Reversible circular dichroism metasurface based on light-operated phase change material GSST and regulation and control method of reversible circular dichroism metasurface

Abstract

The invention provides a reversible circular dichroism metasurface based on a light-operated phase change material GSST and a regulation and control method of the reversible circular dichroism metasurface. The reversible circular dichroism metasurface comprises a plurality of unit structures which are periodically arrayed along an XOY plane, each unit structure comprises a gold substrate layer, a silicon dioxide dielectric layer and a composite functional material layer which are sequentially stacked from bottom to top in the Z-axis direction; the composite functional material layer comprises a gold material rectangular strip and four GSST material rectangular strips; the gold material rectangular strip is arranged in the middle of the upper surface of the silicon dioxide dielectric layer, and the length direction is parallel to the Y axis; the length directions of the four GSST material rectangular strips are parallel to the X axis, and the four GSST material rectangular strips are perpendicularly connected to the two sides of the two ends of the gold material rectangular strip correspondingly, so that the overall shape of the composite function material layer is of an I-shaped symmetrical structure. Reversible circular dichroism regulation and control are realized, and the circular dichroism regulation and control device has the advantages of simple structure, high response speed and repeatability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electromagnetic metamaterials, and particularly relates to a reversible circular dichroism metasurface based on light-controlled phase change material GSST and a regulation method thereof. BACKGROUND

[0002] Metamaterials are artificial composite materials or structures with super-normal macroscopic physical properties, the properties of which are determined by the geometric configuration of sub-wavelength artificial structures. By changing the material and customizing the geometric size of the structure, the effective permittivity and permeability of the metamaterial can be adjusted, and the ability to control the amplitude, phase and polarization of electromagnetic waves in the sub-wavelength size range can be achieved. Metasurfaces are a two-dimensional form of metamaterials, which have greater advantages in realizing compact optical devices and reducing optical loss. Metasurface technology plays an important role in the field of optics. By using metasurface design methods to replace traditional optical design, new functions that cannot be achieved by traditional optics can be achieved.

[0003] Dynamic polarization regulation technology has urgent application needs in the fields of optical information communication, sensing and detection, and spectral detection. In order to realize dynamic polarization regulation, the existing technology proposes a variety of reconfigurable circular dichroism metasurfaces based on external force stretching, temperature-controlled phase change materials, and electrically controlled two-dimensional materials. Among them, the control method of external force stretching is difficult to operate and is only suitable for structures of larger size, so its working wavelength range is limited to a longer wavelength range; and the electrical control characteristics of graphene based on intraband and interband transitions are limited to longer wavelength ranges such as mid-infrared and terahertz. Therefore, there are relatively few reconfigurable metasurface control methods that can be applied to visible light and near-infrared wavelength ranges.

[0004] Unlike the control methods of external force stretching and electrically controlled graphene, reconfigurable metasurfaces based on phase change materials (VO2, GST) can be applied to a larger wavelength range from visible light to terahertz. Among them, GST (Ge2Sb2Te5) has attracted widespread attention due to its fast response, good stability, and significant refractive index contrast between amorphous and crystalline states. However, GST has significant loss in the amorphous state, which leads to the problem of a large imaginary part when it is applied to the circular dichroism regulation of metasurfaces, making it difficult to form high circular dichroism.

[0005] In addition, once the existing reconfigurable circular dichroism metasurface is designed, it can only achieve polarization selection for one type of circularly polarized light, and the regulation of circular dichroism is not reversible. Therefore, further improvement and perfection are needed. SUMMARY

[0006] The purpose of this invention is to address the problems existing in the prior art by providing a reversible circular dichroism metasurface based on the optically controlled phase change material GSST and its control method. It has reversible circular dichroism and can switch its working mode through a simple control method to achieve polarization selection of left-handed and right-handed circularly polarized light respectively.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A reversible circular dichroic metasurface based on the light-controlled phase change material GSST includes several unit structures arranged in a periodic array along the XOY plane. Each unit structure includes a gold substrate layer, a silicon dioxide dielectric layer and a composite functional material layer stacked sequentially from bottom to top along the Z-axis. The composite functional material layer includes one gold material rectangular strip and four GSST material rectangular strips; the gold material rectangular strip is disposed in the middle of the upper surface of the silicon dioxide dielectric layer, and its length direction is parallel to the Y-axis; the length direction of the four GSST material rectangular strips is parallel to the X-axis, and the four GSST material rectangular strips are respectively perpendicularly connected to the two sides of the gold material rectangular strip, so that the overall shape of the composite functional material layer is an "I" symmetrical structure. The four GSST material rectangular strips are designated as a first GSST material rectangular strip, a second GSST material rectangular strip, a third GSST material rectangular strip, and a fourth GSST material rectangular strip. The positive X-axis end of the first GSST material rectangular strip is perpendicularly connected to the negative X-axis side of the positive Y-axis end of the gold material rectangular strip. The negative X-axis end of the second GSST material rectangular strip is perpendicularly connected to the positive X-axis side of the positive Y-axis end of the gold material rectangular strip. The positive X-axis end of the third GSST material rectangular strip is perpendicularly connected to the negative X-axis side of the negative Y-axis end of the gold material rectangular strip. The negative X-axis end of the fourth GSST material rectangular strip is perpendicularly connected to the positive X-axis side of the negative Y-axis end of the gold material rectangular strip.

[0008] Furthermore, the length of each unit structure is L1 = 2340 nm, and the width is W1 = 1660 nm.

[0009] Furthermore, the thickness of the gold substrate layer is H1=100nm, the thickness of the silicon dioxide dielectric layer is H2=1220nm, and the thickness of the gold material rectangular strips and the GSST material rectangular strips in the composite functional material layer is H3=253nm.

[0010] Furthermore, the length of the gold material rectangular strip is L2=1210nm and the width is W2=390nm; the length of the GSST material rectangular strip is L3=560nm and the width is W3=325nm.

[0011] Further, the dielectric constant of the silicon dioxide medium layer is 2.07, and the dielectric constant of the GSST material rectangular strip is defined by the Lorentz model.

[0012] The circular dichroism control method of the reversible circular dichroism metasurface based on the light-controlled phase change material GSST includes: The GSST material rectangular strip is controlled to convert between the crystalline state and the amorphous state by applying pump laser beams with different energy densities to the GSST material rectangular strip. The chiral structure is formed in the composite functional material layer by adjusting the phase states of the four GSST material rectangular strips in each unit structure, thereby realizing positive control or reverse control of circular dichroism. When the reverse control of circular dichroism is performed, the first GSST material rectangular strip and the fourth GSST material rectangular strip are converted to the crystalline state, and the second GSST material rectangular strip and the third GSST material rectangular strip are converted to the amorphous state by the pump laser beam, so that the composite functional material layer in the unit structure forms a first chiral structure. When the positive control of circular dichroism is performed, the first GSST material rectangular strip and the fourth GSST material rectangular strip are converted to the amorphous state, and the second GSST material rectangular strip and the third GSST material rectangular strip are converted to the crystalline state by the pump laser beam, so that the composite functional material layer in the unit structure forms a second chiral structure which is mirror-symmetric to the first chiral structure.

[0013] Further, the method of controlling the GSST material rectangular strip to convert between the crystalline state and the amorphous state by applying pump laser beams with different energy densities to the GSST material rectangular strip includes: The GSST material rectangular strip is converted from the amorphous state to the crystalline state by applying a single-pulse pump laser beam with an energy density of 30-32 mJ / cm² to the GSST material rectangular strip. The GSST material rectangular strip is converted from the crystalline state to the amorphous state by applying a multi-pulse pump laser beam with an energy density of 50-52 mJ / cm² to the GSST material rectangular strip.

[0014] Further, the method of applying pump laser beams to the GSST material rectangular strip is: A pump laser dot array is generated using a dot laser and projected onto the composite functional material layer of the reversible circular dichroism metasurface; the array distribution of each pump laser beam in the pump laser dot array corresponds to the array distribution of the first GSST material rectangular strip and the fourth GSST material rectangular strip in the composite functional material layer. When phase transformation is performed on the first GSST material rectangular strip and the fourth GSST material rectangular strip, the pump laser point array is moved to the first GSST material rectangular strip and the fourth GSST material rectangular strip, so that each first GSST material rectangular strip and each fourth GSST material rectangular strip is projected with a pump laser beam to synchronously change the phase state of the first GSST material rectangular strip and the fourth GSST material rectangular strip; When phase transformation is performed on the second GSST material rectangular strip and the third GSST material rectangular strip, the pump laser point array is translated to the second GSST material rectangular strip and the third GSST material rectangular strip, so that each second GSST material rectangular strip and each third GSST material rectangular strip is projected with a pump laser beam to synchronously change the phase state of the second GSST material rectangular strip and the third GSST material rectangular strip.

[0015] Further, the point array laser is connected with a spatial light modulator, and the spatial light modulator is used for modulating the energy density of the pump laser beam output by the point array laser; When it is needed to transform the GSST material rectangular strip from an amorphous state to a crystalline state, the point array laser outputs, after modulation by the spatial light modulator, a plurality of laser pulses with an energy density of 31 mJ / cm², a wavelength of 800 nm and a pulse width of 50 fs as the pump laser beam; When it is needed to transform the GSST material rectangular strip from a crystalline state to an amorphous state, the point array laser outputs, after modulation by the spatial light modulator, a single laser pulse with an energy density of 51 mJ / cm², a wavelength of 800 nm and a pulse width of 50 fs as the pump laser beam.

[0016] The reversible circular dichroism metasurface based on the light-controlled phase change material GSST and the control method thereof have the advantages of simple structure, fast response speed and repeatability. By changing the phase state of the GSST material rectangular strip at a specific position by using a laser beam, the present application can realize polarization selection of left-handed circularly polarized light and right-handed circularly polarized light in different working modes, and realize efficient reversible circular dichroism control characteristics. The control method has the advantages of fast phase change speed, non-volatility and repeatability, and provides a simple and reliable scheme for the design of multifunctional dynamic polarization control metasurface devices in the near-infrared band. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the overall structure schematic diagram of a unit structure in the reversible circular dichroism metasurface based on the light-controlled phase change material GSST provided by the embodiment of the present application.

[0018] Figure 2 is the top view of a unit structure in the reversible circular dichroism metasurface based on the light-controlled phase change material GSST provided by the embodiment of the present application.

[0019] Figure 3 This is a schematic diagram of the process of circular dichroism modulation using a pumped laser array in an embodiment of the present invention.

[0020] Figure 4 This is a comparison chart of left and right optical rotation absorptivity in the RCP selection mode of this invention embodiment.

[0021] Figure 5 This is a comparison chart of left and right rotational absorptivity in LCP selection mode according to an embodiment of the present invention.

[0022] Figure 6 This is a simulation result of the circular dichroism spectrum according to an embodiment of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1 and Figure 2 As shown, the present invention provides a reversible circular dichroic metasurface based on the light-controlled phase change material GSST, comprising several unit structures arranged in a periodic array along the XOY plane. Each unit structure comprises a gold substrate layer 1, a silicon dioxide dielectric layer 2, and a composite functional material layer stacked sequentially from bottom to top along the Z-axis. The composite functional material layer includes a gold material rectangular strip 3 and four GSST material rectangular strips 4; the gold material rectangular strip 3 is disposed in the middle of the upper surface of the silicon dioxide dielectric layer 2, and its length direction is parallel to the Y-axis; the length directions of the four GSST material rectangular strips 4 are all parallel to the X-axis, and the four GSST material rectangular strips 4 are respectively perpendicularly connected to the two sides of the two ends of the gold material rectangular strip 3, so that the overall shape of the composite functional material layer is an "I" shaped symmetrical structure.

[0025] Specifically, in combination Figure 2 As shown, the four GSST material rectangular strips 4 are respectively the first GSST material rectangular strip 41, the second GSST material rectangular strip 42, the third GSST material rectangular strip 43, and the fourth GSST material rectangular strip 44. The positive X-axis end of the first GSST material rectangular strip 41 is perpendicularly connected to the negative X-axis side of the positive Y-axis end of the gold material rectangular strip 3. The negative X-axis end of the second GSST material rectangular strip 42 is perpendicularly connected to the positive X-axis side of the positive Y-axis end of the gold material rectangular strip 3. The positive X-axis end of the third GSST material rectangular strip 43 is perpendicularly connected to the negative X-axis side of the negative Y-axis end of the gold material rectangular strip 3. The negative X-axis end of the fourth GSST material rectangular strip 44 is perpendicularly connected to the positive X-axis side of the negative Y-axis end of the gold material rectangular strip 3.

[0026] Further, in this embodiment of the invention, each unit structure has a length L1 = 2340 nm and a width W1 = 1660 nm. The dimensions of each part in the unit structure are designed as follows: the thickness of the gold substrate layer 1 is H1 = 100 nm, the thickness of the silicon dioxide dielectric layer 2 is H2 = 1220 nm, and the thickness of the gold material rectangular strip 3 and the GSST material rectangular strip 4 in the composite functional material layer is H3 = 253 nm. The length of the gold material rectangular strip 3 is L2 = 1210 nm and the width is W2 = 390 nm; the length of the GSST material rectangular strip 4 is L3 = 560 nm and the width is W3 = 325 nm. The dielectric constant of the silicon dioxide dielectric layer 2 is 2.07, and the dielectric constant of the GSST material rectangular strip 4 is defined by the Lorentz model.

[0027] GSST (Ge₂Sb₂Se₄Te₁) material is obtained by doping Ge₂Sb₂Se₄Te₁ with Se. Compared to Ge₂Sb₂Se₄Te₁, GSST exhibits ultra-low loss in its amorphous state and possesses characteristics such as fast phase transition response and high uniformity of phase transition over small areas. Utilizing the high energy density of laser pulses, GSST material can be rapidly heated in a short time, thereby achieving its phase transition. Furthermore, by applying laser pulses of different energy densities, GSST material can freely transform between crystalline and amorphous states.

[0028] Based on the above characteristics, this invention applies a laser beam to the asymmetric region of the "I"-shaped symmetric structure of the composite functional material layer, specifically inducing a phase transition in the GSST material rectangular strips 4 at specific locations, thereby altering the optical properties of the reversible circular dichroism metasurface. Specifically, the four GSST material rectangular strips 4 in the "I"-shaped symmetric structure are divided into two groups: the first GSST material rectangular strip 41 and the fourth GSST material rectangular strip 44 form one group, while the second GSST material rectangular strip 42 and the third GSST material rectangular strip 43 form the other group. By setting these two groups of GSST material rectangular strips 4 to opposite phase states, two mirror-symmetric chiral structures can be generated. These two chiral structures have opposite polarization selectivity, enabling the reversible circular dichroism metasurface of this invention to achieve highly efficient and reversible circular dichroism control.

[0029] Regarding the reversible circular dichroism metasurface based on the light-controlled phase change material GSST described above, this invention also provides a method for controlling circular dichroism, including: By applying pump laser beams of different energy densities to rectangular strips of GSST material, the transformation between crystalline and amorphous states of the rectangular strips of GSST material can be controlled. By adjusting the phase state of the four GSST material rectangular strips in each unit structure, a chiral structure is formed in the composite functional material layer, thereby achieving positive or negative control of circular dichroism. When the reverse regulation of circular dichroism is performed, the first GSST material rectangular strip and the fourth GSST material rectangular strip are converted into a crystal state by the pump laser beam, and the second GSST material rectangular strip and the third GSST material rectangular strip are converted into an amorphous state, so that the composite functional material layer in the unit structure forms a first chiral structure; When the forward regulation of circular dichroism is performed, the first GSST material rectangular strip and the fourth GSST material rectangular strip are converted into an amorphous state by the pump laser beam, and the second GSST material rectangular strip and the third GSST material rectangular strip are converted into a crystal state, so that the composite functional material layer in the unit structure forms a second chiral structure which is mirror-symmetric to the first chiral structure.

[0030] Specifically, the method for controlling the conversion of the GSST material rectangular strip between the crystal state and the amorphous state by applying the pump laser beam with different energy densities to the GSST material rectangular strip specifically includes: The GSST material rectangular strip is converted from the amorphous state to the crystal state by applying a single-pulse pump laser beam with an energy density of 30-32 mJ / cm2 to the GSST material rectangular strip, and the GSST material rectangular strip is converted from the crystal state to the amorphous state by applying a multi-pulse pump laser beam with an energy density of 50-52 mJ / cm2 to the GSST material rectangular strip.

[0031] Experiments show that when the amorphous GSST material is irradiated by a multi-laser pulse with an energy density of 31 mJ / cm2, a wavelength of 800 nm and a pulse width of 50 fs, the amorphous GSST material can be converted into a crystal state after its temperature exceeds the crystallization temperature; and when the crystal GSST material is irradiated by a single laser pulse with an energy density of 51 mJ / cm2, a wavelength of 800 nm and a pulse width of 50 fs, the crystal GSST material liquefies after its temperature exceeds the melting point, and then is converted into an amorphous state after rapid cooling. It should be noted that the specific parameters of the pump laser beam provided above are only preferred parameters obtained through experiments, and are not used to limit the protection scope of the present application. The key of the present application is to change the phase state of the GSST material rectangular strip 4 at different positions by the laser beam, so as to change the polarization selectivity of the reversible circular dichroism super surface, and realize the forward and reverse regulation of circular dichroism. Therefore, other laser characteristic parameters capable of realizing the phase state conversion of the GSST material should be included in the protection scope of the present application.

[0032] Further, the present application adopts the following method to apply the pump laser beam to the GSST material rectangular strip: The dot array laser is used to generate a pump laser dot array which is projected onto the composite functional material layer of the reversible circular dichroism super surface; the dot array laser is connected with a spatial light modulator which is used to modulate the energy density of the pump laser beam output by the dot array laser; When it is necessary to transform the rectangular strip of GSST material from an amorphous state to a crystalline state, the array laser is modulated by a spatial light modulator and outputs multiple laser pulses with an energy density of 31 mJ / cm², a wavelength of 800 nm, and a pulse width of 50 fs as the pump laser beam. When it is necessary to transform the rectangular strips of GSST material from a crystalline state to an amorphous state, the array laser is modulated by a spatial light modulator to output a single laser pulse with an energy density of 51 mJ / cm², a wavelength of 800 nm, and a pulse width of 50 fs as the pump laser beam.

[0033] like Figure 3 As shown in (a), the array distribution of each pump laser beam in the pump laser array corresponds to the array distribution of the first and fourth GSST material rectangular strips in the composite functional material layer. By translating the pump laser array along the X-axis, the irradiation area of ​​each pump laser beam in the pump laser array can be adjusted.

[0034] Specifically, when performing phase transformation on the first and fourth GSST material rectangular strips, the pump laser array is moved onto the first and fourth GSST material rectangular strips, so that a pump laser beam is projected onto each of the first and fourth GSST material rectangular strips to synchronously change the phase state of the first and fourth GSST material rectangular strips.

[0035] When performing phase transformation on the second and third GSST material rectangular strips, the pump laser array is translated onto the second and third GSST material rectangular strips, so that a pump laser beam is projected onto each of the second and third GSST material rectangular strips, thereby synchronously changing the phase state of the second and third GSST material rectangular strips.

[0036] like Figure 3 As shown in (b), when the first GSST material rectangular strip 41 and the fourth GSST material rectangular strip 44 are crystalline, and the second GSST material rectangular strip 42 and the third GSST material rectangular strip 43 are amorphous, the reversible circular dichroism metasurface operates in the RCP (right-hand circularly polarized light) selection mode, obtains the selective absorption capability of right-hand circularly polarized light, and realizes the reverse control of circular dichroism.

[0037] like Figure 3As shown in (c) in the figure, when the first GSST material rectangular strip 41 and the fourth GSST material rectangular strip 44 are in an amorphous state, and the second GSST material rectangular strip 42 and the third GSST material rectangular strip 43 are in a crystalline state, the reversible circular dichroism metasurface works in an LCP (left circularly polarized light) selection mode, obtains selective absorption capability for left circularly polarized light, and realizes positive regulation of circular dichroism.

[0038] Regarding circular dichroism of the metasurface, the circular dichroism can be calculated by the formula CD = A LCP -A RCP , wherein A LCP is an absorption rate of left circularly polarized light, and A RCP is an absorption rate of right circularly polarized light. At the same time, the absorption rate A = 1-R-T, wherein R is reflectivity and T is transmittance. For the reversible circular dichroism metasurface of the embodiment of the present application, the function of the gold substrate layer with a thickness of 100 nm is to prevent electromagnetic waves from being transmitted into the structure, so T = 0 of the embodiment of the present application, and the absorption rate formula can be simplified as A = 1-R.

[0039] Figure 4 is a left-right circular light absorption rate comparison diagram of the embodiment of the present application in the RCP selection mode, Figure 5 is a left-right circular light absorption rate comparison diagram of the embodiment of the present application in the LCP selection mode, Figure 6 is a circular dichroism spectrum simulation result diagram of the embodiment of the present application under electromagnetic wave normal incidence. The above simulation results are calculated by the CST Microwave Studio 2019 software. In combination with Figure 4 and Figure 6 , in the RCP selection mode, the absorption rate of the embodiment of the present application to the right circularly polarized light with a wavelength of 1642 nm is close to 1, and the absorption rate of the left circularly polarized light with a wavelength of 1642 nm is about 0.19, the circular dichroism of the metasurface reaches a minimum negative value of -0.81, and the reverse regulation of circular dichroism is realized. In combination with Figure 5 and Figure 6 , in the LCP selection mode, the absorption rate of the embodiment of the present application to the left circularly polarized light with a wavelength of 1642 nm is close to 1, and the absorption rate of the right circularly polarized light with a wavelength of 1642 nm is about 0.19, the circular dichroism of the metasurface reaches a maximum positive value of 0.81, and the positive regulation of circular dichroism is realized. As can be seen, by using a laser beam to change the phase state of the GSST material rectangular strip at a specific position, the embodiment of the present application can freely select left circularly polarized light (LCP) or right circularly polarized light (RCP), realize reversible circular dichroism from -0.81 to +0.81, and realize efficient reversible circular dichroism regulation characteristics from negative to positive.

[0040] In conclusion, the reversible circular dichroism metasurface based on light-controlled phase change material GSST and the regulation method thereof have the advantages of simple structure, fast response speed and repeatability. By changing the phase state of the GSST material rectangular strip at a specific position by using a laser beam, the present application can realize polarization selection of left-handed circularly polarized light and right-handed circularly polarized light in different working modes, and realize the high-efficiency reversible circular dichroism regulation characteristics. The regulation method has the advantages of fast phase change speed, non-volatility and repeatability, and provides a simple and reliable scheme for the design of multifunctional dynamic polarization regulation metasurface devices in the near-infrared band.

[0041] The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A reversible circular dichroic metasurface based on the light-controlled phase change material GSST, characterized in that, It includes several unit structures arranged in a periodic array along the XOY plane. Each unit structure includes a gold substrate layer, a silicon dioxide dielectric layer and a composite functional material layer stacked sequentially from bottom to top along the Z-axis. The composite functional material layer includes a gold material rectangular strip and four GSST material rectangular strips; the gold material rectangular strip is disposed in the middle of the upper surface of the silicon dioxide dielectric layer, and its length direction is parallel to the Y-axis; the length direction of the four GSST material rectangular strips is parallel to the X-axis, and the four GSST material rectangular strips are respectively perpendicularly connected to the two sides of the gold material rectangular strip, so that the overall shape of the composite functional material layer is an "I" shaped symmetrical structure. The four GSST material rectangular strips are designated as a first GSST material rectangular strip, a second GSST material rectangular strip, a third GSST material rectangular strip, and a fourth GSST material rectangular strip. The positive X-axis end of the first GSST material rectangular strip is perpendicularly connected to the negative X-axis side of the positive Y-axis end of the gold material rectangular strip. The negative X-axis end of the second GSST material rectangular strip is perpendicularly connected to the positive X-axis side of the positive Y-axis end of the gold material rectangular strip. The positive X-axis end of the third GSST material rectangular strip is perpendicularly connected to the negative X-axis side of the negative Y-axis end of the gold material rectangular strip. The negative X-axis end of the fourth GSST material rectangular strip is perpendicularly connected to the positive X-axis side of the negative Y-axis end of the gold material rectangular strip.

2. The reversible circular dichroic metasurface based on the light-controlled phase change material GSST according to claim 1, characterized in that, Each unit structure has a length L1 = 2340 nm and a width W1 = 1660 nm.

3. The reversible circular dichroic metasurface based on the light-controlled phase change material GSST according to claim 2, characterized in that, The thickness of the gold substrate layer is H1=100nm, the thickness of the silicon dioxide dielectric layer is H2=1220nm, and the thickness of the gold material rectangular strips and the GSST material rectangular strips in the composite functional material layer is H3=253nm.

4. The reversible circular dichroic metasurface based on the light-controlled phase change material GSST according to claim 3, characterized in that, The length of the gold material rectangular strip is L2=1210nm and the width is W2=390nm; the length of the GSST material rectangular strip is L3=560nm and the width is W3=325nm.

5. The reversible circular dichroic metasurface based on the light-controlled phase change material GSST according to claim 4, characterized in that, The dielectric constant of the silicon dioxide dielectric layer is 2.07, and the dielectric constant of the rectangular strips of GSST material is defined by the Lorentz model.

6. A method for controlling the circular dichroism of a reversible circular dichroism metasurface based on photocontrolled phase change material GSST as described in any one of claims 1 to 5, characterized in that, include: By applying pump laser beams of different energy densities to rectangular strips of GSST material, the transformation between crystalline and amorphous states of the rectangular strips of GSST material can be controlled. By adjusting the phase state of the four GSST material rectangular strips in each unit structure, a chiral structure is formed in the composite functional material layer, thereby achieving positive or negative control of circular dichroism. In the process of reverse control of circular dichroism, the first and fourth GSST material rectangular strips are converted into crystalline state by the pump laser beam, and the second and third GSST material rectangular strips are converted into amorphous state, so that the composite functional material layer in the unit structure forms a first chiral structure. During the positive modulation of circular dichroism, the first and fourth GSST material rectangular strips are converted into an amorphous state by a pump laser beam, and the second and third GSST material rectangular strips are converted into a crystalline state, so that the composite functional material layer in the unit structure forms a second chiral structure that is mirror-symmetrical to the first chiral structure.

7. The method for controlling circular dichroism according to claim 6, characterized in that, Methods for controlling the transition between crystalline and amorphous states of GSST material rectangular strips by applying pump laser beams of different energy densities include: By applying a single-pulse pump laser beam with an energy density of 30~32 mJ / cm² to rectangular strips of GSST material, the rectangular strips of GSST material are transformed from an amorphous state to a crystalline state. By applying a multi-pulse pump laser beam with an energy density of 50~52 mJ / cm² to rectangular strips of GSST material, the crystalline state of the rectangular strips can be transformed into an amorphous state.

8. The method for controlling circular dichroism according to claim 7, characterized in that, The method for applying a pump laser beam to a rectangular strip of GSST material is as follows: A pump laser array is generated using a lattice laser and projected onto a composite functional material layer of a reversible circular dichroic metasurface. The array distribution of each pump laser beam in the pump laser array corresponds to the array distribution of the first and fourth GSST material rectangular strips in the composite functional material layer. When performing phase transformation on the first GSST material rectangular strip and the fourth GSST material rectangular strip, the pump laser array is moved onto the first GSST material rectangular strip and the fourth GSST material rectangular strip, so that a pump laser beam is projected onto each of the first GSST material rectangular strip and each of the fourth GSST material rectangular strip, so as to synchronously change the phase state of the first GSST material rectangular strip and the fourth GSST material rectangular strip. When performing phase transformation on the second and third GSST material rectangular strips, the pump laser array is translated onto the second and third GSST material rectangular strips, so that a pump laser beam is projected onto each of the second and third GSST material rectangular strips, thereby synchronously changing the phase state of the second and third GSST material rectangular strips.

9. The method for controlling circular dichroism according to claim 8, characterized in that, The array laser is connected to a spatial light modulator, which is used to modulate the energy density of the pump laser beam output by the array laser. When it is necessary to transform the rectangular strip of GSST material from an amorphous state to a crystalline state, the array laser is modulated by a spatial light modulator and outputs multiple laser pulses with an energy density of 31 mJ / cm², a wavelength of 800 nm, and a pulse width of 50 fs as the pump laser beam. When it is necessary to transform the rectangular strips of GSST material from a crystalline state to an amorphous state, the array laser is modulated by a spatial light modulator to output a single laser pulse with an energy density of 51 mJ / cm², a wavelength of 800 nm, and a pulse width of 50 fs as the pump laser beam.

Images