Fano resonance sensor based on graphene-grating and performance regulation and control method thereof

Abstract

The invention discloses a graphene-grating-based fano resonance sensor and a performance regulation and control method thereof. The sensor sequentially comprises a prism, a graphene layer, a silver dielectric layer, a silicon dioxide layer, a silicon grating and a sensing medium from top to bottom. A simple metal grating structure with a rectangular outline is used in a simple two-dimensional metamaterial, the sensitivity of the whole sensor model is influenced by adjusting the height and the thickness of the model, and the function of tunable incident range is achieved. The sensitivity is optimized through Fano resonance, and compared with the prior art, the sensitivity is greatly improved. In order to better optimize the sensitivity, the graphene-grating structure is introduced to form Fano resonance, under the condition of wave vector matching, a continuous state generated in the graphene-silver layer structure is coupled with a discrete state generated in the grating structure, Fano resonance is formed through excitation, and the performance indexes such as the sensitivity are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the field of sensor technology, and in particular relates to a graphene-grating-based Fano resonance sensor and a performance control method thereof. When the refractive index of the sensing medium changes, the sensing characteristics of the model of the present invention will respond to it with high sensitivity. Background Art

[0002] Fano resonance sensing is a pollution-free, label-free, real-time optical sensing technology, usually excited by light waves incident on the sensor surface. Unlike the Lorentz resonance line, which presents a symmetrical resonance line in the spectrum, the Fano resonance line is caused by destructive interference between continuous light and discrete light under specific phase matching conditions. Its main feature is that it can change rapidly within a narrow incident range. Therefore, sensors designed based on Fano resonance have become popular optical devices in the field of biosensing. Some people have proposed biosensors designed by two-dimensional materials TMDCs or graphene, and have performed relevant calculations. Although the unique optical properties of two-dimensional materials are taken into account, it is lacking that it only analyzes the surface plasmon resonance of the sensor, and does not consider the influence of Fano resonance on sensitivity. Therefore, the results obtained need further discussion and analysis.

[0003] In nano-optics, grating structures are often used to achieve Fano resonance. This is because grating structures can be combined with various dielectrics or metal materials, making it easier to excite narrower resonance peak spectral curves, thereby achieving higher sensitivity. The design of existing Fano resonance sensors focuses on the novelty of the design structure, such as Otto prism-coupled micro-nano structures composed of multilayer graphene and graphene prisms and subwavelength grating all-dielectric multilayer film structures. Patent CN 111239082 A discloses a silver grating surface plasma resonance sensor, which is a tunable resonant double-sided dielectric grating structure excited by vertically incident plane waves. The maximum sensitivity of the sensor can reach 192° / RIU. However, these structures are relatively complex, and the preparation also has high requirements on the process, making it difficult to use them on a large scale in industrial production. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a graphene-grating based Fano resonance sensor and its performance control method. The continuous state generated by the graphene-silver layer is coupled with the discrete state generated by the grating to form an asymmetric linear Fano resonance. By continuously adjusting the thickness of the material and the structure of the model, the influence of the change of the resonance structure parameters on the simulation results is analyzed, and then the optimal parameters when the sensor sensitivity and FOM are maximized are locked. It is concluded that the sensor model obtained by this structure has the advantages of high sensitivity, adjustable incident range, and simple preparation.

[0005] Technical solution: A graphene-grating-based Fano resonance sensor of the present invention comprises, from top to bottom, a coupling prism, a graphene layer, a silver dielectric layer, a silicon dioxide layer, a silicon grating and a sensing medium.

[0006] Furthermore, the prism material is SF10, the silver dielectric layer is composed of silver, and the graphene layer is composed of multiple layers of single-layer graphene with a thickness of 0.34 nm; at an incident wavelength of 633 nm, the refractive indices of the prism, silver layer, and graphene are 1.732, 0.0803+4.2347i, and 3+1.1491i, respectively; the initial refractive index of the sensing medium is 1.33, and then changes to 1.332, and the refractive index difference before and after is 0.002.

[0007] Furthermore, the graphene layer is a multi-layer structure with 1-8 layers, and the thickness of the graphene is:

[0008] d eff =n×H g

[0009] Where n is the number of graphene layers, H g is the thickness of a single layer of graphene.

[0010] Furthermore, the number of graphene layers is 3.

[0011] Furthermore, the sensing medium is a plasma water sensing medium.

[0012] The present invention also discloses a performance control method based on a graphene-grating-based Fano resonance sensor, comprising the following steps:

[0013] Step 1: construct a Fano resonance sensor based on graphene-grating;

[0014] Step 2, by setting the periodic port from top to bottom in the input direction to simulate the incident light, and taking the incident angle θ as a variable parameter to calculate the change curve of the reflectivity as the incident angle θ moves; when the refractive index of the sensing medium changes, the sensing characteristics of the Fano resonance sensor will respond to it with high sensitivity, which is manifested as a phase shift of the spectrum line, and the concentration of the sensing medium is adjusted to make the sensing medium change, and a second set of refractive indices is obtained;

[0015] Step 3, calculate the two sets of reflectivity data in step 2 by using the sensitivity calculation formula, obtain the sensitivity change curve, change the refractive index by changing the thickness or height of the material, and repeat steps 2-3 to adjust the sensitivity;

[0016] Step 4: After sensitivity adjustment, set the full width at half maximum as the sensor evaluation index.

[0017] Furthermore, in step 2, the concentration of the sensing medium is adjusted so that the sensing medium changes to Δn=10 -3 .

[0018] Furthermore, in step 3, the sensitivity S refers to the sensitivity of the detected variable to the change in refractive index, and the sensitivity S is expressed as:

[0019]

[0020] Wherein ΔR is the reflectivity change caused by the change of the sensing medium, and Δn is the change of the sensing medium. Substituting the two sets of different refractive index data into the above sensitivity formula, the sensitivity change curve is obtained.

[0021] Further, step 4 is specifically as follows: the full width at half maximum FWHM is an evaluation index of the sensor, which indicates the width of the incident light wavelength when the resonance depth reaches half. The narrower the FWHM of the resonance peak, the higher the resolution and the smaller the sensor loss. The quality factor FOM value can be evaluated by the shape of the resonance peak of the spectrum, which is equal to the ratio of the sensitivity S to the full width at half maximum FWHM of the resonance curve. The quality factor FOM is expressed as follows:

[0022]

[0023] From the definition of the quality factor FOM, we can see that when the sensitivity S is large, the smaller the FWHM is, the larger the FOM is, which means the performance of the sensor is better, otherwise it means the performance of the sensor is worse.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention can use a simple rectangular profile metal grating structure in a simple two-dimensional metamaterial, and by adjusting the height and thickness of the model, the sensitivity of the entire sensor model is affected, and the incident range can be tuned. Compared with other complex grating structures, the present invention has a simple structure and low requirements for the preparation process. The sensitivity is optimized by Fano resonance, and the sensitivity is greatly improved compared with the prior art. In order to better optimize the sensitivity, the present invention introduces a graphene-grating structure to form a Fano resonance. The structure is to deposit a layer of graphene on the Ag nanostructure. Under the condition of wave vector matching, the continuous state in the graphene-silver layer structure is coupled with the discrete state in the grating structure to excite and form a Fano resonance. Within the existing parameter adjustment range, the sensitivity can reach 265° / RIU. Compared with previous traditional sensors, performance indicators such as sensitivity have been significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the structure of the graphene-grating sensor of the present invention;

[0026] Figure 2is the curve of graphene-grating reflectivity R(θ) changing with the incident angle θ;

[0027] Figure 3 (a) is the change of reflectivity of the sensing medium with the incident angle when the RI is 1.332 and 1.333, (b) is the curve of the change of sensitivity with the incident angle obtained in (a);

[0028] Figure 4 (a) is the sensitivity peak S max The curve of the change of the thickness of the dielectric silver layer T3, (b) is the sensitivity peak S max Curve changing with grating height T4;

[0029] Figure 5 (a) is the sensitivity peak S max (a) is the curve showing the change of FOM value with the number of graphene layers, and (b) is the curve showing the change of FOM value with the number of graphene layers. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0031] like Figure 1 As shown, the model of the present invention is a graphene-grating composite sensing structure based on Fano resonance. When establishing the geometric model, the z-axis direction is taken as the vertical direction, and the material layers from top to bottom are prism (Prism), graphene layer (Graphene), silver dielectric layer (Ag), silicon dioxide layer (SiO2), silicon grating (Si) and plasma water sensing medium (Analyte). In this structure, the graphene coated on the silver layer can make the energy more localized and also play a role in preventing metal oxidation. When the imaginary part of the graphene conductivity is greater than zero, the graphene will show metallic properties.

[0032] When a transverse magnetic wave (TM) is incident on the graphene-silver layer from one side of the sensing medium at a certain angle, the metallic properties exhibited will stimulate the surface equidistribution excitation in the TM mode, producing a strong field localization effect. Under the condition of wave vector matching, the incident light passes through the graphene to the dielectric silver layer, forming a wider band in the reflection spectrum curve, providing a continuous state for the Fano resonance, and the optical effect is stable. As the light reaches the grating and is refracted by the high-refractive-index grating, part of the refracted light will be absorbed and consumed by the graphene for the second time and cannot return to the incident medium again, causing the energy of the reflected light to drop sharply, thereby forming the discrete state required for the Fano resonance. Under the condition of satisfying wave vector matching, the discrete state curve will redshift or blueshift within a certain wavelength range as the environmental parameters to be measured change, and then couple with the continuous state component of the same frequency, causing the shape of the reflection spectrum line to change dramatically, forming a sharp and narrow-linewidth asymmetric line type Fano resonance. As shown in Figure 2As shown, when the refractive index of the sensing medium changes, the sensing characteristics of the model of the present invention will respond highly sensitively to it.

[0033] In order to achieve the best performance of the designed structure, it is necessary to optimize and analyze the relevant structural parameters. By changing a single structural parameter to analyze the reflection spectrum, the optimal performance of the sensor is found, and the optimization of the sensor structural parameters is finally completed. The present invention modulates by changing the incident angle. One of the performance parameters of the sensor, sensitivity S, refers to the sensitivity of the detected variable to the change of the refractive index. The sensitivity S can be expressed as:

[0034]

[0035] Where ΔR is the reflectivity change caused by the change of the sensing medium, and Δn is the change of the sensing medium. By adjusting the concentration of the sensing medium so that Δn = 10 -3 , substitute the two sets of different refractive index data into the above sensitivity formula to obtain the sensitivity change curve.

[0036] The full width at half maximum (FWHM) is also an evaluation index of the sensor. It indicates the width of the incident light wavelength when the resonance depth reaches half. The narrower the FWHM of the resonance peak, the higher the resolution and the smaller the sensor loss. The quality factor FOM value can be evaluated by the shape of the resonance peak of the spectrum, which is equal to the ratio of the sensitivity S to the full width at half maximum (FWHM) of the resonance curve. The quality factor FOM is expressed as follows:

[0037]

[0038] From the definition of the quality factor FOM, we can know that when the sensitivity S is large, the smaller the FWHM is, the larger the FOM is, which means the performance of the sensor is better, otherwise it means the performance of the sensor is worse.

[0039] Example 1

[0040] In this embodiment, the grating is made of silicon material, the graphene deposited on the dielectric silver layer is a carbon nanomaterial, the incident wavelength is 633 nm, and the period P of the grating is 100 nm.

[0041] In this embodiment, the geometric construction of the above-mentioned Fano resonance sensor can be obtained. The steps are as follows:

[0042] (1) In order to construct a reflectivity Figure 2 The asymmetric linear Fano resonance shown in the figure is applied to the metallic properties of the two-dimensional material graphene. g =0.34nm is very thin. The present invention better simulates the thickness of graphene by setting transition boundary conditions. The thickness of graphene is d eff =n×H g, where n is the number of graphene layers, H g is the thickness of a single layer of graphene. In order to simulate the light wave excitation Fano resonance, the incident light is simulated by setting the periodic port from top to bottom in the input direction, and the incident angle θ is used as a variable parameter to calculate the change curve of the reflectivity as the incident angle θ moves.

[0043] (2) Figure 3 As shown in (a), when the refractive index of the sensing medium changes, the sensing characteristics of the model of the present invention will respond to it with high sensitivity, which is manifested as a phase shift of the spectrum line. Adjust the concentration of the sensing medium so that the sensing medium changes Δn=10 -3 , and obtain the second set of refractive indices.

[0044] (3) The two sets of reflectivity data in step (2) are calculated using the sensitivity calculation formula to obtain a sensitivity change curve. The sensitivity changes with the incident angle as shown in Figure 3 (b) as shown. Figure 3 The peak value of the curve in (b) is defined as S max , the peak value of sensitivity is selected as the identification index for judging the Fano sensor.

[0045] (4) Change the refractive index by changing the thickness or height of the material and repeat steps (2) and (3) to adjust the sensitivity.

[0046] Example 2

[0047] In this embodiment, the calculation and comparison of the sensitivity of the Fano resonance sensor can be obtained. The steps are as follows:

[0048] (1) The thickness of the silver layer of the dielectric layer is selected as a variable to analyze the sensitivity spectrum. Figure 4 (a) shows a curve showing the change of sensor sensitivity with dielectric layer thickness, which is determined by the thickness of the silicon dioxide layer. Figure 4 In (a), the sensitivity first increases gradually with the increase of the thickness of the silver layer of the dielectric layer, and then Ag The sensitivity reaches the highest value at 30 nm, and then decreases with the increase of the thickness of the silver layer of the dielectric layer. This is because at the beginning, as the thickness of the silver layer of the dielectric layer increases, the reflected signal in the graphene-silver layer and the light signal generated by the grating gradually couple to produce Fano resonance, thus obtaining a higher sensitivity peak. Ag After =30nm, as the thickness of the dielectric layer further increases, the coupling between graphene and the grating gradually decays, and the peak value of the Fano resonance sensitivity gradually decreases.

[0049] (2) Select the thickness of the adhesion layer silicon dioxide as a variable to analyze the sensitivity spectrum. Figure 4(b) shows a curve in which the thickness of the dielectric silver layer determines the sensitivity of the sensor as the thickness of the dielectric layer changes. Figure 4 (b) It can be seen that the sensitivity first increases with the increase of the thickness of the silver layer of the dielectric layer, and then increases with the thickness of the silver layer of the dielectric layer. SiO2 =400nm, and then the sensitivity decreases with the increase of the thickness of the silver layer of the dielectric layer. This is because the increase of silicon dioxide weakens the localization ability of photons. As the height of silicon dioxide continues to increase, the resonance curve gradually shifts to the right phase, and the peak sensitivity gradually decreases.

[0050] (3) Select the number of graphene layers as a variable to analyze the sensitivity spectrum. Figure 5 As shown in (a), this is a curve of the sensitivity of a sensor with a certain dielectric silver layer thickness and a certain silicon dioxide layer thickness changing with the dielectric layer thickness. Figure 5 (a) It can be seen that when the number of graphene layers changes from 1 to 8 layers, the sensitivity of the Fano resonance sensor increases first and then decreases; when covered with 3 layers of graphene, the maximum sensitivity of the Fano resonance sensor can reach 265° / RIU. The FOM value of the sensor under different numbers of graphene layers is calculated by the quality factor FOM value formula, as shown in Figure 5 (b) shows that the maximum FOM value is 577RIU -1 It can be seen that the performance of the Fano resonance sensor based on the graphene-grating structure of the present invention reaches the best when there are three layers of graphene.

[0051] Therefore, the present invention can verify the method of improving sensitivity through the graphene-grating composite micro-nano structure. Compared with the maximum sensitivity value of 192° / RIU in the graphene-silver grating sensor of patent CN 111239082A, the graphene-grating structure in the present invention can obtain a maximum value of 265° / RIU, and the sensitivity is greatly improved.

[0052] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A Fano resonance sensor based on graphene-grating, characterized in that: From top to bottom, it includes prism, graphene layer, silver dielectric layer, silicon dioxide layer, silicon grating and sensing medium.

2. A graphene-grating based Fano resonance sensor according to claim 1, characterized in that: The prism material is SF10, the silver dielectric layer is composed of silver, and the graphene layer is composed of multiple layers of single-layer graphene with a thickness of 0.34nm; at an incident wavelength of 633nm, the refractive indices of the prism, silver layer, and graphene are 1.732, 0.0803+4.2347i, and 3+1.1491i, respectively; the initial refractive index of the sensing medium is 1.33, and then changes to 1.332, and the refractive index difference before and after is 0.

002.

3. A graphene-grating based Fano resonance sensor according to claim 1, characterized in that: The number of graphene layers is 1-8, and the thickness of graphene is: d eff =n×H g Where n is the number of graphene layers, H g is the thickness of a single layer of graphene.

4. A graphene-grating based Fano resonance sensor according to claim 2, characterized in that: The number of graphene layers is 3.

5. The graphene-grating based Fano resonance sensor according to claim 1, characterized in that: The sensing medium is a plasma water sensing medium.

6. A method for controlling the performance of the graphene-grating based Fano resonance sensor according to claim 1, characterized in that: The steps include: Step 1: construct a Fano resonance sensor based on graphene-grating; Step 2, by setting the periodic port from top to bottom in the input direction to simulate the incident light, and taking the incident angle θ as a variable parameter to calculate the change curve of the reflectivity as the incident angle θ moves; when the refractive index of the sensing medium changes, the sensing characteristics of the Fano resonance sensor will respond to it with high sensitivity, which is manifested as a phase shift of the spectrum line, and the concentration of the sensing medium is adjusted to make the sensing medium change, and a second set of refractive indices is obtained; Step 3, calculate the two sets of reflectivity data in step 2 by using the sensitivity calculation formula, obtain the sensitivity change curve, change the refractive index by changing the thickness or height of the material, and repeat steps 2-3 to adjust the sensitivity; Step 4: After sensitivity adjustment, set the full width at half maximum as the sensor evaluation index.

7. The performance control method according to claim 6, characterized in that: In step 2, the concentration of the sensing medium is adjusted so that the sensing medium changes to Δn=10 -3 .

8. The performance control method according to claim 6, characterized in that: In step 3, the sensitivity S refers to the sensitivity of the detected variable to the change of the refractive index, and the sensitivity S is expressed as: Wherein ΔR is the reflectivity change caused by the change of the sensing medium, and Δn is the change of the sensing medium. Substituting the two sets of different refractive index data into the above sensitivity formula, the sensitivity change curve is obtained.

9. The performance control method according to claim 6, characterized in that: Step 4 is as follows: The full width at half maximum (FWHM) is an evaluation index of the sensor, which indicates the width of the incident light wavelength when the resonance depth reaches half. The narrower the FWHM of the resonance peak, the higher the resolution and the smaller the sensor loss. The quality factor FOM value can be evaluated by the shape of the resonance peak of the spectrum, which is equal to the ratio of the sensitivity S to the full width at half maximum (FWHM) of the resonance curve. The quality factor FOM is expressed as follows: From the definition of the quality factor FOM, we can see that when the sensitivity S is large, the smaller the FWHM is, the larger the FOM is, which means the performance of the sensor is better, otherwise it means the performance of the sensor is worse.

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