Fano resonance sensor based on surface plasmon coupled planar waveguide

Abstract

The invention discloses a Fano resonance sensor based on a surface plasmon coupled planar waveguide. The Fano resonance sensor sequentially comprises a zinc selenide prism, a bismuth selenide layer Bi2Se3, a Teflon layer Teflon, a silicon dioxide layer SiO2, a TiO2 layer and a dielectric layer to be measured from top to bottom. Compared with a traditional sensor, the sensing characteristic spectrum line width of the model is narrower, the local electromagnetic field is greatly enhanced, the radiation loss of the traditional SPR sensor is remarkably reduced, and the sensitivity is improved by at least two orders of magnitude. The SPR effect excited by the bismuth selenide material is coupled with a PWG mode generated by a planar waveguide structure composed of silicon dioxide, titanium dioxide and a to-be-detected medium to generate the optical sensor with Fano resonance as a mechanism, the sensitivity can reach 7700 RIU <-1 > or above within an existing parameter adjusting range, and compared with a traditional SPR sensor, the sensitivity of the optical sensor is greatly improved. Performance indexes such as sensitivity are improved by 2-3 orders of magnitude.

Description

Technical Field

[0001] The invention belongs to the field of optical sensing, and in particular relates to a Fano resonance sensor based on a surface plasmon coupled planar waveguide. Background Art

[0002] Surface plasmon resonance (SPR) technology has the advantages of fast response speed, label-free detection, real-time dynamic detection, etc., and is widely used in many fields such as biomedicine, environmental pollution detection, and food safety. The SPR technology sensor based on the traditional configuration generally excites the corresponding SPR resonance mode through precious metal materials such as gold and silver, but it faces unavoidable intrinsic loss, resulting in the detection sensitivity and resolution of the instrument being too low, and the sensing performance needs to be further improved. Although the biosensor based on molybdenum disulfide nanoflowers and monolayer graphene sensitization designed in CN116754535A solves the problems of difficult modification and insufficient functionalization of the sensor, the improved sensing performance is still limited. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a Fano resonance sensor based on surface plasmon coupled planar waveguide to improve the sensing characteristics of existing traditional optical sensors.

[0004] Technical solution: The Fano resonance sensor based on a surface plasmon coupled planar waveguide of the present invention comprises, from top to bottom, a zinc selenide prism ZnSe Prism, a bismuth selenide layer Bi2Se3, a Teflon layer Teflon, a silicon dioxide layer SiO2, a titanium dioxide layer TiO2 and a medium layer to be measured.

[0005] Furthermore, the thickness of the zinc selenide prism ZnSe Prism is set to 0.9-1.2 μm, and under the premise of an operating wavelength of 1.89 μm, the corresponding refractive index is 2.4479.

[0006] Furthermore, the thickness of the bismuth selenide layer Bi2Se3 is set at 0.048-0.052 μm.

[0007] Furthermore, the thickness of the Teflon layer is set to 2.8-3.2 μm, and the refractive index is 1.3.

[0008] Furthermore, the silicon dioxide layer SiO2 has a thickness of 0.12-0.16 μm, and a corresponding refractive index of 1.4318.

[0009] Furthermore, the thickness of the titanium dioxide layer TiO2 is 0.06-0.08 μm, and the corresponding refractive index is 2.1237.

[0010] Furthermore, the medium to be tested includes water and ethanol.

[0011] Furthermore, when water is selected as the medium to be tested, the thickness of the medium to be tested is 0.5-1 μm, and the refractive index is 1.333.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) Compared with traditional sensors, the sensing characteristic spectral line width of the model of the present invention is narrower, the local electromagnetic field is greatly enhanced, and the radiation loss of traditional SPR sensors is significantly reduced, and the sensitivity is improved by at least two orders of magnitude.

[0014] (2) Due to the addition of the Teflon material protective layer, on the one hand, the degree of oxidation and corrosion of the metal material layer is reduced, the intrinsic loss is controlled, and the excitation of the SPR effect is promoted to a certain extent. On the other hand, since the refractive index of the Teflon and Bi2Se3 material layers is similar, a long-range surface plasma resonance phenomenon can be formed, which extends the propagation depth of the SPR to a certain extent and significantly prolongs the existence time of the effect.

[0015] (3) Compared with existing SPR sensors, the factors affecting the sensing characteristics of this model are more diverse, and the degree of tunability is higher.

[0016] (4) Fano resonance generally comes from the destructive interference between the broadband mode in the plasma resonance and the narrowband mode in the planar waveguide. It has the characteristics of low radiation loss, narrow half-maximum full width, and asymmetric spectral line shape. Its application in the field of sensing will greatly improve the sensing performance of optical sensors. Therefore, based on the SPR sensor, it is proposed to electromagnetically couple the SPP mode with the PWG mode to produce Fano resonance with more sensitive detection performance, and use this as a mechanism to form a new type of optical refractive index sensor.

[0017] (5) The present invention couples the SPR effect excited by bismuth selenide (Bi2Se3) material with the PWG mode generated by a planar waveguide structure composed of silicon dioxide (SiO2), titanium dioxide (TiO2) and the medium to be measured to produce an optical sensor based on the Fano resonance mechanism, and the sensitivity can reach 7700RIU within the existing parameter adjustment range. -1 Compared with the previous traditional SPR sensors, performance indicators such as sensitivity have been improved by 2-3 orders of magnitude. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the model structure of the present invention.

[0019] Figure 2 It is the ATR curve diagram of the model of the present invention.

[0020] Figure 3It is a schematic diagram of the change of the ATR curve of the model of the present invention with the change of the refractive index.

[0021] Figure 4 This is a graph showing the sensitivity changing with the thickness of materials Bi2Se3 and Teflon. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0023] like Figure 1 As shown, the model of the present invention is a metal multilayer dielectric film composite sensing structure based on the coupling of SPP and PWG to generate Fano resonance. The model uses Rsoft simulation software to establish the sensing geometric model, with the z-axis direction as the vertical direction, and the material layers selected from top to bottom are zinc selenide prism (ZnSe Prism), Bi2Se3, Teflon (Teflon), SiO2, TiO2 and the medium to be measured (water is selected as the analyte here).

[0024] When the transverse magnetic wave (TM) is incident on the metal compound material layer Bi2Se3 from one side of the prism at a certain angle, it will cause the collective oscillation of free electrons on the surface of the metal film, forming a surface plasma wave (SPW) propagating along the interface direction of the metal and Teflon. When the incident light is incident on the medium layer with a low refractive index from the high refractive index prism, an evanescent wave that penetrates a certain depth will be generated. According to the dispersion equation, when the wave vectors of the evanescent wave and the surface plasma wave propagate along the interface meet the corresponding matching conditions, the coupling of the two will produce the surface plasma resonance SPR phenomenon, which is manifested as a wide resonance of the bright mode in the spectral response curve. Below the sensing structure is a planar waveguide structure composed of SiO2, TiO2 and the medium to be measured. Since the refractive index of the waveguide layer TiO2 is higher than that of the cladding SiO2 and the medium to be measured, the incident light can propagate in it. The waveguide structure can excite the PWG mode. Different from the wide resonance corresponding to the SPR mode, it is manifested as a narrow resonance of the dark mode in the spectral response curve.

[0025] When the evanescent field of the surface plasmon (SPP) overlaps with the PWG mode in a certain area of ​​space, electromagnetic interaction occurs, thereby generating a sharp and asymmetric Fano resonance with a narrow resonance line width. Once the refractive index of the medium to be measured changes slightly, the model of the present invention based on Fano resonance will respond to it with high sensitivity, showing excellent sensing performance. In the field of optical sensing, one of the most important indicators for measuring sensor performance is sensitivity. Under the premise of intensity modulation, its calculation formula is defined as: Where ΔR(θ) represents the change in the reflectivity of the incident light, which changes with the incident angle, and Δn is the change in the refractive index of the medium to be measured. Sensitivity is essentially the rate of change of the reflectivity of the incident light in the sensing structure as the refractive index of the medium to be measured changes.

[0026] For the metal film multi-media layer sensing structure, its sensing performance will be affected by many factors. Among them, the sensitivity of the structure can be affected by changing the material's own parameters such as thickness. Since Fano resonance is achieved by electromagnetic coupling between the SPP mode and the PWG mode, and the excitation of these two modes is closely related to the material layer parameters, the thickness of the material is now adjusted. The purpose is to continuously optimize during the parameter adjustment process to find the material parameters corresponding to the best sensing performance.

[0027] The model proposed in the present invention is a multilayer metal dielectric film sensor structure based on Fano resonance mechanism generated by coupling SPP and PWG. The working wavelength is selected at 1.89μm. Under the premise of this wavelength, the refractive index of materials such as ZnSe prism, Teflon, SiO2, TiO2, etc. is calculated by the Sellimeier equation, which describes the empirical relationship between the refractive index and wavelength in a specific transparent medium.

[0028] The specific models and theoretical details involved in the present invention are divided into two embodiments and introduced as follows:

[0029] Example 1

[0030] Figure 2 The figure is a schematic diagram of the change of the attenuated total reflection (ATR) curve of the model of the present invention. In the incident angle range of 31° to 35°, there is an obvious wide resonance and a sharp Fano resonance, wherein the resonance inclination angles of SPR and Fano are 32.067° and 33.082°, respectively, corresponding to points A and B in the figure. This shows that the metal film Bi2Se3 excites the surface plasmon mode under the stimulation of the incident light, forms a surface plasmon resonance phenomenon with the evanescent wave under the wave vector matching condition that satisfies the dispersion equation, and then generates the Fano resonance through electromagnetic interaction with the PWG mode formed by the planar waveguide structure.

[0031] Figure 3 Schematic diagram of the ATR curve of the model of the present invention as the refractive index of the medium to be measured changes. In the embodiment, the sensing medium is set to be water, whose refractive index at the working wavelength of 1.89 μm is 1.333. When the refractive index changes from 1.333 to 1.3331, that is, the refractive index changes by 10 -4, within the incident angle range of 33.06° to 33.1°, the Fano resonance has a significant shift. This shows that the Fano resonance is sensitive to changes in the refractive index of the medium. The sensitivity of the model can be calculated based on the rate of change of the ATR change at a specific angle with the refractive index.

[0032] Example 2

[0033] Figure 4 (a) reflects the change trend of sensitivity when the thickness of Bi2Se3 changes from 0.046μm to 0.054μm in the angle change range of 33.06° to 33.10°. As the thickness increases, the sensitivity value generally shows a downward trend. Within the adjusted range, when the thickness of Bi2Se3 is 0.046μm, the sensitivity reaches the extreme value, which exceeds 8000RIU. -1 The reason is that as the thickness of the plasma material increases, the coupling effect between the SPR and the waveguide structure weakens, resulting in a decrease in the sensitivity performance of the sensor.

[0034] Figure 4 (b) reflects the sensitivity change trend when the thickness of Teflon changes from 2μm to 4μm in the angle change range of 33.06° to 33.10°. As the thickness increases, the sensitivity generally shows a trend of first rising and then falling. When the thickness is in the range of 3μm-3.5μm, the performance index of the proposed sensor is at the best stage, and the sensitivity exceeds 8000RIU -1 .

[0035] The descriptions of the embodiments all reflect the application characteristics of the model structure of the present invention and highlight the design concept of the present invention. The embodiments are only used to illustrate the design ideas and features of the present invention. This specification selects and specifically describes these embodiments to enable those skilled in the art to better understand and use the model of the present invention. The protection scope of the present invention includes but is not limited to the above embodiments.

Claims

1. A Fano resonance sensor based on surface plasmon coupled planar waveguide, characterized in that: From top to bottom, it includes a zinc selenide prism ZnSe Prism, a bismuth selenide layer Bi2Se3, a Teflon layer Teflon, a silicon dioxide layer SiO2, a titanium dioxide layer TiO2 and a medium layer to be tested.

2. A Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The thickness of the zinc selenide prism ZnSe Prism is set at 0.9-1.2 μm, and under the premise of a working wavelength of 1.89 μm, the corresponding refractive index is 2.4479.

3. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The thickness of the bismuth selenide layer Bi2Se3 is set at 0.048-0.052 μm.

4. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The thickness of the Teflon layer is set to 2.8-3.2 μm, and the refractive index is 1.

3.

5. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The silicon dioxide layer SiO2 has a thickness of 0.12-0.16 μm, and a corresponding refractive index of 1.4318.

6. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The thickness of the titanium dioxide layer TiO2 is 0.06-0.08 μm, and the corresponding refractive index is 2.1237.

7. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 1, characterized in that: The medium to be tested includes water and ethanol.

8. The Fano resonance sensor based on surface plasmon coupled planar waveguide according to claim 7, characterized in that: When water is selected as the medium to be measured, the thickness of the medium to be measured is 0.5-1 μm, and the refractive index is 1.333.

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