Double-state six-channel polarization multiplexing metasurface design method based on phase change material

Abstract

The invention discloses a dual-state six-channel polarization multiplexing metasurface design method based on a phase change material. The method comprises the following steps: designing a structural unit based on the phase change material; a double-state six-channel polarization multiplexing metasurface is constructed by using the designed structural unit; the geometric structures and the orientation angles of the structural units are optimized by adopting a screening algorithm, and the optimized double-state six-channel polarization multiplexing metasurface can record six kinds of irrelevant phase information into the same double-state six-channel polarization multiplexing metasurface. The method is based on the metasurface Jones matrix regulation and control theory, comprehensively utilizes the geometric phase and the transmission / resonance phase of the structural unit, is suitable for most types of metasurface unit structures, has wide applicability, can be applied to the fields of metasurface optical encryption, multifunctional wavefront regulation and control and the like, and has important practical value.

Description

Technical Field

[0001] The present invention belongs to the technical field of polarization multiplexing metasurface design, and specifically is 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 manipulate light flexibly and efficiently 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. As an emerging planar optical component, metasurfaces have attracted widespread attention in recent years due to their compact structural design and subwavelength resolution. Thanks to their high compatibility with modern micro-nano manufacturing technology, metasurfaces have demonstrated excellent optical manipulation capabilities in the fields of superlenses, structured beam generation, holography, optical encryption, and optical communications.

[0003] Optical phase change materials are functional materials that can undergo reversible refractive index changes under external stimuli (such as temperature changes, voltage application, 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 characteristics. Although phase change materials provide new possibilities for the dynamic adjustability of metasurfaces, existing research on 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 phase change. Furthermore, existing methods mostly focus on local phase control rather than overall 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 solved urgently. Summary of the invention

[0004] Purpose of the invention: In order 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, and utilizes the Jones matrix control of the metasurface 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, comprising the following steps:

[0006] Design 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: According to a given working wavelength and a preset height and a preset period of a dual-state six-channel polarization multiplexing metasurface, respectively scan the polarization responses of structural units of different sizes in the crystalline state and the amorphous state to obtain a total database, wherein the total database 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, and 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 the phase change are screened from the total database based on the Jones matrix of the single structural unit, and stored as a transition database, wherein 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 change screened from the total database and the orientation angles corresponding to the geometric structures;

[0012] Step 3: When the structural unit phase changes to a crystalline state, the T-shaped structure 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 with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, so as to determine 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 irradiation 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, and the process is implemented by the finite difference time domain method FDTD.

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

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

[0016]

[0017] In the formula, 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 total database in the amorphous state, and is the phase angle, 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 light irradiation with the polarization direction along the long axis of the structural unit, and the subscript e represents the polarization response under the light irradiation 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, it is possible to apply independent phase control 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 by 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 the threshold to pass the screening and be stored in the transition database, including:

[0021] By regulating the amorphous state of the structural unit and orientation angle θ, and utilize a multi-threshold screening method to screen out a batch of optional geometric structures of structural units from the total database, and store these batches of optional geometric structures of structural units and the orientation angles corresponding to each geometric structure into a transition database.

[0022] Further, 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 are selected from the transition database, so as to determine the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface, and the specific operations include:

[0023] Assuming that 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 changes into 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, a single structural unit Jones matrix, a double structural unit superimposed Jones matrix, and a quadruple structural unit superimposed Jones matrix are arbitrarily selected respectively. The selection only needs to satisfy the following: a single structural unit Jones matrix cannot be used both before and after the phase change.

[0027] Furthermore, the structural unit is any structural unit with birefringence properties that can adjust 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, and 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 the phase change are screened from the total database based on the Jones matrix of the single structural unit, and stored as a transition database, wherein 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 change screened from the total database and the orientation angles corresponding to the geometric structures;

[0031] When the structural unit changes phase 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 change 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, comprehensively utilizing 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 change characteristics of the transmission / resonance phase of the metasurface after the phase change, the four-atom supercell is designed to screen data that meets the requirements for independent regulation of the remaining three polarization channels after the phase change from the initial database, and finally determine 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 regulation, 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 / incident light and the crystal state of the material, independent phase control can be added to the six polarization channels.

[0036] (4) The method of the present invention is universal. As long as the structural unit of the designed metasurface has a transmission / resonance phase and a geometric phase, the present invention 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 according to the designed Jones matrix, the corresponding Jones matrix is ​​directly obtained according to the metasurface structure parameters and then compared with the preset Jones matrix; (2) the design is completely in accordance with 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 is also convenient for designing 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 a method for designing 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 schematic diagram of the top view of the structure unit constituting the super surface in Example 1;

[0041] Figure 3 A flow chart of a method for designing 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 objectives, 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 accompanying drawings and embodiments.

[0045] Embodiment 1:

[0046] This embodiment proposes a dual-state six-channel polarization multiplexing metasurface design method based on phase change material, 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 units shown in the figure each include, from top to bottom, a phase change material nanorod and a substrate. The method proposed in this embodiment is not limited to Figure 2 The structural unit is shown.

[0048] Step 2: Use the designed structural unit to construct a dual-state six-channel polarization multiplexing metasurface, such as Figure 1 As shown, the dual-state six-channel polarization multiplexing metasurface is composed 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: According to the given working wavelength and the preset height and preset period of the metasurface, the polarization responses of the phase change material unit structures of different sizes in the crystalline and amorphous states are scanned respectively to obtain the total database; the polarization response obtained by scanning refers to the transmittance and phase delay of the structure unit under the illumination of linear polarized light along the long / short axis direction (x direction and y direction) of the structure unit without applying the orientation angle but changing the length and width dimensions. 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 more 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. Under the allowable error, a batch of optional sizes (i.e., the length and width of the nanocolumn) that can satisfy the independent phase regulation of the three polarization channels before the phase change 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 nanocolumn) 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) at the pixel point that meet the screening threshold. The specific operations include:

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

[0054]

[0055] In the formula, 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 total database in the amorphous state, and is the phase angle, 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 light irradiation with the polarization direction along the long axis of the structural unit, and the subscript e represents the polarization response under the light irradiation with the polarization direction along the short axis of the structural unit. Only when the nanopillar does not rotate, the direction of the long and short axes of the structural unit overlaps with the x and y directions. 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 also be arbitrarily selected, so independent phase control is applied to the three polarization multiplexing channels by adjusting these three parameters.

[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, it is necessary to consider the error of the Jones matrix, and thus it is necessary to design a suitable screening algorithm. This embodiment focuses on considering the error of the argument at each item of the Jones matrix, that is, the error of the phase. Through the reasonable design of the threshold, a batch of data in the total database that can achieve 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 the 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, storing the data in the transition database; if it does not meet, judging whether the error result meets the medium threshold, if it meets, storing the data in the transition database; if it does not meet, judging whether the error result meets the maximum threshold, and only when it meets, storing the data 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 already fixed and the Jones matrix regulation ability of a single structural unit is limited, it is considered to expand the Jones matrix of a single structural unit into a superposed Jones matrix of multiple structures. That is, the "field" shape composed of four adjacent structural units is regarded as a pixel point, and 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. That is, there are a total of four structural units in the "field" shape, and 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 superposed Jones matrix, select the data from the transition database that can minimize the independent phase regulation error of the other three polarization channels after the phase change, so as 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, make J1 + J2 = J3 + J4 = J target, and by reasonably selecting the data in the transition database, this function is realized 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 when the orientation angle is fixed, the three phase terms of the corresponding superimposed Jones matrix can be independently adjusted, 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 specifically refer to the difference in the phase angle of the phase term in this embodiment.

[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 double-pixel superimposed Jones matrix in the amorphous state. It is also possible to arbitrarily select a single-pixel, double-pixel, or four-pixel Jones matrix in the crystalline and amorphous states, as long as the single-pixel structure Jones matrix is ​​avoided before and after the phase change. Because single-structure pixels are used, the adjustable degrees of freedom are not enough, and theoretically six channels cannot be achieved.

[0064] The design scheme of the present invention of forward searching by library 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 regulate geometric phase and transmission / resonance phase can realize 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 an amorphous state and then a crystalline state. It can also be designed based on a process of first a crystalline state and then an amorphous state.

[0067] This embodiment provides a method for realizing phase modulation by designing the reasonable size and orientation angle of each structural unit of the metasurface, and thereby realizing a multi-focus metalens, which effectively solves the problem that the traditional metasurface cannot be dynamically controlled, has a small information capacity, is difficult to manufacture, and has a high manufacturing cost, and is difficult to meet the needs of actual applications. The method of this embodiment has the advantages of compactness, scalability, and the like, and has 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, from top to bottom, a phase change material Sb2S3 nanocolumn array layer and a S i O2 substrate layer. The diameter of the metasurface is D = 40 μm, the focal length is f = 80 μm, the period is P = 400 μm, the height of the nanopillar is H = 620 μm, and the length and width are reasonably selected from the total database obtained by simulation. The target operating wavelength is λ = 633 μm.

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

[0072] Since the six phase adjustments 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] Among them, λ is the working wavelength and f is the working focal length.

[0075] Figure 4 These are intensity images of metalenses with different polarization channels at the focal point in different crystallization states. It can be seen that by selecting the corresponding crystallization state and polarization channel, the focal 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: Design 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: According to a given working wavelength and a preset height and a preset period of a dual-state six-channel polarization multiplexing metasurface, respectively scan the polarization responses of structural units of different sizes in the crystalline state and the amorphous state to obtain a total database, wherein the total database 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, and 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 the phase change are screened from the total database based on the Jones matrix of the single structural unit, and stored as a transition database, wherein 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 change screened from the total database and the orientation angles corresponding to the geometric structures; Step 3: When the structural unit phase changes to a crystalline state, the T-shaped structure 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 with the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, so as to determine the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface.

2. According to claim 1, a dual-state six-channel polarization multiplexing metasurface design method based on phase change material is characterized by: 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. The process is implemented by the finite difference time domain method FDTD.

3. According to claim 2, a dual-state six-channel polarization multiplexing metasurface design method based on phase change material is characterized by: In step 2, when the structural unit is in an amorphous state, each structural unit is regarded as a pixel point, and under a set error, a batch of structural units that can meet the independent phase regulation of the three polarization channels before phase change are selected from the total database based on the Jones matrix of the single structural unit, and stored as a transition database. The specific operations include: The Jones matrix of a single structural unit is expressed as: In the formula, 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 delay of the structural unit in the amorphous state in the total database, the subscript o represents the polarization response under the light irradiation with the polarization direction along the long axis of the structural unit, and the subscript e represents the polarization response under the light irradiation 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. According to claim 3, a dual-state six-channel polarization multiplexing metasurface design method based on phase change material is characterized by: The amorphous state of the structural unit is controlled by 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 the threshold to pass the screening and be stored in the transition database, including: By regulating the amorphous state of the structural unit and orientation angle θ, and utilize a multi-threshold screening method to screen out a batch of optional geometric structures of structural units from the total database, and store these batches of optional geometric structures of structural units and the orientation angles corresponding to each geometric structure into a 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 has the smallest error and the orientation angle corresponding to each geometric structure are selected from the transition database, so as to determine the specific geometric structure and orientation angle of all structural units of the dual-state six-channel polarization multiplexing metasurface, and the specific operations include: Assuming that 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, and when the structural unit changes into a crystalline state, the shape of four adjacent structural units is regarded as a pixel point, which can be replaced by: When the structural unit is in the amorphous state and the crystalline state, a single structural unit Jones matrix, a double structural unit superimposed Jones matrix, and a quadruple structural unit superimposed Jones matrix are arbitrarily selected respectively. The selection only needs to satisfy the following: a single structural unit Jones matrix cannot be used both 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 adjust 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: The steps 2 and 3 described above 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, and 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 the phase change are screened from the total database based on the Jones matrix of the single structural unit, and stored as a transition database, wherein 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 change screened from the total database and the orientation angles corresponding to the geometric structures; When the structural unit changes phase 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 change 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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