Symmetrically broken BIC-based hexagonal lattice chiral sensor and detection method

Abstract

The invention discloses a hexagonal lattice chiral sensor based on symmetric broken BIC and a detection method, the hexagonal lattice chiral sensor comprises a metasurface structure unit, the metasurface structure unit comprises nanometer substrates, the nanometer substrates are periodically arranged to form a hexagonal lattice structure, the metasurface structure unit also comprises a first nanometer block and a second nanometer block which are vertically arranged to form a T shape, an asymmetric parameter exists between the central axis of the first nano block and the central axis of the second nano block and the central axis of the metasurface structure unit, and symmetric breaking is achieved by adjusting the asymmetric parameter; the method comprises the following steps: dropwise adding a to-be-detected sample solution to the surface of the hand sensor; respectively and vertically irradiating the chiral sensor by using a left-hand circularly polarized wave and a right-hand circularly polarized wave; measuring the transmission response of the chiral sensor to different circularly polarized waves to obtain a CD spectrum; the sensitivity and the quality factor of the metasurface chiral sensor are obtained by measuring the offset of the CD spectrum peak value and the full width at half maximum of the CD peak, and the resolution ratio and the detection capability of the chiral sensor are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical sensing, and particularly relates to a hexagonal lattice chiral sensor based on symmetry-breaking BIC and a detection method. BACKGROUND

[0002] The super surface sensor is a photoelectric sensor with a periodically arranged super surface unit as the core, and can detect certain physical quantities of a detected object. The super surface chiral sensor is a kind of super surface sensor, and is a photoelectric sensor designed based on the principle of circular dichroism (CD). The super surface chiral sensor uses different responses of chiral structures to left circularly polarized waves and right circularly polarized waves to distinguish chiral molecules. The basic structure of the super surface chiral sensor is usually arranged into a specific pattern by a plurality of sub-wavelength units to produce strong optical chirality, so as to realize ultra-sensitive sensing and detection of chiral molecules.

[0003] The traditional super surface chiral sensor has the problems of weak chiral response and low Q factor, which leads to insufficient light-matter interaction and makes it difficult to detect trace chiral molecules. Meanwhile, some chiral sensors based on metal structures also have the defect of high ohmic loss, which further limits the sensing sensitivity and accuracy.

[0004] In order to overcome these limitations, researchers set up asymmetric super surface unit structures on the basis of all-dielectric materials and explored the method of introducing bound states in the continuum (BIC) to enhance chiral response. BIC is a special physical phenomenon in which specific modes can exist in the continuous spectrum without being affected by radiation loss. The electromagnetic wave resonance Q value of such modes in a spectrometer can reach 10 2 -10 3 times that of other structure combinations, showing its great application potential in the field of chiral sensing. More specifically in terms of structure, the narrow linewidth high quality factor chiral sensing is realized by simultaneously introducing in-plane inversion and mirror asymmetry to construct such modes.

[0005] In 2024, He et al. proposed a four-corner lattice "T" type super surface structure (He M, Wang Q, Zhang H, et al., Analog electromagnetic induced transparency of T-type Si-based metamaterial and its applications [J], Physica Scripta, 2024, 99(3): DOI: 10.1088 / 1402-4896 / AD203E), which achieved a 93.2 RIU -1(Refractive Index Unit,RIU) but without realizing chiral sensing.

[0006] In 2025, Yang et al. proposed a square silicon block with two cylindrical four-corner lattice metasurface structures (Xi'an University of Electronic Science and Technology, Yang Rui; Li Zian; Hao Yazheng, based on BIC all-dielectric metasurface chiral sensor, patent application number: ZL202510050265.0, 2025-05-09.), which realized a 10 4 RIU -1 order of magnitude of the quality factor and 172 nm / RIU sensitivity of chiral sensing.

[0007] The chiral metasurface sensor in the prior art has the disadvantages of weak chiral response and low quality factor. SUMMARY

[0008] To solve the above technical problems, the present application provides a hexagonal lattice chiral sensor based on symmetry breaking BIC and a detection method, which not only realizes optical chirality, but also realizes a chiral sensor with a higher order of magnitude of quality factor.

[0009] The specific scheme is as follows: The hexagonal lattice chiral sensor based on symmetry breaking BIC comprises a periodically arranged metasurface structure unit, the metasurface structure unit comprises a nanometer substrate, the nanometer substrate is periodically arranged in a hexagonal lattice structure, the nanometer substrate is fixedly provided with a first nanometer block and a second nanometer block, the first nanometer block and the second nanometer block are vertically arranged in a T shape, and the central axis of the first nanometer block and the central axis of the second nanometer block have an asymmetric parameter with respect to the central axis of the metasurface structure unit. The symmetry is broken by adjusting the asymmetric parameter to excite quasi-BIC.

[0010] The first nanometer block and the second nanometer block are cuboids, the material of the first nanometer block and the second nanometer block is silicon nitride or silicon, the nanometer substrate is a hexagonal prism, and the material of the nanometer substrate is silicon dioxide or silicon.

[0011] The chiral sensor describes the strength of chirality according to the maximum amplitude of CD (Circular dichroism), and the maximum amplitude of CD refers to the difference in transmission caused by the vertical illumination of the metasurface by left-handed circularly polarized waves and right-handed circularly polarized waves from the z direction, and the calculation formula of CD value is: wherein, Tll the co-polarization transmittance of the left-handed circularly polarized wave; T rl the cross-polarization transmittance of the left-handed circularly polarized wave, T rr the co-polarization transmittance of the right-handed circularly polarized wave; T lr the cross-polarization transmittance of the right-handed circularly polarized wave.

[0012] A detection method, comprising the following steps: S1) dropping a sample solution to be detected onto the surface of the chiral sensor; S2) vertically irradiating the chiral sensor with a left-handed circularly polarized wave (LCP) and a right-handed circularly polarized wave (RCP) respectively; S3) measuring the transmission response of the chiral sensor to different circularly polarized waves to obtain a CD spectrum; S4) obtaining the sensitivity of the chiral sensor by measuring the shift of the CD spectrum peak and the full width at half maximum of the CD peak S and the quality factor FOM , the sensitivity S and the quality factor FOM The calculation formula is: wherein, is the change amount of the refractive index of the object to be detected, is the shift of the CD peak when the change of the refractive index is , and is the full width at half maximum.

[0013] The present application provides a kind of hexagonal lattice chiral sensor and detection method based on symmetry broken BIC, chiral sensor includes periodically arranged super surface structure unit, the first nanoblock and the second nanoblock in the super surface structure unit are vertically arranged as T shape, the super surface structure unit generates CD by the difference transmission of left and right circularly polarized wave, realizes optical chirality.

[0014] In addition, by the left-right asymmetry of the central symmetry axis of the first nanoblock and the second nanoblock is controlled, high quality factor and the efficient response of CD maximum amplitude are realized, so that the super surface structure has optical resonance characteristics and extremely narrow resonance line width, improve its resolution and detection capacity as chiral sensor. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the schematic diagram of the chiral sensor of the present application. ​

[0016] Figure 2 is a schematic diagram of a metasurface structure unit.

[0017] Figure 3 is a top view of a metasurface structure unit.

[0018] Figure 4 is a CD spectrum diagram of changing metasurface structure parameters.

[0019] Figure 5 is a spectrum diagram when the refractive index n of the measured object is 1.

[0020] Figure 6 is a detection diagram when the refractive index n of the liquid measured object is 1.333-1.335. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are only part of the implementation of the present application, not all the implementation, and all other embodiments obtained by a person of ordinary skill in the art without creative labor based on the embodiments of the present application are within the scope of protection of the present application.

[0022] As shown in Figure 1 and Figure 2 , a chiral sensor based on symmetry-breaking BIC of a hexagonal lattice, the chiral sensor includes periodically arranged metasurface structure units, the metasurface structure units include a nanosubstrate 1, the nanosubstrate 1 is periodically arranged into a hexagonal lattice structure, the nanosubstrate 1 is fixedly provided with a first nanoblock 2 and a second nanoblock 3, the first nanoblock 2 and the second nanoblock 3 are vertically arranged into a T shape, and the center axis of the first nanoblock 2 and the second nanoblock 3 has an asymmetric parameter with the center axis of the metasurface structure unit. By adjusting the asymmetric parameter , symmetry breaking is realized, and quasi-BIC is excited.

[0023] As shown in Figure 1 , the incident electromagnetic wave includes a left circular polarization wave (LCP) and a right circular polarization wave (RCP), the incident electromagnetic wave is vertically incident on the metasurface array from the z direction, due to the generation of symmetry-breaking BIC, the transmitted electromagnetic wave is different from the incident electromagnetic wave, and chiral sensing is realized.

[0024] As shown in Figure 2As shown, the first nanoblock 2 and the second nanoblock 3 are cuboids, and the materials of the first nanoblock 2 and the second nanoblock 3 are silicon nitride or silicon. The heights of the first nanoblock 2 and the second nanoblock 3 are... h 1. The nano-substrate 1 is a hexagonal prism, the material of the nano-substrate 1 is silicon dioxide or silicon, and the height of the nano-substrate 1 is [missing information]. h 2.

[0025] Top view of metasurface unit as shown Figure 3 As shown, the hexagonal lattice has a side length of P, and the length of the first nanoblock 2 is... l 1, width is w 1. The length of the second nanoblock 3 is l 2, width is w 2. The entire structure is located at the center of the unit. The distance between the central axis of the first nanoblock 2 and the central axis of the second nanoblock 3 and the central axis of the unit is adjusted. Adjusting the strength of optical chirality and the sensing quality factor.

[0026] The chiral sensor describes the strength of chirality based on the maximum amplitude of the circular dichroism (CD). The maximum amplitude of CD refers to the change in CD value caused by the difference in transmission between left-handed and right-handed circularly polarized waves perpendicularly irradiating the metasurface from the z-direction. The formula for calculating the CD value is as follows: in, T ll This represents the co-polarization transmittance of a left-handed circularly polarized wave; T rl This represents the cross-polarization transmittance of a left-handed circularly polarized wave. T rr This represents the co-polarization transmittance of a right-hand circularly polarized wave; T lr This represents the cross-polarization transmittance of a right-hand circularly polarized wave.

[0027] The chiral sensor structural parameters are optimized as follows: Figure 4 As shown, by changing the unit structure parameters of the metasurface, that is, changing the hexagonal lattice side length to P, the length of the first nanoblock 2 is... l 1. Width of the first nanoblock 2 w 1. Length of the second nanoblock 3 l 2. Width of the second nanoblock 3 w 2 and asymmetric parameters The CD value and the resonance peak wavelength can be adjusted. In this embodiment, only one parameter is changed in each experiment. Figure 4In (a) to (f), the horizontal axis represents wavelength in nanometers (nm), and the vertical axis represents the absorption difference, i.e., circular dichroism.

[0028] Figure 4 In (a), the parameter that is changed is the hexagonal lattice side length P, and P is changed to 570nm, 575nm, 580nm, 585nm and 590nm respectively; Figure 4 In (b), the parameter that is changed is the length of the first nanoblock 2. l 1. Change l 1 represents 680nm, 700nm, 720nm, 740nm, 760nm, and 780nm respectively; Figure 4 The parameter changed in (c) is the length of the second nanoblock 3. l 2. Change l The two are 440nm, 460nm, 480nm, 500nm, 520nm and 540nm respectively; Figure 4 The parameter that is changed in (d) is the width of the first nanoblock 2. w 1. Change w 1 represents 110nm, 120nm, 130nm, 140nm, 150nm, and 160nm respectively; Figure 4 The parameter changed in (e) is the width of the second nanoblock 3. w 2. Change w The two are 80nm, 90nm, 100nm, 110nm, 120nm and 130nm respectively; Figure 4 The parameter that changes in (f) is an asymmetric parameter. ,Change They are 0nm, 10nm, 20nm, 30nm, 40nm and 50nm respectively; from Figure 4 Asymmetric parameters can be seen in (a) to (f). The structural parameters have the greatest impact on the CD value, while other parameters have a smaller impact on the CD value. For the full width half maximum (FWHM), the structural parameters have a relatively small impact.

[0029] Based on the parameter optimization results, P=580nm. l 1 = 780nm, l 2 = 510nm, w 1 = 160nm w 2 = 100nm =50nm. This structure combines high CD value and FWHM. Based on this structure, a chiral sensor is designed, and the sensor's sensitivity, quality factor and other characteristics are studied.

[0030] like Figure 5 As shown, the metasurface, under the condition that the ambient refractive index n=1, Figure 5 (a) shows the CD spectrum in this case, with the horizontal axis representing wavelength in nanometers (nm) and the vertical axis representing the absorption difference, i.e., circular dichroism. Figure 5 (b) shows the transmission of left-handed and right-handed circularly polarized waves irradiating the metasurface. The horizontal axis represents wavelength in nanometers (nm), and the vertical axis represents transmittance.

[0031] A detection method, based on the chiral sensor structure, provides an application for detecting the refractive index of the environment, comprising the following steps: S1): The sample solution to be tested is dropped onto the surface of the chiral sensor; S2): The chiral sensor is vertically irradiated with left-handed circularly polarized waves (LCP) and right-handed circularly polarized waves (RCP), respectively; S3): Measure the transmission response of the chiral sensor to different circularly polarized waves to obtain the CD spectrum; S4): By measuring the shift of the CD spectrum peaks and the full width at half maximum (FWHM) of the CD peak To obtain the sensitivity of the chiral sensor S and quality factor FOM Sensitivity S and quality factor FOM The calculation formula is: in, The change in refractive index of the analyte is given by the analyte. The change in refractive index is The offset of the CD peak value, It is half the full width of the peak.

[0032] like Figure 6 As shown, a 1 μm thick layer of liquid analyte was added to the upper surface of the aforementioned metasurface structure, and two refractive index ranges were tested: the refractive index range of the liquid analyte was n = 1.333–1.335, and the refractive index range of the liquid analyte was n = The case range is 1.363 to 1.365.

[0033] Figure 6(a) shows the CD spectrum of the liquid analyte with a refractive index n of 1.333 to 1.335; Figure 6 Figure (b) shows the relationship between the position of the CD resonance peak and the refractive index for the liquid analyte with refractive indices n = 1.333–1.335. Figure 6 (c) shows the relationship between the refractive index and the resonance peak FOM for the refractive index n = 1.333 to 1.335 of the liquid analyte; Figure 6 (d) in the figure shows the CD spectrum of the liquid analyte with a refractive index n of 1.363 to 1.365; Figure 6 Figure (e) shows the relationship between the peak position of CD and the refractive index for the liquid analyte with refractive index n = 1.363–1.365; Figure 6 Figure (f) shows the relationship between the refractive index and FOM for the liquid analyte with refractive index n = 1.363 to 1.365.

[0034] Compared with existing metasurface chiral sensors, this invention has a simpler structure and is easier to fabricate. The all-dielectric material avoids ohmic losses, while achieving high sensitivity and quality factor under strong CD conditions. Experimental results show that the sensitivity of this invention can reach 562. nm / RIU The quality factor reached 2.08×10. 5 RIU -1 This greatly enhances the sensor's high spectral resolution and detection capabilities. The chiral sensor can be used in fields such as biochemical analysis, medical diagnosis, and environmental monitoring.

[0035] This invention provides a hexagonal lattice chiral sensor and detection method based on symmetry-broken BIC. The chiral sensor includes periodically arranged metasurface structural units. The first and second nanoblocks in the metasurface structural units are vertically arranged in a T-shape. The metasurface structural units generate CD by differentially transmitting left-hand and right-hand circularly polarized waves, thereby realizing optical chirality.

[0036] Furthermore, by controlling the left-right asymmetry of the central symmetry axis of the first and second nanoblocks, a high-efficiency response with high quality factor and maximum CD amplitude is achieved, enabling the metasurface structure to have optical resonance characteristics and extremely narrow resonance linewidth, thereby improving its resolution and detection capability as a chiral sensor.

[0037] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A hexagonal lattice chiral sensor based on a symmetry-broken BIC, characterized in that: The chiral sensor comprises periodically arranged metasurface structural units, each including a nanosubstrate (1). The nanosubstrate (1) is periodically arranged in a hexagonal lattice structure. A first nanoblock (2) and a second nanoblock (3) are fixedly disposed on the nanosubstrate (1). The first nanoblock (2) and the second nanoblock (3) are vertically arranged in a T-shape. The central axis of the first nanoblock (2) and the second nanoblock (3) has an asymmetric parameter with respect to the central axis of the metasurface structural unit. By adjusting the asymmetric parameter Symmetry breaking is achieved, and quasi-continuous bound states (quasi-BIC) are excited.

2. The hexagonal lattice chiral sensor based on symmetry-broken BIC according to claim 1, characterized in that: The first nanoblock (2) and the second nanoblock (3) are cuboids, and the materials of the first nanoblock (2) and the second nanoblock (3) are silicon nitride or silicon. The nanosubstrate (1) is a hexagonal prism, and the material of the nanosubstrate (1) is silicon dioxide or silicon.

3. The hexagonal lattice chiral sensor based on symmetry-broken BIC according to claim 1, characterized in that: The chiral sensor describes the strength of chirality based on the maximum amplitude of the circular dichroism (CD). The maximum amplitude of CD refers to the change in CD value caused by the difference in transmission between left-handed and right-handed circularly polarized waves perpendicularly irradiating the metasurface from the z-direction. The formula for calculating the CD value is as follows: in, T ll This represents the co-polarization transmittance of a left-handed circularly polarized wave; T rl This represents the cross-polarization transmittance of a left-handed circularly polarized wave. T rr This represents the co-polarization transmittance of a right-hand circularly polarized wave; T lr This represents the cross-polarization transmittance of a right-hand circularly polarized wave, where the z-direction refers to the direction perpendicular to the plane of the chiral sensor.

4. A detection method, employing a hexagonal lattice chiral sensor based on symmetry-broken BIC as described in any one of claims 1-3, characterized in that, Includes the following steps: S1): The sample solution to be tested is dropped onto the surface of the chiral sensor; S2): The chiral sensor is vertically irradiated with left-handed circularly polarized waves (LCP) and right-handed circularly polarized waves (RCP), respectively; S3): Measure the transmission response of the chiral sensor to different circularly polarized waves to obtain the CD spectrum; S4): By measuring the shift of the CD spectrum peaks and the full width at half maximum (FWHM) of the CD peak To obtain the sensitivity of the chiral sensor S and quality factor FOM Sensitivity S and quality factor FOM The calculation formula is: in, The change in refractive index of the analyte is given by the analyte. The change in refractive index is The offset of the CD peak value, It is half the full width of the peak.

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