VO2-based polarization modulator, polarization characteristic analysis method and modulation method

Abstract

The invention discloses a VO2-based polarization modulator, a polarization characteristic analysis method and a modulation method, and belongs to the field of optical devices, the VO2-based polarization modulator comprises a metal substrate layer, a Si dielectric layer and a metasurface unit periodically arranged at the top end of the Si dielectric layer, and the metasurface unit is of a chiral structure formed by compounding VO2 and metal; each metasurface unit comprises a middle structure composed of a first middle metal frame and a second middle metal frame and side metal strips arranged on the two sides of the middle structure, and VO2 is embedded in the middle positions of the opposite sides of the first middle metal frame and the second middle metal frame. Metal protrusions are connected to the middle positions of the opposite sides of the first middle metal frame and the second middle metal frame. By adopting the VO2-based polarization modulator, the polarization characteristic analysis method and the modulation method, the polarization state of incident light can be adjusted by the metasurface by adjusting the conductivity of vanadium dioxide, and a dynamic tunable function is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and in particular to a VO2-based polarization modulator, a polarization characteristic analysis method, and a modulation method. Background Art

[0002] In nature and artificial systems, the polarization state of light carries a wealth of information, so it has important application value in many fields such as science, industry, medicine and communications. From basic physical phenomena to cutting-edge technology applications, the development of polarization modulation technology has greatly expanded the ability to manipulate light, and has been widely used in polarization gratings, holography, polarization imaging, vector beams, etc.

[0003] In traditional technology, polarization modulation of light waves transmitted in free space is mainly carried out by using electro-optical or magneto-optical crystals, and then changing the polarization state of the light waves through the action of an external electromagnetic field. This type of technology has a limited modulation dynamic range, and the device size and power consumption are large. In addition, there is currently no mature spatial wave polarization modulation technology in the terahertz band.

[0004] With the progress of nanotechnology and materials science, new polarization modulation devices and methods are constantly emerging, especially the emergence of metasurface technology, which provides new possibilities for more efficient, compact and intelligent polarization control. Metasurfaces are thin, flat and easy to manufacture, with reduced losses, and are suitable for frequencies ranging from microwaves to visible light. They transmit or reflect electromagnetic waves through the sudden phase of the structure surface, thus providing new degrees of freedom to control the phase, amplitude and polarization response of the light field, thereby realizing various functions.

[0005] In recent years, chiral metasurfaces have become a research hotspot in the field of metasurfaces. Chirality is a unique geometric property that means an object cannot completely overlap with its mirror image through rotation and translation. There are many chiral objects in nature, and the optical response of natural chiral compounds is usually weak, limited by the matching of light wavelength and molecular size.

[0006] To solve the above problems, scholars have further developed artificial chiral metasurfaces, which are divided into three-dimensional and two-dimensional chiral structures in terms of structure, and metal and all-dielectric chiral metasurfaces in terms of materials. Among them, although the three-dimensional chiral structure has good chiral optical response, its processing and application are complex. It is difficult for two-dimensional metal chiral metasurfaces to achieve significant chiral optical response and circular dichroism due to the difficulty in generating in-plane magnetic dipole moment and ohmic loss.

[0007] Metal-compound composite metasurfaces have attracted increasing attention from researchers due to their excellent performance in controlling the phase, amplitude and polarization of electromagnetic waves, and can realize the design of multifunctional integrated optical components. However, existing metal-compound composite metasurfaces still have defects such as narrow bandwidth and fixed operating frequency. Summary of the invention

[0008] The purpose of the present invention is to provide a VO2-based polarization modulator, a polarization characteristic analysis method and a modulation method to solve the above-mentioned technical problems.

[0009] To achieve the above object, the present invention provides a VO2-based polarization modulator, comprising a metal substrate layer, a Si dielectric layer arranged on the top of the metal substrate layer, and a metasurface unit periodically arranged on the top of the Si dielectric layer, wherein the metasurface unit is a chiral structure formed by a composite of VO2 and metal;

[0010] The metasurface unit includes an intermediate structure consisting of a first intermediate metal frame and a second intermediate metal frame and side metal strips arranged on both sides of the intermediate structure. The middle positions of the opposite sides of the first intermediate metal frame and the second intermediate metal frame are inlaid with VO2, and the middle positions of the opposite sides of the first intermediate metal frame and the second intermediate metal frame are connected with metal protrusions.

[0011] Preferably, the left and right sides of the first intermediate metal frame and the second intermediate metal frame are connected to the side metal bars via connecting metal bars;

[0012] The middle structure, metal protrusions, side metal strips and metal base layer are all made of gold.

[0013] Preferably, the basic period P of the metasurface unit is 300 um.

[0014] Preferably, the width of the side metal strip a=18μm; the first intermediate metal frame and the second intermediate metal frame are both square frame structures, and the inner side length of the first intermediate metal frame and the second intermediate metal frame b=70μm; the thickness of the VO2 embedded metal layer c=2μm; the distance d=30μm between the side metal strip and the super unit boundary; the width of the connecting metal strip is the same as the thickness of VO2, and the width of the connecting metal strip e=10μm; the distance f=35μm between the intermediate structure and the super surface unit boundary; the length g=20μm of the metal protrusion.

[0015] The polarization characteristic analysis method of the polarization modulator based on VO2 includes the following steps:

[0016] S1. Determine the linear polarization reflection coefficient to determine the relationship between the reflected electric field and the incident electric field:

[0017]

[0018] In the formula, E r (r, t) represents the reflected electric field vector; and Respectively represent the x-component and y-component of the reflected electric field; r xx and r yy are all co-polarization components, among which r xx represents the reflection coefficient of the incident wave in the x direction, r yy represents the reflection coefficient of the incident wave in the y direction; r xy and r yx are cross-polarization components, among which r xy represents the reflection coefficient of the incident wave in the y direction in the x direction, r yx It represents the reflection coefficient of the incident wave in the x direction in the y direction; and They represent the incident electric field vector; R represents the reflection matrix; E i (r, t) represents the x-component and y-component of the incident electric field;

[0019] S2. Determine the circular polarization reflection coefficient using the relationship between the linear polarization and circular polarization components:

[0020]

[0021] In the formula, r RR 、r RL 、r LR and r LL are the reflection coefficients of the circular polarization component, where r RR represents the reflection coefficient of right-hand circularly polarized wave on right-hand circularly polarized wave, r RL represents the reflection coefficient of left-handed circularly polarized wave on right-handed circularly polarized wave, r LR represents the reflection coefficient of right-hand circularly polarized wave on left-hand circularly polarized wave, r LL represents the reflection coefficient of a left-handed circularly polarized wave on a left-handed circularly polarized wave; i represents an imaginary unit;

[0022] S3. Based on the circular polarization reflection coefficient, calculate the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave:

[0023] A L =1-r LL 2 -r RL 2 (3);

[0024] A R =1-r LR 2 -r RR2 (4);

[0025] In the formula, A L and A R They represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and the absorptivity to right-handed circularly polarized waves respectively;

[0026] S4. Compare the absorption rate of the metasurface unit to the left-handed circularly polarized wave A L and the absorptivity A of the metasurface unit to right-handed circularly polarized waves R , and obtain the evaluation results of the chiral characteristics of the metasurface;

[0027] S5. Based on the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave, the circular dichroism parameter CD is calculated to quantify the response degree of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave:

[0028] CD=A L -A R (5);

[0029] S6. Introduce the rotation angle ψ and ellipticity χ to characterize the polarization ellipticity of the metasurface unit:

[0030]

[0031] In the formula, E 0x and E 0y Respectively represent r RL and r LL The linear amplitude of ; δ represents the phase difference;

[0032] S7. Use electromagnetic simulation software to perform simulation verification.

[0033] A modulation method for a polarization modulator based on VO2 includes the following steps: incident on a metasurface unit under specific incident conditions, changing the conductivity of VO2 by regulating the phase change degree of VO2, and then changing the amplitude ratio and phase difference of the x component and y component of the reflected electric field, thereby regulating the polarization state of the polarization modulator.

[0034] Preferably, the specific incident conditions are: selecting an incident frequency of 0.192THZ and linearly polarized light with vertical incident y-direction polarization.

[0035] Preferably, when VO2 is in an insulating state and the conductivity is 200 S / m, the phase difference between the incident y-direction linear polarization wave and the modulated output x-direction linear polarization wave is 106.4°, the conversion rate between the y-direction linear polarization wave and the x-direction linear polarization wave is 41.65%, and the polarization state is circular polarization;

[0036] When the conductivity of VO2 increases to 2000S / m, the phase difference between the incident wave and the reflected wave is 116.5°, the conversion rate between the linear polarization wave in the y direction and the linear polarization wave in the x direction is 81.3%, and the polarization state is elliptical polarization;

[0037] When VO2 undergoes a phase change to reach a metallic state and the conductivity increases to 200,000 S / m, the phase difference between the incident wave and the reflected wave is 145.2°, the conversion rate of the linear polarization wave in the y direction to the linear polarization wave in the x direction is 92.53%, and the polarization state is linear polarization.

[0038] Therefore, the present invention adopts the above-mentioned VO2-based polarization modulator, polarization characteristic analysis method and modulation method, which has the following beneficial effects:

[0039] 1. Dynamically adjustable polarization characteristics: By changing the phase change degree and incident angle of VO2, effective modulation of circular polarization (RCP and LCP) and linear polarization can be achieved, which provides great flexibility for practical applications;

[0040] 2. High selectivity and high circular dichroism: At a frequency of 0.192THz, the absorption of right-handed circular polarization (RCP) in the insulating state is much higher than that of left-handed circular polarization (LCP), showing high circular dichroism (CD value close to 0.8), which means that it can efficiently distinguish and process different types of circularly polarized light, thus having significant advantages in the field of polarization control;

[0041] 3. Adaptability to a wide range of incident angles: Changing the incident angle will affect the metasurface's absorption rate of RCP and LCP, especially in the range of 0° to 50°, where the absorption rate of RCP increases significantly. This feature enables the metasurface to maintain efficient polarization modulation capabilities under incident light at different angles, broadening its application scenarios.

[0042] In summary, due to the above-mentioned unique polarization modulation capability and high circular dichroism, the metasurface described in the present invention has broad application prospects in multiple fields, such as optical communications, polarization imaging, sensing technology, etc.

[0043] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A three-dimensional diagram of a VO2-based polarization modulator according to the present invention;

[0045] Figure 2 A plan view of a VO2-based polarization modulator according to the present invention;

[0046] Figure 3 It is a schematic structural diagram of a single metasurface unit of a VO2-based polarization modulator of the present invention;

[0047] Figure 4 The simulation results of the insulating state of the metasurface before phase transition in the simulation experiment of the present invention are shown in Figure 1, wherein (a) is a chiral spectrum diagram, (b) is a result diagram of the absorptivity of the metasurface to LCP and RCP, (c) is a surface electric field distribution diagram of the metasurface when LCP and RCP are incident at 0.192THZ, and (d) is a surface current vector distribution diagram of the metasurface when LCP and RCP are incident at 0.192THZ;

[0048] Figure 5 The graph is a result of the change of the circular dichroism of the metasurface when the conductivity of vanadium dioxide (VO2) in the simulation experiment of the present invention is gradually increased from 200S / m to 200000S / m, wherein (a) is a schematic diagram of the CD of the metasurface when the conductivity and frequency change, and (b) is a result diagram of the CD value when the conductivity changes at 0.192THZ;

[0049] Figure 6 Figure 1 is the absorption result of the super surface structure of the simulation experiment of the present invention for left-handed circularly polarized light and right-handed circularly polarized light, where (a), (c), and (e) are the r when the conductivity is equal to 200, 2000, and 200000, respectively. LL and r RL Schematic diagram of reflection coefficient, (b) (d) (f) are r when conductivity is 200, 2000, and 200000 respectively LL and r RL Schematic diagram of reflection phase and corresponding polarization ellipse;

[0050] Figure 7 The diagrams are the results of the impact of the change in the incident angle on the performance of the metasurface structure of the simulation experiment described in the present invention, (a) is a schematic diagram of the metasurface's LCP absorption rate when the circular polarization incident angle is changed, (b) is a schematic diagram of the metasurface's RCP absorption rate when the circular polarization incident angle is changed, and (c) is a schematic diagram of the corresponding azimuth angle and polarization ellipse under different conductivities when the left-handed linear polarization incident angle is 20° at 0.192THZ.

[0051] Reference numerals

[0052] 1. Metal base layer; 2. Si dielectric layer; 3. Metasurface unit; 31. First intermediate metal frame; 32. VO2; 33. Metal protrusion; 34. Second intermediate metal frame; 35. Side metal strip; 36. Connecting metal strip. DETAILED DESCRIPTION

[0053] 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.

[0054] 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.

[0055] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0056] Vanadium dioxide (VO2) has become a highly regarded material due to its unique phase change properties. That is, VO2 has the ability to undergo a reversible phase change from an insulating state (high resistance state) to a metallic state (low resistance state) at a specific temperature. This transition occurs at a temperature node of about 340K. During this process, its conductivity may experience a change from 2×10 2 S / m to 2×10 5 It is worth noting that the change in VO2 conductivity is mainly regulated by temperature rather than frequency, so the temperature factor plays a decisive role in the phase change process.

[0057] Based on the above analysis, the present invention is designed as follows: Figure 1-Figure 3 As shown, a VO2-based polarization modulator includes a metal substrate layer 1, a Si dielectric layer 2 arranged on the top of the metal substrate layer 1, and a metasurface unit 3 periodically arranged on the top of the Si dielectric layer 2, wherein the metasurface unit 3 is a chiral structure formed by a composite of VO232 and metal; the metasurface unit includes an intermediate structure composed of a first intermediate metal frame 31 and a second intermediate metal frame 34, and side metal strips 35 arranged on both sides of the intermediate structure, VO232 is inlaid in the middle positions of the opposite sides of the first intermediate metal frame 31 and the second intermediate metal frame 34, and metal protrusions 33 are connected to the middle positions of the opposite sides of the first intermediate metal frame 31 and the second intermediate metal frame 34.

[0058] Specifically, the left and right sides of the first middle metal frame 31 and the second middle metal frame 34 are connected to the side metal strips 35 via the connecting metal strips 36; the middle structure, the metal protrusions, the side metal strips 35 and the metal base layer 1 are all made of gold.

[0059] The basic period of the super surface unit is P = 300um. The width of the side metal strip 35 is a = 18μm; the first intermediate metal frame 31 and the second intermediate metal frame 34 are both square frame structures, and the inner length of the first intermediate metal frame 31 and the second intermediate metal frame 34 is b = 70μm; the thickness of the VO232 embedded metal layer is c = 2μm; the distance d from the side metal strip 35 to the super unit boundary is 30μm; the width of the connecting metal strip 36 is the same as the thickness of VO232, and the width of the connecting metal strip 36 is e = 10μm; the distance f from the intermediate structure to the super surface unit boundary is 35μm; the length of the metal protrusion 33 is g = 20μm.

[0060] The polarization characteristic analysis method of the polarization modulator based on VO2 includes the following steps:

[0061] S1. Determine the linear polarization reflection coefficient to determine the relationship between the reflected electric field and the incident electric field:

[0062]

[0063] In the formula, E r (r, t) represents the reflected electric field vector; and Respectively represent the x-component and y-component of the reflected electric field; r xx and r yy are all co-polarization components, among which r xx represents the reflection coefficient of the incident wave in the x direction, r yy represents the reflection coefficient of the incident wave in the y direction; r xy and r yx are cross-polarization components, among which r xy represents the reflection coefficient of the incident wave in the y direction in the x direction, r yx It represents the reflection coefficient of the incident wave in the x direction in the y direction; and They represent the incident electric field vector; R represents the reflection matrix; E i (r, t) represents the x-component and y-component of the incident electric field;

[0064] S2. Determine the circular polarization reflection coefficient using the relationship between the linear polarization and circular polarization components:

[0065]

[0066] In the formula, rRR 、r RL 、r LR and r LL are the reflection coefficients of the circular polarization component, where r RR represents the reflection coefficient of right-hand circularly polarized wave on right-hand circularly polarized wave, r RL represents the reflection coefficient of left-handed circularly polarized wave on right-handed circularly polarized wave, r LR represents the reflection coefficient of right-hand circularly polarized wave on left-hand circularly polarized wave, r LL represents the reflection coefficient of a left-handed circularly polarized wave on a left-handed circularly polarized wave; i represents an imaginary unit;

[0067] S3. Based on the circular polarization reflection coefficient, calculate the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave:

[0068] A L =1-r LL 2 -r RL 2 (3);

[0069] A R =1-r LR 2 -r RR 2 (4);

[0070] In the formula, A L and A R They represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and the absorptivity to right-handed circularly polarized waves respectively;

[0071] S4. Compare the absorption rate of the metasurface unit to the left-handed circularly polarized wave A L and the absorptivity A of the metasurface unit to right-handed circularly polarized waves R , and obtain the evaluation results of the chiral characteristics of the metasurface;

[0072] S5. Based on the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave, the circular dichroism parameter CD is calculated to quantify the response degree of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave:

[0073] CD=A L -A R (5);

[0074] S6. Introduce the rotation angle ψ and ellipticity χ to characterize the polarization ellipticity of the metasurface unit:

[0075]

[0076] In the formula, E 0x and E 0yRespectively represent r RL and r LL The linear amplitude of ; δ represents the phase difference;

[0077] S7. Use electromagnetic simulation software to perform simulation verification.

[0078] Simulation experiment:

[0079] In this simulation experiment, the boundary range of the simulation area is set from 0mm to 300mm in the three z directions, and the boundary condition is set to open (addspace). First, the simulation is performed when VO2 is in an insulating state before the phase transition, and the results are shown in Figures 4 and 5. Figure 5 As shown in the figure, Figure 4 It can be seen that obvious chiral characteristics are observed in the entire spectral range of the metasurface. In particular, at the frequency point of 0.192THz, the reflection coefficient of left-handed circularly polarized wave (LCP) r RL The reflection coefficient of right-hand circularly polarized wave (RCP) LR It is effectively suppressed below 0.13. Under the condition of circularly polarized light incidence, the metasurface structure shows a significant difference in absorption characteristics at a frequency of 0.192THz: for right-handed circularly polarized waves (RCP), the metasurface absorbs almost completely, while for left-handed circularly polarized waves (LCP), the absorption is relatively weak. This phenomenon can be explained by the fact that at a frequency of 0.192THz, the polarization state of the incident RCP light is effectively converted into LCP light after passing through the metasurface structure, thereby proving the chiral resolution ability of the metasurface shown in the present invention. The absorptivity of the metasurface for RCP is close to 0.9, while the absorptivity for LCP is relatively low, which further verifies the chiral characteristics of the metasurface described in the present invention. For RCP incidence, the metasurface not only exhibits a capacitor-like effect, but also the aggregation position of its free charges shows chiral characteristics. In sharp contrast to the LCP incidence situation, it further highlights the chiral response characteristics of the metasurface described in the present invention when 0.192THz circularly polarized light is incident.

[0080] Depend on Figure 5 It can be seen that as the conductivity of VO2 increases, the circular dichroism (CD) of the metasurface gradually weakens. When 0.192THz is selected as the operating frequency, as the conductivity of VO2 increases, the CD value gradually decreases, thus simulating the change in VO2 conductivity caused by temperature change, which in turn affects the dynamic adjustment of the CD value of the metasurface.

[0081] There is a large difference in the absorption of left-handed circularly polarized light and right-handed circularly polarized light by the metasurface structure, and the reason for this difference is the strong chiral effect of the metasurface. It can be observed that the metasurface structure described in the present invention has a strong circular dichroism at a frequency of 0.192THz. This discovery not only reveals the correlation between the circular dichroism of the metasurface and the conductivity of VO2, but also provides an experimental basis for the dynamic adjustment of the optical properties of the metasurface through temperature control. It proves the feasibility of adjusting the CD value of the metasurface by precisely controlling the temperature of VO2, adjusting the phase change degree of VO2, and thus realizing more efficient and flexible optical device design in the fields of optical communication, sensing and imaging.

[0082] In addition, in this simulation experiment, the effect of the incident angle change on the performance of the metasurface structure is also investigated. That is, by gradually changing the incident angle of circularly polarized light from 0° to 80°, the results are as follows: Figure 7 As shown, it can be seen that with the increase of the incident angle, the absorptivity of the metasurface structure to left-handed circularly polarized light (LCP) gradually increases, although the increase is small, and the absorptivity is roughly maintained in the range of 0.3 to 0.6. At the same time, for right-handed circularly polarized light (RCP), the structure exhibits an extremely high absorptivity, close to 0.9. That is, by changing the incident angle, it can be observed that the absorptivity of the metasurface to RCP changes with the increase of the incident angle. In the range of 0° to 50°, the absorptivity increases with the increase of the incident angle; while in the range of 50° to 80°, the absorptivity decreases with the increase of the incident angle. For LCP, although the absorptivity also increases with the increase of the incident angle, the increase is relatively small. In particular, it reaches the maximum value in the frequency range of 0.18 to 0.19 THz. Therefore, 20° is taken as the incident angle, and the polarization state of the reflected light is very close to circularly polarized light. As the conductivity of VO2 gradually increases, the polarization state of the reflected light transitions from circularly polarized light to elliptically polarized light, and finally to linearly polarized light when VO2 is transformed into a metallic state, thereby verifying the effectiveness of the present invention.

[0083] The modulation method of the polarization modulator based on VO2 includes the following steps: incident on the metasurface unit under specific incident conditions, changing the conductivity of VO2 by adjusting the phase change degree, and then changing the amplitude ratio and phase difference of the x component and the y component of the reflected electric field, thereby adjusting the polarization state of the polarization modulator. Among them, the specific incident condition is: selecting linearly polarized light with an incident frequency of 0.192THZ and an incident angle of 20° in the y direction.

[0084] like Figure 6 As shown, when VO2 is in an insulating state and the conductivity is 200S / m, the phase difference between the incident y-direction linear polarization wave and the modulated output x-direction linear polarization wave is 106.4°, the conversion rate between the y-direction linear polarization wave and the x-direction linear polarization wave is 41.65%, and the reflection coefficient of the left-handed circularly polarized wave is rRL =0.94, and the polarization state is circular polarization; when the conductivity of VO2 increases to 2000S / m, the phase difference between the incident wave and the reflected wave is 116.5°, the conversion rate of the linear polarization wave in the y direction to the linear polarization wave in the x direction is 81.3%, and the polarization state is elliptical polarization; when VO2 undergoes a phase change and reaches a metallic state, the conductivity increases to 200000S / m, the phase difference between the incident wave and the reflected wave is 145.2°, the conversion rate of the linear polarization wave in the y direction to the linear polarization wave in the x direction is 92.53%, and the polarization state is linear polarization.

[0085] 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 VO2-based polarization modulator, characterized in that: It includes a metal substrate layer, a Si dielectric layer arranged on the top of the metal substrate layer, and a super surface unit periodically arranged on the top of the Si dielectric layer, wherein the super surface unit is a chiral structure formed by a composite of VO2 and metal; The metasurface unit includes an intermediate structure consisting of a first intermediate metal frame and a second intermediate metal frame and side metal strips arranged on both sides of the intermediate structure. The middle positions of the opposite sides of the first intermediate metal frame and the second intermediate metal frame are inlaid with VO2, and the middle positions of the opposite sides of the first intermediate metal frame and the second intermediate metal frame are connected with metal protrusions.

2. The VO2-based polarization modulator according to claim 1, characterized in that: The left and right sides of the first middle metal frame and the second middle metal frame are connected to the side metal bars via connecting metal bars; The middle structure, metal protrusions, side metal strips and metal base layer are all made of gold.

3. The VO2-based polarization modulator according to claim 2, characterized in that: The basic period of the metasurface unit is P = 300um.

4. The VO2-based polarization modulator according to claim 3, characterized in that: The width of the side metal strip is a=18μm; the first intermediate metal frame and the second intermediate metal frame are both square frame structures, and the inner side length of the first intermediate metal frame and the second intermediate metal frame is b=70μm; the thickness of the VO2 embedded metal layer is c=2μm; the distance between the side metal strip and the super unit boundary is d=30μm; the width of the connecting metal strip is the same as the thickness of VO2, and the width of the connecting metal strip is e=10μm; the distance between the intermediate structure and the super surface unit boundary is f=35μm; the length of the metal protrusion is g=20μm.

5. The polarization characteristic analysis method of the VO2-based polarization modulator according to claim 4, characterized in that: The following steps are involved: S1. Determine the linear polarization reflection coefficient to determine the relationship between the reflected electric field and the incident electric field: In the formula, E r (r, t) represents the reflected electric field vector; and Respectively represent the x-component and y-component of the reflected electric field; r xx and r yy are all co-polarization components, among which r xx represents the reflection coefficient of the incident wave in the x direction, r yy represents the reflection coefficient of the incident wave in the y direction; r xy and r yx are cross-polarization components, among which r xy represents the reflection coefficient of the incident wave in the y direction in the x direction, r yx It represents the reflection coefficient of the incident wave in the x direction in the y direction; and They represent the incident electric field vector; R represents the reflection matrix; E i (r, t) represents the x-component and y-component of the incident electric field; S2. Determine the circular polarization reflection coefficient using the relationship between the linear polarization and circular polarization components: In the formula, r RR 、r RL 、r LR and r LL are the reflection coefficients of the circular polarization component, where r RR represents the reflection coefficient of right-hand circularly polarized wave on right-hand circularly polarized wave, r RL represents the reflection coefficient of left-handed circularly polarized wave on right-handed circularly polarized wave, r LR represents the reflection coefficient of right-hand circularly polarized wave on left-hand circularly polarized wave, r LL represents the reflection coefficient of a left-handed circularly polarized wave on a left-handed circularly polarized wave; i represents an imaginary unit; S3. Based on the circular polarization reflection coefficient, calculate the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave: A L ＝1-r LL 2 -r RL 2 (3)； A R ＝1-r LR 2 -r RR 2 (4)； In the formula, A L and A R They represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and the absorptivity to right-handed circularly polarized waves respectively; S4. Compare the absorption rate of the metasurface unit to the left-handed circularly polarized wave A L and the absorptivity A of the metasurface unit to right-handed circularly polarized waves R , and obtain the evaluation results of the chiral characteristics of the metasurface; S5. Based on the absorptivity of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave, the circular dichroism parameter CD is calculated to quantify the response degree of the metasurface unit to the left-handed polarized wave and the right-handed polarized wave: CD=A L -THE R (5); S6. Introduce the rotation angle ψ and ellipticity χ to characterize the polarization ellipticity of the metasurface unit: In the formula, E 0x and E 0y Respectively represent r RL and r LL The linear amplitude of ; δ represents the phase difference; S7. Use electromagnetic simulation software to perform simulation verification.

6. The modulation method of the VO2-based polarization modulator according to claim 4, characterized in that: The method comprises the following steps: incident light onto a metasurface unit under specific incident conditions, changing the conductivity of VO2 by regulating the phase change degree thereof, thereby changing the amplitude ratio and phase difference of the x-component and y-component of the reflected electric field, and thus regulating the polarization state of the polarization modulator.

7. The modulation method of the VO2-based polarization modulator according to claim 6, characterized in that: The specific incident conditions are: the incident frequency is 0.192THZ, and the linearly polarized light is vertically incident in the y direction.

8. The modulation method of the VO2-based polarization modulator according to claim 7, characterized in that: When VO2 is in an insulating state and the conductivity is 200S / m, the phase difference between the incident y-direction linear polarization wave and the modulated output x-direction linear polarization wave is 106.4°, the conversion rate between the y-direction linear polarization wave and the x-direction linear polarization wave is 41.65%, and the polarization state is circular polarization; When the conductivity of VO2 increases to 2000S / m, the phase difference between the incident wave and the reflected wave is 116.5°, the conversion rate between the linear polarization wave in the y direction and the linear polarization wave in the x direction is 81.3%, and the polarization state is elliptical polarization; When VO2 undergoes a phase change to reach a metallic state and the conductivity increases to 200,000 S / m, the phase difference between the incident wave and the reflected wave is 145.2°, the conversion rate of the linear polarization wave in the y direction to the linear polarization wave in the x direction is 92.53%, and the polarization state is linear polarization.

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