Optical element design method and optical element

Abstract

The invention provides a design method of an optical element and the optical element, the optical element comprises a super-structure grating for deflecting incident light, the design method comprises the following steps: obtaining the period of a grating unit, and determining the number and period of nano structures in the grating unit; bloch boundary scanning is carried out on the nanostructures, nanostructure feature sizes close to working wave band phase requirements are screened out from scanning results, and the nanostructures with the corresponding feature sizes are arranged in the grating units; after the grating units are periodically arranged, a super-structure grating is obtained; according to the technical scheme of the invention, the nanostructures arranged in the grating units are screened, so that the screened nanostructures basically meet the phase requirements of all wavelengths in the working wave band, and therefore, when the optical element realizes abnormal deflection by using the super-structure grating, the influence of chromatic aberration can be reduced, and the modulation effect of the optical element is ensured.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a design method of an optical element and an optical element. Background Art

[0002] As a two-dimensional metamaterial, metasurfaces have made important progress in anomalous deflection, superlens imaging, holographic imaging, etc. In the prior art, when optical elements use metasurfaces to achieve anomalous deflection, they will be affected by chromatic aberration, that is, there is a deviation in the deflection angle of incident light of different wavelengths after modulation, thereby affecting the modulation effect of the optical element. Summary of the invention

[0003] The object of the present invention is to provide a design method of an optical element and an optical element which ensures a modulation effect.

[0004] To achieve one of the above-mentioned objects of the invention, an embodiment of the present invention provides a design method of an optical element, wherein the optical element includes a metagrating for deflecting incident light, and the design method includes:

[0005] Obtaining the period of the grating unit, and determining the number and period of the nanostructures in the grating unit;

[0006] Performing B l och boundary scanning on the nanostructure, selecting the nanostructure characteristic size close to the phase requirement of the working band from the scanning results, and arranging the nanostructure with the corresponding characteristic size in the grating unit;

[0007] After arranging the grating units periodically, a metagrating is obtained.

[0008] As a further improvement of an embodiment of the present invention, the characteristic size of the nanostructure close to the phase requirement of the working band is selected from the scanning results, specifically:

[0009] The ideal phase of each nanostructure in the grating unit is obtained, and the characteristic size of the nanostructure corresponding to each ideal phase is screened out from the scanning results.

[0010] As a further improvement of an embodiment of the present invention, the difference between the phase value of the screened nanostructure in the working band and the ideal phase is the smallest.

[0011] As a further improvement of an embodiment of the present invention, the ideal phase of each nanostructure is determined based on the number of nanostructures in the grating unit.

[0012] As a further improvement of an embodiment of the present invention, the number of the nanostructures is determined based on the shapes of the nanostructures.

[0013] As a further improvement of an embodiment of the present invention, after selecting a preset nanostructure height, a B l och boundary scan is performed on the nanostructure.

[0014] As a further improvement of an embodiment of the present invention, a preset wavelength of incident light is selected from the working band, and the period of the grating unit is determined according to the incident angle and the exit angle required by the metagrating.

[0015] As a further improvement of an embodiment of the present invention, the central wavelength of the working band is selected as the preset wavelength of the incident light.

[0016] As a further improvement of an embodiment of the present invention, the sum of the exit angle and the incident angle of the metagrating is 90°.

[0017] As a further improvement of an embodiment of the present invention, the cross section of the nanostructure is symmetrical with respect to the X-axis and the Y-axis.

[0018] As a further improvement of one embodiment of the present invention, the optical element further includes a multilayer film structure for reflecting incident light, and the metagrating is configured to reflect incident light in a working band.

[0019] As a further improvement of an embodiment of the present invention, the design method further includes:

[0020] The theoretical film thickness of different film materials is obtained, and the different film materials are arranged cyclically, and a multilayer film structure is obtained by adjusting the number of cycles and / or the film thickness coefficient.

[0021] As a further improvement of an embodiment of the present invention, the theoretical film thickness of each film layer material is determined based on the incident light wavelength, incident angle and film layer material of the multilayer film structure.

[0022] As a further improvement of one embodiment of the present invention, after the design of the multilayer film structure is completed, the metagrating is designed.

[0023] As a further improvement of an embodiment of the present invention, the multilayer film structure is composed of different film layer materials arranged in a cyclic manner, or the multilayer film structure is composed of different nanostructure layers arranged in a cyclic manner.

[0024] In order to achieve one of the purposes of the above invention, the present invention further provides an optical element, which is designed by any of the above design methods.

[0025] Compared with the prior art, in an embodiment of the present invention, the nanostructures arranged in the grating unit are screened so that the screened nanostructures basically meet the phase requirements of all wavelengths in the working band. Therefore, when the optical element uses the metagrating to achieve abnormal deflection, the influence of chromatic aberration can be reduced, thereby ensuring the modulation effect of the optical element. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the optical path of an optical element in a preferred embodiment of the present invention;

[0027] Figure 2 is a cross-sectional view of a top view of a grating unit in a metagrating;

[0028] Figure 3 It is a schematic diagram of the light path when the optical element is applied to a prism;

[0029] Figure 4 is a schematic flow chart of a design method of a metagrating in a preferred embodiment of the present invention;

[0030] Figure 5 is a graph showing the relationship between the incident light wavelength, the nanostructure radius and the reflection efficiency obtained after performing Bloch boundary scanning on the nanostructure;

[0031] Figure 6 is a graph showing the relationship between the incident light wavelength, the nanostructure radius and the phase obtained after performing Bloch boundary scanning on the nanostructure;

[0032] Figure 7 is a cross-sectional view of a top view of a grating unit in a metagrating in a preferred embodiment of the present invention;

[0033] Figure 8 is a cross-sectional view of a top view of a metagrating in a preferred embodiment of the present invention;

[0034] Fig. 9 is the phase diagram of the characteristic size of the screened nanostructure under multiple incident light wavelengths;

[0035] Fig.10 is a test spectrum diagram of a multilayer film structure in one embodiment of the present invention;

[0036] Fig.11 is a test spectrum diagram of a multilayer film structure in another embodiment of the present invention;

[0037] Fig.12 It is a test spectrum diagram of the multilayer film structure in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below in conjunction with 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 a person skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0039] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0040] In various drawings of the present invention, for the convenience of illustration, 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.

[0041] The optical element provided by the preferred embodiment of the present invention can be used for imaging of a lens, such as a periscope lens of a mobile phone, and can reduce the volume of the optical element by using a meta-grating to achieve abnormal deflection (i.e., the incident angle is not equal to the exit angle).

[0042] Mate Reference Figure 1 As shown, specifically, the optical element includes a metagrating 10 for deflecting incident light. In this embodiment, the metagrating is a metasurface, which refers to an artificial layered material with a thickness less than the wavelength, and can be regarded as the two-dimensional counterpart of the metamaterial. The metasurface can achieve the regulation of the polarization, phase, amplitude, frequency, propagation mode and other characteristics of the electromagnetic wave through the sub-wavelength nanostructure of the surface, and realize the characteristics of beam shaping, beam deflection, super lens, super holography, optical rotation, anti-reflection and anti-reflection.

[0043] Specifically, the metasurface (e.g., a metagrating) includes a plurality of array-arranged superstructure units, and the superstructure unit is a structural unit obtained by dividing the metasurface. A nanostructure 101 is provided at the center and / or vertex position of each superstructure unit. The superstructure unit is obtained by dividing the metasurface to obtain a structural unit centered on each nanostructure 101. The nanostructures 101 in each period constitute a superstructure unit. The superstructure unit is a densely packed figure, such as a regular quadrilateral, a regular hexagon, a fan, etc., each period contains a nanostructure 101, and the vertex and / or center of the superstructure unit can be provided with a nanostructure 101. In the case where the superstructure unit is a regular hexagon, at least one nanostructure 101 is provided at each vertex and center position of the regular hexagon. Similarly, the same is true for the fan-shaped and square cases.

[0044] Exemplarily, the nanostructure 101 is configured as a polarization-dependent structure or a polarization-independent structure. The nanostructure 101 can select a polarization-dependent structure or a polarization-independent structure according to different usage scenarios. Polarization-independent structures include, for example, cylindrical, square cylindrical, cross cylindrical, square cylindrical with round holes, etc. Polarization-dependent structures include, for example, elliptical cylindrical, rectangular cylindrical, hexagonal prism, etc.

[0045] Specifically, the metasurface also includes a protective layer 103 covering the nanostructure 101. The material of the protective layer 103 can be silicon dioxide, SU-8 (a negative, near-ultraviolet resistant and thermosetting epoxy resin material), glue, polymer, etc., or a temperature-controlled or electrically-controlled refractive index variable material, or air (i.e., no protective layer 103 is set).

[0046] Specifically, the metagrating is composed of a plurality of grating units, and the plurality of grating units are arranged periodically. Figure 2 , each grating unit has a plurality of nanostructures 101. Therefore, the period of the grating unit (e.g., the period along the X-axis direction) is equal to the sum of the periods of all the nanostructures 101 in the grating unit (e.g., the period along the X-axis direction), that is, the period of the grating unit is equal to n×P, where n is the number of nanostructures 101 in the grating unit, and P is the period of the nanostructures 101.

[0047] Exemplarily, the cross section of the nanostructure 101 is symmetrical with respect to the X-axis and the Y-axis. In this embodiment, in order to simultaneously satisfy the phase consistency of the nanostructure 101 under any polarization, for example, under X polarization and Y polarization, the cross section of the nanostructure 101 can be selected to be symmetrical with respect to the X-axis and the Y-axis, such as Figure 2 The cross section of the nanostructure 101 is circular, cross-shaped, ring-shaped, square-shaped, or I-shaped.

[0048] Preferably, the cross section of the nanostructure 101 is symmetrical with respect to the X-axis and the Y-axis, and the cross section of the nanostructure 101 is a centrally symmetrical figure, such as Figure 2 The cross section of the nanostructure 101 is circular, cross-shaped, ring-shaped, or square-shaped.

[0049] In some embodiments, the metagrating 10 is configured to reflect incident light in the working band. In this embodiment, the metagrating 10 is configured as a reflective metasurface, and the emission angle is the reflection angle.

[0050] Of course, in some other embodiments, the metagrating 10 can also be configured as a transmissive metasurface.

[0051] In some embodiments, the sum of the exit angle b and the incident angle a of the metagrating 10 is 90°. Figure 3The optical element is configured as a reflective prism, and the sum of the optical element's exit angle b and incident angle a is 90°, so that it can be applied to a periscope optical system. The cross section of the optical element is an unequal right triangle, including two right-angled sides and a hypotenuse. The metagrating 10 is disposed on the hypotenuse as a metasurface, which can save the volume of the optical element compared to a conventional prism with an equilateral right triangle cross section.

[0052] Exemplarily, the incident angle a of the optical element (ie, the metagrating 10) is 30°, and the exit angle b of the optical element (ie, the metagrating 10) is 60°.

[0053] Furthermore, the optical element further includes a multilayer film structure 20 for reflecting incident light. In this embodiment, the multilayer film structure 20 can enable the optical element to reflect incident light in the working band. Compared with traditional metal reflectors, the multilayer film structure 20 can reduce reflection loss.

[0054] Exemplarily, the optical element further includes a substrate 102, wherein the substrate 102, the multilayer film structure 20, and the meta-grating 10 are arranged in sequence. The material of the multilayer film structure 20 includes but is not limited to silicon dioxide, MgF 2 、Si 3 N 4 、Si、TiO 2 The material of the substrate 102 can be silicon dioxide, silicon nitride, SU-8, glue, etc., depending on the working band. The substrate 102 is used to carry the multilayer film structure 20 and the meta-grating 10.

[0055] Of course, the film material constituting the multilayer film structure 20 can also be a phase change material or any material with adjustable refractive index. The change of the refractive index can change the central wavelength, so that the multilayer film structure 20 can be dynamically adjustable.

[0056] In some embodiments, the multilayer film structure 20 is formed by cyclically arranging different film layer materials. In this embodiment, the multilayer film structure 20 can be realized by a conventional coating method, that is, different film layer materials (such as high refractive index materials and low refractive index materials) are selected and cyclically coated in sequence.

[0057] In other embodiments, the multilayer film structure 20 is composed of different nanostructured layers arranged in a row. In this embodiment, the multilayer film structure 20 can be realized by making multiple nanostructured layers (ie, supersurfaces), that is, making multiple supersurfaces in sequence.

[0058] It should be noted that the incident angle a and the exit angle b (or reflection angle) described in this article can be the angles of the optical element, the metagrating or the multilayer film structure, and the angles of the three are the same.

[0059] The specific implementation of the present invention further relates to a design method of an optical element. The structure and function of the optical element are as described above and will not be repeated here.

[0060] Specific, with reference Figure 4 As shown, the design method of the metagrating includes:

[0061] The period of the grating unit is obtained, and the number and period of the nanostructures 101 in the grating unit are determined. In this embodiment, since the period of the grating unit is equal to the sum of the periods of all the nanostructures 101 in the grating unit, that is, equal to n (the number of nanostructures 101 in the grating unit) × P (the period of the nanostructures 101 in the grating unit). Therefore, after obtaining the period of the grating unit, the number of nanostructures 101 in the grating unit and the period of the nanostructures 101 can be determined by using the relationship between the number of nanostructures 101 in the grating unit (i.e., n) and the period of the nanostructures 101 (i.e., P).

[0062] The nanostructure 101 is subjected to a B l och boundary scan, and the characteristic size of the nanostructure 101 close to the phase requirement of the working band is screened out from the scanning result, and the nanostructure 101 with the corresponding characteristic size is arranged in the grating unit.

[0063] In this embodiment, after performing B l och boundary scanning on the nanostructure 101, the relationship between the incident light wavelength, the characteristic size of the nanostructure 101 (such as the radius of the cylinder) and the reflectivity is obtained (such as Figure 5 ), and obtain the relationship between the incident light wavelength, the characteristic size of the nanostructure 101 (such as the radius of the cylinder) and the phase (such as Figure 6 ).

[0064] When screening the scanning results, if the nanostructures in the grating unit are arranged according to a phase gradient of 0-2π, the emission angle b (eg, reflection angle) required by the optical element (ie, the metagrating 10) can be obtained.

[0065] It should be noted that when screening the scanning results, the characteristic size of the nanostructure 101 equal to the phase requirement of the working band is preferentially screened out. When it is impossible to screen out the equal situation (for example, the nanostructure 101 is a cylinder), the one closest to the phase requirement of the working band can be screened out, that is, the phase difference value is the smallest.

[0066] The characteristic size of the nanostructure 101 refers to a size that can change the phase of the nanostructure 101. For example, when the nanostructure 101 is a cylinder, the characteristic size of the nanostructure 101 may be the radius of the cylinder.

[0067] For example, the following description is based on the case where the nanostructure 101 is a cylinder. In this case, the characteristic dimension of the nanostructure 101 is the radius of the cylinder.

[0068] like Figure 7 , after the nanostructures 101 of corresponding characteristic sizes are arranged in the grating unit, the grating unit is formed.

[0069] like Figure 8 After the grating units are arranged periodically, a metagrating 10 is obtained.

[0070] The nanostructures 101 arranged in the grating unit are screened so that the screened nanostructures 101 basically meet or are close to the phase requirements of all wavelengths in the working band. Therefore, when the optical element uses the metagrating 10 to achieve abnormal deflection, the influence of chromatic aberration can be reduced, thereby ensuring the modulation effect of the optical element.

[0071] Moreover, since the characteristic size of the selected nanostructure 101 meets or is close to the phase requirement of all wavelengths of light in the working band (such as the visible light band), the bandwidth of the working band of the metagrating 10 is increased, and broadband abnormal deflection is achieved.

[0072] In some embodiments, since the metagrating is configured as a reflective metasurface, Figure 6 Before selecting the nanostructure 101 characteristic size that meets the phase requirements, you can first Figure 5 The characteristic size of the nanostructure 101 with higher reflection efficiency is screened out, thereby improving the reflection efficiency of the metagrating.

[0073] Specifically, the characteristic size of the nanostructure 101 close to the phase requirement of the working band is selected from the scanning results, specifically:

[0074] The ideal phase of each nanostructure 101 in the grating unit is obtained, and the characteristic size of the nanostructure 101 corresponding to each ideal phase is screened out from the scanning results. In this embodiment, according to the different ideal phases of each nanostructure 101 in the grating unit, the characteristic size of the nanostructure 101 corresponding to the ideal phase is screened out, so as to ensure that the grating unit obtained by combining multiple nanostructures 101 can meet the phase requirements, that is, meet the phase requirements of 0-2π. In addition, compared with the method of "screening out the phase requirements that meet the grating unit", the phase of each nanostructure 101 in the grating unit is screened separately, which can increase the difficulty of screening, improve the accuracy of the screening results, better eliminate chromatic aberration, and increase the bandwidth of the working band.

[0075] Specifically, the difference between the phase value of the screened nanostructure 101 in the working band and the ideal phase is the smallest. In this embodiment, when the scanning results are screened, the difference between the phase value of each characteristic dimension of the nanostructure 101 in the working band and the ideal phase is compared, and the characteristic dimension of the nanostructure 101 with the smallest difference is the final screening result. Fig. 9 The characteristic size of the nanostructure 101 finally selected (for example, the second nanostructure along the X-axis in the figure, whose ideal phase is 1 / 5*2π) is close to the ideal phase at different wavelengths, and has only small fluctuations, that is, it is close to the ideal phase.

[0076] It can be seen that even if the characteristic size of the screened nanostructure 101 cannot meet the ideal phase at a part of the wavelengths (a part of the wavelengths within the working band), it can also ensure that the phase value of the characteristic size of the screened nanostructure 101 at all wavelengths (within the working band) is closer to the ideal phase, thereby ensuring that the actual emission angle of all wavelengths (within the working band) is closer to the emission angle required by the optical element, reducing the influence of dispersion and increasing the bandwidth of the working band.

[0077] Specifically, based on the number of nanostructures 101 in the grating unit, the ideal phase of each nanostructure 101 is determined. In this embodiment, according to the number of nanostructures 101 in the grating unit, the grating unit that meets the 0-2π phase requirement is divided into an order (i.e., five orders) corresponding to the number of nanostructures 101 (e.g., five). At this time, the ideal phase in the grating unit is 0 (e.g., Figure 7 The first nanostructure along the X-axis), 1 / 5*2π (e.g. Figure 7 The second nanostructure along the X-axis), 2 / 5*2π (e.g. Figure 7 The third nanostructure along the X-axis), 3 / 5*2 (e.g. Figure 7 The fourth nanostructure along the X-axis), 4 / 5*2π (e.g. Figure 7 The fifth nanostructure along the X-axis in the figure).

[0078] Specifically, the number of nanostructures 101 is determined based on the shape of the nanostructure 101. In this embodiment, by keeping other influencing factors (such as the radius of the nanostructure 101 and the height of the nanostructure 101) unchanged and selecting different shapes of the nanostructure 101 (such as cylinders, any free forms), different phases can be obtained. After determining the period of the grating unit, nanostructures 101 of different shapes are selected, and the corresponding number of nanostructures 101 can be obtained, thereby meeting the phase requirement.

[0079] Exemplarily, when the nanostructure 101 is cylindrical, the period of the grating unit is 1666nm. At this time, the number of nanostructures 101 is preferably five. After the number of nanostructures 101 is determined, the period of the nanostructure 101 is also determined. At this time, the period of the nanostructure is 333nm (i.e., 1666 / 5=333nm). Compared with the solution of "the number of nanostructures 101 is four", the number of five is more conducive to optimizing the meta-grating to obtain higher efficiency. Compared with the solution of "the number of nanostructures 101 is six", the number of five is more conducive to the manufacture of nanostructures 101, because when the number is six, the period of nanostructure 101 is small (277nm), which is not conducive to manufacture.

[0080] Of course, the nanostructure 101 can break this limitation by using a free-form structure, and the period of the nanostructure 101 can be smaller because there is no restriction on the diameter and side length.

[0081] Further, after selecting a preset height of the nanostructure 101, the nanostructure 101 is subjected to B l och boundary scanning. In this embodiment, considering that the height of the nanostructure 101 will affect the phase, under the same radius of the nanostructure 101, the higher the nanostructure 101, the more phase it carries. Controlling the height of the nanostructure 101 (e.g., 2000nm) to remain unchanged and scanning different characteristic sizes of the nanostructure 101 (e.g., radius) can reduce the amount of scanning results and the amount of screening required. The scanning results are shown in FIG. Figure 5 and Figure 6 shown.

[0082] In some other embodiments, different heights of the nanostructures 101 may be selected for scanning respectively, thereby increasing more scanning results for screening.

[0083] Specifically, a preset incident light wavelength is selected from the working band, and the period of the grating unit is determined according to the incident angle a and the exit angle b required by the meta-grating 10. In this embodiment, the period of the grating unit can be obtained by substituting the selected incident light wavelength (e.g., 610 nm), incident angle a (e.g., 30°), and exit angle b (e.g., 60°) into the grating formula.

[0084] Exemplarily, the grating formula is: n 0 ×k 0 ×si nθ 0 +m×2π / P 0 =n out ×k 0 ×si nθ out .

[0085] Among them, n 0 is the refractive index of the medium in the incident direction; k0 is the incident wave vector 2π / λ 0 θ 0 is the incident angle in the X-axis direction; m is the diffraction order, which can be 0, ±1, ±2, etc.; P 0 is the period of the grating unit along the X-axis direction; n out is the refractive index of the medium in the outgoing direction; θ out is the diffraction angle.

[0086] Exemplarily, the central wavelength of the working band is selected as the preset wavelength of the incident light. In this embodiment, compared with selecting other wavelengths (such as the end points of the working band), when the central wavelength of the working band is selected as the preset wavelength of the incident light, the period of the determined grating unit can be more tolerant to other wavelengths.

[0087] Exemplarily, the working band is preferably a visible light band, such as 400-750nm, and its central wavelength can be 610nm, which is suitable for the periscope lens of a mobile phone. Of course, the working band is not limited to visible light or near infrared, and can be any band. Among them, the working band refers to the working band of the optical element, that is, the working band of the meta-grating 10 and the multi-layer film structure 20, thereby increasing the bandwidth of the working band of the optical element (that is, the meta-grating 10 and the multi-layer film structure 20) and realizing broadband modulation.

[0088] Specifically, the design method of the multilayer film structure 20 includes:

[0089] Obtain the theoretical film thickness of different film materials. In this embodiment, the theoretical film thickness of the film material is multiplied by the film thickness coefficient (for example Figure 1 The final film thickness can be obtained by using S1, S2, and S3, such as Figure 1 The high refractive index material layer 201 and the low refractive index material layer 202.

[0090] Different film materials are arranged cyclically. Figure 1 The high refractive index material layer 201 and the low refractive index material layer 202 are arranged cyclically in sequence, that is, they are arranged cyclically according to the theoretical film thickness of 0.5H, L, and 0.5H.

[0091] By adjusting the number of cycles and / or the film thickness coefficient, a multilayer film structure is obtained. In this embodiment, in a simulation test, by adjusting the number of cycles (e.g., 10 times) and the film thickness coefficient (e.g., coefficient S1 is 0.77, coefficient S2 is 1, and coefficient S3 is 1.22), a broadband light (i.e., working band, such as visible light band 400-750nm) total reflection film (i.e., total reflection rate greater than 99.9%) that meets the requirements is obtained.

[0092] It is preferred to adjust the number of cycles and the film thickness coefficient simultaneously, so as to obtain the ideal multilayer film structure 20 more quickly, that is, to achieve broadband total reflection within the working band. Figure 1 The larger the number after the ^, the flatter the spectrum (i.e. the closer the reflectivity is to 100%). Adjust the film thickness factor (e.g. Figure 1 S1, S2, S3) in the figure can adjust the bandwidth of the spectrum line, so as to finally adjust it to achieve total reflection in the entire working band (such as the visible light band).

[0093] For example, first, the film thickness coefficients S1, S2 and S3 are all set to 1, the number of cycles is set to 3, and the test spectrum is as follows: Fig.10 It can be seen that reflection can be achieved near the 600nm wavelength, but the reflection efficiency and bandwidth are poor. Then, the film thickness coefficients S1, S2 and S3 are all set to 1, and the number of cycles is adjusted to 30 times. The test spectrum is as follows Fig.11 , it can be seen that the reflection efficiency reaches 100%, but the bandwidth is still small. Finally, adjust the film thickness coefficient S1 to 0.77, the film thickness coefficient S2 to 1, the film thickness coefficient S3 to 1.22, and the number of cycles in each film thickness coefficient to 10, that is, arrange them in a cycle in the manner of (0.77*0.5H, 0.77*L, 0.77*0.5H)^10, (1*0.5H, 1*L, 1*0.5H)^10, (1.22*0.5H, 1.22*L, 1.22*0.5H)^10. The final test spectrum is as follows Fig.12 , the light within the visible working band (400-700nm) can obtain 100% reflectivity, achieving the effect of broadband total reflection.

[0094] Specifically, based on the wavelength of the incident light, the angle of incidence a and the film material of the multilayer film structure, the theoretical film thickness of each film material is determined. In this embodiment, after determining the wavelength of the incident light (selecting the central wavelength of the working band, for example, 610nm), the angle of incidence a (for example, 30°) and the film material (the material of the high refractive index material layer 201 is silicon nitride, with a refractive index of 2.3; the material of the low refractive index material layer 202 is silicon dioxide, with a refractive index of 1.45), the theoretical film thickness of different film materials can be obtained. For example, the theoretical film thickness of the high refractive index material layer 201 is h=0.5H=0.5*1 / 4 / 2.3*610nm=33.15nm, and the theoretical film thickness of the low refractive index material layer 202 is l=L=1 / 4 / 1.45*610nm=105.17nm. Among them, the different central wavelengths of the incident light, the angle of incidence a and the film material correspond to different theoretical film thicknesses of the corresponding film materials.

[0095] In some embodiments, after the design of the multilayer film structure 20 is completed, the metagrating 10 is designed. In this embodiment, it is preferred to design the multilayer film structure 20 first, and then design the metagrating 10. Therefore, when screening the characteristic size of the nanostructure 101 of the metagrating 10, a nanostructure 101 with low reflectivity can be selected, because the multilayer film structure 20 achieves total reflection for light in the working band (i.e., the total reflectivity is greater than 99.9%). Therefore, the selectivity of the nanostructure 101 can be increased, and it is easier to select a nanostructure 101 that is closer to the phase requirement of the grating unit.

[0096] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description 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 mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0097] 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 method for designing an optical element, It is characterized in that The optical element includes a metagrating for deflecting incident light, and the design method includes: Obtaining the period of the grating unit, and determining the number and period of the nanostructures in the grating unit; Perform Bloch boundary scanning on the nanostructure, select the nanostructure characteristic size close to the phase requirement of the working band from the scanning results, and arrange the nanostructure with the corresponding characteristic size in the grating unit; After arranging the grating units periodically, a metagrating is obtained.

2. The method for designing an optical element according to claim 1, It is characterized in that From the scanning results, select the nanostructure feature size close to the phase requirement of the working band, specifically: The ideal phase of each nanostructure in the grating unit is obtained, and the characteristic size of the nanostructure corresponding to each ideal phase is screened out from the scanning results.

3. The method for designing an optical element according to claim 2, It is characterized in that The difference between the phase value of the screened nanostructure and the ideal phase in the working band is the smallest.

4. The method for designing an optical element according to claim 2, It is characterized in that Based on the number of nanostructures within a grating unit cell, the ideal phase for each nanostructure is determined.

5. The method for designing an optical element according to claim 1, It is characterized in that Based on the shapes of the nanostructures, the number of nanostructures is determined.

6. The method for designing an optical element according to claim 1, It is characterized in that After selecting a preset nanostructure height, a Bloch boundary scan is performed on the nanostructure.

7. The method for designing an optical element according to claim 1, It is characterized in that A preset wavelength of incident light is selected from the working band, and the period of the grating unit is determined according to the incident angle and the exit angle required by the meta-grating.

8. The method for designing an optical element according to claim 7, It is characterized in that The central wavelength of the working band is selected as the preset incident light wavelength.

9. The method for designing an optical element according to claim 7, It is characterized in that The sum of the exit angle and the incident angle of the metagrating is 90°.

10. The method for designing an optical element according to claim 1, It is characterized in that The cross section of the nanostructure is symmetrical with respect to the X-axis and the Y-axis.

11. The method for designing an optical element according to claim 1, It is characterized in that The optical element also includes a multilayer film structure for reflecting incident light, and the meta-grating is configured to reflect incident light in a working band.

12. The method for designing an optical element according to claim 11, It is characterized in that The design method further comprises: The theoretical film thickness of different film materials is obtained, and the different film materials are arranged cyclically, and a multilayer film structure is obtained by adjusting the number of cycles and / or the film thickness coefficient.

13. The method for designing an optical element according to claim 12, It is characterized in that Based on the incident light wavelength, incident angle and film layer material of the multilayer film structure, the theoretical film layer thickness of each film layer material is determined.

14. The method for designing an optical element according to claim 11, It is characterized in that After the design of the multilayer film structure is completed, the metagrating will be designed.

15. The method for designing an optical element according to claim 11, It is characterized in that The multilayer film structure is formed by arranging different film layer materials in a cycle, or the multilayer film structure is formed by arranging different nanostructure layers.

16. An optical element, It is characterized in that The optical element is designed by any one of the design methods described in claims 1-15.

Images