structure <NUM> that includes an arm <NUM>, which houses a projector (e.g., a laser projector, a micro-LED projector, a Liquid Crystal on Silicon (LCOS) projector, or the like). The projector is configured to project images toward the eye of a user via a curved lightguide, such that the user perceives the projected images as being displayed in a field of view (FOV) area <NUM> of a display at one or both of lens elements <NUM>, <NUM>. In the depicted embodiment, the eyewear display system <NUM> is a near-eye display system in the form of a WHUD in which the support structure <NUM> is configured to be worn on the head of a user and has a general shape and appearance (that is, form factor) of an eyeglasses (e.g., sunglasses) frame.

The support structure <NUM> contains or otherwise includes various components to facilitate the projection of such images toward the eye of the user, such as a projector and a curved lightguide. In some embodiments, the support structure <NUM> further includes various sensors, such as one or more front-facing cameras, rear-facing cameras, other light sensors, motion sensors, accelerometers, and the like. In some embodiments, the support structure <NUM> includes one or more radio frequency (RF) interfaces or other wireless interfaces, such as a Bluetooth(TM) interface, a WiFi interface, and the like. Further, in some embodiments, the support structure <NUM> further includes one or more batteries or other portable power sources for supplying power to the electrical components of the eyewear display system <NUM>. In some embodiments, some or all of these components of the eyewear display system <NUM> are fully or partially contained within an inner volume of support structure <NUM>, such as within the arm <NUM> in region <NUM> of the support structure <NUM>. It should be noted that while an example form factor is depicted, it will be appreciated that in other embodiments the eyewear display system <NUM> may have a different shape and appearance from the eyeglasses frame depicted in <FIG>. It should be understood that instances of the term "or" herein refer to the non-exclusive definition of "or", unless noted otherwise. For example, herein the phrase "X or Y" means "either X, or Y, or both".

One or both of the lens elements <NUM>, <NUM> are used by the eyewear display system <NUM> to provide an augmented reality (AR) display in which rendered graphical content can be superimposed over or otherwise provided in conjunction with a real-world view as perceived by the user through the lens elements <NUM>, <NUM>. For example, a projection system of the eyewear display system <NUM> uses light to form a perceptible image or series of images by projecting the display light onto the eye of the user via a projector of the projection system, a curved lightguide formed at least partially in the corresponding lens element <NUM> or <NUM>, and one or more optical elements (e.g., one or more scan mirrors, one or more optical relays, or one or more collimation lenses that are disposed between the projector and the curved lightguide or integrated with the curved lightguide), according to various embodiments.

One or both of the lens elements <NUM>, <NUM> includes at least a portion of a curved lightguide that routes display light received by an incoupler of the curved lightguide to an outcoupler of the curved lightguide, which outputs the display light toward an eye of a user of the eyewear display system <NUM>. The display light is modulated and projected onto the eye of the user such that the user perceives the display light as an image. In addition, each of the lens elements <NUM>, <NUM> is sufficiently transparent to allow a user to see through the lens elements to provide a field of view of the user's real-world environment such that the image appears superimposed over at least a portion of the real-world environment.

In some embodiments, the projector of the projection system of the display <NUM> is a digital light processing-based projector, a scanning laser projector, or any combination of a modulative light source, such as a laser or one or more light-emitting diodes (LEDs), and a dynamic reflector mechanism such as one or more dynamic scanners, reflective panels, or digital light processors (DLPs). In some embodiments, the projector includes a microdisplay panel, such as a micro-LED display panel (e.g., a micro-AMOLED display panel, or a micro inorganic LED (i-LED) display panel) or a micro-Liquid Crystal Display (LCD) display panel (e.g., a Low Temperature PolySilicon (LTPS) LCD display panel, a High Temperature PolySilicon (HTPS) LCD display panel, or an In-Plane Switching (IPS) LCD display panel). In some embodiments, the projector includes a Liquid Crystal on Silicon (LCOS) display panel. In some embodiments, a display panel of the projector is configured to output light (representing an image or portion of an image for display) into the lightguide of the projector. The curved lightguide expands the display light and outputs the display light toward the eye of the user via an outcoupler.

The projector is communicatively coupled to the controller and a non-transitory processor-readable storage medium or memory storing processor-executable instructions and other data that, when executed by the controller, cause the controller to control the operation of the projector. In some embodiments, the controller controls the projector to selectively set the location and size of the FOV area <NUM>. In some embodiments, the controller is communicatively coupled to one or more processors (not shown) that generate content to be displayed at the eyewear display system <NUM>. The projector outputs display light toward the FOV area <NUM> of the eyewear display system <NUM> via the curved lightguide. In some embodiments, at least a portion of an outcoupler of the curved lightguide overlaps the FOV area <NUM>. Herein, the range of different user eye positions that will be able to see the display is referred to as the eyebox of the display.

To enlarge the eyebox of the eyewear display system <NUM>, the incoupler is thicker than the curved lightguide and the outcoupler is tilted with respect to the curved lightguide to receive more than one interaction (bounce) of display light before the display light is directed out of the curved lightguide. To dim side images introduced by the thicker incoupler and multiple outcoupler light bounces, the eyewear display system <NUM> employs one or more artifact mitigation techniques.

According to a first artifact mitigation technique, the eyewear display system <NUM> includes a sunglass coating on the lens and a low-index coating on portions of the curved lightguide that receive interactions (bounces) of main image light and a gap in the low-index coating on one or more portions of the curved lightguide that receive interactions of side image light. Whereas the main image light is reflected off the low-index coating to remain within the curved lightguide, the side image light escapes through the gap in the low-index coating to the sunglass coating on the lens, which absorbs the side image light.

According to a second artifact mitigation technique, the eyewear display system <NUM> includes a polarized light source, a half-wave plate (HWP) disposed along one side of the curved lightguide (either the world-side or the eye-side), and a dielectric mirror. Because the main image takes an odd number of bounces on the world-side of the curved lightguide and the side images take an even number of bounces on the world-side of the curved lightguide, the HWP flips the input polarization for the main image to the orthogonal polarization and preserves the linear polarization for the side images. The polarization splitting of the dielectric mirror then acts as a weak analyzer to dim the side images by an order of magnitude.

<FIG> illustrates an embodiment of a display system <NUM> including a thin curved lightguide <NUM> having a world-side surface <NUM> and an eye-side surface <NUM>. The curved lightguide <NUM> is configured to receive display light <NUM> at a proximal end from a microdisplay <NUM> and transmit the display light <NUM> through the curved lightguide <NUM> via total internal reflection to a distal end to an outcoupler <NUM>, which couples the display light <NUM> out of the curved lightguide <NUM> to a user's eye <NUM>. The display system <NUM> includes an incoupler <NUM> that is thicker than the curved lightguide <NUM> configured to direct display light <NUM> from the microdisplay <NUM> into the curved lightguide <NUM> and an outcoupler <NUM> that is tilted with respect to the curved lightguide <NUM> at an angle such that the outcoupler <NUM> receives two bounces of display light <NUM>.

The microdisplay <NUM> of the display system <NUM> emits an image into a full width, centered approximately normal to the display surface. Evaluated at the pupil, the Lagrange invariant is <NUM> units.

Therefore, for a <NUM> half-height display source, a <NUM>-degree half emission cone would satisfy this Lagrange invariant requirement. This is a mild emission cone and most sources with sufficient luminance are Lambertian, easily satisfying the cone angle requirement. The thick incoupler <NUM> receives a larger portion of display light emitted from the microdisplay <NUM> than an incoupler that is limited to the thickness of the curved lightguide <NUM>, and therefore couples more display light into the curved lightguide <NUM>. Likewise, by tilting the outcoupler <NUM> to receive more than one bounce of display light <NUM>, the outcoupler <NUM> couples display light out of the curved lightguide <NUM> into a larger eyebox than an outcoupler that receives only one bounce of display light <NUM>. Although an additional bounce at the outcoupler <NUM> results in an additional loss of display light <NUM>, the advent of microdisplays <NUM> that emit more display light <NUM> mitigates the additional loss of display light <NUM> at the outcoupler <NUM>.

<FIG> illustrates an eyeglasses frame <NUM> configured to house the curved lightguide <NUM>. In some embodiments, the eyeglasses frame <NUM> carries a lens <NUM> that includes at least a portion of the curved lightguide <NUM>. In the illustrated example, at least a portion of the incoupler <NUM> and a portion of the curved lightguide <NUM> are inside a tab portion <NUM> of the eyeglasses frame <NUM>. The tab portion <NUM> of the eyeglasses frame <NUM> obscures the thickness of the incoupler <NUM>, such that the aesthetics of the display system <NUM> are not negatively impacted by the thick incoupler <NUM>. In addition, the tab portion <NUM> provides a guideline for where blackening can occur to mitigate artifacts in some embodiments. An overlaid standard <NUM> ophthalmic puck dimension <NUM> is also illustrated. In some embodiments, the "tab" <NUM> is implemented with an edger. Artifact mitigation approaches include coatings, apertures, blackening, adjusting the emission cone of the microdisplay, adjusting the tilt of the microdisplay, adjusting the incoupler geometry, and adjusting the outcoupler geometry.

In some embodiments, the incoupler <NUM> includes a spherical eye-side surface portion that is carried within the lens <NUM> and a non-spherical eye-side surface portion that is carried within the tab portion <NUM> of the eyeglasses frame <NUM>. In some embodiments, the lens <NUM> is coated with a sunglasses coating that acts as either a polarizer or as an absorber to dim artifact light.

<FIG> illustrates a pupil diameter <NUM> of an eyewear display. In a view <NUM>, the curved lightguide (not shown) is disposed within the lens <NUM>. The microdisplay <NUM> is housed within the eyeglasses frame (not shown), and the thick incoupler <NUM> couples display light from the microdisplay <NUM> into the curved lightguide to produce a display within a pupil diameter <NUM>. Increasing the pupil diameter <NUM> increases the eyebox of the eyewear display, such that the eyewear display can be used by a larger population of potential users with a wider range of facial sizes and geometries. A view <NUM> illustrates a thickness of the incoupler <NUM> that is thicker than the lens <NUM>, and therefore necessarily thicker than the curved lightguide disposed within the lens <NUM>.

<FIG> illustrates how transmission of display light through the outcoupler <NUM> causes artifacts caused by three side images from the curved lightguide <NUM> in the absence of mitigation techniques. In a view <NUM>, display light <NUM> is transmitted through the curved lightguide <NUM> to the outcoupler <NUM>, which is tilted at an angle to receive two bounces of the display light <NUM> before directing the display light <NUM> out of the eye-side surface <NUM> of the curved lightguide <NUM>. In a view <NUM>, the main image <NUM> is the third image from the left and appears as a grid pattern. The two side images <NUM>, <NUM> to the left of the main image are artifacts caused by transmission of display light through the outcoupler <NUM>. The side image <NUM> to the right of the main image <NUM> is an artifact caused by a bounce on the eye-facing side of the combiner.

<FIG> is a diagram <NUM> illustrating placement of a low-index coating <NUM> on the world-side surface <NUM> of the curved lightguide <NUM> to reflect main image light and a gap <NUM> in the low-index coating <NUM> to allow side image light to escape the curved lightguide <NUM>. The side image light that escapes through the gap <NUM> in the low-index coating <NUM> is absorbed by a sunglass coating <NUM> on a lens <NUM> of a display system <NUM> in accordance with some embodiments.

Polarized display light <NUM> is input to the curved lightguide <NUM> via the thick incoupler (not shown). The polarized display light <NUM> includes light of a main image <NUM> and light of side images, such as side images <NUM>, <NUM>, <NUM>. The main image light and the side image light have distinct footprints with non-overlapping areas. The low-index coating <NUM> causes incident light to be reflected within the curved lightguide <NUM> to be directed toward the user's eye <NUM>. By placing the gap <NUM> in the low-index coating <NUM> at a location where only side image light (but not main image light) is incident on the world-side <NUM> of the curved lightguide <NUM>, the display system <NUM> allows the side image light incident on the world-side surface <NUM> of the curved lightguide <NUM> at the gap <NUM> to be transmitted out of the curved lightguide <NUM> through the gap <NUM>. The sunglass coating <NUM> absorbs the side image light that escapes through the gap <NUM>.

<FIG> illustrates a view <NUM> of placement of the gap <NUM> through which side image light escapes the lightguide to be dimmed by the light-absorbing or polarizing coating on the lens <NUM>. In the illustrated example, the microdisplay <NUM> emits display light toward the thick incoupler <NUM>. The thick incoupler <NUM> couples the display light <NUM> into the curved lightguide (not shown). Regions <NUM> illustrate the bounce locations of main image light, while the region <NUM> illustrates an area at which the side image light experiences bounces at the world-side <NUM> of the curved lightguide <NUM>, but the main image light does not experience any bounces. The regions <NUM> are coated with a low-index coating, whereas the region <NUM> is not coated with the low-index coating; thus, the gap <NUM> is within the region <NUM>.

The side image light escapes the curved lightguide through the gap <NUM>, where it is absorbed by the sunglass coating on the lens <NUM> (not shown). The main image light experiences total internal reflection against the low-index coating and remains within the curved lightguide <NUM> until the main image light is directed out of the curved lightguide via the outcoupler <NUM> (not shown) toward the user's eye <NUM>.

An additional artifact mitigation technique uses the differing number of world-side bounces experienced by the main image and side image light to further dim side images. <FIG> illustrates a number of bounces on the world-facing side of the curved lightguide experienced by a left side image <NUM>, a main image <NUM>, and a right side image <NUM>. Both the left side image <NUM> and the right side image <NUM> take an even number of bounces on the world-side <NUM> of the curved lightguide <NUM>, with the left side image <NUM> taking two bounces and the right side image <NUM> taking four bounces in the illustrated example. The main image <NUM>, by contrast, takes an odd number of bounces on the world-side <NUM> of the curved lightguide <NUM> (three, in the illustrated example).

To facilitate dimming the side images <NUM>, <NUM> while preserving the main image <NUM>, the curved lightguide <NUM> includes a half-wave plate (HWP) <NUM> in conjunction with a dielectric mirror <NUM>. The HWP <NUM> flips the input polarization for the main image <NUM> to the orthogonal polarization while preserving the linear polarization for the side images <NUM>, <NUM>. In some embodiments, the HWP <NUM> follows the curve of the world-side <NUM> of the curved lightguide <NUM>. In some embodiments, the HWP <NUM> is a film on the world-side <NUM> of the curved lightguide <NUM>.

The polarization-splitting of the dielectric mirror <NUM> acts as a weak analyzer to dim the side images <NUM>, <NUM> by an order of magnitude. In some embodiments, the dielectric mirror <NUM> provides approximately <NUM>:<NUM> contrast. In some embodiments, the main image polarization is aligned to be s- for higher luminance and p- for the side images to dim them. The dielectric mirror <NUM> is positioned on at least one of the outcoupler <NUM> and the eye-side <NUM> of the curved lightguide <NUM>.

<FIG> is a graph <NUM> illustrating the polarization splitting of the dielectric mirror <NUM>. In the illustrated example, the dielectric mirror <NUM> is a <NUM>-layer polarization splitting dielectric mirror coating with alternating layers of nb2o5 and si02 with approximately <NUM>:<NUM> coating. The x-axis shows wavelength in nanometers and the y-axis shows % reflectance. The solid curve <NUM> shows p- reflectivity and the dashed curve <NUM> shows s- reflectivity.

Thus, the dielectric mirror <NUM> reflects more p- polarized light than s- polarized light. If the display light <NUM> has p- polarization, the HWP <NUM> will flip the main image light to s-polarization due to the odd number of bounces of main image light against the world-side surface <NUM> of the curved lightguide <NUM> and will preserve the p- polarization of the side image light due to the even number of bounces of side image light against the world-side surface <NUM> of the curved lightguide <NUM>. The dielectric mirror <NUM> on the eye-side <NUM> of the curved lightguide <NUM> and on the outcoupler <NUM> reflects more of the main image light than the side image light, thereby further dimming the side images <NUM>, <NUM>.

<FIG> illustrates the log illuminance <NUM> for a baseline left side image, main image, and right side image and the log illuminance <NUM> for dimmed side images resulting from the HWP <NUM> and dielectric mirror <NUM> of some embodiments. As illustrated in <FIG>, for approximately <NUM> mil rays, the side images are dimmed by an order of magnitude compared to the baseline.

In some embodiments, certain aspects of the techniques described above may be implemented by one or more processors of a processing system executing software.

Claim 1:
A device comprising:
a microdisplay (<NUM>);
a curved lightguide (<NUM>) configured to receive light (<NUM>, <NUM>) from the microdisplay and to transmit the light from a proximal end of the curved lightguide to a distal end of the curved lightguide;
an incoupler (<NUM>) configured to direct light from the microdisplay into the curved lightguide, wherein the incoupler is thicker than the curved lightguide; and
an outcoupler (<NUM>) disposed at the distal end of the curved lightguide, the outcoupler configured to direct a portion of the light out of the curved lightguide toward a user's eye (<NUM>), wherein the outcoupler is disposed at an angle with respect to the curved lightguide to receive two interactions of the light at a side of the outcoupler facing the user's eye.