Camera modules incorporating metasurfaces

Abstract

An example apparatus includes a camera module that includes an image sensor, and a lens unit disposed over the image sensor. The lens unit includes first and second encapsulated metasurfaces stacked one over the other, the lens unit further including an aperture layer disposed between the first and second metasurfaces, wherein the aperture layer defines an aperture stop.

Description

CAMERA MODULES INCORPORATING METASURFACESFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to camera modules.BACKGROUND

[0002] Various types of miniature camera modules are available. Eye-tracking sensor modules, for example, facilitate measuring the point of gaze and / or the motion of an eye relative to an individual’s head. Eye-tracking technology can convert eye movements into a data stream that contains information such as pupil position, the gaze vector for each eye, and gaze point. In some instances, non-contact, optical techniques can be used for measuring eye movement. An eye-tracking system may include, for example, one or more cameras, one or more light sources, and computing capabilities. In some instances, light (e.g., near infrared) is imaged as a virtual image “glint” on the individual's eye (e.g., cornea) and is detected by an optical sensor. Information from the sensor then is analyzed to extract, for example, gaze direction for the user's eye. The computing capabilities of the eye-tracking system may include, for example, image processing to detect features of the eye(s), as well as mathematical models to calculate the eye’s position and the gaze point.

[0003] A wide range of applications can make use of small camera modules, including those used for eye-tracking applications. Such applications include, for example, gaming, consumer applications and scientific research, and professional training. Eyetracking technology can facilitate hands-free device interaction and may be integrated, for example, into virtual reality (VR) or augmented reality (AR) headsets, as well as eyetracking glasses. The eye-tracking technology also can be integrated into other consumer electronics such as smartphones and laptops, among others.SUMMARY

[0004] In one aspect, the present disclosure describes an apparatus that includes a camera module. The camera module includes an image sensor, and a lens unit disposed over the image sensor. The lens unit includes first and second encapsulated metasurfaces stacked one over the other, the lens unit further including an aperture layer disposed between the first and second metasurfaces, wherein the aperture layer defines an aperture stop.

[0005] Some implementations include one or more of the following features. For example, in some implementations, the aperture stop is operable to cancel or reduce at least some optical aberrations. The aperture layer can be composed, for example, of black chrome or black resist.

[0006] In some implementations, the first metasurface is on a first substrate, the second metasurface is on a second substrate, and the first and second substrates are bonded to one another in a back-to-back arrangement such that the first and second metasurfaces face away from one another. In some implementations, the first and second substrates are composed of a glass, a plastic, or a polymer. In some implementations, the first and second substrates are bonded to one another by an adhesive, which in some cases is optically clear at a particular wavelength which may be index matched to the first and second substrates. In some implementations, each of the first and second metasurfaces is encapsulated by a respective encapsulation layer composed of a material that is optically clear at a particular wavelength. In some implementations, at least one of the first or second metasurfaces is rectangular with rounded corners.

[0007] In some implementations, the lens unit further includes an optical filter, wherein the optical filter includes an angle-of-incidence (AOI) filter or a bandpass filter. The AOI filter can be operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence at a particular wavelength. The bandpass filter can be operable selectively to block or attenuate rays of electromagneticradiation outside of a defined passband of wavelengths. In some implementations, the optical filter comprises a coating. In some implementations, the optical filter is a discrete component bonded at a backside of the lens unit. In some implementations, the optical filter is closer to a metasurface in the lens unit than to the image sensor.

[0008] In some implementations, the lens unit further includes at least one baffle to prevent at least some stray light from reaching a light sensitive surface of the image sensor. The at least one baffle can be composed, for example, of black resist or black chrome. In some cases, the at least one baffle is rectangular with rounded corners.

[0009] In some implementations, sidewalls of the lens unit are at least partially blackened. In some implementations, the first metasurface is closer to a front of the lens unit than is the second metasurface, and the apparatus further includes an anti-reflection coating (ARC) over the first metasurface.

[0010] In some implementations, the camera module further includes a cover glass over the image sensor, wherein the lens unit includes a spacer that is bonded to the cover glass. In some implementations, the lens unit is bonded to an active surface of the image sensor or to a cover glass over the image sensor.

[0011] In some implementations, the apparatus further includes an electronic circuit board, wherein the image sensor is mounted to the electronic circuit board. In some cases, the lens unit is bonded to the active surface of the image sensor without an air gap therebetween. In some implementations, the lens unit is mounted in a barrel that is aligned in a holder attached to the circuit board.

[0012] The camera modules can be used in a wide range of applications, including for example eye-tracking, presence detection, depth mapping, driver monitoring, face recognition, iris recognition or lips recognition, among others.

[0013] One or more of the following advantages can be achieved in some implementations. For example, use of optical elements (i.e., MOEs) employing flat technology can, in some cases, help reduce the overall size (e.g., diameter and height) of the camera module. In some instances, incorporating a stack of metasurfaces in the lens unit can facilitate improved thermal and mechanical stability. In some instances, incorporating a stack of metasurfaces in the lens unit can facilitate a wide range of optical functionalities by having a resonant interaction between the stacked metasurfaces, thereby improving or enhancing the optical characteristics of the camera module.

[0014] Other aspects, features and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates a first example of a camera module.

[0016] FIG. 2 illustrates a second example of a camera module.

[0017] FIG. 3 illustrates a third example of a camera module.

[0018] FIG. 4 illustrates a fourth example of a camera module.

[0019] FIG. 5 illustrates a fifth example of a camera module.

[0020] FIG. 6 illustrates a sixth example of a camera module.

[0021] FIG. 7 illustrates a seventh example of a camera module.

[0022] FIG. 8 illustrates an eighth example of a camera module.

[0023] FIG. 9 illustrates a ninth example of a camera module.

[0024] FIG. 10 is a block diagram of an eye-tracking system that includes a camera module.DETAILED DESCRIPTION

[0025] The present disclosure describes various miniature camera modules. In the following paragraphs, examples for eye-tracking applications are described. However, the camera modules can be used in other applications as well. Examples of such other applications include, but are not limited to, presence detection, depth mapping, driver monitoring, face recognition, iris recognition or lips recognition, among others.

[0026] As shown in FIG. 1, an example eye-tracking sensor module 20 A includes an image sensor 22 and a lens unit 26 disposed over the sensor. The image sensor 22 can be mounted on and coupled electrically to an electronic circuit board (e.g., a printed circuit board (PCB)) 24, for example, by wire bonds or conductive pads 23. The electronic circuit board 24, in turn, can be connected electrically to other components a host device (e.g., a headset or smartphone). The other components may include, for example, one or more light sources (e.g., vertical cavity surface emitting lasers (VCSELs); light emitting diodes (LEDs)) and processing circuitry configured to detect features of an individual’s eye and calculate the eye’s position and / or the gaze point based on signals output by the image sensor 22.

[0027] The image sensor 22 can include a light sensitive region 25 that includes, for example, an array of spatially distributed light sensitive elements 25 (e.g., active demodulation detection pixels). The sensor 22 can be implemented, for example, in a semiconductor chip using charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) technologies. In some implementations, a cover glass 44 may be provided over the image sensor 22. The image sensor 22 is operable to detect light signals passing through the lens unit 26. The detect signals then can be used, forexample, by processing circuitry (not shown) for tracking movement of an individual’s eye(s).

[0028] Depending on the particular application, the operational wavelength for the module may be, for example, in the near-infrared range (700 - 1400 nm), although other wavelengths may be appropriate for some applications.

[0029] The lens unit 26 includes at least two meta optical elements (e.g., MOE lenses) stacked one over the other. As shown in the example of FIG. 1, a first MOE lens includes a first metasurface 28A disposed on an optically transparent or at least partially transparent substrate 30A (e.g., a glass, plastic or polymer material). Likewise, a second MOE lens includes a second metasurface 28B disposed on an optically transparent or at least partially transparent substrate 30B (e.g., a glass, plastic or polymer material). The substrates 30A, 30B, may be composed, for example, of glass (e.g., borosilicate glass such as D 263® glass manufactured by Schott) and can provide mechanical support for the metasurfaces 28 A, 28B. Incorporating a stack of metasurfaces in the lens unit 26 can, in some instances, facilitate a wide range of optical functionalities by having a resonant interaction between the stacked metasurfaces.

[0030] Each metasurface 28A, 28B has carefully arranged “unit cells” or “meta-atoms” with sub -wavelength structures (e.g., nanostructures). The term “sub wavelength” indicates that the nanostructures have at least one lateral dimension (parallel to the substrate on which they are disposed) that is less than a wavelength of light that is to be incident thereon. The meta-atoms can be composed, for example, of silicon. In general, the dimensions of the nanostructures scale with the shortest wavelength of interest. For example, in some implementations, the nanostructures can be in the form of nanoscale features having dimensions less than 1 micron. By adjusting the geometry of these unit cell elements, one can modify the phase above the elements in response to a plane wave. With the knowledge of the phase in terms of the geometry parameters, it is possible to create a metalens with an arbitrary phase profile by placing the meta-atoms at the necessary positions. In general, the derivative of the phase profile determines the raybending. Each metasurface 28A, 28B on the substrate 30 forms a respective metal optical element (MOE) that employs a flat optic technology. Use of optical elements employing flat technology can, in some cases, help reduce the overall size (e.g., diameter and height) of the module 20A.

[0031] In some implementations, the metasurfaces have a circular or round shape. In other cases, the metasurfaces are rectangular, and may have rounded corners, which can be tailored to optimize the lens size. Such an arrangement can, in some cases, allow for a smaller glass die for a given edge spacing.

[0032] As further illustrated in the example of FIG. 1, an aperture layer 45 can define an aperture stop to limit the solid angle of rays passing through the system from an on-axis object point, which defines the cone of light reaching the image plane of the sensor 22. In some implementations, the aperture layer 45 defines a hole (e.g., a circular opening) in a light blocking material such as a layer of black chrome or black resist disposed on the surface of at least one of the substrates 30A, 30B.

[0033] The first and second substrates 30A, 30B can be bonded, for example, back-to- back to one another. That is, the substrates 30A, 30B can be bonded to one another such that the respective metasurfaces 28A, 28B face away from one another, with the aperture layer 45 disposed between the two substrates 30A, 30B. In some cases, the substrates 30A, 30B are bonded to one another by an optically clear adhesive 46 (e.g., a polymer glue). Thus, the MOEs can be stacked over one another without an air gap between them. By providing an aperture stop between the MOEs, aberrations such as lateral chromatic aberrations, distortions, and / or off-axis aberrations (e.g., coma) can, in some cases, be canceled out or reduced. The reduction in lateral color aberration can be particularly advantageous in an MOE-based imaging system in which the color aberrations tend to be relatively large compared to classic bulk refractive lenses. In some implementations, the reduction of lateral color aberration can be targeted to values smaller than the smallest pixel sizes of near-infrared CMOS image sensors (e.g., < 1 pm).

[0034] As further indicated in FIG. 1, each of the metasurfaces 28 A, 28B can be encapsulated. Such an arrangement can provide protection for the metasurfaces. In some implementations, each of the metasurfaces 28A, 28B is encapsulated by a respective encapsulation layer 32 composed of a material that is optically clear at the application wavelength. For example, in some instances, the encapsulation layers 32 are composed of a polymer. The encapsulation layers 32 can be relatively thin (e.g., 1-3 pm in some instances) so as to reduce the extent of any adverse impact on optical performance. Other materials and / or thicknesses for the encapsulation layers 32 may be used in some implementations.

[0035] Some implementations include an anti -reflective coating (ARC) 36 over the encapsulation layer 32 on the upper metasurface 28A (i.e., the metasurface further away from the image sensor 22).

[0036] As further shown in the example of FIG. 1, a stray light aperture 34 can be provided at the front of the lens unit 26 (i.e., over the first metasurface 28A where light enters the module). The aperture 34 may be composed, for example, of black chrome or a structured resist.

[0037] The lens unit 26 can be mounted over the image sensor 22. In general, depending on the implementation, the lens unit can be bonded to an active surface of the image sensor 26 or to the cover glass 44, if present. In some cases, the lens unit 26 is attached by an adhesive over the image sensor 22. As shown in the example of FIG. 1, the lens unit 26 is bonded (e.g., by adhesive 64A) to a glass spacer 62, which in turn is bonded (by adhesive 64B) to the cover glass 44. If there is no cover glass 44, then the spacer 62 can be bonded, for example, directly to the upper surface of the image sensor 22. The adhesives 64A, 64B can be, for example, a polymer glue that is optically clear at the operating wavelength for the eye-tracking module 20A. The thickness and material of the adhesive layers 64A and / or 64B can be adjusted to help achieve the desired focus at the sensor 25. The spacer 62 can help provide a specified distance between the lens unit and the image sensor. In some implementations, as shown in the eye-tracking sensormodule 20B of FIG. 2, the spacer 62 has an opening 66 such that an air gap is present between the lens unit (e.g., 26) and the cover glass 44. In the example of FIG. 2, the spacer 62 need not be transmissive to the operating wavelength.

[0038] The outer sidewalls of the substrate 30 and the encapsulation layers 32, as well as the spacer 62, the ARC, and coverglass 44, can be blackened or at least partially blackened, e.g., with a layer of black chrome or other opaque material 38, to prevent or reduce stray light from entering the lens unit 26.

[0039] In some implementations, as shown in the eye-tracking sensor module 20C of FIG. 3, instead of a glass spacer, the lens unit 26 is bonded (e.g., by adhesive 64A) to an optical filter 50, which in turn is bonded (by adhesive 64B) to the cover glass 44. Thus, in this example, the optical filter 50 is implemented as a discrete component and also serves as a spacer disposed between the lens unit 26 and the image sensor 22. The optical filter 50 can be implemented, for example, as an angle-of-incidence (AOI) filter and / or a bandpass filter (BPF). As shown in the example of FIG. 3, the optical filter 50 is bonded by adhesive 64A to the encapsulant 32 that encapsulates the second metasurface 28B. In some cases, as shown in the eye-tracking sensor module 20D of FIG. 4, the optical filter 50 is bonded by the adhesive 64A (e.g., polymer glue) directly to the glass substrate 30B. In the latter implementation, the adhesive 64A also serves to encapsulate the second metasurface 28B.

[0040] In some implementations, as shown in the eye-tracking sensor module 20E of FIG. 5, an optical filter is implemented as a coating 48 on a surface of one of the glass substrates 30A, 30B. The coating 48 can be provided on a surface opposite the surface on which the respective metasuface (28A or 28B) is disposed.

[0041] As noted above, the optical filter 50 (or 48) can be implemented, for example, as a narrow-band filter (e.g., a bandpass filter (BPF)) and / or an angle-of-incidence (AOI) filter. In some implementations, the optical filter is operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence atthe operational wavelength. In some implementations, providing an optical filter that selectively blocks or attenuates rays of electromagnetic radiation greater than a particular angle of incidence can provide optical performance benefits (e.g., stray -light filtering). For example, in some cases, an optical output from the lens unit 26 includes imaging rays and rays of higher diffractive orders, wherein the higher diffractive orders are diffractive orders higher than the imaging order. An AOI filter disposed optically between the lens unit 26 and the image sensor 22 can help reduce an amount of light of at least one of the higher diffractive order rays from reaching the light sensitive surface of the image sensor. In some instances, the location of the AOI filter 50 is closer to the second metasurface 28B than to the sensor 25 to improve functionality.

[0042] As an example, in some implementations the imaging order is a first transmitted converging order (m: ±1), and the higher diffractive orders include one or more higher transmitted converging or diverging orders (m: ±2, ±3, . . .), wherein the angle-of- incidence filter is operable to prevent at least some rays of a transmitted second order (m: ±2) and / or higher orders (m: ±3, ±4. . .) from reaching the light sensitive surface of the image sensor. More generally, the unwanted diffractive orders are all orders other than the imaging order. The unwanted orders can arise, for example, from each MOE surface, and combinations of theses unwanted orders can be present in the optical stack. The zero diffractive order also may be included among the unwanted orders. In some situations, the unwanted orders will have a higher angle-of-incidence toward the sensor than the imaging order and can thereby be reduced or partially blocked with an optical filter.

[0043] A narrow-band filter, for example, can be selective for the specific wavelength spectra used in the eye-tracking application and can be configured to pass only rays with a specific wavelength used in the illumination part of the eye-tracking system. Further, a BPF can help an AOI-filter to block and / or reduce unwanted orders at very high angles. Thus, in some implementations, the optical filter can be operable to block or significantly attenuate rays using a BPF and an AOI filter. Depending on the application, the filter can block rays of light, for example, by one or more of absorption, reflection, or deflection of the incoming rays away from the image sensor area.

[0044] In some implementations, the optical filter 50 (or 48) includes both an AOI filter as well as a BPF arranged such that rays blocked by the BPF are of higher diffractive orders than the diffractive orders reduced by the AOI filter. In some cases, the optical filter can be implemented as an optical interference bandpass filter that exhibits a degree of shift with the angle of incidence. In some implementations, the properties of the AOI filter are position dependent; for example, they may vary in the radial direction.

[0045] Some implementations of an eye-tracking sensor module include one or more baffles (which also may be referred to as stray light apertures). In some cases, the baffle(s) can prevent at least some stray light (e.g., rays resulting from higher diffractive orders, Fresnel reflections or other scattered light) from reaching the light sensitive surface of the image sensor 22. In some implementations, incorporating the baffle(s) into the eye-tracking sensor module can help prevent the appearance on the light sensitive surface of the image sensor 22 of an artifact resulting from stray light rays at one or more of the higher diffractive orders or other scattered light. In some cases, providing the baffle(s) in combination with the metalenses can prevent stray light from unwanted rays beyond what may be achievable using conventional (e.g., refractive) optics. That is, in addition to preventing stray light from scattered rays, providing the baffle(s) in combination with the metalenses can, in some instances, help prevent stray light from unwanted diffractive orders or combination of orders and / or stray light caused by “not- transmitted” rays, which appear at specific conditions in the generalized Snell’s law.

[0046] FIG. 6 illustrated an example of an eye-tracking sensor module 20F that includes baffles 60A, 60B disposed below the lower metasurface 28B to prevent or reduce the amount of stray light reaching the image sensor 22. For some implementations that also include an AOI filter or BPF, the baffles 60A, 60B can be configured to stop unwanted rays. Thus, in some implementations, the baffles stop or reduce the amount of stray light, the AOI filter enhances this feature by stopping or reducing unwanted orders, and the BPF filters out the appropriate wavelength spectra used in the particular application.

[0047] The baffles 60A, 60B can be composed, for example, of black resist, black chrome, or other ray blocking material. In some instances, there is a distance (d) that provides a margin between the edge of the baffle and the light rays for the imaging order(s). Such an arrangement can allow the baffle not to interfere with the imaging order(s) for all field points to avoid vignetting.

[0048] In some implementations, the baffles have a circular or round shape. In other cases, the baffles are rectangular, and may have rounded comers, which can be tailored for stray light control. Such an arrangement can allow for a smaller glass die for a given edge spacing, in some cases.

[0049] In the foregoing examples of FIGS. 1-6, the lens unit, including the MOEs, has substantially the same lateral dimensions as the image sensor 22. In other implementations, as shown in the eye-tracking sensor module 20G of FIG. 7, the lateral dimension(s) of the lens unit, including the MOEs, can be smaller than the corresponding dimension(s) of the image sensor 22.

[0050] Although the foregoing examples of FIGS. 1-7 include an air gap between the image cover glass 44 and the image sensor 22, some implementations include an index- matched adhesive (e.g., bonding glue) or other optically clear material 70 between the cover glass 44 and the image sensor 22 such that no air gap is present, as shown in the example eye-tracking sensor module 20H of FIG. 8.

[0051] As noted above, in some implementations, the cover glass 44 can be omitted, and an index-matched adhesive (e.g., bonding glue) or other optically clear material 70 can be provided, for example, to bond an optical filter 50 (e.g., a BPF or AOI filter) and the image sensor, as shown in the example of the eye-tracking sensor module 201 of FIG. 9.

[0052] In some implementations, the lens unit 26 is mounted in a barrel that is aligned in a holder attached to the electronic circuit board. The barrel mechanics can, in some cases, facilitate precise alignment of the lens unit to the image sensor.

[0053] FIG. 10 is a block diagram of an eye-tracking system that includes an eyetracking sensor module as described above, as well as one or more light sources (e.g., near-infrared vertical cavity surface emitting lasers (VCSELs) or light emitting diodes (LEDs)), and a microcontroller operable to control, drive and synchronize the light source(s) and eye-tracking sensor module. The light source emits near-infrared light toward the user’s eye, and light reflected by the eye is detected by the image sensor in the eye-tracking sensor module. A computer, which can include, e.g., one or more processors, is configured to detect features of an individual’s eye and calculate the eye’s position and / or the gaze point based on signals output by the image sensor in the eyetracking sensor module. The computing capabilities of the eye-tracking system may include, for example, image processing to detect features of the eye(s), as well as mathematical models to calculate the eye’s position and the gaze point. In some implementations, the computing capabilities also can include machine learning algorithms, which use images of the eye captured by the eye tracking camera (i.e., the image sensor). Further, in some implementations, the eye-tracking camera can be used for face recognition (e.g., based on eye brow expressions). Further, in some implementations, the eye-tracking system can be used for iris recognition and / or artificial intelligent (Al) applications (e.g., based on lip recognition).

[0054] Various aspects of the subject matter and the functional operations described in this specification (e.g., the computing capabilities of the eye-tracking system) can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Thus, aspects of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them.The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware.

[0055] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0056] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Computer readable media suitable for storing computer program instructions and data include all forms of non volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0057] While this specification contains many specifics, these should not be construed as limitations on the scope of the disclosure or of what may be claimed, but rather as descriptions of features specific to particular implementations. Certain features that are described in this specification in the context of separate implementations may also be combined in the same implementation. Conversely, various features that are described in the context of a single implementation may also be implemented in multiple implementations separately or in any suitable sub-combination. Various modifications can be made to the foregoing examples. Accordingly, other implementations also are within the scope of the claims.

Claims

What is claimed is:

1. An apparatus comprising: a camera module that includes: an image sensor; and a lens unit including first and second encapsulated metasurfaces stacked one over the other, the lens unit further including an aperture layer disposed between the first and second metasurfaces, wherein the aperture layer defines an aperture stop, and wherein the lens unit is disposed over the image sensor.

2. The apparatus of claim 1 wherein the aperture stop is operable to cancel or reduce at least some optical aberrations.

3. The apparatus of any one of claims 1-2 wherein the aperture layer is composed of black chrome or black resist.

4. The apparatus of any one of claims 1-3 wherein: the first metasurface is on a first substrate, the second metasurface is on a second substrate, and the first and second substrates are bonded to one another in a back-to-back arrangement such that the first and second metasurfaces face away from one another.

5. The apparatus of any one of claims 1-4 wherein the first and second substrates are composed of a glass, a plastic, or a polymer.

6. The apparatus of any one of claims 4-5 wherein the first and second substrates are bonded to one another by an adhesive.

7. The apparatus of claim 6 wherein the adhesive is optically clear at a particular wavelength.

8. The apparatus of any one of claims 6-7 wherein the adhesive is index matched to the first and second substrates.

9. The apparatus of any one of claims 1-8 wherein each of the first and second metasurfaces is encapsulated by a respective encapsulation layer composed of a material that is optically clear at a particular wavelength.

10. The apparatus of any one of claims 1-9 wherein at least one of the first or second metasurfaces is rectangular with rounded comers.

11. The apparatus of any one of claims 1-10 wherein the lens unit further includes an optical filter, wherein the optical filter includes an angle-of-incidence (AO I) filter operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence at a particular wavelength.

12. The apparatus of any one of claims 1-10 wherein the lens unit further includes an optical filter, wherein the optical filter includes a bandpass filter operable selectively to block or attenuate rays of electromagnetic radiation outside of a defined passband of wavelengths.

13. The apparatus of any one of claims 11-12 wherein the optical filter comprises a coating.

14. The apparatus of any one of claims 11-12 wherein the optical filter is a discrete component bonded at a backside of the lens unit.

15. The apparatus of any one of claims 11-12 wherein the optical filter is closer to a metasurface in the lens unit than to the image sensor.

16. The apparatus of any one of claims 1-15 wherein the lens unit further includes at least one baffle to prevent at least some stray light from reaching a light sensitive surface of the image sensor.

17. The apparatus of claim 16 wherein the at least one baffle is composed of black resist or black chrome.

18. The apparatus of any one of claims 16-17 wherein the at least one baffle is rectangular with rounded corners.

19. The apparatus of any one of claims 1-18 wherein sidewalls of the lens unit are at least partially blackened.

20. The apparatus of any one of claims 1-19 wherein the first metasurface is closer to a front of the lens unit than is the second metasurface, the apparatus further including an anti -refl ection coating (ARC) over the first metasurface.

21. The apparatus of any one of claims 1-20 wherein the camera module further includes: a cover glass over the image sensor; and wherein the lens unit includes a spacer that is bonded to the cover glass.

22. The apparatus of any one of claims 1-21 wherein the lens unit is bonded to an active surface of the image sensor or to a cover glass over the image sensor.

23. The apparatus of claim 22 wherein the lens unit is bonded to the active surface of the image sensor without an air gap therebetween.

24. The apparatus of any one of claims 1-23 further including an electronic circuit board, wherein the image sensor is mounted to the electronic circuit board.

25. The apparatus of claim 24 where the lens unit is mounted in a barrel that is aligned in a holder attached to the circuit board.

26. The apparatus of any one of claims 1-25 wherein the camera module is an eye- tracking sensor module.

Images