Dual-wavelength circular dichroism refractive index sensor

Abstract

The invention discloses a dual-wavelength circular dichroism refractive index sensor, which belongs to the optoelectronic device technology, and comprises an MgF2 substrate, first elliptical nano-columns are arranged on the MgF2 substrate in a rectangular array, second elliptical nano-columns are arranged on the MgF2 substrate in a rectangular array, and the first elliptical nano-columns and the second elliptical nano-columns are arranged in a staggered manner. The orientation angle of the first elliptical nano-column is theta 1, the orientation angle of the second elliptical nano-column is theta 2, and theta 1 is not equal to theta 2 and-theta 2. According to the mode, based on the principle of a continuous spectrum bound state, chiral resonance with strong circular dichroism and high quality factors is realized at the same time of mid-infrared dual wavelengths; in the refractive index sensing application, the sensor has a single-wavelength circular dichroism sensing mode and shows ultrahigh sensitivity and an excellent sensing merit figure; meanwhile, the refractive index sensor has a dual-wavelength circular dichroism sensing mode, the refractive index change is represented by wavelength spacing, the stability of the sensor is effectively improved, and the refractive index sensor with high performance and high stability is realized by combining the two sensing modes.

Description

Technical Field

[0001] The invention relates to the technical field of optoelectronic devices, and in particular to a dual-wavelength circular dichroism refractive index sensor. Background Art

[0002] Biochemical sensors have broad application prospects in medical diagnosis, environmental monitoring, food safety, drug development, industrial production and other fields. With the continuous advancement of sensing technology and the continuous improvement of sensor performance requirements in practical applications, biochemical sensors are gradually developing towards high sensitivity, high selectivity and multifunctional integration. For refractive index sensors, key performance indicators include sensitivity and figure of merit (FOM). Sensitivity reflects the device's ability to respond to changes in its surface refractive index and is an important parameter for measuring its detection efficiency; the figure of merit (FOM) comprehensively considers the sensitivity and the quality factor (Q-factor) of the resonance mode to evaluate the sensor performance more comprehensively. Therefore, improving sensitivity and optimizing the figure of merit are the core goals of improving the performance of refractive index sensors. The current mainstream refractive index sensor design uses subwavelength microstructure metamaterials to achieve light field control. However, the electromagnetic resonance mode commonly used in the microstructure has a high radiation loss, resulting in an excessively large resonance linewidth, which makes the figure of merit (FOM) low and difficult to meet the requirements of high-performance refractive index sensing. To address this issue, the emerging optical resonance mode of the bound state continuum (BIC) has become a research hotspot. The continuum bound state is a resonant mode that coexists with the continuum but remains non-radiatively localized. It has an ultra-high quality factor and extremely low loss, and can significantly enhance the interaction between light and matter. This feature has opened up new directions and ideas for the design of high-performance refractive index sensors.

[0003] Circular dichroism (CD), as an important means of detecting and characterizing chiral enantiomers, has also been widely used in refractive index sensing. Compared with traditional sensing methods based on transmission peaks or absorption peaks, circular dichroism sensing has significant advantages. For example, it can simultaneously detect the refractive index and molecular chirality, thereby improving the versatility of the device. In addition, this method can also effectively eliminate the interference of non-chiral molecules on the sensing results, further improving the selectivity and accuracy of the detection. However, the current technology for refractive index sensing based on circular dichroism mainly focuses on single-wavelength circular dichroism sensing. This single-wavelength method is easily interfered by external temperature, humidity changes and instrument drift, which has an adverse effect on the accuracy of sensing and limits its practicality and reliability.

[0004] Existing circular dichroism-based refractive index sensors generally use single-wavelength circular dichroism for refractive index detection. In 2022, Liu Q et al. proposed a metasurface refractive index sensor based on a nanohole double-layer silicon flat plate array structure based on the principle of continuous domain bound state [see reference: QS Liu, M.-H. Chao, W.-J. Zhang, et al., Annalen der Physik, 534, 2200263 (2022)], such as Figure 8 The structure realizes two chiral resonances in the near-infrared band, and uses these two circular dichroism peaks to sense the refractive index separately. The simulation results show that the sensitivity of the device is 283nm / RIU and 80nm / RIU, respectively, and the figure of merit is 720RIU -1 and 228RIU -1 .

[0005] In 2024, Cheng Y et al. proposed a cross-hole structure based on the principle of continuous domain bound state [see reference: Y.Cheng, J.Li, D.Zeng, W.Liu, Z.Liu, et al., Optics Letters, 49, 165-168 (2024)], such as Fig. 9 As shown. The structure realizes a chiral resonance with a high quality factor in the near-infrared band, and uses the circular dichroism peak for refractive index sensing. Simulation results show that the sensitivity of the sensor device is 136.2nm / RIU and the figure of merit (FOM) is 1135RIU -1 .

[0006] Based on this, the present invention designs a dual-wavelength circular dichroism refractive index sensor to solve the above problems. Summary of the invention

[0007] In view of the above-mentioned shortcomings of the prior art, the present invention provides a dual-wavelength circular dichroism refractive index sensor.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] A dual-wavelength circular dichroism refractive index sensor comprises a MgF2 substrate: a first elliptical nanocolumn is arranged in a rectangular array on the MgF2 substrate, a second elliptical nanocolumn is arranged in a rectangular array on the MgF2 substrate, and the first elliptical nanocolumn and the second elliptical nanocolumn are arranged alternately, an orientation angle of the first elliptical nanocolumn is θ1, an orientation angle of the second elliptical nanocolumn is θ2, θ1≠θ2 and θ1≠-θ2.

[0010] Furthermore, the first elliptical nanorod and the second elliptical nanorod are made of amorphous silicon.

[0011] Furthermore, the short axis d1 = 1 μm and the long axis d2 = 2.4 μm of the first elliptical nanorod and the second elliptical nanorod.

[0012] Furthermore, the height of the first elliptical nanorod and the second elliptical nanorod is h=1.35 μm.

[0013] Furthermore, θ1 = 32.5°.

[0014] Furthermore, θ2 = 37.5°.

[0015] Furthermore, the period of the first elliptical nanorod and the second elliptical nanorod in the x and y directions is P x =3.92μm, P y =2.8μm.

[0016] Beneficial Effects

[0017] The present invention is based on the principle of continuous spectrum bound states, and simultaneously realizes chiral resonance of strong circular dichroism and high quality factor in mid-infrared dual wavelengths; in the application of refractive index sensing, the sensor has a single-wavelength circular dichroism sensing mode that exhibits ultra-high sensitivity and excellent sensing figure of merit; at the same time, it has a dual-wavelength circular dichroism sensing mode that characterizes the refractive index change with the wavelength spacing, which effectively improves the stability of the sensor. Combining these two sensing modes, a high-performance and high-stability refractive index sensor is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 The main structure of the dual-wavelength circular dichroism refractive index sensor of the present invention is three-dimensional. Figure 1 ;

[0020] Figure 2 The structure diagram of the dual-wavelength circular dichroism refractive index sensor of the present invention is a three-dimensional structure diagram. Figure 2 ;

[0021] Figure 3 A top view of a first elliptical nanocolumn and a second elliptical nanocolumn of a dual-wavelength circular dichroism refractive index sensor structure of the present invention;

[0022] Figure 4The transmission spectrum and circular dichroism spectrum of a dual-wavelength circular dichroism refractive index sensor of the present invention under the conditions of θ1=-32.5° and θ2=-37.5° orientation angles;

[0023] Figure 5 Transmission spectra and CD spectra of a dual-wavelength circular dichroism refractive index sensor of the present invention at the orientation angles of (a) θ1 = θ2 = 0°, (b) θ1 = θ2 = -30°, and (c) θ1 = -30°, θ2 = -45° for a metasurface;

[0024] Figure 6 The electric field distribution diagram on the resonant xy plane at 50.48 THz under (a) RCP and (b) LCP excitation of the present invention; the electric field distribution diagram on the resonant xy plane at 51.84 THz under (c) LCP and (d) RCP excitation;

[0025] Figure 7 (a) CD spectra under different ambient refractive indices of the present invention, (b) and (c) showing the relationship between the frequency of qBIC1 and qBIC2 modes and their frequency intervals and the refractive index;

[0026] Figure 8 (a) and (b) are structural diagrams of circular dichroism refractive index sensors in the prior art, and (c) and (d) are environmental refractive index sensing effect diagrams;

[0027] Fig. 9 (a) The structure diagram of the circular dichroism refractive index sensor in the prior art and (b) the environmental refractive index sensing effect diagram.

[0028] The numbers in the figure represent:

[0029] 1. MgF2 substrate 2. First elliptical nanocolumn 3. Second elliptical nanocolumn. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The present invention will be further described below in conjunction with the embodiments.

[0032] Example 1

[0033] Please refer to the instruction manual Figure 1-6A dual-wavelength circular dichroism refractive index sensor comprises a MgF2 substrate 1: a first elliptical nanocolumn 2 is arranged in a rectangular array on the MgF2 substrate 1, a second elliptical nanocolumn 3 is arranged in a rectangular array on the MgF2 substrate 1, and the first elliptical nanocolumn 2 and the second elliptical nanocolumn 3 are arranged alternately, an orientation angle of the first elliptical nanocolumn 2 is θ1, an orientation angle of the second elliptical nanocolumn 3 is θ2, θ1≠θ2 and θ1≠-θ2.

[0034] The first elliptical nanorod 2 and the second elliptical nanorod 3 are made of amorphous silicon.

[0035] The short axis d1 = 1 μm and the long axis d2 = 2.4 μm of the first elliptical nanocolumn 2 and the second elliptical nanocolumn 3 .

[0036] The height of the first elliptical nanorod 2 and the second elliptical nanorod 3 is h=1.35 μm.

[0037] θ1=32.5°.

[0038] θ2=37.5°.

[0039] The period of the first elliptical nanorod 2 and the second elliptical nanorod 3 in the x and y directions is P x =3.92μm, P y =2.8μm.

[0040] like Figure 5 As shown, the present application achieves CDs of up to -0.88 / 0.92 at frequencies of 50.48THz and 51.82THz, respectively, and Q values ​​of 3873 / 7196, thereby realizing dual-channel chiral resonance based on quasi-continuous domain bound states;

[0041] Figure 6 An in-depth analysis of the physical mechanism of these two resonances, the surface charge distribution and the current vector show that the 50.48THz mode qBIC1 is regarded as a pair of reverse electric dipoles along the long axis, and the 51.83THz mode qBIC2 is regarded as a pair of reverse magnetic dipoles perpendicular to the long axis section of the ellipse. When the in-plane symmetry breaking is not introduced, the electromagnetic field modes equivalent to these two resonances cancel each other out and thus form a local field that cannot be observed in the far field. After the breaking is introduced, a quasi-continuous domain bound state is formed. By introducing a structural design method that introduces in-plane symmetry breaking, the circular dichroism and the quality factor of the resonance are controlled. In addition, the two resonances show huge differences under the incidence of left-handed circularly polarized and right-handed circularly polarized light, resulting in ultra-high circular dichroism.

[0042] Figure 7It is shown that by changing the refractive index of the environment around the device, the change of the far-field information (transmittance) of the metasurface is observed, and the environmental refractive index is characterized by the far-field information. Affected by temperature, humidity fluctuations and inherent drift of the instrument, the obtained spectrum will be artificially offset, which may make traditional single resonance sensing inaccurate, limiting its application in complex environments. However, this problem can be solved by converting single resonance sensing into dual resonance sensing, and converting the tracking of the resonance position into analysis of the distance between the two resonance peaks. When external conditions fluctuate, the two resonance peaks are red-blue shifted at the same time, thereby reducing the spectral shift caused by environmental and instrument fluctuations to a certain extent. The present application not only achieves excellent sensing sensitivity and sensing merit by utilizing two resonance peaks for separate sensing, but also proposes to use the change in the spacing of the dual circular dichroism peaks to characterize the change in the environmental refractive index, thereby improving the stability of the sensing. As shown in FIG. Figure 7 As shown in the figure, when the ambient refractive index increases from 1 to 1.3, the two resonance positions move significantly, and the distance between the double resonances changes almost linearly. When the two circular dichroism peaks are used for refractive index sensing alone, the sensing sensitivities are as high as 18.2THz / RIU and 9.26THz / RIU, respectively, and the corresponding merits are 1397RIU -1 、1286RIU -1 When the spacing between two resonances is used for refractive index sensing, the sensing sensitivity is slightly reduced to 8.94 THz / RIU, but the spectral shift caused by environmental and instrument fluctuations can be effectively reduced, thus enhancing the stability of the sensing.

[0043] The present invention is based on the principle of continuous spectrum bound states, and simultaneously realizes chiral resonance of strong circular dichroism and high quality factor in mid-infrared dual wavelengths; in the application of refractive index sensing, the sensor has a single-wavelength circular dichroism sensing mode that exhibits ultra-high sensitivity and excellent sensing figure of merit; at the same time, it has a dual-wavelength circular dichroism sensing mode that characterizes the refractive index change with the wavelength spacing, which effectively improves the stability of the sensor. Combining these two sensing modes, a high-performance and high-stability refractive index sensor is realized.

[0044] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-wavelength circular dichroism refractive index sensor, comprising a MgF2 substrate (1), characterized in that: A first elliptical nanocolumn (2) is arranged in a rectangular array on a MgF2 substrate (1), and a second elliptical nanocolumn (3) is arranged in a rectangular array on the MgF2 substrate (1), and the first elliptical nanocolumn (2) and the second elliptical nanocolumn (3) are arranged in a staggered manner, the orientation angle of the first elliptical nanocolumn (2) is θ1, the orientation angle of the second elliptical nanocolumn (3) is θ2, θ1≠θ2 and θ1≠-θ2.

2. The dual-wavelength circular dichroism refractive index sensor according to claim 1, characterized in that: The first elliptical nanocolumn (2) and the second elliptical nanocolumn (3) are made of amorphous silicon.

3. The dual-wavelength circular dichroism refractive index sensor according to claim 2, characterized in that: The short axis d1 of the first elliptical nanocolumn (2) and the long axis d2 of the second elliptical nanocolumn (3) is 1 μm and 2.4 μm respectively.

4. The dual-wavelength circular dichroism refractive index sensor according to claim 3, characterized in that: The height of the first elliptical nanocolumn (2) and the second elliptical nanocolumn (3) is h=1.35 μm.

5. The dual-wavelength circular dichroism refractive index sensor according to claim 4, characterized in that: θ1=32.5°.

6. The dual-wavelength circular dichroism refractive index sensor according to claim 5, characterized in that: θ2=37.5°.

7. The dual-wavelength circular dichroism refractive index sensor according to claim 6, characterized in that: The period of the first elliptical nanorod (2) and the second elliptical nanorod (3) in the x and y directions is P x =3.92μm, P y =2.8μm.

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