Chiral metasurface devices with tunable strong circular dichroism based on vanadium dioxide

Abstract

The present invention provides a chiral metasurface device with strong circular dichroism based on adjustable vanadium dioxide. The device is characterized in that it is composed of a gold substrate (1), a silicon dioxide dielectric layer (2), a vanadium dioxide layer (3), a silicon dioxide dielectric layer (4), a gold split ring resonator (5), and a gold three-circular arc resonator (6). Due to the interaction between the top metal structure and the dielectric layer, a strong circular dichroism is generated, and the conductivity of the vanadium dioxide can be changed by changing the temperature of the vanadium dioxide, so that the height of the circular dichroism peak can be adjusted. The present invention has the advantages of good circular dichroism effect, a peak value of up to 0.91, adjustable peak height and left and right, reversible circular dichroism, and insensitivity to the incident angle and polarization angle, etc. It can be used in the fields of optical detection and medical detection, and has a very broad application prospect.

Description

Technical Field

[0001] The present invention relates to a chiral metasurface device with adjustable strong circular dichroism based on vanadium dioxide, which can be used in the fields of optical detection and medical detection, and belongs to the field of terahertz metasurface wave absorption. Background Art

[0002] Since the concept of metamaterials was proposed, they have been widely studied by scientists in various fields due to their unique electromagnetic properties. However, due to the complex structure of metamaterials, metasurfaces as their alternatives have received increasing attention. In many studies in recent years, metasurfaces have made outstanding progress in controlling the amplitude, phase, and polarization state of electromagnetic waves. Many functions of metasurfaces, such as polarization conversion, absorption of electromagnetic waves, and circular dichroism, have developed rapidly. Among them, circular dichroism has been widely studied due to its absorption difference between left-handed and right-handed circularly polarized light. However, most of the chiral metasurfaces proposed so far have 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, efficiency, and functions should be considered comprehensively. Vanadium dioxide is a popular phase change material whose conductivity can be controlled by temperature, thereby realizing the mutual switching between the insulating state and the metallic state, and has very good applications in the terahertz band.

[0003] The present invention proposes a new chiral metasurface structure. The top layer has a split ring resonator and a three-arc resonator with a height difference, which will react strongly to the incident circularly polarized light and form a very high circular dichroism. Vanadium dioxide is added to the structure, and its adjustable conductivity is used to achieve the adjustability of the height of the circular dichroism peak. By changing the overall size of the structure, the circular dichroism peak can also be red-shifted and blue-shifted without changing the intensity, which can be flexibly adjusted according to actual needs. Summary of the invention

[0004] The present invention designs a chiral metasurface device with adjustable strong circular dichroism based on vanadium dioxide, which provides a strong circular dichroism, and the circular dichroism peak can be flexibly adjusted in height, left and right. The mirror structure of the structure can also achieve the circular dichroism opposite to the original structure. The circular dichroism of this structure can reach a maximum of 0.91 at 5.483THz.

[0005] The object of the present invention is achieved in that:

[0006] The chiral metasurface circular dichroism device is composed of a multilayer structure, wherein the main structure includes a gold substrate (1), a silicon dioxide dielectric layer (2), a vanadium dioxide layer (3), a silicon dioxide dielectric layer (4), a gold split ring resonator (5), and a gold three-circular arc resonator (6). The top layer of the gold split ring resonator and the gold three-circular arc resonator have a height difference so as to achieve a strong response to circularly polarized light.

[0007] Preferably, the period P of the chiral metasurface circular dichroism device is 9150 nm.

[0008] Preferably, the thickness of the gold substrate is h1=200 nm, the thickness of the lower silicon dioxide layer and the upper silicon dioxide layer are both h2=2900 nm, and the thickness of the middle vanadium dioxide layer is h3=100 nm.

[0009] Preferably, the thickness of the outer gold split ring resonator is h4=100nm, and the deflection angle θ1=51° relative to the positive half axis of the y-axis; the thickness of the inner gold three-arc resonator is h5=13nm, and the deflection angle θ2=12° relative to the positive half axis of the y-axis.

[0010] Preferably, the outer ring radius R1 of the gold split ring resonator is 4500nm, the inner ring radius R2 is 4300nm, and the opening width L1 is 1100nm; the gold three-arc resonator is composed of a double-open gold ring with an opening width L2=2200nm and a section of an independent ring, wherein the outer ring radius R3=3600nm of the double-open ring and the inner ring radius R4=3000nm, and the independent ring is a part of a ring with an outer ring radius R5 and an inner ring radius R6 of 8500nm and 7900nm respectively.

[0011] Preferably, the dielectric layer uses silicon dioxide material with a dielectric constant of 2.25, and the vanadium dioxide in the middle is defined by the Drude model, and its conductivity is adjustable between 200 S / m and 200000 S / m. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the three-dimensional structure of a chiral metasurface device with tunable strong circular dichroism based on vanadium dioxide.

[0013] Figure 2 This is a top-down view of a chiral metasurface device based on tunable strong circular dichroism of vanadium dioxide.

[0014] Figure 3 It is the left-right optical absorption and circular dichroism diagram of the chiral device when the conductivity of vanadium dioxide is 200S / m.

[0015] Figure 4 It is a graph showing the change in circular dichroism peak when the conductivity of vanadium dioxide is adjusted between 200 S / m and 200,000 S / m.

[0016] Figure 5 When the conductivity of vanadium dioxide is 200S / m, the overall scaling of the chiral device causes the circular dichroism peak to move left and right.

[0017] Figure 6 This is the circular dichroism diagram of the original chiral device and its mirror image device when the conductivity of vanadium dioxide is 200S / m. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with specific embodiments.

[0019] like Figure 1 , 2 As shown, the present invention proposes a chiral metasurface device with adjustable strong circular dichroism based on vanadium dioxide. The device is composed of a multilayer structure, mainly including a gold substrate (1), a silicon dioxide dielectric layer (2), a vanadium dioxide layer (3), a silicon dioxide dielectric layer (4), a gold split ring resonator (5) and a gold three-circular arc resonator (6).

[0020] As an example, the dimensions of each unit structure are as follows: the lattice period is P = 9150nm, the thickness of the gold substrate is h1 = 200nm, the thickness of the lower silicon dioxide layer and the upper silicon dioxide layer are both h2 = 2900nm, and the thickness of the middle vanadium dioxide layer is h3 = 100nm. The top layer of gold split ring resonator and gold three-arc resonator are both made of gold. The thickness of the gold split ring resonator is h4=100nm, its outer ring radius is R1=4500nm, the inner ring radius is R2=4300nm, the opening width is L1=1100nm, and the deflection angle relative to the positive half axis of the y-axis is θ1=51°; the gold three-arc resonator is composed of a double-open gold ring with an opening width of L2=2200nm and an independent ring, wherein the outer ring radius of the double-open ring is R3=3600nm, the inner ring radius is R4=3000nm, and the independent ring is a part of a ring with an outer ring radius R5 and an inner ring radius R6 of 8500nm and 7900nm respectively. The overall thickness of the gold three-arc resonator is h5=13nm, and the deflection angle relative to the positive half axis of the y-axis is θ2=12°. The dielectric constant of the silicon dioxide in the dielectric layer is 2.25, and the vanadium dioxide layer in the middle is defined by the Drude model, and its conductivity is adjustable between 200 S / m and 200,000 S / m.

[0021] Regarding circular dichroism, the formula CD = A LCP -A RCP Calculated, where A LCP , A RCP are the absorptivity of left-handed circularly polarized light and right-handed circularly polarized light, respectively, and A(ω)=1-R(ω)-T(ω), where R(ω) and T(ω) are reflectivity and transmittance, respectively. For this structure, the function of the 200nm thick gold substrate is to prevent the electromagnetic waves entering the structure from transmitting out, so T(ω)=0, so the absorptivity formula can be simplified to A(ω)=1-R(ω).

[0022] The circular dichroism of this embodiment under normal incidence of electromagnetic wave is as follows Figure 4As shown in the figure, the simulation results are calculated by CST MicrowaveStudio 2019 software. By adjusting the temperature of vanadium dioxide so that its conductivity varies between 200S / m and 200000S / m, it can be seen that the circular dichroism reaches a maximum value of 0.91 at 5.483THz and is adjustable from 0.91 to 0.3.

Claims

1. A chiral metasurface device with adjustable strong circular dichroism based on vanadium dioxide, characterized by: It is composed of a multi-layer structure, which is composed of, from bottom to top: a gold substrate (1), a silicon dioxide dielectric layer (2), a vanadium dioxide layer (3), a silicon dioxide dielectric layer (4), a gold split ring resonator (5), and a gold three-arc resonator (6). The gold split ring resonator and the gold three-arc resonator on the top layer of the system are both made of gold materials. The thickness of the gold split ring resonator is h4=100nm, its outer ring radius is R1=4500nm, the inner ring radius is R2=4300nm, the opening width is L1=1100nm, and the deflection angle relative to the positive half axis of the y-axis is θ1=51°; the gold three-arc resonator is composed of a double-open gold ring with an opening width of L2=2200nm and a section of an independent ring, wherein the outer ring radius of the double-open ring is R3=3600nm, the inner ring radius is R4=3000nm, and the independent ring is a part of a ring with an outer ring radius R5 and an inner ring radius R6 of 8500nm and 7900nm respectively. The overall thickness of the gold three-arc resonator is h5=13nm, and the deflection angle relative to the positive half axis of the y-axis is θ2=12°. This part is the key to forming strong circular dichroism; The structure composed of the gold split-ring resonator and the gold three-arc resonator on the top layer will react strongly to the incident circularly polarized light. Coupled with the lossy medium composed of the middle silicon dioxide dielectric layer, the incident left-handed circularly polarized light is dissipated in the medium and absorbed by the structure. However, 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 conductivity of the middle vanadium dioxide layer is 200S / m, the circular dichroism reaches the best, up to 0.

91.

2. The chiral metasurface device with adjustable strong circular dichroism based on vanadium dioxide according to claim 1, characterized in that: The period of the overall structure is P = 9150nm, and from bottom to top, it is a gold substrate, a lower silicon dioxide layer, a vanadium dioxide layer, and an upper silicon dioxide layer. The thickness of the gold substrate is h1 = 200nm, the thickness of the lower silicon dioxide layer and the upper silicon dioxide layer are both h2 = 2900nm, and the thickness of the middle vanadium dioxide layer is h3 = 100nm; the dielectric constant of silicon dioxide is 2.25, and vanadium dioxide is defined by the Drude model. By changing the temperature of the vanadium dioxide layer, its conductivity can be adjusted; when the conductivity reaches 200000S / m, the circular dichroism of the structure is the lowest, only 0.3, forming a high-low adjustment, and realizing the function of circular dichroism "on" or "off"; the structure can also change the size of the period, and realize the blue shift or red shift of the frequency without changing the peak intensity; the mirror structure of the structure can reverse the absorption of left-handed and right-handed circularly polarized light, and realize the circular dichroism opposite to the original structure; and the structure is insensitive to the incident angle and polarization angle, which can meet the requirements of complex real-world environments.

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