High bandwidth imaging system

Abstract

A system includes: one or more elements configured to receive light of different wavelengths in a wavelength range from a light source and separate the received light at different angles across a field of view based on the different wavelengths; an image sensor including a sensor surface; a metalens including a surface including a plurality of regions, wherein each region is configured to receive light incident within a respective incidence angle range, wherein each respective incidence angle range corresponds to a wavelength subrange of the separated light, and wherein each region is configured to focus light from the respective wavelength subrange on the sensor surface; and an optical aperture having an aperture size configured to limit the respective incidence angle range at each of the plurality of regions of the metalens.

Description

HIGH BANDWIDTH IMAGING SYSTEMTECHNICAL FIELD

[0001] This specification relates to optical systems and imaging systems incorporating optical systems.BACKGROUND

[0002] Meta optical elements (MOEs) are optical elements that employ a flat optic technology. Meta optical elements include a metasurface with distributed meta-atoms. Meta-atoms are subwavelength structures (e.g., nanostructures) arranged to interact with light in a particular manner. 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. MOEs can be used, for example, in optical applications to take advantage of the flat surface and reduced thickness, compared to classic, curved refractive lenses.

[0003] Flat optical lenses such as MOEs can suffer from chromatic aberrations, especially when used with large bandwidth sources such as light emitting diodes (LEDs). If chromatic aberrations are not addressed, an imaging system that incorporates such optical elements may also exhibit chromatic aberrations which can lead to limited (e.g., narrow) operational spectral bandwidth (e.g., of only a few nanometers). Such constraints can place substantial limitations on the choice of light sources for scene illumination and / or may limit the overall efficiency of these imaging systems since the modulation transfer function (MTF) may be substantially reduced if the bandwidth of the light source is broad, e.g., broader than the bandwidth of a typical vertical cavity surface emitting laser (VCSEL) or laser.SUMMARY

[0004] This specification describes technologies relating to optical systems and imaging systems incorporating optical systems. In general, one or more aspects of the subject matter described in this specification can be embodied in a system including: one or more elements configured to receive light of different wavelengths in a wavelength range from a light source and separate the received light at different angles across a field of view based on the different wavelengths; an image sensor including a sensor surface; a metalens including a surface including a plurality of regions, wherein each region is configured to receive light incident within a respective incidence angle range, wherein each respective incidence angle range corresponds to a wavelength subrange of the separated light, and wherein each region is configured to focus light from the respective wavelength subrange on the sensor surface; and an optical aperture having an aperture size configured to limit the respective incidence angle range at each of the plurality of regions of the metalens.

[0005] These and other aspects can each, optionally, include one or more of the following features.

[0006] Each of the plurality of regions can include a respective plurality of meta-atoms. Each respective meta-atom of the plurality of meta-atoms can have a respective geometric characteristic for each of the plurality of regions. The respective plurality of meta-atoms has one or more of a different shape, a different size, or a different inter- meta-atom spacing for each of the plurality of different regions.

[0007] The one or more elements can include one or more of a bandpass filter, a diffraction grating, a prism, or a metaoptical element configured to separate the light from the light source to different angles across the field of view based on the different wavelengths.

[0008] At least a first region of the plurality of regions can be configured to focus light from a first infrared subrange. At least a second region of the plurality of regions can be configured to focus light from a second infrared subrange.

[0009] At least a third region of the plurality of different regions can be configured to focus light from an infrared subrange. At least a fourth region of the plurality of different regions can be configured to focus light from a visible subrange.

[0010] At least a fifth region of the plurality of regions can be configured to focus light from a first visible subrange. At least a sixth region of the plurality of different regions can be configured to focus light from a second visible subrange.

[0011] The light of different wavelengths can include light in a wavelength range of 50 nm or more or 100 nm or more. The light of different wavelengths can include light in a wavelength range of substantially 920 to 960 nm.

[0012] Each of the plurality of different regions can be configured to focus light incident with the respective angle of incidence range at substantially a same optical resolution on the sensor surface.

[0013] The system can further include one or more light sources configured to generate the light of different wavelengths in the wavelength range.

[0014] Each region of the plurality of regions is configured to focus light from a wavelength subrange of substantially 10 nm or less, 5 nm or less, or 2 nm or less.

[0015] In general, one or more aspects of the subject matter described in this specification can also be embodied in a system including: one or more elements configured to receive light of different wavelengths in a wavelength range from a light source and separate the received light at different angles across a field of view based on the different wavelengths; an image sensor including a sensor surface; a metalens including a surface including a plurality of meta-atoms, wherein the metalens is configured to receive light incident at a plurality of incidence angles within an incidence angle range, wherein each respective incidence angle corresponds to a wavelength of the separated light, and wherein a respective geometric characteristic of the plurality of meta- atoms varies across the metalens as a continuous function of the wavelength of the separated light incident at a respective incidence angle; and an optical aperture having an aperture size configured to limit the respective incidence angle range at each of the plurality of regions of the metalens.

[0016] These and other aspects can each, optionally, include one or more of the following features.

[0017] The respective geometric characteristic includes one or more of a different shape, a different size, or different inter-meta-atom spacing.

[0018] The one or more elements can include one or more of a bandpass filter, a diffraction grating, a prism, or a metaoptical element configured to separate the light from the light source to different angles across the field of view based on the different wavelengths.

[0019] The light of different wavelengths can include light in a wavelength range of 50 nm or more or 100 nm or more. The light of different wavelengths can include light in a wavelength range of substantially 920 to 960 nm.

[0020] The system can further include one or more light sources configured to generate the light of different wavelengths in the wavelength range.

[0021] Particular embodiments of the subject matter described in this specification can be implemented to realize one or more of the following advantages. MOEs such as metalenses with reduced chromatic aberration can be provided. In particular, specific regions of an MOE can be adapted to a predetermined wavelength range. The MOEs described herein can be incorporated into an imaging system to reduce chromatic aberrations. The imaging system can incorporate one or more optical elements configured to spatially separate the wavelengths of one or more light sources across a field of view (FOV) of the imaging system. Each part of the field of view can corresponds to a localized region of one or more MOEs incorporated into the imaging system, and each localized region of the one or more MOEs can be adapted to a predetermined wavelength range.

[0022] Concepts described in this specification can help enhance the operational spectral bandwidth of the imaging system and make the system compatible with the bandwidth of standard light sources such as light emitting diodes (LEDs). This can improve the overall performance, quality, and / or efficiency of imaging systems with different operational spectral bandwidths. The systems described herein also can be incorporated in other types of optical systems.

[0023] The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows an example of an imaging system including optical systems.

[0025] FIG. 2A shows a cross-section on an example of an MOE.

[0026] FIG. 2B shows a top view of the example of an MOE.

[0027] FIG. 3 shows a cross-section of an example of an MOE.

[0028] FIG. 4 shows a cross-section of an example of an MOE.

[0029] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0030] The optical materials of lenses generally have a degree of wavelength dispersion because the refractive index of the lens material typically depends, at least to some extent, on the wavelength of light propagating through a medium. This phenomenon is due to the dependence of the phase velocity of a wave on its frequency. A consequence of dispersion is the change in the angle of refraction depending on the wavelength.Diffraction-based flat optics such as MOEs introduce significantly larger dispersions due to the wavelength dependency. These dispersion effects impact the image formation quality and introduce chromatic aberrations.

[0031] FIG. 1 shows an example of an imaging system 100 including optical systems. The imaging system 100 can include an emitter side 105 and a receiver side (e.g., a camera) 110.

[0032] The emitter side 105 can include one or more light sources 115 (e.g., a light source) configured to generate light of different wavelengths in a wavelength range. Depending on the particular application, the wavelength can be, for example, in the visible range (approx. 400 nm to 700 nm) or the infrared range (approx. 700 nm to 1 mm), e.g., in the near-infrared range (approx. 700 nm to 1400 nm) or short-wave infrared range (approx. 900 nm to 3000 nm). In some examples, the light source can provide light in the infrared (e.g., near-infrared) and / or visible range.

[0033] In some examples, the light source includes a conventional light source, such as an LED. In some examples, the wavelength range is 50 nm or more or 100 nm or more. In some examples, the wavelength range is substantially 920 nm to 960 nm. In other examples, the light source includes a VCSEL array. Other types of light emitting or reflecting devices can be used in some examples.

[0034] Imaging system 100 can include one or more elements 120 configured to receive, from the light source 115, light of different wavelengths in the wavelength range provided by the light source 115 and separate the received light at different angles across a field of view based on the different wavelengths 121, 122, 123. In the example of FIG. 1, received light rays, each having a different wavelength 121, 122, 123, are separated at different angles across the field of view based on their respective wavelengths. The one or more elements 120 can include optical elements such as one or more of a bandpass filter, a diffraction grating, a prism, a diffractive optical element, an MOE or any other optical element configured to separate light from the light source 115 to different angles across a field of view based on the different wavelengths.

[0035] The receiver side 110 (e.g., a camera) can include an image sensor 130 having a sensor surface 131. An MOE 140, such as a metalens, can be configured to focus light on the sensor surface 131. The metalens can include a surface, e.g., a metasurface disposed on an optically translucent or at least partially transparent substrate (e.g., a glass, plastic, or polymer material). The substrate can provide mechanical support for the metasurface.

[0036] The imaging system can include an optical aperture 150 limiting the angular range hitting each point of the meta optical element 140. For example, in FIG. 1, the aperture size limits the rays hitting point 149 so that the field of view of point 149 is limited to a. For example, the aperture can be included in an aperture layer 160 including a hole (e.g., a circular opening) as aperture 150 in a light blocking material.

[0037] Since each part of the FOV corresponds to a localized region of the MOE 140, specific regions of the meta optical element can be adapted to the wavelength range to which it is exposed.

[0038] The aperture size can be selected depending on a desired image quality (e.g., MTF or image resolution) and / or application(s) of the imaging system. If the aperture is very large, rays from a wide-angle range (and thus from a broad wavelength range) can hit arespective region of the sensor. This would decrease the benefits in terms of chromatic aberration reduction. On the other hand, if the aperture is very small, a very small angle range would reach a respective region of the sensor and thus each region can be adapted to a very specific wavelength range, highly reducing chromatic aberrations. However, the reduction in aperture size (usually quantified with the inverse f-number F# given by the focal length divided by the aperture diameter) reduces the amount of light reaching the sensor, making it challenging to obtain images in low light conditions.

[0039] The metaoptical element 140 can include a surface (e.g., a metasurface) including a plurality of regions, for examples regions 141, 142, 143 as shown in FIG. 1. Each region can be configured to receive light incident within a respective incidence angle range. Each respective incidence angle range can correspond to a wavelength subrange of the light separated by the one or more elements 120. For example, region 141 can receive light rays of wavelength 121, such as a light ray 151. For example, region 142 can receive light rays of wavelength 122, such as a light ray 152. For example, region 143 can receive light rays of wavelength 123, such as a light ray 153. Each region 141, 142, 143 is configured to focus light from the respective wavelength subrange on the sensor surface. Since each specific regions of the meta optical element 140 is adapted to the wavelength range to which it is exposed, chromatic aberrations can be reduced.

[0040] FIG. 2A shows a cross-section of an example of an MOE 240. FIG. 2B shows a top view of MOE 240. In this example, the MOE has a circular shape, but other shapes are possible. For example, an elliptical shape or other polygonal or irregular shapes are possible.

[0041] The MOE 240 can be a metalens that is configured to receive light from one or more sources. For example, light from an LED that emits light within a wavelength range of 900±50 nm (850 nm to 950 nm) can be received. In other examples, the one or more light sources can emit light within a wavelength range of 940±20 nm (920 nm to 960 nm). The light from the one or more sources can be separated at different angles based on the wavelength. For example, an optical element such as element 120 can be used to separate the light of different wavelengths to different angles in the field of view.

[0042] In the example of FIGs. 2A and 2B, light of first wavelength range AM mostly hits the MOE 240 at high incidence angles. In this example, light of second wavelengthrange AX2 mostly hits the MOE 240 at low incidence angles. Since each part of the FOV corresponds to a localized region of the MOE 140, specific regions of the MOE 140 can be adapted to the wavelength range to which it is exposed.

[0043] For example, the MOE 240 can be divided in two regions 141, 142, each one targeting a respective wavelength subrange. For example, if the light source emits in the wavelength range of 900±50 nm (850 nm to 950 nm), the region 141 can be adapted to focus light of a wavelength subrange of AXl=800±50 nm, covering a subrange of 100 nm and the region 142 can be adapted to focus light of a wavelength subrange of AX2=900±50 nm, also covering a subrange of 100 nm. In other examples, the MOE 240 can be divided in a higher number of regions to increase wavelength specificity. For example, each region of the MOE can be adapted to focus light of a wavelength in a subrange of 50 nm or less, 10 nm or less, 5 nm or less, or 2 nm or less.

[0044] 5. In some examples, at least a region can be configured to focus light from an infrared subrange while another region can be configured to focus light from another infrared subrange. Additionally or alternatively, in some examples, at least a region can be configured to focus light from an infrared subrange while another region can be configured to focus light from a visible subrange. Additionally or alternatively, in some examples, at least a region can be configured to focus light from a first visible subrange while at least a region can be configured to focus light from a second visible subrange.

[0045] Each of the plurality of regions 141, 142 includes a respective plurality of metaatoms (e.g., meta-atoms 261, 262 in region 141and meta-atoms 271, 272 in region 142), wherein each respective meta-atom of the plurality of meta-atoms has a respective geometric characteristic for each of the plurality of regions. For example, the respective plurality of meta-atoms has one or more of a different width, a different height, or a different inter-atom spacing for each of the plurality of different regions. In the example of FIG. 2A, the height of the meta-atoms varies discretely from one region to another, as shown by envelope 280. In the example of FIG. 2A, the width of the meta-atoms and the inter-spacing of meta-atoms is also different in each region and varies discretely from one region to another.

[0046] Each of the plurality of different regions can be configured to focus light incident with the respective angle of incidence range (e.g., with the respective wavelengthsubrange) at substantially a same quality or resolution on the sensor surface. The geometric characteristics of the meta-atoms for each of the particular region can be selected so that the performance for each respective wavelength subrange is substantially the same. The MTF, image quality, or image resolution, can still be high for all even if a high-bandwidth light source is used.

[0047] For example, an optimization method for the phase function of the metalens can be performed to determine geometric characteristics of meta-atoms of each region of the metalens, for example, one or more of shape (e.g., width and / or height), size, location, or inter-meta-atom spacing, etc. that are adapted to the wavelength subrange and quality or resolution requirements.

[0048] FIG. 3 shows a cross-section of an example of an MOE 340. MOE 340 can be a metalens that receives light from one or more light sources (not shown). In this example, the MOE has a circular shape, but other shapes are possible. For example, light from an LED that emits light within a wavelength range of 900±50 nm can be received. The light from the one or more light sources can be separated at different angles based on the wavelength. For example, an optical element such as element 120 can be used to separate the light of different wavelengths to different angles in the FOV.

[0049] In this example, the MOE 340 is divided in five regions 341, 342, 343, 344, and 345, each one configured for a different wavelength subrange of e.g., a 900±50 nm wavelength range. In other examples, the MOE 340 can be divided into a higher or lower number of regions to increase or decrease wavelength specificity and / or cover other wavelength ranges. For example, a wavelength range of 940±20 nm can be covered by eight regions of 5 nm subrange each, which is a typical wavelength range that meta lenses can handle, while still providing a desired image quality for each range.

[0050] Although not shown in FIG. 3, each of the plurality of regions 341, 342, 343, 344, and 345 includes a respective plurality of meta-atoms. Each respective meta-atom of the plurality of meta-atoms has a respective geometric characteristic for each of the plurality of regions. For example, the respective plurality of meta-atoms has one or more of a different width, a different height, or a different inter-atom spacing for each of the plurality of different regions.

[0051] Each of the plurality of different regions can be configured to focus light incident at the respective angle of incidence range (e.g., with the respective wavelength subrange) at substantially a same quality or resolution on the sensor surface. The geometric characteristics of the meta-atoms for each of the particular regions can be selected so that the performance for each respective wavelength subrange is substantially the same.

[0052] For example, an optimization method for the phase functions of each region can be performed to determine the geometric characteristics that are adequate for the wavelength subrange and image quality or resolution requirements.

[0053] FIG. 4 shows a cross-section of an example of an MOE. In this example, the MOE 440 has a circular shape, but other shapes are possible. MOE 440 can be a metalens that receives illumination from one or more sources. For example, light from an LED that emits light within a predetermined wavelength range can be received. The light from the one or more light sources can be separated at different angles based on the wavelength. For example, an optical element such as element 120 can be used to separate the light of different wavelengths to different angles in the FOV.

[0054] However, the light of different wavelengths is not completely localized. The intensity of each separated wavelength varies with the angle of incidence, presenting intensity maxima at certain angle(s) and intensity minima at other angle(s). Rather than assuming that each part of the FOV corresponds to a very localized region of the meta optical element 140 and dividing the MOE into distinctive regions with a discrete change in a geometric characteristic from one region to another, such as the MOE 240, in the case of MOE the 340, one or more geometric characteristics of the meta-atoms varies as a continuous function across the metalens. For example, it can vary as a continuous function of the angle of incidence, and, thus, of the wavelength of the separated light incident at a respective incidence angle, for example, the dominant wavelength of the separated light at a respective incidence angle.

[0055] An optimization method for the phase function of the metalens can be performed to determine geometric characteristics of meta-atoms. For example, a phase function for a metalens with a plurality of regions can be optimized to determine geometric characteristics of meta-atoms for each region of the metalens (e.g., one or more of shape, size, location, or inter-meta-atom spacing, etc.) that are adapted to the wavelengthsubrange and quality or resolution requirements. Then, an interpolation of the resulting geometric characteristics across regions can be performed to obtain a continuous function for the one or more geometric characteristics across the metalens. The geometric characteristic can be one or more of a shape (e.g., width, height), size, location or inter- meta-atom spacing, etc. In the example of FIG. 4, the envelope 480 shows the height of the meta-atoms as a continuous function of the wavelength or incidence angle. All the wavelengths in the wavelength range can be focused at substantially a same quality or resolution on the sensor surface.

[0056] 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 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

CLAIMS1. A system comprising: one or more elements configured to receive light of different wavelengths in a wavelength range from a light source and separate the received light at different angles across a field of view based on the different wavelengths; an image sensor comprising a sensor surface; a metalens comprising a surface comprising a plurality of regions, wherein each region is configured to receive light incident within a respective incidence angle range, wherein each respective incidence angle range corresponds to a wavelength subrange of the separated light, and wherein each region is configured to focus light from the respective wavelength subrange on the sensor surface; and an optical aperture having an aperture size configured to limit the respective incidence angle range at each of the plurality of regions of the metalens.

2. The system of claim 1 , wherein each of the plurality of regions comprises a respective plurality of meta-atoms, wherein each respective meta-atom of the plurality of meta-atoms has a respective geometric characteristic for each of the plurality of regions.

3. The system of claim 2, wherein the respective plurality of meta-atoms has one or more of a different shape, a different size, or a different inter-meta-atom spacing for each of the plurality of different regions.

4. The system of claim 1 , wherein the one or more elements comprises one or more of a bandpass filter, a diffraction grating, a prism, a diffractive optical element, or a metaoptical element configured to separate the light from the light source to different angles across the field of view based on the different wavelengths.

5. The system of claim 1, wherein at least a first region of the plurality of regions is configured to focus light from a first infrared subrange and wherein at least a second region of the plurality of regions is configured to focus light from a second infrared subrange.

6. The system of any preceding claim, wherein at least a third region of the plurality of different regions is configured to focus light from an infrared subrange and wherein at least a fourth region of the plurality of different regions is configured to focus light from a visible subrange.

7. The system of any preceding claim, wherein at least a fifth region of the plurality of regions is configured to focus light from a first visible subrange and wherein at least a sixth region of the plurality of different regions is configured to focus light from a second visible subrange.

8. The system of claim 1, wherein the light of different wavelengths comprises light in a wavelength range of 50 nm or more or 100 nm or more.

9. The system of claim 1, wherein the light of different wavelengths comprises light in a wavelength range of substantially 920 to 960 nm.

10. The system of claim 1, wherein each of the plurality of different regions is configured to focus light incident with the respective angle of incidence range at substantially a same optical resolution on the sensor surface.

11. The system of any preceding claim, further comprising one or more light sources configured to generate the light of different wavelengths in the wavelength range.

12. The system of claim 1, wherein each region of the plurality of regions is configured to focus light from a wavelength subrange of substantially 10 nm or less, 5 nm or less, or 2 nm or less.

13. A system comprising: one or more elements configured to receive light of different wavelengths in a wavelength range from a light source and separate the received light at different angles across a field of view based on the different wavelengths; an image sensor comprising a sensor surface; a metalens comprising a surface comprising a plurality of meta-atoms, wherein the metalens is configured to receive light incident at a plurality of incidence angles within an incidence angle range, wherein each respective incidence angle corresponds to a wavelength of the separated light, and wherein a respective geometric characteristic of the plurality of meta-atoms varies across the metalens as a continuous function of the wavelength of the separated light incident at a respective incidence angle; and an optical aperture having an aperture size configured to limit the respective incidence angle range at each of the plurality of regions of the metalens.

14. The system of claim 13, wherein the respective geometric characteristic comprises one or more of a different shape, a different size, or different inter-meta-atom spacing.

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