Performance Optimization Design Of Surface Plasmon Resonance Optical Fiber Sensor

The sensor made of optical fiber has the characteristics of small size,strong anti electromagnetic interference ability and long-distance transmission.By combining it with the surface plasmon resonance generated at the interface between metal and medium,an optical fiber SPR sensor with the advantages of on-site measurement,high sensitivity,fast response,no marking and high resolution can be made.Since the generation of SPR is closely related to the change of the refractive index of the medium,we can use the SPR sensor to monitor the refractive index of the external environment.At present,Optical fiber SPR-based sensors are mainly used in the fields of biochemistry,environmental protection and food safety.In order to improve the performance of the sensor,this paper is mainly based on the sensing principle of SPR and the current research on fiber SPR sensors at home and abroad,and propose two configurations of single-mode tapered optical fiber SPR sensor and D-type two core photonic crystal fiber SPR sensor.The structure of the sensor is modeled and optimized by COMSOL multiphysics simulation software based on finite element method.The main contents of this paper are as follows:1.Based on the principle and conditions of surface plasmon resonance,the single-mode tapered fiber is used as the model structure,and the influence of different metal layer materials on the reflection characteristics and electric field distribution of the SPR sensor were studied by COMSOL Multiphysics.It lays the foundation for designing a high-performance sensor structure later.2.A single-mode tapered fiber SPR sensor with graphene/silver/TiO₂as sensing layer is proposed,and its structural parameters are optimized by COMSOL Multiphysics.The research results show that the performance of the sensor is improved by adding a graphene layer and a titanium dioxide layer compared to the sensor with the traditional structure.After optimization,the number and thickness of graphene,silver,and titanium dioxide layers are 15,40nm,and 20nm,respectively,and the refractive index detection range of the sensor can reach 1.32-1.38,the sensitivity can reach 8570nm/RIU when the refractive index of medium is 1.38.The electric field strength and amplitude distribution of the sensor when SPR occurs were also studied,the results show that graphene and TiO₂can indeed enhance the electric field coupling strength of SPR and improve the performance of the sensor.3.A D-type dual-core photonic crystal fiber sensor is proposed,which is decorated with silver/titanium dioxide film and silver/titanium dioxide nanocolumns respectively.COMSOL Multiphysics is used to optimize the structural parameters of D-type photonic crystal fiber（air hole diameter and dspacing）,the thickness of the sensing layer Ag/TiO₂film,the diameter,number and spacing of silver nanopillars and the thickness of titanium dioxide coating on the surface of silver nanopillarse.The optimized sensor performance is compared.The results show that the sensor modified by silver/titanium dioxide nano column has higher sensitivity than that modified by silver/titanium dioxide film（the sensitivity increases by 11.7%when RI=1.37）,but its refractive index detection range is reduced,indicating that the sensors modified by different shapes of sensitive layers have their own advantages.