Optical lens system comprising a metasurface and an optical filter selective to the angle of incidence

Abstract

The present disclosure describes example apparatuses that include at least one optical metasurface, an image sensor arranged to receive electromagnetic radiation rays that pass through the at least one metasurface, and an optical filter optically disposed between the at least one optical metasurface and a light-sensitive surface of the image sensor. The optical filter is selectively operable to block or attenuate electromagnetic radiation rays for a working wavelength that are greater than a particular angle of incidence.

Description

Technical Field

[0001] This disclosure relates to optical lens systems. Background Technology

[0002] Some lenses, such as super-optical elements (MOEs and DOEs), employ planar optics. These planar optical elements are extremely thin, typically on the order of micrometers. Despite their thinness, these active optical structures often require a fairly thick substrate (e.g., several hundred micrometers) to provide mechanical stability for the planar element. Furthermore, aperture stops (sometimes referred to as the aperture-shifting principle) are sometimes used at a certain optical distance from the active MOE / DOE structure to compensate for different types of pupil and field aberrations. Including aperture stops typically increases the build height of the optical system, also known as the total track length (TTL).

[0003] In some instances, the distance between the aperture stop and the MOE surface tends to increase the total TTL of the system, which may be undesirable for some applications, or it may have other undesirable effects on the optomechanical stability of the imaging system. Summary of the Invention

[0004] This disclosure describes an optical lens system and an imaging system incorporating such a lens system.

[0005] For example, in one aspect, this disclosure describes an apparatus comprising an optical metasurface, an image sensor arranged to receive electromagnetic radiation light passing through the metasurface, and an optical filter optically disposed between the optical metasurface and a photosensitive surface of the image sensor. The optical filter can be selectively operated to block or attenuate electromagnetic radiation light with an operating wavelength greater than a specific angle of incidence.

[0006] Some implementations include one or more of the following features. For example, in some implementations, the optical filter forms part of an imaging system having a principal ray angle of the image sensor equal to or close to zero degrees. In some implementations, the optical filter is operable to block or attenuate electromagnetic radiation at the operating wavelength that penetrates the image plane outside the diffraction-limited spot or circle of confusion (CoC) surrounding the principal ray or centroid ray that forms the image on the image plane. In some implementations, the optical filter is an incident angle filter that is selectively operable to block or attenuate aberration rays. In some implementations, the device does not include a mechanical aperture on the front side of at least one metasurface.

[0007] In some embodiments, the optical filter is an angle-of-incident filter. In some embodiments, the optical filter has a cutoff angle of no more than 20°, no more than 10°, or in the range of 5° to 7°. The optical filter may be disposed, for example, on the cover glass of an image sensor, or at other locations in the optical path between at least one metasurface and the photosensitive 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, optical modules with a TTL of less than 1 mm can be achieved. In some implementations, by providing optical filters that selectively block or attenuate electromagnetic radiation rays greater than a specific angle of incidence, the TTL can be reduced while reducing or avoiding aberrations. In addition to mechanical advantages, some implementations may also provide optical performance advantages (e.g., wavelength and stray light filtering).

[0009] Other aspects, features, and advantages will become readily apparent from the following detailed description, drawings, and claims. Attached Figure Description

[0010] Figure 1 An example of an imaging system including an aperture stop is shown.

[0011] Figure 2 An example of an imaging system including an optical filter that is sensitive to the angle of incidence of incident light is shown.

[0012] Figure 3 This is a graph illustrating an example of the relationship between the incident angle and intensity transmittance of an optical filter.

[0013] Figure 4 This is another example of a graph showing the relationship between the incident angle and intensity transmittance of an optical filter.

[0014] Figure 5 Another example of an imaging system is shown, which includes an optical filter that is sensitive to the angle of incidence of the incident light.

[0015] Figure 6 Another example of an imaging system is shown, which includes an optical filter that is sensitive to the angle of incidence of the incident light.

[0016] Figure 7 Another example of an imaging system including an optical filter that is sensitive to the angle of incidence of incident light is shown. Detailed Implementation

[0017] As described in more detail below, the lens system includes a metasurface and an optical filter that is selective for the angle of incidence. The optical filter can have a relatively low cutoff angle to prevent or reduce the passage of light rays incident at a relatively large angle.

[0018] In some instances, optical filters that are selective for the angle of incidence effectively provide a function similar to an aperture in selecting which rays are incident on the sensor, thereby allowing the lens system to be designed without mechanical aperture stops (e.g., diaphragms or baffles) and contributing to a reduction in total track length (TTL). For example, in some implementations, by removing the mechanical aperture and placing the optical filter in front of the image sensor in the image-side telecentric lens module, the TTL of the lens module can be reduced, while aberrations can be reduced or avoided.

[0019] Figure 1 An example of an imaging system 10 is shown, which 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, having distributed small subwavelength structures (e.g., nanostructures or other superatoms) arranged to interact with light in a specific manner. For example, superatoms can interact with light waves individually and / or collectively to alter the local amplitude, local phase, or both of the incident light wave. The aperture stop 20 is positioned at a specific distance in front of the metasurface 16, referred to as the stop distance (D). The aperture stop 20 operates to limit the solid angle of light rays 21 passing through the system from an on-axis object point, which defines the light cone reaching the image plane of the sensor 14. Without the mechanical stop 18, greater aberrations and blurring tend to occur in the image captured by the image sensor 14.

[0020] The aperture stop 20 also restricts the incident light cone projected from different field angles / positions in object space to different positions. This light cone has a finite area along the metasurface, which reduces unwanted light but allows near-perpendicular principal ray angles (CRA) to be incident on the image sensor 14. An alternative to achieving this is to place an angle-dependent filter in front of the sensor so that only light rays with incident angles present, for example, in a diffraction-limited spot around the CRA, are allowed to pass through, while blocking light rays with large incident angles that would otherwise cause aberrations in the image. In such an implementation, the optical filter is operable to block or attenuate electromagnetic radiation rays that pierce the image plane at the operating wavelength outside the diffraction-limited spot or circle of confusion (CoC) surrounding the principal ray or centroid ray that forms the image on the image plane. Figure 2 An example of this is shown.

[0021] like Figure 2As shown, the imaging system 100 includes an optical filter 22 in front of the image sensor 14 (e.g., a CMOS-based image sensor), but the optical filter 22 is omitted. Figure 1 The mechanical aperture 18 is shown. In the example shown, the optical filter 22 is optically disposed between the metasurface 16 and the photosensitive surface of the image sensor 14. As previously described, the metasurface 16 may include distributed small subwavelength structures (e.g., nanostructures or other superatoms) arranged to interact with light in a specific manner. For example, superatoms may interact with light waves individually and / or collectively to alter the local amplitude, local phase, or both of the incident light wave. The metasurface 16 may be, for example, part of a superlens or other MOE. Although the optical filter 22 is optically disposed between the metasurface 16 and the photosensitive surface of the image sensor 14, in some embodiments, the optical path may intersect with more than one metasurface and may also intersect with one or more other diffractive or refractive lenses. Some or all of these other optical elements may also be optically disposed between the metasurface 16 and the photosensitive surface of the image sensor 14.

[0022] Optical filter 22 can be implemented as, for example, a narrowband filter (e.g., a bandpass filter) selective for the angle of incidence of incident light. The narrowband characteristic allows only small-angle light to pass through and blocks light with angles greater than the cutoff angle, and the filter has a relatively low cutoff angle. That is, optical filter 22 can be operated to block or significantly attenuate light with an angle greater than a specific angle of incidence (i.e., the cutoff angle) for a given wavelength (e.g., 940 nm). In this context, the angle of incidence α refers to the angle formed between the light ray striking the surface and a line perpendicular to the surface. Depending on the application, filter 22 can block light, for example, by absorbing, reflecting, or deflecting the incident light away from the image sensor region.

[0023] As another example, optical filter 22 can be implemented as an optical interference bandpass filter, which exhibits a shift in degree with the angle of incidence (AOI). Figure 3 As shown, an incident angle deviating from zero degrees results in a spectral shift toward shorter center and cutoff wavelengths. The filter will still transmit the center wavelength under perpendicular incident (e.g., 750 nm) until the maximum tilt, such as a 15° incident angle, which in the example shown limits the filter's functionality to a full cone angle of approximately 30°.

[0024] In some implementations, the cutoff angle of filter 22 is approximately 20° (see...). Figure 4 In some implementations, the cutoff angle of filter 22 is approximately 10° (see...). Figure 5The cutoff angle of filter 22 may differ from the aforementioned value in some embodiments. For example, in some embodiments, the cutoff angle may be less than 10° (e.g., in the range of 5° to 7°). Furthermore, as... Figure 3 and Figure 4 As shown in the example, optical filter 22 can have a relatively abrupt transition at the cutoff angle from near 100% transmittance to about 0% transmittance, while in other cases, the transition can be more gradual. In some cases, for the operating wavelength, the intensity transmittance at an angle equal to or slightly smaller than the incident cutoff angle can be, for example, only about 90%.

[0025] In some implementations, the characteristics of the incident angle filters 22 are position-dependent; for example, they can vary in the radial direction.

[0026] Combined with the following text Figure 6 and Figure 7 The optical filter 22 discussed can be optically arranged between the metasurface 16 and the image sensor 14 in various ways. For example, Figure 6 Further details of an imaging system 200 according to some embodiments are shown. Figure 5 As shown, the metasurface 16 can be disposed on an optically transparent or at least partially transparent substrate 24 (e.g., glass, plastic, or polymer material). The substrate 24 can provide mechanical support for the metasurface 16. Although Figure 6 The diagram shows metasurface 16 on the sensor side of substrate 24, but in other embodiments, metasurface 16 may be disposed on the opposite (i.e., front) side of substrate 24. For example... Figure 6 As further shown, the optical filter 22 can be disposed on, for example, the cover glass 26 of the image sensor 14. That is, the metasurface 16 can be disposed on the first substrate 24, and the optical filter 22 can be disposed on, for example, a separate second substrate (e.g., the cover glass 26).

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

[0028] Depending on the specific application, the operating wavelength of the lens system can be, for example, in the visible light range (400 nm to 700 nm), the near-infrared range (700 nm to 1400 nm), the short-wave infrared range (1.4 μm to 3 μm), or the mid-wave infrared range (3 μm to 8 μm).

[0029] The aforementioned imaging system can be used as a small camera, for example, integrated into compact electronic devices (such as smartphones, laptops, televisions, or wearable devices) as well as larger devices or systems (such as motor vehicles).

[0030] While this specification includes numerous details, these details should not be construed as limiting the scope of this disclosure or the claims, but rather as descriptions of specific features of particular embodiments. Certain features described in the context of individual embodiments in this specification may also be combined in the same embodiment. Conversely, various features described in the context of a single embodiment may also be implemented individually or in any suitable sub-combination in multiple embodiments. Various modifications can be made to the above examples. Therefore, other embodiments are also within the scope of the claims.

Claims

1. An apparatus comprising: At least one optical metasurface; An image sensor is arranged to receive electromagnetic radiation light passing through the at least one metasurface; as well as An optical filter is optically disposed between the at least one optical metasurface and the photosensitive surface of the image sensor, wherein the optical filter is selectively operable to block or attenuate electromagnetic radiation light with an incident angle greater than a specific wavelength.

2. The apparatus according to claim 1, wherein, The optical filter has a cutoff angle of no more than 20°.

3. The apparatus according to claim 1, wherein, The optical filter has a cutoff angle of no more than 10°.

4. The apparatus according to claim 1, wherein, The optical filter has a cutoff angle in the range of 5° to 7°.

5. The apparatus according to claim 1, wherein, The optical filter is an incident angle filter.

6. The apparatus according to any one of claims 1 to 5, wherein, The optical filter is mounted on the cover glass of the image sensor.

7. The apparatus according to any one of claims 1 to 6, wherein, The optical filter forms part of the image-side telecentric lens system.

8. The apparatus according to any one of claims 1 to 7, wherein the apparatus does not include a mechanical aperture on the front side of the at least one metasurface.

9. The apparatus according to claim 1, wherein, The optical filter is operable to block or attenuate electromagnetic radiation at the operating wavelength, which penetrates the image plane outside the diffraction-limited spot or circle of confusion (CoC) of the principal ray or centroid ray that forms the image on the image plane.

10. The apparatus according to any one of claims 1 to 9, wherein, The at least one metasurface includes superatoms arranged to interact with light waves to alter the local amplitude, local phase, or both of the incident light waves.

11. The apparatus according to claim 10, wherein, The superatom has a size smaller than the operating wavelength.

12. The apparatus according to any one of claims 1 to 11, wherein, The optical filter is an angle-of-incident filter that can be selectively operated to block or attenuate aberration rays.

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