Optical stack including flat optics elements and a baffle

Abstract

An example apparatus includes an optical stack including first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to an operational wavelength The apparatus further includes a baffle disposed between the first and second one of the flat optics elements, wherein the baffle is parallel to, and in a same plane as, the bonding adhesive. Methods of using the apparatus are described as well.

Description

OPTICAL STACK INCLUDING FLAT OPTICS ELEMENTS AND A BAFFLEFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to optical stacks that include flat optics elements and a baffle.BACKGROUND

[0002] Some lenses, such as meta optical elements (MOEs) and diffractive optical elements (DOEs), employ a flat optic technology. MOEs, for example, have a metasurface that includes distributed small subwavelength structures (e.g., nanostructures or other meta-atoms) arranged to interact with light in a particular manner. 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. Likewise, DOEs have microstructure patterns that alter and control the phase of an incoming light wave. By altering the microstructures, it is possible for a DOE to produce a range of beam intensity profiles or beam shapes.

[0003] Diffraction- based flat optics elements such as MOEs or DOEs can be used, for example, in optical applications to take advantage of their flat surface and reduced thickness, compared to classic, curved refractive lenses. For example, compared to refractive lenses, MOEs can have fewer surfaces and less performance degradation due to tolerances. Further, MOEs can be stacked with flat glass surfaces, can have low thermal impact and / or can be designed easily with high sensitivity (e.g., high numerical aperture) across the field (i.e., telecentric at the image plane).SUMMARY

[0004] The present disclosure describes optical stacks that include flat optics elements and one or more baffles. Imaging systems that include the optical stack also are described.

[0005] For example, in one aspect, the present disclosure describes an apparatus that includes an optical stack including first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to an operational wavelength. The apparatus further includes a baffle disposed between the first and second flat optics elements, wherein the baffle is parallel to, and in a same plane as, at least part of the bonding adhesive.

[0006] Some implementations include one or more of the following features. For example, in some instances, at least one of the first or second flat optics elements includes a metasurface. In some implementations, the first flat optics element includes a metasurface on a first substrate, and the second flat optics element includes a second metasurface on a second substrate. In some cases, the bonding adhesive bonds the first and second substrates together. In some instances, the bonding adhesive is index- matched to a material of the first and second substrates. In some instances, at least one (or both) of the bonding adhesive or baffle are substantially index-matched to a material of the first and second substrates.

[0007] In some implementations, the baffle is composed of a black resist or black chrome. In some instances, the baffle is disposed so as not to interfere with incident light rays of an imaging diffractive order. In some implementations, the optical stack is configured such that there is a distance between an edge of the baffle and incident light rays of an imaging diffractive order. In some cases, the distance is in a range of 50-100 pm. In some instances, the bonding material is substantially index-matched to a material of the first and second substrates such that they do not deviate from one another by more than 0.4 in refractive index of either of the substrates. In some instances, the bonding material is substantially index-matched to a material of the first and second substrates such that they do not deviate from one another by more than 0.2 in refractive index of either of the substrates.

[0008] In some implementations, the apparatus includes an image sensor having a light sensitive surface, wherein the baffle is configured to allow light rays of an imaging orderto reach the light sensitive surface, and to prevent at least some rays of light of one or more higher diffractive orders from reaching the light sensitive surface, wherein the one or more higher diffractive orders are diffractive orders higher than the imaging order. In some implementations, the baffle is configured to prevent appearance on the light sensitive surface of the image sensor of an artifact resulting from stray light rays at one or more higher diffractive orders, wherein the one or more higher diffractive orders are diffractive orders higher than an imaging order.

[0009] In some implementations, the bonding adhesive is optically transparent to the operational wavelength. Depending on the application, the operational wavelength can be in the infra-red or near infra-red range of the electromagnetic spectrum, the visible range of the electromagnetic spectrum, or the ultra-violet range of the electromagnetic spectrum.

[0010] Some implementations include a flat optical element stacked with one or more other flat optical elements, pure glass substrates, substrates containing apertures, cover glasses, substrates containing wavelength or other optical filters, or other flat elements, where baffles are included at one or more, or all, of the interfaces where elements are bonded together.

[0011] The present disclosure also describes a method that includes receiving light incident on an optical stack. The optical stack includes first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to the light, wherein a baffle is disposed between the first and second one of the flat optics elements, the baffle being parallel to, and in a same plane as, at least part of the bonding adhesive. The method includes preventing, by the baffle, at least some rays of the light of a higher diffractive order from passing to the second one of the flat optics elements, wherein the higher diffractive order is a diffractive order higher than an imaging order, and wherein the baffle is disposed so as not to interfere with incident light rays of the imaging order.

[0012] Some implementations include one or more of the following advantages. For example, in some implementations, the baffle can prevent at least some stray light (e.g., rays resulting from higher diffractive orders or other scattered light) from reaching the light sensitive surface of an image sensor that, together with the optical stack, forms part of an imaging system. In some implementations, incorporating the baffle can help prevent the appearance on the light sensitive surface of the image sensor of an artifact (e.g., an unwanted image) resulting from stray light rays at one or more of the higher diffractive orders or other scattered light. In some cases, providing the baffle in combination with flat optics can prevent stray light from unwanted rays beyond what may be achievable using conventional (e.g., refractive) optics. That is, in addition to preventing stray light from scattered rays, providing the baffle in combination with flat optics (e.g., meta lenses) can, in some instances, help prevent stray light from unwanted diffractive orders or combination of orders and / or stray light caused by "not-transmitted" rays, which appear at specific conditions in the generalized Snell's law.

[0013] Other aspects, features, and advantages will be readily apparent from the following detailed description, the accompanying drawings, and the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates an example of an imaging system including an optical stack.

[0015] FIG. 2 illustrates an example of light rays of an imaging diffractive order passing through the optical stack.

[0016] FIG. 3 illustrates another example of an optical stack that includes baffle.DETAILED DESCRIPTION

[0017] The present disclosure describes apparatus that include an optical stack including first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to an operational wavelength. A baffle is disposed between the first and second flat optics elements, wherein the baffle is parallel to, and in a sameplane as, at least part of the bonding adhesive. In general, each of the flat optics elements can be a flat element having two substantially parallel surfaces and at least partially transparent to light at a specified (e.g., operational) wavelength. Examples of flat optics elements include MOE elements, DOE elements, substrates containing apertures, spacers, pure glass substrates, cover glasses, elements acting as filters, spaceplates, or other flat elements having an optical function.

[0018] As shown in the example of FIG. 1, an imaging system (e.g., a camera) 20 includes a CMOS-based or other image sensor having a light-sensitive surface 22 that is operable to capture an image of an object 24. The imaging system 20 includes an optical stack 10 through which light, reflected by the object 24, passes before impinging on the light-sensitive surface 22 of the image sensor. An aperture stop can be present, for example, at the front surface of the optical stack 10. In some implementations, a bandpass filter (BPF) or an angle-of-incidence (AOI) filter 26 is disposed between the optical stack 10 and the light-sensitive surface 22 of the image sensor. In some cases, the baffle is operable to stop unwanted rays that are not stopped by the AOI filter and / or BPF.

[0019] The optical stack 10 includes back-to-back flat diffractive optical elements 12, 14. Each flat diffractive optical element 12, 14 can be implemented, for example, as a MOE or DOE. In an example implementation, the first flat optics element 12 includes a first metasurface 30 disposed on a first substrate 32 (e.g., a glass, plastic or polymer material), and the second flat optics element 14 includes a second metasurface 34 disposed on a second substrate 36 (e.g., a glass, plastic or polymer material). In the illustrated example. The first metasurface 30 is on the front surface of the first substrate 32, and the second metasurface 34 is on the back surface of the second substrate 36. The substrates 32, 36 can be transparent, or at least partially transparent, to an operational wavelength. Depending on the particular application, the operational wavelength for the optical stack 10 and the imaging system 20 may be, for example, in the visible range (400 - 700 nm), the near-infrared range (700 - 1400 nm), the short-wavelength infrared range (1.4 - 3 pm), the mid-wavelength infrared (3 - 8 pm) or the low-wavelength infrared (8 -14 pm). The substrates 32, 36 can provide mechanical support for the respective metasurfaces 30, 34.

[0020] In the case of MOEs, each metasurface can be composed of distributed small subwavelength structures (e.g., nanostructures or other meta-atoms) arranged to interact with light in a particular manner. The meta-atoms of a respective metasurface can, individually and / or collectively, interact with light waves to change a local amplitude, a local phase, or both, of an incoming light wave. Thus, when the meta-atoms (e.g., nanostructures) of a metasurface are in a particular arrangement, the metasurface can act as an optical element such as a metalens, which includes carefully arranged “unit cells” or “meta-atoms” with sub-wavelength structures (e.g., nanostructures). The term “subwavelength” indicates that the nanostructures have lateral dimensions (parallel to the substrate on which they are disposed) that are less than a wavelength of light that is to be incident thereon. In general, the dimensions of the nanostructures scale with the shortest wavelength of interest. For example, the nanostructures can be in the form of nanoscale features having dimensions less than 1 micron. By adjusting the geometry of these unit cell elements, one can modify the phase above the elements in response to a plane wave. With the knowledge of the phase in terms of the geometry parameters, it is possible to create a metalens with an arbitrary phase profile by placing the meta-atoms at the necessary positions.

[0021] The substrates 32, 36 of the flat optics elements 12, 14 can be attached to one another, for example, by an optically clear bonding glue or other adhesive 18 that preferably is index-matched to the material of the surrounding substrates 32, 36. In some implementations, the respective refractive indices of the optical elements 12, 14 and bonding adhesive 18 are substantially index- matched such that they do not deviate from one another by more than 0.2 in refractive index. The adhesive 18 preferably is transparent, or at least partially transparent, to the operational wavelength.

[0022] In some cases, the flat optics elements 12, 14 can be manufactured with the same rectangular aspect ratio as the image sensor, which allows the footprint of the lenses to bereduced. In some cases, gluing together the various lenses in a single optical stack can help improve mechanical stability. Using wafer-level stacking of the lenses, relatively complex optical systems can, in some instances, be manufactured more easily, and many lenses can be manufactured in parallel.

[0023] Light rays in an imaging system that includes one or more diffractive optical elements (e.g., diffractive lenses and / or metalenses) can include an imaging order and one or more unwanted diffractive orders (i.e., orders other than the imaging order). In some imaging applications, for example, the imaging order is the first transmitted converging order (m:l), and the unwanted diffractive orders may include higher diffractive orders as well as the 0thdiffractive order. In that case, the higher diffractive orders can include one or more of the higher transmitted converging orders (m: 2, 3, ... ) and / or diverging orders (m: -2, -3, ... ). In other applications, the imaging order is the first transmitted diverging order (m:-l), and the unwanted diffractive orders may include one or more of the higher transmitted diverging orders (m: -2, -3, ... ) and / or converging orders (m: 2, 3, ... ) as well as the 0thdiffractive order. In general, higher diffractive orders refers to those diffractive orders for which the absolute value of the order is higher than the absolute value of the imaging order. For example, all orders (±2, ±3... ) are higher orders to the orders 1 or -1. In some applications, a diffractive order other than the first transmitted converging order (m:l) or the first transmitted diverging order (m:-l) may serve as the imaging order.

[0024] Higher diffractive orders can cause potential issues in image systems incorporating flat diffractive optical elements such as MOEs (e.g., the presence of artifacts or reduced contrast in the image performance). Further, some applications (e.g., time-of-flight (ToF) systems) can be particularly sensitive to these unwanted higher-order rays. In some cases, the flat optics elements (e.g., metalens) 30, 34 themselves can be configured so that the higher diffractive orders, are somewhat reduced. Nevertheless, the remaining rays from the higher diffractive orders still can cause potential issues. For example, more than one diffractive order may be present at the same point on the image sensor, which cannot discriminate between the desired imaging order and the undesiredhigher order diffraction effects. In such situations, stray light from higher diffractive orders may be displayed as a haze or artifact at the sensor. In some cases, the stray light may result in a blurred or out-of-focus image resulting from combinations of unwanted orders.

[0025] In general, the higher the diffractive order, the higher the angle-of-incidence. For example, the highest angle-of-incidence (AOI) for the second diffractive order (m:2) may be significantly larger than the highest angle-of-incidence for the first diffractive order (m: 1). To reduce the potential impact of the unwanted light rays (i.e., diffractive orders other than the imaging order), a baffle 16 can be disposed at the interface between the substrates 32, 36. That is, the baffle 16 can be provided in parallel with, and in the same plane as, the bonding adhesive 18, as shown in the example of FIG. 1. The baffle 16 can be composed, for example, of black resist, black chrome, or other ray blocking material. As illustrated in FIG. 2, preferably there is a distance (d) that provides a margin between the edge of the baffle 16 and the light rays 40 for the imaging order(s). That is, the baffle 16 should not interfere with the imaging order(s) for all field points to avoid vignetting. In some implementations, the distance (d) is in the range of 50-100 microns (pm).

[0026] In some implementations, the baffle 16 can prevent at least some stray light (e.g., rays resulting from higher diffractive orders or other unwanted rays) from reaching the light sensitive surface 22 of the image sensor. In some implementations, incorporating the baffle 16 can help prevent the appearance on the light sensitive surface 22 of the image sensor of an artifact (e.g., an unwanted image) resulting, for example, from stray light rays at one or more of the higher diffractive orders.

[0027] In operation, light incident on the first optical element 12 passes through the metasurface 30 and substrate 32. Such light may include rays of the imaging order (e.g., m: 1), as well as unwanted stray light that may include light rays of higher diffractive orders (e.g., m: +2; m: +3). The baffle 16 prevents at least some of the unwanted light, including light from higher order rays, from passing through to the second optical element 14 and, thus, from impinging on the light sensitive surface 22 of the imagesensor. By placing the baffle 16 in the light path between the two flat optics elements 12, 14, unwanted rays, including light from at least some of the higher diffractive orders, can be blocked at least partially, thereby enhancing the quality of the image detected by the image sensor. Although the baffle 16 prevents at least some of the higher diffractive order rays from passing, it preferably is configured to allow all of the imaging rays (e.g., m: 1) to pass to the image sensor.

[0028] In some implementations, as illustrated in the examples of FIGS. 1 and 2, the thickness (t) of the baffle 16 is substantially the same as the thickness of the bonding adhesive 18. In some implementations, however, as shown in the example of FIG. 3, the bonding adhesive 18 extends over both the aperture and the baffle material. In this case, the baffle 18 is parallel to, and in a same plane as, at least part of the bonding adhesive 16.

[0029] 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

What is claimed is:

1. An apparatus comprising: an optical stack including first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to an operational wavelength; and a baffle disposed between the first and second flat optics elements, wherein the baffle is parallel to, and in a same plane as, at least part of the bonding adhesive.

2. The apparatus of claim 1 wherein at least one of the first or second flat optics elements includes a metasurface.

3. The apparatus of claim 1 wherein the first flat optics element includes a metasurface on a first substrate, and the second flat optics element includes a second metasurface on a second substrate.

4. The apparatus of claim 3 wherein the bonding adhesive bonds the first and second substrates together.

5. The apparatus of claim 4 wherein the bonding adhesive is index- matched to a material of the first and second substrates.

6. The apparatus of claim 4 wherein the bonding adhesive is substantially index-matched to a material of the first and second substrates such that they do not deviate from one another by more than 0.2 in refractive index.

7. The apparatus of any one of claims 3-6 wherein the baffle is substantially index- matched to a material of the first and second substrates such that they do not deviate from one another by more than 0.4 in refractive index.

8. The apparatus of any one of claims 1-7 wherein the baffle is composed of a black resist.

9. The apparatus of any one of claims 1-7 wherein the baffle is composed of black chrome.

10. The apparatus of any one of claims 1-9 wherein the baffle is disposed so as not to interfere with incident light rays of an imaging diffractive order.

11. The apparatus of any one of claims 1-10 configured to have a distance between an edge of the baffle and incident light rays of an imaging diffractive order.

12. The apparatus of claim 11 wherein the distance is in a range of 50-100 pm.

13. The apparatus of any one of claims 1-12 further including an image sensor having a light sensitive surface, wherein the baffle is configured to allow light rays of an imaging order to reach the light sensitive surface, and to prevent at least some rays of light of one or more higher diffractive orders from reaching the light sensitive surface, wherein the one or more higher diffractive orders are diffractive orders higher than the imaging order.

14. The apparatus of any one of claims 1-10 further including an image sensor having a light sensitive surface, wherein the baffle is configured to prevent appearance on the light sensitive surface of the image sensor of an artifact resulting from stray light rays at one or more higher diffractive orders, wherein the one or more higher diffractive orders are diffractive orders higher than an imaging order.

15. The apparatus of any one of claims 1-14 wherein the bonding adhesive is optically transparent to the operational wavelength.

16. The apparatus of any one of claims 1-15 wherein the operational wavelength is in the infra-red or near infra-red range of the electromagnetic spectrum.

17. The apparatus of any one of claims 1-16 wherein the operational wavelength is in the visible range of the electromagnetic spectrum.

18. A method comprising: receiving light incident on an optical stack that includes first and second flat optics elements attached to one another by a bonding adhesive that is at least partially transparent to the light, wherein a baffle is disposed between the first and second one of the flat optics elements, the baffle being parallel to, and in a same plane as, at least part of the bonding adhesive; and preventing, by the baffle, at least some rays of the light of a higher diffractive order from passing to the second one of the flat optics elements, wherein the higher diffractive order is a diffractive order higher than an imaging order, and wherein the baffle is disposed so as not to interfere with incident light rays of the imaging order.

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