| The optical fiber surface plasmon resonance(SPR)sensors are very sensitive to the changes in the refractive index of the external environment,which are widely used in biological,chemical and medical fields due to their advantages such as high sensitivity,excellent resolution and real-time detection.In order to improve the sensitivity of the optical fiber SPR sensor,the study is carried out from the perspective of the structure and material of the sensor.The two structures of online transmission type optical fiber SPR sensor and side-polished optical fiber SPR sensor are mainly studied using N-layers model and finite element analysis method to systematically study the factors that affect the performance of the sensor.By adding the two-dimensional material tungsten disulfide,changing the thickness of each film and the structure of the metal film,the optimal design schemes are proposed.The main research contents are as follows:1.Based on the theory of SPR technology,this paper has analyzed the sensing principle of SPR sensor and studied the SPR wave vector dispersion relationship of the most typical Kretschmann prism structure.The finite element analysis(FEA)method simulation software COMSOL Multiphysics is used to simulate the excitation and propagation of the SPR phenomenon and the refractive index sensing characteristics.The field strength distribution of the sensing structure is simulated to find that the SPR phenomenon would cause a sharp increase in local field strength.The sensing characteristic of the refractive index of the sensing medium can be obtained from the resonance wavelength corresponding to the resonance peak of the transmission spectrum is also studied.All the research work can provide a foundation for the comprehensive design of optical fiber SPR sensors.2.A kind of online transmission type optical fiber sensor is designed which is coated with zinc oxide and tungsten disulfide on the surface of the gold film to increase the transmission depth of the evanescent wave to improve the sensitivity.N-layers model is studied to determine the reflected light intensity and then analyze the optimal sensitivity of the sensor using MATLAB to optimize the thickness of each layer of film,analyze the optimal value of sensor sensitivity and study its light field distribution.The results show that when the refractive index of the external environment is in the range of 1.33 ? 1.37 and the optimal thicknesses modulated with gold film,zinc oxide and tungsten disulfide are 40 nm,5nm and 14 layers respectively,the proposed optical fiber SPR sensor is up to 4310 nm/RIU,which is 36% higher than the structure without tungsten disulfide.The idea of applying the designed optical fiber SPR sensor to glucose concentration detection is also proposed by describing the detection principle and conducting some numerical simulation study.3.This paper also uses FEA method to design a gold nanopillar array side-polished optical fiber SPR sensor modified with tungsten disulfide.The effects of transmission mode,gold film thickness and remaining cladding thickness on the performance of the side polishing optical fiber SPR sensor based on gold film are studied using the COMSOL Multiphysics simulation software firstly.Based on its optimal parameters,the effects of various fiber parameters,gold nanopillar parameters and tungsten disulfide thickness on the performance of SPR sensors are studied.The optimal values of the sensitivity of the side polishing optical fiber SPR sensor based on gold film and gold nanopillar array are 3410 nm/RIU and 4300 nm/RIU,respectively,while the sensitivity of the sensor increases with the increase of the number of tungsten disulfide layers and is up to 4890 nm/RIU.Studies have shown that the modification of tungsten disulfide materials can improve the sensitivity of SPR sensors and the side-polished SPR sensors based on gold nanopillars are generally more sensitive than those based on gold films. |
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