Folded optical system including meta-optical elements

Abstract

An exemplary apparatus includes an image sensor having an optically active surface and a folded optical system including at least one meta-optical element (MOE) configured such that a chief ray impinging on and passing through the at least one MOE travels along a piecewise linear path to the optically active surface of the image sensor.

Description

[Technical field]

[0001] Field of Disclosure The present disclosure relates to folded optical systems that include meta-optical elements. [Background technology]

[0002] background In a camera module, the optical Z height refers to the distance from the optically active surface of the image sensor to the outermost point of the lens. This distance is sometimes referred to as the total track length (TTL). It may be desirable to reduce the optical Z height or TTL to achieve a low-profile camera module, which can facilitate the incorporation of the camera module into small electronic devices or other devices. Summary of the Invention [Problem to be solved by the invention]

[0003] overview The present disclosure describes an apparatus that includes a folded optical system having at least one meta-optical element. [Means for solving the problem]

[0004] For example, in one aspect, the present disclosure describes an apparatus that includes an image sensor having an optically active surface and a folded optical system including at least one meta optical element (MOE) configured such that a chief ray impinging on and passing through the at least one MOE travels along a piecewise linear path to the optically active surface of the image sensor.

[0005] Some implementations include one or more of the following features. For example, in some implementations, the at least one MOE is configured such that a chief ray travels along a path at least a portion of which is tilted relative to the at least one metasurface of the at least one MOE. The at least one MOE can be configured such that the chief ray is focused onto the optically active surface of the image sensor. In some cases, the folded optics includes a plurality of MOEs configured such that a chief ray impinging on a first one of the MOEs passes through the plurality of MOEs and reaches the optically active surface of the image sensor along a piecewise linear path. The plurality of MOEs can be configured such that a chief ray travels from the metasurface of the first one of the MOEs to the optically active surface of the image sensor along a tilted path. In some implementations, the folded optics includes at least three MOEs.

[0006] The at least one MOE can be configured, for example, to direct light of at least one diffraction order in a direction such that light of the at least one diffraction order does not reach the optically active surface of the image sensor. In some cases, the device includes at least one light blocking material arranged to block or absorb light of the at least one diffraction order. In some implementations, the at least one MOE is configured such that light of only a subset of the diffraction orders reaches the optically active surface of the image sensor.

[0007] Some implementations include at least one MOE at a first lens level and at least two MOEs at a second lens level. In some cases, the second lens level is closer to the optically active surface of the image sensor than the first lens level. The MOEs can be arranged such that a first portion of light from the at least one MOE at the first lens level has a first diffraction order subset and passes through a first one of the MOEs at the second lens level, and a second portion of light from the at least one MOE at the first lens level has a second, different diffraction order subset and passes through a second one of the MOEs at the second lens level.

[0008] Some embodiments include a first lens level, a second lens level, and a third lens level, and the MOEs are distributed across the first lens level, the second lens level, and the third lens level, and the MOEs are arranged such that a chief ray passes through an MOE at the first lens level, then through at least one MOE at the second lens level, and then through at least one MOE at the third lens level. Some embodiments include at least two MOEs at the third lens level. In some cases, the third lens level is closer to the optically active surface of the image sensor than the second lens level. The MOEs can be arranged such that a first portion of light from the at least one MOE at the second lens level has a first diffraction order subset and passes through a first one of the MOEs at the third lens level, and a second portion of light from the at least one MOE at the second lens level has a second, different diffraction order subset and passes through a second one of the MOEs at the third lens level.

[0009] In some embodiments, at least one of the MOEs is asymmetric. Each MOE can be implemented, for example, as a respective metalens. In some implementations, the optical axis of at least one MOE is tilted with respect to the plane of the optically active surface of the image sensor. The bending optics can be configured such that after passing through the metasurface of the at least one MOE, the light of the imaging diffraction orders propagates through a material having a higher refractive index than the material of the metasurface.

[0010] Implementations may include one or more of the following advantages: For example, some implementations may achieve a relatively small TTL, which may help facilitate providing a low-profile module that can be integrated into small electronic or other devices.

[0011] Other aspects, features, and advantages will become readily apparent from the following detailed description, the accompanying drawings, and the claims.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 illustrates an example of a camera module including a metasurface. [Diagram 2] FIG. 13 shows another example of a camera module including a metasurface. [Diagram 3] FIG. 13 shows yet another example of a camera module including a metasurface and a light blocker or absorber. [Figure 4] FIG. 13 shows another example of a camera module including a metasurface. [Diagram 5] FIG. 13 illustrates a further example of a camera module. [Figure 6] FIG. 1 illustrates an example of a camera module including three lens levels with metasurfaces. [Figure 7] FIG. 13 shows another example of a camera module including three lens levels with metasurfaces. [Figure 8] FIG. 13 shows yet another example of a camera module including three lens levels with metasurfaces. [Figure 9] FIG. 1 illustrates an example of a camera module including a metasurface. [Figure 10] FIG. 13 shows another example of a camera module including a metasurface. [Figure 11] FIG. 13 shows further examples of camera modules including metasurfaces. [Figure 12] FIG. 13 shows yet another example of a camera module including a metasurface. [Figure 13] FIG. 13 shows another example of a camera module including a metasurface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Detailed Description The present disclosure describes devices such as camera modules that include a folded optical system that uses one or more meta-optical elements (MOEs). A meta-optical element (e.g., a metalens) has a metasurface (i.e., a surface with a distributed array of small structures such as meta-atoms that are configured to interact with light in a specific manner). For example, a metasurface can be a surface with a distributed array of nanostructures. The nanostructures can interact with light waves, either individually or collectively. For example, the nanostructures or other meta-atoms can be configured to change the local amplitude, local phase, or both, of an outgoing light wave.

[0015] Bent optics refers to an optics in which a light beam (e.g., infrared or visible) is bent such that the light path is longer than a dimension (e.g., height) of the optics. According to the present disclosure, one or more MOEs are configured such that a chief ray of a light beam passing through the MOE and focused onto an image sensor of a camera module travels along a piecewise linear path. That is, the chief (i.e., normal) light ray travels along a path at least a portion of which is inclined (e.g., travels at an oblique angle) with respect to at least one metasurface of the MOE. Thus, the chief ray travels along an inclined path throughout the entire stack (i.e., from the metasurface of the first MOE in the stack to the optically active surface of the image sensor).

[0016] FIG. 1 illustrates an example of a camera module including a system of folded optics using a first MOE 20 and a second MOE 22. Light (e.g., infrared or visible) 28 impinging on the first MOE 20 passes through the first MOE 20 and the second MOE 22 and is focused onto an optically active surface of an image sensor 26 operable to detect light signals impinging on its surface. The total track length (TTL) in this case is the sum of the distance D1 between the metasurfaces of the MOEs 20, 22 and the distance D2 from the metasurface of the second MOE 22 to the optically active surface of the image sensor. The image sensor 26 may be implemented, for example, as a CCD or SPAD sensor and may be operable, for example, as a camera to capture digital image frames including image data that may be used to reproduce and display the digital image.

[0017] In the example of FIG. 1, the two MOEs 20, 22 are disposed on either side of a substrate 24 that is transparent or substantially transparent to the wavelength or wavelength range of interest (e.g., infrared or visible). The substrate 24 may be composed of, for example, glass, silicon, germanium, or a polymer. In some implementations, the MOE 20 is a circular transmissive metalens. In the example of FIG. 1, the first MOE 20 is asymmetric (e.g., not rotationally symmetric), which allows an incident beam 28 to propagate through the substrate 24 at an oblique angle. The light 28 passes through both MOEs 20, 22, travels along a piecewise linear path, and is focused onto the optically active surface of the image sensor 26.

[0018] In some implementations, the second MOE 22 is also asymmetric (e.g., not rotationally symmetric), as shown in Figure 2. Such an arrangement can potentially allow the TTL (i.e., the sum of distances D1+D2') to be further shortened.

[0019] Allowing incident light to occur along a graded path through the entire stack can also facilitate blocking or redirecting certain diffraction orders of light. That is, the metasurface of the MOE 20, 22 can be configured such that incident light is diffracted into multiple diffraction orders, and, for example, the 1st (±1) diffraction order is directed toward the optically active surface of the image sensor 26, while the 0th and higher diffraction orders (i.e., ±2 and above) are blocked or directed away from the optically active surface of the image sensor 26. For example, maximizing the detection efficiency for the 1st (±1) order can help ensure increased light collection. An example is shown in FIG. 3.

[0020] As shown in Figure 3, a chief ray 30 is incident on a first MOE 20 configured such that light in the zeroth diffraction order 32 travels towards a light blocking material 34 (e.g., black epoxy or black chrome) where it is absorbed. Light in the other diffraction orders 31 travels towards a second MOE 22 configured such that light in the ±1 diffraction orders 38 is directed towards the optically active surface of the image sensor 26, while light in the ±2 and higher diffraction orders 39 is directed away from the optically active surface of the image sensor 26. This configuration thus allows light in the specified diffraction orders (e.g., ±1) to be directed towards and detected by the image sensor 26, while light in the other diffraction orders (e.g., the zeroth order, and ±2 and higher) is blocked or otherwise prevented from impinging on the optically active surface of the image sensor 26.

[0021] In the above examples, the MOEs 20, 22 are disposed on opposite sides of the same substrate 24. However, in some embodiments, the MOEs 20, 22 may be disposed on different substrates. Additionally, in some embodiments, the space between the MOEs 20, 22 may simply be an air gap.

[0022] In the above examples of Figures 1, 2, and 3, each lens level includes a single MOE. That is, the first lens level, which is farther from the image sensor 26, includes one MOE 20. Similarly, the second lens level, which is closer to the image sensor 26, includes one MOE 22. However, in some implementations, one or both of the lens levels may include multiple MOEs. Such an arrangement may help achieve improved performance over a larger field of view (FOV). An example is shown in Figure 4.

[0023] As shown in FIG. 4, the first lens level 40A includes multiple MOEs 20A, 20B. Similarly, the second lens level 40B includes multiple MOEs 22A, 22B. MOE 20A is configured to direct incident chief rays to MOE 22A, which is configured to direct light to the optically active surface of image sensor 26. Similarly, MOE 20B is configured to direct incident chief rays to MOE 22B, which is configured to direct light to the optically active surface of image sensor 26. Thus, the multi-level lens configuration of MOEs is operable to tilt incident light by an amount that depends at least at the port on the angle of incidence.

[0024] An arrangement such as that of Figure 4 may be advantageous in embodiments where different lens systems are placed, for example, in front of the same array camera. The various lens systems may be optimized, for example, for different wavelengths (or wavelength ranges), or for different portions of the field of view.

[0025] In some implementations, one of the lens levels may have multiple MOEs while the other lens level may have only a single MOE. An example is shown in FIG. 5. As shown in FIG. 5, the first lens level 40A includes an MOE 20C configured to tilt light by an amount that depends at least in part on the polarization of the incident light. Light 50A having a first type of polarization is directed to a first MOE of the MOEs 22A in the second lens level 40B, and light 50B having a second, different type of polarization is directed to a second MOE of the MOEs 22B in the second lens level 40B. In some implementations, the MOE 20C of the first lens level 40A is configured such that each polarization type sees half of the field of view (FOV). The MOEs 22A, 22B in the second lens level 40B are configured to redirect the respective polarized signals towards the optically active surface of the image sensor 26. By combining the two MOEs 20A, 20B at the first lens level of FIG. 4 into a single MOE 20C (FIG. 5) and discriminating incident light based on its polarization, a smaller package for the module can potentially be achieved.

[0026] The above examples show embodiments in which the chief ray travels along an inclined path through a stack including two lens levels. In some embodiments, the stack includes three or more lens levels, each of which includes at least one optical element having an optical metasurface. In these embodiments, the MOE is also configured such that the chief ray of a light beam passing through the MOE and focused onto the image sensor of the camera module travels along a piecewise linear path. That is, the chief (i.e., normal) light ray travels along a path at least a portion of which is inclined (e.g., travels at an oblique angle) with respect to at least one metasurface of the MOE. Thus, the chief ray travels along an inclined path throughout the entire stack (i.e., from the metasurface of the outermost MOE to the optically active surface of the image sensor).

[0027] For example, Figure 6 shows a camera module including a stack of three MOEs 20D, 20E, 20F. The MOEs are constructed and arranged such that incident light 30 (e.g., a chief ray) passes through a first MOE 20D along an oblique path to the optically active surface of the image sensor 26. After passing through the first MOE 20D, the light travels to a second MOE 20E, which is configured such that the 0th diffraction order light 62 and the ±2 and higher diffraction orders 64 are directed along one or more paths outward from the optically active surface of the image sensor 26. Meanwhile, the ±1 diffraction orders light 66 travels along a path from the second MOE 22E to a third MOE 20F, which directs light 68 toward the optically active surface of the image sensor 26.

[0028] 7 shows another example of a camera module including a stack of three lens levels. The MOEs are constructed and arranged such that light of different diffraction orders is treated differently, and a portion of the incident light (e.g., a chief ray) 30 passes through a first MOE 20D along an inclined path to reach the optically active surface of the image sensor 26. In the illustrated example, the first lens level includes MOE 20D, the second lens level includes MOE 20H, and the third lens level includes MOEs 20J, 20K. After passing through the first MOE 20D, the light travels to a second MOE 20H, which is configured such that light 62 of a particular diffraction order (e.g., the zeroth diffraction order) is directed outward from the optically active surface of the image sensor 26. Meanwhile, a first portion 66A of the light of the other diffraction order is directed along a path from the second MOE 22H to the first MOE 20J at the third lens level, and a second portion 66B of the light of the other diffraction order is directed along a path from the second MOE 22H to the second MOE 20K at the third lens level. In some implementations, the first portion 66A and the second portion 66B of the light may include light of different diffraction orders. Each of the MOEs 20J, 20K in the third lens level directs a respective light 68A, 68B to a respective portion of the optically active surface of the image sensor 26.

[0029] 8 shows another example of a camera module including a stack of three lens levels. In this example, the MOE is again constructed and arranged to process light of different diffraction orders such that they are treated differently. In particular, some of the diffraction orders of light can be blocked and prevented from impinging on the optically active surface of the image sensor 26.

[0030] In the illustrated example of FIG. 8, the first lens level includes MOE 20L, the second lens level includes MOE 20M, and the third lens level includes MOEs 20N and 20P. The MOEs are constructed and arranged such that a portion of the incident light (e.g., the main ray) 30 passes through the first MOE 20L along an inclined path to reach the optically active surface of the image sensor 26. The first MOE 20L is configured such that light 81 of a particular diffraction order (e.g., the zeroth diffraction order) travels toward and is absorbed by the light blocking material 34A. The remaining light 80 travels to the second MOE 20M, which is configured such that light 82 of a particular diffraction order (e.g., the zeroth diffraction order) travels toward and is absorbed by the light blocking material 34B. Meanwhile, a first portion 84A of the light of the other diffraction order is directed along a path from the second MOE 22M to the first MOE 20N at the third lens level, and a second portion 84B of the light of the other diffraction order is directed along a path from the second MOE 22M to the second MOE 20P at the third lens level. In some implementations, the first portion 84A and the second portion 84B of the light can include light of different diffraction orders from each other. Each of the MOEs 20N, 20P in the third lens level directs a respective light 86A, 86B to a respective portion of the optically active surface of the image sensor 26. Some implementations can include more than three MOEs in the stack through which the incident light (e.g., the chief ray) travels along a path to the optically active surface of the image sensor.

[0031] In some implementations, the folded optical system includes only one optical element (e.g., a single MOE, such as a metalens with a metasurface). FIG. 9 shows an example in which light 30 is incident on the MOE 20. As the light 30 passes through the metasurface of the MOE, the MOE structure separates the light of different diffraction orders from one another, such that different diffraction order subsets travel in different directions. In particular, the tilt angle can, in some implementations, help to reduce overlap between the imaging diffraction order (e.g., +1) and other diffraction orders. Thus, in the example of FIG. 9, after the light 30 passes through the metasurface of the MOE, a portion of the light (e.g., light of ±1 diffraction orders) 38 travels toward the optically active surface of the image sensor 26 along a path at least some of which is tilted relative to the metasurface of the MOE 20. The light 32 of the other diffraction orders travel in one or more different directions. For example, a portion of the light 32 (e.g., the zeroth diffraction order of light) may travel toward a light blocking or absorbing material 34 or other suitable material and be directed along a path outward from the optically active surface of the image sensor 26. In some cases, light of higher diffraction orders (e.g., ±2 or more) may be lost through total internal reflection within the MOE 20.

[0032] In some implementations, the optical axis of one or more MOEs is rotated (e.g., tilted) relative to the plane of the optically active surface of the image sensor. FIG. 9 shows one example. FIG. 10 shows another example. Such a configuration can potentially reduce the lens chief ray angle (i.e., the angle between the optical axis and the lens chief ray). The relative tilt can potentially help to cause more chief rays to impinge on the sensor 26 at an angle perpendicular (or close to perpendicular) to the optically active surface of the sensor, which can help increase the amplitude of the detected signal.

[0033] In some implementations, the camera module includes additional components. For example, Figures 10, 11, and 12 show examples in which the incident light passes through an aperture 100 before impinging on the folded optics including one or more MOEs 20. In the example of Figure 12, the aperture 100 is tilted relative to the folded optics. Such an arrangement can be useful in some cases to reduce TTL. Some implementations may include additional or other optical components (e.g., bandpass filters).

[0034] In some implementations, after passing through the metasurface of the MOE 20, the light in the imaging diffraction orders propagates through air (see, e.g., FIG. 9). In some implementations, as shown in the example of FIG. 13, after passing through the metasurface 101 of the MOE, the light in the imaging diffraction orders propagates through a material 103 having a higher refractive index than air. More generally, the optical system can be configured such that after passing through the metasurface 101, the light in the imaging diffraction orders propagates through a material 103 having a higher refractive index than the material of the metasurface 101. The transition to a higher refractive index can be useful in some cases to improve the modulation transfer function (MTF), improve resolution, and / or reduce optical aberrations.

[0035] Depending on the implementation, any of the camera modules described above can be integrated into a variety of small electronic or other devices, including, for example, a smartphone or other type of mobile device, such as a tablet, laptop computer, game controller, or other type of handheld computing device.

[0036] Various modifications can be made to the examples described above, and therefore, other implementations are within the scope of the following claims.

Claims

1. an image sensor having an optically active surface; a folded optical system including at least one meta-optical element (MOE), the at least one MOE being configured such that a chief ray impinging on and passing through the at least one MOE travels along a piecewise linear path to the optically active surface of the image sensor; An apparatus comprising:

2. 2. The apparatus of claim 1, wherein the at least one MOE is configured such that the chief ray travels along a path such that at least a portion of the chief ray is tilted relative to the at least one metasurface of the at least one MOE.

3. 3. The apparatus of claim 1, wherein the folded optical system includes a plurality of MOEs configured such that the chief ray striking a first one of the MOEs passes through the plurality of MOEs and reaches the optically active surface of the image sensor along the piecewise linear path.

4. 4. The apparatus of claim 3, wherein the plurality of MOEs are configured such that the chief ray travels from the metasurface of the first one of the MOEs to the optically active surface of the image sensor along a tilted path.

5. 3. The apparatus of claim 1, wherein the at least one MOE is configured to focus the chief ray onto the optically active surface of the image sensor.

6. The apparatus of claim 3 , wherein the plurality of MOEs includes at least three MOEs.

7. 3. The apparatus of claim 1, wherein the at least one MOE is configured to direct light of at least one diffraction order in a direction such that the light of the at least one diffraction order does not reach the optically active surface of the image sensor.

8. 8. The apparatus of claim 7, further comprising at least one light blocking material arranged to block or absorb light of the at least one diffraction order.

9. 3. The apparatus of claim 1, wherein the at least one MOE is configured such that only the light of a subset of diffraction orders reaches the optically active surface of the image sensor.

10. The apparatus of claim 3 , wherein the plurality of MOEs includes at least one MOE at a first lens level and at least two MOEs at a second lens level.

11. 11. The device of claim 10, wherein the second lens level is closer to the optically active surface of the image sensor than the first lens level, and the MOEs are arranged such that a first portion of light from the at least one MOE at the first lens level has a first diffraction order subset and passes through a first MOE among the MOEs at the second lens level, and a second portion of light from the at least one MOE at the first lens level has a second, different diffraction order subset and passes through a second MOE among the MOEs at the second lens level.

12. 4. The apparatus of claim 3, comprising a first lens level, a second lens level, and a third lens level, the plurality of MOEs being distributed across the first lens level, the second lens level, and the third lens level, the MOEs being arranged such that the chief ray passes through the first MOE, then passes through at least one MOE at the second lens level, and then passes through at least one MOE at the third lens level.

13. The device of claim 12 , including at least two MOEs at the third lens level.

14. 14. The apparatus of claim 13, wherein the third lens level is closer to the optically active surface of the image sensor than the second lens level, and the MOEs are arranged such that a first portion of light from the at least one MOE at the second lens level has a first diffraction order subset and passes through a first MOE among the MOEs at the third lens level, and a second portion of light from the at least one MOE at the second lens level has a second, different diffraction order subset and passes through a second MOE among the MOEs at the third lens level.

15. The device of claim 3 , wherein at least one of the MOEs is asymmetric.

16. 3. The device of claim 1 or 2, wherein each of the at least one MOE is a metalens.

17. 3. The apparatus of claim 1, wherein the optical axis of the at least one MOE is tilted relative to the plane of the optically active surface of the image sensor.

18. 3. The apparatus of claim 1, wherein the bending optics is configured such that after passing through the metasurface of the at least one MOE, the light in the imaging diffraction orders propagates through a material having a higher refractive index than a material of the metasurface.

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