Design And Simulation Of Refractive Index Sensor Based On Microstructure Photonic Crystal Fiber

Optical fiber refractive index sensor is widely used in various fields,but with the development of industry,the capability of optical fiber refractive index sensor is becoming more and more demanding.Photonic Crystal fibers（PCF）have become popular in the research of Fiber sensing in recent years due to their flexible structure design and excellent and controllable light transmission characteristics.At the same time,PCF is one of the hot spots in the field of new optoelectronic devices because of its small size and easy combination with other optical devices.Due to the porous structure of PCF,its preparation process is too complex,so the sensing applications of PCF are not widely used at present.Therefore,a large number of simulation analysis and experimental research are needed to fully exploit its potential performance.In this paper,three PCF sensors with different structures are proposed.Firstly,a PCF refractive index sensor based on Sagnac microstructure is proposed,and the structural beneficial simulation analysis is carried out.It is proved that the designed refractive index sensor has better sensing ability than the basic single-mode fiber-photonic crystal fiber-single-mode fiber（SMF-PCF-SMF）sensing unit.On this basis,the fabrication of Sagnac microstructured PCF sensor and SMF-PCF-SMF sensor and the sensing experiment analysis of refractive index sensing ability and temperature stability were carried out.The experimental results show that Sagnac ring structure can improve the refractive index sensitivity and reduce the influence of temperature on the sensor.In the range of refractive index 1.3355～1.3560,Sagnac microstructure PCF sensor has the highest refractive index sensitivity of 234.78252nm/RIU,which is 158%higher than SMF-PCF-SMF structure.In order to improve the sensitivity,and make the sensor more miniaturized,integrated and remote dynamic detection.A PCF refractive index sensor based on unilateral polished microstructure is designed and numerically analyzed by finite element method.Silver is plated on the polished plane,and the transmission characteristics of the sensor are reflected by the coupling between the fiber core mode and the surface plasma mode.The simulation results show that the sensor can perform RI sensing in visible and infrared wavelength bands when the refractive index of analyte gradually changes from 1.33 to 1.39.Under the final structural parameters,the sensor’s performance is a maximum wavelength sensitivity of1.48×10⁴nm/RIU,a maximum amplitude sensitivity of 766.7008 RIU^-1,a resolution of 6.7568×10^-6RIU,a maximum figure of merit（FOM）of 548.1481 and a maximum confinement loss of 988.8448 d B/cm.A microstructured PCF refractive index sensor based on bilateral polishing is presented and numerically analyzed.The influence of parameters such as thickness,polishing depth,pore size and spacing on the sensing performance is studied.Numerical results show that the maximum wavelength sensitivity is 2.15×10⁴nm/RIU and the average wavelength sensitivity is 9.55×10³nm/RIU in the refractive index range of 1.35-1.39.The amplitude sensitivity is-1057.1756 RIU^-1,R²is 0.9829,FOM is 250,and the maximum resolution is 4.68×10^-8.