A high refractive index optical metasurface sensor based on fusion bic and design method and application thereof

Abstract

The application provides a high-refractive-index optical super surface sensor based on fusion BIC and a design method and application thereof. The application realizes Q factor enhancement based on coupling of FW-BIC and SP-BIC. Here, a simple method is introduced to realize high-Q resonance in a metal structure. The structure is composed of two metal block structures, and a FW-BIC can be generated when the distance between the two metal blocks is changed. On the basis of the obtained quasi-BIC, SP-BIC is introduced by changing the symmetry of the structure. The coupling of the two kinds of BIC can realize obvious enhancement of the Q factor. Meanwhile, the resonance of the structure is sensitive to the refractive index of the environment, and the refractive index sensitivity can reach 1325GHz / RIU. Therefore, the structure can be applied to the fields of biological, gas, liquid and solid sensing detection.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical sensing and detection, and particularly relates to a high-refractive-index optical metasurface sensor based on fusion of BICs and a design method and application thereof. BACKGROUND

[0002] Metallic metasurfaces with high-quality (Q) factor resonances have important application prospects in high-sensitivity refractive index optical sensing, and thus have attracted extensive attention. Recently, the introduction of bound states in the continuum (BIC) in photonics provides a solution to obtain high-Q factor resonances. In practical applications, a very small perturbation is needed to obtain a very large Q factor. However, as the structural asymmetry parameter increases, the Q factor rapidly decreases to a very low level. Defects and other problems inevitably introduced in the processing will greatly reduce the resonance Q factor obtained by the actual sample. Therefore, new methods are needed to improve the Q factor.

[0003] A method for improving the quality factor and robustness of symmetry-protected (SP) BICs through a generalized approach was proposed by Cong et al. Unlike the conventional method of obtaining quasi-BICs by uniformly breaking the symmetry of the resonator, this method selectively breaks the symmetry of the resonator at the lattice level, thereby reducing the radiation intensity of the entire period and improving the Q factor. In addition, Liu et al. demonstrated a metasurface structure composed of two BIC-coupled all-dielectric metasurfaces. By adjusting the distance between the two metasurfaces, SP-BIC and Fabry-Perot (FP) BICs were merged into the parameter space, and this simple strategy produced a Q factor three orders of magnitude higher than those of individual BIC metasurface structures.

[0004] However, few people have studied the coupling of Friedrich-Winger (FW) BICs and SP-BICs to achieve Q factor enhancement. Here, we introduce a simple method to achieve high-Q resonances in metallic structures. The structure is composed of two metal block structures, which can produce a FW-BIC when the distance between the two metal blocks is changed. On the basis of the obtained quasi-BIC, SP-BIC is introduced by changing the symmetry of the structure. The coupling of the two types of BICs can achieve a significant enhancement of the Q factor and has high refractive sensitivity. SUMMARY

[0005] The present application overcomes the deficiencies of the prior art and proposes a high-refractive-index optical metasurface sensor based on fusion of BICs and a design method and application thereof. The coupling of FW-BICs and SP-BICs achieves a high Q factor, thereby realizing high refractive index sensitivity sensing. The problem of low sensitivity of existing sensors is solved.

[0006] The application discloses a high-refractive-index optical super surface sensor based on fused continuous domain bound state, which comprises a substrate layer and a plurality of metal microstructure units arranged on the substrate layer in a periodic manner; the metal microstructure unit comprises first metal microstructures and second metal microstructures arranged at intervals; and the first metal microstructures and the second metal microstructures are metal blocks.

[0007] The first metal microstructure is a square metal block, and the second metal microstructure is a rectangular metal block.

[0008] The metal block structure is copper, and the conductivity is 5.71*10 7 S / m.

[0009] The refractive index of the substrate layer is 1.4-1.6.

[0010] The interval between the first metal microstructure and the second metal microstructure is 14 mu m.

[0011] The application discloses a design method of a high-refractive-index optical super surface sensor based on fused BIC, which comprises the following steps:

[0012] 1) by adjusting the interval between the two metal blocks to 14 mu m, resonance with a narrow line width can be obtained;

[0013] 2) by adjusting the width of the second metal microstructure to 20 mu m, resonance with a narrower line width can be further obtained;

[0014] 3) by fusing the Friedrich-Wing continuous domain bound state and the symmetry-protected continuous domain bound state respectively through the above two steps, resonance with a quality factor of 385 is obtained, and the design of the high-refractive-index optical super surface sensor based on fused BIC is completed based on the above structure.

[0015] The application discloses a high-refractive-index optical super surface sensor based on fused BIC, which is applied to a solution, wherein a light source irradiates the asymmetric metal block structure from top to bottom, the structure is fixed on a sample holder, and a spectrometer is arranged below the structure to collect data. Different spectral information can be obtained from the spectrometer by dropping solutions with different refractive indexes on the surface of the structure, the corresponding spectrum of the solution with different refractive indexes can be known by analyzing the spectral information, and the refractive index sensitivity of the structure can be calculated according to the spectrum of the solution with different refractive indexes. When the solution with unknown refractive index is dropped, the refractive index of the unknown solution can be calculated according to the known spectral information and the refractive index sensitivity. Specifically, when the refractive index of the solution is 1.2-1.6, the refractive index sensitivity of the asymmetric metal block structure is 1325 GHz / RIU.

[0016] Further, a high refractive index optical super surface sensor based on fusion BIC, the technical scheme is: including substrate layer and metal super surface structure array on the substrate layer, the metal super surface structure unit structure is formed by 2 metal copper blocks periodic arrangement, the 2 metal copper block unit is square block structure, the second metal block structure is shortened in the x direction and forms asymmetric structure, the size in y direction is same, the electric field of light source is along y axis, excitation is along z axis, and the Q factor of enhanced BIC is obtained by adjusting the spacing of 2 metal blocks and the SP-BIC of asymmetric degree of metal block, the refractive index sensitivity of 1325GHz / RIU is realized after the fusion of 2 kinds of BIC.

[0017] The high refractive index optical sensor based on the metal super surface structure of fusion BIC, the resonance unit is composed of metal copper microstructure and PDMS flexible substrate.

[0018] Preferably, the metal material is copper, the conductivity of copper is 5.71*10 7 S / m, and the thickness is 0.2um.

[0019] Preferably, the substrate material is flexible PDMS, the refractive index is 1.4, and the thickness is 20um.

[0020] Preferably, the period unit length L of the super surface is 100um.

[0021] Preferably, the wide period unit W of the super surface is 50um.

[0022] Preferably, the side length L1 of the metal copper block is 30um.

[0023] Preferably, the side length L2 of the metal copper block is 20um.

[0024] Preferably, the spacing between the metal copper blocks is 14um.

[0025] Preferably, the material of the metal block can be gold, silver, aluminum, copper and the like.

[0026] Preferably, the thickness of the flexible PDMS is 0.2um.

[0027] Preferably, the refractive index of the flexible PDMS can be 1.4-1.6 material.

[0028] Compared with the prior art, the present application has the following beneficial effects:

[0029] Currently, high Q-factor resonant structures are mainly achieved by low asymmetry or specific structure size. The present application is based on the coupling of FW-BIC and SP-BIC to achieve Q-factor enhancement. Here, we introduce a simple method to achieve high Q resonances in metallic structures. The structure consists of two metal block structures, and a FW-BIC can be generated when the distance between the two metal blocks is changed. On the basis of the obtained quasi-BIC, SP-BIC is introduced by changing the symmetry of the structure. The coupling of the two BICs can achieve significant enhancement of the Q factor. In addition, the resonance of the structure is sensitive to the refractive index of the environment, so it can be applied to the fields of biological, gas, liquid, solid, etc. sensing and detection. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A three-dimensional structure diagram of a high refractive index optical metasurface sensor based on fusion BIC and a unit structure top view are provided for the embodiments of the present application;

[0031] Figure 2 Transmission spectra and corresponding Q factors of the metal metasurface structure with the spacing G between the metal blocks changing from 0 to 40 μm;

[0032] Figure 3 Transmission spectra and calculated Q factors under different symmetries of the metal metasurface structure with the spacing G between the metal blocks being 2 μm and 14 μm and the metal block side length L2 changing from 0 to 30 μm;

[0033] Figure 4 Multi-stage decomposition dispersion power curves of the metal metasurface structure with the spacing G between the metal blocks being 2 μm and 14 μm and the metal block side length L2 being 0 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, respectively;

[0034] Figure 5 Transmission spectra of the metal metasurface structure with the change of the refractive index of the environment;

[0035] Figure 6 Relationship diagram of the metal metasurface structure with the increase of the refractive index and the resonance peak wavelength; DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] AsFigure 1 As shown, the embodiment of the present application provides a high refractive index optical metasurface sensor based on fusion BIC. It includes a substrate layer 1, metal microstructure 2, 3, the metal microstructure 2, 3 is composed of two metal copper blocks; the metal microstructure 3 is a square with constant size; the size of the metal microstructure 2 is along the z axis, and the FW-BIC is obtained by adjusting the distance between the two metal blocks, and the SP-BIC is obtained by changing the asymmetry of the metal block 2, after the fusion of the two continuous domain bound states (BIC), the enhanced Q factor can be obtained, and the refractive index sensitivity is 1325GHz / RIU. The refractive index optical sensor is a periodic structure composed of metal microstructure 2, 3 and substrate 1. The unit structure includes two asymmetric metal block structures and a flexible substrate, the metal material is copper, the conductivity of copper is 5.71×10 7 S / m, the material thickness is 0.2μm; the substrate material is flexible polydimethylsiloxane (PDMS), the refractive index is 1.4, and the thickness is 20μm; the side length L of the unit structure is 100μm, and L is 50μm.

[0038] As Figure 2 shown, when the metal metasurface structure L1=L2=30μm, the transmission spectrum obtained by changing the distance between the two metal block structures from 0μm-40μm, the FW-BIC can be obtained when the distance is 20μm. And the Q factor obtained by changing the distance from 0μm-40μm, the closer to the BIC position, the higher the Q factor. In theory, when the distance is 20μm, the Q factor can be infinite.

[0039] As Figure 3 shown, when the distance between the metal block structures is 2μm and 14μm respectively, the transmission curve of L2 length from 0μm-30μm. L2 is 0μm and 30μm respectively, which can produce SP-BIC1 and SP-BIC2, and with the increase of G, only the resonance line width of SP-BIC2 is narrowed, and the line width of SP-BIC1 almost has no change. Because SP-BIC2 fuses FW-BIC, the line width is narrowed, and the corresponding Q factor is also obviously improved.

[0040] As Figure 4As shown in the figure, the multi-stage decomposition dispersion power curve of SP-BIC2 when the pitch of the metal block structure is 2 μm and 14 μm respectively, and the side length L2 of the metal block is 0 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm and 30 μm respectively. When L2 is 0 μm, 5 μm and 10 μm, the resonance is mainly magnetic resonance (MD); when L2 is 15 μm, 20 μm, 25 μm and 30 μm, the resonance is mainly electric resonance (ED).

[0041] As shown in the figure, the multi-stage decomposition dispersion power curve of SP-BIC2 when the pitch of the metal block structure is 2 μm and 14 μm respectively, and the side length L2 of the metal block is 0 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm and 30 μm respectively. When L2 is 0 μm, 5 μm and 10 μm, the resonance is mainly magnetic resonance (MD); when L2 is 15 μm, 20 μm, 25 μm and 30 μm, the resonance is mainly electric resonance (ED). Figure 5 As shown in the figure, the transmission spectrum of the metal super surface structure changes with the environment refractive index. With the increase of the environment refractive index, the resonance is obviously red-shifted, and this characteristic has important application in the detection of biology, gas, liquid, solid and the like.

[0042] As shown in the figure, the transmission spectrum of the metal super surface structure changes with the environment refractive index. With the increase of the environment refractive index, the resonance is obviously red-shifted, and this characteristic has important application in the detection of biology, gas, liquid, solid and the like. Figure 6 As shown in the figure, the transmission spectrum of the metal super surface structure changes with the environment refractive index. With the increase of the environment refractive index, the resonance is obviously red-shifted, and this characteristic has important application in the detection of biology, gas, liquid, solid and the like.

[0043] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high refractive index optical metasurface sensor based on fused continuous domain bound states, characterized in that, The application relates to a high-refractive-index optical super-surface sensor based on fused continuous domain bound states. The application comprises a substrate layer (1) and a plurality of metal microstructure units periodically distributed on the substrate layer (1). The metal microstructure units comprise first metal microstructures (3) and second metal microstructures (2) arranged at intervals. The first metal microstructures and the second metal microstructures are both metal blocks; the first metal microstructures are square metal blocks, and the second metal microstructures are rectangular metal blocks; the interval between the first metal microstructures and the second metal microstructures is 14 mu m; the metal block structure is copper, the side length L1 of the square metal block is 30 mu m, the side length L2 of the rectangular metal block is 0-30 mu m, and the Friedrich-Wing continuous domain bound state and the symmetry-protected continuous domain bound state are fused.

2. The fused-continuum-band bound-state based high refractive index optical metasurface sensor of claim 1, wherein, The metal block structure is copper, the electrical conductivity is 5.71 x 10 7 S / m.

3. The fused-continuum-band bound-state based high refractive index optical metasurface sensor of claim 1, wherein, The refractive index of the substrate layer is 1.4-1.

6.

4. A method of designing a high refractive index optical metasurface sensor based on fused continuous domain bound states as claimed in claim 1, wherein, The application comprises the following steps: 1) the resonance with a narrow line width is obtained by adjusting the interval between the two metal blocks to be 14 mu m; 2) the resonance with a narrower line width is further obtained by adjusting the width of the second metal microstructure to be 20 mu m; 3) the resonance with a quality factor of 385 is obtained after the Friedrich-Wing continuous domain bound state and the symmetry-protected continuous domain bound state are fused through the steps 1) and 2), and the design of the high-refractive-index optical super-surface sensor based on the fused continuous domain bound states is completed.

5. Use of a high refractive index optical supersurface sensor based on fused continuous domain bound states according to any one of claims 1 to 3 for detecting the refractive index of a solution, characterized in that, Specifically, the high-refractive-index optical super-surface sensor based on the fused continuous domain bound states is fixed on a sample holder, a light source irradiates the asymmetric metal blocks from top to bottom, a spectrometer is arranged below the metal blocks to collect data, different spectral information is obtained from the spectrometer by dropping solutions with different refractive indexes on the structure surface, the corresponding spectrum of the solution with different refractive indexes is known by analyzing the spectral information, and the refractive index sensitivity of the structure is calculated according to the spectrum of the solution with different refractive indexes; When the solution with an unknown refractive index is dropped, the refractive index of the unknown solution is calculated according to the known spectral information and the refractive index sensitivity. ​

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