Optical lens systems including a metasurface and an optical filter selective for angle of incidence

Abstract

This disclosure describes example apparatus that includes at least one optical metasurface, an image sensor arranged to receive rays of electromagnetic radiation passing through the at least one metasurface, and an optical filter disposed optically between the at least one optical metasurface and a light sensitive surface of the image sensor. The optical filter is operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence for an operational wavelength.

Description

OPTICAL LENS SYSTEMS INCLUDING A METASURFACE AND AN OPTICAL FILTER SELECTIVE FOR ANGLE OF INCIDENCEFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to optical lens systems.BACKGROUND

[0002] Some lenses, such as meta optical elements (MOEs and DOEs), employ a flat optic technology. The structure of these flat optical elements is very thin and usually in the micrometer scale. Despite the fact that these active optical structures are very thin, they generally need a rather thick substrate (e.g., several hundreds of microns) for mechanical stability of the flat element. In addition, an aperture stop is sometimes used at a certain optical distance from the active MOE / DOE structure (sometimes referred to as the stop-shift principle) to compensate for different types of pupil and field aberrations. Including an aperture stop generally increases the build height of the optical system, also referred to as the total track length (TTL) of the optical system.

[0003] In some instances, the distance between the aperture stop and the MOE surface tends to increase the overall TTL of the system, which may be undesirable for some applications, or it can have other undesirable implications for the optomechanical stability of the imaging system.SUMMARY

[0004] The present disclosure describes optical lens systems, as well as imaging systems incorporating such lens systems.

[0005] For example, in one aspect, the present disclosure describes an apparatus that includes an optical metasurface, an image sensor arranged to receive rays ofelectromagnetic radiation passing through the metasurface, and an optical filter disposed optically between the optical metasurface and a light sensitive surface of the image sensor. The optical filter is operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence for an operational wavelength.

[0006] Some implementations include one or more of the following features. For example, in some implementations, the optical filter forms part of an image system with image sensor chief ray angles at or close to zero degrees. In some implementations, the optical filter is operable to block or attenuate rays of electromagnetic radiation at the operational wavelength that pierce an image plane outside a diffraction limited spot or circle-of-confusion (CoC) around a chief ray or centroid ray forming an image on the image plane. In some implementations, the optical filter is an angle-of-incidence filter operable selectively to block or attenuate aberrated rays. In some implementations, the apparatus does not include a mechanical stop at a front side of the at least one metasurface.

[0007] In some implementations, the optical filter is an angle-of-incidence filter. In some implementations, the optical filter has a cut-off angle of no more than 20°, of no more than 10°, or in the range of 5° to 7°. The optical filter can be disposed, for example, on a cover glass of the image sensor or elsewhere in the light path between the at least one metasurface and the light sensitive surface of the image sensor.

[0008] Some implementations include one or more of the following advantages. For example, in some implementations, the TTL can be reduced. In some cases, an optical module having a TTL of less than 1 mm can be achieved. In some implementations, by providing an optical filter that selectively blocks or attenuates rays of electromagnetic radiation greater than a particular angle of incidence, the TTL can be reduced, while also reducing or avoiding aberrations. In addition to mechanical benefits, some implementations also may provide optical performance benefits (e.g., wavelength and stray-light filtering).

[0009] Other aspects, features and advantages will be readily apparent from the following detailed description, the accompany drawings and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 illustrates an example of an imaging system including an aperture stop.

[0011] FIG. 2 illustrates an example of an imaging system including an optical filter that is sensitive to the angle of incidence of incoming rays.

[0012] FIG. 3 is a graph illustrating an example of incident angle versus intensity transmission for an optical filter.

[0013] FIG. 4 is a graph illustrating another example of incident angle versus intensity transmission for an optical filter.

[0014] FIG. 5 illustrates another example of an imaging system including an optical filter that is sensitive to the angle of incidence of incoming rays.

[0015] FIG. 6 illustrates yet another example of an imaging system including an optical filter that is sensitive to the angle of incidence of incoming rays.

[0016] FIG. 7 illustrates another example of an imaging system including an optical filter that is sensitive to the angle of incidence of incoming rays.DETAILED DESCRIPTION

[0017] As described in greater detail below, a lens system includes a metasurface and an optical filter that is selective for angle-of-incidence. The optical filter can have arelatively low cut-off angle to prevent or reduce light rays that are incident at relatively large angles from passing through the filter.

[0018] In some instances, an optical filter that is selective for angle-of incidence effectively provides a similar functionality to that of an aperture in selecting which rays are incident on the sensor, thereby allowing the lens system to be designed without a mechanical aperture stop (e.g., a diaphragm or baffle) and facilitating a reduction in the total track length (TTL). For example, in some implementations, by removing the mechanical aperture and placing the optical filter in front of an image sensor in an imagespace telecentric lens module, the TTL of the lens module can be reduced, while also reducing or avoiding aberrations.

[0019] FIG. 1 illustrates an example of an imaging system 10 that includes a lens system 12, an image sensor 14, and a mechanical stop (e.g., a circular opening) 18 defining an aperture stop 20. The lens system 12 includes a diffractive surface, such as a metasurface 16 that has distributed small subwavelength structures (e.g., nanostructures or other metaatoms) arranged to interact with light in a particular manner. For example, the metaatoms can, individually and / or collectively, interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave. The aperture stop 20 is positioned at a particular distance, referred to as the stop distance (D), in front of the metasurface 16. The aperture stop 20 operates to limit the solid angle of rays 21 passing through the system from an on-axis object point, which defines the cone of light reaching the image plane of the sensor 14. In the absence of the mechanical stop 18, greater aberration and blurring of the image captured by the image sensor 14 would tend to occur.

[0020] The aperture stop 20 also limits the cone of incoming light that is being projected from different field angles / positions in object space to a different position with a limited area along the metasurface which can reduce the unwanted light rays, but allows close-to normal- incidence chief ray angles (CRAs) to be incident on the image sensor 14. An alternative way to achieve this situation is to have an angle-of-incidence-dependent filterin front of the sensor, so as to allow, for example, only rays at angles of incidence present in a diffraction limited spot around the CRA to pass through, and to block the rays at high incidence angles that would otherwise contribute to aberrations in the image. In such an implementation, the optical filter can be operable to block or attenuate rays of electromagnetic radiation at the operational wavelength that pierce the image plane outside a diffraction limited spot or circle-of-confusion (CoC) around a chief ray or centroid ray forming an image on the image plane. FIG. 2 illustrates such an example.

[0021] As shown in FIG. 2, an imaging system 100 includes an optical filter 22 at a front-side of an image sensor 14 (e.g., a CMOS-based image sensor), but omits the mechanical stop 18 of FIG. 1. In the illustrated example, the optical filter 22 is disposed optically between the metasurface 16 and a light sensitive surface of the image sensor 14. As before, the metasurface 16 can include distributed small subwavelength structures (e.g., nanostructures or other meta-atoms) arranged to interact with light in a particular manner. For example, the meta-atoms can, individually and / or collectively, interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave. The metasurface 16 can be, for example, part of a metalens or other MOE. Although the optical filter 22 is disposed optically between the metasurface 16 and the light sensitive surface of the image sensor 14, in some implementations, the light path may intersect more than one metasurface, and also may intersect one or more other diffractive lenses, or refractive lenses. Some, or all, of these other optical elements also may be disposed optically between the metasurface 16 and the light sensitive surface of the image sensor 14.

[0022] The optical filter 22 can be implemented, for example, as a narrow-band filter (e.g., a bandpass filter) that is 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, and that has a relatively low cut-off angle. That is, the optical filter 22 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 angleformed between a ray of light striking a surface and the line perpendicular to the surface. Depending on the application, the filter 22 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.

[0023] As a further example, the optical filter 22 can be implemented as an optical interference bandpass filter that exhibits a degree of shift with the angle of incidence (AOI). As shown in FIG. 3, a departure of angle-of-incidence from zero degrees results in a spectral shift towards a shorter center and cut-off wavelengths. The filter will still transmit the center wavelength at normal incidence (e.g., 750 nm) up to a maximum tilt, e.g., of 15° angle-of-incidence, which limits the function of the filter in the illustrated example to about a 30° full cone angle.

[0024] In some implementations, the cut-off angle of the filter 22 is about 20° (see FIG. 4); in some implementations, the cutoff angle of the filter 22 is about 10° (see FIG. 5). The cut-off angle of the filter 22 may differ from the foregoing values in some implementations. For example, in some implementations, the cut-off angle may be less than 10° (e.g., in the range of 5° to 7°). Further, as shown in the examples of FIGS. 3 and 4, the optical filter 22 may have a relatively abrupt transition at the cut-off angle from close to 100% transmission to about 0% transmission, whereas in other cases the transition may be more gradual. In some cases, the intensity transmission for the operational wavelength at, or slightly less than, the cut-off angle of incidence may be, e.g., only about 90%.

[0025] In some implementations, the properties of the angle-of-incidence filter 22 are position dependent; for example, they may vary in the radial direction.

[0026] As discussed below in connection with FIGS. 6 and 7, the optical filter 22 can be arranged optically between the metasurface 16 and the image sensor 14 in a variety of ways. For example, FIG. 6 illustrates further details of an imaging system 200 in accordance with some implementations. As shown in FIG. 5, the metasurface 16 can bedisposed on an optically translucent or at least partially transparent substrate 24 (e.g., a glass, plastic or polymer material). The substrate 24 can provide mechanical support for the metasurface 16. Although FIG. 6 shows the metasurface 16 on the sensor-side of the substrate 24, in other implementations, the metasurface 16 can be disposed on the opposite (i.e., front) side of the substrate 24. As further shown in FIG. 6 the optical filter 22 can be disposed, for example, on a cover glass 26 for the image sensor 14. That is, the metasurface 16 may be disposed on a first substrate 24, and the optical filter 22 may be disposed, for example, on a separate second substrate (e.g., the cover glass 26).

[0027] In some implementations, as shown in the example of an imaging system 300 in FIG. 7, each of the metasurface 16 and the optical filter 22 is disposed, respectively, at opposite sides of the same substrate 28. For example, the metasurface 16 can be disposed on a first (front) side of the substrate 28, and the optical filter 22 can be disposed at a second (back) side of the substrate 28. Thus, the metasurface 16, the substrate 28 and the optical filter 22 can be arranged with the optical filter 22 at the back side closer to the image sensor 14. The substrate 28 can be composed, for example, of an optically translucent or at least partially transparent material (e.g., a glass, plastic or polymer material) and can provide mechanical support for the metasurface 16.

[0028] Depending on the particular application, the operational wavelength for the lens system 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 um), or the mid-wavelength infrared (3 - 8 um).

[0029] The imaging systems described above may serve, for example, as small cameras integrated for example, into compact electronic devices such as smart phones, laptops, televisions, or wearable devices, as well as larger devices or systems such as automotive vehicles.

[0030] 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 asdescriptions of features specific to particular implementations. Certain features described in this specification in the context of separate implementations also may be combined in the same implementation. Conversely, various features described in the context of a single implementation also may 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: at least one optical metasurface; an image sensor arranged to receive rays of electromagnetic radiation passing through the at least one metasurface; and an optical filter disposed optically between the at least one optical metasurface and a light sensitive surface of the image sensor, wherein the optical filter is operable selectively to block or attenuate rays of electromagnetic radiation greater than a particular angle of incidence for an operational wavelength.

2. The apparatus of claim 1 wherein the optical filter has a cut-off angle of no more than 20°.

3. The apparatus of claim 1 wherein the optical filter has a cut-off angle of no more than 10°.

4. The apparatus of claim 1 wherein the optical filter has a cut-off angle in the range of 5° to 7°5. The apparatus of claim 1 wherein the optical filter is an angle-of-incidence filter.

6. The apparatus of any one of claims 1-5 wherein the optical filter is disposed on a cover glass of the image sensor.

7. The apparatus of any one of claims 1 -6 wherein the optical filter forms part of an image-space telecentric lens system.

8. The apparatus of any one of claims 1-7 not including a mechanical stop at a front side of the at least one metasurface.

9. The apparatus of claim 1 wherein the optical filter is operable to block or attenuate ray of electromagnetic radiation at the operational wavelength that pierce an image plane outside a diffraction limited spot or circle-of-confusion (CoC) around a chief ray or centroid ray forming an image on the image plane.

10. The apparatus of any one of claims 1-9 wherein the at least one metasurface comprises meta-atoms arranged to interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave.

11. The apparatus of claim 10, wherein the meta-atoms have a dimension smaller than the operational wavelength.

12. The apparatus of any one of claims 1-11 wherein the optical filter is an angle-of- incidence filter operable selectively to block or attenuate aberrated rays.

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