On-demand active tuning high-performance refractive index sensor

Abstract

The invention discloses a high-performance refractive index sensor capable of actively tuning on demand, and relates to the technical field of micro-nano optical devices. The sensor comprises a strip-shaped grating which is made of Dirac semimetal and serves as a sensor main body; the gold electrodes are arranged at the ports on the two sides of the strip-shaped grating; the refractive index sensing background field is composed of a gas background, and the strip-shaped grating and the gas to be measured are both arranged in the refractive index sensing background field. Generally, along with increase or decrease of the ambient background refractive index, the performance of the sensor is reduced due to leakage of a resonance state. When the sensor is used, the Fermi level of the Dirac semimetal grating is regulated and controlled by increasing or reducing the bias voltage on the gold electrode, so that the leakage of a resonance state is inhibited, and the performance of the sensor is enhanced. Essentially, according to the invention, the active adjustable bias voltage and the topological characteristics of a bound state (BIC) in a continuous spectrum are utilized, so that the BIC under the background of different refractive indexes reciprocates, the resonance state is always maintained at the level of a high Q factor, and the performance of the sensor is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of micro-nano optical device equipment, and in particular to a high-performance refractive index sensor that can be actively tuned on demand. Background Art

[0002] For refractive index sensors, the range of sensing detection, detection sensitivity, detection advantage value and whether it is actively adjustable are the focus of attention. However, for sensors based on surface plasmon and exciton resonance modes, there is a large radiation loss in the mode itself, which makes the quality factor and sensing performance not excellent. At the same time, for such devices, when it comes to different refractive index ranges, it is often necessary to adjust the structure according to the required refractive index range, which not only limits the application range of refractive index sensors, but also increases the cost of application. Therefore, the use of new materials of active adjustable type can efficiently and flexibly respond to changes in the refractive index environment by regulating the voltage bias method. As a new type of three-dimensional graphene material, Dirac semimetals exhibit different properties in different frequency modes. In the low and medium frequencies of the terahertz band, they are mainly metal responses, mainly showing reflection properties. At medium and high frequencies, they show the response properties of the medium, mainly transmission. And compared with two-dimensional materials such as graphite, Dirac semimetals can be designed in three-dimensional structures. While having adjustable dynamic conductivity, they are not easily disturbed by the external electromagnetic environment, which makes their application prospects broader.

[0003] Current refractive index sensors generally have the problem of decreased sensing performance as the ambient refractive index changes, and their detection range is not wide enough, which is also a difficulty. For this reason, it is particularly important to design a wide-range high-performance sensor device that is actively adjustable according to the refractive index requirements. The bound state in the continuous spectrum is a type of localized state that is located in the continuous spectrum but remains bound. Its biggest feature is that it does not radiate outward and cannot be directly excited by the external field. Therefore, it has an infinite quality factor and lifetime, providing an ideal way for sensing detection. The present invention provides a high-performance refractive index sensor that can be actively tuned on demand to solve the technical problems of the current refractive index sensor devices with limited sensing range and decreased sensing performance as the ambient refractive index changes, as well as the goal of active regulation and optimization for the optimization of a specific refractive index. Summary of the invention

[0004] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0005] A high-performance refractive index sensor with on-demand active tuning, comprising:

[0006] A strip grating, which is made of a Dirac semimetal and constitutes a sensor body;

[0007] A gold electrode, arranged at the port of the strip grating;

[0008] The refractive index sensing background field is composed of a gas background, and the strip grating and the gas to be measured are filled in the refractive index sensing surrounding environment.

[0009] Furthermore, Dirac semimetals specifically include Na 3 Bi、Cd 3 As 2 One or more of these.

[0010] Furthermore, the gold electrode is made of gold.

[0011] Furthermore, the strip grating is arranged in a periodic structure in the x direction and is designed as an infinitely long structure in the y direction, and its thickness is equal to the period.

[0012] Furthermore, the period w of the strip grating in the x direction is 3500 nm, and the duty cycle of the strip grating is 60%.

[0013] Furthermore, the strip grating structure width P x =0.6*w=2100nm, and its height h=w=3500nm.

[0014] Furthermore, when performing measurements, the bias voltage of the metal electrode needs to be adjusted so that the Fermi of the strip grating changes, thereby adapting to changes in the refractive index sensing background field.

[0015] Furthermore, during detection, the incident light wave emitted into the strip grating is within the terahertz range.

[0016] Furthermore, the resonance wavelength of the strip grating is the same as the wavelength band of the incident light wave.

[0017] The beneficial effects of the present invention are as follows:

[0018] 1. The present invention combines BIC and Dirac semimetal to efficiently and accurately detect the ambient refractive index, and uses an adjustable bias voltage to change the Fermi level of the Dirac semimetal, so that the quasi-BIC under different refractive index backgrounds maintains a high Q factor level.

[0019] 2. When the present invention is used, when the ambient background refractive index changes to a certain extent, whether it increases or decreases, the performance of the sensor will decrease due to the leakage of the resonance state. At this time, the bias voltage on the gold electrode can be actively adjusted to increase or decrease the Fermi level of the Dirac semi-metal grating, so that the field of the resonance state is re-bound in the sensor, thereby enhancing the sensing performance of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the main structure of the present invention;

[0021] Figure 2 is a schematic diagram of the structure of the refractive index sensor in the environment of the present invention;

[0022] Figure 3 It is the electric field and magnetic field distribution diagram of the quasi-BIC mode in the present invention;

[0023] Figure 4 is the transmission spectrum of the Dirac semi-metallic grating refractive index sensor under different refractive indices of the present invention;

[0024] Figure 5 It is a diagram showing the change of sensor performance, environmental refractive index and Fermi level in the structure of the present invention.

[0025] Figure numerals: 1, strip grating; 2, gold electrode; 3, refractive index sensing background field. DETAILED DESCRIPTION

[0026] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0027] The present application provides a high-performance refractive index sensor with active tuning on demand, which aims to solve the technical problems that the sensing range of current refractive index sensors is limited and the advantage value decreases with the change of the ambient refractive index, and provides the following technical solutions. Figure 1-Figure 5 Make a detailed description:

[0028] A high-performance refractive index sensor with on-demand active tuning, comprising:

[0029] A strip grating 1, wherein the strip grating 1 is made of a Dirac semimetal and constitutes a sensor body;

[0030] A metal electrode 2, arranged at the port of the strip grating 1;

[0031] The refractive index sensing background field 3 is composed of a gas background, and the strip grating 1 and the gas to be measured are both arranged in the refractive index sensing background field 3 .

[0032] In order to better explain the characteristics of the high-performance refractive index sensor that can be actively tuned on demand according to the present invention, additional explanations are given first:

[0033] The main performance indicators of the refractive index sensor include sensitivity (Sensitivity, S) and figure of merit (FOM), where sensitivity refers to the ratio between the sensor output variable and the change in the measured signal. If the change in the measured signal causes a greater change in the sensor output signal, the higher the sensor sensitivity is, and the more accurately it can detect tiny signal changes. The calculation formula for sensitivity is as follows:

[0034]

[0035] Where: Δλ is the offset of the resonant wavelength, Δn is the change in the refractive index of the object to be measured;

[0036] In addition to sensitivity and detection limit, sensor size, Q value and sensing range are also commonly used performance indicators. Under the same performance, the smaller the sensor, the easier it is to integrate.

[0037] Q factor refers to the ratio of the total energy stored in the resonant cavity to the leaked energy per unit time, which characterizes the ability of the resonant device to store light fields. Devices with high Q factors can bind more light fields, enhance the interaction between light and the object to be measured in the resonant cavity, and play a positive role in improving the performance of the sensor. The calculation formula of Q factor is as follows:

[0038]

[0039] Where: R is the wavelength at the resonance mode, and FWHM corresponds to the half-maximum width of its resonance peak.

[0040] The FOM (Figure Of Merit) value represents the normalized sensing performance index of the device. The larger the FOM value, the better the performance of the device in response to changes in the external refractive index environment.

[0041] Depending on the dimensions of the periodic structure, the design of metasurface structure devices can be divided into one-dimensional, two-dimensional and three-dimensional. Structures of different dimensions require different designs and price processes, and have different photon energy bands.

[0042] The periodic device in the present invention is a one-dimensional infinitely long grating array, which is periodically arranged in one direction and infinitely long in another direction. The structure is simple in design and easy to prepare.

[0043] Specifically in this embodiment, the specific implementation steps and principle of the grating structure in the present invention are as follows:

[0044] During measurement, the strip grating 1 is placed in the refractive index sensing background field 3. When the refractive index of the refractive index sensing background field 3 changes (achieved by changing the type of gas introduced), the spectrum corresponding to the resonance mode in the strip grating 1 will move, and the degree of movement is related to the magnitude of the refractive index change. If the refractive index sensing background field 3 changes significantly, in order to improve the performance of the sensor, it is necessary to control the bias voltage of the metal electrode 2 so that the Fermi of the strip grating 1 changes, thereby adapting to the change in the refractive index of the refractive index sensing background field 3. By changing the type of air environment, that is, the refractive index of the refractive index sensing background field 3, the resonant wavelength in the resonant cavity is shifted, thereby showing corresponding movement in the corresponding transmission and reflection spectra, and finally obtaining the detection of the refractive index change.

[0045] Furthermore, by optimizing the structural parameters, the period is set to w = 3500nm, the height h = w, and the period in the x direction P x =0.6*w, specifically, the Dirac semimetal type used in this periodic structure is Na 3 Bi and Cd 3 As 2 These two types of materials have large background dielectric constants and small degeneracy factors. The key core problem of conventional refractive index sensors is that their performance often decreases significantly with the change of refractive index, and their detection range is very narrow. In addition, sensors with metasurface structure design have the characteristic of high processing difficulty. Through the grating design, it is possible to maintain excellent sensing performance over a wider detection range. The grating can also significantly reduce the difficulty of its processing and manufacturing, which is convenient for the miniaturization and integration of devices. It should be noted that when the incident light wave is in the terahertz band and the wavelength of the incident light wave matches the period of the strip grating 1 structure, the light wave can be coupled into the grating and interact with each other, thereby producing a resonance phenomenon.

[0046] In order to verify the effect of the present invention, the incident light is set to a plane wave with normal TE incidence, and the surrounding background environment is initially set to air, that is, n = 1, as shown in FIG. Figure 1 shown.

[0047] In order to make the sensor device angle-insensitive and universal, we solved the resonance band of the structure and selected a mode on the TE energy band as the sensing mode.

[0048] The simulated electric field of this resonance mode is as follows Figure 2 As shown, its electromagnetic field is mainly concentrated in the Dirac semi-metal grating structure layer and the grating slits.

[0049] By changing the refractive index of the background air environment, such as Figure 3As shown, the S value and FOM parameter under different refractive indices can be obtained. In addition, by tuning the Fermi level of the Dirac semimetal, it is obtained that the designed sensor has extremely high FOM values ​​in a wide background range, that is, has extremely high sensing performance.

[0050] To provide the physical origin of high-performance sensing, we introduce the far-field polarization of the light field and prove that the mechanism of the extremely high FOM value comes from the reciprocating movement of two pairs of topological BICs in momentum space. Figure 4 As shown, with the change of refractive index and Fermi level, the quasi-BIC mode at the center of momentum space always remains near BIC (circle), and therefore has an ultra-high Q factor. Therefore, the quasi-BIC mode can maintain an extremely high FOM as a sensing detection signal.

[0051] Figure 5 The figure shows the superimposed transmission spectra under different refractive index environmental backgrounds, where n is the environmental background refractive index. When the refractive index changes linearly, the change in the obtained resonant wavelength is also linear, which means that when the device is used for sensing, there is no need to record the refractive indices corresponding to all resonant wavelengths. It is only necessary to record the positions of the resonant wavelengths under the initial few refractive indices to infer the refractive indices corresponding to different resonant wavelengths.

[0052] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-performance refractive index sensor with active tuning on demand, characterized in that: include: A strip grating (1), wherein the strip grating (1) is composed of a Dirac semimetal and constitutes a sensor body; A metal electrode (2) arranged at the port of the strip grating (1); The refractive index sensing background field (3) is composed of a gas background, and the strip grating (1) and the gas to be measured are both arranged in the refractive index sensing background field.

2. The high-performance refractive index sensor with active tuning on demand according to claim 1, characterized in that: The Dirac semimetal specifically includes one or more of Na3Bi and Cd3As2.

3. The high-performance refractive index sensor with active tuning on demand according to claim 1, characterized in that: The metal electrode (2) is made of gold.

4. The high-performance refractive index sensor with active on-demand tuning according to claim 1, characterized in that: The strip grating (1) is arranged in a periodic structure in the x direction and is designed as an infinitely long structure in the y direction, and its thickness is equal to the period.

5. The high-performance refractive index sensor with active tuning on demand according to claim 4, characterized in that: The period w of the strip grating (1) in the x direction is 3500 nm, and the duty cycle of the strip grating (1) is 60%.

6. The high-performance refractive index sensor with active on-demand tuning according to claim 5, characterized in that: The strip grating (1) has a structural width Px=0.6*w=2100nm, and a height h=w=3500nm.

7. The high-performance refractive index sensor with active tuning on demand according to claim 1, characterized in that: When measuring, the bias voltage of the metal electrode (2) can be adjusted to change the Fermi of the strip grating (1), thereby dynamically adapting to the change of the refractive index sensing background field (3).

8. The high-performance refractive index sensor with active tuning on demand according to claim 1, characterized in that: When performing detection, the incident light wave emitted into the strip grating (1) is within the terahertz band.

9. The high-performance refractive index sensor with active tuning on demand according to claim 8, characterized in that: The resonance wavelength of the strip grating (1) appears within the wavelength band of the incident light wave.

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