Integrated eye-tracking system in VR pancake lens assembly

Abstract

A lens assembly for a head-mounted display (HMD) comprises a reflective polarizer and an eye-tracking waveguide. The reflective polarizer is in an optical element. The eye-tracking waveguide is also included in the optical element. The eye-tracking waveguide is configured to direct near-infrared received illumination light to an eye-tracking camera.

Description

INTEGRATED EYE-TRACKING SYSTEM IN VR PANCAKE LENS ASSEMBLYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional Application No. 63 / 604,419 filed November 30, 2023.TECHNICAL FIELD

[0002] This disclosure relates generally to optics, and in particular to head-mounted display (HMD) optics.BACKGROUND INFORMATION

[0003] High quality optical assemblies that may include a combination of lenses, filters, and / or polarizers are used extensively in both commercial and consumer products. An optical assembly may be utilized to focus images from a display for a user of a head-mounted display (HMD) in the context of Virtual Reality (VR) and / or Mixed Reality (MR). In these and other contexts, it may be desirable to provide an optical assembly that is space efficient as well as including other features.SUMMARY OF PARTICULAR EMBODIMENTS

[0004] Embodiments according to the invention are in particular disclosed in the attached claims directed to lens assemblies and a head-mounted display (HMD), wherein any feature mentioned in one claim category, e.g. lens assembly, can be claimed in another claim category, e.g. HMD, system, method, storage medium, and computer program product, as well. The dependencies or references back in the attached claims are chosen for formal reasons only. However, any subject matter resulting from a deliberate reference back to any previous claims (in particular multiple dependencies) can be claimed as well, so that any combination of claims and the features thereof is disclosed and can be claimed regardless of the dependencies chosen in the attached claims. The subject-matter which can be claimed comprises not only the combinations of features as set out in the attached claims but also any other combination of features in the claims, wherein each feature mentioned in the claims can be combined with any other feature or combination of other features in the claims. Furthermore, any of the embodiments and features described or depicted herein can be claimed in a separate claim and / or in any combination with any embodiment or feature described or depicted herein or with any of the features of the attached claims.

[0005] In accordance with a first aspect, there is provided a head-mounted display (HMD) comprising: a light source configured to illuminate an eyebox region with near-infrared illumination light; an eye-tracking camera configured to capture eye-tracking images; a display configured to generate display light comprising a virtual image; and a lens assembly for focusing the display light to the eyebox region, the lens assembly comprising:a first optical element comprising a partially reflective surface; and a second optical element comprising: (1) a reflective polarizer; and (2) an eye-tracking waveguide configured to direct near-infraredreceived illumination light to the eye-tracking camera, the near-infrared received illumination light being the near-infrared illumination light reflecting or scattering from the eyebox region.

[0006] The reflective polarizer may be disposed on a planar surface of the second optical element.

[0007] The reflective polarizer may be configured to reflect a first polarization orientation of the display light and pass a second polarization orientation of the display light that is orthogonal to the first polarization orientation.

[0008] The eye-tracking waveguide may comprise: (1) an incoupling optical element configured to incouple the near-infrared received illumination light into the eye-tracking waveguide; and (2) an outcoupling optical element configured to outcouple the near-infrared received illumination light to the eye-tracking camera.

[0009] The incoupling optical element may be disposed in an on-axis position with respect to the eyebox region so that the eye-tracking camera captures on-axis eye-tracking images.

[0010] The incoupling optical element may comprise a holographic optical element (HOE) configured to incouple the near-infrared received illumination light into the eye-tracking waveguide.

[0011] The first optical element may comprise a first curvature and a second curvature. The partially reflective surface may be disposed along the first curvature of the first optical element and the partially reflective surface is disposed between the second curvature and the display. The first optical element and the second optical element may function (together) as a pancake lens assembly.

[0012] The light source may comprise an LED or a laser.

[0013] The eye-tracking camera may be included in the second optical element.

[0014] The eye-tracking waveguide may rely on total internal reflection (TIR) to confine the near-infrared received illumination light.

[0015] In a second aspect, there is provided a lens assembly for a head-mounted display (HMD), the lens assembly comprising: a reflective polarizer in an optical element; and an eyetracking waveguide included in the optical element, wherein the eye-tracking waveguide is configured to direct near-infrared received illumination light to an eye-tracking camera.

[0016] The eye-tracking camera may be included in the optical element that also comprises the reflective polarizer and the eye-tracking waveguide.

[0017] The lens assembly may further comprise another optical element comprising: (1) a partially reflective surface disposed along a first curvature; and (2) a second curvature. The second curvature may be disposed between the reflective polarizer and the partially reflective surface.

[0018] The reflective polarizer may be disposed on a planar surface of the optical element.

[0019] The reflective polarizer may be configured to reflect a first polarization orientation of display light and pass a second polarization orientation of the display light that is orthogonal to the first polarization orientation.

[0020] The eye-tracking waveguide may comprise: (1) an incoupling optical element configured to incouple the near-infrared received illumination light into the eye-tracking waveguide; and (2) an outcoupling optical element configured to outcouple the near-infrared received illumination light to the eye-tracking camera.

[0021] The incoupling optical element may be disposed in an on-axis position with respect to an eyebox region so that the eye-tracking camera captures on-axis eye-tracking images.

[0022] The incoupling optical element may comprise a holographic optical element (HOE) configured to incouple the near-infrared received illumination light into the eye-tracking waveguide.

[0023] In a third aspect, there is provided a method comprising: emitting near-infrared illumination light toward an eyebox region; receiving near-infrared received illumination light with an eye-tracking waveguide, wherein the near-infrared received illumination light is the near-infrared illumination light reflecting or scattering from the eyebox region and wherein the eye-tracking waveguide is included in an optical element that also comprises a reflective polarizer; and directing, with the eye-tracking waveguide in the optical element, the nearinfrared received illumination light to an eye-tracking camera.

[0024] The eye-tracking camera may be included in the optical element that also comprises the reflective polarizer and the eye-tracking waveguide.

[0025] It will be appreciated that any features described herein as being suitable for incorporation into one or more aspects are intended to be generalizable across any and all aspects described herein. Other aspects can be understood by those skilled in the art in light of the description, the claims and the drawings. The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Non-limiting and non-exhaustive embodiments of the invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0027] FIG. 1 illustrates an example head mounted display (HMD) including a top structure, a rear securing structure, and a side structure attached with a viewing structure, in accordance with aspects of the disclosure.

[0028] FIG. 2 illustrates an optical system that may be included in the HMD, in accordance with aspects of the disclosure.

[0029] FIG. 3A illustrates a reflective polarizer (RP) layer and an eye-tracking waveguideincluded in an example optical element, in accordance with aspects of the disclosure.

[0030] FIG. 3B illustrates a quarter-waveplate (QWP) that may be disposed above a reflective polarizer layer in an optical element, in accordance with aspects of the disclosure.

[0031] FIG. 4 illustrates a flow chart of an example process of eye-tracking with an optical element that includes an eye-tracking waveguide and reflective polarizer, in accordance with aspects of the disclosure.DETAILED DESCRIPTION

[0032] Embodiments of an integrated eye-tracking system in a Virtual Reality (VR) or Mixed Reality (MR) lens assembly 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.

[0033] 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 of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0034] In some implementations of the disclosure, the term “near-eye” may be defined as including an element that is configured to be placed within 50 mm of an eye of a user while a near-eye device is being utilized. Therefore, a “near-eye optical element” or a “near-eye system” would include one or more elements configured to be placed within 50 mm of the eye of the user.

[0035] In aspects of this disclosure, visible light may be defined as having a wavelength range of approximately 380 nm - 700 nm. Non-visible light may be defined as light having wavelengths that are outside the visible light range, such as ultraviolet light and infrared light. Infrared light having a wavelength range of approximately 700 nm - 1 mm includes nearinfrared light. In aspects of this disclosure, near-infrared light may be defined as having a wavelength range of approximately 700 nm - 1 .6 m.

[0036] In aspects of this disclosure, the term “transparent” may be defined as having greater than 90% transmission of light. In some aspects, the term “transparent” may be defined as a material having greater than 90% transmission of visible light.

[0037] A VR or MR headset typically includes a display and viewing optics to focus the display light to an eyebox region to focus a virtual image for a user of the VR headset.Conventional VR headsets separate eye-tracking and viewing optics. In implementations of this disclosure, an eye-tracking system is included in a lens assembly that focuses display light to an eyebox region. This allows the viewing optics to have reduced eye-relief which expands the design space. Additionally, integrating the eye-tracking system into the viewing optics makes the overall system more compact and potentially less costly. These and other embodiments are described in more detail in connection with FIGs. 1-4.

[0038] FIG. 1 illustrates an example head mounted display (HMD) 100 including a top structure 141 , a rear securing structure 143, and a side structure 142 attached with a viewing structure 140, in accordance with aspects of the disclosure. The illustrated HMD 100 is configured to be worn on a head of a user of the HMD. In one embodiment, top structure 141 includes a fabric strap that may include elastic. Side structure 142 and rear securing structure 143 may include a fabric as well as rigid structures (e.g. plastics) for securing the HMD to the head of the user. HMD 100 may optionally include earpiece(s) configured to deliver audio to the ear(s) of a wearer of HMD 100.

[0039] In the illustrated embodiment, viewing structure 140 includes an interface membrane 118 for contacting a face of a wearer of HMD 100. Interface membrane 118 may function to block out some or all ambient light from reaching the eyes of the wearer of HMD 100.

[0040] Example HMD 100 also includes a chassis for supporting hardware of the viewing structure 140 of HMD 100. Hardware of viewing structure 140 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 embodiment, viewing structure 140 may be configured to receive wired power. In one embodiment, viewing structure 140 is configured to be powered by one or more batteries. In one embodiment, viewing structure 140 may be configured to receive wired data including video data. In one embodiment, viewing structure 140 is configured to receive wireless data including video data.

[0041] FIG. 2 illustrates an optical system 200 that may be included in the HMD 100 of FIG. 1 , in accordance with aspects of the disclosure. Optical system 200 includes a display 210, a first optical element 220, a second optical element 230, and one or more light sources 240. First optical element 220 and second optical element 230 are spaced apart from each other. First optical element 220 and second optical element 230 may form a lens assembly that may operate as a pancake lens. Display 210 emits display light 211 including a virtual image to be focused to an eyebox region 285 for an eye 288 of a user.

[0042] Optical element 220 includes a partially reflective surface 221 disposed along a first curvature of first optical element 220. First optical element 220 also includes a second curvature 223 that may be coated with an anti-reflective (AR) film. Second optical element230 includes a reflective polarizer (RP) layer 231 and an eye-tracking waveguide 235.

[0043] The one or more light sources 240 are configured to illuminate eyebox region 285 with illumination light 241 . Illumination light 241 may be near-infrared illumination light.

[0044] In operation, display 210 emits display light 211 that encounters partially reflective surface 221 . Partially reflective surface 221 may be a 50 / 50 mirror, for example. A portion of the display light 211 propagates through partially reflective surface 221 and encounters second curvature 223. Second curvature 223 may impart refractive optical power to display light 211. Display light 211 propagates through second curvature 223 and encounters the reflective polarizer (RP) layer 231 of optical element 230. The RP layer 231 reflects a first polarization orientation of the display light 211 and passes a second polarization orientation of the display light 211 that is orthogonal to the first polarization orientation. Hence, the first polarization orientation of display light 211 is reflected back toward optical element 220 where partially reflective surface 221 reflects (at least a portion of) display light 211 back toward optical element 230. Display light 211 received by RP layer 231 for the second time has been changed to the second polarization orientation and therefore passes through the RP layer 231 to eyebox region 285. The display light 211 is changed from the first polarization orientation to the second polarization orientation based on reflections and / or waveplates (not specifically illustrated) that may be included in first optical element 220 in the optical path of display light 211.

[0045] FIG. 3A illustrates an RP layer 331 and an eye-tracking waveguide 335 included in an example optical element 330, in accordance with aspects of the disclosure. FIG. 3A shows display light 211 A of a first polarization orientation being reflected by RP layer 331 and then display light 211 B of the second polarization orientation being passed to eye 288 by RP layer 331. In the illustration of FIG. 3A, display light 211A is illustrated as linearly polarized light that is vertically oriented (first polarization orientation) and display light 211 B is illustrated as linearly polarized light that is horizontally oriented (second polarization orientation). The first polarization orientation of display light 211 A may be orthogonal to the second polarization orientation of display light 211 B. In some implementations, display light 211 A is linearly polarized light that is horizontally oriented and display light 211 B is linearly polarized light that is vertically oriented.

[0046] FIG. 3B illustrates a quarter-waveplate (QWP) 329 may be disposed above RP layer 331 , in accordance with aspects of the disclosure. QWP 329 may be disposed between RP layer 331 and partially reflective surface 221 , in some implementations. QWP 329 may be included in optical element 220, in some implementations. QWP 329 is configured to shift the polarization axis of incident light by TT / 4 (45 degrees). Therefore, incident linearly polarized light may be converted to circularly polarized light by QWP 329. Likewise, incident circularly polarized light may be converted to linearly polarized light by QWP 329. QWP 329 may bemade of birefringent materials such as quartz, organic material sheets, or liquid crystal, for example. In one embodiment, QWP 329 is designed to be a so called “zero order waveplate” so that the retardance imparted by the QWP 329 remains close to a quarter of a wave independent of the wavelength and angle of incidence of incoming light.

[0047] In the example illustration of FIG. 3B, display light 211 A is right-hand circularly polarized light 391 prior to encountering QWP 329. QWP 329 converts right-hand circularly polarized light 391 to vertically oriented linearly polarized light 392. Vertically oriented linearly polarized light 392 is reflected by RP layer 331 because RP layer 331 is configured to reflect vertically oriented linearly polarized light 392 and pass horizontally oriented linearly polarized light, in the example of FIG. 3B. Display light 211 B reflected by RP layer 331 retains its orientation as vertically oriented linearly polarized light 393 and propagates toward QWP 329. As display light 211A encounters QWP 329 for the second time, QWP 329 converts vertically oriented linearly polarized light 393 to right-hand circularly polarized light 394.

[0048] Right-hand circularly polarized light 394 may be reflected (e.g. by partially reflective surface 221) as left-hand circularly polarized light 395 propagating toward RP layer 331. QWP 329 converts left-hand circularly polarized light 395 to horizontally oriented linearly polarized light 396 that passes through RP layer 331 toward eyebox 285, in FIG. 3B.

[0049] Still referring to FIG. 3B, display light 211 B may propagate through the eyetracking waveguide 335 along its optical path to eye 288. To facilitate eye-tracking, nearinfrared illumination light 241 illuminates eye 288 and a portion of near-infrared illumination light 241 is reflected or scattered by eye 288 as near-infrared received illumination light 243. Near-infrared received illumination light 243 is incoupled into eye-tracking waveguide 335 by incoupling optical element 332. Incoupling optical element 332 may be a diffractive optical element configured to incouple the wavelength of light 243, in some implementations. Incoupling optical element 332 may include an immersed slanted mirror or etched slanted reflective surface. Incoupling optical element 332 may be a holographic optical element (HOE) that is configured to incouple a narrow-band near-infrared wavelength that matches illumination light 241 emitted by light source 240 while passing other wavelengths (e.g. visible light such as display light 211). By way of example, if light source 240 emits 940 nm light, incoupling optical element 332 may be configured to incouple 940 nm light. Incoupling optical element 332 may be disposed in an on-axis position with respect to the eyebox region 285 so that the eye-tracking camera 370 captures on-axis eye-tracking images. In some examples, a middle of incoupling optical element 332 is disposed to align with a middle of eyebox region 285 to facilitate capturing on-axis eye-tracking images.

[0050] Camera 370 may include a lens assembly configured to focus image light to a complementary metal-oxide semiconductor (CMOS) image sensor, in some implementations. A near-infrared filter that receives a narrow-band near-infrared wavelength may be placedover the image sensor so it is sensitive to the narrow-band near-infrared wavelength while rejecting visible light and wavelengths outside the narrow-band.

[0051] Near-infrared received illumination light 243 propagates within eye-tracking waveguide 335 and is outcoupled to eye-tracking camera 370 by outcoupling optical element 333. Outcoupling optical element 333 may include an immersed slanted mirror or etched slanted reflective surface. Outcoupling optical element 333 may be a diffractive optical element, in some implementations. Outcoupling optical element 333 may be an HOE, in some implementations. Eye-tracking waveguide 335 may confine light 243 to propagate in waveguide 335 using total internal reflection (TIR). Sides 336 and 337 of waveguide 335 may be planar so that display light 211 passes through waveguide 335 undistorted.

[0052] FIG. 4 illustrates a flow chart of an example process 400 of eye-tracking with an optical element that includes an eye-tracking waveguide and reflective polarizer, in accordance with aspects of the disclosure. The order in which some or all of the process blocks appear in process 400 should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in a variety of orders not illustrated, or even in parallel.

[0053] In process block 405, near-infrared illumination light (e.g. near-infrared illumination light 241) is emitted toward an eyebox region.

[0054] In process block 410, near-infrared received illumination light (e.g. near-infrared received illumination light 243) is received by an eye-tracking waveguide (e.g. waveguide 335) included in an optical element (e.g. optical element 330) that also included a reflective polarizer (e.g. reflective polarizer 331).

[0055] In process block 415, the eye-tracking waveguide in the optical element directs the near-infrared received illumination light to an eye-tracking camera (e.g. eye-tracking camera 370).

[0056] In implementations of process 400, the eye-tracking camera is included in the optical element that also includes the reflective polarizer and the eye-tracking waveguide.

[0057] Embodiments of the invention 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, orsome 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.

[0058] The term “processing logic” in this disclosure may include one or more processors, microprocessors, multi-core processors, Application-specific integrated circuits (ASIC), and / or Field Programmable Gate Arrays (FPGAs) to execute operations disclosed herein. In some embodiments, memories (not illustrated) are integrated into the processing logic to store instructions to execute operations and / or store data. Processing logic may also include analog or digital circuitry to perform the operations in accordance with embodiments of the disclosure.

[0059] A “memory” or “memories” described in this disclosure may include one or more volatile or non-volatile memory architectures. The “memory” or “memories” may be removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Example memory technologies may include RAM, ROM, EEPROM, flash memory, CD-ROM, digital versatile disks (DVD), high-definition multimedia / data storage disks, or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information for access by a computing device.

[0060] Networks may include any network or network system such as, but not limited to, the following: a peer-to-peer network; a Local Area Network (LAN); a Wide Area Network (WAN); a public network, such as the Internet; a private network; a cellular network; a wireless network; a wired network; a wireless and wired combination network; and a satellite network.

[0061] Communication channels may include or be routed through one or more wired or wireless communication utilizing IEEE 802.1 1 protocols, short-range wireless protocols, SPI (Serial Peripheral Interface), l2C (Inter-Integrated Circuit), USB (Universal Serial Port), CAN (Controller Area Network), cellular data protocols (e.g. 3G, 4G, LTE, 5G), optical communication networks, Internet Service Providers (ISPs), a peer-to-peer network, a Local Area Network (LAN), a Wide Area Network (WAN), a public network (e.g. “the Internet”), a private network, a satellite network, or otherwise.

[0062] A computing device may include a desktop computer, a laptop computer, a tablet, a phablet, a smartphone, a feature phone, a server computer, or otherwise. A server computer may be located remotely in a data center or be stored locally.

[0063] The processes explained above are described in terms of computer software and hardware. The techniques described may constitute machine-executable instructionsembodied within a tangible or non-transitory machine (e.g., computer) readable storage medium, that when executed by a machine will cause the machine to perform the operations described. Additionally, the processes may be embodied within hardware, such as an application specific integrated circuit (“ASIC”) or otherwise.

[0064] A tangible non-transitory machine-readable storage medium includes any mechanism that provides (i.e. , stores) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). For example, a machine-readable storage medium includes recordable / non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0065] The above description of illustrated embodiments of the invention, 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 of, and examples for, the invention are described herein for illustrative purposes, various modifications are possible within the scope of the invention, as defined in the appended claims, as those skilled in the relevant art will recognize.

[0066] These modifications can be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims.

Claims

CLAIMS:1 . A head mounted display (HMD) comprising: a light source configured to illuminate an eyebox region with near-infrared illumination light; an eye-tracking camera configured to capture eye-tracking images; a display configured to generate display light comprising a virtual image; and a lens assembly for focusing the display light to the eyebox region, the lens assembly comprising: a first optical element comprising a partially reflective surface; and a second optical element comprising: (1) a reflective polarizer; and (2) an eyetracking waveguide configured to direct near-infrared received illumination light to the eyetracking camera, the near-infrared received illumination light being the near-infrared illumination light reflecting or scattering from the eyebox region.

2. The HMD of claim 1 , wherein the reflective polarizer is disposed on a planar surface of the second optical element.

3. The HMD of claim 1 or claim 2, wherein the reflective polarizer is configured to reflect a first polarization orientation of the display light and pass a second polarization orientation of the display light that is orthogonal to the first polarization orientation.

4. The HMD of any preceding claim, wherein the eye-tracking waveguide comprises: (1) an incoupling optical element configured to incouple the near-infrared received illumination light into the eye-tracking waveguide; and (2) an outcoupling optical element configured to outcouple the near-infrared received illumination light to the eye-tracking camera; optionally, wherein the incoupling optical element is disposed in an on-axis position with respect to the eyebox region so that the eye-tracking camera captures on-axis eye-tracking images; optionally, wherein the incoupling optical element comprises a holographic optical element (HOE) configured to incouple the near-infrared received illumination light into the eyetracking waveguide.

5. The HMD of any preceding claim, wherein the first optical element comprises a first curvature and a second curvature, the partially reflective surface disposed along the first curvature of the first optical element, and wherein the partially reflective surface is disposed between the second curvature and the display, and wherein the first optical element and the second optical element function as a pancake lens assembly.

6. The HMD of any preceding claim, wherein the light source comprises an LED or a laser.

7. The HMD of any preceding claim, wherein the eye-tracking camera is included in the second optical element.

8. The HMD of any preceding claim, wherein the eye-tracking waveguide relies on totalinternal reflection (TIR) to confine the near-infrared received illumination light.

9. A lens assembly for a head-mounted display (HMD) comprising: a reflective polarizer in an optical element; and an eye-tracking waveguide included in the optical element, wherein the eye-tracking waveguide is configured to direct near-infrared received illumination light to an eye-tracking camera.

10. The lens assembly for the HMD of claim 9, wherein the eye-tracking camera is included in the optical element that also comprises the reflective polarizer and the eye-tracking waveguide.11 . The lens assembly for the HMD of claim 9 or claim 10 further comprising: another optical element comprising: (1) a partially reflective surface disposed along a first curvature; and (2) a second curvature, wherein the second curvature is disposed between the reflective polarizer and the partially reflective surface.

12. The lens assembly for the HMD of claim any one of claims 9 to 11 and one or more of the following:(i) wherein the reflective polarizer is disposed on a planar surface of the optical element;(ii) wherein the reflective polarizer is configured to reflect a first polarization orientation of display light and pass a second polarization orientation of the display light that is orthogonal to the first polarization orientation.

13. The lens assembly for the HMD of any one of claims 9 to 12, wherein the eye-tracking waveguide comprises: (1) an incoupling optical element configured to incouple the nearinfrared received illumination light into the eye-tracking waveguide; and (2) an outcoupling optical element configured to outcouple the near-infrared received illumination light to the eyetracking camera; optionally, wherein the incoupling optical element is disposed in an on-axis position with respect to an eyebox region so that the eye-tracking camera captures on-axis eye-tracking images; optionally, wherein the incoupling optical element comprises a holographic optical element (HOE) configured to incouple the near-infrared received illumination light into the eyetracking waveguide.

14. A method comprising: emitting near-infrared illumination light toward an eyebox region; receiving near-infrared received illumination light with an eye-tracking waveguide, wherein the near-infrared received illumination light is the near-infrared illumination light reflecting or scattering from the eyebox region, and wherein the eye-tracking waveguide is included in an optical element that also comprises a reflective polarizer; anddirecting, with the eye-tracking waveguide in the optical element, the near-infrared received illumination light to an eye-tracking camera.

15. The method of claim 14, wherein the eye-tracking camera is included in the optical element that also comprises the reflective polarizer and the eye-tracking waveguide.

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