A design method for dual-state six-channel polarization multiplexing metasurface based on phase change materials

Abstract

The present invention discloses a method for designing a dual-state six-channel polarization multiplexing metasurface based on phase change materials, comprising the following steps: designing a structural unit based on phase change materials; constructing a dual-state six-channel polarization multiplexing metasurface using the designed structural unit; optimizing the geometric structure and orientation angle of the structural unit by adopting a screening algorithm, so that the optimized dual-state six-channel polarization multiplexing metasurface can record six unrelated phase information into the same dual-state six-channel polarization multiplexing metasurface; based on the metasurface Jones matrix control theory, the present invention comprehensively utilizes the geometric phase and transmission / resonance phase of the structural unit and is applicable to most types of metasurface unit structures. The method of the present invention has wide applicability and can be applied to the fields of metasurface optical encryption, multifunctional wavefront control, etc., and has important practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization multiplexing metasurface design, and specifically provides a dual-state six-channel polarization multiplexing metasurface design method based on phase change materials. Background Art

[0002] With the rapid development of modern optical technology, the ability to flexibly and efficiently manipulate light has become an important criterion for measuring the performance of optical devices. However, achieving multi-dimensional control of light usually relies on bulky optical components and complex device layouts. Metasurfaces, as emerging planar optical components, have attracted widespread attention in recent years due to their compact structural design and subwavelength resolution. Thanks to their high compatibility with modern micro- and nano-fabrication technologies, metasurfaces have demonstrated excellent optical manipulation capabilities in fields such as superlenses, structured beam generation, holography, optical encryption, and optical communications.

[0003] Optical phase-change materials are functional materials that can undergo reversible changes in refractive index under external stimuli (such as temperature changes, applied voltage, or mechanical strain). This type of material, including GeSbTe alloys, vanadium dioxide (VO2), and Sb2S3, has been widely used to replace traditional dielectric materials or metal materials, bringing excellent dynamic control capabilities to metasurfaces while retaining their efficient optical manipulation properties. Although phase-change materials provide new possibilities for the dynamic adjustability of metasurfaces, existing research using phase-change materials to achieve polarization multiplexing is mainly limited to co-polarization or cross-polarization channels, and can only achieve multiplexing of a total of four polarization channels before and after the phase change. Furthermore, existing methods mostly focus on local phase control rather than global phase control, which increases the crosstalk problem between channels and severely limits the practical application of metasurfaces. Therefore, the development of a phase-change material metasurface with low crosstalk and multi-channel polarization multiplexing has become a key scientific and technological issue that needs to be addressed urgently. Summary of the Invention

[0004] Purpose of the invention: To make up for the shortcomings of existing phase-change material metasurfaces in polarization multiplexing capabilities, the present invention proposes a design method for a dual-state six-channel polarization multiplexing metasurface based on phase-change materials. The Jones matrix control of the metasurface is used to achieve independent control of a total of six polarization channels in two states, achieving the upper limit of the number of polarization multiplexing channels of the dual-state metasurface while maintaining high efficiency and low crosstalk, providing ideas for further increasing the number of polarization multiplexing channels of the metasurface.

[0005] Technical solution: A design method for a dual-state six-channel polarization multiplexing metasurface based on phase change materials, including the following steps:

[0006] Designing building blocks based on phase-change materials;

[0007] Using the designed structural units, a dual-state six-channel polarization multiplexing metasurface was constructed;

[0008] By using a screening algorithm to optimize the geometric structure and orientation angle of the structural unit, the optimized dual-state six-channel polarization multiplexing metasurface can record six unrelated phase information into the same dual-state six-channel polarization multiplexing metasurface;

[0009] The screening algorithm optimizes the geometric structure and orientation angle of the structural unit, and the specific operations include:

[0010] Step 1: Based on a given operating wavelength and a preset height and a preset period of the dual-state six-channel polarization multiplexing metasurface, the polarization responses of structural units of different sizes in the crystalline and amorphous states are scanned to obtain a total database, which includes a variety of optional geometric structures of the structural units;

[0011] Step 2: When the structural unit is in an amorphous state, each structural unit is regarded as a pixel point. Under a set error, based on the Jones matrix of a single structural unit, all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before the phase transition are screened from the total database, and the resulting structures are stored as a transition database. The transition database includes all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before the phase transition selected from the total database and the orientation angles corresponding to the geometric structures.

[0012] Step 3: When the structural unit undergoes a phase transition to a crystalline state, the T-shaped structure formed by four adjacent structural units is regarded as a pixel point, and the Jones matrix at this pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line. Based on the Jones matrix at this pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase transition with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface.

[0013] Furthermore, the polarization response includes: the transmittance and phase delay of the structural unit under the illumination of linearly polarized light along the long / short axis direction of the structural unit without applying an orientation angle but changing the length and width dimensions. This process is implemented by the finite difference time domain method FDTD.

[0014] Furthermore, in step 2, when the structural unit is in the amorphous state, each structural unit is regarded as a pixel point. Under a set error, based on the Jones matrix of a single structural unit, all optional geometric structures of a batch of structural units that can meet the independent phase control of the three polarization channels before phase transition are screened from the total database and stored as a transition database. The specific operations include:

[0015] The Jones matrix of a single structural unit is expressed as:

[0016]

[0017] Where, and denote the polarization response of the structural unit along its major and minor axes, respectively. t o and t e is the modulus value, corresponding to the transmittance of the structural unit in the amorphous state in the total database, and is the angle of magnitude, corresponding to the phase delay of the structural unit in the amorphous state in the total database. The subscript o represents the polarization response under the illumination of light with the polarization direction along the long axis of the structural unit, and the subscript e represents the polarization response under the illumination of light with the polarization direction along the short axis of the structural unit. R(-θ) represents the rotation matrix with an orientation angle of θ, and R(θ) is its inverse matrix.

[0018] By regulating the amorphous state of the structural unit and orientation angle θ, allowing a batch of optional geometric structures of structural units in the total database that can achieve Jones matrix errors less than a threshold to pass the screening and be stored in the transition database;

[0019] And stored in the transition database and orientation angle θ, independent phase control can be applied to two co-polarization channels and one cross-polarization channel, that is, three parameters determine three equations.

[0020] Furthermore, the amorphous state of the structural unit is controlled and orientation angle θ, allowing a group of optional geometric structures of structural units in the total database that can achieve Jones matrix error less than a threshold to pass the screening and be stored in the transition database, specifically including:

[0021] By regulating the amorphous state of the structural unit and orientation angle θ, and a multi-threshold screening method is used to screen out a batch of optional geometric structures of structural units from the total database, and the optional geometric structures of this batch of structural units and the orientation angles corresponding to each geometric structure are stored in the transition database.

[0022] Furthermore, in step 3, when the structural unit phase changes to a crystalline state, the field shape composed of four adjacent structural units is regarded as a pixel point, and the Jones matrix at the pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line; based on the Jones matrix at the pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase change and has the smallest error and the orientation angle corresponding to each geometric structure is selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface. The specific operations include:

[0023] Assuming we start from the structural unit in the upper left corner of the field shape, the corresponding Jones matrix is ​​expressed as: J1, J2, J3, J4;

[0024] Assume that the target Jones matrix of the pixel is J target By selecting the structural parameters and orientation angles of the structural units from the transition database, J1+J2=J3+J4=J target .

[0025] Furthermore, when the structural unit is in an amorphous state, each structural unit is regarded as a pixel point, and when the structural unit undergoes a phase transition to a crystalline state, the shape of four adjacent structural units is regarded as a pixel point, which can be replaced by:

[0026] When the structural unit is in the amorphous state and the crystalline state, the Jones matrix of a single structural unit, the Jones matrix of a double structural unit superposition, and the Jones matrix of a quadruple structural unit superposition are arbitrarily selected. The selection only needs to satisfy the following: the Jones matrix of a single structural unit cannot be used before and after the phase change.

[0027] Furthermore, the structural unit is any structural unit with birefringence properties that can regulate the geometric phase and the transmission / resonance phase.

[0028] Furthermore, the structural unit includes, from top to bottom, a phase change material nanocolumn and a substrate.

[0029] Furthermore, the steps 2 and 3 can be replaced by the following steps:

[0030] When the structural unit is in a crystalline state, each structural unit is regarded as a pixel point. Under a set error, all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before phase transition are screened from the total database based on the Jones matrix of the single structural unit, and the structures are stored as a transition database. The transition database includes all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before phase transition selected from the total database and the orientation angles corresponding to the geometric structures;

[0031] When the structural unit undergoes a phase transition to an amorphous state, the T-shaped structure composed of four adjacent structural units is regarded as a pixel point, and the Jones matrix at this pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line. Based on the Jones matrix at this pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase transition with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0033] (1) The method of the present invention is based on the metasurface Jones matrix control theory and comprehensively utilizes the geometric phase and transmission / resonance phase of the structural unit, and is applicable to most types of metasurface unit structures;

[0034] (2) The method of the present invention first establishes an initial database that meets the requirements for independent regulation of the three polarization channels before the phase change. Then, combined with the changing characteristics of the transmission / resonance phase of the metasurface after the phase change, the method designs a four-atom supercell to screen data from the initial database that meets the requirements for independent regulation of the remaining three polarization channels after the phase change, and finally determines all the parameters of the metasurface design. The method of the present invention has a wide range of applicability and can be applied to the fields of metasurface optical encryption, multifunctional wavefront control, etc., and has important practical value.

[0035] (3) The method of the present invention can reach the theoretical upper limit of the dual-state single-layer metasurface in terms of the number of channels for polarization multiplexing. By changing the polarization state of the outgoing / incoming light and the crystalline state of the material, independent phase control can be added to the six polarization channels.

[0036] (4) The method of the present invention is universally applicable. As long as the structural unit of the designed metasurface has a transmission / resonance phase and a geometric phase, the present method can be used for design.

[0037] (5) The method of the present invention completely adopts the forward design method, including: (1) instead of inversely designing the metasurface structure parameters based on the designed Jones matrix, the corresponding Jones matrix is ​​directly obtained based on the metasurface structure parameters and then compared with the preset Jones matrix; (2) the design is completely based on the forward process of first amorphous state and then crystalline state, without repeated iterations, which reduces the amount of calculation while retaining the accuracy of the results, and also facilitates the design of optimization algorithms to further improve performance;

[0038] (6) The method of the present invention combines the single-structure unit Jones matrix and the multi-structure unit Jones matrix in a metasurface through phase change materials, providing ideas for in-depth research on phase change material metasurfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a functional schematic diagram of the design method for a dual-state six-channel polarization multiplexing metasurface of a phase change material proposed in Example 1;

[0040] Figure 2 Schematic diagram of the three-dimensional structure and the top view of the structural unit constituting the metasurface in Example 1;

[0041] Figure 3 This is a flow chart of the design method for a dual-state six-channel polarization multiplexing metasurface of a phase change material proposed in Example 1;

[0042] Figure 4This is a simulation result diagram of the focal field obtained by the metasurface used in Example 1;

[0043] Figure 5 This is a design diagram. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following will further illustrate the design method of a dual-state six-channel polarization multiplexing metasurface of a phase change material proposed by the present invention in combination with the drawings and embodiments.

[0045] Example 1:

[0046] This embodiment proposes a design method for a dual-state six-channel polarization multiplexing metasurface based on phase change materials, which mainly includes the following steps:

[0047] Step 1: Design a structural unit based on phase change material; this embodiment takes phase change material nanorods and substrates as an example to form Figure 2 The structural unit shown in the figure includes, from top to bottom, a phase change material nanocolumn and a substrate. Figure 2 The structural unit is shown.

[0048] Step 2: Using the designed structural unit, construct a dual-state six-channel polarization multiplexing metasurface, such as Figure 1 As shown, the dual-state six-channel polarization multiplexing metasurface consists of multiple structural units.

[0049] Step 3: Phase modulation is achieved by optimizing the nanopillar geometry and orientation angle using a screening algorithm, thereby recording the phase information of six unrelated offset-focus metalenses into the same dual-state six-channel polarization multiplexing metasurface.

[0050] Now combined Figure 3 The screening algorithm used in this embodiment is further described.

[0051] Step 1: Based on a given operating wavelength and a preset height and period of the metasurface, the polarization responses of different-sized phase-change material unit structures in the crystalline and amorphous states are scanned to obtain a total database. The scanned polarization response refers to the transmittance and phase delay of the structure unit under the condition that no orientation angle is applied but the length and width dimensions are changed when the structure unit is illuminated by linearly polarized light along the long / short axis (x and y directions). This process is implemented by the finite-difference time-domain method (FDTD), where the phase delay is obtained by detecting the center of the far-field projection on the monitor above the phase-change material unit structure, and the transmittance is defined as the total power (relative to the source) passing through the monitor above the phase-change material unit structure. In this embodiment, the total database stores a variety of optional sizes (i.e., length and width combinations) of more finger nanopillars.

[0052] Step 2: When the structural unit is in an amorphous state, each structural unit is regarded as a pixel point. Within the allowable error, a batch of optional sizes (i.e., the length and width of the nanopillars) that can satisfy the independent phase regulation of the three polarization channels before the phase transition are screened from the total database based on the Jones matrix of a single structural unit and stored as a transition database; the transition database stores this batch of optional sizes (i.e., the length and width of the nanopillars) and the orientation angles corresponding to these optional sizes. For a certain pixel point, the dimension of the transition database at this pixel point is n*3, where n is the number of all parameter combinations (i.e., length, width, and orientation angle) that meet the screening threshold at the pixel point. The specific operations include:

[0053] Since the Jones matrix of a single pixel point is designed before phase change, the Jones matrix of the phase change material structural unit with anisotropic structure can be expressed as:

[0054]

[0055] Where, and denote the polarization response of the structural unit along its major and minor axes, respectively. t o and t e is the modulus value, corresponding to the transmittance of the structural unit in the amorphous state in the total database, and is the phase angle, corresponding to the phase retardation of the structural unit in the amorphous state in the total database. The subscript o represents the polarization response to light polarized along the long axis of the structural unit, and the subscript e represents the polarization response to light polarized along the short axis of the structural unit. The long and short axes of the structural unit only overlap with the x and y directions when the nanopillars are not rotated. R(-θ) represents the rotation matrix with an orientation angle of θ, and R(θ) is its inverse matrix.

[0056] When considering a general planar metasurface, due to its in-plane symmetry, its diagonal terms are always equal, so at most three polarization channels can be independently controlled, including two co-polarization channels and one cross-polarization channel. and Furthermore, the orientation angle θ can be arbitrarily selected, so by regulating these three parameters, independent phase control is applied to the three polarization multiplexing channels.

[0057] Due to the discreteness of the total database, it is not always possible to precisely control the structural parameters so that the Jones matrix of the designed metasurface unit meets the required Jones matrix. Therefore, the error of the Jones matrix needs to be considered, and a suitable screening algorithm needs to be designed. In this embodiment, the error of the argument at each term of the Jones matrix, that is, the error of the phase, is mainly considered. Through reasonable design of the threshold, a batch of data in the total database with a Jones matrix error less than the threshold is allowed to pass through the screening and stored in the transition database.

[0058] This embodiment designs a multi-threshold forward screening system to reduce the average error. Figure 3 The screening steps of three thresholds are shown, including: comparing the error point by point in the total database according to the target phase data of the amorphous state; judging whether the error result meets the minimum threshold. If it meets, the data is stored in the transition database; if not, judging whether the error result meets the medium threshold. If it meets, the data is stored in the transition database; if not, judging whether the error result meets the maximum threshold. Only when it meets, the data is stored in the transition database. Since the amount of data that meets the same error threshold at different pixel points of the metasurface varies significantly, when the amount of data in the transition database at this pixel point is too small, the error tolerance is increased, and when the amount of data is too large, the error tolerance is decreased.

[0059] Step3: When the structural unit changes to the crystalline state, since the orientation angle of the structural unit is fixed and the Jones matrix regulation ability of a single structural unit is limited, the Jones matrix of a single structural unit is considered to be extended to the superposition Jones matrix of multiple structures. That is, the "field" shape composed of four adjacent structural units is regarded as a pixel point. The Jones matrix at this pixel point can be regarded as the superposition of the Jones matrices of the two structural units at the diagonal corners. That is, there are a total of four structural units in the "field" shape. The superposition of the unit structures in the upper left and lower right, and the lower left and upper right can each form the required Jones matrix. In addition to this cross arrangement, other similar arrangement methods can also achieve this function.

[0060] Based on this superposition Jones matrix, the data with the smallest independent phase regulation error of the other three polarization channels after phase change is selected from the transition database to determine the specific structural parameters and orientation angles at all positions of the metasurface. The specific operations include:

[0061] As Figure 5 shown, if a certain "field" shape starts from the structural unit in the upper left corner, its corresponding Jones matrix can be considered as J1, J2, J3, J4. If the target Jones matrix at this pixel point is J target , then by selecting appropriate structural parameters and rotation angles, J1 + J2 = J3 + J4 = J targetAnd by reasonably selecting the data in the transition database, this function is achieved under the premise of minimizing the error. And because the optical properties of the metasurface structural unit will change after the material phase change, by combining the four parameters of the dual structural unit under the condition of fixed orientation angle, the three phase terms of the corresponding superimposed Jones matrix can be independently controlled, thereby realizing independent phase control of the three new polarization channels after the phase change. The Jones matrix mentioned above is a complex matrix with amplitude terms and phase terms. In order to maximize the number of channels when designing the metasurface, this embodiment only considers independently controlling the phase term of the Jones matrix.

[0062] The errors involved in Step 2 and Step 3 refer to the difference between the ideal Jones matrix and the actual Jones matrix, and in this embodiment, specifically refer to the difference in the phase angle of the phase term.

[0063] The Jones matrix-based design proposed in this embodiment is not limited to designing a single-pixel Jones matrix in the crystalline state and designing a dual-pixel superimposed Jones matrix in the amorphous state. A single-pixel, dual-pixel, or four-pixel Jones matrix can also be arbitrarily selected in the crystalline and amorphous states, as long as the use of a single-pixel structure Jones matrix before and after the phase change is avoided. Because single-structure pixels are used, the adjustable degrees of freedom are not enough, and theoretically six channels cannot be achieved.

[0064] The library-based forward search design of the present invention is not limited to the application of two-state metasurfaces, and can also be applied to the design of three-state or more-state metasurfaces if the database is reasonable.

[0065] Any structural unit with birefringence properties that can control the geometric phase and transmission / resonance phase can achieve the functions shown in the present invention, including metal materials, dielectric materials, composite materials, multilayer materials, etc.

[0066] In this embodiment, the design is based on a forward process of first amorphous state and then crystalline state, and it can also be designed according to a process of first crystalline state and then amorphous state.

[0067] This embodiment provides a method for achieving phase modulation by designing the appropriate size and orientation angle of each structural unit of the metasurface, thereby realizing a multifocal metalens. This effectively addresses the problems of traditional metasurfaces, such as the lack of dynamic control, small information capacity, difficulty in manufacturing, and high manufacturing costs, which make them difficult to meet practical application requirements. This embodiment method has the advantages of compactness, scalability, and broad application prospects in the fields of information encryption and multifunctional switchable wavefront control.

[0068] Example 2

[0069] Based on the method proposed in Example 1, its function is specifically manifested as six different independent phase control results, such as Figure 1The dual-state six-channel polarization multiplexing metasurface based on phase change material proposed in this embodiment consists of a two-layer structure, which is composed of a phase change material Sb2S3 nanocolumn array layer and a S i O2 substrate layer. The metasurface has a diameter of D = 40 μm, a focal length of f = 80 μm, a period of P = 400 μm, and a nanopillar height of H = 620 μm. The length and width were selected from a database derived from simulations. The target operating wavelength is λ = 633 μm.

[0070] When the phase change material Sb2S3 nanorods are in the amorphous state, based on the single nanorod Jones matrix, the metasurface adds three independent phases to the three outgoing lights through the three polarization channels (xx, yy, xy (or yx)).

[0071] When the phase change material Sb2S3 nanorods are in the crystalline state, based on the double nanorod Jones matrix, the metasurface adds three independent phases to the three outgoing lights through the three polarization channels (xx, yy, xy (or yx)).

[0072] Since the six phase controls can be designed independently, this embodiment adds the phase distribution of the multi-focal metalens to The phase information of six unrelated off-focus metalenses is recorded into the same metasurface. They are focused on six preset positions on the focal plane, which are: x1 = -3μm; y1 = 4μm; x2 = 3μm; y2 = 4μm; x3 = 5μm; y3 = 0μm; x4 = 3μm; y4 = -4μm; x5 = -3μm; y5 = -4μm; x6 = -5μm; y6 = 0μm. The pixel point at the metalens (x, y) is about the preset focus (x i ,y i )'s phase distribution It can be expressed as follows:

[0073]

[0074] Where λ is the operating wavelength and f is the operating focal length.

[0075] Figure 4 These are the intensity images of the metalenses with different polarization channels at the focus in different crystallization states. It can be seen that by selecting the corresponding crystallization state and polarization channel, the focus distribution can be observed at the preset position on the focal plane.

Claims

1. A design method for a dual-state six-channel polarization multiplexing metasurface based on phase change materials, characterized by: The following steps are involved: Designing building blocks based on phase-change materials; Using the designed structural units, a dual-state six-channel polarization multiplexing metasurface was constructed; By using a screening algorithm to optimize the geometric structure and orientation angle of the structural unit, the optimized dual-state six-channel polarization multiplexing metasurface can record six unrelated phase information into the same dual-state six-channel polarization multiplexing metasurface; The screening algorithm optimizes the geometric structure and orientation angle of the structural unit, and the specific operations include: Step 1: Based on a given operating wavelength and a preset height and a preset period of the dual-state six-channel polarization multiplexing metasurface, the polarization responses of structural units of different sizes in the crystalline and amorphous states are scanned to obtain a total database, which includes a variety of optional geometric structures of the structural units; Step 2: When the structural unit is in an amorphous state, each structural unit is regarded as a pixel point. Under a set error, based on the Jones matrix of a single structural unit, all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before the phase transition are screened from the total database, and the resulting structures are stored as a transition database. The transition database includes all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before the phase transition selected from the total database and the orientation angles corresponding to the geometric structures. Step 3: When the structural unit undergoes a phase transition to a crystalline state, the T-shaped structure formed by four adjacent structural units is regarded as a pixel point, and the Jones matrix at this pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line. Based on the Jones matrix at this pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase transition with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface.

2. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: The polarization response includes: the transmittance and phase delay of the structural unit under the illumination of linearly polarized light along the long / short axis direction of the structural unit without applying an orientation angle but changing the length and width dimensions. This process is achieved by the finite difference time domain method FDTD.

3. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 2, characterized in that: In step 2, when the structural unit is in the amorphous state, each structural unit is regarded as a pixel point. Under the set error, based on the Jones matrix of a single structural unit, all optional geometric structures of a batch of structural units that can meet the independent phase control of the three polarization channels before phase transition are screened from the total database and stored as a transition database. The specific operations include: The Jones matrix of a single structural unit is expressed as: Where, and denote the polarization response of the structural unit along its major and minor axes, respectively. t o and t e is the modulus value, corresponding to the transmittance of the structural unit in the amorphous state in the total database, and is the angle of magnitude, corresponding to the phase delay of the structural unit in the amorphous state in the total database. The subscript o represents the polarization response under the illumination of light with the polarization direction along the long axis of the structural unit, and the subscript e represents the polarization response under the illumination of light with the polarization direction along the short axis of the structural unit. R(-θ) represents the rotation matrix with an orientation angle of θ, and R(θ) is its inverse matrix. By regulating the amorphous state of the structural unit and orientation angle θ, allowing a batch of optional geometric structures of structural units in the total database that can achieve Jones matrix errors less than a threshold to pass the screening and be stored in the transition database; And stored in the transition database and orientation angle θ, independent phase control can be applied to two co-polarization channels and one cross-polarization channel, that is, three parameters determine three equations.

4. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 3, characterized in that: The amorphous state of the structural unit is controlled by and orientation angle θ, allowing a group of optional geometric structures of structural units in the total database that can achieve Jones matrix error less than a threshold to pass the screening and be stored in the transition database, specifically including: By regulating the amorphous state of the structural unit and orientation angle θ, and a multi-threshold screening method is used to screen out a batch of optional geometric structures of structural units from the total database, and the optional geometric structures of this batch of structural units and the orientation angles corresponding to each geometric structure are stored in the transition database.

5. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: In step 3, when the structural unit phase changes to a crystalline state, the field shape composed of four adjacent structural units is regarded as a pixel point, and the Jones matrix at the pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line; based on the Jones matrix at the pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase change and the minimum error and the orientation angle corresponding to each geometric structure are selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface. The specific operations include: Assuming we start from the structural unit in the upper left corner of the field shape, the corresponding Jones matrix is ​​expressed as: J1, J2, J3, J4; Assume that the target Jones matrix of the pixel is J target By selecting the structural parameters and orientation angles of the structural units from the transition database, J1+J2=J3+J4=J target .

6. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: When the structural unit is in an amorphous state, each structural unit is regarded as a pixel point. When the structural unit undergoes a phase transition to a crystalline state, the shape of four adjacent structural units is regarded as a pixel point. This can be replaced by: When the structural unit is in the amorphous state and the crystalline state, the Jones matrix of a single structural unit, the Jones matrix of a double structural unit superposition, and the Jones matrix of a quadruple structural unit superposition are arbitrarily selected. The selection only needs to satisfy the following: the Jones matrix of a single structural unit cannot be used before and after the phase change.

7. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: The structural unit is any structural unit with birefringence properties that can regulate the geometric phase and the transmission / resonance phase.

8. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: The structural unit includes, from top to bottom, a phase change material nanocolumn and a substrate.

9. The design method of a dual-state six-channel polarization multiplexing metasurface based on phase change material according to claim 1, characterized in that: Steps 2 and 3 can be replaced by the following steps: When the structural unit is in a crystalline state, each structural unit is regarded as a pixel point. Under a set error, all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before phase transition are screened from the total database based on the Jones matrix of the single structural unit, and the structures are stored as a transition database. The transition database includes all optional geometric structures of a batch of structural units that can satisfy the independent phase regulation of the three polarization channels before phase transition selected from the total database and the orientation angles corresponding to the geometric structures; When the structural unit undergoes a phase transition to an amorphous state, the T-shaped structure composed of four adjacent structural units is regarded as a pixel point, and the Jones matrix at this pixel point is regarded as the superposition of the Jones matrices of the two structural units at the diagonal line. Based on the Jones matrix at this pixel point, the geometric structure of the structural unit that can satisfy the independent phase control of the other three polarization channels after the phase transition with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, thereby determining the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface.

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