Metasurface and near-infrared imaging system having same

Abstract

Provided in the present invention are a metasurface and a near-infrared imaging system having same. The metasurface comprises a plurality of metastructure units arranged in an array, the metasurface having a first region and a second region in which the metastructure units are arranged. The center of the first region and the center of the second region coincide with one another, the first region being closer to the center compared to the second region. The radial periods of the metastructure units in the second region are correspondingly smaller than the radial periods of the metastructure units in the first region, and / or the circumferential periods of the metastructure units in the second region are correspondingly smaller than the circumferential periods of the metastructure units in the first region. The radial periods and / or the circumferential periods of the plurality of metastructure units are arranged in variable periods, so that the metastructure units in the second region have a better modulation effect on incident light at a large angle, are suitable for a large numerical aperture (NA) system and a wide-angle imaging scenario, and may improve the efficiency of the large NA system or the quality of wide-angle imaging.

Description

Metasurface and near-infrared imaging system having the same

[0001] This application is based on the Chinese patent application with application number 202311140514.2 and application date September 5, 2023, and claims the priority of the aforementioned Chinese patent application. The entire content of the above-mentioned patent application is hereby introduced into this application as a reference. Technical Field

[0002] The present invention relates to the technical field of optical lenses, and in particular to a metasurface. Background Art

[0003] The period of the metastructure unit of the metasurface mostly adopts a constant period, and the phase control mechanism is generally based on normal incidence or small-angle incidence. There is less consideration of the optical performance under large-angle oblique incidence. However, in fields such as wide-angle imaging, it is necessary to consider large-angle incident light. At this time, the metasurface will have problems with reduced imaging quality, such as phase mutation, which makes the metasurface unsuitable for scenarios with large-angle incidence. Summary of the Invention

[0004] The object of the present invention is to provide a metasurface suitable for wide-angle imaging scenarios and a near-infrared imaging system having the same.

[0005] To achieve one of the above-mentioned objects of the invention, one embodiment of the present invention provides a metasurface comprising a plurality of array-arranged metastructure units, the metasurface having a first region and a second region in which the superstructure units are arranged, the center of the first region coincides with the center of the second region, the first region is closer to the center than the second region, the radial period of the superstructure units in the second region is correspondingly smaller than the radial period of the superstructure units in the first region, and / or the circumferential period of the superstructure units in the second region is correspondingly smaller than the circumferential period of the superstructure units in the first region.

[0006] As a further improvement of an embodiment of the present invention, the radial period of each superstructure unit decreases from the first region to the second region, and the circumferential period of each superstructure unit is equal.

[0007] As a further improvement of an embodiment of the present invention, the radial period and the circumferential period of each superstructure unit decrease from the first region to the second region.

[0008] As a further improvement of one embodiment of the present invention, the metasurface also has a third area for arranging the superstructure units, the centers of the first area, the third area and the second area coincide with each other, and the outer diameters increase successively, and the radial period and / or circumferential period of the superstructure units in the third area decreases from the first area to the second area.

[0009] As a further improvement of an embodiment of the present invention, the radial period and the circumferential period of the superstructure units in the first region and / or the second region remain unchanged.

[0010] As a further improvement of an embodiment of the present invention, the radial period and / or circumferential period of the superstructure units in the third region decreases proportionally from the first region to the second region.

[0011] As a further improvement of one embodiment of the present invention, the third region includes a first region, a second region, and a third region with outer diameters increasing in sequence, the radial period and / or circumferential period of the superstructure unit in the first region decreases proportionally from the first region to the second region, the radial period and / or circumferential period of the superstructure unit in the second region decreases proportionally from the first region to the third region, and the radial period and / or circumferential period of the superstructure unit in the third region decreases proportionally from the second region to the second region.

[0012] As a further improvement of an embodiment of the present invention, a nanostructure is provided at the center and / or vertex of each superstructure unit, and the nanostructure is configured as a polarization-dependent structure or a polarization-independent structure.

[0013] As a further improvement of one embodiment of the present invention, the metasurface also includes a substrate connecting the nanostructures, a filler connecting the nanostructures and the substrate, and an anti-reflection film provided on the substrate and / or the filler, wherein the anti-reflection film includes a first material layer and a second material layer, and the first material layer or the second material layer is connected to the metasurface.

[0014] In order to achieve the purpose of the above invention, the present invention also provides a near-infrared imaging system, which includes the metasurface as described above.

[0015] Compared with the prior art, in an embodiment of the present invention, the radial period and / or circumferential period of multiple superstructure units are arranged in a variable period, and the period of the superstructure units in the second area is correspondingly smaller than that of the superstructure units in the first area, so that the superstructure units in the second area have a better modulation effect on incident light at a large angle, are suitable for large numerical aperture (NA) systems and wide-angle imaging scenarios, and can improve the efficiency of large NA systems or the quality of wide-angle imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is a schematic diagram of an optical path in an application scenario of the metasurface of the present invention and a top view of the metasurface;

[0017] FIG2 is a schematic diagram of the optical path of another application scenario of the metasurface of the present invention and a top view of the metasurface;

[0018] Figure 3 is a schematic diagram of the optical path of another application scenario of the metasurface of the present invention and a top view of the metasurface;

[0019] FIG4 is a top view of a metasurface in a preferred embodiment of the present invention;

[0020] FIG5 is a top view of a metasurface in another preferred embodiment of the present invention;

[0021] FIG6 shows the metasurface efficiency of the metasurfaces in FIG4 and FIG5 at different incident angles;

[0022] FIG7 is a schematic diagram of the optical path at the metasurface in FIG1 ;

[0023] FIG8 is a cross-sectional view of point A in FIG7 according to an embodiment;

[0024] FIG9 is another embodiment of a cross-sectional view of point A in FIG7;

[0025] FIG10 is the metasurface efficiency of the metasurface in FIG1 at different incident angles;

[0026] FIG11 is a measured image of the white screen focal plane of a fixed-period metasurface module;

[0027] FIG12 is a measured image of the focal plane of a white screen after passing through the variable-period metasurface module of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional changes made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0029] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0030] Furthermore, it should be understood that although the terms "first," "second," etc. may be used herein to describe various elements or structures, these described objects should not be limited by these terms. The above terms are merely used to distinguish these described objects from each other. For example, a first region may be referred to as a second region, and similarly, a second region may be referred to as a first region, without departing from the scope of protection of this application.

[0031] In the various drawings of the present invention, for the sake of convenience, some sizes of structures or parts are exaggerated relative to other structures or parts, and thus, only the basic structure of the subject matter of the present invention is illustrated.

[0032] Referring to Figures 1 through 9 , a preferred embodiment of the present invention provides a metasurface 10, an artificial layered material with a thickness less than a wavelength, which can be considered a two-dimensional counterpart of a metamaterial. Metasurface 10 can manipulate the polarization, phase, amplitude, frequency, and propagation mode of electromagnetic waves through its subwavelength metastructure units 12, enabling properties such as beam shaping, beam deflection, superlensing, superholography, optical rotation, and anti-reflection and anti-reflection.

[0033] Specifically, the metasurface 10 in FIG1 is applied to a collimating lens, the metasurface 10 in FIG2 is applied to a focusing lens, and the metasurface in FIG3 is applied to a deflecting focusing lens.

[0034] Specifically, a metasurface 10 includes a plurality of arrayed metastructure units 12. In this embodiment, the metastructure units 12 are structure units obtained by dividing the metasurface 10.

[0035] Furthermore, the metasurface 10 has a first region 101 and a second region 102 in which the metastructure units 12 are arranged. In this embodiment, the metasurface 10 includes at least two regions. After the metasurface 10 is divided into different regions, the superstructure units 12 can be arranged in each region. The number of superstructure units 12 is obtained based on the arrangement function, and the structural parameters of the superstructure units 12 can be obtained based on the corresponding phase distribution formula. The superstructure units 12 in the same region can have the same period or different periods.

[0036] For ease of description, the following embodiments are all based on Figure 1 as an example, that is, the metasurface 10 is applied to the scene of the collimating lens. Due to the reversibility of the optical path, the metasurface 10 is also applicable when applied to other scenes. When the same laser is used to illuminate the metasurface 10, the incident angles of the light irradiated at different locations on the metasurface 10 are different. Within the same incident plane, the metasurface 10 is divided into regions according to the different incident angles. In addition, each region does not overlap with each other and can be adjacent or spaced apart.

[0037] Furthermore, the center of the first area 101 and the center of the second area 102 coincide with each other. In this embodiment, the superstructure units 12 on the metasurface 10 are preferably distributed in a ring shape, and the ring can be a closed structure as shown in Figures 1 and 2, or a non-closed structure as shown in Figure 3. Therefore, the center of each area is at the center of the ring, that is, point C in Figures 1-3. Moreover, the center point C and the focus of the metasurface 10 are arranged along the Z-axis direction. For example, the laser in Figure 1 is directly incident on the center point C, the laser and the metasurface 10 are arranged on the same optical axis, and the laser is located in the focal plane of the metasurface 10. For another example, the light passing through the center point C in Figures 2 and 3 is directly incident on the CMOS / CCD.

[0038] 4 and 5 , further, the radial period 121 of the superstructure unit 12 in the second region 102 is correspondingly smaller than the radial period 121 of the superstructure unit 12 in the first region 101 , and / or the circumferential period 122 of the superstructure unit 12 in the second region 102 is correspondingly smaller than the circumferential period 122 of the superstructure unit 12 in the first region 101 .

[0039] In this embodiment, the radial period 121 and the circumferential period 122 of the superstructure units 12 in the second region 102 are both smaller than the radial period 121 and the circumferential period 122 of the superstructure units 12 in the first region 101. Alternatively, the radial period 121 of the superstructure units 12 in the second region 102 is smaller than the radial period 121 of the superstructure units 12 in the first region 101, and the circumferential period 122 of the superstructure units 12 in the second region 102 is equal to the circumferential period 122 of the superstructure units 12 in the first region 101. Alternatively, the circumferential period 122 of the superstructure units 12 in the second region 102 is smaller than the circumferential period 122 of the superstructure units 12 in the first region 101, and the radial period 121 of the superstructure units 12 in the second region 102 is equal to the radial period 121 of the superstructure units 12 in the first region 101.

[0040] Specifically, different superstructure unit 12 periods are used in the first region 101 and the second region 102. These different superstructure unit 12 periods may be different in radial period 121 and / or circumferential period 122, that is, different in radial period 121, circumferential period 122, or both. The radial period 121 refers to the period value along the radius of an imaginary circle formed in the plane containing the X-axis and the Y-axis with center C as the center (as indicated by L1 in Figures 4 and 5 ). Similarly, the circumferential period 122 refers to the period value along the circumference of an imaginary circle formed in the plane containing the X-axis and the Y-axis with center C as the center (as indicated by L2 in Figures 4 and 5 ), or in other words, the period value along the central angle of the imaginary circle.

[0041] As shown in conjunction with FIG7 , preferably, the first region 101 is closer to the center C than the second region 102. Taking FIG1 , in which the metasurface 10 is applied to a collimating lens, as an example, the incident angles of the light irradiated by the laser on the first region 101 and the second region 102 are different, that is, the incident angle at the second region 1021 is greater than the incident angle at the first region 101. At this time, relative to the first region 101, the light irradiated on the second region 102 is incident at a large angle. The period of the metastructure unit 12 in the second region 102 is set to be smaller than the superstructure unit 12 in the first region 101, so that the superstructure unit 12 in the second region 102 has a better modulation effect on the incident light at a large angle. This is suitable for large numerical aperture (NA) systems and wide-angle imaging scenarios, and can improve the efficiency of large NA systems or the quality of wide-angle imaging.

[0042] Preferably, the first region 101 is located at the center point C, and the second region 102 is located at the edge of the metasurface 10 away from the center point C. In this case, taking the metasurface 10 as an example of a collimating lens, the incident light of the laser irradiating the first region 101 is normal incidence or small angle incidence (for example, the incident angle is 0° to 5°), and the incident light of the laser irradiating the second region 102 is large angle incidence (for example, the incident angle is 45° to 50°).

[0043] Specifically, a nanostructure 123 is provided at the center and / or vertex of each superstructure unit 12. In this embodiment, the superstructure unit 12 is obtained by dividing the supersurface 10 to obtain a structural unit centered on each nanostructure 123. The supersurface 10 also includes a substrate 11 to which the nanostructures 123 are connected, and a plurality of nanostructures 123 are arranged on the substrate 11, wherein the nanostructures 123 in each period constitute a superstructure unit 12. The superstructure unit 12 is a densely packed figure, for example, a regular quadrilateral, a regular hexagon, a fan, etc., each period contains a nanostructure 123, and the vertex and / or center of the superstructure unit 12 can be provided with a nanostructure 123. In the case where the superstructure unit 12 is a regular hexagon, at least one nanostructure 123 is provided at each vertex and center of the regular hexagon. Similarly, the same is true for the fan-shaped and square cases.

[0044] Furthermore, the nanostructure 123 is configured as a polarization-dependent structure or a polarization-independent structure. In this embodiment, the nanostructure 123 can be configured as either a polarization-dependent structure or a polarization-independent structure depending on the application scenario. Polarization-independent structures include, for example, cylindrical, square, cross-shaped, or square-shaped cylinders with circular holes. Polarization-dependent structures include, for example, elliptical cylinders, rectangular cylinders, and hexagonal prisms.

[0045] The substrate 11 can be made of a translucent or opaque material. When the substrate 11 transmits light, it forms a transmissive metasurface, i.e., a transmissive metalens, such as the lens shown in Figures 1-3. When the substrate 11 is opaque or reflects light, it forms a reflective metasurface, i.e., a reflective metalens. Materials for the substrate 11 include, but are not limited to, quartz glass, crystalline and amorphous silicon, aluminum oxide, silicon nitride, and calcium fluoride. Materials for the nanostructures 123 include, but are not limited to, titanium oxide, tantalum oxide, hafnium oxide, silicon nitride, photoresist, quartz glass, aluminum oxide, crystalline and amorphous silicon, gallium nitride, crystalline germanium, selenium sulfide, selenium sulfide, and chalcogenide glass.

[0046] Preferably, after the multiple nanostructures 123 are arranged on the substrate 11, they are circular when viewed from a top view, that is, they are circular in the plane where the X-axis and the Y-axis are located. At this time, the first area 101 and the second area 102 are both closed circles, and the center of the first area 101 and the center of the second area 102 both coincide with the center C. The first area 101 is located at the center of the circle, and the second area 102 is located at the outer circle.

[0047] Of course, as shown in FIG3 , the first area 101 may not be located at the center of the circle, and the second area 102 may not be located at the outer circle.

[0048] Moreover, in this manner, the multiple nanostructures 123 on the substrate 11 are centrally symmetric within the planes where the X-axis and the Y-axis are located, so that the metasurface 10 can modulate the light beam in multiple directions, making it applicable to more scenarios.

[0049] As shown in Figure 4, the present invention provides a top view and a partially enlarged schematic diagram of a preferred embodiment of a metasurface 10. Compared with a metasurface with a constant period, this embodiment only changes the radial period 121.

[0050] Specifically, the radial period 121 of each superstructure unit 12 decreases from the first region 101 to the second region 102, and the circumferential period 122 of each superstructure unit 12 is equal. In this embodiment, the direction from the first region 101 to the second region 102 refers to the direction from the center of the circle (i.e., center C) to the outer circle. In the direction from the center of the circle (i.e., center C) to the outer circle, the radial period 121 of all superstructure units 12 on the metasurface 10 shows a decreasing trend, and the circumferential period 122 of all superstructure units 12 remains unchanged. It can be seen that the entire metasurface 10 adopts a variable period solution. Therefore, compared to a metasurface with a constant period, the nanostructures 123 of the metasurface 10 in this embodiment are denser along the radial direction of the first region 101 (i.e., the L1 direction in the figure), which satisfies the requirement of having a better modulation effect on incident light at a large angle while having a relatively simple structure and low manufacturing difficulty.

[0051] In addition, in this embodiment, at the edge of the metasurface 10 , the centers of four adjacent nanostructures 123 form a rectangle, and as the distance from the center C increases, the aspect ratio of the rectangle becomes larger.

[0052] In an embodiment not shown, it is also possible that the circumferential period 122 of all superstructure units 12 on the metasurface 10 shows a decreasing trend in the direction from the center of the circle (i.e., the center C) to the outer circle, and the radial period 121 of all superstructure units 12 remains unchanged, which can also meet the requirements of having a better modulation effect for incident light at a large angle.

[0053] As shown in Figure 5 , the present invention provides a top view and a partially enlarged schematic diagram of another preferred embodiment of the metasurface 10. Compared with the above embodiment, this embodiment changes both the radial period 121 and the circumferential period 122.

[0054] Specifically, the radial period 121 and circumferential period 122 of each superstructure unit 12 decrease from the first region 101 to the second region 102. In this embodiment, the direction from the first region 101 to the second region 102 refers to: from the center of the circle (i.e., center C) to the outer circle. From the center of the circle (i.e., center C) to the outer circle, the radial period 121 and circumferential period 122 of all superstructure units 12 on the metasurface 10 show a decreasing trend. It can be seen that the entire metasurface 10 adopts a variable period scheme. Therefore, compared with the metasurface in the above embodiment, the nanostructure 123 of the metasurface 10 in this embodiment is denser in the radial and circumferential directions of the first region 101, and has a better modulation effect on incident light at a large angle.

[0055] In addition, in this embodiment, at the edge of the metasurface 10 , the centers of four adjacent nanostructures 123 form a square.

[0056] In the above two embodiments, variable period is adopted in all areas of the entire metasurface 10. After combining the improvements of the above two embodiments, the efficiency of the metasurface 10 at different incident angles is finally obtained as shown in Figure 6. In the figure, the horizontal axis corresponds to the incident angle, the vertical axis corresponds to the metasurface efficiency, the broken line drawn by the dotted line (Mode A in the figure) is the metasurface of the variable period scheme of the embodiment of Figure 5, the broken line drawn by the dotted line (Mode B in the figure) is the metasurface of the variable period scheme of the embodiment of Figure 4, and the broken line drawn by the solid line is the metasurface of the fixed period (period is 425nm) scheme. It can be seen from the figure that in the two embodiments of the metasurface with variable period provided by the present invention, the efficiency at any incident angle is greater than that of the fixed period metasurface, and the embodiment corresponding to Figure 5 has higher efficiency.

[0057] Furthermore, as shown in FIG7 , the metasurface 10 further includes a third region 103 where the metastructure units 12 are arranged. The centers of the first region 101, the third region 103, and the second region 102 coincide with each other, and the outer diameters increase in sequence. In this embodiment, the third region 103 is located between the first region 101 and the second region 102. The centers of the three regions coincide with the center C, and do not coincide with each other. As shown in FIG1 , the third region 103 is preferably arranged adjacent to the first region 101 and the second region 102. Therefore, the metasurface 10 sequentially arranges the first region 101, the third region 103, and the second region 102 from the center (i.e., the center C) to the outer circle.

[0058] Of course, as shown in FIG. 2 , the third area 103 may be spaced apart from the first area 101 and the second area 102 .

[0059] Alternatively, as shown in FIG3 , the first area 101 , the third area 103 and the second area 102 may all be in the form of an open ring.

[0060] Specifically, the radial period 121 and / or the circumferential period 122 of the superstructure units 12 in the third region 103 decreases from the first region 101 to the second region 102 .

[0061] In this embodiment, when the third region 103 is disposed adjacent to the first region 101 and the second region 102, the period (including the radial period 121 and / or the circumferential period 122) of the superstructure units 12 in the third region 103 decreases from the center of the circle (i.e., the center C) toward the outer circle. Therefore, all superstructure units 12 in the region between the first region 101 and the second region 102 adopt a variable period scheme, while the region outside the first region 101 and the second region 102 can adopt a constant period or a variable period scheme, thereby achieving a better modulation effect for incident light at different angles between the first region 101 and the second region 102.

[0062] When the third region 103 is spaced apart from the first region 101 and the second region 102, for example, one or more regions are spaced between the first region 101 and the second region 102, the radial period 121 and / or circumferential period 122 of the superstructure units 12 in the third region 103 decreases from the center (i.e., center C) to the outer circle. That is, from the center (i.e., center C) to the outer circle, the radial period 121 and / or circumferential period 122 of the superstructure units 12 in at least one of the multiple regions between the first region 101 and the second region 102 decreases, while the period of the superstructure units 12 in the other regions remains constant.

[0063] The above two methods enable at least part of the metasurface 10 to adopt a variable period solution, while the remaining areas can adopt a constant period solution.

[0064] Of course, in an embodiment not shown, the period (including the radial period 121 and / or the circumferential period 122 ) of the superstructure units 12 in the third region 103 may also be a constant period.

[0065] Furthermore, the radial period 121 and circumferential period 122 of the superstructure units 12 in the first region 101 and / or the second region 102 remain unchanged. In this embodiment, the superstructure units 12 in the first region 101 have a constant period, while the superstructure units 12 in the second region 102 have a variable period. Alternatively, the superstructure units 12 in the first region 101 have a variable period, while the superstructure units 12 in the second region 102 have a constant period. Alternatively, the superstructure units in both the first region 101 and the second region 102 have a constant period.

[0066] Taking the application of the metasurface 10 to a collimating lens as an example, since the incident light irradiated by the laser on the first region 101 is normal incidence or small-angle incidence, the use of a variable period for the metastructure units 12 in this region has little effect on the modulation effect. Similarly, the incident light irradiated by the laser on the second region 102 is large-angle incidence, and the use of a variable period for the metastructure units 12 in this region has little effect on the modulation effect, and the edge of the second region 102 cannot accommodate more nanostructures 123. Therefore, using a constant period for the period (including the radial period 121 and the circumferential period 122) within the first region 101 and / or the second region 102 can reduce the manufacturing difficulty of the metasurface 10 and has a minimal impact on the metasurface efficiency.

[0067] Furthermore, the radial period 121 and / or circumferential period 122 of the superstructure units 12 in the third region 103 decreases proportionally from the first region 101 to the second region 102. In this embodiment, the period (including the radial period 121 and / or circumferential period 122) of the superstructure units 12 in the third region 103 is correspondingly smaller than that of the superstructure units 12 in the first region 101 and correspondingly larger than that of the superstructure units 12 in the second region 102. The proportional change in the period of the superstructure units 12 in the third region 103 eliminates the need to obtain period values ​​corresponding to all incident angles in the third region 103, facilitating the manufacture of the metasurface 10.

[0068] Specifically, by obtaining the incident angle and period value corresponding to the first region 101 and the second region 102 or their average value (for example, when there are multiple incident angles in the first region 101 or the second region 102), a first linear function is established between the incident angle and the period value. The period and corresponding incident angle of the superstructure unit 12 in the third region 103 can be obtained by substituting the first linear function, thereby simplifying the design and manufacturing process of the metasurface 10.

[0069] Of course, in some embodiments, other functions, such as a quadratic function, may be established according to the incident angles and period values ​​corresponding to the first region 101 and the second region 102 .

[0070] Furthermore, the third region 103 has a first region 1031, a second region 1032, and a third region 1033, the outer diameters of which increase in sequence. In this embodiment, as shown in FIG1 , the third region 103 is further divided to obtain a first region 1031, a second region 1032, and a third region 1033, the centers of which coincide with each other. Taking the application of the metasurface 10 to a collimating lens as an example, the incident angles of the incident light irradiating the three regions are different. For example, the incident angle irradiating the first region 1031 is between 5° and 15°, the incident angle irradiating the second region 1032 is between 15° and 30°, and the incident angle irradiating the third region 1033 is between 30° and 45°.

[0071] Specifically, the radial period 121 and / or circumferential period 122 of the superstructure unit 12 in the first region 1031 decreases proportionally from the first region 101 to the second region 1032. In this embodiment, by obtaining the incident angle and period value corresponding to the first region 101 and the second region 1032, or their average value (for example, when there are multiple incident angles in the first region 101 or the second region 1032), a second linear function is established between the incident angle and the period value. The period of the superstructure unit 12 in the first region 1031 and the corresponding incident angle can be obtained by substituting the second linear function into the second linear function. This eliminates the need to obtain the period values ​​corresponding to all incident angles in the first region 1031, thereby facilitating the manufacture of the metasurface 10.

[0072] Specifically, the radial period 121 and / or circumferential period 122 of the superstructure unit 12 in the second zone 1032 decreases proportionally from the first zone 1031 to the third zone 1033. In this embodiment, by obtaining the incident angle and period value corresponding to the first zone 1031 and the third zone 1033, or their average value (for example, when there are multiple incident angles in the first zone 1031 or the third zone 1033), a third linear function is established between the incident angle and the period value. The period of the superstructure unit 12 in the second zone 1032 and the corresponding incident angle can be obtained by substituting the third linear function into the third linear function. This eliminates the need to obtain the period values ​​corresponding to all incident angles in the second zone 1032, thereby facilitating the manufacture of the metasurface 10.

[0073] Specifically, the radial period 121 and / or circumferential period 122 of the superstructure unit 12 in the third zone 1033 decreases proportionally from the second zone 1032 to the second region 102. In this embodiment, by obtaining the incident angle and period value corresponding to the second zone 1032 and the second region 102, or their average value (for example, when there are multiple incident angles in the second zone 1032 or the second region 102), a fourth linear function is established between the incident angle and the period value. The period of the superstructure unit 12 in the third zone 1033 and the corresponding incident angle can be obtained by substituting the fourth linear function into the fourth linear function. This eliminates the need to obtain the period values ​​corresponding to all incident angles in the third zone 1033, thereby facilitating the manufacture of the metasurface 10.

[0074] Therefore, the third region 103 is further divided into regions, and the linear functions corresponding to each region are calculated, so as to more accurately arrange the superstructure units 12, so that the modulation effect generated by the period of the superstructure units 12 in the third region 103 is better, and the overall efficiency of the metasurface 10 is higher.

[0075] Of course, in other embodiments, the third area 103 may be divided into other numbers of zones, such as two zones, four zones, five zones, etc.

[0076] As shown in Figures 8 and 9, the metasurface 10 further includes a substrate 11 connecting the nanostructure 123, a filler 14 connecting the nanostructure 123 and the substrate 11, and an anti-reflection film 13 provided on the substrate 11 and / or the filler 14. In this embodiment, it is preferred that an anti-reflection film 13 is provided on both the substrate 11 and the filler 14. At this time, one layer of anti-reflection film 13 covers the surface of the filler 14 on the side away from the substrate 11, and another layer of anti-reflection film 13 covers the surface of the substrate 11 on the side away from the nanostructure 123. That is, as shown in Figure 7, the light incident side and the light emitting side of the metasurface 10 are covered with an anti-reflection film 13. By providing the anti-reflection film 13, the reflectivity can be reduced, thereby improving the transmittance of the metasurface, and further improving the efficiency of the metasurface.

[0077] Specifically, the antireflection film 13 includes a first material layer 131 and a second material layer 132. In this embodiment, the first material layer 131 is preferably silicon nitride, and the second material layer 132 is preferably silicon oxide, so as to meet the high transmittance condition when the light beam is incident at a large angle.

[0078] Specifically, the first material layer 131 or the second material layer 132 is connected to the metasurface 10. In this embodiment, different material layers are selected to connect the substrate 11 and the filler 14 based on their different materials. For example, as shown in Figures 8 and 9, when both the substrate 11 and the filler 14 are made of silicon oxide, the first material layer 131 (i.e., silicon nitride) is connected to the substrate 11 and the filler 14, and the second material layer 132 is connected to the outer side of the first material layer 131. Similarly, when the substrate 11 and the filler 14 are made of other materials, the second material layer 132 can also be connected to the substrate 11 and the filler 14.

[0079] Preferably, as shown in FIG8 , the antireflection coatings 13 on both sides of the metasurface 10 each use a first material layer 131 and a second material layer 132. When the wavelength of the incident light is 940 nm, the thickness of the first material layer 131 is preferably 50 nm ± 5 nm, and the thickness of the second material layer 132 is preferably 215 nm ± 5 nm, so as to obtain the optimal metasurface efficiency.

[0080] Preferably, as shown in FIG9 , the antireflection film 13 on both sides of the metasurface 10 uses two first material layers 131 and two second material layers 132. When the wavelength of the incident light is 940 nm, on the light-emitting side of the metasurface 10, in the direction from the light-entering side to the light-emitting side, the thickness of the first material layer 131 is preferably 40 nm ± 5 nm, and the thickness of the second material layer 132 is preferably 55 nm ± 5 nm. The thickness of the first material layer 131 is preferably 380 nm ± 5 nm, and the thickness of the second material layer 132 is preferably 165 nm ± 5 nm, so as to obtain the optimal metasurface efficiency.

[0081] After summarizing the improvements of the above embodiments, the efficiency of the metasurface 10 at different incident angles is finally obtained, as shown in Figure 10. In the figure, the horizontal axis corresponds to the incident angle, and the vertical axis corresponds to the metasurface efficiency. The dotted line represents the preferred metasurface with a variable period solution, and the solid line represents the metasurface with a fixed period solution (a period of 425nm). As can be seen from the figure, the efficiency of the metasurface with a variable period provided by the present invention is greater than that of the metasurface with a fixed period at any incident angle.

[0082] From FIG11 and FIG12 , it can be seen that after focusing through the variable-period metasurface of the present invention, the uniformity and efficiency of different fields of view are greatly improved, the sudden changes in light intensity are reduced, and the practicality is greatly increased.

[0083] According to another aspect of the present invention, a near-infrared imaging system is provided. The near-infrared imaging system is provided with a metasurface 10 according to the present invention. The metasurface 10 is preferably a focusing lens.

[0084] Specifically, the near-infrared imaging system also includes a lens barrel, an optical detector module, and an optical narrowband filter. During use, light reflected or scattered by the object being imaged is focused by the metasurface 10. After light of other wavelengths is filtered out by the optical narrowband filter, it is collected by the optical detector module and imaged onto the photosensitive surface of the optical detector module. The photosensitive surface absorbs the near-infrared light from the object being imaged and converts it into an electrical image signal for output.

[0085] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0086] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A metasurface comprising a plurality of array-arranged metastructure units, characterized in that: The metasurface has a first area and a second area where superstructure units are arranged, the center of the first area coincides with the center of the second area, the first area is closer to the center than the second area, the radial period of the superstructure units in the second area is correspondingly smaller than the radial period of the superstructure units in the first area, and / or the circumferential period of the superstructure units in the second area is correspondingly smaller than the circumferential period of the superstructure units in the first area.

2. The supersurface according to claim 1, characterized in that The radial period of each superstructure unit decreases from the first region to the second region, and the circumferential period of each superstructure unit is equal.

3. The supersurface according to claim 1, characterized in that The radial period and the circumferential period of each superstructure unit decrease from the first region to the second region.

4. The supersurface according to claim 1, characterized in that The metasurface also has a third area where the superstructure units are arranged, the centers of the first area, the third area and the second area coincide with each other, and the outer diameters increase successively, and the radial period and / or circumferential period of the superstructure units in the third area decreases from the first area to the second area.

5. The supersurface according to claim 4, characterized in that The radial period and the circumferential period of the superstructure units in the first region and / or the second region remain unchanged.

6. The supersurface according to claim 4, characterized in that The radial period and / or circumferential period of the superstructure units in the third region decreases proportionally from the first region to the second region.

7. The supersurface according to claim 4, characterized in that The third region comprises a first region, a second region and a third region with outer diameters increasing in sequence, the radial period and / or circumferential period of the superstructure unit in the first region decreases proportionally from the first region to the second region, the radial period and / or circumferential period of the superstructure unit in the second region decreases proportionally from the first region to the third region, and the radial period and / or circumferential period of the superstructure unit in the third region decreases proportionally from the second region to the second region.

8. The supersurface according to claim 1, characterized in that A nanostructure is disposed at the center and / or a vertex of each superstructure unit, and the nanostructure is configured as a polarization-dependent structure or a polarization-independent structure.

9. The supersurface according to claim 8, characterized in that The metasurface also includes a substrate connecting the nanostructures, a filler connecting the nanostructures and the substrate, and an anti-reflection film arranged on the substrate and / or the filler, wherein the anti-reflection film includes a first material layer and a second material layer, and the first material layer or the second material layer is connected to the metasurface.

10. A near-infrared imaging system, characterized in that: Including a super surface as described in any one of claims 1-9.

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