Camera modules incorporating metasurfaces

Abstract

An apparatus includes a camera module The camera module includes an image sensor, a lens unit disposed over the image sensor, and an aperture stop. The lens unit includes at least two encapsulated metasurfaces stacked one over the other.

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. Time-of-flight (ToF) sensor modules, for example, can be used to detect the distance to an object. In general, indirect time-of-flight (iToF) systems are based on a phase-measurement technique of emitted intensity-modulated light, which is reflected by a scene. The reflected light is imaged onto a sensor, and the photo-generated electrons are demodulated in the sensor. Based on the phase information, the distance to a point in the scene for each pixel is determined by processing circuitry associated with the sensor. Additionally, ToF-based systems can provide depth and / or distance information via a pulse-measurement technique. In a pulse-measurement technique, distance is determined based on the time for emitted light to reflect back onto the sensor.

[0003] Integrating camera modules (e.g., ToF sensors including their lenses) into devices such as smart phones, tablets and other handheld devices, however, can be challenging for several reasons. For example, space in the host device typically is at premium. Thus, there is a need to achieve accurate ToF sensor and other camera modules having a relatively small height. Further, it can be desirable for ToF sensor modules to have low F-numbers (which indicates the ratio of the focal length (f) to the entrance pupil diameter (EPD)) and it can be advantageous to have a low effective F-number (i.e., a low F- number for all field points). Achieving such F-numbers, however, can present a challenge when using conventional lens configurations. For example, rather complex, large conventional lens stacks may be needed in order to achieve similar low effective F- numbers.SUMMARY

[0004] In one aspect, the present disclosure describes an apparatus that includes a camera module. The camera module includes an image sensor, a lens unit disposed over the image sensor, and an aperture stop. The lens unit includes at least two encapsulated metasurfaces stacked one over the other.

[0005] The lens unit can have a front side and a back side, wherein the back side of the lens unit is closer to the image sensor than is the front side of the lens unit. In some implementations, the aperture stop is disposed at the front side of the lens unit.

[0006] Some implementations include one or more of the following features. For example, in some implementations, the lens unit includes an optical filter, wherein the optical filter includes an angle-of-incidence (AOI) filter operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence at a particular wavelength. In some implementations, the lens unit includes first and second optical filters, wherein each of the optical filters includes an angle-of-incidence (AOI) filter, the first AOI filter being disposed in the lens unit after the first metasurface and having a first cut-off angle, and the second AOI filter being disposed in the lens unit after the second metasurface and having a second, different cut-off angle.

[0007] In some implementations, the camera module 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. In some implementations, the optical filter comprises a coating in or on the lens unit. In some implementations, the optical filter is a discrete component bonded at the back side 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 camera module further includes a barrel disposed within a holder, wherein the lens unit is disposed within the barrel, and the optical filter is a discrete component disposed within the barrel or within the holder.

[0009] In some implementations, the aperture stop is at the front side of the lens unit. 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. In some implementations, the at least one baffle includes a first baffle disposed at the back side of the lens unit. In some implementations, the at least two encapsulated metasurfaces include a first metasurface and a second metasurface, wherein the at least one baffle further includes a second baffle disposed between the first and second metasurfaces. The baffle(s) can be composed, for example, of black resist or black chrome.

[0010] In some implementations, the aperture stop is defined by an aperture layer composed of black chrome or black resist. In some implementations, sidewalls of the lens unit are at least partially blackened. In some implementations, the lens unit includes an anti-reflection coating (ARC).

[0011] In some implementations, the at least two encapsulated metasurfaces include a first metasurface and a second metasurface on opposite sides of a single glass substrate. In some implementations, the at least two encapsulated metasurfaces include a first metasurface on a first glass substrate, and a second metasurface on a second glass substrate that is bonded to the first glass substrate. In some implementations, the first and second glass substrates are bonded to one another by an adhesive. The adhesive can be optically clear at a particular wavelength (e.g., an operating wavelength for the camera module). In some implementations, the adhesive is index matched to the first and second glass substrates.

[0012] In some implementations, at least one of the metasurfaces is encapsulated by a polymer. In some implementations, at least one of the metasurfaces is encapsulated by an adhesive that bonds the first and second glass substrates together. In someimplementations, each of the at least two metasurfaces is encapsulated by a respective encapsulation layer composed of a material that is optically clear at a particular wavelength.

[0013] In some implementations, the camera module further includes a cover glass over the image sensor, and a spacer, wherein the lens unit is bonded to the spacer, which in turn 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. In some implementations, the lens unit is bonded to the active surface of the image sensor without an air gap therebetween.

[0014] In some implementations, the apparatus further includes an electronic circuit board, wherein the image sensor is mounted to the electronic circuit board. In some implementations, the lens unit is mounted in a barrel that is aligned in a holder attached to the circuit board. In some implementations, the camera module is a time-of-flight (ToF) sensor module.

[0015] 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 correcting different aberrations of the optical system, thereby improving or enhancing the optical performance of the camera module.

[0016] 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

[0017] FIG. 1 illustrates a first example of a camera module.

[0018] FIG. 2 illustrates a second example of a camera module.

[0019] FIG. 3 illustrates a third example of a camera module.

[0020] FIG. 4 illustrates a fourth example of a camera module.

[0021] FIGS. 5 through 9 illustrate examples of camera modules that include an optical filter.

[0022] FIGS. 10 through 14 illustrate examples of camera modules that include at least one baffle.

[0023] FIGS. 15 through 17 illustrate examples of camera modules that include a spacer between the lens unit and the image sensor.DETAILED DESCRIPTION

[0024] The present disclosure describes various miniature camera modules. In the following paragraphs, examples for applications using time-of-flight sensors are described. However, the camera modules also can be used in other applications that incorporates other types of image sensors.

[0025] As shown in FIG. 1, an example camera module is a ToF sensor module 20 that includes an image sensor (e.g., a ToF sensor) 22 and a lens unit 26 disposed over the sensor. The ToF 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 connectedelectrically to other components within a host device (e.g., a smart phone or tablet). 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.

[0026] The ToF sensor 22 can include a light sensitive region 25 that includes, for example, an array of spatially distributed light sensitive elements (e.g., active demodulation detection pixels), as well as reference pixels. The detection pixels provide the primary signals for determining the distance to an object outside the module 20. Signals from the reference pixels can be used to compensate, for example, for drift and / or to provide a zero distance measurement. The sensor 22 can be implemented, for example, in a semiconductor chip using charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) technologies or single photon avalanche diode (SPAD) technologies. In some implementations, a cover glass 44 may be provided over the ToF sensor 22.

[0027] Depending on the particular application, the operational wavelength for the module may be, for example, in the visible range (400 - 700 nm), the near-infrared range (700 - 1400 nm), the short-wavelength infrared range (1.4 - 3 pm), the mid-wavelength infrared range (3 - 8 pm), or the long- wavelength infra-red range (8 - 14 pm).

[0028] The lens unit 26 includes one or more substrates 30 that collectively have at least two metasurfaces 28A, 28B stacked one over the other. Each metasurface 28A, 28B, together with the substrate on which it is disposed, forms a metalens. 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. The metasurfaces 28A, 28B can be disposed on an optically transparent or at least partially transparent substrate 30 (e.g., a glass, plastic or polymer material). In the illustrated example of FIG. 1, the metasurfaces 28A, 28B are disposed on opposite sides of the same substrate 30, which 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.

[0029] Each metasurface 28A, 28B has carefully arranged “unit cells” or “meta-atoms” with sub-wavelength structures (e.g., nanostructures). The term “subwavelength” 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 ray bending. 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 20.

[0030] As indicated in FIG. 1, each of the metasurfaces 28A, 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., 1-5 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.

[0031] Some implementations include an anti-reflective coating (ARC) over the encapsulation layer 32 on the upper metasurface 28 A (i.e., the metasurface further away from the ToF sensor 22). In some implementations, an ARC is applied to other air-to- glass interfaces of the lens unit.

[0032] As further shown in the example of FIG. 1, an aperture layer 34 is provided at the front of the lens unit 26 (e.g., on, over or close to the first metasurface 28A where light enters the module). The aperture layer 34 defines an aperture stop that operates 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 ToF sensor 22. The aperture layer 34 may be composed, for example, of black chrome or black resist.

[0033] The outer sidewalls of the substrate 30 and the encapsulation layers 32, as well as the ARC (if present), can be blackened or at least partially blackened, for example, with a layer 38 of black polymer material or other opaque material to prevent or reduce stray light from entering the lens unit 26. The lens unit 26 can be held in a barrel 40, which in turn, is held, for example, by a holder 42 that maintains a specified distance between the ToF sensor 22 and the lens unit 26. The lower end(s) of the holder can rest, for example, on the surface of the electronic circuit board 24. Thus, the lens unit 26 can be mounted in a barrel 40 that is aligned in a holder 42 attached to the circuit board 24.

[0034] Various modifications can be made to the lens unit in some implementations. For example, in some instances, as shown in FIG. 2, instead of two metasurfaces on opposite sides of the same substrate, the lens unit 26A includes metasurface 28A, 28B, each of which is disposed on a different respective substrate 30A, 30B. The substrates 30A, 30B can be bonded back-to-back together, for example, by an adhesive 46 (e.g., a thin layer of polymer glue) that is optically clear at the operating wavelength for the module 20A. In some implementations, the adhesive 46 is index matched to the glass substrates 30A, 30B. Further, in some implementations, as shown in the example module 20B of FIG. 3, the two substrates 30A, 30B of the lens unit 26B are bonded together in a front-to-back arrangement. That is, the front side of the second substrate 30B (i.e., the side on whichthe encapsulated metasurface 28B is present) is bonded to the backside of the first substrate 30A (i.e., the side opposite the encapsulated metasurface 28A). In some implementations of a front-to-back arrangement, as shown in the lens unit 26C of the module 20C of FIG. 4, the metasurface 28B on the second substrate 30B can be encapsulated by the adhesive 46 that bonds the two substrates 30 A, 3 OB together. In that case, the separate encapsulant material 32 for the second metasurface 28B can be omitted. In each of the examples of FIGS. 1-4, there is no air gap between the metasurfaces 28A, 28B in the lens unit.

[0035] Any of the foregoing implementations can, in some cases, include an optical filter disposed, for example, between the lens unit 26 and the ToF sensor 22. The optical filter can be implemented, for example, as a narrow-band filter (e.g., a bandpass filter (BPF)) and / or an angle-of-incidence (AOI) filter. An AOI filter, for example, can be selective for the angle of incidence of incoming rays of light. The narrow bandwidth properties only allow rays with small angles to pass through and will block rays with angles larger than the cut-off angle. That is, the optical filter is operable to block or significantly attenuate rays greater than a particular angle of incidence (i.e., the cut-off angle) for a given wavelength (e.g., 940 nm). In this context, the angle of incidence (a) refers to the angle formed between a ray of light striking a surface and the line perpendicular to the surface.

[0036] 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 ToF 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 is closer to the second metasurface 28B than to the ToF sensor 22 to improve functionality.

[0037] 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.

[0038] Implementing the optical filter as a narrow- band filter (e.g., a BPF) can allow the optical filter to be selective for the specific wavelength spectra used in the ToF application and can be configured to pass only rays with a specific wavelength used in the illumination part of the ToF 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. For example, the BPF can block and / or reduce mainly the wavelengths not used in the ToF application illumination part, whereas the AOI filter can reduce rays with an angle-of-incidence toward the sensor higher than the imaging order. The optical design’s F-number determines the cut-off angle. In this context, the angle-of-incidence (a) refers to the angle formed between a ray of light striking a surface and the line perpendicular to the surface. 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.

[0039] In some implementations, the optical filter 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 beimplemented 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.

[0040] FIG. 5 illustrates an example in which an optical filter (e.g., an AOI filter and / or BPF) as described above is implemented as a coating 48 on the surface of the glass substrate 30B opposite the surface on which the metasuface 28B is disposed. In other instances, the optical filter can be implemented as a discrete component that is bonded (e.g., by an adhesive such as polymer glue) to the lens stack, as shown in the examples of FIG. 6 and 7. In FIG. 6, the optical filter 50 is bonded by adhesive 52 to the encapsulant 32 that encapsulates the second metasurface 28B. In FIG. 7, the optical filter 50 is bonded by adhesive 52 (e.g., polymer glue) directly to the glass substrate 30. In the latter implementation, the adhesive 52 also serves to encapsulate the second metasurface 28B. In the foregoing examples of FIG. 5-7, the black chrome or other layer of opaque material 38 also can extend along the sidewalls of the optical filter.

[0041] In some implementations, the optical filter 50 can be spaced somewhat from the lens stack 26 and can be held in place by the barrel 40. For example, in some cases, as shown in FIG. 8, the optical filter 50 can be glued to one or more supports 54 extending laterally inward from the holder. In other cases, as shown in FIG. 9, the optical filter 50 can be held by the holder 42. For example, the optical filter 50 can be glued to one or more supports 56 extending laterally inward from the holder 42.

[0042] Some implementations of a ToF module include one or more baffles. 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 ToF sensor 22. In some implementations, incorporating the baffle(s) into the ToF module can help prevent the appearance on the light sensitive surface of the ToF 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 raysbeyond 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.

[0043] FIGS. 10 and 11 illustrate examples of ToF modules in which a first baffle 60A is disposed on a lower surface of the lens unit (i.e., between the metalenses and the ToF sensor). FIGS. 12 and 13 illustrate examples that also include a second baffle 60B disposed in the lens unit between the first and second metalenses. For some implementations that also include an AOI filter or BPF (see FIG. 14), the baffle(s) can be configured to stop unwanted rays that are not stopped by the AOI filter and / or BPF. In general, the AOI filter 50 can be positioned after any of the metasurfaces, but preferably is positioned after the last metasurface (i.e., the metasurface closets to the ToF sensor). In such cases, the distance from the AOI filter to the ToF sensor should be longer than the half optical path length between the metasurface and the sensor. It also is possible to have more than one AOI filter in the lens unit. For example, a first AOI filter can be disposed after the first metasurface and have a first cut-off angle, and the second AOI filter can be disposed after the second metasurface and have a second, different cut-off angle. Each cut-off angle is determined by the corresponding metasurface to let the imaging order pass through and to reduce the unwanted orders that have a higher angle of incidence.

[0044] The baffle(s) 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. In some implementations, the respective positions of the baffle 60B and the aperture stop 34 can be interchanged such that the baffle is positioned at the front metasurface and the aperture stop is positioned between the two metasurfaces.

[0045] In the example implementations of FIGS. 1-14, the lens unit (e.g., 26) is held by a barrel 40 disposed within a holder 42, which is mounted (over the ToF sensor 22) on the same electronic circuit board 24 as the ToF sensor itself. In other implementations, however, the lens unit can be mounted, for example, to the cover glass 44 that is disposed over the ToF sensor 22. For example, as shown in FIG. 15, the lens unit 26 is bonded (e.g., by adhesive 64 A) to a glass spacer 62, which in turn is bonded (by adhesive 64B) to the cover glass 44. The adhesives 64A, 64B can be, for example, a polymer glue that is optically clear at the operating wavelength for the ToF module. In some implementations, instead of a glass spacer, the lens unit 26 is bonded (e.g., by adhesive 64A) to an optical filter 50 (e.g., an AOI filter or BPF), which in turn is bonded (by adhesive 64B) to the cover glass 44 (see FIG. 16). Thus, in this example, the optical filter 50 also serves as a spacer. In some implementations, as shown in FIG. 17, 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. 17, the spacer 62 need not be transmissive to the operating wavelength. In each of the examples of FIGS. 14-16, the spacer can help provide a specified distance between the lens unit and the ToF sensor.

[0046] Although the foregoing examples of FIGS. 1-17 include an air gap between the cover glass 44 and the image sensor 22, some implementations include an index-matched adhesive (e.g., bonding glue) or other optically clear material between the cover glass 44 and the image sensor 22 such that no air gap is present. Further, in some implementations, the cover glass 44 can be omitted, and an index-matched adhesive (e.g., bonding glue) or other optically clear material can be provided, for example, to bond an optical filter 50 (e.g., a BPF or AOI filter) or spacer 62 directly to the image sensor 22 such that, in some cases, there is no air gap present between the lens unit and the image sensor.

[0047] 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 becombined 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, wherein the camera module comprises: an image sensor; a lens unit including at least two encapsulated metasurfaces stacked one over the other, the lens unit being disposed over the image sensor and having a front side and a back side, wherein the back side of the lens unit is closer to the image sensor than is the front side of the lens unit; and an aperture stop.

2. The apparatus of claim 1 wherein the aperture stop is at the front side of the lens unit.

3. The apparatus of claim 1 wherein the camera module further includes an optical filter, wherein the optical filter includes an angle-of-incidence (AOI) filter operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence at a particular wavelength.

4. The apparatus of claim 1 wherein the lens unit further includes first and second optical filters, wherein each of the optical filters includes an angle-of-incidence (AOI) filter, the first AOI filter being disposed in the lens unit after the first metasurface and having a first cut-off angle, and the second AOI filter being disposed in the lens unit after the second metasurface and having a second, different cut-off angle.

5. The apparatus of claim 1 wherein the camera module 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.

6. The apparatus of any one of claims 2-5 wherein the optical filter comprises a coating in or on the lens unit.

7. The apparatus of any one of claims 2-5 wherein the optical filter is a discrete component bonded at the back side of the lens unit.

8. The apparatus of any one of claims 2-5 wherein the camera module further includes a barrel disposed within a holder, wherein the lens unit is disposed within the barrel, and the optical filter is a discrete component disposed within the barrel.

9. The apparatus of any one of claims 2-5 wherein the camera module further includes a barrel disposed within a holder, wherein the lens unit is disposed within the barrel, and the optical filter is a discrete component disposed within the holder.

10. The apparatus of any one of claims 2-9 wherein the optical filter is closer to a metasurface in the lens unit than to the image sensor.

11. The apparatus of any one of claims 1 -9 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.

12. The apparatus of claim 10 wherein the at least one baffle includes a first baffle disposed at the back side of the lens unit.

13. The apparatus of claim 12 wherein the at least two encapsulated metasurfaces include a first metasurface and a second metasurface, and wherein the at least one baffle further includes a second baffle disposed between the first and second metasurfaces.

14. The apparatus of any one of claims 11-13 wherein the at least one baffle is composed of black resist or black chrome.

15. The apparatus of any one of claims 1-14 wherein sidewalls of the lens unit are at least partially blackened.

16. The apparatus of any one claims 1-15 wherein the lens unit includes an anti-reflection coating (ARC).

17. The apparatus of any one of claims 1-16 wherein the at least two encapsulated metasurfaces include a first metasurface and a second metasurface on opposite sides of a single glass substrate.

18. The apparatus of any one of claims 1-16 wherein the at least two encapsulated metasurfaces include: a first metasurface on a first glass substrate; and a second metasurface on a second glass substrate that is bonded to the first glass substrate.

19. The apparatus of any one of claims 1-16 wherein the first and second glass substrates are bonded to one another by an adhesive.

20. The apparatus of claim 19 wherein the adhesive is optically clear at a particular wavelength.

21. The apparatus of any one of claims 19-20 the adhesive is index matched to the first and second glass substrates.

22. The apparatus of claim 19 wherein at least one of the metasurfaces is encapsulated by a polymer.

23. The apparatus of 19 wherein at least one of the metasurfaces is encapsulated by an adhesive that bonds the first and second glass substrates together.

24. The apparatus of any one of claims 1 -23 wherein each of the at least two metasurfaces is encapsulated by a respective encapsulation layer composed of a material that is optically clear at a particular wavelength.

25. The apparatus of any one of claims 1-24 wherein the aperture stop is defined by an aperture layer composed of black chrome or black resist.

26. The apparatus of any one of claims 1-25 wherein the camera module further includes: a cover glass over the image sensor; and a spacer, wherein the lens unit is bonded to the spacer, which in turn is bonded to the cover glass.

27. The apparatus of any one of claims 1 -25 wherein the lens unit is bonded to an active surface of the image sensor or to a cover glass over the image sensor.

28. The apparatus of claim 27 wherein the lens unit is bonded to the active surface of the image sensor without an air gap therebetween.

29. The apparatus of any one of claims 1 -28 further including an electronic circuit board, wherein the image sensor is mounted to the electronic circuit board.

30. The apparatus of claim 29 where the lens unit is mounted in a barrel that is aligned in a holder attached to the circuit board.

31. The apparatus of any one of claims 1-30 wherein the camera module is part of a time- of-flight (ToF) sensor module.

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