Multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene and preparation method thereof

Abstract

The invention discloses a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, the metasurface is formed by periodically arranging M * N metasurface units with multilayer structures in an array, the metasurface units are in M * N two-dimensional distribution, and both M and N are positive integers; the metasurface unit comprises a metal substrate, a first dielectric layer, a graphene layer, a second dielectric layer and a resonant layer unit which are sequentially arranged from bottom to top. According to the metasurface, by reasonably utilizing the phase change characteristic of VO2 and the tunability of graphene, efficient multifunctional response is achieved, and the problems that a traditional metasurface is few in function, single in regulation and control mode and low in efficiency are solved. The invention further provides a preparation method of the multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene.

Description

Technical Field

[0001] This invention belongs to the field of terahertz metasurface technology, specifically relating to a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, and also to a method for preparing a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene. Background Technology

[0002] Terahertz (THz) waves generally refer to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. Due to their low energy, strong penetrability, and unique frequency and wavelength, terahertz waves and related technologies have become a research hotspot in various fields. Terahertz metasurfaces, as fundamental functional devices for terahertz applications, are widely used in absorbers, detectors, spectral imaging, stealth, and other fields.

[0003] Metamaterials are a class of artificially designed materials whose unit structures are much smaller than the operating wavelength and whose structural units are arranged periodically. By appropriately designing the geometry and parameters of the unit structures, electromagnetic properties not found in natural materials can be obtained, such as negative refractive index and the inverse Doppler effect. It is noteworthy that, unlike natural materials, the unique electromagnetic properties of metamaterials depend on their structural composition rather than the inherent properties of the material itself. Furthermore, analogous to the compositional patterns of natural materials, the unit structures of metamaterials can be viewed as artificial atoms or molecules. By adjusting the shape and size of the unit structures, researchers can artificially control the interaction between the structure and incident electromagnetic waves to achieve superior electromagnetic functions, such as efficient absorption, polarization conversion, and optical imaging that breaks the diffraction limit. Further, with in-depth research, researchers have extended the three-dimensional structure of metamaterials to two-dimensional planes, forming ultrathin metasurfaces.

[0004] Chirality, a crucial property of metamaterials and metasurfaces, refers to a geometric structure that cannot be superimposed on its mirror image through translation or rotation. Compared to natural chiral materials, artificial chiral metamaterials possess stronger electromagnetic responses and designability, enabling unique electromagnetic properties such as significant dichroism and efficient conversion between multiple polarization states. In the terahertz band, chiral metasurfaces are widely used in optical communication, polarization imaging, sensing, and absorber design due to their excellent polarization selectivity. Dichroism is an important physical quantity characterizing chiral metasurfaces, referring to the structure's ability to absorb differences in incident waves with different polarization states. Based on the polarization form of the incident wave, dichroism can be divided into circular dichroism (CD) and linear dichroism (LD). CD reflects the absorption difference between left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) waves, while LD reflects its different responses to transversely electric (TE) and transversely magnetic (TM) polarized waves. In addition to selective absorption of different polarization states, chiral metasurfaces can also achieve efficient conversion between various polarization modes such as line-to-line, line-to-circle, and circle-to-circle through ingenious structural design, thereby further expanding their application potential in polarization control and terahertz photonic devices.

[0005] Currently, although the design and fabrication of terahertz chiral metasurfaces based on metamaterials have been extensively studied, most work still focuses on single-function, dual-function, or finitely tunable structures. These designs often suffer from limited functionality, singular control methods, low efficiency, and structural complexity. This restricts the application scenarios of terahertz chiral metasurfaces and severely hinders the development of high integration and miniaturization of terahertz devices. Therefore, there is an urgent need to develop a terahertz chiral metasurface that is multifunctional, structurally simple, easy to fabricate, and flexibly tunable to meet the needs of practical terahertz applications. Summary of the Invention

[0006] The first objective of this invention is to propose a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene. This metasurface achieves a highly efficient multifunctional response by making reasonable use of the phase transition characteristics of VO2 and the tunability of graphene, thus solving the problems of limited functionality, single control method, and low efficiency of traditional metasurfaces.

[0007] The second objective of this invention is to propose a method for preparing a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene.

[0008] The first technical solution adopted in this invention is a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene. The metasurface is composed of M×N metasurface units with multilayer structures arranged in a periodic array. The metasurface units are distributed in two dimensions of M×N, where M and N are both positive integers. The metasurface unit comprises, from bottom to top, a metal substrate, a first dielectric layer, a graphene layer, a second dielectric layer, and a resonant layer unit.

[0009] The invention is further characterized in that: The metal substrate, the first dielectric layer, and the second dielectric layer are all rectangular structures with a rectangular cross-section in the horizontal direction. The length and width of the rectangular cross-sections of the metal substrate, the first dielectric layer, and the second dielectric layer are equal.

[0010] The metal substrate is made of copper with an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, length P x The width is 54µm-58µm, and the P width is... y The thickness is 47µm-51µm, and the thickness H1 is 2µm-2.5µm.

[0011] The first dielectric layer is made of SiO2 with a relative permittivity of 3.9 and a length of P. x The width is 54µm-58µm, and the P width is... y The thickness H2 is 47µm-51µm, and the thickness H2 is 3µm-3.5µm.

[0012] The second dielectric layer is made of SiO2 with a relative permittivity of 3.9 and a length of P. x The width is 54µm-58µm, and the P width is... y The thickness is 47µm-51µm, and the thickness H3 is 10µm-12µm.

[0013] The graphene layer is ring-shaped, and it is a single layer of graphene with a thickness H. g The diameter is 0.34 nm, the outer diameter R1 is 9 µm-10 µm, and the inner diameter R2 is 7 µm-8 µm.

[0014] The resonant layer unit includes two U-shaped metal elements disposed on the upper surface of the second dielectric layer. The two U-shaped metal elements are centrally symmetrical about the center point of the upper surface of the second dielectric layer. The U-shaped metal component includes a crossbeam, with a first protrusion and a second protrusion at each end of the crossbeam, the length of the first protrusion being greater than the length of the second protrusion; A VO2 patch is also provided at the end of the first protrusion of one of the concave metal elements; The concave-shaped metal component is made entirely of copper, with an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, thickness H4 is 2µm-2.5µm; the length L1 of the second bump is 8µm-9µm, and the width a1 is 6µm-7µm; the length L2 of the crossbeam is 22µm-23µm, and the width a2 is 6µm-7µm; the length L3 of the first bump is 28µm-29µm, and the width b1 is 5µm-6µm; the length L4 of the VO2 patch is 4µm-5µm, and the width b2 is 5µm-6µm, and the thickness of the VO2 patch is the same as the thickness of the concave metal element.

[0015] The second technical solution adopted in this invention is a method for preparing a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, specifically including the following steps: Step 1: Preparation of the metal substrate; Step 2: Deposition of the first dielectric layer; Step 3: Preparation of the graphene layer; Step 4: Deposition of the second dielectric layer; Step 5: Fabrication of the resonant layer unit.

[0016] The invention is further characterized in that: Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10-15 minutes to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃-120℃ for 30-40 minutes. Step 1.2, Metal Thin Film Deposition: Copper thin films were deposited using electron beam evaporation. Step 1.3, Annealing treatment: Annealing at 300℃~350℃ for 30min-40min improves the crystal quality and conductivity of the copper thin film, thus obtaining a metal substrate; Step 2 is as follows: Step 2.1, SiO2 thin film preparation: SiO2 thin films were deposited on a metal substrate using chemical vapor deposition; Step 2.2, Curing treatment: The first dielectric layer is obtained by curing at 150℃-160℃ for 1-2 hours. Step 3 specifically involves: Step 3.1, Graphene Growth and Transfer: A single layer of graphene was grown on copper foil using chemical vapor deposition and then transferred to the surface of the first dielectric layer using a wet process. Step 3.2, Graphene Patterning: Electron beam lithography was used to define a ring structure to obtain a graphene layer; Step 4 is as follows: Step 4.1, SiO2 thin film preparation: SiO2 thin films were deposited on graphene layers using chemical vapor deposition. Step 4.2, Curing treatment: The second dielectric layer is obtained by curing at 150℃-160℃ for 1-2 hours. Step 5 specifically involves: Step 5.1, Photolithographic Patterning: On the surface of the cured second dielectric layer, the designed concave metal element pattern is defined using electron beam lithography. Step 5.2, Copper Thin Film Deposition: A copper film is deposited using electron beam evaporation. Step 5.3, Peeling and Shaping: The photoresist and excess copper film on it are removed using a stripping method, leaving the designed structure.

[0017] Step 5.4, Photolithography defines the VO2 region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.5, VO2 thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.6, Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by a stripping method, leaving the designed structure to obtain the resonant layer unit.

[0018] The beneficial effects of this invention are: (1) This invention is based on a multifunctional terahertz chiral metasurface of vanadium dioxide and graphene. By making reasonable use of the phase transition characteristics of VO2 and the tunability of graphene, it realizes four functions: efficient three-frequency CD response, single-band reversible LD response, and line-to-line and circle-to-circle polarization conversion. It achieves efficient multifunctional response and solves the problems of limited functions, single control method, and low efficiency of traditional metasurfaces. The metasurface structure is simple and easy to realize.

[0019] (2) The preparation method of the present invention is simple and easy to operate. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the periodic structure of the multifunctional terahertz chiral metasurface of the present invention; Figure 2 This is a schematic diagram of the metasurface unit structure of the multifunctional terahertz chiral metasurface of the present invention; Figure 3 This is a schematic diagram of the resonant layer unit in the multifunctional terahertz chiral metasurface of the present invention; Figure 4 This is a schematic diagram of the graphene layer in the multifunctional terahertz chiral metasurface of the present invention; Figure 5 This is the circularly polarized absorption spectrum of the terahertz chiral metasurface in Embodiment 1 of the present invention when VO2 is a metallic phase and the chemical potential of graphene is 0.8 eV. Figure 6This is a circular dichroism chromatogram of a terahertz chiral metasurface when VO2 is a metallic phase and the chemical potential of graphene is 0.8 eV, as shown in Example 1 of this invention. Figure 7 This is a circular dichroism chromatogram of the metasurface of Example 1 of the present invention as a function of the chemical potential of graphene; Figure 8 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 1.62 THz and in the side-view direction is shown under LCP wave incident. Figure 9 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 2.89 THz and in the side-view direction is shown under LCP wave incident. Figure 10 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 3.19 THz and in the side-view direction is shown under LCP wave incident. Figure 11 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 1.62 THz and in the side-view direction is shown under RCP wave incident. Figure 12 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 2.89 THz and in the side-view direction is shown under RCP wave incident. Figure 13 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 3.19 THz and in the side-view direction is shown under RCP wave incident. Figure 14 This is the linear polarization absorption and linear dichroism spectrum of the terahertz chiral metasurface when VO2 is the insulating phase and the chemical potential of graphene is 1.0 eV, as described in Embodiment 1 of the present invention. Figure 15 This is a line dichroism chromatogram of the metasurface of Example 1 of the present invention as a function of the chemical potential of graphene; Figure 16 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 4.093 THz and in the side-view direction is shown under TE wave incident. Figure 17 The electric field distribution of the metasurface of Embodiment 1 of the present invention at 4.093 THz and in the side-view direction is shown under TM wave incident. Figure 18 The co-polarization reflectance, cross-polarization reflectance, and PCR value of the metasurface of Example 1 of the present invention are presented in the range of 1.26-1.59 THz under TE wave incident conditions. Figure 19 The copolarization reflectance, crosspolarization reflectance, and PCR value of the metasurface of Example 1 of the present invention are presented in the range of 2.9-3.31 THz under TE wave incident conditions. Figure 20 The copolarization reflectance, crosspolarization reflectance, and PCR value of the metasurface of Example 1 of the present invention are presented in the range of 1.25-1.94 THz under LCP wave incident conditions. Figure 21 The copolarization reflectance, crosspolarization reflectance, and PCR value of the metasurface of Example 1 of the present invention are presented in the range of 2.78-3.34 THz under LCP wave incident conditions.

[0021] In the figure, 1. Metal substrate, 2. First dielectric layer, 3. Graphene layer, 4. Second dielectric layer, 5. Resonant layer unit; 5-1. U-shaped metal component; 5-1-1. Crossbeam; 5-1-2. First protrusion; 5-1-3. Second protrusion; 5-2.VO2 patch. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] This invention provides a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, such as... Figure 1 As shown, the metasurface is composed of a periodic array of M×N metasurface units with multi-layer structures. The metasurface units are distributed in an M×N two-dimensional pattern, where M and N are both positive integers. The metasurface unit includes a metal substrate 1, a first dielectric layer 2, a graphene layer 3, a second dielectric layer 4, and a resonant layer unit 5 arranged sequentially from bottom to top.

[0024] Metal substrate 1, first dielectric layer 2, and second dielectric layer 4 are all rectangular structures with a rectangular cross-section in the horizontal direction. The length and width of the rectangular cross-sections of metal substrate 1, first dielectric layer 2, and second dielectric layer 4 are equal.

[0025] The metal substrate 1 is made of copper and has an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, length P x The width is 54µm-58µm, and the P width is... y The thickness is 47µm-51µm, and the thickness H1 is 2µm-2.5µm.

[0026] The first dielectric layer 2 is made of SiO2 with a relative permittivity of 3.9 and a length of P. x The width is 54µm-58µm, and the P width is... y The thickness H2 is 47µm-51µm, and the thickness H2 is 3µm-3.5µm.

[0027] The second dielectric layer 4 is made of SiO2 with a relative permittivity of 3.9 and a length of P. x The width is 54µm-58µm, and the P width is...y The thickness is 47µm-51µm, and the thickness H3 is 10µm-12µm.

[0028] The graphene layer 3 is ring-shaped and is a single layer of graphene. The thickness H of the graphene layer 3 is [not specified]. g The diameter is 0.34 nm, the outer diameter R1 is 9 µm-10 µm, and the inner diameter R2 is 7 µm-8 µm.

[0029] The resonant layer unit 5 includes two U-shaped metal elements 5-1 disposed on the upper surface of the second dielectric layer 4. The two U-shaped metal elements 5-1 are centrally symmetrical about the center point of the upper surface of the second dielectric layer 4. The U-shaped metal element 5-1 includes a crossbeam 5-1-1, with a first protrusion 5-1-2 and a second protrusion 5-1-3 at both ends of the crossbeam 5-1-1, the length of the first protrusion 5-1-2 being greater than the length of the second protrusion 5-1-3; A VO2 patch 5-2 is also provided at the end of the first protrusion 5-1-2 of one of the concave metal elements 5-1; The concave-shaped metal component 5-1 is made entirely of copper, with an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, thickness H4 is 2µm-2.5µm; the length L1 of the second protrusion 5-1-3 is 8µm-9µm, and the width a1 is 6µm-7µm; the length L2 of the crossbeam 5-1-1 is 22µm-23µm, and the width a2 is 6µm-7µm; the length L3 of the first protrusion 5-1-2 is 28µm-29µm, and the width b1 is 5µm-6µm; the length L4 of the VO2 patch 5-2 is 4µm-5µm, and the width b2 is 5µm-6µm, and the thickness of the VO2 patch 5-2 is the same as the thickness of the concave metal element 5-1.

[0030] This invention also provides a method for preparing the above-mentioned multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, specifically including the following steps: Step 1: Preparation of metal substrate 1; Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10-15 minutes to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃-120℃ for 30-40 minutes. Step 1.2, Metal Thin Film Deposition: Copper thin films were deposited using electron beam evaporation. Step 1.3, Annealing treatment: Annealing at 300℃~350℃ for 30min-40min improves the crystal quality and conductivity of the copper thin film, resulting in metal substrate 1; Step 2, Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1, SiO2 thin film preparation: A SiO2 thin film was deposited on a metal substrate 1 by chemical vapor deposition; Step 2.2, Curing treatment: Curing at 150℃-160℃ for 1-2 hours yields the first dielectric layer 2. Step 3: Preparation of graphene layer 3; Step 3 specifically involves: Step 3.1, Graphene Growth and Transfer: A single layer of graphene was grown on copper foil using chemical vapor deposition and then transferred to the surface of the first dielectric layer 2 by a wet process. Step 3.2, Graphene Patterning: Electron beam lithography was used to define a ring structure to obtain graphene layer 3; Step 4: Deposition of the second dielectric layer 4; Step 4 is as follows: Step 4.1, SiO2 thin film preparation: SiO2 thin films were deposited on graphene layer 3 using chemical vapor deposition; Step 4.2, Curing treatment: Curing at 150℃-160℃ for 1-2 hours yields the second dielectric layer 4. Step 5: Fabrication of resonant layer unit 5.

[0031] Step 5 specifically involves: Step 5.1, Photolithographic Patterning: On the surface of the cured second dielectric layer 4, the designed concave metal element pattern is defined using electron beam lithography. Step 5.2, Copper Thin Film Deposition: A copper film is deposited using electron beam evaporation. Step 5.3, Peeling and Shaping: The photoresist and excess copper film on it are removed using a stripping method, leaving the designed structure.

[0032] Step 5.4, Photolithography defines the VO2 region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.5, VO2 thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.6, Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by a stripping method, leaving the designed structure, to obtain the resonant layer unit 5.

[0033] Example 1 like Figures 1-4 As shown, the chiral metasurface in this embodiment includes 3×3 metasurface units. The number of units does not affect the overall performance. Each metasurface unit includes, from bottom to top, a metal substrate 1, a first dielectric layer 2, a graphene layer unit (graphene layer 3), a second dielectric layer 4, and a top resonant layer unit (resonant layer 5). The metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are all cuboid structures with a rectangular cross-section in the horizontal direction. The length and width of the rectangular cross-sections of the metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are correspondingly equal.

[0034] The metal substrate 1 is made of copper and has an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, length P of metal substrate 1 x It is 54µm wide and has a P-value of 100µm. y The thickness is 47µm and the thickness H1 is 2µm, which is much greater than the skin depth of metal in the terahertz band, ensuring that the transmittance of the metasurface is T=0.

[0035] Both dielectric layers are made of SiO2 with a relative permittivity of 3.9 and a length of P. x It is 54µm wide and has a P-value of 100µm. y The thickness of the first dielectric layer 2 is 47µm, the thickness of the second dielectric layer 4 is 3µm, and the thickness of the third dielectric layer 4 is 10µm.

[0036] Graphene layer 3 is a single layer of graphene with a thickness of H. g The diameter is 0.34 nm, the outer diameter R1 is 9 µm, and the inner diameter R2 is 7 µm.

[0037] The resonant layer unit 5 includes two U-shaped metal elements 5-1 disposed on the upper surface of the second dielectric layer 4. The two U-shaped metal elements 5-1 are centrally symmetrical about the center point of the upper surface of the second dielectric layer 4. The U-shaped metal element 5-1 includes a crossbeam 5-1-1, with a first protrusion 5-1-2 and a second protrusion 5-1-3 at both ends of the crossbeam 5-1-1, the length of the first protrusion 5-1-2 being greater than the length of the second protrusion 5-1-3; A VO2 patch 5-2 is also provided at the end of the first protrusion 5-1-2 of one of the concave metal elements 5-1; The concave-shaped metal component 5-1 is made entirely of copper, with an electrical conductivity of 5.8 × 10⁻⁶. 7The thickness H4 is 2µm; the length L1 of the second protrusion 5-1-3 is 8µm, and the width a1 is 6µm; the length L2 of the crossbeam 5-1-1 is 22µm, and the width a2 is 6µm; the length L3 of the first protrusion 5-1-2 is 28µm, and the width b1 is 5µm; the length L4 of the VO2 patch 5-2 is 4µm, and the width b2 is 5µm. The thickness of the VO2 patch 5-2 is the same as the thickness of the concave metal element 5-1. When the ambient temperature is below 340K, vanadium dioxide is in the insulating phase, and its conductivity is 200S / m. When the ambient temperature is above 340K, vanadium dioxide is in the metallic phase, and its conductivity is 200000S / m.

[0038] Figure 5 This is an embodiment of the invention showing the circularly polarized absorption spectrum of a terahertz chiral metasurface when VO2 is a metallic phase and the graphene chemical potential is 0.8 eV. It can be seen that the absorption intensities of the metasurface for RCP and LCP waves differ significantly at 1.62 THz, 2.89 THz, and 3.19 THz. Specifically, at 1.62 THz, 2.89 THz, and 3.19 THz, the absorption rates of RCP waves reach 98.9%, 91.1%, and 95.9%, respectively, significantly higher than the 4.5%, 8.2%, and 8.3% of LCP waves at the corresponding frequencies. These absorption differences directly lead to a strong three-frequency CD effect.

[0039] Figure 6 This is a circular dichroism chromatogram of a terahertz chiral metasurface when VO2 is a metallic phase and the graphene chemical potential is 0.8 eV, as described in this embodiment of the invention. It can be seen that the metasurface exhibits distinct narrow-band CD peaks (denoted as I, II, and III) at 1.62 THz, 2.89 THz, and 3.19 THz, respectively, with corresponding peak values ​​of 0.944, 0.829, and 0.876.

[0040] Figure 7 This is a circular dichroism spectral density (CPD) of the metasurface as a function of the graphene chemical potential in an embodiment of the present invention. It can be seen that as the graphene chemical potential (E) increases... f As E gradually decreases, the frequency positions and CD intensities of the three resonance peaks all change. Resonance peak I shows the smallest change; although its CD intensity decreases slightly, it remains above 0.9, and its frequency only undergoes a slight redshift. In contrast, the changes in peaks II and III are more significant: as E... f As E decreases, the CD intensity of peak II gradually weakens and eventually disappears, accompanied by a significant redshift. For peak III, when E... f As the voltage drops from 0.8 eV to 0.2 eV, its CD intensity gradually decreases; when E f When the voltage is further reduced to 0.1 eV, the CD intensity rebounds. Simultaneously, its resonant frequency increases with E. fThe decrease in E leads to a sustained redshift. This demonstrates that the three CD peaks can be modulated to varying degrees by adjusting the chemical potential of graphene. It is noteworthy that when E... f At 0.1 eV, the CD peaks changed from three to two, with corresponding CD intensities of 0.913 and 0.754, respectively. This demonstrates that the number of CD peaks can be controlled through the combined regulation of VO2 and graphene, overcoming the limitation of fixed and untunable CD peak numbers in traditional metasurfaces.

[0041] To further investigate the physical mechanism of the strong circular dichroism of this terahertz chiral metasurface at all three frequencies, the electric field distribution of the metasurface at each peak frequency was measured, and the results are as follows: Figures 8-13 As shown. Among them, Figures 8-10 The electric field distributions of the resonant layer unit and the side-view direction at 1.62THz, 2.89THz and 3.19THz under LCP wave incident conditions are shown respectively. Figures 11-13 The electric field distributions of the resonant layer unit and the side-view direction at 1.62THz, 2.89THz and 3.19THz under RCP wave incident conditions are shown respectively.

[0042] like Figures 8-10 As shown, under LCP wave incidence, the electric field intensity at the three resonant frequencies is generally weak, mainly distributed in the edge region of the top metal resonant unit. At this time, the impedance matching between the incident wave and the structure is poor, resulting in strong reflection and weak absorption. In contrast, the electric field intensity under RCP wave incidence is significantly enhanced, with a wider distribution range, exhibiting typical strong coupling characteristics, such as... Figures 11-13As shown. At 1.62 THz, the electric field is mainly distributed at the edges of the two concave metal elements 5-1 and the VO2 patch 5-2, indicating that energy is mainly absorbed through the electric dipole mode of the top resonant unit. At 2.89 THz, the electric field is mainly distributed at the edges of the two concave metal elements 5-1, around the VO2 patch 5-2, and in the second dielectric layer 4 above the graphene layer 3. Among these, the electric field intensity inside the second dielectric layer 4 is the most significant. From the side view of the xz section, it can be seen that the second dielectric layer 4 exhibits a clear standing wave junction-antinode structure. This indicates that the resonance at this frequency is a hybrid mode formed by the coupling of the top electric dipole resonance and the Fabry-Perot (FP) cavity resonance, in which the FP cavity effect dominates. At 3.19 THz, the electric field is mainly distributed in the concave metal element 5-1 with the VO2 patch 5-2, the VO2 patch 5-2, and the dielectric layer regions on both sides of the graphene layer 3. Among these, the electric field intensity of the resonant layer unit 5 is the most significant. This indicates that the resonance at this frequency is also a hybrid mode formed by the coupling of the top electric dipole resonance and the Fabry-Perot (FP) cavity resonance, but the top electric dipole resonance is dominant. Overall, the resonance under LCP wave incidence is weaker, while the resonance under RCP wave incidence forms a stronger local field and cavity resonance. The significant difference between the two leads to the metasurface exhibiting obvious circular dichroism at all three frequencies.

[0043] Figure 14 This is an embodiment of the invention showing the linear polarization absorption and linear dichroism spectrum of a terahertz chiral metasurface when VO2 is the insulating phase and the chemical potential of graphene is 1.0 eV. It can be seen that at 4.093 THz, the absorption rate A of the TE polarized wave is... x It reaches a peak value of 0.92, while the absorption rate A of the TM polarized wave... y The efficiency is only 0.02, corresponding to an LD value as high as 0.90. This indicates that the metasurface can efficiently distinguish terahertz waves of different linear polarization states, overcoming the limitation of low LD response efficiency of traditional metasurfaces.

[0044] Figure 15 This is a line dichroism chromatogram of the metasurface as a function of the chemical potential of graphene in an embodiment of the present invention. From... Figure 15 As can be seen from this, LD increases with E f As E decreases, it gradually decreases. f At 0.2 eV, the amplitude of the LD is close to zero. As E... f As the potential of graphene decreases, the LD intensity gradually weakens, while the resonant frequency exhibits a significant redshift. The maximum and minimum values ​​of the LD reach 0.9 and 0.076, respectively, achieving the "on" and "off" states of the LD functional state. This indicates that the LD intensity of the proposed metasurface can be dynamically adjusted by modifying the chemical potential of graphene.

[0045] To further investigate the physical mechanism of the strong linear dichroism in the single-band of this terahertz chiral metasurface, the electric field distribution of the metasurface at the peak frequency was measured, and the results are as follows: Figures 16-17 As shown. Among them, Figure 16 The electric field distribution of resonant layer unit 5 and the side-view direction at 4.093 THz under TE wave incidence; Figure 17 The image shows the electric field distribution of resonant layer unit 5 at 4.093 THz and along the side-view direction under TM wave incident light. Figure 16 As shown, when a TE wave is incident, the electric field is mainly distributed in the region of the concave metal element 5-1 with the VO2 patch 5-2, the VO2 patch 5-2, and the second dielectric layer 4 above the graphene layer 3. This indicates that the incident energy is effectively coupled into the interior of the structure, forming a mixed mode generated by the coupling between the top electric dipole resonance and the Fabry-Perot (FP) cavity, resulting in strong absorption characteristics. In contrast, as... Figure 17 As shown, when a TM wave is incident, the overall electric field strength is weak, mainly distributed in the edge region of the two concave metal elements 5-1 in the horizontal direction, with almost no obvious field distribution in the dielectric layer. This indicates that the impedance matching between the incident wave and the structure is poor, coupling is limited, and most of the energy is reflected. It is this significant difference in absorption capability for different linearly polarized waves that causes the device to produce a significant LD effect at this frequency.

[0046] like Figure 18 As shown, Figure 18 The co-polarization reflectivity, cross-polarization reflectivity, and PCR value of the metasurface in this embodiment of the invention are presented under TE wave incident light in the 1.26-1.59 THz range. It can be seen that when TE wave is incident, the device achieves efficient polarization conversion in the 1.26-1.59 THz frequency band, and its PCR remains above 0.8 throughout the entire frequency range. This is because the co-polarization reflectivity R0 at this time... xx Approaching 0, the total reflectivity is almost entirely determined by the cross-polarization reflectivity R. yx This decision allows PCR to be maintained at a high level. It demonstrates that the incident TE wave is efficiently converted into TM wave within this frequency band.

[0047] like Figure 19 As shown, Figure 19 The co-polarization reflectivity, cross-polarization reflectivity, and PCR value of the metasurface in this embodiment of the invention are presented under TE wave incident conditions within the 2.9-3.31 THz range. It can also be seen that when TE waves are incident, the device achieves efficient polarization conversion in the 2.9-3.31 THz frequency band, and its PCR remains above 0.8 across the entire frequency range. This is because the co-polarization reflectivity R0 at this time... xx Approaching 0, the total reflectivity is almost entirely determined by the cross-polarization reflectivity R. yxThis decision allows PCR to be maintained at a high level. It demonstrates that the incident TE wave is also efficiently converted into TM wave within this frequency band.

[0048] like Figure 20 As shown, Figure 20 The co-polarization reflectivity, cross-polarization reflectivity, and PCR value of the metasurface in this embodiment of the invention are presented under LCP wave incident conditions within the 1.25-1.94 THz range. It can be seen that when LCP wave is incident, the device achieves efficient polarization conversion in the 1.25-1.94 THz frequency band, and its PCR remains above 0.8 throughout the entire frequency range. This is because the co-polarization reflectivity Rc at this time... LL Approaching 0, the total reflectivity is almost entirely determined by the cross-polarization reflectivity R. RL This decision allows PCR to be maintained at a high level. It demonstrates that the incident LCP wave is efficiently converted into an RCP wave within this frequency band.

[0049] like Figure 21 As shown, Figure 21 The co-polarization reflectivity, cross-polarization reflectivity, and PCR value of the metasurface in this embodiment of the invention within the 2.78-3.34 THz frequency band under LCP wave incident conditions are presented. It can also be seen that when LCP wave is incident, the device achieves efficient polarization conversion in the 2.78-3.34 THz frequency band, and its PCR remains above 0.8 throughout the entire frequency range. This is because the co-polarization reflectivity Rc at this time... LL Approaching 0, the total reflectivity is almost entirely determined by the cross-polarization reflectivity R. RL This decision allows PCR to be maintained at a high level. It is evident that the incident LCP wave is also efficiently converted into RCP wave within this frequency band.

[0050] In summary, a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, through dual modulation of vanadium dioxide and graphene, achieves four functions: efficient three-frequency CD response, single-band reversible LD response, and line-to-line and circular-to-circular polarization conversion. Specifically: 1. When vanadium dioxide is in the metallic phase and the graphene chemical potential is 0.8 eV, the metasurface exhibits absorption rates of 98.9%, 91.1%, and 95.9% for RCP waves at 1.62 THz, 2.89 THz, and 3.19 THz, respectively, while the absorption rates for LCP waves are only 4.5%, 8.2%, and 8.3%. This difference in absorption directly leads to a strong CD effect, thus the metasurface displays a significant three-band CD response, with corresponding CD peak values ​​of 0.944, 0.829, and 0.876, respectively.

[0051] 2. When vanadium dioxide is in the insulating phase and the chemical potential of graphene is 1.0 eV, the metasurface exhibits an absorption rate of 92% for TE waves at 4.093 THz, while the absorption rate for TM waves is only 2%. This absorption difference directly leads to a strong LD effect, thus the metasurface exhibits a significant single-band LD response, with a corresponding LD peak value of 0.9.

[0052] 3. When vanadium dioxide is in the insulating phase and the chemical potential of graphene is 1.0 eV, this metasurface exhibits polarization conversion capabilities. When TE-polarized waves are incident, the metasurface achieves efficient polarization conversion in the 1.26–1.59 THz and 2.90–3.31 THz frequency bands, with a PCR rate consistently above 80% across the entire frequency range. Specifically, the PCR rate reaches 100% at 1.44 THz and 3.1 THz, indicating that the incident TE-polarized waves are completely converted to TM-polarized waves. When LCP waves are incident, the metasurface achieves efficient polarization conversion in the 1.25–1.94 THz and 2.78–3.34 THz frequency bands, with a PCR rate consistently above 80% across the entire frequency range. Specifically, the PCR rate reaches 100% at 1.63 THz and 3.04 THz, indicating that the incident LCP waves are completely converted to RCP waves.

[0053] This invention's metasurface achieves highly efficient, multifunctional response by rationally utilizing the phase transition properties of VO2 and the tunability of graphene, solving the problems of limited functionality, single control method, and low efficiency of traditional metasurfaces. The metasurface structure is simple and easy to implement.

[0054] Example 2 This embodiment of the chiral metasurface includes 3×3 metasurface units. The number of units does not affect the overall performance. Each metasurface unit includes, from bottom to top, a metal substrate 1, a first dielectric layer 2, a graphene layer unit (graphene layer 3), a second dielectric layer 4, and a top resonant layer unit (resonant layer 5). The metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are all cuboid structures with a rectangular cross-section in the horizontal direction. The length and width of the rectangular cross-sections of the metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are correspondingly equal.

[0055] The metal substrate 1 is made of copper and has an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, length P of metal substrate 1 x It is 55µm wide and has a P-value of 100µm. y The thickness is 48µm and the thickness H1 is 2.1µm, which is much greater than the skin depth of metal in the terahertz band, ensuring that the transmittance of the metasurface is T=0.

[0056] Both dielectric layers are made of SiO2 with a relative permittivity of 3.9 and a length of P. x It is 55µm wide and has a P-value of 100µm. y The thickness of the first dielectric layer 2 is 48µm, the thickness of the second dielectric layer 4 is 3.1µm, and the thickness of the third dielectric layer 4 is 10.2µm.

[0057] Graphene layer 3 is a single layer of graphene with a thickness of H. g The diameter is 0.34 nm, the outer diameter R1 is 9.2 µm, and the inner diameter R2 is 7.2 µm.

[0058] The resonant layer unit 5 includes two U-shaped metal elements 5-1 disposed on the upper surface of the second dielectric layer 4. The two U-shaped metal elements 5-1 are centrally symmetrical about the center point of the upper surface of the second dielectric layer 4. The U-shaped metal element 5-1 includes a crossbeam 5-1-1, with a first protrusion 5-1-2 and a second protrusion 5-1-3 at both ends of the crossbeam 5-1-1, the length of the first protrusion 5-1-2 being greater than the length of the second protrusion 5-1-3; A VO2 patch 5-2 is also provided at the end of the first protrusion 5-1-2 of one of the concave metal elements 5-1; The concave-shaped metal component 5-1 is made entirely of copper, with an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, thickness H4 is 2.1µm; the length L1 of the second protrusion 5-1-3 is 8.2µm, and the width a1 is 6.2µm; the length L2 of the crossbeam 5-1-1 is 22.2µm, and the width a2 is 6.2µm; the length L3 of the first protrusion 5-1-2 is 28.2µm, and the width b1 is 5.2µm; the length L4 of the VO2 patch 5-2 is 4.2µm, and the width b2 is 5.2µm. The thickness of the VO2 patch 5-2 is the same as the thickness of the concave metal element 5-1.

[0059] When the ambient temperature is below 340K, vanadium dioxide is in the insulating phase with a conductivity of 200 S / m. When the ambient temperature is above 340K, vanadium dioxide is in the metallic phase with a conductivity of 200,000 S / m.

[0060] Example 3 This embodiment of the chiral metasurface includes 3×3 metasurface units. The number of units does not affect the overall performance. Each metasurface unit includes, from bottom to top, a metal substrate 1, a first dielectric layer 2, a graphene layer unit (graphene layer 3), a second dielectric layer 4, and a top resonant layer unit (resonant layer 5). The metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are all cuboid structures with a rectangular cross-section in the horizontal direction. The length and width of the rectangular cross-sections of the metal substrate 1, the first dielectric layer 2, and the second dielectric layer 4 are correspondingly equal.

[0061] The metal substrate 1 is made of copper and has an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, length P of metal substrate 1 x It is 58µm wide and has a P-value of 100µm. y The thickness is 51µm and the thickness H1 is 2.5µm, which is much greater than the skin depth of metal in the terahertz band, ensuring that the transmittance of the metasurface is T=0.

[0062] Both dielectric layers are made of SiO2 with a relative permittivity of 3.9 and a length of P. x It is 58µm wide and has a P-value of 100µm. y The thickness of the first dielectric layer 2 is 51µm, the thickness of the second dielectric layer 4 is 3.5µm, and the thickness of the third dielectric layer 4 is 12µm.

[0063] Graphene layer 3 is a single layer of graphene with a thickness of H. g The diameter is 0.34 nm, the outer diameter R1 is 10 µm, and the inner diameter R2 is 8 µm.

[0064] The resonant layer unit 5 includes two U-shaped metal elements 5-1 disposed on the upper surface of the second dielectric layer 4. The two U-shaped metal elements 5-1 are centrally symmetrical about the center point of the upper surface of the second dielectric layer 4. The U-shaped metal element 5-1 includes a crossbeam 5-1-1, with a first protrusion 5-1-2 and a second protrusion 5-1-3 at both ends of the crossbeam 5-1-1, the length of the first protrusion 5-1-2 being greater than the length of the second protrusion 5-1-3; A VO2 patch 5-2 is also provided at the end of the first protrusion 5-1-2 of one of the concave metal elements 5-1; The concave-shaped metal component 5-1 is made entirely of copper, with an electrical conductivity of 5.8 × 10⁻⁶. 7 S / m, thickness H4 is 2.5µm; the length L1 of the second protrusion 5-1-3 is 9µm, and the width a1 is 7µm; the length L2 of the crossbeam 5-1-1 is 23µm, and the width a2 is 7µm; the length L3 of the first protrusion 5-1-2 is 29µm, and the width b1 is 6µm; the length L4 of the VO2 patch 5-2 is 5µm, and the width b2 is 6µm. The thickness of the VO2 patch 5-2 is the same as the thickness of the concave metal element 5-1.

[0065] When the ambient temperature is below 340K, vanadium dioxide is in the insulating phase with a conductivity of 200 S / m. When the ambient temperature is above 340K, vanadium dioxide is in the metallic phase with a conductivity of 200,000 S / m.

[0066] Example 4 The preparation method of a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene specifically includes the following steps: Step 1: Preparation of metal substrate 1; Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 10 minutes to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 110℃ for 30 minutes. Step 1.2, Metal Thin Film Deposition: Copper thin films were deposited using electron beam evaporation. Step 1.3, Annealing treatment: Annealing at 300℃ for 30 min improves the crystal quality and conductivity of the copper thin film, resulting in metal substrate 1; Step 2, Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1, SiO2 thin film preparation: SiO2 thin films were deposited on a metal substrate using chemical vapor deposition; Step 2.2, Curing treatment: The first dielectric layer 2 is obtained by curing at 150℃ for 1 hour. Step 3: Preparation of graphene layer 3; Step 3 specifically involves: Step 3.1, Graphene Growth and Transfer: A single layer of graphene was grown on copper foil using chemical vapor deposition and then transferred to the surface of the first dielectric layer 2 by a wet process. Step 3.2, Graphene Patterning: Electron beam lithography was used to define a ring structure to obtain graphene layer 3.

[0067] Step 4: Deposition of the second dielectric layer 4; Step 4 is as follows: Step 4.1, SiO2 thin film preparation: SiO2 thin films were deposited on graphene layer 3 using chemical vapor deposition; Step 4.2, Curing treatment: The second dielectric layer 4 was obtained by curing at 150°C for 1 hour. Step 5: Fabrication of resonant layer unit 5.

[0068] Step 5 specifically involves: Step 5.1, Photolithographic Patterning: On the surface of the cured second dielectric layer 4, the designed concave metal element double J-shaped metal element pattern is defined using electron beam lithography. Step 5.2, Copper Thin Film Deposition: A copper film is deposited using electron beam evaporation. Step 5.3, Peeling and Shaping: The photoresist and excess copper film on it are removed using a stripping method, leaving the designed structure.

[0069] Step 5.4, Photolithography defines the VO2 region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.5, VO2 thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.6, Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by a stripping method, leaving the designed structure, to obtain the resonant layer unit 5.

[0070] Example 5 The preparation method of a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene specifically includes the following steps: Step 1: Preparation of metal substrate 1; Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 13 minutes to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 115℃ for 35 minutes. Step 1.2, Metal Thin Film Deposition: Copper thin films were deposited using electron beam evaporation. Step 1.3, Annealing treatment: Annealing at 320℃ for 35 min improves the crystal quality and conductivity of the copper thin film, resulting in metal substrate 1; Step 2, Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1, SiO2 thin film preparation: SiO2 thin films were deposited on a metal substrate using chemical vapor deposition; Step 2.2, Curing treatment: The first dielectric layer 2 was obtained by curing at 155℃ for 1.5 hours. Step 3: Preparation of graphene layer 3; Step 3 specifically involves: Step 3.1, Graphene Growth and Transfer: A single layer of graphene was grown on copper foil using chemical vapor deposition and then transferred to the surface of the first dielectric layer 2 by a wet process. Step 3.2, Graphene Patterning: Electron beam lithography was used to define a ring structure to obtain graphene layer 3.

[0071] Step 4: Deposition of the second dielectric layer 4; Step 4 is as follows: Step 4.1, SiO2 thin film preparation: SiO2 thin films were deposited on graphene layer 3 using chemical vapor deposition; Step 4.2, Curing treatment: The second dielectric layer 4 was obtained by curing at 155℃ for 1.5 hours. Step 5: Fabrication of resonant layer unit 5.

[0072] Step 5 specifically involves: Step 5.1, Photolithographic Patterning: On the surface of the cured second dielectric layer 4, the designed concave metal element double J-shaped metal element pattern is defined using electron beam lithography. Step 5.2, Copper Thin Film Deposition: A copper film is deposited using electron beam evaporation. Step 5.3, Peeling and Shaping: The photoresist and excess copper film on it are removed using a stripping method, leaving the designed structure.

[0073] Step 5.4, Photolithography defines the VO2 region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.5, VO2 thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.6, Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed using a stripping method, leaving the designed structure.

[0074] Example 6 The preparation method of a multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene specifically includes the following steps: Step 1: Preparation of metal substrate 1; Step 1 is as follows: Step 1.1, Substrate cleaning: High-purity silicon was selected as the substrate and ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 15 minutes to remove surface contaminants; after drying with nitrogen, it was dried in an oven at 120℃ for 40 minutes. Step 1.2, Metal Thin Film Deposition: Copper thin films were deposited using electron beam evaporation. Step 1.3, Annealing treatment: Annealing at 350℃ for 40 min improves the crystal quality and conductivity of the copper thin film, resulting in metal substrate 1; Step 2, Deposition of the first dielectric layer 2; Step 2 is as follows: Step 2.1, SiO2 thin film preparation: SiO2 thin films were deposited on a metal substrate using chemical vapor deposition; Step 2.2, Curing treatment: The first dielectric layer 2 was obtained by curing at 160℃ for 2 hours. Step 3: Preparation of graphene layer 3; Step 3 specifically involves: Step 3.1, Graphene Growth and Transfer: A single layer of graphene was grown on copper foil using chemical vapor deposition and then transferred to the surface of the first dielectric layer 2 by a wet process. Step 3.2, Graphene Patterning: Electron beam lithography was used to define a ring structure to obtain graphene layer 3.

[0075] Step 4: Deposition of the second dielectric layer 4; Step 4 is as follows: Step 4.1, SiO2 thin film preparation: SiO2 thin films were deposited on graphene layer 3 using chemical vapor deposition; Step 4.2, Curing treatment: The second dielectric layer 4 was obtained by curing at 160℃ for 2 hours. Step 5: Fabrication of resonant layer unit 5.

[0076] Step 5 specifically involves: Step 5.1, Photolithographic Patterning: On the surface of the cured second dielectric layer 4, the designed concave metal element double J-shaped metal element pattern is defined using electron beam lithography. Step 5.2, Copper Thin Film Deposition: A copper film is deposited using electron beam evaporation. Step 5.3, Peeling and Shaping: The photoresist and excess copper film on it are removed using a stripping method, leaving the designed structure.

[0077] Step 5.4, Photolithography defines the VO2 region: The vanadium dioxide pattern area is defined in a pre-designed location using photolithography; Step 5.5, VO2 thin film deposition: A vanadium dioxide thin film was deposited in a designated area using pulsed laser deposition. Step 5.6, Peeling and Shaping: The photoresist and excess vanadium dioxide film on it are removed by a stripping method, leaving the designed structure, to obtain the resonant layer unit 5.

Claims

1. A multifunctional terahertz chiral metasurface based on vanadium dioxide and graphene, characterized in that, The super surface is arranged by a periodic array of MxN super surface units with a multi-layer structure, and the super surface units are distributed in MxN two-dimensional distribution, wherein M and N are positive integers. The super surface unit comprises, from bottom to top, a metal substrate (1), a first dielectric layer (2), a graphene layer (3), a second dielectric layer (4) and a resonance layer unit (5).

2. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 1, wherein, The metal substrate (1), the first dielectric layer (2) and the second dielectric layer (4) are all cuboid structures with long rectangular cross sections in the horizontal direction, and the length and width of the long rectangular cross sections of the metal substrate (1), the first dielectric layer (2) and the second dielectric layer (4) correspond to each other.

3. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 2, wherein, The metal substrate (1) is made of copper with an electrical conductivity of 5.8 x 10 7 S / m, length P x 54 µm - 58 µm, width P y 47 µm - 51 µm, thickness H1 2 µm - 2.5 µm.

4. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 2, wherein, The material of the first dielectric layer (2) is SiO2, the relative dielectric constant is 3.9, the length P x is 54 µm-58 µm, the width P y is 47 µm-51 µm, and the thickness H2 is 3 µm-3.5 µm.

5. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 2, wherein, The material of the second dielectric layer (4) is SiO2, the relative dielectric constant is 3.9, the length P x is 54 µm-58 µm, the width P y is 47 µm-51 µm, and the thickness H3 is 10 µm-12 µm.

6. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 1, wherein, The graphene layer (3) is ring-shaped, and is a single layer of graphene with a thickness H. g The diameter is 0.34 nm, the outer diameter R1 is 9 µm-10 µm, and the inner diameter R2 is 7 µm-8 µm.

7. The vanadium dioxide and graphene based multifunctional terahertz chiral metasurface of claim 1, wherein, The resonance layer unit (5) comprises two concave- shaped metal elements (5-1) arranged on the upper surface of the second dielectric layer (4), and the two concave- shaped metal elements (5-1) are centrally symmetric with the center point of the upper surface of the second dielectric layer (4) as the symmetric point. The concave- shaped metal element (5-1) comprises a crossbeam (5-1-1), and the two ends of the crossbeam (5-1-1) are respectively provided with a first protrusion (5-1-2) and a second protrusion (5-1-3), and the length of the first protrusion (5-1-2) is greater than the length of the second protrusion (5-1-3). A VO2 patch (5-2) is further arranged at the end of the first protrusion (5-1-2) of one of the concave- shaped metal elements (5-1). The material of the concave-shaped metal element (5-1) is copper, and the electrical conductivity is 5.8 x 10 7 S / m, and the thickness H4 is 2 µm-2.5 µm; the length L1 of the second protrusion (5-1-3) is 8 µm-9 µm, and the width a1 is 6 µm-7 µm; the length L2 of the crossbeam (5-1-1) is 22 µm-23 µm, and the width a2 is 6 µm-7 µm; the length L3 of the first protrusion (5-1-2) is 28 µm-29 µm, and the width b1 is 5 µm-6 µm; the length L4 of the VO2 patch (5-2) is 4 µm-5 µm, and the width b2 is 5 µm-6 µm, and the thickness of the VO2 patch (5-2) is the same as the thickness of the concave-shaped metal element (5-1).

8. The method for preparing a vanadium dioxide and graphene based multifunctional terahertz chiral metasurface according to any one of claims 1-7, characterized in that, Specifically comprising the following steps: Step 1, preparation of the metal substrate (1); Step 2, deposition of the first dielectric layer (2); Step 3, preparation of the graphene layer (3); Step 4, deposition of the second dielectric layer (4); Step 5, preparation of the resonance layer unit (5).

9. The method for preparing a vanadium dioxide and graphene based multifunctional terahertz chiral metasurface according to claim 8, characterized in that, Step 1 specifically comprises: Step 1.1, substrate cleaning: High- purity silicon is selected as the substrate, and the surface contaminants are removed by ultrasonic cleaning with acetone, anhydrous ethanol and deionized water for 10- 15min; after drying with nitrogen, the substrate is dried in an oven at 110- 120℃ for 30- 40min; Step 1.2, metal film deposition: Copper thin film is deposited by electron beam evaporation method; Step 1.3, annealing treatment: Annealing at 300- 350℃ for 30- 40min to improve the crystalline quality and conductivity of the copper thin film, and obtain the metal substrate (1); Step 2 specifically comprises: Step 2.1, preparation of SiO2 thin film: SiO2 thin film is deposited on the metal substrate (1) by chemical vapor deposition; Step 2.2, curing treatment: Curing at 150- 160℃ for 1- 2h to obtain the first dielectric layer (2); Step 3 specifically comprises: Step 3.1, graphene growth and transfer: Single- layer graphene is grown on a copper foil by chemical vapor deposition, and then transferred to the surface of the first dielectric layer (2) by wet transfer; Step 3.2, graphene patterning: A circular ring structure is defined by electron beam lithography to obtain the graphene layer (3); Step 4 specifically comprises: Step 4.1, preparation of SiO2 thin film: SiO2 thin film is deposited on the graphene layer (3) by chemical vapor deposition; Step 4.2, curing treatment: Curing at 150- 160℃ for 1- 2h to obtain the second dielectric layer (4); Step 5 specifically comprises: Step 5.1, photoetching patterning: On the surface of the solidified second medium layer (4), use electron beam lithography technology to define the designed concave letter-shaped metal element pattern; Step 5.2, copper film deposition: Use electron beam evaporation to deposit a layer of copper film; Step 5.3, stripping shaping: Use stripping method to remove the photoresist and the excess copper film on it, leaving the designed structure; Step 5.4, photoetching defining VO2 area: Define the vanadium dioxide pattern area at the pre-designed position through photoetching; Step 5.5, VO2 film deposition: Use pulsed laser deposition to deposit a layer of vanadium dioxide film in the specified area; Step 5.6, stripping shaping: Use stripping method to remove the photoresist and the excess vanadium dioxide film on it, leaving the designed structure, obtaining the resonance layer unit (5).

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