Bimodal strong circular dichroism terahertz chiral metasurface of Tai Chi configuration

Abstract

The invention provides a strong circular dichroism terahertz chiral metasurface device with a split ring structure. The Taiji-shaped silver disk is characterized by comprising a gold substrate (1), a topas dielectric layer (2), a half Taiji-shaped silver disk (3), a vanadium dioxide Taiji eye (4) and a silver Taiji eye (5). Silver of the Tai Chi configuration in the structure generates strong reaction on incident circularly polarized light to form very high circular dichroism, and the circular dichroism can be changed by changing a silver Tai Chi eye and a vanadium dioxide Tai Chi eye, so that the double-peak frequency height of circular dichroism waves can be adjusted. The structure has potential application prospects in the fields of adjustable dynamic imaging and other communication.

Description

(1) Technical Field

[0001] The present invention relates to a terahertz chiral metasurface with a Tai Chi configuration and double-peak strong circular dichroism, which plays an important role in fields such as analytical chemistry, industrial pharmacy, and biological monitoring, and belongs to the field of terahertz metasurface wave absorption. (2) Background Art

[0002] Chirality refers to the unique property that an object and its mirror image cannot be completely coincident through rotation or translation operations. This property widely exists in molecules, crystals, and biological structures in nature. Circular Dichroism (CD), as the core characterization parameter of chiral systems, reflects the absorption difference of materials for left-handed circularly polarized light (LCP) and right-handed circularly polarized light (RCP). Compared with natural chiral molecules (such as proteins, amino acids, and virus molecules), artificial chiral materials can achieve a more significant CD effect due to their designable electromagnetic response characteristics, thus showing important application values in fields such as biomolecule detection, polarization-sensitive imaging, and super-resolution spectroscopy. In recent years, with the rapid development of electromagnetic metamaterials, chiral structures based on artificial metasurfaces have received extensive attention due to their precise electromagnetic wave manipulation capabilities, especially their potential in enhancing CD responses and breaking through the performance limits of natural materials. However, the existing chiral metasurface designs still face significant challenges: Firstly, most structures rely on complex unit geometries (such as multi-layer nesting, three-dimensional spirals, or asymmetric resonant rings), resulting in high processing difficulty and being difficult to fabricate on a large scale; Secondly, the problem of single-function is prominent. Once the traditional metasurface is processed, its chiral response is often fixed and cannot dynamically adapt to the requirements of multiple scenarios; Thirdly, the efficiency is limited. Some designs sacrifice energy utilization efficiency or working bandwidth while achieving high CD values. These bottlenecks severely restrict the practical applications of chiral metasurfaces in frontier fields such as real-time sensing and reconfigurable communication.

[0003] The present invention proposes a new chiral metasurface structure. In this structure, Tai Chi silver with different radii, different thicknesses, and different positions produces a strong reaction to incident circularly polarized light, forming a circular dichroism with very high double peaks. By changing the overall size of the structure or changing the size and position of the Tai Chi yin-yang eyes, the peaks of circular dichroism can be changed, or by changing the incident light angle, the height of the circular dichroism peaks can be changed, realizing the adjustment of circular dichroism. It can be flexibly adjusted according to actual needs. (3) Summary of the Invention

[0004] The present invention designs a strong circular dichroism double-peak chiral metasurface device, providing a strong circular dichroism. The circular dichroism of this structure can reach up to 0.81 at 7.70 THz and up to -0.68 at 7.86 THz.

[0005] To solve the above problems, the present invention is implemented through the following technical solutions:

[0006] The chiral tunable metasurface circular dichroism device consists of a multi-layer structure, and its main structure includes a gold substrate (1), a topas dielectric layer (2), a silver disk in the shape of half of a Tai Chi diagram (3), a vanadium dioxide Tai Chi eye (4), and a silver Tai Chi eye (5). The silver Tai Chi eye can move left and right, up and down, which can change the variation of the double peaks to achieve a strong response to circularly polarized light.

[0007] Preferably, the period P of the chiral tunable metasurface circular dichroism device is 27 μm.

[0008] Preferably, the thickness of the gold substrate is h1 = 0.3 μm, the thickness of the lower-layer topas is h2 = 8.6 μm, the thickness of the upper-layer silver Tai Chi configuration is h3 = 4 μm, and the thickness of the vanadium dioxide Tai Chi eye is h4 = 3.6 μm.

[0009] Preferably, the overall radius of the top-layer Tai Chi is R3 = 12.5 μm; the radii of the top-layer silver Tai Chi eye and the vanadium dioxide Tai Chi eye are equal, R1 = 2 μm; R3 of the top-layer structure is twice R2.

[0010] Preferably, the relative permittivity of the lower-layer topas is ε = 2.35, the conductivity of the bottom-layer gold is 4.56×10 7 S·m -1 , the conductivity of silver is 6.30×10 7 S·m -1 , and the conductivity of vanadium dioxide in the metallic state is 2×10 5 S·m -1 .

[0011] Preferably, the silver Tai Chi eye and the vanadium dioxide Tai Chi eye are centrosymmetric about the center. The moving distance a of the silver Tai Chi eye relative to the x-axis is 0 μm, and the moving distance b of the silver Tai Chi eye relative to the y-axis is 0 μm. (IV) BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a three-dimensional structural schematic diagram of a strong circular dichroism chiral tunable metasurface device.

[0013] Figure 2 is a top view of a strong circular dichroism chiral tunable metasurface device.

[0014] Figure 3 is a diagram of the left-handed and right-handed light absorption and circular dichroism of the chiral device with the top-layer Tai Chi structure being centrosymmetric, the silver Tai Chi eye a = 0, and b = 0.

[0015] Figure 4 is a diagram of the peak size of circular dichroism caused by the change of the device period p when the Tai Chi structure remains unchanged.

[0016] Figure 5 It is a graph of the peak size of circular dichroism when the overall radius R3 of the Taiji structure changes while the Taiji structure remains unchanged.

[0017] Figure 6 It is a graph of the peak size of circular dichroism when the thickness h2 of the topas dielectric layer changes while the Taiji structure remains unchanged.

[0018] Figure 7 It is a graph of the peak size of circular dichroism when the silver Taiji eye changes along the y-axis b while the Taiji disk structure remains unchanged.

[0019] Figure 8 It is a graph of the peak size of circular dichroism when the silver Taiji eye changes along the x-axis a while the Taiji disk structure remains unchanged. (V) Specific implementation manners

[0020] The present invention will be further elaborated below in conjunction with specific embodiments.

[0021] As Figure 1 、 2 shown, a dual-peak strong circular dichroism terahertz chiral metasurface device with a Taiji configuration proposed by the present invention. The device consists of a multi-layer structure, and its main structures include a gold substrate (1), a topas dielectric layer (2), a half-Taiji-shaped silver disk (3), a vanadium dioxide Taiji eye (4), and a silver Taiji eye (5).

[0022] As an example, the size of each unit structure is as follows: the lattice period P = 27 um. The thickness of the gold substrate is h1 = 0.3 um, the thickness of the lower-layer topas is h2 = 8.6 um, the thickness of the upper-layer silver Taiji configuration is h3 = 4 um, and the thickness of the vanadium dioxide Taiji eye is h4 = 3.6 um. The overall radius R3 of the top-layer Taiji is 12.5 um; the radii of the top-layer silver Taiji eye and the vanadium dioxide Taiji eye are equal, R1 = 2 um; R3 of the top-layer structure is 2 times R2. The relative dielectric constant of the lower-layer topas is ε = 2.35, the conductivity of the bottom-layer gold is 4.56×107 S·m-1, the conductivity of silver is 6.30×107 S·m-1, and the conductivity of vanadium dioxide in the metallic state is 2×105 S·m-1. The silver Taiji eye and the vanadium dioxide Taiji eye are centrosymmetric, the moving distance a of the silver Taiji eye relative to the x-axis is 0 um, and the moving distance b of the silver Taiji eye relative to the y-axis is 0 um.

[0023] Regarding the calculation of circular dichroism, it can be obtained from the formula CD = ALCP - ARCP, where ALCP and ARCP represent the absorption rates of left-handed circularly polarized light and right-handed circularly polarized light respectively. At the same time, there is the formula A(ω) = 1 - R(ω) - T(ω), where R(ω) and T(ω) represent the reflectivity and transmittance respectively. Also, since the main function of the gold substrate is to prevent the electromagnetic wave entering the structure from being transmitted, so T(ω) = 0, and thus the absorption rate formula can be simplified to A(ω) = 1 - R(ω).

[0024] The circular dichroism under the incidence of circularly polarized light in this embodiment is as Figure 3 shown, and this simulation result is calculated by the CSTMicrowaveStudio2021 software. By adjusting the position of the silver taiji eye, when maintaining the central symmetry position with a = 0 and b = 0, it can be seen that the circular dichroism can reach up to 0.81 at 7.70 THz and up to -0.68 at 7.86 THz.

Claims

1. A dual-peak strong circular dichroism terahertz chiral metasurface device with a tai chi configuration, characterized in that It includes a gold substrate (1), a topas dielectric layer (2), and a top functional structure stacked from bottom to top in sequence; the top functional structure is composed of a silver disk (3) in the shape of half of a Tai Chi, a vanadium dioxide Tai Chi eye (4) embedded in the silver disk, and a silver Tai Chi eye (5); the vanadium dioxide Tai Chi eye (4) and the silver Tai Chi eye (5) are symmetrically distributed about the center of the device, and their radii are equal; the silver Tai Chi eye (5) can be translated along the x-axis and / or y-axis directions to adjust the circular dichroism double-peak response; the thickness of the gold substrate (1) is 0.3 μm, the thickness of the topas dielectric layer (2) is 8.6 μm, the thickness of the silver disk (3) is 4 μm, the thickness of the vanadium dioxide Tai Chi eye (4) is 3.6 μm, and the device period is 27 μm.

2. The metasurface device according to claim 1, wherein In the top functional structure, the overall radius R3 of the Tai Chi silver disk is 12.5 μm, and the radii R1 of both the silver Tai Chi eye (5) and the vanadium dioxide Tai Chi eye (4) are 2 μm, and they satisfy the relationship R3 = 2R2, where R2 is the characteristic radius of the yin-yang dividing line in the Tai Chi silver disk.

3. The metasurface device according to claim 1, characterized in that, The conductivity of the gold substrate (1) is 4.56×107 S·m-1, the conductivity of the silver disk (3) and the silver Tai Chi eye (5) is 6.30×107 S·m-1, the conductivity of the vanadium dioxide Tai Chi eye (4) in the metallic state is 2×105 S·m-1, and the relative dielectric constant of the topas dielectric layer (2) is 2.

35.

4. The metasurface device according to claim 1, wherein The circular dichroism adjustment is achieved by at least one of the following methods: changing the translation amount a of the silver Tai Chi eye (5) along the x-axis and / or the translation amount b along the y-axis (0 ≤ |a|, |b| ≤ 4 μm); adjusting the size of the device period P within the range of 24 - 30 μm; changing the size of the overall radius R3 of the Tai Chi silver disk within the range of 10 - 15 μm; adjusting the parameter of the thickness h2 of the topas dielectric layer (2) within the range of 7 - 10 μm.

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