Design method of metasurface and metasurface

Abstract

The invention provides a metasurface design method and a metasurface, and the method comprises the steps: selecting a plurality of incident angles, carrying out the Bloch boundary scanning of a superstructure unit, and obtaining a period value-nanostructure height number set corresponding to each incident angle from the Bloch boundary scanning result based on a first screening principle; selecting the intersection of the nanostructure heights in all the period value-nanostructure height number sets, and determining the optimal nanostructure height from the intersection based on a second screening principle; based on the optimal nanostructure height, determining period values corresponding to different incident angles; according to the method, the optimal nanostructure height can be determined only by screening the Bloch boundary scanning results corresponding to the multiple incident angles and screening the intersection of the period value-nanostructure height number set, so that the calculation amount of adjusting parameter variables is reduced, and the design process of the metasurface is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of optical lenses, and particularly to a design method for a metasurface and a metasurface. Background Art

[0002] Existing metasurfaces usually rely on a constant period value of the superstructural unit, and the phase modulation mechanism of metasurfaces generally is based on normal incidence or small-angle incidence, with less consideration given to the optical performance under large-angle oblique incidence. However, in fields such as wide-angle imaging, light incident at large angles needs to be considered. Therefore, when designing a metasurface, by changing the structural parameters at different metasurface regions, the metasurface can meet the optical performance under different incident angles. However, the structural parameters include the height and radius of the nanostructure, as well as the period value of the superstructural unit, etc. Changing multiple parameter variables simultaneously will result in an overly large computational amount, making the design process of the metasurface rather cumbersome. Summary of the Invention

[0003] An object of the present invention is to provide a design method for a metasurface applicable to wide-angle imaging scenarios.

[0004] To achieve one of the above-mentioned objects of the present invention, an embodiment of the present invention provides a design method for a metasurface, including:

[0005] Select multiple incident angles, perform a Bloch boundary scan on the superstructural unit, and based on a first screening principle, obtain a period value-nanostructure height number set corresponding to each incident angle from the results of the Bloch boundary scan;

[0006] Select the intersection of the nanostructure heights in all the period value-nanostructure height number sets, and based on a second screening principle, determine the optimal nanostructure height from the aforementioned intersection;

[0007] Based on the optimal nanostructure height, determine the period values corresponding to different incident angles.

[0008] As a further improvement of an embodiment of the present invention, based on the optimal nanostructure height, continue to select multiple incident angles, perform a Bloch boundary scan on the superstructural unit, and based on the first screening principle, after obtaining an incident angle-period value number set from the results of the Bloch boundary scan, determine the period values corresponding to different incident angles from the incident angle-period value number set.

[0009] As a further improvement of an embodiment of the present invention, based on a third screening principle, determine the optimal period values corresponding to different incident angles from the incident angle-period value number set, and establish a correspondence between the incident angles and the optimal period values, so as to obtain the optimal period values corresponding to other unselected incident angles.

[0010] As a further improvement of an embodiment of the present invention, the multiple incident angles include a first incident angle and a second incident angle. A first linear function is established between the incident angle and the optimal period value, so as to obtain the optimal period values corresponding to other angles between the first incident angle and the second incident angle, and / or obtain the optimal period values corresponding to other angles outside the first incident angle and the second incident angle.

[0011] As a further improvement of an embodiment of the present invention, the first screening principle specifically refers to: a phase that satisfies 0-2π coverage and changes smoothly, and a transmittance that is relatively high and relatively stable. The second screening principle specifically refers to: selecting a relatively small aspect ratio of the nanostructure.

[0012] As a further improvement of an embodiment of the present invention, the third screening principle specifically refers to: an inverse relationship between the period value and the incident angle.

[0013] As a further improvement of an embodiment of the present invention, the multiple incident angles include at least three incident angles. Multiple linear functions are established between the incident angle and the optimal period value, so as to obtain the optimal period values corresponding to other angles between adjacent incident angles.

[0014] As a further improvement of an embodiment of the present invention, the multiple incident angles form an arithmetic progression.

[0015] As a further improvement of an embodiment of the present invention, the multiple incident angles include a first incident angle and a second incident angle that increase in sequence. The first incident angle is greater than the minimum incident angle of the metasurface, and the second incident angle is less than the maximum incident angle of the metasurface. The optimal period values corresponding to other angles between the first incident angle and the second incident angle are obtained through the corresponding relationship. The period values corresponding to other incident angles between the minimum incident angle and the first incident angle and / or the period values corresponding to other incident angles between the second incident angle and the maximum incident angle remain unchanged.

[0016] As a further improvement of an embodiment of the present invention, the period value specifically refers to: the radial period and / or the circumferential period of the superstructure unit.

[0017] To achieve the purpose of the above invention, the present invention also provides a metasurface, which is designed by the above design method.

[0018] Compared with the prior art, in the embodiments of the present invention, only the Bloch boundary scanning results corresponding to multiple incident angles need to be screened, and the intersection of the period value-nanostructure height set needs to be screened, and then the optimal nanostructure height can be determined, thereby reducing the computational amount of adjusting parameter variables and simplifying the design process of the metasurface. Description of the Drawings

[0019] Figure 1 is a schematic optical path diagram of a metasurface in an application scenario of the present invention and a top view of the metasurface;

[0020] Figure 2 is a schematic optical path diagram of a metasurface in another application scenario of the present invention and a top view of the metasurface;

[0021] Figure 3 is a schematic optical path diagram of a metasurface in yet another application scenario of the present invention and a top view of the metasurface;

[0022] Figure 4 is a top view of the metasurface in a preferred embodiment of the present invention;

[0023] Figure 5 is a top view of the metasurface in another preferred embodiment of the present invention;

[0024] Figure 6 is Figure 4 and Figure 5 the metasurface efficiency of the metasurface at different incident angles;

[0025] Figure 7 is Figure 1 a schematic optical path diagram at the metasurface in;

[0026] Figure 8 is Figure 7 an embodiment of the cross-sectional view at A in;

[0027] Figure 9 is Figure 7 another embodiment of the cross-sectional view at A in;

[0028] Figure 10 is a schematic flow diagram of the design method of the metasurface in a preferred embodiment of the present invention;

[0029] Figure 11 is a mapping relationship diagram of the period value, the radius of the nanostructure and the transmittance at the same incident angle obtained after performing a Bloch boundary scan on the superstructural unit;

[0030] Figure 12 is a mapping relationship diagram of the period value, the radius of the nanostructure and the phase at the same incident angle obtained after performing a Bloch boundary scan on the superstructural unit;

[0031] Figure 13 is a relative phase span percentage diagram at a certain incident angle during the screening process of the first screening principle;

[0032] Figure 14is the phase average gradient diagram at an incident angle during the screening process according to the first screening principle;

[0033] Figure 15 is the coefficient of variation diagram at an incident angle during the screening process according to the second screening principle;

[0034] Figure 16 is the period value - nanostructure height number set diagram corresponding to an incident angle obtained from the results of scanning the Bloch boundary;

[0035] Figure 17 is the period value - nanostructure height number set diagram corresponding to another incident angle obtained from the results of scanning the Bloch boundary;

[0036] Figure 18 is the period value - nanostructure height number set diagram corresponding to yet another incident angle obtained from the results of scanning the Bloch boundary;

[0037] Figure 19 is Figure 16 、 Figure 17 and Figure 18 is the combined diagram of the period value - nanostructure height number sets in

[0038] Figure 20 is the mapping relationship diagram between the period value, nanostructure radius and transmittance at different incident angles obtained after scanning the Bloch boundary of the superstructure unit;

[0039] Figure 21 is the mapping relationship diagram between the period value, nanostructure radius and phase at different incident angles obtained after scanning the Bloch boundary of the superstructure unit;

[0040] Figure 22 is the incident angle - period value number set diagram obtained from the results of scanning the Bloch boundary;

[0041] Figure 23 is the relationship diagram between the incident angle and the metasurface efficiency obtained after simulating the metasurface. Specific implementation mode

[0042] The present invention will be described in detail below in conjunction with the specific embodiments shown in the drawings. However, these embodiments do not limit the present invention, and any structural, methodical, or functional transformations made by those of ordinary skill in the art based on these embodiments are included within the protection scope of the present invention. It should be understood that the terms such as "having", "including", and "comprising" used herein do not exclude the presence or addition of one or more other elements or their combinations. Furthermore, it should be understood that although the terms first, second, etc. may be used herein to describe various elements or structures, the described objects should not be limited by the above terms. The above terms are only used to distinguish these described objects from each other. For example, the first region may be referred to as the second region, and similarly, the second region may also be referred to as the first region, which does not depart from the protection scope of this application. In the various drawings of the present invention, for the convenience of illustration, the dimensions of certain structures or parts are exaggerated relative to other structures or parts. Therefore, it is only used to illustrate the basic structure of the subject matter of the present invention.

[0043] Referring Figures 1 to 9 as shown, the metasurface 10 provided by the preferred embodiment of the present invention refers to an artificial layered material with a size less than or approximately equal to the wavelength, which can be regarded as the two-dimensional counterpart of metamaterials. The metasurface 10 can achieve the regulation of characteristics such as polarization, phase, amplitude, frequency, and propagation mode of electromagnetic waves through sub-wavelength superstructure units 12 on the surface, and realize characteristics such as beam shaping, beam deflection, superlens, superholography, optical rotation, and anti-reflection and anti-reflection enhancement.

[0044] Specifically, Figure 1 the metasurface 10 in Figure 2 is applied to a collimating lens, Figure 3 the metasurface 10 in

[0045] is applied to a focusing lens,

[0046] the metasurface in

[0047] is applied to a deflecting focusing lens. Figure 1For example, the metasurface 10 is applied to the scene of the collimating lens. According to the reversibility of the optical path, the metasurface 10 is also applicable to other scenes. When the same laser is used to irradiate the metasurface 10, the incident angles of the light irradiated at different locations on the metasurface 10 are different. In 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.

[0048] Furthermore, the center of the first region 101 coincides with the center of the second region 102. In this embodiment, the superstructure units 12 on the supersurface 10 are preferably distributed in a ring shape, and the ring shape can be as follows: Figure 1 and Figure 2 The closed structure in Figure 3 Therefore, the center of each region is at the center of the ring, that is, Figures 1 - 3 Moreover, the center point C and the focus of the metasurface 10 are arranged along the Z-axis direction, for example Figure 1 The laser in the image is irradiated directly at the center point C, the laser and the metasurface 10 are arranged coaxially, and the laser is located in the focal plane of the metasurface 10. Figure 2 and Figure 3 The light passing through the center point C is incident on the CMOS / CCD.

[0049] Mate Reference Figure 4 and Figure 5 As shown, further, the radial period 121 of the superstructure unit 12 in the second area 102 is correspondingly smaller than the radial period 121 of the superstructure unit 12 in the first area 101, and / or the circumferential period 122 of the superstructure unit 12 in the second area 102 is correspondingly smaller than the circumferential period 122 of the superstructure unit 12 in the first area 101.

[0050] In this embodiment, the radial period 121 and the circumferential period 122 of the superstructure unit 12 in the second region 102 are both smaller than the radial period 121 and the circumferential period 122 of the superstructure unit 12 in the first region 101. Alternatively, the radial period 121 of the superstructure unit 12 in the second region 102 is smaller than the radial period 121 of the superstructure unit 12 in the first region 101, and the circumferential period 122 of the superstructure unit 12 in the second region 102 is equal to the circumferential period 122 of the superstructure unit 12 in the first region 101. Alternatively, the circumferential period 122 of the superstructure unit 12 in the second region 102 is smaller than the circumferential period 122 of the superstructure unit 12 in the first region 101, and the radial period 121 of the superstructure unit 12 in the second region 102 is equal to the radial period 121 of the superstructure unit 12 in the first region 101.

[0051] Specifically, different superstructure unit 12 periods are adopted in the first region 101 and the second region 102. The different superstructure unit 12 periods can be differences in the radial period 121 and / or the circumferential period 122, that is, the different superstructure unit 12 periods can be differences in the radial period 121, the circumferential period 122, or both the radial period 121 and the circumferential period 122. The radial period 121 refers to the period value along the radial direction of an imaginary circle formed in the plane of the X-axis and Y-axis with the center C as the center of the circle (such as the direction shown by L1 in Figure 4 and Figure 5 ). Similarly, the circumferential period 122 refers to the period value along the circumferential direction of an imaginary circle formed in the plane of the X-axis and Y-axis with the center C as the center of the circle (such as the direction shown by L2 in Figure 4 and Figure 5 ), or it can be said to be the period value along the central angle direction of the imaginary circle.

[0052] With reference to Figure 7 shown, preferably, the first region 101 is closer to the center C than the second region 102. Taking the metasurface 10 applied to a collimating lens as an Figure 1 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 into the second region 102 is incident at a large angle. The period of the superstructure unit 12 in the second region 102 is set to be smaller than that of 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 large-angle incident light, which 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.

[0053] Preferably, the first region 101 is located at the center C point, and the second region 102 is located at the edge of the metasurface 10 far from the center C point. At this time, taking the metasurface 10 applied to a collimating lens as an example, the incident light of the laser irradiated on 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 irradiated on the second region 102 is large-angle incidence (for example, the incident angle is 45° to 50°).

[0054] Specifically, nanostructures 123 are provided at the center and / or vertex positions of each superstructural unit 12. In this embodiment, the superstructural unit 12 is obtained by dividing the metasurface 10 into structural units centered on each nanostructure 123. The metasurface 10 further includes a substrate 11 connecting the nanostructures 123, and a plurality of nanostructures 123 are arranged on the substrate 11, and the nanostructures 123 in each period form a superstructural unit 12. The superstructural unit 12 is a closely packable pattern, such as a regular quadrilateral, a regular hexagon, a sector, etc. Each period contains one nanostructure 123, and nanostructures 123 can be provided at the vertices and / or centers of the superstructural unit 12. When the superstructural unit 12 is a regular hexagon, at least one nanostructure 123 is provided at each vertex and center position of the regular hexagon. Similarly, the same is true for sectors and squares.

[0055] Further, the nanostructure 123 is configured as a polarization-related structure or a polarization-unrelated structure. In this embodiment, the nanostructure 123 can select a polarization-related structure or a polarization-unrelated structure according to different usage scenarios. Polarization-unrelated structures, such as cylindrical, square-columnar, cross-columnar, round-hole square-columnar, etc. Polarization-related structures, such as elliptical-columnar, rectangular-columnar, hexagonal-columnar, etc.

[0056] Preferably, the nanostructure 123 is configured as cylindrical.

[0057] Among them, the substrate 11 can be made of a light-transmitting or light-impermeable material. When the substrate 11 transmits light, a transmissive metasurface is formed, that is, a transmissive superlens, such as the lens in Figures 1 - 3 . When the substrate 11 is light-impermeable or reflects light, it is a reflective metasurface, that is, a reflective superlens. The materials of the substrate 11 include but are not limited to quartz glass, crystalline and amorphous silicon, alumina, silicon nitride, calcium fluoride, and the materials of the nanostructures 123 include but are not limited to titanium oxide, tantalum oxide, hafnium oxide, silicon nitride, photoresist, quartz glass, alumina, crystalline and amorphous silicon, gallium nitride, germanium crystal, selenium sulfide, selenium sulfide, chalcogenide glass.

[0058] Preferably, after a plurality of nanostructures 123 are arranged on the substrate 11, when viewed from the top view, they are circular, that is, circular in the plane of the X-axis and the Y-axis. At this time, both the first region 101 and the second region 102 are closed rings, and the centers of the first region 101 and the second region 102 coincide with the center C. The first region 101 is located at the center of the circle, and the second region 102 is located at the outer circle.

[0059] Of course, as in Figure 3 , it is also possible that the first region 101 is not located at the center of the circle and the second region 102 is not located at the outer circle.

[0060] Moreover, the multiple nanostructures 123 on the substrate 11 in this manner are centrosymmetric in the plane where the X-axis and the Y-axis are located, so that the metasurface 10 can modulate the light beam in multiple directions, thus being applicable to more scenarios.

[0061] Such as Figure 4 , the present invention provides a top view and a partial enlarged schematic diagram of the metasurface 10 in a preferred embodiment. Compared with the metasurface with a constant period, only the radial period 121 is changed in this embodiment.

[0062] Specifically, the radial period 121 of each superstructure unit 12 decreases in the direction 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., the center C) to the outer circle. In the direction from the center of the circle (i.e., the center C) to the outer circle, the radial periods 121 of all the superstructure units 12 on the metasurface 10 show a decreasing trend, and the circumferential periods 122 of all the superstructure units 12 remain unchanged. It can be seen that the entire metasurface 10 adopts a variable-period scheme. Therefore, compared with the 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 direction of L1 in the figure), which can satisfy better modulation effects on large-angle incident light while having a relatively simple structure and low manufacturing difficulty.

[0063] In addition, in this embodiment, at the edge of the metasurface 10, the centers of adjacent four nanostructures 123 approximately form a rectangle, and as the distance from the center C increases, the aspect ratio of this rectangle is larger.

[0064] In an embodiment not shown, it can also be that in the direction from the center of the circle (i.e., the center C) to the outer circle, the circumferential periods 122 of all the superstructure units 12 on the metasurface 10 show a decreasing trend, and the radial periods 121 of all the superstructure units 12 remain unchanged, which can also satisfy better modulation effects on large-angle incident light.

[0065] Such as Figure 5 , the present invention provides a top view and a partial enlarged schematic diagram of the metasurface 10 in another preferred embodiment. Compared with the above embodiment, both the radial period 121 and the circumferential period 122 are changed in this embodiment.

[0066] Specifically, the radial period 121 and the circumferential period 122 of each superstructural unit 12 decrease in the direction 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 the direction from the center of the circle (i.e., the center C) to the outer circle. In the direction from the center of the circle (i.e., the center C) to the outer circle, the radial period 121 and the circumferential period 122 of all the superstructural units 12 on the metasurface 10 both 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 nanostructures 123 of the metasurface 10 in this embodiment are denser along the radial and circumferential directions of the first region 101, and have a better modulation effect on incident light at large angles.

[0067] In addition, in this embodiment, at the edge of the metasurface 10, the centers of four adjacent nanostructures 123 approximately form a square.

[0068] In the above two embodiments, a variable period is adopted in all regions of the entire metasurface 10. After integrating the improvements of the above two embodiments, the efficiency of the metasurface 10 at different incident angles is finally obtained as Figure 6 . In the figure, the abscissa corresponds to the incident angle, the ordinate corresponds to the metasurface efficiency, and the broken line (Mode A in the figure) drawn with a dotted line is the Figure 5 metasurface with the variable-period scheme of the embodiment, and the broken line (Mode B in the figure) drawn with a dash-dotted line is the Figure 4 metasurface with the variable-period scheme of the embodiment. The solid-line drawn broken line is the metasurface with a fixed period (the period is 425 nm). It can be seen from the figure that in the two embodiments of the metasurface with a variable period provided by the present invention, the efficiency at any incident angle is greater than that of the metasurface with a fixed period, and Figure 5 the corresponding embodiment has a higher efficiency.

[0069] Further, continuing to refer to Figure 7 shown, the metasurface 10 further has a third region 103 for arranging the superstructural units 12. The centers of the first region 101, the third region 103, and the second region 102 coincide with each other, and their outer diameter sizes increase in sequence. In this embodiment, the third region 103 is located between the first region 101 and the second region 102, and the centers of all three coincide with the center C and do not coincide with each other. As Figure 1 , it is preferred that the third region 103 is adjacent to the first region 101 and the second region 102. Therefore, the metasurface 10 arranges the first region 101, the third region 103, and the second region 102 in sequence from the center of the circle (i.e., the center C) to the outer circle.

[0070] Of course, as Figure 2 , it is also possible that the third region 103 is spaced from the first region 101 and the second region 102.

[0071] Alternatively, as Figure 3 , the first region 101, the third region 103, and the second region 102 can also be in the form of non-closed rings.

[0072] Specifically, the radial period 121 and / or the circumferential period 122 of the superstructural unit 12 in the third region 103 decrease in the direction from the first region 101 to the second region 102.

[0073] In this embodiment, when the third region 103 is 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 superstructural unit 12 in the third region 103 decreases in the direction from the center (i.e., the center C) to the outer circle. Therefore, a variable-period scheme is adopted for all the superstructural units 12 in the region between the first region 101 and the second region 102, while a constant-period or variable-period scheme can be adopted for the regions outside the first region 101 and the second region 102, which has a better modulation effect on incident light at different angles between the first region 101 and the second region 102.

[0074] When the third region 103 is spaced from the first region 101 and the second region 102, for example, there is one or more regions between the first region 101 and the second region 102. In the direction from the center (i.e., the center C) to the outer circle, the radial period 121 and / or the circumferential period 122 of the superstructural unit 12 in the third region 103 show a decreasing trend. That is, in the direction from the center (i.e., the center C) to the outer circle, the radial period 121 and / or the circumferential period 122 of the superstructural unit 12 in at least one of the multiple regions between the first region 101 and the second region 102 show a decreasing trend, while the periods of the superstructural units 12 in the other regions of the multiple regions can remain constant.

[0075] In the above two ways, at least part of the regions of the metasurface 10 adopt a variable-period scheme, and the remaining regions can adopt a constant period.

[0076] Of course, in an embodiment not shown, the period (including the radial period 121 and / or the circumferential period 122) of the superstructural unit 12 in the third region 103 can also adopt a constant period.

[0077] Furthermore, the radial period 121 and the circumferential period 122 of the superstructural units 12 in the first region 101 and / or the second region 102 remain unchanged. In this embodiment, the superstructural units 12 in the first region 101 adopt a constant period, and the superstructural units 12 in the second region 102 adopt a variable period. Alternatively, the superstructural units 12 in the first region 101 adopt a variable period, and the superstructural units 12 in the second region 102 adopt a constant period. Or, the superstructural units in both the first region 101 and the second region 102 adopt a constant period.

[0078] Taking the application of the metasurface 10 to a collimating lens as an example, since the incident light from the laser on the first region 101 is normal incidence or small-angle incidence, the use of a variable period for the superstructural units 12 in this region has little effect on the modulation effect. Similarly, the incident light from the laser on the second region 102 is large-angle incidence, and the use of a variable period for the superstructural units 12 in this region has little effect on the modulation effect, and more nanostructures 123 cannot be accommodated at the edge of the second region 102. Therefore, adopting a constant period for the periods (including the radial period 121 and the circumferential period 122) in the first region 101 and / or the second region 102 can reduce the manufacturing difficulty of the metasurface 10 and have little impact on the metasurface efficiency.

[0079] Furthermore, the radial period 121 and / or the circumferential period 122 of the superstructural units 12 in the third region 103 decrease proportionally from the first region 101 to the second region 102. In this embodiment, the periods (including the radial period 121 and / or the circumferential period 122) of the superstructural units 12 in the third region 103 are correspondingly smaller than those of the superstructural units 12 in the first region 101 and correspondingly larger than those of the superstructural units 12 in the second region 102. The periods of the superstructural units 12 in the third region 103 change proportionally, so that it is not necessary to obtain the period values corresponding to all incident angles in the third region 103, which is convenient for the manufacture of the metasurface 10.

[0080] Specifically, by obtaining the incident angles and period values corresponding to the first region 101 and the second region 102 or their average values (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 periods of the superstructural units 12 in the third region 103 and the corresponding incident angles can be obtained by substituting into the first linear function, thereby simplifying the design and manufacturing process of the metasurface 10.

[0081] Of course, in some embodiments, other functions, such as quadratic functions, can also be established according to the incident angles and period values corresponding to the first region 101 and the second region 102.

[0082] Further, the third region 103 has a first region 1031, a second region 1032, and a third region 1033 with successively increasing outer diameter dimensions. In this embodiment, as Figure 1 , the third region 103 is further divided to obtain a first region 1031, a second region 1032, and a third region 1033 with coincident centers. Taking the metasurface 10 applied to a collimating lens as an example, the incident angles of the incident light on the three regions are different. For example, the incident angle on the first region 1031 is between 5° and 15°, the incident angle on the second region 1032 is between 15° and 30°, and the incident angle on the third region 1033 is between 30° and 45°.

[0083] Specifically, the radial period 121 and / or the circumferential period 122 of the superstructural units 12 in the first region 1031 decrease proportionally from the first region 101 to the second region 1032. In this embodiment, by obtaining the incident angles and period values corresponding to the first region 101 and the second region 1032 or their average values (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 superstructural units 12 in the first region 1031 and the corresponding incident angle can be obtained by substituting into the second linear function, so that it is not necessary to obtain the period values corresponding to all incident angles in the first region 1031, facilitating the manufacture of the metasurface 10.

[0084] Specifically, the radial period 121 and / or the circumferential period 122 of the superstructural units 12 in the second region 1032 decrease proportionally from the first region 1031 to the third region 1033. In this embodiment, by obtaining the incident angles and period values corresponding to the first region 1031 and the third region 1033 or their average values (for example, when there are multiple incident angles in the first region 1031 or the third region 1033), a third linear function is established between the incident angle and the period value. The period of the superstructural units 12 in the second region 1032 and the corresponding incident angle can be obtained by substituting into the third linear function, so that it is not necessary to obtain the period values corresponding to all incident angles in the second region 1032, facilitating the manufacture of the metasurface 10.

[0085] Specifically, the radial period 121 and / or the circumferential period 122 of the superstructural units 12 in the third region 1033 decrease proportionally from the second region 1032 to the second area 102. In this embodiment, by obtaining the incident angles and period values corresponding to the second region 1032 and the second area 102 or their average values (for example, when there are multiple incident angles in the second region 1032 or the second area 102), a fourth linear function is established between the incident angle and the period value. The period of the superstructural units 12 in the third region 1033 and the corresponding incident angles can be obtained by substituting into the fourth linear function, thus eliminating the need to obtain the period values corresponding to all incident angles in the third region 1033, which facilitates the fabrication of the metasurface 10.

[0086] Therefore, the third region 103 is further divided into sub-regions, and the linear functions corresponding to each sub-region are calculated, so as to arrange the superstructural units 12 more accurately, making the modulation effect generated by the periods of the superstructural units 12 in the third region 103 better and the overall efficiency of the metasurface 10 higher.

[0087] Of course, in other embodiments, the third region 103 can also be divided into other numbers of sub-regions, such as two sub-regions, four sub-regions, five sub-regions, etc.

[0088] With reference to Figure 8 and Figure 9 shown, further, the metasurface 10 further includes a substrate 11 connecting the nanostructures 123, a filler 14 connecting the nanostructures 123 and the substrate 11, and an antireflection film 13 disposed on the substrate 11 and / or the filler 14. In this embodiment, it is preferred to provide the antireflection film 13 on both the substrate 11 and the filler 14. At this time, one layer of the antireflection film 13 covers the surface of the filler 14 facing away from the substrate 11, and the other layer of the antireflection film 13 covers the surface of the substrate 11 facing away from the nanostructures 123. That is, as in Figure 7 the antireflection film 13 covers both the light-incident side and the light-emitting side of the metasurface 10. By providing the antireflection film 13, the reflectivity can be reduced, thereby increasing the transmittance of the metasurface and further improving the metasurface efficiency.

[0089] 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 (such as trisilicon tetranitride), and the second material layer 132 is preferably silicon oxide (such as silicon dioxide), so as to meet the high-transmittance conditions for large-angle incidence of light beams.

[0090] Specifically, the first material layer 131 or the second material layer 132 is connected to the metasurface 10. In this embodiment, depending on the materials of the substrate 11 and the filler 14, different material layers are selected to be connected to them. For example, as in Figure 8 and Figure 9When both the substrate 11 and the filling 14 are made of silicon oxide, the first material layer 131 (i.e., silicon nitride) is connected to the substrate 11 and the filling 14, and the second material layer 132 is connected to the outside of the first material layer 131. Similarly, when the substrate 11 and the filling 14 are made of other materials, the second material layer 132 can also be connected to the substrate 11 and the filling 14.

[0091] Preferably, as Figure 8 shown, on both sides of the metasurface 10, the antireflection film 13 is composed of one layer of the first material layer 131 and one layer of the 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.

[0092] Preferably, as Figure 9 shown, on both sides of the metasurface 10, the antireflection film 13 is composed of two layers of the first material layer 131 and two layers of the second material layer 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-incident side to the light-emitting side, the thickness of the first material layer 131 is preferably 40 nm ± 5 nm, 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.

[0093] The specific embodiment of the present invention also relates to a design method of the metasurface 10. The composition and function of the metasurface 10 are as described above and will not be elaborated here. Refer to Figure 10 shown, which shows a flowchart of an embodiment of the design method of the metasurface 10. The provided flowchart is only for illustrative purposes and should not be construed as limiting the scope of any solution of the present invention.

[0094] Specifically, the design method of the metasurface 10 includes the following steps:

[0095] In step S10, different phase formulas are selected to determine the phase required by the metasurface 10.

[0096] Specifically, in this embodiment, in step S10, the metasurface 10 can be applied to different scenarios, such as Figure 1 applied to a collimating lens, such as Figure 2 applied to a focusing lens, such as Figure 3 applied to a deflecting focusing lens, and can also be applied to beam shaping, etc. When the metasurface 10 is applied to different scenarios, different phase formulas can be selected to calculate the phase required by the metasurface 10.

[0097] Similarly, for the convenience of description, the following embodiments will all be based on Figure 1For example, when the metasurface 10 is applied to the scenario of a collimating lens, according to the reversibility of the optical path, the metasurface 10 is also applicable to other scenarios. Based on parameters such as the wavelength of the incident light irradiated by the laser on the metasurface 10, the lens radius of the metasurface 10, and the focal length of the metasurface 10, the phase distribution of different regions of the metasurface 10 can be calculated.

[0098] Specifically, according to the wavelength of the incident light, the value range of the structural parameters of the superstructural unit 12 is obtained. Taking the incident light wavelength of 940 nm as an example, it is determined that the period value of the superstructural unit 12 is between 280 and 500 nm, and the height of the nanostructure 123 is between 400 and 800 nm, etc. Taking the field of view angle of 100° as an example, the value range of the incident angle is between 0° and 50°.

[0099] In step S20, multiple incident angles are selected, and the Bloch boundary scanning is performed on the superstructural unit 12. Based on the first screening principle, the period value-nanostructure height number set corresponding to each incident angle is obtained from the results of the Bloch boundary scanning.

[0100] Specifically, in this embodiment, in step S20, multiple incident angles are selected within the value range of the incident angle, that is, at least two incident angles are selected. When the number of incident angles is greater than three, it is preferable that the multiple incident angles form an arithmetic sequence. For example, the incident angles of 0°, 25°, and 50° are selected, that is, the minimum incident angle, the incident angle located in the middle between the maximum incident angle and the minimum incident angle, and the maximum incident angle.

[0101] Specifically, in this embodiment, in step S20, the Bloch boundary scanning is performed on the superstructural unit 12 to obtain the mapping relationships between the period value, the nanostructure radius, and the transmittance, and between the period value, the nanostructure radius, and the phase corresponding to different nanostructure heights at each incident angle. Exemplarily, Figure 11 when the Bloch boundary scanning is performed on the superstructural unit 12, the mapping relationships between the period value, the nanostructure radius, and the transmittance corresponding to different nanostructure heights at the incident angle of 50° are obtained. As Figure 12, perform a Bloch boundary scan on the superstructure unit 12 to obtain the mapping relationship between the period values corresponding to different nanostructure heights and the nanostructure radius and phase when the incident angle is 50°. In the mapping relationship, the radius of the nanostructure (preferably between 40 and 190 nm) generally corresponds to the period value of the superstructure unit 12 (preferably between 280 and 430 nm), that is, after the period value is determined, the radius of the nanostructure is also confirmed, meeting the processing requirements of the nanostructure, and filtering out nanostructures with low transmittance. The height of the nanostructure is preferably between 600 and 700 nm, also considering the processing and transmittance requirements of the nanostructure. Thus, the computational amount in the metasurface design is reduced.

[0102] Of course, in the embodiments not shown, parameters such as the period value, nanostructure height, and nanostructure radius can be any values within the allowable processing range.

[0103] Specifically, the first screening principle specifically refers to: a phase that satisfies 0-2π coverage and varies smoothly, and a transmittance that is relatively high and relatively stable. In this embodiment, the first screening principle should also meet the prerequisite of being within the allowable processing range of the nanostructure, or in other words, considering the prerequisite of facilitating the processing of the nanostructure. The allowable processing range of the nanostructure includes height and diameter. For example, when the radius of the nanostructure is too large, the gap between adjacent nanostructures is too small, and the nanostructure is not easy to process at this time and should be excluded.

[0104] Specifically, in the first screening principle, when screening for a phase that satisfies 0-2π coverage, it can be judged by the Relative phase span percentage (RP). The calculation formula for the relative phase span percentage: RP = Span / 2π×100, where Span is the absolute value of the difference between the maximum phase and the minimum phase in the phase data. As Figure 13 , when the incident angle is 50°, the larger the relative phase span percentage, the larger the phase coverage area, thereby judging the 0-2π coverage degree of the phase.

[0105] Specifically, in the first screening principle, when screening for a phase that varies smoothly, it can be judged by the Phase-averaged gradient (AG). The calculation formula for the phase average gradient: AG = ∑ n |dPhi| / n, where dPhi is the differential value (difference) between adjacent phases, and n is the number of sampled phases. As Figure 14 , the larger the phase average gradient, the larger the change rate of the phase and the less smooth it is, thereby judging the change rate and smoothness of the phase.

[0106] Specifically, in the first screening principle, when screening for a relatively high and relatively stable transmittance, it can be judged by the coefficient of variation (CV). The calculation formula of the coefficient of variation: CV = S / M × 100, where CV is the coefficient of variation, S is the standard deviation, and M is the mean. The coefficient of variation is the ratio of the standard deviation to the mean, indicating that the coefficient of variation in terms of mathematical meaning is directly proportional to the standard deviation and inversely proportional to the mean. The level of the coefficient of variation measures the overall level and stability of the transmittance. The lower the coefficient of variation, the higher the overall mean and relatively stable the transmittance. For example Figure 15 , a smaller coefficient of variation indicates that the data as a whole is relatively stable because the standard deviation is relatively small; a larger coefficient of variation indicates that the data as a whole is less stable. The value of the coefficient of variation measures the size of the standard deviation relative to the mean, thereby judging the level and stability of the transmittance value.

[0107] Further, in step S20, after screening by the first screening principle, a set of period values - nanostructure heights corresponding to each incident angle is obtained from the results of the Bloch boundary scan. For example Figure 16 , each point in the figure represents a set of preferred period values and nanostructure heights (in the case where the incident angle is 50°, for example, when the period value is 305 nm, the nanostructure height can be 680 nm, 690 nm, or 700 nm). Therefore, when the incident angle is 50°, the nanostructure parameters corresponding to the surface 10 exceeding the standard can be selected from the set of period values - nanostructure heights.

[0108] Exemplarily, in the embodiments of the present invention, using the method in step S20, a set of period values - nanostructure heights with an incident angle of 25° is also obtained (such as Figure 17 ), and a set of period values - nanostructure heights with an incident angle of 0° (such as Figure 18 ). Moreover, the more incident angles selected in step S20, the more accurate the finally determined optimal nanostructure height.

[0109] Further, in step S30, the intersection of the nanostructure heights in all sets of period values - nanostructure heights is selected, and based on the second screening principle, the optimal nanostructure height is determined from the aforementioned intersection.

[0110] Specifically, in this embodiment, after combining all sets of period values - nanostructure heights corresponding to all incident angles, a period value - nanostructure height relationship diagram as shown in Figure 19 is obtained. The intersection of the nanostructure heights is selected from this combination, that is, the nanostructure heights that are all present at incident angles of 50°, 25°, and 0°, such as 670 nm, 680 nm, 690 nm, and 700 nm in the relationship diagram.

[0111] Specifically, the second screening principle specifically refers to: selecting a relatively small aspect ratio of the nanostructure. In this embodiment, similarly, the second screening principle should also meet the premise within the allowable processing range of the nanostructure, or rather, considering the premise that is convenient for the processing of the nanostructure. The aspect ratio refers to the ratio of the height of the nanostructure to the diameter of the nanostructure. Compared with the nanostructure with a smaller aspect ratio, the nanostructure with a larger aspect ratio is more slender, which is not conducive to the processing of the nanostructure. Therefore, the metasurface screened by the second screening principle is easier to process.

[0112] Thus, after screening by the second screening principle, the optimal nanostructure height is determined to be 670 nm.

[0113] Further, in step S40, based on the optimal nanostructure height, the period values corresponding to different incident angles are determined. In this embodiment, after setting the optimal nanostructure height as the nanostructure height of the entire metasurface 10, while keeping the nanostructure height unchanged, the metasurface is made to satisfy the optical properties under different incident angles by changing the period values, such as changing the radial period and / or the circumferential period of the superstructural unit.

[0114] Only by screening the Bloch boundary scanning results corresponding to multiple incident angles, and screening the intersection of the period value-nanostructure height number set, can the optimal nanostructure height be determined, thereby reducing the computational amount of adjusting parameter variables and simplifying the design process of the metasurface.

[0115] Further, in step S40, based on the optimal nanostructure height, multiple incident angles are continuously selected, and the superstructural unit is subjected to Bloch boundary scanning. Based on the first screening principle, after obtaining the incident angle-period value number set from the results of the Bloch boundary scanning, the period values corresponding to different incident angles are determined from the incident angle-period value number set.

[0116] Specifically, in this embodiment, in step S40, it is preferred that the multiple incident angles form an arithmetic progression. For example, the incident angles of 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°.

[0117] Specifically, in this embodiment, in step S40, after performing Bloch boundary scanning on the superstructural unit 12, the mapping relationships between the nanostructure radius, period value, and transmittance under different incident angles (such as Figure 20 ), and the mapping relationships between the nanostructure radius, period value, and phase (such as Figure 21 ) are obtained. After screening by the first screening principle, the results are as shown in Figure 22The set of incident angle - period value numbers shown (i.e., the multiple dots in the figure), where there is at least one corresponding period value for each incident angle. One of the period values can be selected as the nanostructure parameter at this incident angle as needed, so that the metasurface 10 meets the transmittance and phase requirements at the above - mentioned multiple incident angles.

[0118] Further, in step S50, based on the third screening principle, the optimal period value corresponding to different incident angles is determined from the set of incident angle - period value numbers, and a correspondence is established between the incident angle and the optimal period value, so as to obtain the optimal period value corresponding to other unselected incident angles.

[0119] Specifically, the third screening principle specifically means that the period value is inversely proportional to the incident angle. In this embodiment, the period value decreases as the incident angle increases, and the period value decreases proportionally as a whole, meeting the requirement that a small period is needed at a large incident angle to improve the efficiency of the metasurface, and it is also convenient for the manufacturing of the metasurface 10.

[0120] In addition, during the screening process by the third screening principle, it is preferred to screen the incident angles from large to small. Considering that the number of period values corresponding to larger incident angles is smaller, the situation of being unable to obtain a period value is avoided. On the premise that the period value is inversely proportional to the incident angle, a relatively small period value is preferred, so as to reduce the difference in period values between adjacent incident angles, which is convenient for the manufacturing of the metasurface 10.

[0121] Specifically, in this embodiment, in step S50, after screening by the third screening principle, the optimal period value corresponding to each incident angle is determined. When selecting incident angles, as many incident angles as possible are selected to obtain the optimal period values corresponding to more incident angles. Using multiple corresponding incident angles and optimal period values, a correspondence, or a functional relationship, is established between the two. In this way, for other incident angles that have not undergone boundary scanning and screening, they can be obtained by directly substituting this correspondence, without having to exhaust all incident angles in step S40, which simplifies the design process.

[0122] Further, in step S50, after determining the optimal period value corresponding to the incident angle, in the metasurface regions corresponding to different incident angles, the super - structure units corresponding to the optimal period values are arranged, and nanostructures with corresponding structure parameters determined by specific scanning conditions are placed in these super - structure units.

[0123] In this embodiment, in step S50, the metasurface region specifically refers to different incident regions, such as the first region, the second region, the third region, or other regions not described above. That is, when the same laser is irradiated on the metasurface 10, the incident angles of the light irradiated on different metasurface regions are different. Moreover, the metasurface region is preferably annular, and the annulus is a circle centered on the center point C. Therefore, the distances between different metasurface regions and the center point C are different, that is, different incident angles correspond to metasurface regions with different outer diameter sizes.

[0124] Specifically, after selecting different incident angles, according to the focal length of the metasurface 10 (or other situations such as the distance from the aperture to the metasurface) and the incident angle, the metasurface region corresponding to different incident angles can be obtained by using the tangent function, that is, the distance between the metasurface region and the center point C is determined, thereby determining the metasurface region with the outer diameter size corresponding to different incident angles.

[0125] Specifically, by arranging the optimal period value in the metasurface region corresponding to the incident angle, the superstructure unit 12 in the metasurface region can better modulate the incident light, and the optimal metasurface efficiency can be obtained. Subsequently, each different metasurface region of the metasurface 10 has the optimal metasurface efficiency.

[0126] The present invention provides a preferred embodiment of the correspondence relationship between the incident angle and the optimal period value. In this embodiment, a first linear function is established to obtain the optimal period value corresponding to other incident angles, thereby simplifying the design process of the metasurface.

[0127] Specifically, in step S40, the multiple incident angles include a first incident angle and a second incident angle. In this embodiment, the first incident angle is configured as a normal incidence or a small-angle incidence (for example, the incident angle is 0° to 5°). The second incident angle is configured as a large-angle incidence (for example, the incident angle is 45° to 50°). Through step S50, the first optimal period value corresponding to the first incident angle and the second optimal period value corresponding to the second incident angle can be obtained.

[0128] In step S50, a first linear function is established between the incident angle and the optimal period value. In this embodiment, according to the fact that the first optimal period value is greater than the second optimal period value, the change relationship between the incident angle and the optimal period value can be obtained, that is, as the incident angle increases, the optimal period value decreases accordingly. By establishing a linear function, that is, a linear function, between the incident angle and the obtained optimal period value, the above change relationship can be satisfied, so as to obtain the optimal period value corresponding to other incident angles, and then meet the optimal metasurface efficiency corresponding to different incident angles.

[0129] Of course, in other embodiments not shown, other functional relationships may also be established between the incident angle and the optimal period value, such as a quadratic function, or other non-linear functions.

[0130] Specifically, in step S50, the slope k1 of the first linear function is k1 = (P1 - P2) / (θ1 - θ2), where θ1 is the first incident angle, θ2 is the second incident angle, P1 is the first optimal period value, and P2 is the second optimal period value. In this embodiment, in step S50, by calculating the ratio of the difference between two optimal period values to the difference between two incident angles, the slope k1 of the first linear function can be obtained. Only by obtaining the optimal period values corresponding to two incident angles can the first linear function be obtained, thereby simplifying the difficulty of obtaining the corresponding relationship.

[0131] In step S50, after establishing the first linear function, the optimal period values corresponding to other angles between the first incident angle and the second incident angle, and / or the optimal period values corresponding to other angles outside the first incident angle and the second incident angle can be obtained.

[0132] In this embodiment, in step S50, when the first incident angle is selected as 0° and the second incident angle is selected as 45°, the optimal period values corresponding to the incident angles between 0° and 45° can be calculated through the first linear function.

[0133] In step S50, the first incident angle can also be other angles between 0° and 5°, such as 3°, and similarly, the second incident angle can also be other angles between 45° and 50°, such as 48°. At this time, the optimal period values corresponding to the incident angles between 3° and 48° can be obtained by using the first linear function, and the optimal period values corresponding to the incident angles between 0° and 3° and between 48° and 60° can also be obtained by using the first linear function.

[0134] The present invention provides another preferred embodiment of the corresponding relationship between the incident angle and the optimal period value. In this embodiment, multiple linear functions are established to respectively obtain the optimal period values corresponding to other incident angles within the corresponding angle intervals, thereby improving the metasurface efficiency of the overall metasurface.

[0135] Specifically, in step S40, the multiple incident angles include at least three incident angles, and multiple linear functions are established between the incident angle and the optimal period value, so as to obtain the optimal period values corresponding to the other angles between adjacent incident angles. In this embodiment, by further dividing the incident angles between the first incident angle and the second incident angle, multiple linear functions with the same or different slopes are obtained, so that within each divided angle region (such as Figure 22The connecting lines of the dots in , that is, the corresponding relationship between the incident angles and the optimal period values within the ranges of 0° - 5°, 5° - 10°, 10° - 15°, 15° - 20°, 20° - 25°, 25° - 30°, 30° - 35°, 35° - 40°, 40° - 45°, 45° - 50°) is more accurate and closer to the optimal metasurface efficiency corresponding to each incident angle, thereby improving the overall metasurface efficiency of the metasurface 10. Among them, the slope calculation formula of multiple linear functions can refer to the calculation method of the first linear function, which will not be elaborated here.

[0136] Preferably, in step S40, the multiple incident angles form an arithmetic sequence. In this embodiment, as Figure 22 In , the multiple incident angles include eleven equally divided angles. While refining the incident angles, the incident angle range is evenly divided, making the error of the calculation results of multiple linear functions smaller and making the optimal period value of the entire metasurface tend to a linear function, which is convenient for manufacturing.

[0137] Of course, in some embodiments not shown, in step S40, more or fewer angular regions can also be divided for the incident angles between the first incident angle and the second incident angle, or the incident angles between the first incident angle and the second incident angle are not evenly divided.

[0138] The present invention provides another preferred implementation manner of the corresponding relationship between the incident angle and the optimal period value. In this embodiment, by controlling the period value within a part of the angular region to remain unchanged, the design process of the metasurface is simplified.

[0139] Specifically, in step S40, the multiple incident angles include a first incident angle and a second incident angle that increase in sequence. The first incident angle is greater than the minimum incident angle of the metasurface, and the second incident angle is less than the maximum incident angle of the metasurface. In this embodiment, the minimum incident angle is 0°, the first incident angle is greater than 0°, and can be configured between 1° and 10°, such as 5°. The maximum incident angle is 50°, and the second incident angle is less than 50°, and can be configured between 40° and 50°, such as 45°.

[0140] Specifically, in step S50, the optimal period values corresponding to the other angles between the first incident angle and the second incident angle are obtained through the corresponding relationship. In this embodiment, in step S50, when the first incident angle is selected as 5° and the second incident angle is selected as 45°, at this time, the incident angles between the first incident angle (i.e., 5°) and the second incident angle (i.e., 45°) can all obtain the corresponding optimal period values through the corresponding relationship (such as the first linear function).

[0141] Specifically, in step S50, the period values corresponding to other incident angles between the minimum incident angle and the first incident angle and / or the period values corresponding to other incident angles between the second incident angle and the maximum incident angle remain unchanged.

[0142] In this embodiment, in step S50, when the first incident angle is selected as 5° and the second incident angle is selected as 45°, the period values corresponding to the incident angles between the minimum incident angle (i.e., 0°) and the first incident angle (i.e., 5°) at this time adopt constant values, and / or the period values corresponding to the incident angles between the second incident angle (i.e., 45°) and the maximum incident angle (i.e., 50°) adopt constant values, which can simplify the design process of the metasurface 10. This method includes: the period values corresponding to the incident angles between 0° and 5° adopt constant values, and the period values corresponding to the incident angles between 45° and 50° do not adopt constant values, but adopt the metasurface unit 12 with variable periods; or, the period values corresponding to the incident angles between 0° and 5° do not adopt constant values, but adopt the metasurface unit 12 with variable periods, and the period values corresponding to the incident angles between 45° and 50° adopt constant values; or, the period values corresponding to the incident angles between 0° and 5° and between 45° and 50° both adopt constant values.

[0143] Considering that when the laser irradiates the metasurface area between the minimum incident angle and the first incident angle, it is normal incidence or small-angle incidence (the incident angle is 0° to 5°), and the use of variable periods for the metasurface unit 12 in this area has little impact on the modulation effect. And when the laser irradiates the metasurface area between the second incident angle and the maximum incident angle, it is large-angle incidence (the incident angle is 45° to 50°), and the use of variable periods for the metasurface unit 12 in this area has little impact on the modulation effect, and it is not easy to manufacture when the period value of the metasurface unit is small. Therefore, the period values corresponding to the incident angles between 0° and 5° adopt constant values, and / or the period values corresponding to the incident angles between 45° and 50° adopt constant values, which can reduce the manufacturing difficulty of the metasurface 10 and have little impact on the metasurface efficiency.

[0144] Specifically, the period value specifically refers to: the radial period and / or the circumferential period of the metasurface unit. In this embodiment, in step S50, in the metasurface areas corresponding to different incident angles, the metasurface units arranged with the corresponding optimal period values are arranged, that is, the metasurface units with different period values are arranged. Here, the different period values can be the differences in the radial period 121 and / or the circumferential period 122, and the other periods of the metasurface unit 12 remain unchanged.

[0145] Specifically, when the metasurface unit 12 of the metasurface 10 is arranged according to Figure 4When arranging, different period values are different for the radial period 121. Similarly, when the superstructural units 12 of the metasurface 10 are arranged according to Figure 5 When arranging, different period values are different for the radial period 121 and the circumferential period 122.

[0146] Of course, in some embodiments not shown, the different period values can also be different for the circumferential period 122, or different for the periods in the X-axis and / or Y-axis directions.

[0147] After simulating the arranged metasurface, the incident angle-metasurface efficiency relationship diagram as shown in Figure 23 is obtained. In the figure, the abscissa corresponds to the incident angle, the ordinate corresponds to the metasurface efficiency, and the broken line (example in the figure) drawn with a dotted line is the metasurface of the variable period scheme of the Figure 22 embodiment, and the broken line drawn with a solid line is the metasurface of the fixed period (period is 425 nm) scheme. It can be seen from the figure that in the embodiment of the metasurface with variable period provided by the present invention, the efficiency at any incident angle is greater than that of the metasurface with a fixed period, and the metasurface efficiency at each part of the metasurface is greater than 80%, improving the overall metasurface efficiency of the metasurface 10.

[0148] It should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not used to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method of a metasurface, characterized in that, Including: Select a plurality of incident angles, perform a Bloch boundary scan on the superstructure unit, and based on the first screening principle, obtain the set of period values - nanostructure height numbers corresponding to each incident angle from the results of the Bloch boundary scan; Select the intersection of the nanostructure heights in all the sets of period values - nanostructure height numbers, and based on the second screening principle, determine the optimal nanostructure height from the aforementioned intersection; Based on the optimal nanostructure height, determine the period values corresponding to different incident angles.

2. The design method of the metasurface according to claim 1, wherein Based on the optimal nanostructure height, continue to select a plurality of incident angles, perform a Bloch boundary scan on the superstructure unit, and based on the first screening principle, after obtaining the set of incident angle - period values from the results of the Bloch boundary scan, determine the period values corresponding to different incident angles from the set of incident angle - period values.

3. The design method of the metasurface according to claim 2, characterized in that Based on the third screening principle, determine the optimal period values corresponding to different incident angles from the set of incident angle - period values, and establish a corresponding relationship between the incident angles and the optimal period values, so as to obtain the optimal period values corresponding to other unselected incident angles.

4. The design method of the metasurface according to claim 3, wherein, The plurality of incident angles include a first incident angle and a second incident angle. Establish a first linear function between the incident angle and the optimal period value, so as to obtain the optimal period values corresponding to other angles between the first incident angle and the second incident angle, and / or obtain the optimal period values corresponding to other angles outside the first incident angle and the second incident angle.

5. The design method of the metasurface according to claim 1, characterized in that, The first screening principle specifically refers to: satisfying the phase that covers 0 - 2π and changes smoothly, and satisfying a relatively high and relatively stable transmittance. The second screening principle specifically refers to: selecting a relatively small nanostructure aspect ratio.

6. The design method of the metasurface according to claim 3, wherein, The third screening principle specifically refers to: the period value is inversely proportional to the incident angle.

7. The design method of the metasurface according to claim 3, wherein The plurality of incident angles include at least three incident angles. Establish a plurality of linear functions between the incident angle and the optimal period value, so as to obtain the optimal period values corresponding to other angles between adjacent incident angles.

8. The design method of the metasurface according to claim 1, characterized in that, The plurality of incident angles form an arithmetic progression.

9. The design method of the metasurface according to claim 3, characterized in that The plurality of incident angles include a first incident angle and a second incident angle that increase in sequence. The first incident angle is greater than the minimum incident angle of the metasurface, and the second incident angle is less than the maximum incident angle of the metasurface. The optimal period values corresponding to other angles between the first incident angle and the second incident angle are obtained through the corresponding relationship, and the period values corresponding to other incident angles between the minimum incident angle and the first incident angle and / or the period values corresponding to other incident angles between the second incident angle and the maximum incident angle remain unchanged.

10. The design method of the metasurface according to claim 1, characterized in that, The period value specifically refers to: the radial period and / or the circumferential period of the superstructure unit.

11. A metasurface, characterized in that, Including a metasurface designed by any of the design methods described in claims 1 - 10 above.

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