Chiral metasurface and application method thereof in beam vector polarization conversion

Abstract

The invention discloses a chiral metasurface and an application method thereof in beam vector polarization conversion, and belongs to the field of optical devices, the chiral metasurface comprises a plurality of superatoms arranged periodically, each superatom comprises a bottom end cuboid substrate and a top end resonator growing at the top end of the bottom end cuboid substrate and breaking in mirror symmetry, the top resonator comprises a top cuboid and elliptic cylinders located on the two sides of the top cuboid. By adopting the chiral metasurface and the application method of the chiral metasurface in beam vector polarization conversion, accurate regulation and control of a terahertz wave full Poincare sphere vector polarization state and generation of any vector wave beams are realized through mirror symmetry breaking design, geometric parameter spatial evolution, mirror overturning operation and in-plane rotation operation of a superatom structure; the limitation of the coverage range and the regulation and control dimension of the traditional polarization control technology is broken through.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a chiral metasurface and an application method thereof in light beam vector polarization conversion. Background Art

[0002] Polarization is one of the key parameters of light waves, and the description of the vibration direction of its electric field vector is of special importance in scientific research and technological applications in the terahertz band. It is not only the core carrier of information carried by terahertz waves, but also can indirectly reflect the intrinsic chirality of optical media through changes in polarization state. Polarization control of terahertz waves is of strategic significance in the fields of terahertz imaging, spectral analysis, wireless communications, etc., and is one of the core technical bottlenecks in the manipulation of terahertz multi-dimensional light fields. The current mature polarization control scheme is mainly based on bulk optical elements of birefringent crystals, which change the phase difference of orthogonal linear polarization components through the polarization-dependent dielectric response of anisotropic molecules to achieve polarization filtering and conversion. However, this scheme faces the inherent defects of large device size and single control dimension in the terahertz band.

[0003] In the cross section of a terahertz beam, the difference in the uniformity of the local polarization distribution forms the essential difference between a scalar beam and a vector beam. The generation and control of vector beams in the terahertz band presents significant technical challenges and must meet the requirements for fine control of spatial polarization states at the subwavelength scale. To meet this requirement, existing technical solutions include the intracavity method of directly exciting a specific vector beam with a laser resonant cavity, the extracavity conversion method based on coherent synthesis of the phase distribution of scalar polarized beams, and the direct conversion method using new devices such as subwavelength gratings and combined wave plates. However, the above solutions generally have the problems of limited polarization state coverage and low control efficiency in the terahertz band.

[0004] In recent years, the development of nanophotonics and metasurface technology has provided an innovative path for the manipulation of terahertz vector polarized beams. Among them, the subwavelength chiral meta-atomic structure, through the shape birefringence effect and mirror symmetry breaking design, has the ability to coordinate the multi-dimensional control of terahertz wave amplitude, phase, and polarization. Based on the polarization decomposition and synthesis theory, the core of terahertz wave polarization state control lies in the precise adjustment of the amplitude ratio and phase difference of orthogonal polarization components. Although the existing metasurface phase response mechanism (resonance phase, geometric phase, transmission phase, etc.) can realize the conversion between linear polarization and circular polarization, it is limited to the pure phase control mode, and the polarization state coverage on the Poincare sphere is limited. The solution of achieving complex amplitude control through interference of meta-atomic wave components has the engineering difficulties of doubling the size of the unit structure and low near-field interference efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a chiral metasurface and its application method in light beam vector polarization conversion to solve the above technical problems.

[0006] To achieve the above objectives, the present invention provides a chiral metasurface, comprising a plurality of periodically arranged superatoms, each of which comprises a bottom rectangular substrate and a top resonator grown on the top of the bottom rectangular substrate and having broken mirror symmetry, wherein the top resonator comprises a top rectangular block and elliptical cylinders located on both sides of the top rectangular block.

[0007] Preferably, the arrangement period of the multiple superatoms is P = 300 μm;

[0008] The height H1 of the bottom rectangular substrate is 600 μm. The cross-section of the bottom rectangular substrate is a square, and the side length of the square is equal to the arrangement period of the multiple super atoms.

[0009] The top of the top resonator is flat, and the height of the top resonator is H1 = 400μm; the length of the top rectangular parallelepiped is L = 200μm, and the width is d = 20μm; the length of the minor axis of the elliptical cylinder is W1 = 30μm, and the length of half of the major axis of the elliptical cylinder is W2∈(0μm, 130μm). The translation amount D∈(0μm, 60μm) after the two elliptical cylinders are symmetrically translated up and down.

[0010] Preferably, the bottom rectangular parallelepiped substrate and the top resonator are both made of high-resistance silicon with a dielectric constant ε=11.9.

[0011] A method for applying a chiral metasurface to polarization conversion of a light beam vector comprises the following steps:

[0012] S1. Construct chiral metasurface and set metaatom geometry parameters;

[0013] S2. Determine the factors that affect the complex amplitude of the transmitted electric field, including mirror symmetry breaking, superatom geometric parameters, mirror flip operation and in-plane rotation angle;

[0014] S3, mirror symmetry breaking: breaking the superatom mirror symmetry, triggering the polarization conversion effect, and generating the fundamental polarization state on the Poincare sphere;

[0015] S4. Hyperatom geometry parameter setting: Evolve the parameters D and W2 in the ranges of (0μm, 130μm) and (0μm, 60μm) respectively to obtain different linear polarization transmission amplitude and phase combinations, preliminarily expanding the coverage of the Poincare sphere polarization state;

[0016] S5, mirror flip operation: Perform mirror reflection on the meta-atom to generate its chiral enantiomer. Utilize the complementarity between the transmitted polarization state of the chiral enantiomer and the original structure to further expand the polarization state coverage of the Poincare sphere.

[0017] S6, in-plane rotation angle: Under the premise of setting D, the in-plane rotation angle θ of the top resonator is changed, and the polarization state coverage of the Poincare sphere is further expanded through different θ-W2 combinations;

[0018] S7. Design a chiral metasurface device to verify vector beam generation: Divide the chiral metasurface area and configure corresponding meta-atoms according to the target polarization state distribution to achieve vector polarization transformation of the transmitted light beam.

[0019] Preferably, step S2 specifically includes the following steps:

[0020] S21. Correlating the transmitted electric field of the chiral metasurface using the transmission matrix T in a linear polarization basis With the incident electric field

[0021]

[0022] Where, and Represent the complex amplitude of the outgoing light in the x and y polarization directions respectively; and Represents the complex amplitude of the incident light in the x and y polarization directions respectively; t xx represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component; t xy represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component; t yx The transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component; t yy The transmission coefficient represents the direct transmission of the incident y-polarization component as the outgoing y-polarization component;

[0023] S22. Set the transmission matrix T(θ) after the in-plane rotation θ to be:

[0024]

[0025] in,

[0026]

[0027] Where M -1 (θ) represents the inverse rotation matrix of the in-plane rotation θ; M(θ) represents the forward rotation matrix of the in-plane rotation θ; T xx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T xy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T yx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ; T yy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ;

[0028] S23. Using trigonometric function relationships, transform formula (4) to obtain:

[0029]

[0030] S24. The electric field of the transmitted terahertz wave when the linearly polarized wave is incident is obtained:

[0031]

[0032] Where, represents the complex amplitude of the electric field along the x-polarization direction in the transmitted terahertz wave; represents the complex amplitude of the electric field along the y-polarization direction in the transmitted terahertz wave;

[0033] S25, from formula (4) and formula (5), the factors affecting the complex amplitude of the transmitted electric field include the intrinsic polarization component term, the same polarization angle modulation term and the cross polarization angle modulation term, among which the intrinsic polarization component term is determined by the meta-atom geometric parameters, and the same polarization angle modulation term is determined by the transmission coefficient t xx and t yy and θ, the cross-polarization angle modulation term is determined by the transmission coefficient t xy and t yx and θ determination.

[0034] Preferably, the control step length in step S3 is 2 μm.

[0035] Preferably, in step S7, when generating a fully linearly polarized vector beam, the linear polarization state of the S3=0 region on the Poincare sphere is selected, and the chiral metasurface is divided into multiple regions. Metaatoms are configured in each region to generate linearly polarized waves of different azimuth angles, thereby realizing the polarization distribution design of the transmitted beam.

[0036] Preferably, in step S7, when generating a vector beam containing linear polarization, circular polarization, and elliptical polarization components, polarization states at different positions on the Poincare sphere are selected, the metasurface area is divided, and metaatoms are configured to achieve a combined distribution of multiple polarization states.

[0037] Therefore, the present invention uses the above-mentioned chiral metasurface and its application method for beam vector polarization conversion, which has the following beneficial effects:

[0038] 1. Full Poincare sphere polarization state coverage: Utilizing hyperatom geometric parameter evolution and mirror flipping operations, a set of complementary polarization states is generated, expanding the coverage of the Poincare sphere.

[0039] 2. Multi-dimensional polarization control capability: Through the control of intrinsic polarization characteristics by geometric parameters, the introduction of geometric phase by in-plane rotation, and the generation of chiral enantiomers by mirror flipping, the coordinated modulation of amplitude ratio, phase difference, and chirality-dependent phase is achieved, supporting the free conversion of linear polarization, circular polarization, and elliptical polarization;

[0040] 3. Customized generation of vector beams: By configuring meta-atoms in partitions, a spatial gradient distribution of polarization states within the cross section can be achieved, enabling the generation of complex vector beams such as radial polarization and azimuthal polarization.

[0041] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of a method for applying a chiral metasurface to light beam vector polarization conversion according to the present invention;

[0043] Figure 2 Schematic diagram of polarization state conversion achieved by using mirror symmetry breaking, geometric parameter spatial evolution, and mirror flipping as described in the simulation experiment of the present invention; (a) is a flowchart of the operation of obtaining the polarization state; (b) is a diagram illustrating the geometric parameters of the meta-atom; (c) is the x-polarization transmission amplitude |t at 0.7 THz obtained by adjusting the geometric parameters D and W2 xx | distribution diagram; (d) is the x-polarization transmission amplitude arg(t xx ) distribution diagram; (e) is the y-polarization transmission amplitude at 0.7 THz obtained by adjusting the geometric parameters D and W2 |t yx | Distribution diagram; (f) is the y-polarization transmission amplitude arg(t yx ) distribution diagram; (g) is the polarization state obtained after the mirror flip operation on the Poincare sphere;

[0044] Figure 3 Schematic diagram of the expansion of polarization state by using in-plane rotation of superatoms as described in the simulation experiment of the present invention; (a) is a schematic diagram of the operation of obtaining the in-plane rotation angle of the polarization state; (b) is the x-polarization transmission amplitude |t at 0.7 THz obtained after adjusting the in-plane rotation angle θ xx | distribution diagram; (c) is the x-polarization transmission amplitude arg(t xx ) distribution diagram; (d) is the y-polarization transmission amplitude at 0.7 THz obtained after adjusting the in-plane rotation angle θ |t yx | Distribution diagram; (e) is the y-polarization transmission amplitude arg(t yx) distribution diagram; (f) is a schematic diagram of the polarization state obtained by the in-plane rotation operation represented by the Poincare sphere; (g) is an example diagram of the obtained polarization state (D = 30 μm, W2 = 4 μm);

[0045] Figure 4 Result diagrams of cases of generating vector beams using a metasurface as described in the simulation experiment of the present invention; (a) is a Poincare sphere representation of the polarization state of the first case; (b) is a schematic diagram of the regional division of the metasurface of the first case; (c) is a simulation result diagram of the cross section of the transmitted beam of the first case; (d) is a Poincare sphere representation of the polarization state of the second case; (e) is a schematic diagram of the regional division of the metasurface of the second case; (f) is a simulation result diagram of the cross section of the transmitted beam of the second case.

[0046] Reference numerals

[0047] 1. Bottom rectangular substrate; 2. Top resonator; 21. Top rectangular; 22. Elliptical cylinder. DETAILED DESCRIPTION

[0048] In order to make the purposes, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0049] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0050] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0051] A chiral metasurface includes multiple metaatoms arranged in a periodic pattern. Each of the multiple metaatoms includes a bottom rectangular substrate 1 and a top resonator 2 grown on the top of the bottom rectangular substrate 1 and having broken mirror symmetry. The top resonator 2 includes a top rectangular block 21 and elliptical cylinders 22 located on both sides of the top rectangular block 21.

[0052] Specifically, the arrangement period of multiple superatoms is P = 300 μm; the height of the bottom rectangular substrate 1 is H1 = 600 μm; the cross-section of the bottom rectangular substrate 1 is a square, and the side length of the square is equal to the arrangement period of multiple superatoms; the top of the top resonator 2 is flat, and the height of the top resonator 2 is H1 = 400 μm; the length of the top rectangular 21 is L = 200 μm, and the width is d = 20 μm; the short axis length of the elliptical cylinder 22 is W1 = 30 μm, and the length of half the long axis of the elliptical cylinder 22 is W2∈(0 μm, 130 μm), and the translation amount D∈(0 μm, 60 μm) after the two elliptical cylinders 22 are symmetrically translated up and down, that is, the parameters D and W2 are variables.

[0053] The materials of the bottom rectangular parallelepiped substrate 1 and the top resonator 2 are both high-resistance silicon with a dielectric constant ε=11.9.

[0054] like Figure 1 As shown, a method for applying a chiral metasurface to polarization conversion of a light beam vector includes the following steps:

[0055] S1. Construct chiral metasurface and set metaatom geometry parameters;

[0056] S2. Determine the factors that affect the complex amplitude of the transmitted electric field, including mirror symmetry breaking, superatom geometric parameters, mirror flip operation and in-plane rotation angle;

[0057] Step S2 specifically includes the following steps:

[0058] S21. Correlating the transmitted electric field of the chiral metasurface using the transmission matrix T in a linear polarization basis With the incident electric field

[0059]

[0060] Where, and Represent the complex amplitude of the outgoing light in the x and y polarization directions respectively; and Represents the complex amplitude of the incident light in the x and y polarization directions respectively; t xx represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component; t xy represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component; t yx The transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component; t yy The transmission coefficient represents the direct transmission of the incident y-polarization component as the outgoing y-polarization component;

[0061] S22. Set the transmission matrix T(θ) after the in-plane rotation θ to be:

[0062]

[0063] in,

[0064]

[0065] Where M -1 (θ) represents the inverse rotation matrix of the in-plane rotation θ; M(θ) represents the forward rotation matrix of the in-plane rotation θ; T xx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T xy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T yx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ; T yy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ;

[0066] S23. Using trigonometric function relationships, transform formula (4) to obtain:

[0067]

[0068] S24. The electric field of the transmitted terahertz wave when the linearly polarized wave is incident is obtained:

[0069]

[0070] Where, represents the complex amplitude of the electric field along the x-polarization direction in the transmitted terahertz wave; represents the complex amplitude of the electric field along the y-polarization direction in the transmitted terahertz wave;

[0071] S25, from formula (4) and formula (5), the factors affecting the complex amplitude of the transmitted electric field include the intrinsic polarization component term, the same polarization angle modulation term and the cross polarization angle modulation term, among which the intrinsic polarization component term is determined by the meta-atom geometric parameters, and the same polarization angle modulation term is determined by the transmission coefficient t xx and t yy and θ, the cross-polarization angle modulation term is determined by the transmission coefficient t xy and t yx These modulation terms are deeply coupled with the rotation operation through the structural properties of the metaatom, so that the polarization state of the transmitted wave can be designed from the perspectives of mirror symmetry breaking, metaatom geometric parameters, mirror flip operation and in-plane rotation angle.

[0072] S3, mirror symmetry breaking: breaking the superatom mirror symmetry, triggering the polarization conversion effect, and generating the fundamental polarization state on the Poincare sphere;

[0073] The control step size in step S3 is 2 μm.

[0074] S4. Hyperatom geometry parameter setting: Evolve the parameters D and W2 in the ranges of (0μm, 130μm) and (0μm, 60μm) respectively to obtain different linear polarization transmission amplitude and phase combinations, preliminarily expanding the coverage of the Poincare sphere polarization state;

[0075] S5, mirror flip operation: Perform mirror reflection on the meta-atom to generate its chiral enantiomer. Utilize the complementarity between the transmitted polarization state of the chiral enantiomer and the original structure to further expand the polarization state coverage of the Poincare sphere.

[0076] S6, in-plane rotation angle: Under the premise of setting D, change the in-plane rotation angle θ of the top resonator 2, and further expand the polarization state coverage of the Poincare sphere through different θ-W2 combinations;

[0077] S7. Design a chiral metasurface device to verify vector beam generation: Divide the chiral metasurface area and configure corresponding meta-atoms according to the target polarization state distribution to achieve vector polarization transformation of the transmitted light beam.

[0078] In step S7, when generating a fully linearly polarized vector beam, the linear polarization state of the S3=0 region on the Poincare sphere is selected, and the chiral metasurface is divided into multiple regions. Metaatoms are configured in each region to generate linearly polarized waves of different azimuth angles, thereby realizing the polarization distribution design of the transmitted beam.

[0079] In step S7, when generating a vector beam containing linear polarization, circular polarization, and elliptical polarization components, the polarization states at different positions on the Poincare sphere are selected, the metasurface area is divided, and metaatoms are configured to achieve a combined distribution of multiple polarization states.

[0080] Simulation experiment

[0081] The chiral metasurface described in the present invention is constructed and evolved with a step size of 2 μm within the range of parameters D and W2. The simulated linear polarization transmission amplitude and phase are as follows: Figure 2 As shown in the figure, near the middle of the geometric parameter space, the mirror symmetry breaking of the meta-atom triggers a significant polarization conversion effect. The amplitude of the cross-polarization component is large, and the phase of the co-polarization component undergoes a sudden change. From the perspective of the entire geometric parameter space of the simulation, a large number of amplitude ratio-phase difference combinations, i.e., various polarization states, can be obtained. The above-mentioned various polarization states are plotted on the Poincare sphere, and the following is obtained: Figure 2The area covered by the dots in (g) almost covers half of the Poincare sphere. In order to further increase the coverage area, a mirror symmetry operation is performed to obtain a chiral enantiomer, whose transmission polarization state is Figure 2 From the square points in (g), we can see that the total coverage area of ​​the two operations has occupied more than two-thirds of the sphere.

[0082] Furthermore, Figure 3 As shown, the top resonator 2 is rotated clockwise around its longitudinal symmetry center, that is, the in-plane rotation angle is set to θ. At this time, a curve with D = 30μm is selected for analysis. The values ​​of the in-plane rotation angle θ are set to 0°, 22.5°, 45° and 67.5°, respectively, and the following is obtained: Figure 3 (b)- Figure 3 From the modulus and phase of the transmission coefficient shown in (e), it can be seen that with the change of the in-plane rotation angle θ, the amplitude and phase of the co-polarized and cross-polarized components in the transmitted wave change significantly. Therefore, it can be seen that different polarization states can be obtained by selecting different in-plane rotation angles θ-W2. The new polarization states obtained by the above rotation operation are plotted on the Poincare sphere, showing that the polarization state undergoes significant changes in both longitude and latitude on the sphere under different values ​​of the in-plane rotation angle θ. At this time, the polarization states of linear polarization, circular polarization, and elliptical polarization components (D = 30μm, W2 = 4μm) are selected as examples to plot polarization ellipses. It can be seen that the change of the in-plane rotation angle θ has a significant impact on the azimuth and ellipticity of the polarization ellipse. These results show that the in-plane rotation operation of the meta-atom can effectively expand the coverage of the polarization state on the Poincare sphere (the rotation of the meta-atom causes an angle-dependent additional phase in the cross-circularly polarized component of the transmitted wave, thereby changing the complex amplitude of the resultant wave).

[0083] Functional verification: Verify that the polarization state of almost any position on the Poincare sphere can be obtained by using the mirror symmetry breaking, parameter space evolution, mirror flipping and in-plane rotation operations of the meta-atom, so that arbitrarily distributed terahertz vector beams can also be generated.

[0084] In this simulation experiment, Figure 4 Two types of cases are shown. First, a fully linearly polarized vector beam: Figure 2 From the result of (g), select all linear polarization states, that is, the area where S3=0 on the Poincare sphere; further, select 8 polarization states with adjacent polarization azimuths differing by 22.5° from the above results. Using the selected 8 polarization states, design Figure 4The metasurface shown in (b) is used to generate a transmitted vector beam. The metasurface is divided into eight regions with a total of 60×60 units. Each region is filled with corresponding meta-atoms to generate the above-mentioned different types of linearly polarized waves. Finally, the cross section of the transmitted beam is observed in the simulation (at a distance of 1700 μm from the device) and the transmitted electric field at each point is plotted as shown below. Figure 4 From the corresponding polarization ellipse shown in (c), it can be seen that the polarization distribution of the transmitted vector beam is basically consistent with the design effect, and its center is a polarization singular point.

[0085] Second, vector beams containing linear polarization, circular polarization, and elliptical polarization components: This design method is the same as the first one, except that Figure 4 The positions of the four polarization states (x-linear polarization, y-linear polarization, left-hand circular polarization, and right-hand circular polarization) selected in (d) on the Poincare sphere. At this time, the device is divided into four regions (x-linear polarization region, y-linear polarization region, left-hand circular polarization region, and right-hand circular polarization region). The final transmitted beam cross section is as follows: Figure 4 As shown in (f), the four regions are orthogonal linear polarization, circular polarization and elliptical polarization, respectively.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A chiral metasurface comprising a plurality of periodically arranged metaatoms, characterized in that: Each of the multiple superatoms includes a bottom rectangular parallelepiped substrate and a top resonator grown on the top of the bottom rectangular parallelepiped substrate and having broken mirror symmetry. The top resonator includes a top rectangular parallelepiped and elliptical columns located on both sides of the top rectangular parallelepiped.

2. The chiral metasurface according to claim 1, wherein: The arrangement period of multiple superatoms is P = 300 μm; The height H1 of the bottom rectangular substrate is 600 μm. The cross-section of the bottom rectangular substrate is a square, and the side length of the square is equal to the arrangement period of the multiple super atoms. The top of the top resonator is flat, and the height of the top resonator is H1 = 400μm; the length of the top rectangular parallelepiped is L = 200μm, and the width is d = 20μm; the length of the minor axis of the elliptical cylinder is W1 = 30μm, and the length of half of the major axis of the elliptical cylinder is W2∈(0μm, 130μm). The translation amount D∈(0μm, 60μm) after the two elliptical cylinders are symmetrically translated up and down.

3. The chiral metasurface according to claim 2, wherein: The materials of the bottom rectangular substrate and the top resonator are both high-resistance silicon with a dielectric constant ε=11.

9.

4. A method for applying a chiral metasurface to polarization conversion of light beam vectors, characterized by: The following steps are involved: S1. Constructing a chiral metasurface as described in claim 2 or 3, and setting superatom geometric parameters; S2. Determine the factors that affect the complex amplitude of the transmitted electric field, including mirror symmetry breaking, superatom geometric parameters, mirror flip operation and in-plane rotation angle; S3, mirror symmetry breaking: breaking the superatom mirror symmetry, triggering the polarization conversion effect, and generating the fundamental polarization state on the Poincare sphere; S4. Hyperatom geometry parameter setting: Evolve the parameters D and W2 in the ranges of (0μm, 130μm) and (0μm, 60μm) respectively to obtain different linear polarization transmission amplitude and phase combinations, preliminarily expanding the coverage of the Poincare sphere polarization state; S5, mirror flip operation: Perform mirror reflection on the meta-atom to generate its chiral enantiomer. Utilize the complementarity between the transmitted polarization state of the chiral enantiomer and the original structure to further expand the polarization state coverage of the Poincare sphere. S6, in-plane rotation angle: Under the premise of setting D, the in-plane rotation angle θ of the top resonator is changed, and the polarization state coverage of the Poincare sphere is further expanded through different θ-W2 combinations; S7. Design a chiral metasurface device to verify vector beam generation: Divide the chiral metasurface area and configure corresponding meta-atoms according to the target polarization state distribution to achieve vector polarization transformation of the transmitted light beam.

5. The method for applying a chiral metasurface to light beam vector polarization conversion according to claim 4, characterized in that: Step S2 specifically includes the following steps: S21. Correlating the transmitted electric field of the chiral metasurface using the transmission matrix T in a linear polarization basis With the incident electric field Where, and Represent the complex amplitude of the outgoing light in the x and y polarization directions respectively; and Represents the complex amplitude of the incident light in the x and y polarization directions respectively; t xx represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component; t xy represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component; t yx The transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component; t yy The transmission coefficient represents the direct transmission of the incident y-polarization component as the outgoing y-polarization component; S22. Set the transmission matrix T(θ) after the in-plane rotation θ to be: in, Where M -1 (θ) represents the inverse rotation matrix of the in-plane rotation θ; M(θ) represents the forward rotation matrix of the in-plane rotation θ; T xx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T xy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing x-polarization component after the in-plane rotation θ; T yx (θ) represents the transmission coefficient of the incident x-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ; T yy (θ) represents the transmission coefficient of the incident y-polarization component directly transmitted as the outgoing y-polarization component after the in-plane rotation θ; S23. Using trigonometric function relationships, transform formula (4) to obtain: S24. The electric field of the transmitted terahertz wave when the linearly polarized wave is incident is obtained: Where, represents the complex amplitude of the electric field along the x-polarization direction in the transmitted terahertz wave; represents the complex amplitude of the electric field along the y-polarization direction in the transmitted terahertz wave; S25, from formula (4) and formula (5), the factors affecting the complex amplitude of the transmitted electric field include the intrinsic polarization component term, the same polarization angle modulation term and the cross polarization angle modulation term, among which the intrinsic polarization component term is determined by the meta-atom geometric parameters, and the same polarization angle modulation term is determined by the transmission coefficient t xx and t yy and θ, the cross-polarization angle modulation term is determined by the transmission coefficient t xy and t yx and θ determination.

6. The chiral metasurface according to claim 4, wherein: The control step size in step S3 is 2 μm.

7. The chiral metasurface according to claim 4, wherein: In step S7, when generating a fully linearly polarized vector beam, the linear polarization state of the S3=0 region on the Poincare sphere is selected, and the chiral metasurface is divided into multiple regions. Metaatoms are configured in each region to generate linearly polarized waves of different azimuth angles, thereby realizing the polarization distribution design of the transmitted beam.

8. The chiral metasurface according to claim 7, characterized in that: In step S7, when generating a vector beam containing linear polarization, circular polarization, and elliptical polarization components, the polarization states at different positions on the Poincare sphere are selected, the metasurface area is divided, and metaatoms are configured to achieve a combined distribution of multiple polarization states.

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