Circular dichroism metasurface device based on catenary structure and design method

Abstract

The invention relates to the technical field of super-structure surfaces, and provides a catenary structure-based circular dichroism super-structure surface device and a design method, the catenary structure-based circular dichroism super-structure surface device comprises a bottom layer and a top layer which are sequentially stacked from bottom to top, the bottom layer is a substrate dielectric layer, and the top layer is a structure layer. The structural layer is of a structure formed by periodically arranging super units, each super unit comprises two catenary structures, and the two catenary structures in the same super unit are symmetrical about the center; wherein one catenary structure is a three-dimensional nano-column formed by stretching a plane figure of a closed area formed by translating one catenary. According to the invention, relatively good circular dichroism can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of metasurfaces, and more specifically, to a circular dichroism metasurface device based on a catenary structure and a design method thereof. Background Art

[0002] A metasurface is an artificial surface composed of subwavelength unit structures, which can flexibly modulate multiple degrees of freedom of light at the subwavelength scale, including amplitude, phase, polarization, and frequency. The dichroic response of traditional materials is usually weak, and a long optical path is required for accumulation to achieve sufficient contrast, which limits the further integration and miniaturization of such devices. The emergence of metasurfaces provides a new way to solve the above problems. Circular dichroism refers to the phenomenon that the structure has different absorption rates for left-handed circularly polarized light and right-handed circularly polarized light. This difference causes the amplitude of the circularly polarized light to change after passing through the structure, thereby generating a circular dichroism effect. Summary of the Invention

[0003] The content of the present invention is to provide a circular dichroism metasurface device based on a catenary structure and a design method thereof, which can achieve good circular dichroism and selectively absorb the transmission effect of electromagnetic waves.

[0004] A circular dichroism metasurface device based on a catenary structure according to the present invention includes a bottom layer and a top layer stacked in sequence from bottom to top. The bottom layer is a substrate dielectric layer, and the top layer is a structure layer. The structure layer is a structure composed of periodically arranged supercells. Each supercell includes two catenary structures, and the two catenary structures in the same supercell are centrosymmetric. One of the catenary structures is a three-dimensional nanocolumn formed by stretching a planar graph of a closed region formed by translating a catenary.

[0005] Preferably, the materials of the substrate dielectric layer and the structure layer are selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide.

[0006] Preferably, the thickness of the substrate dielectric layer is Z, and λ0 / 20 < Z < λ0 / 10. The structural period of the metasurface device is P. The substrate dielectric layer is a square periodic structure of P×P, and λ0 < P < 2λ0, where λ0 is the central wavelength of the incident light.

[0007] Preferably, the expression of the catenary y is:

[0008]

[0009] where the coefficient is α, and α needs to satisfy λ0 / 2 < α < λ0.

[0010] The present invention provides a design method for a circular dichroism metasurface device based on a catenary structure. It adopts a circular dichroism metasurface device based on the catenary structure as described above, and includes the following steps:

[0011] Step 1: Build a substrate dielectric layer with a centrosymmetric period of P. The material of the substrate dielectric layer is selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide;

[0012] Step 2: Make a catenary according to the catenary expression, and obtain another catenary after copying and translating the catenary. The translation distance of the catenary is A, and A satisfies λ0 / 10 < A < λ0 / 5. The two catenaries need to be truncated by a truncation coefficient D, and D satisfies λ0 / 3 < D < λ0, forming a two-dimensional catenary pattern. The two-dimensional catenary pattern is stretched by a distance of H to form a catenary nanocolumn, and H satisfies λ0 / 3 < H < λ0. The catenary nanocolumn is horizontally translated by -P / 2 - B, and B satisfies λ0 / 10 < B < λ0 / 5. At the same time, it is vertically translated by -P / 2 + C, and C satisfies λ0 / 20 < C < λ0 / 5. Copy and rotate the above catenary nanocolumn by 180° to form a centrosymmetric catenary structure. The centrosymmetric catenary structure forms a supercell, and the supercells are arranged periodically to form a catenary device.

[0013] The present invention can achieve good circular dichroism and selectively absorb the transmission effect of electromagnetic waves. The metasurface with good circular dichroism can realize functions such as polarization control, filtering, and reflection of light waves, thus promoting the miniaturization and integration of optical devices. This is of great significance for fields such as optical communication and optical information processing, which can reduce the volume and weight of devices and improve the performance and reliability of the system. Description of the Drawings

[0014] Figure 1 3D schematic diagram of the catenary structure in the embodiment;

[0015] Figure 2 Top view of the catenary structure in the embodiment;

[0016] Figure 3 [[ID=Z3]]Schematic diagram of the transmission amplitude under different circular polarization incidences in the embodiment;

[0017] Figure 4 Schematic diagram of the absorption rate under different circular polarization incidences in the embodiment. Detailed Embodiments

[0018] To further understand the content of the present invention, the present invention will be described in detail in combination with the drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention and not for limiting it.

[0019] Embodiment

[0020] This embodiment provides a circular dichroism metasurface device based on a catenary structure, which includes a bottom layer and a top layer stacked in sequence from bottom to top. The bottom layer is a substrate dielectric layer, and the top layer is a structure layer. The structure layer is a structure composed of periodically arranged supercells. Each supercell includes two catenary structures, and the two catenary structures in the same supercell are centrosymmetric. One of the catenary structures is a three-dimensional nanocolumn formed by stretching a planar graph of a closed region formed by translating a catenary line.

[0021] The materials of the substrate dielectric layer and the structure layer are selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide.

[0022] The thickness of the substrate dielectric layer is Z, and λ0 / 20 < Z < λ0 / 10. The structural period of the metasurface device is P. The substrate dielectric layer is a square periodic structure of P×P, and λ0 < P < 2λ0, where λ0 is the central wavelength of the incident light.

[0023] The expression of the catenary line y is:

[0024]

[0025] where the coefficient is α, and α needs to satisfy λ0 / 2 < α < λ0.

[0026] This embodiment provides a design method for a circular dichroism metasurface device based on a catenary structure. It uses the above-mentioned circular dichroism metasurface device based on a catenary structure and includes the following steps:

[0027] Step 1: Build a substrate dielectric layer with a centrosymmetric period of P. The material of the substrate dielectric layer is selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide;

[0028] Step 2: Create a catenary according to the catenary expression. After copying and translating the catenary, another catenary is obtained. The translation distance of the catenary is A, and A satisfies λ0 / 10 < A < λ0 / 5. The two catenaries need to be truncated by the truncation coefficient D, and D satisfies λ0 / 3 < D < λ0, forming a two-dimensional catenary graph. The two-dimensional catenary graph is stretched by a distance of height H to form a catenary nanocolumn, and H satisfies λ0 / 3 < H < λ0. The catenary nanocolumn is horizontally translated by -P / 2 - B, and B satisfies λ0 / 10 < B < λ0 / 5. At the same time, it is vertically translated by -P / 2 + C, and C satisfies λ0 / 20 < C < λ0 / 5. The above catenary nanocolumn is copied and rotated 180° to form a catenary structure with central symmetry. The catenary structure with central symmetry constitutes a supercell, and the supercells are arranged periodically to form a catenary device.

[0029] During the simulation process, the selected wavelength range is 2λ0 / 3 < λ0 < 3λ0 / 2. The unit cell is used as the boundary condition in both the X-axis and Y-axis directions, and open is used as the boundary condition in the Z-axis direction, where the azimuth angle of the electromagnetic wave The incident angle θ = 90°. This structure emits circularly polarized plane electromagnetic waves in circular polarization modes (LCP and RCP).

[0030] The following further describes the present invention in conjunction with the drawings and embodiments;

[0031] In the bandwidth range of 1.2μm - 1.39μm, when the central wavelength is λ0 = 1.29μm, the period P of the unit structure is 1.1μm, and the thickness Z of the bottom substrate dielectric layer of the designed metasurface device is 0.1μm (silicon layer in this example). In this embodiment, as Figure 2 shown, a catenary can be obtained from the catenary equation. The catenary is vertically translated by a distance of A = 0.27μm, and the coefficient of the intercepted catenary is D = 1.1μm, obtaining a closed two-dimensional catenary plane graph. As Figure 1 shown, the catenary plane structure is stretched into a three-dimensional structure with a height of H. The height H of the catenary structure is 0.7μm. Then it is horizontally translated by a distance of -P / 2 - B, where B = 0.2μm, and vertically translated by a distance of -P / 2 + C, where C = 0.1μm, forming the first catenary nanocolumn. The first catenary nanocolumn is rotated 180° around the Z-axis to obtain the second catenary nanocolumn, forming a pair of catenary structures with central symmetry, constituting a supercell, and arranging the supercells periodically to form the catenary device.

[0032] Result analysis:

[0033] As Figure 3It can be seen that through the image, when left-handed circularly polarized light (LCP) is incident, part of the left-handed circularly polarized light (LCP) of the device will be converted into right-handed circularly polarized light (RCP), with the amplitude in the range of about 0.2 - 0.7, and the average amplitude of its cross-polarization is 0.48. When the wavelength is 1.28 μm, the amplitude reaches the maximum value, which is about 0.68. When the wavelength is 1.39 μm, the amplitude reaches the minimum value, which is 0.19. When right-handed circularly polarized light (RCP) is incident, the right-handed circularly polarized light (RCP) of the device will be converted into left-handed circularly polarized light (LCP), and the amplitude is maintained in the range of 0.02 - 0.30, and the average cross-polarization amplitude is 0.17. When the wavelength is 1.22 μm, the amplitude reaches the maximum value, which is about 0.23. When the wavelength is 1.32 μm, the amplitude reaches the minimum value, which is 0.02. From the above comparison, it can be found that there is a large difference in the amplitude, indicating that the device has good circular dichroism.

[0034] As Figure 4 shown, the figure represents the absorption rates of different polarized electromagnetic waves passing through the device. The absorption rates of circularly polarized electromagnetic waves are represented by CDT R and CDT L respectively. The expression of its circular dichroism is defined as:

[0035]

[0036] In the formula: T RCP / RCP and T LCP / RCP respectively represent the co-polarization transmittances when the incident light is right-handed polarized light (RCP) and left-handed circularly polarized light (LCP). T RCP / LCP and T LCP / RCP respectively represent the cross-polarization transmittances when the incident light is right-handed circularly polarized light (RCP) and left-handed circularly polarized light (LCP).

[0037] It can be seen from the figure that when left-handed circularly polarized light (LCP) is incident, the absorption rate of the device is in the range of 10% - 70%, and its average absorption rate is about 46%. When the wavelength is 1.27 μm, the absorption rate reaches the maximum value, which is about 70%. When the wavelength is about 1.38 μm, the absorption rate reaches the minimum value, which is about 7%. When right-handed circularly polarized light (RCP) is incident, the absorption rate of the device is in the range of 2% - 25%, and its average absorption rate is about 12%. Among them, when the wavelength is 1.39 μm, the absorption rate reaches the maximum value, which is about 22%. When the wavelength is near 1.20 μm, the absorption rate reaches the minimum value, which is about 5%. The above results show that when different polarized electromagnetic waves pass through the device, the device can selectively absorb. It shows that the device has good circular dichroism.

[0038] In this embodiment, the good circular dichroism of the device under the incidence of electromagnetic waves with different polarizations is verified from two aspects of cross-polarization amplitude and absorption rate, which helps to further reveal the physical mechanism of the interaction between light and matter, and then promotes the development of fields such as optics, electromagnetics, and materials science.

[0039] The above schematically describes the present invention and its implementation manners. This description is not restrictive. What is shown in the drawings is only one of the implementation manners of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and design similar structural manners and embodiments to this technical solution without creative efforts without departing from the purpose of the present invention, they shall fall within the protection scope of the present invention.

Claims

1. A circular dichroism metasurface device based on a catenary structure, characterized in that: It includes a bottom layer and a top layer stacked from bottom to top. The bottom layer is a substrate dielectric layer, and the top layer is a structural layer; The structural layer is a structure composed of periodically arranged supercells. Each supercell includes two catenary structures, and the two catenary structures in the same supercell are centrosymmetric. One of the catenary structures is a three-dimensional nanocolumn formed by stretching a planar graph of a closed region formed by translating a catenary.

2. The circular dichroism metasurface device based on a catenary structure according to claim 1, characterized in that: The materials of the substrate dielectric layer and the structural layer are selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide.

3. The circular dichroism metasurface device based on a catenary structure according to claim 2, wherein: The thickness of the substrate dielectric layer is Z, and λ0 / 20 < Z < λ0 / 10. The structural period of the metasurface device is P. The substrate dielectric layer is a square periodic structure of P×P, and λ0 < P < 2λ0, where λ0 is the central wavelength of the incident light.

4. The circular dichroism metasurface device based on a catenary structure according to claim 3, characterized in that: The expression of the catenary y is: Among them, the coefficient is α, and α needs to satisfy λ0 / 2 < α < λ0.

5. A design method for a circular dichroism metasurface device based on a catenary structure, characterized in that: It adopts a circular dichroism metasurface device based on a catenary structure as described in any one of claims 1-4, and includes the following steps: Step 1: Build a substrate dielectric layer with a centrosymmetric period of P. The material of the substrate dielectric layer is selected from any one or two of silicon, silicon dioxide, magnesium fluoride, calcium fluoride, and aluminum oxide; Step 2: Make a catenary according to the catenary expression, copy and translate the catenary to get another catenary. The translation distance of the catenary is A, and A satisfies λ0 / 10 < A < λ0 / 5. The two catenaries need to be truncated by a truncation coefficient D, and D satisfies λ0 / 3 < D < λ0, forming a two-dimensional catenary graph; the two-dimensional catenary graph is stretched by a distance of height H to form a catenary nanocolumn, and H satisfies λ0 / 3 < H < λ0. The catenary nanocolumn is horizontally translated by -P / 2 - B, and B satisfies λ0 / 10 < B < λ0 / 5. At the same time, it is vertically translated by -P / 2 + C, and C satisfies λ0 / 20 < C < λ0 / 5. The above catenary nanocolumn is copied and rotated 180° to form a catenary structure that is centrosymmetric. The centrosymmetric catenary structure forms a supercell, and the supercells are periodically arranged to form a catenary device.

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