Strong circular dichroic chiral metasurface with four-connected split ring structure

Abstract

The invention provides a strong circular dichroic chiral metasurface with a four-connected split ring structure. The invention is characterized in that the device is composed of a gold substrate (1), a polyimide dielectric layer (2), and four semicircular gold rings (3) and an arc gold ring (4) which are the same and are connected with each other. The four split rings which are connected and have the same size in the structure generate strong reaction on incident circularly polarized light to form very high circular dichroism, and the circular dichroism can be changed by changing the size of the split rings and the thickness of the polyimide layer, so that the peak height of the circular dichroism can be adjusted; and the circular dichroism can be changed by changing the angle of the incident light, so that the circular dichroism peak height can be adjusted. The structure has potential application prospects in the fields of adjustable dynamic imaging and other communication.

Description

(I) Technical field

[0001] The present invention relates to a four-connected split ring structure strong circular dichroism chiral metasurface, which plays an important role in analytical chemistry, industrial pharmacy, biological monitoring and other fields, and belongs to the field of terahertz metasurface wave absorption. (II) Background technology

[0002] Chirality refers to the property that the mirror image structure of an object cannot be superimposed with its phase by any rotation or translation. Circular dichroism (CD) is usually used to characterize chirality, which is generally defined as the difference in the absorption of the structure to left-hand circularly polarized light (LCP) and right-hand circularly polarized light (RCP). Chirality is ubiquitous in nature, such as the interaction between the macroscopic structure of organisms and the microscopic structure of molecules and enzymes. Chirality means that its mirror image cannot be replaced by arbitrary rotation or translation operations. These two non-overlapping configurations are called chiral isomers. Although their structures are formally equivalent, such as left and right hands, they can play different roles on external physical quantities. The traditional method of distinguishing chiral structures is to distinguish their absorption / transmission spectra of interaction with circularly polarized light: the different absorption / transmission of left-hand circular polarization (LCP) and right-hand circular polarization (RCP), that is, circular dichroism (CD). It has good application prospects in analytical chemistry, industrial pharmaceuticals, biological monitoring and other fields. Compared with natural chiral molecules, artificial chiral materials have better CD, so they are widely used in the detection of chiral molecules, such as proteins, amino acids, glucose and some virus molecules. With the development of artificial electromagnetic metamaterials in recent years, many chiral metamaterial structures have been studied, and they have extremely ideal CD response characteristics, which are of great significance in the fields of sensing, imaging, and communication. However, the chiral metasurfaces proposed by people nowadays are mostly complex unit structures, and are inefficient when applied, or have a single function and cannot be adjusted. Therefore, when designing new chiral metasurface devices, multiple factors such as materials, processes, methods, and functions should be considered at the same time.

[0003] The present invention proposes a new chiral metasurface structure, in which four connected gold rings with openings react strongly to incident circularly polarized light, forming a very high circular dichroism. Changing the overall size of the structure or the relative distance of the gold rings can change the peak of the circular dichroism, and changing the angle of the incident light can also change the height of the peak of the circular dichroism, thereby achieving the adjustment of the circular dichroism. It can be flexibly adjusted according to actual needs. (III) Summary of the invention

[0004] The present invention designs a chiral metasurface device with strong circular dichroism, which provides a strong circular dichroism. The circular dichroism of the structure can reach a maximum of 0.91 at 2.97 THz.

[0005] In order to solve the above problems, the present invention is implemented by the following technical solutions:

[0006] The chiral tunable metasurface circular dichroism device is composed of a multilayer structure, the main structure of which includes a gold substrate (1), a polyimide dielectric layer (2), and four adjacent semicircular gold rings (3) and arc-shaped gold rings (4) of the same size, wherein the four top-layer gold rings have deflection angles relative to each other to achieve a strong response to circularly polarized light.

[0007] Preferably, the period P of the chiral tunable metasurface circular dichroism device is 50 um.

[0008] Preferably, the thickness of the gold substrate is h1=2um, the thickness of the lower polyimide layer is h2=9.6um, and the thickness of the upper gold ring is h3=2um.

[0009] As a preference, a coordinate system is established for a single split ring, the deflection angle of the top semicircular ring relative to the positive semi-axis of the x-axis is θ1=0°; the deflection angle of the top arc-shaped gold ring relative to the positive semi-axis of the x-axis is θ2=-5°, and the angle of the arc-shaped gold ring is θ3=145°. The distance between the four gold rings is t=0. The coordinates of the centers of the four gold rings relative to the centers O of the four gold rings are x1=10.75, y1=10.75, x2=-10.75, y2=10.75, x3=10.75, y3=-10.75, x4=-10.75, y4=-10.75.

[0010] Preferably, the radius R of the top semicircular ring and the arc gold ring is 10 um, and the width W is 1.5 um.

[0011] Preferably, the relative dielectric constant of the lower polyimide layer is ε=3.5+0.00945i, and the conductivity of the bottom gold layer is 4.56×107S·m -1 .

[0012] Preferably, the incident light is incident vertically, and the incident angle θ4=0°. (IV) Description of the drawings

[0013] Figure 1 This is a schematic diagram of the three-dimensional structure of a strong circular dichroism chirality-tunable metasurface device.

[0014] Figure 2 This is a top view of the strong circular dichroism chirality-tunable metasurface device.

[0015] Figure 3The deflection angle of the top semicircular ring relative to the positive half axis of the x-axis is θ1=0°; the deflection angle of the top arc-shaped gold ring relative to the positive half axis of the x-axis is θ2=-5°, and the angle of the arc-shaped gold ring is θ3=145°. The left-right optical rotation absorption and circular dichroism diagram of the chiral device.

[0016] Figure 4 It is a graph of the peak size of circular dichroism caused by changing the device period P.

[0017] Figure 5 This is a graph showing the peak size of circular dichroism when the thickness h2 of the lower polyimide layer is changed.

[0018] Figure 6 This is the peak size diagram of circular dichroism when the angle of incident light changes while the four gold rings remain unchanged. (V) Specific implementation methods

[0019] The present invention will be further described below in conjunction with specific embodiments.

[0020] like Figure 1 , 2 As shown, a split ring structure strong circular dichroism terahertz chiral metasurface device proposed by the present invention is composed of a multilayer structure, and its main structure includes a gold substrate (1), a polyimide dielectric layer (2), four identical and connected semicircular gold rings (3) and an arc-shaped gold ring (4).

[0021] As an embodiment, the size of each unit structure is as follows: lattice period P = 50um. The thickness of the gold substrate is h1 = 2um, the thickness of the lower polyimide is h2 = 9.6um, and the thickness of the upper gold ring is h3 = 2um. The deflection angle of the top semicircular ring relative to the positive half axis of the x-axis is θ1 = 0°; the deflection angle of the top arc-shaped gold ring relative to the positive half axis of the x-axis is θ2 = -5°, and the angle of the arc-shaped gold ring is θ3 = 145°. The radius of the top semicircular ring and the top arc-shaped gold ring is R = 10um, and the width is W = 1.5um. The distance between the four gold rings is t = 0. The coordinates of the centers of the four gold rings are x1 = 10.75, y1 = 10.75, x2 = -10.75, y2 = 10.75, x3 = 10.75, y3 = -10.75, x4 = -10.75, y4 = -10.75. The relative dielectric constant of the lower layer polyimide is ε=3.5+0.00945i, and the electrical conductivity of the bottom layer gold is 4.56×107S·m-1.

[0022] The calculation of circular dichroism can be obtained by the formula CD = ALCP-ARCP, where ALCP and ARCP represent the absorptivity of left-handed circularly polarized light and the absorptivity of 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. Since the main function of the gold substrate is to prevent the electromagnetic waves entering the structure from being transmitted, T(ω) = 0, so the absorptivity formula can be simplified to A(ω) = 1-R(ω).

[0023] The circular dichroism of this embodiment under the incident circularly polarized light is as follows Figure 3 As shown in the figure, the simulation results are calculated by CSTMicrowaveStudio2021 software. By adjusting the adjacent distance of the four gold rings, when the distance is t=0, it can be seen that the circular dichroism can reach a maximum of 0.91 at 2.97THz.

Claims

1. A four-connected split ring structure strong circular dichroism chiral metasurface. Its characteristics are: It is composed of a multi-layer structure, which includes, from bottom to top, a gold substrate (1), a polyimide dielectric layer (2), four identical and connected semicircular gold rings (3) and an arc-shaped gold ring (4). The four connected splitting rings in the system are all made of gold. The radius of the top semicircular ring and the arc-shaped gold ring is R = 10um, and the width is W = 1.5um. A coordinate axis is established with a single circular ring. The deflection angle of the top semicircular ring relative to the positive half axis of the x-axis is θ1 = 0°; the deflection angle of the top arc-shaped gold ring relative to the positive half axis of the x-axis is θ2 = -5°, and the angle of the arc-shaped gold ring is θ3 = 145°. The distance between the four gold rings is t = 0. The coordinates of the four gold ring centers relative to the center O are x1=10.75, y1=10.75, x2=-10.75, y2=10.75, x3=10.75, y3=-10.75, x4=-10.75, y4=-10.

75. The incident light is incident vertically. This part is the key to form strong circular dichroism.

2. The strong circular dichroism terahertz chiral metasurface according to claim 1, characterized in that: The period of the overall structure is P = 50um. From bottom to top, it is the gold substrate, the lower polyimide layer and the upper arc-shaped gold ring. The thickness of the gold substrate is h1 = 2um, the thickness of the lower polyimide layer is h2 = 9.6um, and the thickness of the upper gold ring is h3 = 2um. The relative dielectric constant of polyimide is ε = 3.5 + 0.00945i, and the conductivity of gold is 4.56 × 107 S·m -1 .

3. The strong circular dichroism terahertz chiral metasurface device according to claim 1, characterized in that: The structure of a semicircular gold ring and two arc-shaped gold rings on the top layer will react strongly to the incident circularly polarized light, so that the incident left-handed circularly polarized light is absorbed by the structure, while the right-handed circularly polarized light is almost unaffected and will be reflected, thus forming a huge absorption difference between left-handed and right-handed circularly polarized light; when the deflection angle of the large arc-shaped gold ring on the top layer relative to the positive half axis of the x-axis is θ2=-5°, the angle of the large arc-shaped gold ring is θ3=145°; the distance between the four gold rings of the four split rings is t=0. The circular dichroism reaches the best, up to 0.

91. By changing the size of the split ring, the size of its circular dichroism can be adjusted; and the structure is sensitive to the incident angle, and the size of the circular dichroism can be changed by changing the angle of the incident light, so that the peak value of the circular dichroism of the device can be adjusted. This work will promote the development of broadband tunable chiral optical devices.

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