Grating with non-aligned super-optical elements
By adopting non-aligned hyperatomic arrangement in the metasurface grating, the problem of diffraction efficiency of the existing gratings decreases when the incident angle deviates from the normal is solved, and efficient beam control and more uniform efficiency are achieved over a wide incident angle range.
Patent Information
- Application Number
- CN202380076668.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-10-31
- Filing Date
- 2023-10-27
- Publication Date
- 2025-06-13
AI Technical Summary
The diffraction efficiency of the existing metasurface grating is significantly reduced when the incident angle deviates from the normal, and it is difficult to achieve a large receiving angle range and uniform efficiency in the design.
The aberrant hyperatomic arrangement is adopted, and the superatoms are arranged in the first direction and are aligned with respect to the second direction, and are arranged in an asymmetric manner about the first axis of the grating.
Maintain higher diffraction efficiency over a wide incidence angle range, improve grating performance, and provide designs closer to the ideal zigzag phase distribution.
Smart Images
Figure CN120153290A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to gratings. Background Art
[0002] Diffraction gratings are optical elements that can disperse light composed of multiple wavelengths into light components according to wavelength. Optical elements based on metasurfaces can achieve ultra-compact beam control elements, which are ultrathin and flat and, in some cases, easier to fabricate than traditional sawtooth gratings or blazed gratings, and thus can be integrated into various optical systems. The functions of such metasurfaces have sometimes been verified by plane waves perpendicularly incident on the gratings. However, when the angle of incidence deviates from the normal, the diffraction efficiency often decreases significantly. In addition, various factors make it challenging to design metasurfaces that can effectively guide light to large deflection angles (e.g., at visible light wavelengths). However, in some applications, for optical elements, a larger acceptance angle range and more uniform efficiency over the entire angular range are desirable. Summary of the Invention
[0003] The present disclosure describes a grating including a meta-optical element (MOE).
[0004] In one aspect, the present disclosure describes an apparatus including a grating having a first axis oriented in a first direction and a second axis oriented in a second direction different from the first direction, wherein the size of the grating along the first axis is greater than the size of the grating along the second axis. The grating includes units arranged along the first direction, and each unit includes superatoms arranged along the first direction, wherein the superatoms in each specific unit among the units are not aligned with respect to the second direction and are arranged asymmetrically around the first axis of the grating.
[0005] Some embodiments include one or more of the following features. For example, in some embodiments, each unit has the same superatom arrangement as other units of the grating. In some cases, the superatom arrangement in at least one unit is rotated 180° around the central axis of the grating with respect to the superatom arrangement in another unit. In some cases, the superatom arrangement in at least one unit is offset along the second direction with respect to the superatom arrangement in another unit.
[0006] In some embodiments, the superatoms in each specific unit have respective sizes, shapes, or orientations that are different from the sizes, shapes, or orientations of other superatoms in the same unit. In some cases, the corresponding positions of two superatoms in at least one unit partially overlap in the first direction.
[0007] In some cases, the grating is a one-dimensional grating, and in other cases, the grating is a two-dimensional grating (e.g., the superatoms in each specific unit of the grating are arranged two-dimensionally).
[0008] In some embodiments, the size of each unit is smaller than the operating wavelength of the grating. In some embodiments, at least one of the shape, size, or position of the meta-atoms varies between the respective units of the grating. In some cases, the grating is part of a superlens.
[0009] The present disclosure also describes an apparatus that includes a grating, a light source operable to emit light, an optical detector operable to detect light, and at least one reflective or transmissive surface for directing the light emitted by the light source to the grating or directing the light from the grating to the optical detector.
[0010] Some embodiments include one or more of the following advantages. For example, misalignment can provide additional degrees of freedom in the design of the grating. In some embodiments, the arrangement of the meta-atoms can reduce the phase transition region (PTR) and can provide a design with a phase distribution closer to an ideal sawtooth distribution. In some embodiments, the grating exhibits a relatively high diffraction efficiency over a wide range of incident angles. Thus, the performance of the grating can be improved in some cases.
[0011] Other aspects, features, and advantages will be apparent from the following detailed description, the drawings, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 An example of a grating including multiple units is shown.
[0013] Figure 2 An ideal sawtooth phase distribution is shown.
[0014] Figure 3 Another example of a grating including aligned meta-atoms is shown.
[0015] Figure 4 An example of a grating including misaligned meta-atoms is shown.
[0016] Figure 5 Another example of a grating including misaligned meta-atoms is shown.
[0017] Figure 6 Another example of a grating including misaligned meta-atoms is shown.
[0018] Figure 7 Another example of a grating including misaligned meta-atoms is shown.
[0019] Figure 8 Another example of a grating including misaligned meta-atoms is shown.
[0020] Figure 9A An example of a one-dimensional grating including misaligned meta-atoms;Figure 9B An example of a two-dimensional grating including non-aligned meta-atoms.
[0021] Figure 10 An example of an optical system including a grating is shown.
[0022] Figure 11 An example of a superlens including a grating with non-aligned meta-atoms is shown.
[0023] Figure 12 An example of an optical emission system is shown.
[0024] Figure 13 An example of an optical reception system is shown. DETAILED DESCRIPTION
[0025] The present disclosure describes a grating including a meta-optical element (MOE). The MOE is an advanced optical element including a metasurface. A metasurface refers to a surface having a distributed arrangement of small structures (e.g., meta-atoms) that interact with light in a specific manner. A metasurface, also referred to as a superstructure, can be a surface having an array of distributed nanostructures. In some cases, the meta-atoms are columnar or cylindrical, but in some cases other shapes (e.g., meta-atoms with a square cross-section) can also be used. The meta-atoms can interact with light waves individually or collectively. For example, the meta-atoms can change the local amplitude, local phase, or both of the incident light wave. The meta-atoms can be arranged such that the superstructure functions as, for example, a grating.
[0026] As explained in more detail below, the meta-atoms constituting the grating can be distributed along a first direction such that the meta-atoms are not aligned with respect to a second direction different from the first direction. The second direction can be orthogonal (i.e., perpendicular) or non-orthogonal to the first direction. Additionally, the meta-atoms can be arranged such that the non-alignment is asymmetric. In some embodiments, such an arrangement of meta-atoms can provide a grating that exhibits high diffraction efficiency over a relatively wide range of incident angles and / or at relatively large incident angles.
[0027] Figure 1 An example of a grating 20 is shown, which includes a plurality of cells 22, each cell 22 including a sequence of meta-atoms 30, 32, 34 arranged along a first direction (e.g., the x-axis direction, i.e., the long axis of the cell). In Figure 1In the example, the superatoms are arranged with respect to a second direction (e.g., the y-axis direction), which is orthogonal to the first direction. That is, the centers of the respective superatoms 30, 32, 34 are substantially aligned along the same axis. The superatoms in each specific unit may have different sizes (e.g., diameters) from each other. In some embodiments, at least one of the shape, size, or position of the superatoms differs between the units 16. Thus, the superatoms do not have to repeat in a periodic pattern between the respective units. Instead, in some cases, one or more of the shape, size, or position of the superatoms may differ between the respective units. For example, in some embodiments, one or more of the shape, size, or position of the superatoms may differ between the respective units to achieve a desired optical deflection angle. In some embodiments, the unit sizes differ between the respective units.
[0028] Using a superatom arrangement structure as Figure 1 shown, it may be difficult to obtain a smooth sawtooth phase distribution (see Figure 2 ), because the minimum distance between the centers of the largest diameter superatom 34 and the smallest diameter superatom 30 is the sum of their radii (see Figure 3 ). This distance corresponds to the phase transition region (PTR). As the size of this region increases, the performance of the grating may become worse. Even for the smallest PTR ( Figure 2 ), in a conventional column-based MOE grating, the phase distribution will not be a smooth sawtooth. In addition, placing the columns so close may lead to an increase in crosstalk and may reduce the overall transmission ability of the grating.
[0029] According to some embodiments of the present disclosure, as Figure 4 shown in the example, the grating 120 includes a plurality of units 122, and each unit 122 includes a series of superatoms 130, 132, 134 arranged along a first direction (e.g., the x-axis direction corresponding to the longer dimension of the grating). Generally, the respective diameters of the smallest and largest superatoms should be selected to complete a 2π phase transition (i.e., a wrap-around). Compared with the example of Figure 1 , the superatoms 130, 132, 134 are not aligned with respect to a second direction (e.g., the y-axis direction corresponding to the shorter dimension of the grating), which is different from the first direction. That is, the centers of at least some of the respective superatoms 130, 132, 134 are not aligned along the same axis as the other superatoms in the same unit cell 122. Instead, these superatoms are located at different positions in the y-direction. Such an arrangement helps to obtain a design with a significantly reduced PTR (see the lower half of Figure 4 ), and in some cases, a phase distribution closer to Figure 2Design of the ideal distribution. Thus, in some cases, the grating performance can be improved. In some embodiments, the size of each unit cell 122 is shorter than the operating wavelength of the grating 120 (e.g., shorter than the wavelength of light emitted by a VCSEL or other light source used with the grating).
[0030] Generally, the first and second directions can be orthogonal or non-orthogonal to each other, depending on the embodiment. For example, for a rectangular unit 122, the first and second directions can be orthogonal to each other. On the other hand, for a hexagonal unit, the first and second directions can be non-orthogonal to each other.
[0031] As Figure 4 shown in the example of, the meta-atoms can be arranged such that the misalignment is asymmetric. In some embodiments, the refractive index centers of the meta-atoms 130, 132, 134 in the unit cell 122 are located at or near the central axis of the grating (e.g., Figure 4 the line parallel to the x-axis in).
[0032] Although Figure 4 shows two unit cells 122, each having three meta-atoms 130, 132, 134, other embodiments can include different numbers of unit cells and / or meta-atoms per unit cell. For example, in some embodiments, one unit cell 122 can include up to fifteen or more meta-atoms. Using relatively small unit cells 122 can conveniently obtain a grating that operates at a relatively large deflection angle. The unit cells 122 can be replicated several times, dozens of times, hundreds of times, or thousands of times along the first direction (e.g., the x-axis direction), as Figure 5 shown in the grating 220 including unit cells 122(1), 122(2)…122(n). For example, for a grating with a length of several micrometers, in some cases, the unit cell 122 can be replicated approximately one thousand times. Within each specific unit cell 122(1), 122(2)…122(n), the meta-atoms are arranged asymmetrically with respect to the central axis 250 of the grating. In some cases, subtle variations can be added when replicating the unit cell 122, such as the size of the unit elements, the position of the meta-atoms, or the size (e.g., diameter) of the meta-atoms.
[0033] In some cases, one or more unit cells can be a mirror image of other unit cells. For example, the arrangement of the meta-atoms in one unit cell can be rotated 180° with respect to the central axis along the unit distribution direction. For example, as Figure 6As shown, the superatoms 130B, 132B, 134B of the second unit 122B are rotated 180° around the central axis 350 relative to the superatoms 130A, 132A, 134A of the first unit 122A. Within each particular unit 122A, 122B, the superatoms are arranged asymmetrically relative to the central axis 350. Simulations show that flipping the unit 122B relative to the unit 122A along the short side of the grating 320 does not change the optical properties of the grating.
[0034] In some cases, one or more units are laterally offset relative to other units in a second direction (e.g., along the y-axis direction). Figure 7 An example is shown in which the superatoms in the unit 122C are offset relative to the superatoms in the unit 122A in a second direction (i.e., along the shorter dimension of the grating). Simulations show that this lateral offset of the unit 122C relative to the unit 122A does not change the optical properties of the grating.
[0035] As described above, in some embodiments, using an arrangement in which the superatoms are misaligned and arranged asymmetrically (e.g., Figure 4 ) can result in a PTR that is less than the PTR achievable using an arrangement in which the superatoms are aligned ( Figure 1 and Figure 2 ). Although in some cases the final PTR can be reduced, it is not necessary to minimize the PTR. Instead, other variables can be combined to optimize the PTR to achieve the desired phase distribution and optical properties.
[0036] Furthermore, in some embodiments, although the superatoms in the grating arrangement are misaligned and arranged asymmetrically, the PTR can be greater than the PTR achievable using an arrangement in which the superatoms are aligned. Thus, in some cases, the corresponding positions of two adjacent superatoms can at least partially overlap in a first direction (i.e., the longer direction of the grating) (see Figure 4 and Figure 5 ), while in other cases, the corresponding positions of the superatoms can be completely non-overlapping in the first direction (see Figure 8 ). In each case, the misalignment can provide additional degrees of freedom for the design of the grating.
[0037] The superatoms of the grating can be composed of, for example, a material with a relatively high refractive index (such as amorphous silicon), which changes one or more characteristics of the incident light in a specific way. In some cases, the superatoms are columnar nanostructures on a glass or other substrate. As described above, in some embodiments, the superatoms can have other shapes.
[0038] Although the foregoing examples describe the arrangement of superatoms for a one-dimensional (1D) (line) grating, these techniques can also be used for two-dimensional (2D) gratings. For example, Figure 9Ashows an example of a grating, where each unit 122D has three meta - atoms arranged in one - dimension, and Figure 9B shows an example of a grating, where each unit 122E has nine meta - atoms arranged in two - dimensions.
[0039] Figures 4 to 9B Any of the above gratings can be incorporated into various applications, including focusing or emitting lenses, optical collimators, and other applications that utilize optical phase distributions. Generally, non - alignment techniques can be advantageous for arrangements with a limited range of meta - atom diameters. Gratings can also be used in instruments such as spectrometers to separate polychromatic light into its constituent fundamental wavelengths.
[0040] Figure 10 shows an example of an optical system 700 (e.g., a spectrometer), in which a grating 706 as described in any of the above Figures 4 to 8 can be incorporated. System 700 includes a light source 702 that emits polychromatic (e.g., white) light 703 and an optical detector 710 that can detect light 709 over a wide wavelength range. Mirrors or other reflective surfaces 704, 708 can be provided to direct light 703, 709 to the grating 706 or the detector 710, respectively. In some cases, one or more transmissive surfaces can be provided to direct light to the grating 706 or the detector.
[0041] In some embodiments, as Figure 11 shown, any of the above gratings (e.g., grating 120, 220, 320) can be used as a part 401 of a super - lens 400. For example, as Figure 11 shown, grating 120 includes one or more units 122 with non - aligned meta - atoms 130, 132, 134 and forms a part 401 of the annular ring of the super - lens 400. The structure of grating 120 can be repeated to form the annular - ring part of the super - lens. Thus, in some cases, the super - lens can be rotationally symmetric about its center or radially asymmetric. As Figure 12 shown, the super - lens 400 can be integrated into, for example, a light - emitting system 410 that includes a light source 402 operable to generate a light beam 404 that passes through the super - lens. In such an embodiment, the super - lens 400 can provide, for example, a collimation function for the light beam 404. In other cases, as Figure 13 shown, the super - lens 400 can be integrated into a light - receiver system 420 (e.g., a camera), where the super - lens directs a light beam 422 to, for example, an image sensor 424 or other optical detector.
[0042] Although this specification contains many details, these details should not be regarded as limiting the disclosure or the scope of the claims, but rather as descriptions of features of particular embodiments. Some features described in the context of separate embodiments in this specification can also be combined within the same embodiment. Conversely, the various features described in the context of a single embodiment can also be implemented separately in multiple embodiments or in any suitable sub-combination. Various modifications can be made to the foregoing examples. Accordingly, other embodiments are within the scope of the claims.
Claims
1. A device, comprising: a grating having a first axis oriented in a first direction and a second axis oriented in a second direction different from the first direction, wherein the grating has a larger dimension along the first axis than along the second axis, the grating includes units arranged along the first direction, each unit includes superatoms arranged along the first direction, wherein the superatoms in each specific unit among the units are not aligned with respect to the second direction and are arranged asymmetrically around the first axis of the grating.
2. The device according to claim 1, wherein, each unit has the same superatom arrangement as other units of the grating.
3. The device according to claim 1, wherein, the superatom arrangement in at least one unit is rotated 180° around the central axis of the grating with respect to the superatom arrangement in another unit.
4. The device according to claim 1, wherein, the superatom arrangement in at least one unit is offset along the second direction with respect to the superatom arrangement in another unit.
5. The device according to claim 1, wherein: the superatom arrangement in at least one unit is rotated 180° around the central axis of the grating with respect to the superatom arrangement in another unit; and the superatom arrangement in at least one unit is offset along the second direction with respect to the superatom arrangement in another unit.
6. The device according to any one of claims 1 to 5, wherein, the superatoms in each specific unit among the units have respective sizes, shapes or orientations that are different from the sizes, shapes or orientations of other superatoms in the same unit.
7. The device according to any one of claims 1 to 6, wherein, the corresponding positions of two superatoms in at least one unit partially overlap in the first direction.
8. The device according to any one of claims 1 to 7, wherein, the superatoms in each specific unit of the grating are arranged two-dimensionally.
9. The device according to any one of claims 1 to 8, further comprising: a light source operable to emit light; an optical detector operable to detect light; and at least one reflective or transmissive surface for guiding the light emitted by the light source to the grating or guiding the light from the grating to the optical detector.
10. The device according to any one of claims 1 to 9, wherein, the size of each unit is smaller than the operating wavelength of the grating.
11. The device according to any one of claims 1 to 10, wherein, at least one of the shape, size or position of the superatoms is different between the units.
12. The device according to any one of claims 1 to 11, wherein, the unit sizes are different between the units.
13. The device according to any one of claims 1 to 12, wherein, the grating is part of a superlens.