Patent Description:
Some optical systems may benefit from capturing images of a user's eye. Head mounted displays (HMDs), for example, may perform eye-tracking functions which may enhance the user's viewing experience. Eye-tracking may be aided, in some cases, by illuminating the eye of the user and then capturing images of the illuminated eye. However, various contexts may generate challenges to capturing images of the eye that include sufficient contrast for analyzing the images. In particular, stray light may propagate through an optical system and be received by a camera and thereby increase the background noise for the light propagating along the desired imaging optical path.

<CIT> describes a head-mounted display (HMD) that includes a display, an optical assembly and an eye tracking system that determines user's eye tracking information. The optical assembly comprises a front optical element in series with a back optical element adjacent to the display. One surface of the back optical element is coated to reflect infrared (IR) light. The eye tracking system includes an illumination source and an imaging device positioned between the front optical element and the back optical element. The illumination source emits IR light that illuminates the coated surface and reflects towards the user's eye. The imaging device captures an image of the user's eye based on light reflected from the user's eye and from the coated surface. The eye tracking information is determined based on the captured image. The HMD adjusts presentation of images displayed on the display, based on the eye tracking information.

<CIT> describes an eye tracking module for video eyeglasses, comprising: at least two infrared light sources, at least one image sensor component, an infrared light filter unit and a tracking module housing; fixing members are provided on the tracking module housing, and comprise of an infrared light source fixing member, an image sensor component fixing member and a connector; the infrared light source fixing member and image sensor component fixing member are in detachably fixed connection or non-detachably fixed connection with the tracking module housing; the connector is in detachably fixed connection with the tracking module housing.

<CIT> describes an eye tracking device that utilizes light detection devices for determining the visual axis and point of regard of a user. The light detection devices are arranged in such a way, such as embedded in a thin film, so as to be curved around the optical axis of the eye. In this way, the light detection devices are always coincident with source-emitted light reflected from the fovea. The curved arrangement of light detection devices are mounted onto a head or facial apparatus, which has a mild reflector on its outside surface to keep external light noise at a minimum. Conversion circuitry, such as a pyramid cascade circuit or a microprocessor circuit, determines the position of the fovea-reflected light and computes the visual axis and point of regard of the user at a very rapid rate.

<CIT> describes a lens that includes: a plastic lens base material; and a transparent anti-reflection layer formed on the base material through a hard coat layer, wherein ion is radiated to the surface of one layer of the anti-reflection layer to introduce oxygen defect and improve the conductivity.

According to the invention there is provided an optical system according to claim <NUM>.

The first AOI range for the visible light may be greater than plus-or-minus <NUM> degrees. The second AOI range for the narrow-band infrared illumination light may be greater than plus-or-minus <NUM> degrees.

The transmission spectrum of the AR coating may transmit greater than <NUM>% of the visible light over the first AOI. The transmission spectrum of the AR coating may transmit greater than <NUM>% of the narrow-band of infrared light over the second AOI.

A second AR coating may be disposed on a backside of the combiner layer.

The narrow-band infrared illumination light may be above <NUM>.

The optical system may further comprise a display layer configured to provide display light that propagates through the combiner layer and then through the base curvature.

The base curvature may be configured to focus a virtual image included in display light for a user of the optical system.

The AR coating may include a plurality of titanium-dioxide sub-layers. Additionally, or alternatively, the AR coating may include a plurality of silicon-dioxide sub layers.

The AR coating may include a plurality of hafnium dioxide sub-layers. Additionally, or alternatively, the AR coating may include a plurality of magnesium-fluoride sub-layers.

Non-limiting and non-exhaustive embodiments are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

Embodiments of an optical system for eye-tracking are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. One skilled in the relevant art will recognize, however, that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment.

The system and device for suppressing stray light in eye-tracking images that are described in this disclosure include incorporating ghost suppression components into infrared illuminators and including anti-reflection coatings on strategic surfaces of an optical system. Eye-tracking modules may include infrared illuminators to illuminate the eye with infrared light and an eye-tracking camera to image the eye. In some eye-tracking modules, the imaging path of the infrared light encounters various optical components and surfaces before becoming incident on the camera. Therefore, stray light may be generated when a portion of the infrared imaging light is reflected when it encounters different surfaces. This stray light may then propagate within the optical system and eventually become incident on the eye-tracking camera and generate ghost images.

In some cases, <NUM>% of infrared illumination light is lost due to reflection when the infrared illumination light encounters an optical interface. When the infrared illumination light encounters a plurality of optical interfaces, the reflection losses compound and a very large portion of the infrared imaging light is lost and the reflected light is stray light that may become incident on the eye-tracking camera as optical noise. Therefore, in embodiments of this disclosure, AR coatings and other ghost suppression components may be strategically positioned to increase transmission of the infrared imaging light and suppress stray light. The AR coatings in this disclosure may be specially tuned to transmit a very-high percentage of both visible light and infrared light even when the angle of incidence (AOI) includes a wide range. Conventional AR coatings are generally designed for visible light at near-normal angle of incidences and not designed to pass visible light and infrared light over a wide AOI range. Optical systems of the disclosure may benefit from transmission of visible light and infrared light due to the requirements of an optical system to pass visible scene light and/or visible display light, in the context of a head mounted display. These and other embodiments are described in more detail in connections with <FIG>.

<FIG> illustrates an example HMD <NUM>, in accordance with aspects of the present disclosure. The illustrated example of HMD <NUM> is shown as including a frame <NUM>, temple arms 104A and 104B, and near-eye optical elements 110A and 110B. Eye-tracking cameras 108A and 108B are shown as coupled to temple arms 104A and 104B, respectively. <FIG> also illustrates an exploded view of an example of near-eye optical element 110A. Near-eye optical element 110A is shown as including an optically transparent layer 120A, an illumination layer 130A, an optical combiner layer 140A, and a display layer 150A. Illumination layer 130A is shown as including a plurality of in-field light sources <NUM>. The in-field light source <NUM> may be configured to emit infrared illumination light for eye-tracking purposes, for example. Display layer 150A may include a waveguide <NUM> that is configured to direct virtual images to an eye of a user of HMD <NUM>.

As shown in <FIG>, frame <NUM> is coupled to temple arms 104A and 104B for securing the HMD <NUM> to the head of a user. Example HMD <NUM> may also include supporting hardware incorporated into the frame <NUM> and/or temple arms 104A and 104B. The hardware of HMD <NUM> may include any of processing logic, wired and/or wireless data interface for sending and receiving data, graphic processors, and one or more memories for storing data and computer-executable instructions. In one example, HMD <NUM> may be configured to receive wired power and/or may be configured to be powered by one or more batteries. In addition, HMD <NUM> may be configured to receive wired and/or wireless data including video data.

<FIG> illustrates near-eye optical elements 110A and 110B that are configured to be mounted to the frame <NUM>. In some examples, near-eye optical elements 110A and 110B may appear transparent to the user to facilitate augmented reality or mixed reality such that the user can view visible scene light from the environment while also receiving display light directed to their eye(s) by way of display layer 150A. In further examples, some or all of near-eye optical elements 110A and 110B may be incorporated into a virtual reality headset where the transparent nature of the near-eye optical elements 110A and 110B allows the user to view an electronic display (e.g., a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a micro-LED display, etc.) incorporated in the virtual reality headset.

As shown in <FIG>, illumination layer 130A includes a plurality of in-field light sources <NUM>. Each in-field light source <NUM> may be disposed on a transparent substrate and may be configured to emit light towards an eyeward side <NUM> of the near-eye optical element 110A. In some aspects of the disclosure, the in-field light sources <NUM> are configured to emit near infrared light (e.g. <NUM> - <NUM>). Each in-field light source <NUM> may be a micro light emitting diode (micro-LED), an edge emitting LED, a vertical cavity surface emitting laser (VCSEL) diode, or a Superluminescent diode (SLED).

Conventional eye-tracking solutions may provide light sources disposed around a rim/periphery of a lens. However, placing light sources within the field of view of the eye may be advantageous for computation of specular or "glint" reflections that can be imaged by a camera such as eye-tracking camera 108A that is positioned to image the eye of a wearer of HMD <NUM>.

While in-field light sources <NUM> may introduce minor occlusions into the near-eye optical element 110A, the in-field light sources <NUM>, as well as their corresponding routing may be so small as to be unnoticeable or insignificant to a wearer of HMD <NUM>. Additionally, any occlusion from in-field light sources <NUM> will be placed so close to the eye as to be unfocusable by the human eye and therefore assist in the in-field light sources <NUM> being not noticeable or insignificant. In some embodiments, each in-field light source <NUM> has a footprint (or size) that is less than about <NUM> x <NUM> microns.

As mentioned above, the in-field light sources <NUM> of the illumination layer 130A may be configured to emit infrared illumination light towards the eyeward side <NUM> of the near-eye optical element 110A to illuminate the eye of a user. The near-eye optical element 110A is shown as including optical combiner layer 140A where the optical combiner layer 140A is disposed between the illumination layer 130A and a backside <NUM> of the near-eye optical element 110A. In some aspects, the optical combiner 140A is configured to receive reflected infrared light that is reflected by the eye of the user and to direct the reflected infrared light towards the eye-tracking camera 108A. In some examples, the eye-tracking camera 108A is an infrared camera configured to image the eye of the user based on the received reflected infrared light. In some aspects, the optical combiner 140A is transmissive to visible light, such as scene light <NUM> incident on the backside <NUM> of the near-eye optical element 110A. In some examples, the optical combiner 140A may be configured as a volume hologram and/or may include one or more Bragg gratings for directing the reflected infrared light towards the eye-tracking camera 108A. In some examples, the optical combiner includes a polarization-selective hologram (a. polarized volume hologram) that diffracts a particular polarization orientation of incident light while passing other polarization orientations.

Display layer 150A may include one or more other optical elements depending on the design of the HMD <NUM>. For example, the display layer 150A may include a waveguide <NUM> to direct display light generated by an electronic display to the eye of the user. In some implementations, at least a portion of the electronic display is included in the frame <NUM> of the HMD <NUM>. The electronic display may include an LCD, an organic light emitting diode (OLED) display, micro-LED display, pico-projector, or liquid crystal on silicon (LCOS) display for generating the display light.

Optically transparent layer 120A is shown as being disposed between the illumination layer 130A and the eyeward side <NUM> of the near-eye optical element 110A. The optically transparent layer 120A may receive the infrared light emitted by the illumination layer 130A and pass the infrared light to illuminate the eye of the user. As mentioned above, the optically transparent layer 120A may also be transparent to visible light, such as scene light <NUM> received from the environment and/or display light received from the display layer 150A. In some examples, the optically transparent layer 120A has a curvature for focusing light (e.g., display light and/or scene light) to the eye of the user. Thus, the optically transparent layer 120A may, in some examples, may be referred to as a lens. In some aspects, the optically transparent layer 120A has a thickness and/or curvature that corresponds to the specifications of a user. In other words, the optically transparent layer 120A may be a prescription lens. However, in other examples, the optically transparent layer 120A may be a non-prescription lens.

<FIG> is a top view of an example near-eye optical element <NUM> that includes a transparent layer <NUM>, an illumination layer <NUM>, a combiner layer <NUM>, and a display layer <NUM>. A plurality of infrared illuminators <NUM> emit infrared illumination light <NUM> to an eyebox area <NUM> to illuminate eye <NUM>. <FIG> illustrates infrared illuminators 237A- 237E. The different infrared illuminators <NUM> may direct infrared illumination light <NUM> to eye <NUM> at different angles depending on the position of the infrared illuminators with respect to eye <NUM>. For example, infrared illuminators 237A and 237E may include beamforming elements that direct the infrared illumination light to eye <NUM> at steeper angles compared to infrared illuminator 237C directing infrared illumination light <NUM> to eye <NUM> at an angle closer to normal. As described above, infrared illuminators <NUM> may be VCSELs or SLEDs, and consequently infrared illumination light <NUM> may be narrow-band infrared illumination light (e.g. linewidth of <NUM>-<NUM>).

Eye <NUM> reflects at least a portion of the infrared illumination light <NUM> back to element <NUM> as reflected infrared light (not illustrated in <FIG>) and the reflected infrared light propagates through layers <NUM> and <NUM> before encountering combiner layer <NUM>. Combiner layer <NUM> is configured to receive the reflected infrared light and direct the reflected infrared light to the camera <NUM> to generate eye-tracking images. As an example, <FIG> illustrates reflected infrared light propagating along optical path <NUM>(<NUM>) being redirected to camera 108A by combiner layer <NUM>.

Returning to <FIG>, camera 108A is configured to capture eye-tracking images of eye <NUM>. Camera <NUM> may include an infrared bandpass filter to pass the wavelength of the infrared illumination light <NUM> emitted by the infrared illuminators and block other light from becoming incident on an image sensor of camera 108A. Camera 108A may include a complementary metal-oxide semiconductor (CMOS) image sensor.

<FIG> shows that scene light <NUM> (visible light) from the external environment may propagate through display layer <NUM>, combiner layer <NUM>, illumination layer <NUM>, and transparent layer <NUM> to become incident on eye <NUM> so that a user can view the scene of an external environment. <FIG> shows that display layer <NUM> may generate or redirect display light <NUM> to present virtual images to eye <NUM>. Display light <NUM> is visible light and propagates through combiner layer <NUM>, illumination layer <NUM>, and transparent layer <NUM> to reach eye <NUM>.

Transparent layer <NUM> may include a base curvature <NUM> that is the surface closest to eyeward side <NUM>. Base curvature <NUM> may be configured to focus a virtual image included in display light <NUM> for an eye of a user. Base curvature <NUM> may be formed in a refractive material <NUM> of transparent layer <NUM> using a subtractive process. The refractive material <NUM> may have a refractive index of approximately <NUM>, in some embodiments. Illumination layer <NUM> may include a transparent material <NUM> that may encapsulate the infrared illuminators <NUM>. Transparent material <NUM> and refractive material <NUM> are configured to transmit visible light (e.g. <NUM> - <NUM>) and near-infrared light (e.g. <NUM> - <NUM>).

<FIG> illustrates a front view of eye <NUM> through an example illumination layer <NUM>, in accordance with aspects of the disclosure. In the illustrated embodiment, illumination layer <NUM> include twenty-one infrared illuminators (337A-337U). In the illustrated example, infrared illuminators 337A-<NUM> may be considered an "inner ring" of infrared illuminators <NUM> while infrared illuminators 337I-337U are considered an "outer ring" of infrared illuminators <NUM>. As such, infrared illuminators 337I-337U may direct their infrared illumination light to eye <NUM> at a steeper angle (e.g. <NUM>-<NUM> degrees) than infrared illuminators 337A-<NUM> in the inner ring (e.g. <NUM>-<NUM> degrees).

<FIG> illustrates an infrared light source <NUM>. Source <NUM> is configured to emit infrared illumination light from an output aperture <NUM> of the infrared light source <NUM>. Beam shaping element <NUM> is disposed over output aperture <NUM> and configured to direct the infrared illumination light to an eyebox area (e.g. eyebox area <NUM>) through substrate <NUM>. Substrate <NUM> may be an example of transparent material <NUM>. However, beam shaping element <NUM> is formed of a refractive material <NUM> and the interface <NUM> between refractive material <NUM> and substrate <NUM> may cause a portion of the emitted infrared illumination light to be reflected back into the refractive material <NUM> of beam shaping element <NUM>. As a consequence of these reflections, the infrared illumination light <NUM> may not be directed in the designed direction and a significant amount of some of the infrared illumination light may even exit the sides of the beam shaping element <NUM> (e.g. light 477A and 477B). The infrared illumination light that is not directed in the desired direction is stray light that may eventually become incident on an eye-tracking camera and therefore raise the noise floor and decrease the contrast of an eye-tracking image.

<FIG> illustrates an example infrared illuminator <NUM> that may be utilized as infrared illuminators <NUM>/<NUM>, in accordance with aspects of the disclosure. The example infrared illuminator <NUM> illustrated in <FIG> includes an infrared light source <NUM> having an output aperture <NUM> and a beam shaping optic <NUM> disposed over output aperture <NUM>. Beam shaping optic <NUM> is configured to direct the infrared illumination light <NUM> to an eyebox area (e.g. eyebox area <NUM>). In the illustrated embodiment of <FIG>, anti-reflection (AR) coating <NUM> is disposed over a lens curvature <NUM> as a ghost suppression component configured to prevent or suppress stray infrared illumination light from becoming incident on camera <NUM>. Lens curvature <NUM> may be formed by the refractive material of the beam shaping optic <NUM>. AR coating <NUM> significantly reduces the reflection of infrared illumination light <NUM> that would occur at an interface between substrate <NUM> and refractive material <NUM>. Without an AR coating, reflection may be approximately <NUM>% for near-normal angle-of-incidence (AOI) and increases as the AOI increases. Substrate <NUM> is a transparent material. Refractive material <NUM> may be a high-index material having a refractive index of greater than three. In an embodiment, refractive material <NUM> includes gallium-arsenide (GaAs) and has a refractive index of approximately <NUM>. In some embodiments, beam shaping optic <NUM> is approximately <NUM> microns wide.

In an embodiment, AR coating <NUM> is a single layer of silicon-mononitride (SiN) providing <NUM>% or better transmission for infrared light having a wavelength of between <NUM> and <NUM>. In an embodiment, AR coating <NUM> includes multiple sub-layers allowing for <NUM>% transmission for <NUM>-<NUM> near-infrared light over an angle-of-incidence (AOI) range of plus-or-minus <NUM> degrees.

In some embodiments, the illustrated refractive beam shaping optic <NUM> is replaced by, or includes, a diffractive optical element configured to direct the infrared illumination light <NUM> to the eyebox area. In one embodiment, an obscuration element <NUM> is disposed adjacent to the infrared light source <NUM>. Obscuration element <NUM> may be disposed between the output aperture <NUM> of the infrared light source <NUM> and eye-tracking camera <NUM> to block stray light from reaching the camera (at least directly). Obscuration element <NUM> may include a wall having a blackened coating to absorb light, for example.

<FIG> illustrates an example micro-Louver array <NUM> disposed above AR coating <NUM>, in accordance with aspects of the disclosure. The micro-Louver array film <NUM> functions to pass the light <NUM> exiting aperture <NUM> within a designed angle of incidence while light (e.g. rays <NUM> and <NUM>) that are beyond the designed angle of incidence will be absorbed by the micro-Louver array <NUM>. Thus, the designed angle of incidence for passing light of the micro-Louver array <NUM> may be constrained to the AOI between light rays 639A and 639B that will exit material <NUM> and <NUM> without internal reflection. In some embodiments, micro-Louver array <NUM> may be disposed above lens curvature <NUM> as a ghost suppression element without AR coating <NUM> included in infrared illuminator <NUM>.

<FIG> illustrates an example optical system <NUM> including an AR coating <NUM> disposed on a base curvature <NUM> of an example transparent layer <NUM>, in accordance with aspects of the disclosure. In <FIG>, infrared illuminator 237A is configured to direct narrow-band infrared illumination light to an eyebox area <NUM> along optical path <NUM>(<NUM>).

Intersection <NUM> illustrates that the infrared illumination light emitted by infrared illuminator 237A would encounter an interface between the air and refractive material <NUM> of transparent layer <NUM> if AR coating <NUM> was not included. Without AR coating <NUM>, at least <NUM>% of the infrared illumination light would be lost (reflected) at intersection <NUM> and transmission would decrease as the AOI increases. However, AR coating <NUM> significantly reduces the reflection of the infrared illumination light and thereby suppresses the Fresnel reflections that contribute to stray light. Reflected infrared light is the narrow-band infrared illumination light that is reflected off of eye <NUM> and propagates along optical path <NUM>(<NUM>). Intersection <NUM> illustrates that the reflected infrared light would encounter an interface between the air and the refractive material <NUM> of transparent layer <NUM> if AR coating <NUM> was not included. Here again, without AR coating <NUM>, at least another <NUM>% of the reflected infrared light would be lost due to reflection. Yet, with AR coating <NUM> disposed on base curvature <NUM>, stray light from reflections is suppressed and the intensity of the reflected infrared light (that includes the image of eye <NUM>) is preserved at a higher intensity.

The portion of reflected infrared light that propagates through transparent layer <NUM> and illumination layer <NUM> is directed by combiner layer <NUM> to camera <NUM> for generating eye-tracking images along optical path <NUM>(<NUM>). Intersection <NUM> illustrates that the reflected infrared light would encounter a third interface between the air and the refractive material <NUM> of transparent layer <NUM> if AR coating <NUM> was not included. However, AR coating <NUM> reduces the reflections that would contribute to ghost images and preserves the reflected infrared light by allowing a very-high transmission of the reflected infrared light propagating along optical path <NUM>(<NUM>). <FIG> illustrates that the portion of the reflected infrared light that propagates through AR coating <NUM> at intersection <NUM> continues to camera 108A along optical path <NUM>(<NUM>). <FIG> illustrates that example optical system <NUM> may optionally include a second AR coating <NUM> disposed on a backside <NUM> of combiner layer <NUM>.

Notably, reflected infrared light propagating along optical path <NUM>(<NUM>) becomes incident upon AR coating <NUM> at a relatively steep angle. For example, the reflected infrared light may become incident upon AR coating <NUM> at an angle of incidence of <NUM>, <NUM> or even <NUM> degrees. Therefore, AR coating <NUM> has very-high transmission for a narrow-band of infrared light over an AOI range where the narrow-band of infrared light corresponds to the wavelength of the narrow-band infrared illumination light emitted by infrared illuminators <NUM>. AR coating <NUM> also must have very-high transmission of infrared light over a normal and near-normal AOI, as illustrated at intersections <NUM> and <NUM>. <FIG> also shows that visible light wavelengths from scene light <NUM> and display light <NUM> will propagate through AR coating <NUM> to eyebox area <NUM> and, hence, AR coating <NUM> has very-high transmission of visible light. However, conventional AR coatings have poor performance when very-high transmission is required in both the visible light spectrum and the near-infrared spectrum along over a wide AOI. For example, a conventional AR coating may provide approximately very-high transmission for an AOI range of plus-or-minus <NUM> degrees for <NUM> (visible wavelengths), but the transmission of <NUM> (near-infrared wavelength) may erode significantly as the AOI approaches <NUM> degrees or greater.

Conventional AR coatings are generally tuned for visible light incident at near-normal angles of incidence. In contrast, AR coating <NUM> would preferably be tuned for very-high infrared transmission at a wide AOI range in addition to very-high transmission of visible light at a significant AOI range. "Very-high transmission" is defined as above <NUM>%, for purposes of this disclosure.

In some embodiments of AR coating <NUM>, the significant AOI range for the visible light is greater than plus-or-minus <NUM> degrees and the wide AOI range for the narrow-band infrared illumination light is greater than plus-or-minus <NUM> degrees. The transmission spectrum of the AR coating <NUM> may transmit greater than <NUM>% of the visible light over the plus-or-minus <NUM> degrees AOI and the transmission spectrum of the AR coating <NUM> may transmit greater than <NUM>% of the narrow-band of infrared light over plus-or-minus <NUM> degrees AOI. In another embodiment, the transmission spectrum of the AR coating <NUM> transmits greater than <NUM>% of visible light over a plus-or-minus <NUM> degrees AOI and the transmission spectrum of the AR coating <NUM> transmits greater than <NUM>% of the narrow-band of infrared light over the plus-or-minus <NUM> degrees AOI.

An example multilayer AR coating may include titanium-dioxide (TiO<NUM>) and silicon-dioxide (SiO<NUM>) sublayers. Another example multilayer AR coating may include hafnium-dioxide sublayers (HfO<NUM>) and magnesium-fluoride (MgF<NUM>) sublayers. The AR coating <NUM> may be tuned for very-high transmission for visible light over a significant AOI range and very-high transmission for a narrow-band of infrared light (<NUM> - <NUM>) over a wide AOI range. The AR coating may be specifically tuned for very-high transmission of narrow-band infrared illumination light corresponding with a VCSEL or a SLED infrared illuminator <NUM> emitting <NUM> light, for example. In other embodiments, the narrow-band of infrared light may have different wavelengths. The transmission spectrum of an AR coating may be tuned for less than very-high transmission of at least a portion of gap-light having wavelengths between the visible light and the narrow-band of infrared light (e.g. <NUM> - <NUM>), when very-high transmission is defined as <NUM>% transmission. In some embodiments of the disclosure, "very-high transmission" is <NUM>% transmission or better.

<FIG> illustrates an example optical system <NUM> that illustrates an imaging optical path <NUM>, in accordance with aspects of the disclosure. <FIG> illustrates infrared illuminator 237E emitting narrow-band infrared illumination light toward eyebox area <NUM>. Light path <NUM> illustrates a potential stray light path that may be suppressed by incorporating one or more of the ghost suppression components, described with respect to <FIG>, into infrared illuminator 237E. Light path <NUM> may represent stray light exiting the side of a refractive beam shaping optic and then being confined by transparent material <NUM> by way of total-internal-reflection (TIR), before exiting illumination layer <NUM> and becoming incident on the camera <NUM>.

Light path <NUM> illustrates another potential stray light path that may be suppressed by incorporating one or more of the ghost suppression components, described with respect to <FIG>, into infrared illuminator 237E. Light path <NUM> may be taken by infrared illumination light that reflects off of the lens curvature (e.g. <NUM>) of the refractive material (e.g. <NUM>) and then continues to reflect within refractive material <NUM> until exiting along light path <NUM> and becoming incident on camera 108A. By including, AR coating <NUM> or AR coating <NUM> and micro-Louver array film <NUM> over the lens curvature <NUM>, for example, the initial reflection of the infrared illumination light off the lens curvature is suppressed and therefore more of the infrared illumination light exits the beam shaping optic in the intended direction.

Light path <NUM> illustrates a potential stray light path that may be suppressed by incorporating an example AR coating, as described in this disclosure. Light path <NUM> may represent infrared illumination light that encounters base curvature <NUM> subsequent to exiting infrared illuminator 237E. However, by including an AR coating <NUM> over base curvature <NUM>, stray light generated from the interface between refractive material <NUM> and air may be suppressed by decreasing the reflections.

Light path <NUM> illustrates another potential stray light path that may be suppressed by incorporating an example AR coating, as described in this disclosure. Light path <NUM> may represent infrared illumination light that reflects off of eye <NUM> as reflected infrared light and then encounters base curvature <NUM>. However, by including an AR coating <NUM> over base curvature <NUM>, stray light generated from the interface between refractive material <NUM> and air may be suppressed by decreasing the reflections.

Light path <NUM> illustrates yet another potential stray light path that may be suppressed by incorporating an example AR coating, as described in this disclosure. Light path <NUM> may represent infrared illumination light that reflects off of eye <NUM> as reflected infrared light and then encounters an interface between combiner layer <NUM> and another layer. However, by optionally including an AR coating <NUM> disposed on a backside <NUM> of combiner layer <NUM>, stray light generated from the interface between combiner layer <NUM> and another layer may be suppressed by decreasing the reflections.

<FIG> illustrates that adding particular features in accordance with aspects of this disclosure allow stray light suppression in more than one intersection along imaging optical path <NUM>. And, suppressing stray light by increasing transmission of infrared light propagating along imaging optical path <NUM> also assists in retaining the intensity of the infrared light that generates the infrared eye-tracking image. Therefore, embodiments of the disclosure may both suppress stray light and increase the intensity of the desired infrared imaging light and boost the contrast in an eye-tracking image captured by camera <NUM>. Consequently, reduction of ghost images and increase in image contrast may allow for more efficient identification of the pupil, iris, and other portions of the eye that assist in eye-tracking analysis to determine a position of the eye.

Embodiments may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific embodiments and examples are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.

Claim 1:
An optical system comprising:
an infrared illuminator (<NUM>, 237A-237E, 337A-<NUM>, 337I-337U, <NUM>) configured to direct narrow-band infrared illumination light to an eyebox area for eye-tracking;
a camera (108A, 108B) configured to capture eye-tracking images of an eye of a user;
a combiner layer (140A, <NUM>, <NUM>) configured to receive reflected infrared light of the narrow-band infrared illumination light reflecting off the eye of the user and direct the reflected infrared light to the camera to generate the eye-tracking images; and
an anti-reflection, AR, coating (<NUM>, <NUM>) disposed on a base curvature (<NUM>, <NUM>), wherein a transmission spectrum of the AR coating is tuned for very-high transmission for visible light over a first angle of incidence, AOI, range and very-high transmission for a narrow-band of infrared light over a second AOI range, the narrow-band of infrared light corresponding to the narrow-band infrared illumination light.