Research On Fiber Interferometric Refractive Index Sensor Based On Open Cavity Structur

Fiber optic refractive index sensors have been widely used in various fields such as environmental monitoring,biomedical applications,chemical engineering,and food safety due to their high sensitivity,small size,light weight,electromagnetic interference resistance,corrosion resistance,and long-distance transmission capability.In recent years,the development of new types of fiber optic refractive index sensors with simple structures,high sensitivity,and low cost has become a research focus in the field of refractive index sensing.This dissertation presents the development of an open-cavity fiber optic interferometric refractive index sensor based on large-offset fusion splicing.Numerical simulations of the optical characteristics of the open-cavity interferometer were conducted using beam propagation methods.Experimental investigations were performed to study the refractive index,temperature,and concentration sensing characteristics of the open-cavity fiber sensor,as well as its application in monitoring the charging and discharging processes of capacitors.The main contents of this dissertation are as follows:1.An open-cavity fiber optic interferometer was developed by precisely fusion splicing three single-mode fibers together using a commercial fusion splicer,creating a miniature open-cavity structure.The effects of fusion splicer discharge parameters and fiber misalignment on the performance of the interferometer were experimentally studied.By optimizing the fusion parameters,the performance of the open-cavity fiber optic interferometer was improved.The optical characteristics of the open-cavity fiber optic interferometer were simulated using beam propagation methods,and the influences of the cavity length and misalignment on the interferometer characteristics were investigated,providing theoretical guidance for sensor fabrication.2.Transmissive and reflective fiber optic sensors based on the open-cavity structure were developed,and experimental investigations on refractive index,solution concentration,and temperature sensing were conducted.The experimental results showed that the transmissive Mach-Zehnder(M-Z)sensor achieved a refractive index sensitivity of up to-20397.7 nm/RIU,while the reflective Fabry-Perot(F-P)sensor achieved a refractive index sensitivity of 1219.8 nm/RIU.In the salt solution concentration sensing experiment,the transmissive M-Z sensor exhibited a sensitivity of-25.27 nm/%,and the reflective F-P sensor exhibited a sensitivity of 1.874 nm/%.In the temperature sensing experiment,the transmissive M-Z sensor had a temperature sensitivity of 0.0294 nm/°C,and the reflective F-P sensor had a temperature sensitivity of 0.042 nm/°C.3.A sensing system based on the open-cavity M-Z fiber optic interferometer was proposed for charge detection in supercapacitors.Under cyclic voltammetry mode,there was a corresponding relationship between the maximum stored charge(ΔCmax)and the longest drift in the MZI spectrum during CV processes at different scan rates.For scan rates of 10 m V/s,15 m V/s,and 20 m V/s,ΔCmax values were 0.193 C,0.182 C,and0.175 C,with wavelength drifts of 0.240 nm,0.176 nm,and 0.144 nm,respectively.Under galvanostatic charge-discharge mode,GCD tests were conducted with currents of2 m A,3 m A,and 4 m A,resulting in accumulated charge values(ΔCmax)of 0.231 C,0.211 C,and 0.186 C,with wavelength drifts of 0.289 nm,0.250 nm,and 0.179 nm,respectively.The experimental results demonstrated the capability of the sensor to effectively monitor the charging and discharging processes of supercapacitors.