Polarization conversion metasurface and design method and device thereof

Abstract

The invention discloses a polarization conversion metasurface and a design method and device thereof, and the metasurface comprises a substrate which is used for receiving incident light in a polarization state and forming emergent light; the first microstructure surface is arranged at the upstream of the substrate and is used for carrying out polarization state conversion on the incident light; wherein the first microstructure surface comprises a plurality of microstructures which can be periodically arranged, and the microstructures have a birefringence characteristic. The polarization conversion metasurface specifically comprises the substrate and the first microstructure surface, the metasurface can achieve polarization conversion of incident light through the birefringence characteristic of the first microstructure surface, so that the thickness of the composite polaroid is reduced, meanwhile, the manufacturing process is simpler than that of the composite polaroid, the production cost is reduced, and the production efficiency is improved. The overall structure of the optical path system is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of optical metasurfaces, and in particular to a polarization conversion metasurface and a design method and device thereof. Background Art

[0002] With the emergence of the metaverse concept, extended reality (XR) technology has garnered widespread attention and is rapidly developing. To reduce the overall length of XR optical systems and enhance the user experience, most products employ a pancake approach (which can be understood as a folding solution) to fold the optical path. The core component of this pancake approach, the composite polarizer, consists of two layers of polarizing film and a quarter-wave plate. This thickness and weight not only impact the user experience but also increase the overall system cost due to the complex manufacturing process. Furthermore, the thickness of the composite polarizer increases the volume and weight of the entire pancake optical path. Summary of the Invention

[0003] The embodiments of the present invention provide a polarization conversion metasurface and a design method and device thereof, aiming to solve the problem of large thickness of composite polarizers.

[0004] In a first aspect, an embodiment of the present invention provides a polarization conversion metasurface, comprising: a substrate for receiving incident light having a polarization state and forming an outgoing light; The first microstructure surface is arranged upstream of the substrate and is used to convert the polarization state of the incident light; wherein the first microstructure surface includes a plurality of periodically arranged microstructures, and the microstructures have birefringence characteristics.

[0005] Furthermore, the shape of the microstructure includes rectangular nanorods, cross-shaped nanorods, rectangular nanopores or cross-shaped nanopores having birefringence characteristics.

[0006] Furthermore, it also includes: The second microstructure surface is arranged downstream of the substrate and is used for filtering the polarization state of the emergent light.

[0007] Furthermore, the second microstructure surface is provided in the form of a rectangular grating or a rectangular nanocolumn.

[0008] Furthermore, the substrate, the first microstructure surface and the second microstructure surface are all made of materials that are transparent to a specified wavelength band.

[0009] In a second aspect, an embodiment of the present invention provides a polarization conversion metasurface design method, which is applied to the polarization conversion metasurface as described in the first aspect, and the design method includes: Acquiring an initial structure of a first microstructure surface in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; Performing a full-wave forward simulation on the initial structure to obtain the intensity of polarized light; wherein the polarized light is obtained by performing polarization state conversion on incident light through the initial structure; Obtaining the intensity of the incident light, and calculating an evaluation function in combination with the intensity of the polarized light; The initial structure is optimized based on the evaluation function to obtain a final polarization conversion metasurface.

[0010] Furthermore, obtaining the intensity of the incident light and calculating the evaluation function in combination with the intensity of the polarized light includes: The evaluation function is calculated as follows: FOM=I v / I total ; Wherein, FOM represents the evaluation function, I v Represents the intensity of the polarized light, I total represents the intensity of the incident light.

[0011] Furthermore, the initial structure is optimized based on the evaluation function to obtain a final polarization conversion metasurface, including: updating the size of the initial structure according to the evaluation function to obtain an updated structure; Continuing to calculate the evaluation function based on the updated structure, and obtaining a difference between two consecutive evaluation functions, and then comparing the difference with a preset threshold; If the difference is greater than or equal to the preset threshold, continue to iteratively update the update structure, and continue to compare the difference between two consecutive evaluation functions with the preset difference threshold; If the difference is less than a preset difference threshold, or the iterative update reaches a preset number threshold, the iterative update is stopped, and the corresponding updated structure is output as a result of the optimization process.

[0012] Furthermore, it also includes: The second microstructure surface is optimized and designed using a scanning traversal method.

[0013] In a third aspect, an embodiment of the present invention provides a polarization conversion metasurface design device, comprising: A structure acquisition unit, configured to acquire an initial structure of a first microstructure surface in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; a structural simulation unit, configured to perform a full-wave forward simulation on the initial structure to obtain an intensity of polarized light; wherein the polarized light is obtained by performing a polarization state conversion on the incident light via the initial structure; a first calculation unit, configured to obtain the intensity of the incident light and calculate an evaluation function in combination with the intensity of the polarized light; The first optimization unit is used to optimize the initial structure based on the evaluation function to obtain a final polarization conversion metasurface.

[0014] Embodiments of the present invention provide a polarization-conversion metasurface and a design method and device thereof. The polarization-conversion metasurface includes: a substrate for receiving incident light having a polarization state and forming outgoing light; a first microstructured surface disposed upstream of the substrate for performing polarization-state conversion on the incident light; wherein the first microstructured surface includes a plurality of periodically arranged microstructures, each of which has birefringence. The polarization-conversion metasurface described in the embodiments of the present invention specifically includes a substrate and a first microstructured surface. The metasurface can achieve polarization conversion of incident light through the birefringence of the first microstructured surface, thereby reducing the thickness of a composite polarizer. Furthermore, the metasurface has a simpler manufacturing process than a composite polarizer, thereby reducing production costs and simplifying the overall structure of the optical path system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 A schematic diagram of the principle of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 2 A schematic structural diagram of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 3 A schematic flow chart of a polarization conversion metasurface design method provided by an embodiment of the present invention; Figure 4 Another schematic diagram of the principle of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 5 An overall schematic diagram of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 6 A schematic diagram of the conversion results of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 7 A schematic diagram of a first microstructured surface in a polarization conversion metasurface provided by an embodiment of the present invention; Figure 8 A schematic diagram of a second microstructure surface in a polarization conversion metasurface provided by an embodiment of the present invention; Figure 9 Another overall schematic diagram of a polarization conversion metasurface provided by an embodiment of the present invention; FIG10( a ), FIG10 ( b ), and FIG10 ( c ) are schematic diagrams of another conversion result of a polarization conversion metasurface provided by an embodiment of the present invention; Figure 11 A schematic block diagram of a polarization conversion metasurface design device provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0019] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used in the specification and appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0020] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0021] See below Figure 1 and Figure 2 , an embodiment of the present invention provides a polarization conversion metasurface, comprising: Substrate 1, for receiving incident light with a polarization state and forming outgoing light; The first microstructure surface 2 is provided upstream of the substrate 1 and is used to convert the polarization state of the incident light. The first microstructure surface 2 comprises a plurality of periodically arranged microstructures, and the microstructures have birefringence characteristics.

[0022] In this embodiment, the polarization conversion metasurface includes a substrate 1 and a first microstructure surface 2. The substrate 1 is used to receive incident light of a polarization state and form an outgoing light. The first microstructure surface 2 is arranged upstream of the substrate 1, such as Figure 2 As shown in (b), it comprises multiple periodically arranged microstructures with birefringence properties, which are used to convert the polarization state of incident light. This metasurface can achieve polarization conversion of incident light through the birefringence of the first microstructured surface 2, thereby reducing the thickness of the composite polarizer. Furthermore, its manufacturing process is simpler than that of composite polarizers, thereby reducing production costs and simplifying the overall structure of the optical path system.

[0023] In one embodiment, the shape of the microstructure includes rectangular nanorods, cross-shaped nanorods, rectangular nanoholes, or cross-shaped nanoholes having birefringence characteristics.

[0024] In this embodiment, the first microstructure surface 2 is located upstream of the substrate 1, and the polarization state of the incident light can be converted by changing the shape of the specific microstructure, and the microstructure is periodically arranged to obtain the entire microstructure surface. Specifically, the shape of the microstructure can be a rectangular nanorod, a cross-shaped nanorod, a rectangular nanohole, a cross-shaped nanohole with birefringence characteristics, and a microstructure with a specific shape obtained by optimizing the method, and the arrangement of the micro-nanostructure can be a periodic structure such as a tetragonal arrangement, a hexagonal arrangement, or other quasi-crystal arrangement, for example Figure 3 As shown in Figure 2, a nanopillar is a nanoscale material with a columnar structure, typically ranging from a few nanometers to hundreds of nanometers in diameter and from tens of nanometers to micrometers in length. Nanopillar arrays can manipulate the reflection, refraction, and scattering of light. Nanopores are pore structures with pore sizes on the nanometer scale (typically 1 to 100 nm) and can exist in thin films, solid materials, or biomolecules. Nanopores come in a variety of shapes, including circular, elliptical, and irregular, and their size and surface properties can be precisely controlled.

[0025] In one embodiment, if Figure 4 As shown, the polarization conversion metasurface further includes: The second microstructure surface 3 is disposed downstream of the substrate 1 and is used to filter the polarization state of the emitted light.

[0026] Specifically, the second microstructure surface 3 is provided in the form of a rectangular grating or a rectangular nanocolumn.

[0027] This embodiment can also include a second microstructured surface 3 downstream of the substrate 1. This surface is used to further filter the polarization state of the outgoing light to improve the orthogonal polarization extinction ratio of the outgoing light. This surface can be in the form of a rectangular grating or rectangular nanopillars. The shape, size, and arrangement of the rectangular grating and rectangular nanopillars can be optimized according to actual needs. The provision of the second microstructured surface 3 can further enhance the performance of the polarization-converting metasurface, making it more adaptable to different application scenarios.

[0028] In a specific embodiment, the substrate 1 , the first microstructure surface 2 , and the second microstructure surface 3 are all made of a material that is transparent to a specified wavelength band.

[0029] When both the first microstructured surface 2 and the second microstructured surface 3 are provided simultaneously, the substrate 1 is positioned between the two microstructured surfaces and is constructed from a material transparent for the designed wavelength range. The microstructures in the first microstructured surface 2 are made of materials transparent for the designated wavelength range. For example, for the near-infrared wavelength range, the microstructures can be made of amorphous silicon or polycrystalline silicon; for the visible wavelength range, the microstructures can be made of silicon nitride, gallium nitride, titanium dioxide, or the like. Similarly, the second microstructured surface 3 is also constructed from a material transparent for the designed wavelength range. By employing a material transparent for the designated wavelength range, the polarization-converting metasurface can achieve excellent light transmittance and polarization conversion performance within that specific wavelength range.

[0030] like Figure 5 As shown, an embodiment of the present invention further provides a polarization conversion metasurface design method, which is applied to the polarization conversion metasurface described above. The design method includes steps S101 to S104.

[0031] Step S101: obtaining an initial structure of a first microstructure surface 2 in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; Step S102: performing a full-wave forward simulation on the initial structure to obtain the intensity of polarized light; wherein the polarized light is obtained by performing polarization state conversion on the incident light through the initial structure; Step S103: obtaining the intensity of the incident light, and calculating an evaluation function in combination with the intensity of the polarized light; Step S104: Optimizing the initial structure based on the evaluation function to obtain a final polarization conversion metasurface.

[0032] In this embodiment, when designing a polarization-converting metasurface, an initial structure is first determined: a first microstructured surface 2 disposed upstream of a substrate 1. The microstructures within this microstructured surface can be formed by randomly distributing and splicing multiple rectangular blocks. A full-wave forward simulation is then performed on this initial structure to obtain the far-field polarization conditions at various wavelengths. This allows the calculation of an evaluation function, which is then used to optimize the initial structure to meet the required polarization conversion efficiency, thereby obtaining a polarization-converting metasurface structure with optimal performance. By optimizing the design of the first microstructured surface 2, this embodiment achieves a metasurface structure with high polarization conversion efficiency.

[0033] In a specific embodiment, obtaining the intensity of the incident light and calculating the evaluation function in combination with the intensity of the polarized light includes: The evaluation function is calculated as follows: FOM=I v / I total ; Wherein, FOM represents the evaluation function, I v Represents the intensity of the polarized light, I total represents the intensity of the incident light.

[0034] In one embodiment, the optimizing the initial structure based on the evaluation function to obtain a final polarization conversion metasurface includes: updating the size of the initial structure according to the evaluation function to obtain an updated structure; Continuing to calculate the evaluation function based on the updated structure, and obtaining a difference between two consecutive evaluation functions, and then comparing the difference with a preset threshold; If the difference is greater than or equal to the preset threshold, continue to iteratively update the update structure, and continue to compare the difference between two consecutive evaluation functions with the preset difference threshold; If the difference is less than a preset difference threshold, or the iterative update reaches a preset number threshold, the iterative update is stopped, and the corresponding updated structure is output as a result of the optimization process.

[0035] When optimizing the first microstructure surface 2 using the evaluation function, the initial structure is first updated in size according to the evaluation function. The difference between the evaluation function and the result is continuously calculated and compared with a preset threshold. If the difference is greater than or equal to the threshold, the iterative update continues. If the difference is less than the threshold or the preset number of iterations is reached, the update ceases, and the structure at this point becomes the optimized first microstructure surface 2. In practical applications, a gradient update method can be used to update the size of the first microstructure surface 2.

[0036] In one embodiment, the polarization conversion metasurface design method further includes: The second microstructure surface 3 is optimized and designed by a scanning traversal method.

[0037] For the second microstructure surface 3, this embodiment adopts a scanning traversal method for design. Specifically, the height and period of the second microstructure surface 3 can be fixed, and its length and width can be scanned, so that a structure with a high extinction ratio in the designed band can be obtained.

[0038] In a specific embodiment, for a single-wavelength polarization conversion metasurface, the operating wavelength is 632 nm. The schematic diagram of the principle can be shown as follows: Figure 1 As shown, horizontal polarized light will be converted into vertical polarized light after passing through the polarization conversion metasurface. The metasurface consists of a square periodic substrate 1 and a rectangular microstructure on it. The microstructure is rotated 45 degrees relative to the substrate 1, for example Figure 2 As shown in parts (a) and (b) of FIG. , the material of the microstructure is titanium dioxide, the material of substrate 1 is quartz, the period P is 400 nm, and the height H of the microstructure is set to 700 nm.

[0039] Polarization is controlled by changing the length (L) and width (W) of the rectangular microstructure. Specifically, the initial structure is first determined, and random values are used as the initial structure; then a forward simulation is performed, which is a physical optical propagation simulation directly implemented using a numerical algorithm; and the evaluation function FOM is calculated, which is the ratio of the vertical polarized light intensity to the total incident energy. The microstructure is then optimized according to the evaluation function. If the difference in the evaluation function between the two iterative results is less than the preset threshold, or the maximum number of iterations is reached, the structure is output as the final optimized structure. Otherwise, the gradient is calculated according to the FOM, and the size of the microstructure is updated. After the microstructure optimization is completed, it is arranged periodically, for example Figure 3 As shown, the final polarization conversion metasurface can be obtained in this way. Figure 6 The performance of the metasurface is demonstrated, such as Figure 6 As shown in parts (a) and (b), the polarization state of the incident light is horizontal, and the polarization state of the outgoing light is vertical, which is consistent with the design.

[0040] In another specific embodiment, for a multi-wavelength polarization conversion metasurface, polarization conversion is performed on red, green, and blue light (corresponding to wavelengths λ1-632nm, λ2-532nm, and λ3-450nm), converting horizontally polarized light into vertically polarized light. The schematic diagram of the structure can be shown as follows: Figure 4 The polarization converter consists of three parts: a first metasurface (i.e., the first microstructure surface 2), a substrate 1, and a second metasurface (i.e., the second microstructure surface 3). The first metasurface adopts a structure similar to a QR code, that is, multiple microstructures are randomly distributed on the substrate 1, for example Figure 7As shown in parts (a) and (b) of the figure, its main function is to achieve the conversion from horizontal polarization to vertical polarization at three wavelengths. The structure of the second metasurface is as follows: Figure 8 As shown in parts (a) and (b) of the figure, its structure is a wire grating structure, which is used to filter the transmitted horizontally polarized light so that the outgoing light contains only vertically polarized light.

[0041] The specific design process of the polarization-converting metasurface includes: (1) First, determine the initial structure. Specifically, a random value can be used as the initial structure. For example, a unit period P is divided into multiple grids. Each grid is randomly selected to contain a rectangular microstructure. The size of each grid is, for example, 20nm*20nm. (2) Perform forward simulation for each incident wavelength; (3) Calculate the evaluation function FOM. In this embodiment, the evaluation function is the ratio of the vertical polarization intensity to the total incident energy at each wavelength: ; Among them, I v (λ i ) is the intensity of vertically polarized light at the i-th wavelength, I total (λ i ) is the total intensity of incident light at the i-th wavelength; (4) If the difference in the evaluation function between the two iterative results is less than the preset value, or the maximum number of iterations is reached, the structure is output as the final optimized structure. Otherwise, the gradient is calculated according to the FOM and the microstructure size is updated.

[0042] like Figure 9 As shown, the microstructures obtained based on the above design process are periodically arranged to obtain the final polarization conversion metasurface. Figures 10(a)-10(c) demonstrate the performance of this metasurface. The incident light polarization state is horizontal, and the outgoing light polarization state is nearly vertical. After the outgoing light is polarized by the second metasurface, the output light efficiency is 98.6%, 99.2%, and 98.7%.

[0043] like Figure 11 As shown, an embodiment of the present invention further provides a polarization conversion metasurface design device 200, which includes: A structure acquisition unit 201 is configured to acquire an initial structure of a first microstructure surface 2 in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; A structure simulation unit 202 is configured to perform a full-wave forward simulation on the initial structure to obtain an intensity of polarized light; wherein the polarized light is obtained by performing a polarization state conversion on the incident light via the initial structure; A first calculation unit 203 is used to obtain the intensity of the incident light and calculate an evaluation function in combination with the intensity of the polarized light; The first optimization unit 204 is configured to optimize the initial structure based on the evaluation function to obtain a final polarization conversion metasurface.

[0044] In one embodiment, the first calculation unit 203 includes: The second calculation unit is used to calculate the evaluation function according to the following formula: FOM=I v / I total ; Wherein, FOM represents the evaluation function, I v Represents the intensity of the polarized light, I total represents the intensity of the incident light.

[0045] In one embodiment, the first optimization unit 204 includes: a size updating unit, configured to update the size of the initial structure according to the evaluation function to obtain an updated structure; a difference comparison unit, configured to continue calculating the evaluation function based on the updated structure, obtain a difference between two consecutive evaluation functions, and then compare the difference with a preset threshold; an iterative updating unit, configured to continue iteratively updating the update structure if the difference is greater than or equal to a preset threshold, and continue comparing the difference between two consecutive evaluation functions with a preset difference threshold; The result output unit is configured to stop the iterative update if the difference is less than a preset difference threshold, or the iterative update reaches a preset number threshold, and output the corresponding updated structure as a result of the optimization process.

[0046] In one embodiment, the polarization conversion metasurface design device 200 further includes: The second optimization unit is used to optimize the design of the second microstructure surface 3 by scanning.

[0047] Since the embodiments of the apparatus part correspond to the embodiments of the method part, please refer to the description of the embodiments of the method part for the embodiments of the apparatus part, and they will not be repeated here.

[0048] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When executed, the computer program can implement the steps provided in the above embodiment. The storage medium may include a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, an optical disk, or other medium capable of storing program code.

[0049] The present invention also provides a computer device that may include a memory and a processor. The memory stores a computer program, and when the processor calls the computer program in the memory, the steps provided in the above embodiment can be implemented. Of course, the computer device may also include various network interfaces, a power supply, and other components.

[0050] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same and similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of this application, several improvements and modifications can be made to this application, and these improvements and modifications also fall within the scope of protection of the claims of this application.

[0051] It should also be noted that, in this specification, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus comprising the element.

Claims

1. A polarization conversion metasurface, characterized in that: include: a substrate for receiving incident light having a polarization state and forming an outgoing light; The first microstructure surface is arranged upstream of the substrate and is used to convert the polarization state of the incident light; wherein the first microstructure surface includes a plurality of periodically arranged microstructures, and the microstructures have birefringence characteristics.

2. The polarization conversion metasurface according to claim 1, wherein The shape of the microstructure includes a rectangular nanorod, a cross-shaped nanorod, a rectangular nanohole or a cross-shaped nanohole having birefringence characteristics.

3. The polarization conversion metasurface according to claim 1, wherein Also includes: The second microstructure surface is arranged downstream of the substrate and is used for filtering the polarization state of the emergent light.

4. The polarization conversion metasurface according to claim 3, wherein: The second microstructure surface is provided in the form of a rectangular grating or a rectangular nanocolumn.

5. The polarization conversion metasurface according to claim 3, wherein: The substrate, the first microstructure surface and the second microstructure surface are all made of materials that can transmit a specified wavelength band.

6. A polarization conversion metasurface design method, applied to the polarization conversion metasurface according to any one of claims 1 to 5, characterized in that: The design method includes: Acquiring an initial structure of a first microstructure surface in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; Performing a full-wave forward simulation on the initial structure to obtain the intensity of polarized light; wherein the polarized light is obtained by performing polarization state conversion on incident light through the initial structure; Obtaining the intensity of the incident light, and calculating an evaluation function in combination with the intensity of the polarized light; The initial structure is optimized based on the evaluation function to obtain a final polarization conversion metasurface.

7. The polarization conversion metasurface design method according to claim 6, wherein: The obtaining of the intensity of the incident light and calculating the evaluation function in combination with the intensity of the polarized light includes: The evaluation function is calculated as follows: FOM=I v / I total ; Wherein, FOM represents the evaluation function, I v Represents the intensity of the polarized light, I total represents the intensity of the incident light.

8. The polarization conversion metasurface design method according to claim 6, wherein: The optimizing the initial structure based on the evaluation function to obtain a final polarization conversion metasurface includes: updating the size of the initial structure according to the evaluation function to obtain an updated structure; Continuing to calculate the evaluation function based on the updated structure, and obtaining a difference between two consecutive evaluation functions, and then comparing the difference with a preset threshold; If the difference is greater than or equal to the preset threshold, continue to iteratively update the update structure, and continue to compare the difference between two consecutive evaluation functions with the preset difference threshold; If the difference is less than a preset difference threshold, or the iterative update reaches a preset number threshold, the iterative update is stopped, and the corresponding updated structure is output as a result of the optimization process.

9. The polarization conversion metasurface design method according to claim 6, applied to the polarization conversion metasurface according to claim 3, characterized in that: The design method further includes: The second microstructure surface is optimized and designed using a scanning traversal method.

10. A polarization conversion metasurface design device, characterized in that: include: A structure acquisition unit, configured to acquire an initial structure of a first microstructure surface in the polarization conversion metasurface; wherein the initial structure includes a plurality of microstructures; a structural simulation unit, configured to perform a full-wave forward simulation on the initial structure to obtain an intensity of polarized light; wherein the polarized light is obtained by performing a polarization state conversion on the incident light via the initial structure; a first calculation unit, configured to obtain the intensity of the incident light and calculate an evaluation function in combination with the intensity of the polarized light; The first optimization unit is used to optimize the initial structure based on the evaluation function to obtain a final polarization conversion metasurface.

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