Polarization modulator based on VO2, polarization characteristic analysis method and modulation method

Abstract

The present invention discloses a VO2-based polarization modulator, polarization characteristic analysis method, and modulation method, belonging to the field of optical devices. The modulator comprises a metal substrate layer, a Si dielectric layer, and a metasurface unit periodically arranged on top of the Si dielectric layer. The metasurface unit is a chiral structure formed by a composite of VO2 and metal. The metasurface unit includes an intermediate structure composed 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 first intermediate metal frame and the second intermediate metal frame are both inlaid with VO2 in the middle positions on opposite sides of the first intermediate metal frame and the second intermediate metal frame. The middle positions on the opposite sides of the first intermediate metal frame and the second intermediate metal frame are both connected to metal protrusions. Using the above-mentioned VO2-based polarization modulator, polarization characteristic analysis method, and modulation method, the metasurface can adjust the polarization state of incident light by adjusting the conductivity of vanadium dioxide, thus achieving a dynamically tunable function.

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 both natural and artificial systems, the polarization state of light carries a wealth of information, and therefore holds significant application value in a wide range of fields, including science, industry, medicine, and communications. From fundamental physical phenomena to cutting-edge technological applications, the development of polarization modulation technology has greatly expanded the ability to manipulate light, resulting in widespread applications in polarization gratings, holography, polarization imaging, and vector beams.

[0003] Traditionally, polarization modulation of free-space lightwaves has primarily been achieved using electro-optical or magneto-optical crystals, which then alter the polarization state of the lightwaves through the action of an external electromagnetic field. These technologies offer a limited dynamic range, large device size, and high power consumption. Furthermore, there is currently no mature technology for polarization modulation of spatial waves in the terahertz band.

[0004] With advances in nanotechnology and materials science, new polarization modulation devices and methods are constantly emerging. The emergence of metasurface technology, in particular, offers new possibilities for more efficient, compact, and intelligent polarization control. Metasurfaces are thin, flat, and easy to manufacture, reducing losses and being applicable to frequencies from microwaves to visible light. They transmit or reflect electromagnetic waves through abrupt phase shifts on their surface structures, providing new degrees of freedom to control the phase, amplitude, and polarization response of light fields, thereby achieving a variety of 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 be completely aligned with its mirror image through rotation or translation. Many chiral objects exist in nature, but the optical response of naturally occurring chiral compounds is typically weak, limited by the matching of light wavelength and molecular size.

[0006] To address these issues, researchers have further developed artificial chiral metasurfaces. These structures can be categorized into three-dimensional and two-dimensional chiral structures, and into metallic and all-dielectric chiral metasurfaces. While three-dimensional chiral structures exhibit good chiral optical response, their processing and application are complex. Two-dimensional metallic chiral metasurfaces struggle to generate in-plane magnetic dipole moments and ohmic losses, making it difficult to achieve significant chiral optical response and circular dichroism.

[0007] Metal-compound composite metasurfaces are gaining increasing attention from researchers due to their superior performance in controlling phase, amplitude, and polarization in the electromagnetic spectrum, enabling the design of multifunctional integrated optical components. However, existing metal-compound composite metasurfaces still suffer from limitations 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 technical problems.

[0009] To achieve the above objectives, the present invention provides a VO2-based polarization modulator, comprising a metal substrate layer, a Si dielectric layer disposed on top of the metal substrate layer, and a metasurface unit periodically disposed on 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 = 18 μm; 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 = 70 μm; the thickness of the VO2 embedded metal layer c = 2 μm; the distance d from the side metal strip to the super unit boundary is 30 μm; 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 = 10 μm; the distance f from the intermediate structure to the super surface unit boundary is 35 μm; the length of the metal protrusion g = 20 μm.

[0015] A method for analyzing polarization characteristics of a VO2-based polarization modulator includes the following steps:

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

[0017]

[0018] Where, E r (r, t) represents the reflected electric field vector; and They represent the x component and y component of the reflected electric field respectively; r xx and r yy are all co-polarization components, where 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, where 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] Where 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-hand circularly polarized wave on right-hand circularly polarized wave, r LR represents the reflection coefficient of right-handed circularly polarized wave on left-handed 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] Where A L and A R represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and 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 chiral property evaluation results of the metasurface;

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

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

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

[0030]

[0031] Where, 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] 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 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 0.192 THZ and linearly polarized light with vertical y-direction polarization.

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

[0036] When the conductivity of VO2 increases to 2000 S / 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.

[0037] When VO2 undergoes a phase transition and reaches 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 linearly polarized wave in the y-direction to the linearly polarized wave in the x-direction is 92.53%, and the polarization state is linearly polarized.

[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 of VO2 and the incident angle, 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 0.192 THz, the metasurface in the insulating state absorbs much more right-handed circular polarization (RCP) than left-handed circular polarization (LCP), showing high circular dichroism (CD value close to 0.8). This 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 This is a schematic structural diagram of a single metasurface unit of a VO2-based polarization modulator according to the present invention;

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

[0048] Figure 5 The graph shows the change in circular dichroism of the metasurface when the conductivity of vanadium dioxide (VO2) increases from 200 S / m to 200,000 S / m in the simulation experiment described in the present invention. (a) is a schematic diagram of the CD of the metasurface when the conductivity and frequency change, and (b) is a graph showing the CD value as the conductivity changes at 0.192 THZ.

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

[0050] Figure 7 These are the results of the simulation experiment of the present invention showing the effect of the change in the incident angle on the performance of the metasurface structure. (a) is a schematic diagram of the metasurface's absorption rate for LCP when the circular polarization incident angle is changed, (b) is a schematic diagram of the metasurface's absorption rate for RCP 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 0.192 THz.

[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 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.

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

[0055] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0056] Vanadium dioxide (VO2) has become a highly anticipated material due to its unique phase transition properties. VO2 has the ability to undergo a reversible phase transition 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 approximately 340K. During this process, its electrical 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 transition 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 base layer 1, a Si dielectric layer 2 arranged on the top of the metal base layer 1, and a metasurface unit 3 periodically arranged on the top of the Si dielectric layer 2. 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. The middle positions of the opposite sides of the first intermediate metal frame 31 and the second intermediate metal frame 34 are both inlaid with VO232, and the middle positions of the opposite sides of the first intermediate metal frame 31 and the second intermediate metal frame 34 are both connected with metal protrusions 33.

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

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

[0060] A method for analyzing polarization characteristics of a VO2-based polarization modulator includes the following steps:

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

[0062]

[0063] Where, E r (r, t) represents the reflected electric field vector; and They represent the x component and y component of the reflected electric field respectively; r xx and r yy are all co-polarization components, where 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, where 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] Where 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-hand circularly polarized wave on right-hand circularly polarized wave, r LR represents the reflection coefficient of right-handed circularly polarized wave on left-handed 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] Where A L and A R represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and 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 chiral property evaluation results of the metasurface;

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

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

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

[0075]

[0076] Where, 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) r 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 the aggregation position of its free charges also exhibits 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 circularly polarized light is incident at 0.192THz.

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

[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 strong circular dichroism at a frequency of 0.192THz. This discovery not only reveals the correlation between metasurface circular dichroism and VO2 conductivity, but also provides an experimental basis for the dynamic adjustment of metasurface optical properties through temperature regulation. 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 achieving more efficient and flexible optical device design in the fields of optical communications, 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 absorption rate of the metasurface structure for left-handed circularly polarized light (LCP) gradually increases. Although the increase is small, the absorption rate 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 shows an extremely high absorption rate, close to 0.9. It can be seen that by changing the incident angle, it can be observed that the absorption rate of the metasurface for RCP changes with the increase of the incident angle. In the range of 0° to 50°, the absorption rate increases with the increase of the incident angle; while in the range of 50° to 80°, the absorption rate decreases with the increase of the incident angle. For LCP, although the absorption rate 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 0.19THz. Therefore, 20° is taken as the incident angle, at this time 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 transforms into a metallic state, thereby verifying the effectiveness of the present invention.

[0083] The modulation method for a VO2-based polarization modulator includes the following steps: under specific incident conditions, light is incident on a metasurface unit, and by regulating the VO2 phase change degree, its conductivity is changed, thereby changing the amplitude ratio and phase difference between the x and y components of the reflected electric field, thereby regulating the polarization state of the polarization modulator. The specific incident conditions include linearly polarized light with an incident frequency of 0.192 THZ and an incident angle of 20° in the y-direction.

[0084] like Figure 6 As shown, when VO2 is in an insulating state with a conductivity of 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 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 transition and reaches a metallic state and 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 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 VO2-based polarization modulator, characterized in that: It includes a metal base layer, a Si dielectric layer arranged on the top of the metal base 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; 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 first and second intermediate metal frames on opposite sides are both inlaid with VO2, and the middle positions of the first and second intermediate metal frames on opposite sides are both connected with metal protrusions. 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; The middle structure, metal protrusions, side metal strips and metal base layer are all made of gold.

2. The VO2-based polarization modulator according to claim 1, wherein: The basic period of the metasurface unit is P = 300um.

3. The VO2-based polarization modulator according to claim 2, wherein: The width of the side metal strip is a = 18 μm; 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 = 70 μm; the thickness of the VO2 embedded metal layer is c = 2 μm; the distance between the side metal strip and the boundary of the metasurface unit is d = 30 μm; 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 = 10 μm; the distance between the intermediate structure and the boundary of the metasurface unit is f = 35 μm; the length of the metal protrusion is g = 20 μm.

4. The polarization characteristic analysis method of a VO2-based polarization modulator according to claim 3, wherein: The following steps are involved: S1. Determine the linear polarization reflection coefficient to find the relationship between the reflected electric field and the incident electric field: Where, E r (r, t) represents the reflected electric field vector; and They represent the x component and y component of the reflected electric field respectively; r xx and r yy are all co-polarization components, where 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, where 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: Where 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-hand circularly polarized wave on right-hand circularly polarized wave, r LR represents the reflection coefficient of right-handed circularly polarized wave on left-handed 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)； Where A L and A R represent the absorptivity of the metasurface unit to left-handed circularly polarized waves and 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 chiral property evaluation results of the metasurface; S5. Based on the absorptivity of the metasurface unit to left-handed polarized waves and right-handed polarized waves, the circular dichroism parameter CD is calculated to quantify the response degree of the metasurface unit to left-handed polarized waves and right-handed polarized waves: CD=A L -THE R (5); S6. Introduce the rotation angle ψ and ellipticity χ to characterize the polarization ellipticity characteristics of the metasurface unit: Where, 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.

5. The modulation method of the VO2-based polarization modulator according to claim 3, wherein: 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, and thereby 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.

6. The modulation method of the VO2-based polarization modulator according to claim 5, 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.

7. The modulation method of the VO2-based polarization modulator according to claim 6, characterized in that: When VO2 is in an insulating state with a conductivity of 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. When the conductivity of VO2 increases to 2000 S / 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. When VO2 undergoes a phase transition and reaches 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 linearly polarized wave in the y-direction to the linearly polarized wave in the x-direction is 92.53%, and the polarization state is linearly polarized.

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