C2 symmetric chiral metasurface and phase control application and verification method

Abstract

The invention discloses a C2 symmetric chiral metasurface and application and verification methods of phase control, and belongs to the field of micro-nano optics, the C2 symmetric chiral metasurface comprises a surface layer, a middle layer and a back plate layer which are sequentially arranged from top to bottom, the surface layer is composed of a left arc-shaped ring and a right arc-shaped ring which are arranged in a central symmetry mode, and protrusions are arranged on the opposite sides of the left arc-shaped ring and the right arc-shaped ring; the protrusions on the left arc-shaped ring and the protrusions on the right arc-shaped ring are symmetrically arranged about the circle center, and the central angle beta of the notch of the left arc-shaped ring and the central angle beta of the notch of the right arc-shaped ring are obtuse angles. By adopting the C2 symmetric chiral metasurface and the application and verification method of phase control, the spin decoupling phase control of the co-polarized circularly polarized terahertz wave can be realized only through the chiral phase by using the superatoms which have no mirror symmetry and have second-order rotation (C2) symmetry and the mirror atoms thereof.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optical technology, and in particular to an application and verification method of a C2-symmetric chiral metasurface and phase control. Background Art

[0002] Chirality is a ubiquitous phenomenon in nature. The chirality of a substance refers to a geometric feature of its structure, which means that it is impossible to overlap with its mirror image through translation or in-plane rotation operations.

[0003] At the same time, the polarization state characterizes the electric field oscillation of light in a plane perpendicular to the propagation direction. In circularly polarized light, the electric field vector can be decomposed into two linearly polarized components. The two perpendicular electric field vectors oscillate with a 90° phase shift and propagate along a spiral trajectory in a clockwise or counterclockwise direction. Due to the different spiral trajectories of the electric field vector, circularly polarized light can be divided into left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP).

[0004] Chiral media show unique optical responses to LCP and RCP, but the interaction between chiral materials and chiral light fields in nature is very weak. In order to efficiently control chiral light fields and develop them into optical devices, the academic community has proposed and studied artificially designed chiral metamaterials. In recent years, a two-dimensional version has been developed, called chiral metasurfaces, which can achieve magneto-electric resonance coupling and excite chiral optical responses such as super-strong optical rotation and circular dichroism, and are then used in technical fields such as biochemical substance detection and circular polarization optical display.

[0005] From the perspective of light field control, chiral metasurfaces are one of the important ways to independently control orthogonal circularly polarized electromagnetic waves. Exploring electromagnetic theories with spin decoupling control of LCP and RCP wave components and developing corresponding metasurface devices has become one of the research hotspots in academia.

[0006] In the early days, the only independent phase control method for circularly polarized electromagnetic waves was the Pancharatnam-Berry (PB) phase, that is, when the unit structure rotates by an angle θ, an additional ±2θ phase is introduced into the cross-polarization component of its reflection or transmission, which is conjugated to LCP and RCP. Since the geometric phase has a fixed conjugated change in the phase response to LCP and RCP, this greatly limits the spin decoupling function of the metasurface.

[0007] In 2015, Professor Arbabi published in "Dielectric metasurfaces for complete control of phase and polarization with subwavelength spatial resolution and high transmission" a method to combine the polarization-space-dependent PB phase with the parameter-space-dependent resonant phase. Through the joint design of the two types of phases, the independent phase control of LCP and RCP was realized for the first time, and a variety of wavefront designs were demonstrated. Subsequently, by introducing local interference of neighboring metaatoms, the scheme was extended to the phase and amplitude manipulation of arbitrary orthogonal polarization components. However, the above reports all consider non-chiral structures with mirror symmetry, and need to take into account both geometric phase and resonant phase design requirements.

[0008] In recent years, the chiral phase induced by azimuthal rotation and structural parameter adjustment of chiral meta-atoms has become a new method for the design of spin-decoupled metasurfaces. In 2020, Yuan et al. published in "Independent phase modulation for quadruplex polarization channels enabled by chirality-assisted geometric-phase metasurfaces" that introduced chirality-induced phases by using the relative azimuthal differences of multilayer metal resonators, and completed the circular polarization wavefront design of four channels in combination with the resonant phase; in 2021, Chen et al. proposed in "Metasurfaces with Planar Chiral Meta-Atoms for Spin Light Manipulation" that the all-dielectric meta-atoms with C2 symmetry combined with their geometric phases were used to control spin waves; in the same year, Song et al. reported in "Spin-Selective Full-Dimensional Manipulation of Optical Waves with Chiral Mirror" the topological phase induced by singularities in non-Hermitian chiral meta-atoms, and combined with the PB phase to achieve spin-decoupled wavefront control.

[0009] However, the above-mentioned circularly polarized electromagnetic wave control methods based on achiral or chiral meta-atoms still have room for improvement in terms of theoretical complexity, design difficulty, and computational complexity. Moreover, the combination of the resonant phase or chiral phase with the PB phase requires more theoretical description, and the analysis of the polarization space needs to be considered while exploring the parameter space. In addition, the differentiated control of the wave component amplitudes also shows great difficulty. Summary of the invention

[0010] The purpose of the present invention is to provide a C2-symmetric chiral metasurface and an application and verification method of phase control to solve the above-mentioned technical problems.

[0011] To achieve the above-mentioned purpose, the present invention provides a C2-symmetric chiral metasurface, comprising a surface layer, an intermediate layer and a backplane layer arranged in sequence from top to bottom, the surface layer is composed of a left arc ring and a right arc ring arranged symmetrically from the center, the left arc ring and the right arc ring are provided with protrusions on opposite sides, and the protrusions on the left arc ring and the protrusions on the right arc ring are arranged symmetrically about the center of the circle, and the central angle β of the notch of the left arc ring and the right arc ring is an obtuse angle.

[0012] Preferably, the central angle β of the left arc ring and the right arc ring is 40°;

[0013] The distance between the left arc ring and the right arc ring is d = 10um;

[0014] The width of the left arc ring, the right arc ring and the protrusion is w = 25um;

[0015] The length of the protrusion is h=60 um.

[0016] Preferably, the material of the middle layer is polyimide, with a dielectric constant ε=3.4, a loss tangent tanδ=0.002, and a thickness t1=70 um.

[0017] Preferably, the back plate layer is made of gold, with a thickness of t=200 nm.

[0018] Preferably, the reflection phase responses of the chiral metasurface to left-handed polarized light and right-handed polarized light are mirror images, and the reflection efficiency of the chiral metasurface to left-handed polarized light and right-handed polarized light is greater than 71.7%.

[0019] A C2-symmetric chiral metasurface is used for phase control, and the spin-decoupled phase of the co-polarized circularly polarized terahertz wave is controlled by using the chiral phase.

[0020] A verification method for the application of a C2-symmetric chiral metasurface in phase control comprises the following steps:

[0021] S1. Establishing a simulation model: determining the geometric parameters of the chiral metasurface, and then using electromagnetic simulation software to perform frequency domain simulation on the chiral metasurface;

[0022] S2. Scanning the protrusion, the left arc ring and the right arc ring of the chiral metasurface using electromagnetic simulation software to obtain chiral metasurface simulation units under multiple parameter configurations;

[0023] S3, simulation analysis: calculate the reflection amplitude and phase of the chiral metasurface simulation unit under each parameter configuration, and select the chiral metasurface simulation unit that meets the expectations based on the calculated reflection amplitude and phase as the final structure of the chiral metasurface;

[0024] S4. The final structure based on the chiral metasurface is functionally verified in a dual-focusing scenario.

[0025] Preferably, in step S1, the incident wave is defined as left-handed circularly polarized light or right-handed circularly polarized light, and the boundary conditions in the x and y directions are set to unit cell, the boundary condition in the z direction is set to open, and the polarization mode number of the maximum value Zmax of the electromagnetic simulation space and the minimum value Zmin of the electromagnetic simulation space are both set to 2;

[0026] In step S2, the protrusion is scanned from 0um to 160um with a step size of 2um, and the left arc ring and the right arc ring are scanned from 0° to 116° with a step size of 2°.

[0027] Preferably, in step S3, the calculation formula of the reflection amplitude is as follows:

[0028]

[0029] Where R represents the reflection amplitude; R circ Represents the reflection coefficient matrix of circularly polarized waves; r LL and r RR Represent the reflection coefficients of left-handed circularly polarized light and right-handed circularly polarized light respectively; r LR and r RL represents the cross reflection coefficient from left circular polarization to right circular polarization and from right circular polarization to left circular polarization respectively; r xx 、r yy 、r xy and r yx All represent the reflection coefficient matrix elements of linearly polarized waves; i represents the imaginary unit;

[0030] The phase calculation formula is as follows:

[0031]

[0032] In the formula, and They represent the phases of left-handed circularly polarized light and right-handed circularly polarized light respectively; λ represents the operating wavelength; X and Y represent the spatial rectangular coordinates; D represents the lateral offset of the focus; and f represents the design focal length.

[0033] Preferably, step S4 specifically includes the following steps:

[0034] S41. In the parameter space, 10 chiral metasurfaces with 90° phase gradient are selected, including 4 and Chiral metasurfaces that produce the same response;

[0035] At the same time, six chiral metasurfaces with opposite phases are selected from the mirror-symmetric chiral metasurfaces to establish a spin-decoupling structural unit library with a 90° phase gradient using the chiral phase;

[0036] S42, calling 16 superatoms in the spin decoupling structure unit library to generate a chiral metasurface composed of 60*60 superunits, defining the parameters of the chiral metasurface using MATLAB, and importing the generated chiral metasurface into electromagnetic simulation software to perform electromagnetic property simulation;

[0037] S43, respectively regulating the left-handed polarized light and the right-handed polarized light components to regulate the focusing directions of the left-handed polarized light and the right-handed polarized light in the 7000um plane;

[0038] S44, when left-handed circularly polarized light and right-handed circularly polarized light are incident respectively, the boundary conditions in the x, y, and z directions are all set to open, the calculation frequency range is set to 0.5THz-0.7THz, and the electric field monitoring frequency is 0.58THz, the electric field intensity distribution is monitored in the focal plane and the yoz plane, and a focusing effect diagram is generated;

[0039] S45, reading the best focal plane position from the focusing effect diagram, and comparing the best focal plane position with the expected position to determine whether the expected position is reached.

[0040] Therefore, the present invention adopts the above-mentioned C2 symmetric chiral metasurface and phase control application and verification method, which has the following beneficial effects:

[0041] 1. Precise control of structural design: Multi-layer structure: The chiral metasurface consists of a surface layer, an intermediate layer, and a backplane layer. Each layer has clear material and geometric parameter requirements. This multi-layer design makes the structure more stable and can effectively control the propagation characteristics of electromagnetic waves.

[0042] Combination of symmetric and asymmetric elements: The left and right arc rings on the surface are arranged symmetrically and have protrusions. These designs enhance the chiral characteristics of the structure and ensure that the reflection phase response of left and right circularly polarized light presents a mirror relationship.

[0043] 2. High-performance optical properties: High reflection efficiency: The reflection efficiency of the chiral metasurface for both left-handed polarized light and right-handed polarized light is greater than 71.7%, indicating that it has high reflection performance in the terahertz frequency band;

[0044] Phase control capability: Chiral metasurfaces can achieve spin-decoupled phase control of co-polarized circularly polarized terahertz waves, which can be used in fine adjustment of the phase of electromagnetic waves.

[0045] 3. Detailed simulation verification process: Simulation model establishment: Use electromagnetic simulation software to perform frequency domain simulation to ensure that all geometric parameters are accurately calculated and optimized;

[0046] Parameter scanning: Scan the bulge from 0um to 160um with a step of 2um, and scan the left and right arc rings from 0° to 116° with a step of 2°, ensuring that a wide range of parameter configurations are covered, improving the comprehensiveness and reliability of the simulation;

[0047] Reflection amplitude and phase calculation: Provides specific reflection amplitude and phase calculation formulas to ensure the accuracy and repeatability of simulation;

[0048] 4. Practical application potential: Spin decoupling structural unit library: By selecting 10 chiral metasurfaces with a 90° phase gradient and using these unit libraries to generate a chiral metasurface consisting of 60*60 superunits, efficient phase gradient control is achieved;

[0049] Flexible boundary condition setting: During the simulation process, the boundary conditions in the x, y, and z directions are all set to open, the calculation frequency range is set to 0.5THz-0.7THz, and the electric field monitoring frequency is 0.58THz, ensuring the flexibility and accuracy of the simulation;

[0050] 5. Innovation and practicality: Mirror-symmetric chiral metasurfaces: By selecting six chiral metasurfaces with opposite phases, more complex phase gradient control is achieved, which is of great significance for the development of new optical devices and communication systems;

[0051] Determination of the optimal focal plane position: By comparing the simulation results with the expected position, it is convenient to accurately adjust the structural parameters to ensure the optimal focusing effect.

[0052] In summary, the C2-symmetric chiral metasurface described in the present invention not only has unique innovations in design, but also excels in performance and application, and has broad practical application prospects.

[0053] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A schematic diagram of the surface structure of a chiral metasurface of the present invention;

[0055] Figure 2Schematic diagram of the spin decoupling phase response of the simulation experiment; (a) is the reflection amplitude manipulation diagram; (b) is the phase manipulation diagram; (c) is the circular polarization phase distribution diagram when the LCP wave (left-handed polarized light) is incident; (d) is the circular polarization phase distribution diagram when the RCP wave (right-handed polarized light) is incident; (e) is the circular polarization amplitude distribution diagram when the LCP wave (left-handed polarized light) is incident; (f) is the circular polarization amplitude distribution diagram when the RCP wave (right-handed polarized light) is incident;

[0056] Figure 3 These are the functional verification result diagrams of the simulation experiment, where (a) is the electric field intensity distribution diagram on the xoz plane when LCP wave (left-handed polarized light) is incident; (b) is the electric field intensity distribution diagram on the xoz plane when RCP wave (right-handed polarized light) is incident; (c) is the electric field intensity distribution diagram on the plane with the best focal plane position Z=7161 μm at the operating frequency f=0.58 THz when LCP wave (left-handed polarized light) is incident; (d) is the electric field intensity distribution diagram on the plane with the best focal plane position Z=7161 μm at the operating frequency f=0.58 THz when RCP wave (right-handed polarized light) is incident.

[0057] Reference numerals

[0058] 1. Left arc ring; 2. Right arc ring; 3. Bump. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in combination 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 used 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 reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0060] 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 explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0061] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0062] Conventional double split ring resonators have mirror symmetry and can accumulate geometric phase or linear polarization resonant phase in the path of polarization space or parameter space, but do not have chiral response. When the structure is sheared to break the mirror symmetry and maintain the second-order rotational symmetry, chirality may exist; at this time, chiral phase can be accumulated through the path of parameter space, and phase control of spin decoupling can be achieved while keeping the amplitude almost the same.

[0063] Based on the above analysis, the present invention is designed as follows: Figure 1 As shown, a C2-symmetric chiral metasurface includes a surface layer, an intermediate layer and a back plate layer arranged in sequence from top to bottom, the surface layer is composed of a left arc ring 1 and a right arc ring 2 arranged symmetrically from the center, protrusions 3 are provided on opposite sides of the left arc ring 1 and the right arc ring 2, and the protrusions 3 on the left arc ring 1 and the protrusions 3 on the right arc ring 2 are symmetrically arranged about the center of a circle, and the central angle β of the notch of the left arc ring 1 and the right arc ring 2 is an obtuse angle.

[0064] Specifically, the central angle β of the left arc ring 1 and the right arc ring 2 is 40°; the distance d between the left arc ring 1 and the right arc ring 2 is 10um; the width w of the left arc ring 1, the right arc ring 2, and the protrusion 3 is 25um; the length h of the protrusion 3 is 60um. The material of the middle layer is polyimide, with a dielectric constant ε=3.4, a loss tangent tanδ=0.002, and a thickness t1=70um. The material of the backplane layer is gold, with a thickness t=200nm.

[0065] The reflection phase responses of the chiral metasurface to left-handed polarized light and right-handed polarized light are mirror images, and the reflection efficiency of the chiral metasurface to left-handed polarized light and right-handed polarized light is greater than 71.7%.

[0066] A C2-symmetric chiral metasurface is used for phase control, and the spin-decoupled phase of the co-polarized circularly polarized terahertz wave is controlled by using the chiral phase.

[0067] A verification method for the application of a C2-symmetric chiral metasurface in phase control comprises the following steps:

[0068] S1. Establishing a simulation model: determining the geometric parameters of the chiral metasurface, and then using electromagnetic simulation software to perform frequency domain simulation on the chiral metasurface;

[0069] In step S1, the incident wave is defined as left-handed circularly polarized light or right-handed circularly polarized light, and the boundary conditions in the x and y directions are set to unit cell (period), the boundary condition in the z direction is set to open (open), and the polarization mode numbers of the maximum value Zmax of the electromagnetic simulation space and the minimum value Zmin of the electromagnetic simulation space are both set to 2;

[0070] S2. Scanning the protrusion, the left arc ring and the right arc ring of the chiral metasurface using electromagnetic simulation software to obtain chiral metasurface simulation units under multiple parameter configurations;

[0071] In step S2, the protrusion is scanned from 0um to 160um with a step size of 2um, and the left arc ring and the right arc ring are scanned from 0° to 116° with a step size of 2°.

[0072] S3, simulation analysis: calculate the reflection amplitude and phase of the chiral metasurface simulation unit under each parameter configuration, and select the chiral metasurface simulation unit that meets the expectations based on the calculated reflection amplitude and phase as the final structure of the chiral metasurface;

[0073] In step S3, the calculation formula of the reflection amplitude is as follows:

[0074]

[0075] Where R represents the reflection amplitude; R circ Represents the reflection coefficient matrix of circularly polarized waves; r LL and r RR Represent the reflection coefficients of left-handed circularly polarized light and right-handed circularly polarized light respectively; r LR and r RL represents the cross reflection coefficient from left circular polarization to right circular polarization and from right circular polarization to left circular polarization respectively; r xx 、r yy 、r xy and r yx All represent the reflection coefficient matrix elements of linearly polarized waves; i represents the imaginary unit;

[0076] The phase calculation formula is as follows:

[0077]

[0078] In the formula, and represents the phase of left-handed circularly polarized light and right-handed circularly polarized light respectively; λ represents the working wavelength; X and Y represent the spatial rectangular coordinates; D represents the lateral offset of the focus; and f represents the designed focal length. In this embodiment, λ = 517um, f = 7000um, and d = 800um.

[0079] S4. The final structure based on the chiral metasurface is functionally verified in a dual-focusing scenario.

[0080] Step S4 specifically includes the following steps:

[0081] S41. In the parameter space, 10 chiral metasurfaces with 90° phase gradient are selected, including 4 and Chiral metasurfaces that produce the same response;

[0082] At the same time, six chiral metasurfaces with opposite phases are selected from the mirror-symmetric chiral metasurfaces to establish a spin-decoupling structural unit library with a 90° phase gradient using the chiral phase;

[0083] S42, calling 16 superatoms in the spin decoupling structure unit library to generate a chiral metasurface composed of 60*60 superunits, defining the parameters of the chiral metasurface using MATLAB, and importing the generated chiral metasurface into electromagnetic simulation software to perform electromagnetic property simulation;

[0084] S43, respectively regulating the left-handed polarized light and the right-handed polarized light components to regulate the focusing directions of the left-handed polarized light and the right-handed polarized light in the 7000um plane;

[0085] S44, when left-handed circularly polarized light and right-handed circularly polarized light are incident respectively, the boundary conditions in the x, y, and z directions are all set to open, the calculation frequency range is set to 0.5THz-0.7THz, and the electric field monitoring frequency is 0.58THz, the electric field intensity distribution is monitored in the focal plane and the yoz plane, and a focusing effect diagram is generated;

[0086] S45, reading the best focal plane position from the focusing effect diagram, and comparing the best focal plane position with the expected position to determine whether the expected position is reached.

[0087] Simulation experiment

[0088] Based on the present invention, simulation experiments are carried out and the results are as follows: Figure 2 and Figure 3 As shown by Figure 2 (a) It can be seen that when h = 60um and β = 40°, the chiral metasurface is simulated in the frequency domain using electromagnetic simulation software. It can be clearly observed that in the frequency domain range of 0.2THz to 0.8THz, the reflected co-polarized circularly polarized wave R LL and R RR The reflectivity (reflectivity is the square of the reflection coefficient) curves basically coincide with each other.

[0089] Depend on Figure 2 (b) It can be seen that in the frequency domain range of 0.2THz to 0.8THz, the reflection co-polarization circular polarization phase of the observation unit structure and You can see and There is a very obvious phase difference in the range of interest, and the phase difference at the operating frequency of 0.58THz is close to π. The inset shows the local electric field distribution of LCP (left-handed circularly polarized light) and RCP (right-handed circularly polarized light) at this frequency, which provides a more intuitive display of the cause of the phase difference.

[0090] Depend on Figure 2 (c) and (d) show that at the operating frequency of 0.58 THz, the phase of the left arc ring to the reflected co-polarized LCP can be clearly observed. Achieves 360° full coverage, and the phase of the reflected RCP wave Only about 180° of phase coverage is achieved, but its mirror-image chiral structure (right arc ring) can achieve 360° coverage, In addition, when LCP wave is incident, changing the value of h has an effect on have a greater impact on There is basically no effect; when the RCP wave is incident, the convex h basically does not produce resonance, and changing the notch center angle β has an effect on have a greater impact on Basically no effect.

[0091] Depend on Figure 2 (e) and (f) show that at the operating frequency of 0.58 THz, due to the rotational symmetry of the chiral metasurface, R LL and R RR The amplitudes of the components are basically equal, and the R LL and R RR The intensity is basically maintained above 0.7, and the amplitude of the reflected co-polarized beam can be maintained at a high level.

[0092] Depend on Figure 3 As can be seen from (c) and (d), different circularly polarized components are reflected by the metasurface to form eccentrically focused light beams, which are consistent with the designed function, thus proving the effectiveness of the present invention.

[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A C2-symmetric chiral metasurface, characterized in that: It includes a surface layer, a middle layer and a back plate layer arranged in sequence from top to bottom, the surface layer is composed of a left arc ring and a right arc ring arranged symmetrically from the center, protrusions are arranged on the opposite sides of the left arc ring and the right arc ring, and the protrusions on the left arc ring and the protrusions on the right arc ring are arranged symmetrically about the center of the circle, and the central angle β of the notch of the left arc ring and the right arc ring is an obtuse angle.

2. The C2-symmetric chiral metasurface according to claim 1, characterized in that: The central angle β of the left arc ring and the right arc ring is 40°; The distance between the left arc ring and the right arc ring is d = 10um; The width of the left arc ring, the right arc ring and the protrusion is w = 25um; The length of the protrusion is h=60 um.

3. The C2-symmetric chiral metasurface according to claim 1, characterized in that: The material of the middle layer is polyimide, with a dielectric constant ε=3.4, a loss tangent tanδ=0.002, and a thickness t1=70 um.

4. The C2-symmetric chiral metasurface according to claim 1, characterized in that: The material of the back plate layer is gold, with a thickness of t=200nm.

5. The C2-symmetric chiral metasurface according to claim 1, characterized in that: The reflection phase responses of the chiral metasurface to left-handed polarized light and right-handed polarized light are mirror images, and the reflection efficiency of the chiral metasurface to left-handed polarized light and right-handed polarized light is greater than 71.7%.

6. Application of the C2-symmetric chiral metasurface in phase control according to any one of claims 1 to 5, characterized in that: Spin-decoupled phase control of co-polarized circularly polarized terahertz waves using chiral phase.

7. The verification method for the application of the C2-symmetric chiral metasurface in phase control as claimed in claim 6, characterized in that: The following steps are involved: S1. Establishing a simulation model: determining the geometric parameters of the chiral metasurface, and then using electromagnetic simulation software to perform frequency domain simulation on the chiral metasurface; S2. Scanning the protrusion, the left arc ring and the right arc ring of the chiral metasurface using electromagnetic simulation software to obtain chiral metasurface simulation units under multiple parameter configurations; S3, simulation analysis: calculate the reflection amplitude and phase of the chiral metasurface simulation unit under each parameter configuration, and select the chiral metasurface simulation unit that meets the expectations based on the calculated reflection amplitude and phase as the final structure of the chiral metasurface; S4. The final structure based on the chiral metasurface is functionally verified in a dual-focusing scenario.

8. The verification method for the application of the C2-symmetric chiral metasurface in phase control according to claim 7, characterized in that: In step S1, the incident wave is defined as left-handed circularly polarized light or right-handed circularly polarized light, and the boundary conditions in the x and y directions are set to unit cell, the boundary condition in the z direction is set to open, and the polarization mode numbers of the maximum value Zmax of the electromagnetic simulation space and the minimum value Zmin of the electromagnetic simulation space are both set to 2; In step S2, the protrusion is scanned from 0um to 160um with a step size of 2um, and the left arc ring and the right arc ring are scanned from 0° to 116° with a step size of 2°.

9. The verification method for the application of the C2-symmetric chiral metasurface in phase control according to claim 7, characterized in that: In step S3, the calculation formula of the reflection amplitude is as follows: Where R represents the reflection amplitude; R circ Represents the reflection coefficient matrix of circularly polarized waves; r LL and r RR Represent the reflection coefficients of left-handed circularly polarized light and right-handed circularly polarized light respectively; r LR and r RL represents the cross reflection coefficient from left circular polarization to right circular polarization and from right circular polarization to left circular polarization respectively; r xx 、r yy 、r xy and r yx All represent the reflection coefficient matrix elements of linearly polarized waves; i represents the imaginary unit; The phase calculation formula is as follows: In the formula, and They represent the phases of left-handed circularly polarized light and right-handed circularly polarized light respectively; λ represents the operating wavelength; X and Y represent the spatial rectangular coordinates; D represents the lateral offset of the focus; and f represents the design focal length.

10. The verification method for the application of the C2-symmetric chiral metasurface in phase control according to claim 7, characterized in that: Step S4 The specific steps include: S41. In the parameter space, 10 chiral metasurfaces with 90° phase gradient are selected, including 4 and Chiral metasurfaces that produce the same response; At the same time, six chiral metasurfaces with opposite phases are selected from the mirror-symmetric chiral metasurfaces to establish a spin-decoupling structural unit library with a 90° phase gradient using the chiral phase; S42, calling 16 superatoms in the spin decoupling structure unit library to generate a chiral metasurface composed of 60*60 superunits, defining the parameters of the chiral metasurface using MATLAB, and importing the generated chiral metasurface into electromagnetic simulation software to perform electromagnetic property simulation; S43, respectively regulating the left-handed polarized light and the right-handed polarized light components to regulate the focusing directions of the left-handed polarized light and the right-handed polarized light in the 7000um plane; S44, when left-handed circularly polarized light and right-handed circularly polarized light are incident respectively, the boundary conditions in the x, y, and z directions are all set to open, the calculation frequency range is set to 0.5THz-0.7THz, and the electric field monitoring frequency is 0.58THz, the electric field intensity distribution is monitored in the focal plane and the yoz plane, and a focusing effect diagram is generated; S45, reading the best focal plane position from the focusing effect diagram, and comparing the best focal plane position with the expected position to determine whether the expected position is reached.

Images