Vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface and use method thereof

Abstract

The invention discloses a vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface. The unit structure of the metasurface is divided into three reflecting layers; a dielectric layer; the metal layer is of an S-shaped structure and comprises a rectangle in the middle and circular arcs at the two ends, the rectangle is made of gold, and the circular arcs are made of vanadium dioxide; when vanadium dioxide is in a metal state, adjusting an opening angle alpha between the arc and the rectangle and a rotation angle theta of the metal layer around an X axis, and realizing decoupling of left-handed polarized light and right-handed polarized light through combination of a PB phase and a transmission phase; when vanadium dioxide is in an insulated state, the PB phase is regulated and controlled only by rotating the angle theta, and coupling of left-handed polarized light and right-handed polarized light is achieved. Compared with other coding metasurfaces, the modulation mode is simpler, the design is more flexible, the functions are more diversified, the defect that the function of the metasurface is fixed is overcome, the coupling characteristic and the decoupling characteristic of left-handed and right-handed polarized light are integrated together, and the application prospect of a coding metasurface device is expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of coded metasurfaces, and focuses on a spin-coupling and decoupling dynamic switching metasurface based on vanadium dioxide. Through the phase change characteristics of vanadium dioxide, dynamic switching between the coupling and decoupling of the responses to left-handed polarized light and right-handed polarized light can be achieved, so as to realize the construction of a multifunctional coded metasurface device. Background Art

[0002] Metamaterials refer to artificial composite materials composed of sub-wavelength microstructural units arranged periodically or aperiodically, and have electromagnetic characteristics that many natural materials do not possess. Different electromagnetic characteristics can be obtained by designing different artificial microstructures. However, the regulation of electromagnetic waves by electromagnetic metamaterials generally requires the accumulation of phase and amplitude over a relatively long distance, which will make the size of the metamaterials larger, and then increase the processing difficulty and is not conducive to practical applications. As a two-dimensional planar structure form of metamaterials, electromagnetic metasurfaces break through the limitation of the traditional wavefront regulation method that relies on the phase and amplitude accumulation effects in the wave propagation direction. This technology realizes the precise regulation of the electromagnetic wavefront distribution by introducing discrete phase mutations or amplitude modulations on its two-dimensional plane. Compared with traditional three-dimensional metamaterials, metasurfaces significantly reduce the structural thickness. Only a single layer or a few layers of sub-wavelength structures are arranged two-dimensionally periodically or aperiodically on the cross-section in the wave transmission direction to complete complex electromagnetic regulation functions.

[0003] In 2011, the research group of Professor N. Yu and F. Capasso at Harvard University proposed a phase-gradient metasurface based on V-shaped nanostructures and innovatively proposed the generalized Snell's law. In 2014, the research group of Professor Cui Tiejun proposed the concept of coded metasurfaces, using binary digital coding units with specific phase responses to characterize metamaterials. Specifically, 1-bit coding consists of two coding states of "0" and "1", corresponding to phase responses of 0 and π respectively, and the relative phase difference between them is 180°. 2-bit coding consists of four coding states of "00", "01", "10", and "11", corresponding to phase responses of 0, 1 / 2π, π, and 3 / 2π respectively, and the relative phase difference between them is 90°. The coding states with higher bit numbers can be deduced by analogy. The higher the bit number, the higher the degree of freedom for electromagnetic wave regulation. By arranging different coding states in an array, functions such as anomalous refraction, focusing, and vortex beam generation can be realized.

[0004] At the present stage, great research progress has been made in coding metasurfaces for electromagnetic wave regulation. However, when most metasurfaces are fabricated, their structural dimensions are already fixed, which makes it difficult to dynamically regulate electromagnetic waves. In addition, most metasurfaces only focus on the decoupled state of left-handed polarized light and right-handed polarized light while ignoring the coupled state, only paying attention to one state while neglecting the other, not realizing that both states are equally important.

[0005] Vanadium dioxide, as a typical phase change material, has a phase transition temperature of T C = 68 °C. Below T C it has a structure similar to that of monoclinic crystals and is in an insulating state; above Tc, it has a rutile tetragonal phase structure, and its conductivity increases by several orders of magnitude, showing a metallic conduction state. Since the phase transition conditions of vanadium dioxide are relatively simple and can be achieved by multiple means such as electrical regulation, thermal regulation, and optical regulation. Utilizing the phase transition characteristics of vanadium dioxide, rapid switching of different functions of the metasurface can be realized. Therefore, vanadium dioxide has extremely high research value and application potential in the field of dynamic metamaterials. Summary of the Invention

[0006] The present invention designs a vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface, which can realize the dynamic switching between the coupling and decoupling of left-handed polarized light and right-handed polarized light.

[0007] To achieve the above object, the present invention is realized through the following technical solutions:

[0008] A vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface, the metasurface unit structure sequentially includes from bottom to top

[0009] A reflective layer, made of a metallic material;

[0010] A dielectric layer, made of a polymer organic material;

[0011] A metal layer, in an S-shaped structure. The S-shaped structure includes a rectangle in the middle and arc-shaped parts at both ends. The material of the rectangle is gold, and the material of the arc-shaped parts is vanadium dioxide;

[0012] When vanadium dioxide is in the metallic state, by adjusting the opening angle α between the arc-shaped part and the rectangle and the rotation angle θ of the metal layer around the X-axis, through the combination of PB phase and transmission phase, the decoupling of left-handed polarized light and right-handed polarized light is achieved;

[0013] When vanadium dioxide is in the insulating state, only the PB phase is regulated by the rotation angle θ to achieve the coupling of left-handed polarized light and right-handed polarized light.

[0014] Furthermore, the length and width of both the reflective layer and the dielectric layer are P = 10.

[0015] Further, the material of the reflective layer is gold.

[0016] Further, the material of the dielectric layer is polyimide, the dielectric constant is 3.5, and the tangent loss is 0.0027.

[0017] Further, when vanadium dioxide is in the metallic state, by adjusting the opening angle α and the rotation angle θ, there are 8-bit encodings with independent responses to left-handed polarized light and 8-bit encodings with independent responses to right-handed polarized light, and the phase difference between each encoding unit is 42° - 47°. A method of using a spin-coupling and decoupling dynamic switching metasurface based on vanadium dioxide includes the following steps:

[0018] A. Arrange the metasurface unit structures according to phase encoding to form a metasurface array of N×N units;

[0019] B. Heat vanadium dioxide to make it in the metallic state, and left-handed polarized light and right-handed polarized light are incident on the metasurface array. Since the metasurface decouples the two incident lights of left-handed polarized light and right-handed polarized light, the metasurface can achieve the superposition of two different functions;

[0020] C. Cool vanadium dioxide to make it in the insulating state, and left-handed polarized light and right-handed polarized light are incident on the metasurface array. Since the metasurface couples the two incident lights of left-handed polarized light and right-handed polarized light, the metasurface can achieve the function of exhibiting the coupling characteristics of left- and right-handed polarized light.

[0021] Preferably, when vanadium dioxide is in the metallic state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the reflected right-handed polarized light forms a focused beam with a focus at 250 mm; when 10 GHz right-handed polarized light is vertically incident on the metasurface array, the reflected left-handed polarized light forms a vortex beam, and the phase is distributed in a 720° helix, which is the characteristic of a -2 order vortex beam.

[0022] Preferably, when vanadium dioxide is in the insulating state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the reflected right-handed polarized light forms a vortex beam, and the phase is distributed in a 720° helix, which is the characteristic of a +2 order vortex beam; when 10 GHz right-handed polarized light is vertically incident on the metasurface array, the reflected left-handed polarized light forms a vortex beam, and the phase is distributed in a 720° helix, which is the characteristic of a -2 order vortex beam.

[0023] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0024] The present invention adopts the above-mentioned metasurface with dynamic switching of spin coupling and decoupling based on vanadium dioxide. Compared with other programmable metasurfaces, the method for obtaining decoupled phases in the present invention is simpler. It only needs to adjust two parameters, namely the opening angle α and the rotation angle θ, and excellent linear relationships exist between these two parameters and the phases of left-handed polarized light and right-handed polarized light. Thus, the metasurface can achieve the superposition of different functions when vanadium dioxide is in the metallic state, such as the superposition of the above-mentioned vortex beam and beam focusing. Moreover, the present invention also introduces vanadium dioxide as a switch for function switching. When vanadium dioxide is in the insulating state, left-handed polarized light and right-handed polarized light exhibit good coupling characteristics, and vortex beams with opposite topological charges are generated after passing through the metasurface.

[0025] The present invention enables the dynamic switching of the coupling and decoupling of left- and right-handed polarized light by regulating the temperature to cause the transformation of vanadium dioxide from the insulating state to the metallic state. While achieving the decoupling of left- and right-handed circularly polarized light, the coupling characteristics are retained. This is conducive to realizing the multi-functional integration of the metasurface, expanding the application prospects of coded metasurface devices, and having important practical and reference values in the field of electromagnetic regulation. Description of the Drawings

[0026] Figure 1 It is the top view of the unit structure of Embodiment 1 of the present invention.

[0027] Figure 2 It is the top view of the unit structure with the rotation angle θ of Embodiment 1 of the present invention.

[0028] Figure 3 It is the side view of the unit structure of Embodiment 1 of the present invention.

[0029] Figure 4 It is the data chart of 64 coding units of Embodiment 1 of the present invention.

[0030] Figure 5 It is the cross-polarization amplitude and co-polarization amplitude of the unit structure under the incidence of left-handed polarized light and right-handed polarized light when vanadium dioxide is in the insulating state in Embodiment 1. (a) is the incidence of left-handed polarized light; (b) is the incidence of right-handed polarized light.

[0031] Figure 6 It is the cross-polarization amplitude and co-polarization amplitude of the unit structure under the incidence of left-handed polarized light and right-handed polarized light when vanadium dioxide is in the metallic state in Embodiment 1. (a) is the incidence of left-handed polarized light; (b) is the incidence of right-handed polarized light.

[0032] Figure 7Diagram showing the variation of LCP and RCP phases with the opening angle α and the rotation angle θ when vanadium dioxide is in the insulating state in Example 1. (a) Variation of the LCP phase with the opening α; (b) Variation of the RCP phase with the opening α; (c) Variation of the LCP phase with the PB angle θ; (d) Variation of the RCP phase with the PB angle θ.

[0033] Figure 8 Diagram showing the variation of LCP and RCP phases with the opening angle α and the rotation angle θ when vanadium dioxide is in the metallic state in Example 1. (a) Variation of the LCP phase with the opening α; (b) Variation of the RCP phase with the opening α; (c) Variation of the LCP phase with the PB angle θ; (d) Variation of the RCP phase with the PB angle θ.

[0034] Figure 9 Results of the coding arrangement, two-dimensional electric field distribution, and phase distribution of the metasurface unit under the incidence of left-handed polarized light with a frequency of 10 GHz when vanadium dioxide is in the insulating state in Example 1. Among them, (a) is the coding arrangement diagram, (b) is the electric field distribution result of the vortex beam with a mode of +2, and (c) is the phase distribution result of the vortex beam with a mode of +2.

[0035] Figure 10 Results of the coding arrangement, two-dimensional electric field distribution, and phase distribution of the metasurface unit under the incidence of right-handed polarized light with a frequency of 10 GHz when vanadium dioxide is in the insulating state in Example 1. Among them, (a) is the coding arrangement diagram, (b) is the electric field distribution result of the vortex beam with a mode of -2, and (c) is the phase distribution result of the vortex beam with a mode of -2.

[0036] Figure 11 Results of the coding arrangement, normalized energy density distribution on the XOZ and XOY planes of the metasurface unit under the incidence of left-handed polarized light with a frequency of 10 GHz when vanadium dioxide is in the metallic state in Example 1. Among them, (a) is the coding arrangement diagram, (b) is the normalized energy density distribution on the XOZ plane, and (c) is the normalized energy density distribution on the XOY plane.

[0037] Figure 12 Results of the coding arrangement, two-dimensional electric field distribution, and phase distribution of the metasurface unit under the incidence of right-handed polarized light with a frequency of 10 GHz when vanadium dioxide is in the metallic state in Example 1. Among them, (a) is the coding arrangement diagram, (b) is the electric field distribution result of the vortex beam with a mode of -2, and (c) is the phase distribution result of the vortex beam with a mode of -2. Detailed implementation method

[0038] Example 1

[0039] Such as Figures 1 to 3As shown, the programmable metasurface provided in Embodiment 1 has a unit structure including a bottom reflection layer, a dielectric layer disposed on the reflection layer, and a metal layer on the dielectric layer. The material of the reflection layer is gold, the material of the dielectric layer is polyimide, and the metal layer is composed of two materials, gold and vanadium dioxide. The metal layer has an S-shaped structure, including a middle rectangle and arc-shaped portions at both ends of the rectangle. The material of the rectangle is gold, and the material of the arc-shaped portions is vanadium dioxide.

[0040] The length of the rectangle in the metal layer is 2r = 9.2 mm, and the width w = 0.7 mm. The outer radius of the two arc-shaped portions is r = 4.6 mm, the width w = 0.7 mm, and the upper and lower circumferences have the same opening angle α. The thickness h of both the reflection layer and the metal layer is 0.015 mm. The thickness of the dielectric layer is d = 4 mm, the dielectric constant is ε = 3.5, and the tangent loss is tanδ = 0.0027. The length and width of both the reflection layer and the dielectric layer are p = 10 mm.

[0041] As Figure 4 shown, in Embodiment 1, the required coding units are obtained by changing the opening angle α of the vanadium dioxide arc-shaped portions in the metal layer and the rotation angle θ of the metal layer around the x-axis. Figure 3 The opening angle α and rotation angle θ required for 64 coding units are given.

[0042] As Figure 5 and Figure 6 shown, when vanadium dioxide is in the insulating state and the metallic state respectively, under the incidence of left-handed polarized light and right-handed polarized light, the cross-polarization amplitude and co-polarization amplitude of the unit structure. It can be seen from the figure that when vanadium dioxide is in the insulating state, the unit structure has a high cross-polarization amplitude response and a low co-polarization amplitude response to left-handed polarized light and right-handed polarized light in the range of 8 - 11 GHz; when vanadium dioxide is in the metallic state, the unit structure has a high cross-polarization amplitude response and a relatively low co-polarization amplitude response to left-handed polarized light and right-handed polarized light in the range of 8 - 10.5 GHz. The structural unit exhibits good polarization conversion characteristics.

[0043] As Figure 7 shown, when vanadium dioxide is in the insulating state, the LCP and RCP phases change with the change of the opening angle α and the rotation angle θ. At this time, when the rotation angle θ is fixed, changing the opening angle α has no effect on the LCP phase and the RCP phase. When the opening angle α is fixed, changing the rotation angle θ can produce a gradient phase response to both the LCP and RCP phases. Thus, we can obtain that when vanadium dioxide is in the insulating state, the phase modulation method is only by PB phase modulation, and at this time, LCP and RCP are coupled.

[0044] As Figure 8As shown, when vanadium dioxide is in the metallic state, the LCP and RCP phases change with the opening angle α and the rotation angle θ. At this time, when the rotation angle θ is fixed, changing the opening angle α can cause a gradient change in the LCP phase, while having almost no effect on the RCP phase. When the opening angle α is fixed, changing the rotation angle θ can generate a gradient phase response for both the LCP and RCP phases. Thus, we can obtain that when vanadium dioxide is in the metallic state, by precisely controlling the opening angle α and the rotation angle θ, that is, by combining the transmission phase and the PB phase, the decoupling of the two incident lights of left-handed polarized light and right-handed polarized light can be achieved. In summary, through the phase change characteristics of vanadium dioxide, the dynamic switching of the coupling and decoupling of left-handed polarized light and right-handed polarized light can be realized.

[0045] In this Embodiment 1, a metasurface array composed of 25×25 units is designed. The metasurface can achieve different functions when left-handed polarized light and right-handed polarized light are incident, when vanadium dioxide is in the metallic state and the insulating state.

[0046] As Figure 9 shown, when vanadium dioxide is in the insulating state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the coding sequence is as Figure 9 (a) shown, Figure 9 (b) and Figure 9 (c) are the electric field distribution results and phase distribution results obtained by near-field simulation. The reflected right-handed polarized light in the figure forms a vortex beam, and the phase shows a 720° spiral distribution, which is the characteristic of a +2 order vortex beam.

[0047] As Figure 10 shown, when vanadium dioxide is in the insulating state, when 10 GHz right-handed polarized light is vertically incident on the metasurface array, the coding sequence is as Figure 10 (a) shown, Figure 10 (b) and Figure 10 (c) are the electric field distribution results and phase distribution results obtained by near-field simulation. The reflected left-handed polarized light in the figure forms a vortex beam, and the phase shows a 720° spiral distribution, which is the characteristic of a -2 order vortex beam.

[0048] As Figure 11 shown, when vanadium dioxide is in the metallic state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the coding sequence is as Figure 11 (a) shown, Figure 11 (b) and Figure 11 (c) are the normalized energy density distributions on the XOZ and XOY planes. The reflected right-handed polarized light forms a focused beam with the focus at 250 mm.

[0049] As Figure 12As shown, when vanadium dioxide is in the metallic state, when right-handed polarized light at 10 GHz is perpendicularly incident on the metasurface array, the coding sequence is as Figure 12 (a) shown, Figure 12 (b) and Figure 12 (c) are the results of the electric field distribution and phase distribution obtained by near-field simulation. The reflected left-handed polarized light in the figure forms a vortex beam, and the phase shows a 720° spiral distribution, which is the characteristic of a -2 order vortex beam.

[0050] The biggest feature of the present invention is that by changing the conductivity of vanadium dioxide, the metasurface can achieve dynamic switching of the coupling and decoupling of left- and right-handed polarized light before and after the phase change of vanadium dioxide, and can achieve the superposition of more functions. Compared with other coding metasurfaces, the method of obtaining the decoupling phase in the present invention is simpler, the manipulation of electromagnetic waves is more free, and the material is also relatively common, with the characteristics of high efficiency and flexibility, and has certain reference value for the realization of related functions in the same field and the development of related devices.

[0051] The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent replacements or modifications made based on the present invention to solve substantially the same technical problems and achieve substantially the same technical effects are all covered by the protection scope of the present invention.

Claims

1. A vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface, characterized in that: The metasurface unit structure sequentially includes from bottom to top a reflective layer made of a metallic material; a dielectric layer made of a polymer organic material; a metal layer in an S-shaped structure, the S-shaped structure including a rectangle in the middle and arc-shaped portions at both ends, the material of the rectangle being gold and the material of the arc-shaped portions being vanadium dioxide; When the vanadium dioxide is in the metallic state, by adjusting the opening angle α between the arc-shaped portions and the rectangle and the rotation angle θ of the metal layer about the X-axis, through the combination of the PB phase and the transmission phase, the decoupling of left-handed polarized light and right-handed polarized light is achieved; When the vanadium dioxide is in the insulating state, only the PB phase is regulated by the rotation angle θ to achieve the coupling of left-handed polarized light and right-handed polarized light.

2. The spin-coupling and decoupling dynamic switching metasurface based on vanadium dioxide according to claim 1, wherein: The length and width of both the reflective layer and the dielectric layer are P = 10.

3. A vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to claim 1, characterized in that: The material of the reflective layer is gold.

4. A vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to claim 1, characterized in that: The material of the dielectric layer is polyimide, with a dielectric constant of 3.5 and a tangent loss of 0.0027.

5. A vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to claim 1, characterized in that: When the vanadium dioxide is in the metallic state, by adjusting the opening angle α and the rotation angle θ, there are 8-bit encodings with independent responses to left-handed polarized light and 8-bit encodings with independent responses to right-handed polarized light, and the phase difference between each encoding unit is 42° - 47°.

6. A method for using the vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to any one of claims 1 to 5, characterized in that, It includes the following steps: A. Arrange the unit structures of the metasurface according to phase encoding to form a metasurface array of N×N units; B. Heat the vanadium dioxide to make it in the metallic state, and left-handed polarized light and right-handed polarized light are incident on the metasurface array. Since the metasurface decouples the two incident lights of left-handed polarized light and right-handed polarized light, the metasurface can achieve the superposition of two different functions; C. Cool the vanadium dioxide to make it in the insulating state, and left-handed polarized light and right-handed polarized light are incident on the metasurface array. Since the metasurface couples the two incident lights of left-handed polarized light and right-handed polarized light, the metasurface can achieve a function showing the coupling characteristics of left- and right-handed polarized light.

7. A method for using a vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to claim 6, characterized in that: When the vanadium dioxide is in the metallic state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the reflected right-handed polarized light forms a focused beam with a focus at 250 mm; when 10 GHz right-handed polarized light is vertically incident on the metasurface array, the reflected left-handed polarized light forms a vortex beam with a phase distributed in a 720° helix, which is the characteristic of a -2nd order vortex beam.

8. A method for using a vanadium dioxide-based spin coupling and decoupling dynamic switching metasurface according to claim 6, characterized in that: When the vanadium dioxide is in the insulating state, when 10 GHz left-handed polarized light is vertically incident on the metasurface array, the reflected right-handed polarized light forms a vortex beam with a phase distributed in a 720° helix, which is the characteristic of a +2nd order vortex beam; when 10 GHz right-handed polarized light is vertically incident on the metasurface array, the reflected left-handed polarized light forms a vortex beam with a phase distributed in a 720° helix, which is the characteristic of a -2nd order vortex beam.

Images