Double-layer terahertz BIC metasurface sensor based on Ci point group symmetry

Abstract

The invention discloses a Ci point group symmetry-based double-layer terahertz BIC metasurface sensor, which belongs to the field of terahertz functional devices and comprises an upper elliptic cylinder layer, a middle substrate layer and a lower elliptic cylinder layer which are periodically arranged, the upper elliptic cylinder layer comprises a first elliptic cylinder and a second elliptic cylinder, the lower elliptic cylinder layer comprises a third elliptic cylinder and a fourth elliptic cylinder, and Ci point group symmetry is formed to achieve a continuous domain bound state; ci symmetry is broken by adjusting the length difference of the short axis of the first elliptic cylinder and the short axis of the second elliptic cylinder so as to excite QBIC resonance; and switching to a chiral sensing mode by adjusting the angle of incident light so as to realize circular dichroism response detection. According to the invention, the strong field local characteristic in the QBIC mode is ensured, the chiral detection function is also realized, and a brand new multifunctional detection scheme is provided for the fields of terahertz biomedical detection, drug quality control and the like.

Description

Technical Field

[0001] This invention belongs to the field of terahertz functional device technology, and particularly relates to a C-based i A point-group symmetric double-layer terahertz BIC metasurface sensor. Background Technology

[0002] Terahertz sensing technology, due to its unique non-ionizing properties and molecular fingerprint recognition capabilities, shows great promise in fields such as biomedical detection and hazardous materials identification. Traditional metasurface sensors mainly rely on Fano resonance or plasmon resonance mechanisms to detect specific substances. Furthermore, the introduction of the concept of bound states in the continuum (BIC) provides a new approach to improving sensor performance. Theoretical studies show that an ideal BIC possesses an infinitely large Q value and zero radiation loss, but in practical applications, it needs to be converted into a quasi-BIC (QBIC) through symmetry breaking. Existing technologies primarily employ two-dimensional planar structures to realize QBICs, and this structure can improve sensor performance to some extent.

[0003] However, existing terahertz sensors face technical bottlenecks such as insufficient sensitivity and limited quality factor, severely hindering their practical application. Traditional metasurface sensors suffer from high radiation loss and limited mode volume, which restricts their application in high-precision detection. Particularly for chiral molecule detection, conventional devices exhibit weak circular dichroism (CD) response, making it difficult to meet the requirements for trace detection. Existing technologies using two-dimensional planar structures to implement QBIC are limited by Q∝α. -2 The physical laws (α is the degree of asymmetry). When the degree of asymmetry α > 0.1, the Q value drops sharply below the practical level, which is fundamentally contradictory to the large degree of asymmetry required for high CD value sensing.

[0004] To address this technological challenge, recent research has begun exploring three-dimensional metasurface structures. Chen et al. proposed a three-dimensional metamaterial sensor coupled with magneto-plasmo-resonance diffraction, utilizing the narrow-band hybrid resonance mode enhanced by the excited magnetic field to improve the device's sensing performance. Wang et al. proposed a metamaterial absorber based on a three-dimensional resonant structure, which, combined with microfluidic channels, achieves liquid refractive index sensing with a sensitivity of 379 GHz / RIU. However, these methods have failed to simultaneously solve the problem of synergistic optimization of high Q-value preservation and strong chiral response, hindering breakthroughs in the application of terahertz sensing technology in fields such as biomarker detection and asymmetric synthesis monitoring. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method based on C iA point-group symmetric double-layer terahertz BIC metasurface sensor is proposed to address the problems existing in the prior art.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a C-based... i A point-group symmetric bilayer terahertz BIC metasurface sensor, including:

[0007] The upper elliptical cylindrical layer, the middle basal layer, and the lower elliptical cylindrical layer are arranged in a periodic pattern.

[0008] The upper elliptical cylinder layer comprises a first elliptical cylinder and a second elliptical cylinder, and the lower elliptical cylinder layer comprises a third elliptical cylinder and a fourth elliptical cylinder, forming C. i Point group symmetry to realize bound states in continuous domains;

[0009] By adjusting the difference in the minor axis lengths of the first and second elliptical cylinders, C is broken. i Symmetry to stimulate QBIC resonance;

[0010] By adjusting the incident light angle, the chiral sensing mode is switched to achieve circular dichroism response detection.

[0011] Preferably, the elliptical cylinders of the upper and lower elliptical cylinder layers are made of a perfect electrical conductor material, and the intermediate base layer is made of a polyimide material.

[0012] Preferably, the difference in minor axis length between the first elliptical cylinder and the second elliptical cylinder is greater than or equal to 10 μm.

[0013] Preferably, the distance between the first elliptical cylinder and the second elliptical cylinder is adjusted to maintain or improve the circular dichroism response value.

[0014] Preferably, the chiral sensing mode is activated when the incident light angle is 5°.

[0015] Preferably, the quality factor Q of the QBIC resonance is greater than or equal to 800.

[0016] Preferably, the period of the upper elliptical cylindrical layer and the lower elliptical cylindrical layer is 200 μm.

[0017] Preferably, the thickness of the intermediate substrate layer is 20 μm.

[0018] Preferably, the circular dichroism response value in the chiral sensing mode is greater than 0.7.

[0019] Preferably, the sensor has a sensitivity of 21.5 GHz / RIU in QBIC mode.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] This invention provides a C-based i A point-group symmetric bilayer terahertz BIC metasurface sensor comprises: a periodically arranged upper elliptical cylindrical layer, an intermediate substrate layer, and a lower elliptical cylindrical layer; the upper elliptical cylindrical layer includes a first elliptical cylinder and a second elliptical cylinder, and the lower elliptical cylindrical layer includes a third elliptical cylinder and a fourth elliptical cylinder, forming a C1... i Point group symmetry is used to achieve bound states in the continuous domain; by adjusting the difference in the minor axis lengths of the first and second elliptical cylinders, the C-axis is broken. i Symmetry is used to excite QBIC resonance; circular dichroism response detection is achieved by switching to chiral sensing mode by adjusting the incident light angle.

[0022] This invention overcomes the performance limitations of traditional two-dimensional devices by designing a two-layer terahertz BIC metasurface sensor in a three-dimensional spatial configuration. This sensor breaks the inverse quadratic relationship (Q∝α) between Q-value and asymmetry in traditional two-dimensional BIC devices. 2 Despite limitations in the Q-value, complex optical field manipulation was achieved.

[0023] This invention breaks the C-shaped curve by precisely controlling the length difference between the minor axes of the upper elliptical cylinders. i The symmetry enables QBIC resonance with a high Q value, resulting in excellent sensing characteristics. Furthermore, under adjusted oblique incidence conditions, the structure can be converted to a chiral BIC sensing mode, producing a significant circular dichroism response and achieving ultrasensitive detection of chiral molecules. This dual-mode design allows for easy switching of operating modes through simple adjustment of the incident angle, ensuring both the strong-field localization characteristics of QBIC mode and chiral detection functionality, providing a novel multifunctional detection solution for terahertz biomedical detection, pharmaceutical quality control, and other fields. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This embodiment is based on C i A point-group symmetric double-layer terahertz BIC metasurface sensor, (A) is a schematic diagram of the sensor structure, and (B) is a schematic diagram of the unit structure parameters;

[0026] Figure 2The results of calculations performed on the metasurface structure under study using COMSOL in this embodiment are shown in (a), where (a) shows the energy band and Q factor distribution of the metasurface structure in the first Brillouin zone, (b) shows the distribution of Q value in the entire momentum space, (c) shows the far-field polarization distribution, and (d) shows the transmission spectrum of the metasurface under different degrees of symmetry.

[0027] Figure 3 The results of calculations using the multipole model in this embodiment are shown; (a) the multipole decomposition of the metasurface after breaking the symmetry (asymmetry ΔS = 0.2); the inset shows the decomposition of TD in the x, y, and z components; (b) the magnetic field distribution of QBIC in the xoy plane, with arrows indicating the current direction;

[0028] Figure 4 This is the transmittance spectrum and sensitivity for refractive index sensing in this embodiment; wherein, (A) represents the simulation results of the transmission spectrum of x-linearly polarized waves incident on the structure when the equivalent refractive index of the sensor's detection layer varies from 1.0, 1.2, 1.4, 1.6, 1.8 and 2.0; (B) simulates the change of resonant frequency as the refractive index changes from 1.0 to 2.0;

[0029] Figure 5 This embodiment demonstrates how chiral response is achieved by changing a certain incident angle; (A) The size of the minor axis between the upper elliptical cylinders is changed to simulate and obtain a transmission spectrum; where the asymmetry is ΔS = 0.2, ΔS = 0.33 and ΔS = 0.43 respectively; (B) Schematic diagram of circular dichroism values ​​(CD) with asymmetry of ΔS = 0.2, ΔS = 0.33 and ΔS = 0.43; (C) The size of the minor axis of the two upper elliptical cylinders is fixed, and the distance f of one of the upper elliptical cylinders is changed to obtain a transmission spectrum; where f = 50 μm, f = 70 μm and f = 80 μm from top to bottom; (D) Schematic diagram of circular dichroism values ​​obtained by changing the distance f of the elliptical cylinders when the asymmetry is ΔS = 0.33;

[0030] The structure consists of: 1. Upper elliptical cylindrical layer; 2. Lower elliptical cylindrical layer; 3. Middle basal layer. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0033] Example 1

[0034] To address the limitations of traditional two-dimensional BIC metasurfaces, based on C i A three-dimensional bipolar integrated circuit (BIC) metasurface device based on point group symmetry is proposed for sensing functionality. Simulation results verify that the BIC metasurface device implemented using this method possesses advantages such as high Q value and high flexibility, and can meet the practical needs of the current terahertz band.

[0035] like Figure 1 As shown, this embodiment provides a C-based i A point-group symmetric bilayer terahertz BIC metasurface sensor, including:

[0036] The upper elliptical cylindrical layer 1, the middle basal layer 3, and the lower elliptical cylindrical layer 2 are arranged in a periodic pattern.

[0037] The upper elliptical cylinder layer comprises a first elliptical cylinder and a second elliptical cylinder, and the lower elliptical cylinder layer comprises a third elliptical cylinder and a fourth elliptical cylinder, forming C. i Point group symmetry to realize bound states in continuous domains;

[0038] By adjusting the difference in the minor axis lengths of the first and second elliptical cylinders, C is broken. i Symmetry to stimulate QBIC resonance;

[0039] By adjusting the incident light angle, the chiral sensing mode is switched to achieve circular dichroism response detection.

[0040] Specifically, a resonator array is formed by periodically arranging resonator units in two layers above and below the base layer. Each resonator unit consists of four metal elliptical cylinders, which are distributed in pairs on the upper and lower surfaces, forming a C-shaped array. i Point group symmetry enables the realization of bound states in the continuous domain. When the minor axes of the two elliptical cylinders in the upper structure are not aligned, a significant chiral response will be formed in the resonator when light waves are incident obliquely, enabling sensitive detection of chiral molecules.

[0041] In this embodiment, C is maintained. i In the case of symmetry, the major and minor axes of the four elliptical cylinders are the same size. The aforementioned preservation of C... i The symmetric terahertz bilayer metasurface unit structure consists of two upper elliptical cylinders with semi-minor axes r1 = r3 = 10 μm and semi-major axes r2 = r4 = 30 μm. The thickness of the elliptical cylinders is h = 0.2 μm, the distance between the two elliptical cylinders is d = 80 μm, l = 50 μm, and the substrate thickness is H = 20 μm. The semi-major axes of the two lower elliptical cylinders are r1 = r3 = 10 μm and r2 = r4 = 30 μm, respectively. b =30μm, semi-minor axis r a =10μm, the distance between the two elliptical cylinders d=80μm, f=50μm.

[0042] Furthermore, the elliptical cylinders of the upper and lower elliptical cylinder layers are made of a Perfect Electrical Conductor (PEC) material, and the intermediate substrate layer is made of a polyimide material.

[0043] Furthermore, the difference in minor axis length between the first elliptical cylinder and the second elliptical cylinder is greater than or equal to 10 μm.

[0044] Furthermore, the thickness of the intermediate substrate layer is 20 μm.

[0045] Specifically, this embodiment breaks C i The symmetry is achieved by changing the length of the minor axis between the two upper elliptical cylinders, enabling the observation of a quasi-BIC resonance mode with a finite Q factor in the spectrum. This realizes the conversion from BIC to QBIC, achieving a sensing function with a high Q value. The aforementioned breaking of C... i The symmetric terahertz bilayer metasurface unit structure consists of two upper elliptical cylinders with asymmetric semi-minor axes r1 = 10 μm and r3 = 20 μm, and semi-major axes r2 = r4 = 30 μm. The thickness of the elliptical cylinders is h = 0.2 μm, the distance between the two elliptical cylinders is d = 80 μm and l = 50 μm, and the substrate thickness is H = 20 μm. The semi-major axes of the two lower elliptical cylinders are r1 = 10 μm and r3 = 20 μm, respectively. b =30μm, semi-minor axis r a =10μm, the distance between the two elliptical cylinders d=80μm, f=50μm.

[0046] The metasurface structure described in this embodiment is a transmission type.

[0047] Furthermore, the distance between the first elliptical cylinder and the second elliptical cylinder is adjusted to maintain or enhance the circular dichroism response value.

[0048] Specifically, this embodiment can maintain or improve the CD value under different perturbation conditions by adjusting the distance between the two elliptical cylinders. The double-layer metasurface unit structure with the upper elliptical cylinders having semi-minor axes r1 = 10 μm and r3 = 25 μm, semi-major axes r2 = r4 = 30 μm, cylinder thickness h = 0.2 μm, distance between the two cylinders d = 80 μm and f = 80 μm, substrate thickness H = 20 μm, and the lower two elliptical cylinders have semi-major axes r1 = 10 μm and r3 = 25 μm, respectively. a =30μm, semi-minor axis r b =10μm, the distance between the two elliptical cylinders d=80μm, f=50μm.

[0049] Furthermore, the chiral sensing mode is activated when the incident light angle is 5°.

[0050] Specifically, the aforementioned bilayer metasurface structure can achieve chiral response by adjusting the angle of incident light (the angle of incident light θ = 5°), thereby enabling the detection of chiral molecules. The terahertz bilayer metasurface unit structure for achieving chirality consists of two upper elliptical cylinders with semi-minor axes r1 = 10 μm and r3 = 25 μm, and semi-major axes r2 = r4 = 30 μm respectively. The thickness of the elliptical cylinders is h = 0.2 μm, the distance between the two elliptical cylinders is d = 80 μm and l = 50 μm, and the substrate thickness is H = 20 μm; the semi-major axes of the two lower elliptical cylinders are r1 = 10 μm and r3 = 25 μm, respectively. b =30μm, semi-minor axis r a =10μm, the distance between the two elliptical cylinders d=80μm, f=50μm.

[0051] Furthermore, the quality factor Q of the QBIC resonance is greater than or equal to 800.

[0052] Furthermore, the periods of the upper and lower elliptical cylindrical layers are 200 μm.

[0053] Furthermore, the circular dichroism response value in the chiral sensing mode is greater than 0.7.

[0054] Furthermore, the sensor has a sensitivity of 21.5 GHz / RIU in QBIC mode.

[0055] The BIC bilayer metasurface structure described in this embodiment uses the multipole decomposition method to explain the underlying physical principles of the QBIC resonance mechanism. The multipole extension in Cartesian coordinates is used to explore the influence of the QBIC on the far field; the multipole moment is written as follows:

[0056] Electric dipole moment (ED):

[0057] Magnetic dipole moment (MD):

[0058] Electric Quadrupole (EQ):

[0059] Magnetic Quadrupole (MQ):

[0060] Circular dipole (TD):

[0061] Where c is the speed of light, ω is the angular frequency, j is the current density displacement, and r is the distance vector. The formulas for calculating the distribution of these torques are as follows:

[0062]

[0063] The method for representing the asymmetry and Q-factor of the bilayer metasurface structure described in this embodiment is as follows:

[0064]

[0065] Where r1 and r3 represent the lengths of the semi-minor axes of the two upper elliptical cylinders, Δf is the magnitude of the frequency shift, and Δn represents the difference in refractive index of the test object.

[0066] The method for calculating the topological charge of the bilayer metasurface described in this embodiment is as follows:

[0067]

[0068] in The angle between the polarization vector and the x-axis is represented by , and C is the closed path around the center point in a counterclockwise direction.

[0069] The bilayer metasurface described in this embodiment can achieve a relatively perfect chiral response when the incident angle is changed. The formula for calculating circular dichroism (CD) is as follows:

[0070]

[0071] Among them, t LCP and t RCP These represent the transmittance of LCP and RCP light in the transmission spectrum, respectively.

[0072] The electromagnetic response of the aforementioned bilayer metasurface was simulated and analyzed using CST MWS software and COMSOL simulation software.

[0073] Experiment 1

[0074] To verify that the intrinsic mode generated by this metasurface structure is BIC, the experimental scheme is as follows:

[0075] The parameters of the bilayer metasurface structure in this experiment are: period P = 200 μm, substrate thickness H = 20 μm, semi-major axis r2 = r4 = 30 μm, semi-minor axis r1 = r3 = 10 μm of the upper elliptical cylinder, distance between the elliptical cylinders d = 80 μm, f = 50 μm, and semi-major axis r of the lower elliptical cylinder. b =30μm, semi-minor axis r a =10μm, and simulation analysis was performed using CST MWS and COMSOL simulation software.

[0076] The metasurface structure under study was calculated using COMSOL simulation software, such as... Figure 2 As shown. Among them, Figure 2(a) shows the band structure and Q-factor distribution of the metasurface structure in the first Brillouin zone. Notably, in the TM mode, the Q-value at the center point (Γ point) tends to infinity, indicating an extremely high mode-bound state at that point. In contrast, the Q-value decreases sharply along the momentum space away from the Γ point, a phenomenon closely related to the change in momentum k. Specifically, the relationship between Q-value and momentum k follows Q∝1 / k. 2 The characteristic evolution formula shows that within metasurface structures, the Q-factor of the intrinsic modes exhibits a significant dependence on changes in the wave vector position. This phenomenon aligns with the definition of BIC, demonstrating the existence of specific modes within metasurface structures.

[0077] Based on this, the distribution of the Q-value of this mode throughout the momentum space was further calculated, such as... Figure 2 As shown in (b), the results show that at the center of the Brillouin zone, the Q value is infinite, while in regions far from the center, the Q value decays rapidly and drops to 10 after a certain distance. 4 The following phenomenon creates a central "brightness". This fully verifies the characteristics of BIC, namely, the existence of extremely high Q values ​​at specific locations, while other regions exhibit low radiation loss.

[0078] Similarly, this experiment also calculated the far-field polarization distribution of this eigenstate, see... Figure 2 (c) The polarization state at the center point is indeterminate and therefore cannot be directly determined. However, within a certain range from the center point, the polarization vector rotates counterclockwise around the center point axis, reaching a full angle of 2π with the x-axis. This phenomenon suggests that the polarization state in this region exhibits vortex characteristics. Using the formula, the topological charge at the Γ point is calculated to be q = +1. This result indicates that the mode possesses vortex wavefront characteristics, reflecting the topological properties of the metasurface structure. This further confirms that this frequency point exhibits BIC characteristics, revealing the potential of metasurfaces to design bound-state resonances under specific conditions.

[0079] In this experiment, the size of the minor axis of the upper elliptical cylinder was changed, introducing a radius perturbation. After introducing the radius perturbation, the asymmetry was ΔS = 0, 0.2, and 0.33. This operation aims to study its effect on the optical properties of the metasurface. Simulations of these symmetry-breaking metasurface structures were performed using CST, such as... Figure 2 As shown in (d), the transmission spectrum varies under different degrees of symmetry. When the geometry of the metasurface maintains C... iWhen the symmetry is maintained, the BIC in the system cannot be excited, and these features cannot be observed in the transmission spectrum. With the breaking of structural symmetry, the BIC with an infinitely high Q factor transforms into a QBIC and exhibits a tendency to "diverge" into open space. During this process, a sharp Fano resonance peak appears in the transmission spectrum, showing distinct response characteristics. Further observation reveals a significant blue shift in the resonance phenomenon with increasing asymmetry. Simultaneously, the half-width at half-maximum (FWHM) of the resonance peak gradually increases, indicating a decrease in the Q factor, which implies increased energy loss during the interaction between the metasurface and its external environment.

[0080] Experiment 2

[0081] To explain the formation of QBIC, the experimental procedure is as follows:

[0082] The structural parameters of the asymmetric bilayer metasurface device in this experiment are: period P = 200 μm, substrate thickness H = 20 μm, semi-major axis r2 = r4 = 30 μm, semi-minor axis r1 = 10 μm, r3 = 20 μm for the upper elliptical cylinder, distance between the elliptical cylinders d = 80 μm, f = 50 μm, and semi-major axis of the lower elliptical cylinder r2 = r4 = 30 μm, semi-minor axis r1 = 10 μm, r3 = 20 μm, distance between the elliptical cylinders d = 80 μm, f = 50 μm, and semi-major axis of the lower elliptical cylinder r3 = 20 μm. b =30μm, semi-minor axis r a =10μm. The radiation characteristics of metasurface structures under asymmetric conditions were quantitatively analyzed using the multipole decomposition method in Cartesian coordinates, such as... Figure 3 As shown. A logarithmic coordinate system was selected on the y-axis to clearly observe the differences between the different modes (electric dipole ED, magnetic dipole MD, electric quadrupole EQ, magnetic quadrupole MQ, and toroidal dipole TD; see supplementary material for specific formulas). Figure 3 (a) It can be seen that the QBIC mode is mainly dominated by the ring dipole TD. Through the decomposition analysis of the scattered power of the ring dipole in the x, y, and z directions of the QBIC mode, it can be significantly found that the y component of the ring dipole is dominant, and its value is close to the overall scattered power, which further verifies the effectiveness of the mode. It is observed that in the x direction, the circulation direction of the displacement current is the same, while in the y direction, the circulation direction of the displacement current is opposite, see... Figure 3 (b) This symmetry and opposite current direction are key characteristics of ring dipole resonance. In this case, the MD (Multipole Decomposition) is weakly coupled to free space and exhibits resonance with a high Q value. This result is highly consistent with the calculations of multipole decomposition, further demonstrating the crucial role of the ring dipole in generating QBIC modes.

[0083] Example 3

[0084] To illustrate the sensing performance of this double-layer metasurface structure, the following experimental scheme was used:

[0085] The structural parameters of the asymmetric bilayer metasurface device in this experiment are: period P = 200 μm, substrate thickness H = 20 μm, semi-major axis r2 = r4 = 30 μm, semi-minor axis r1 = 10 μm, r3 = 20 μm for the upper elliptical cylinder, distance between the elliptical cylinders d = 80 μm, f = 50 μm, and semi-major axis r of the lower elliptical cylinder. b =30μm, semi-minor axis r a =10μm.

[0086] Using the breaking of C i A symmetrical structure was used to achieve the conversion from BIC to QBIC, obtaining a high Q-value resonance (Q≈853.3) at 1.298 THz for sensing. To demonstrate that the designed structure exhibits a high Q-value resonance for sensing measurements under specific point coupling conditions, the dielectric layer was modeled and simulated in this experiment. The dielectric layer had a thickness of 5 μm and its equivalent refractive index varied from 1.0 to 2.0. The obtained transmission spectrum results are shown below. Figure 4 As shown in (A). From Figure 4 As shown in (B), the QBIC resonant frequency shifts from 1.298 THz to 1.2765 THz in the simulated refractive index, with a sensitivity of 21.5 GHz / RIU. A nonlinear model was used to fit the simulated data, with the fitting equation being y = 0.036823exp(-1.1004x + 0.9692) + 1.2672. The fitting result yields R0. 2 =0.97684, indicating a good fit. Furthermore, the average quality factor Q of this structural resonance reaches 1000.63. Therefore, the designed sensor exhibits good resolution for detecting the analyte.

[0087] Example 4

[0088] To achieve chiral sensing using a double-layer metasurface structure, the following scheme was employed in this experiment:

[0089] The structural parameters of the asymmetric bilayer metasurface device in this experiment are: period P = 200 μm, substrate thickness H = 20 μm, semi-major axis r2 = r4 = 30 μm, semi-minor axis r1 = 10 μm, r3 = 25 μm for the upper elliptical cylinder, distance between the elliptical cylinders d = 80 μm, f = 50 μm, and semi-major and semi-minor axes of the lower elliptical cylinder are r2 = r4 = 30 μm, semi-minor axis r1 = 10 μm, r3 = 25 μm ... b =30μm, r a =10μm.

[0090] The structure was simulated using CST MWS, and the results are as follows: Figure 5 As shown. In the simulation, the incident light angle θ = 5° was set to explore the chiral response of the metasurface structure to light under specific conditions. Figure 5(A) presents the transmission spectra and simulated circular dichroism (CD) values ​​under illumination by left-handed and right-handed circularly polarized light (LCP). The peak CD observed near 1.35 THz gradually increases with increasing asymmetry parameter ΔS. A strong chiral response with a Q value of 900 and a CD value of 0.7 is achieved at 1.4 THz, as shown in the figure. Figure 5 As shown in (B). Figure 5 (B) Shows the magnitude of the circular dichroism response values ​​under different degrees of asymmetry. Among them, the circular dichroism value is the largest, 0.7, when the asymmetry ΔS = 0.43.

[0091] Figure 5 (C) To fix the minor axis size of the two upper elliptical cylinders, change the distance f of the upper elliptical cylinder to obtain the transmission spectrum; where f = 50 μm, f = 70 μm and f = 80 μm from top to bottom, the solid line represents the transmission coefficient of LCP incident, and RCP represents the transmission coefficient of RCP incident.

[0092] Considering that an increase in the incident light angle leads to a decrease in the Q value, the distance between the elliptical cylinders is treated as another degree of freedom. By adjusting the distance between the two elliptical cylinders, the CD value can be maintained or increased under different perturbation conditions. The results show... Figure 5 This is reflected in (D), showing that within a specific adjustment range, the value of CD reaches its optimum with adjustment, and the Q value also improves. Ultimately, the coupling degree between QBIC and circularly polarized light can be adjusted to achieve a chiral response of Q = 1254.6 and CD = 0.8 at 1.336 THz, further improving the sensing performance.

[0093] The beneficial effects of this embodiment:

[0094] This embodiment enables the realization of extremely high Q-factor resonance modes in terahertz metasurfaces. The intrinsic modes of BIC exhibit strong locality, significantly reducing radiation losses and thus improving the performance of the resonant device. This is particularly important for high-sensitivity sensing.

[0095] This embodiment proposes a C-based approach. i The three-dimensional design method based on point group symmetry can maintain good optical performance. By breaking the symmetry, an excellent sensing characteristic with a sensitivity of 21.5 GHz / RIU is achieved.

[0096] In this embodiment, by changing the incident angle, the metasurface can couple QBIC with different circularly polarized light, producing a significant circular dichroism response (CD>0.7) at 1.35 THz. This flexibility allows the metasurface to adapt to various optical applications, improving the applicability and functionality of the device.

[0097] This embodiment demonstrates that by adjusting geometric parameters in the three-dimensional structure (such as the distance between elliptical cylinders), the technical solution can significantly improve the circular dichroism response of the metasurface. This means that the metasurface can more effectively control the propagation path and phase information of circularly polarized light, thereby enhancing optical activity and providing new possibilities for chiral sensing.

[0098] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A C-based i A point-group symmetric double-layer terahertz BIC metasurface sensor, characterized in that, Includes the following steps: The upper elliptical cylindrical layer, the middle basal layer, and the lower elliptical cylindrical layer are arranged in a periodic pattern. The upper elliptical cylinder layer comprises a first elliptical cylinder and a second elliptical cylinder, and the lower elliptical cylinder layer comprises a third elliptical cylinder and a fourth elliptical cylinder, forming C. i Point group symmetry to realize bound states in continuous domains; By adjusting the difference in the minor axis lengths of the first and second elliptical cylinders, C is broken. i Symmetry to stimulate QBIC resonance; By adjusting the incident light angle, the chiral sensing mode is switched to achieve circular dichroism response detection.

2. The sensor according to claim 1, characterized in that, The upper and lower elliptical cylindrical layers are made of a perfectly conductive material, and the intermediate base layer is made of a polyimide material.

3. The sensor according to claim 1, characterized in that, The difference in the minor axis length between the first elliptical cylinder and the second elliptical cylinder is greater than or equal to 10 μm.

4. The sensor according to claim 1, characterized in that, Adjust the distance between the first elliptic cylinder and the second elliptic cylinder to maintain or increase the circular dichroism response value.

5. The sensor according to claim 1, characterized in that, The chiral sensing mode is activated when the incident light angle is 5°.

6. The sensor according to claim 1, characterized in that, The quality factor Q of the QBIC resonance is greater than or equal to 800.

7. The sensor according to claim 1, characterized in that, The period of the upper and lower elliptical cylindrical layers is 200 μm.

8. The sensor according to claim 1, characterized in that, The thickness of the intermediate substrate layer is 20 μm.

9. The sensor according to claim 1, characterized in that, The circular dichroism response value in the chiral sensing mode is greater than 0.

7.

10. The sensor according to claim 1, characterized in that, The sensor has a sensitivity of 21.5 GHz / RIU in QBIC mode.

Images