Mach-Zehnder Fiber Multi-parameter Measurement Sensor Based On Core Mismatc

Optical fiber sensors have the advantages of high sensitivity and small volume.In the development of optical fiber sensing technology,Mach-Zehnder optical fiber sensor has been widely used in environmental monitoring,industrial production,bridge construction and other fields after years of research.In this paper,a core-mismatched Mach-Zehnder fiber multi-parameter measurement sensor is proposed.The no-core fiber is used as a coupler to realize the function of light splitting and coupling.The sensor in this paper has simple structure and high sensitivity.It can measure multiple parameters of refractive index,temperature,curvature and strain,and eliminate temperature crosstalk.The main contents of this paper are as follows:1.In this paper,the core mismatch structure of no-core-single-no-core（NSN）was designed,and its interference principle was analyzed.The reasons of using no-core fiber as a coupler were analyzed by simulation.The structure of the sensor was optimized and the optimal length of both the coupler and the sensing arm is 15mm.According to the different measured physical parameters,the sensing characteristics of refractive index,temperature,curvature and strain were studied respectively.The interference spectra of different parameters were made and the sensitivity was fitted.Fast Fourier transform was performed on the interference spectrum in air to analyze the interference pattern.Finally,the composite parameter sensing was studied to realize multi-parameter measurement.2.Using different production sequence,the sensors with different lengths and optimized length were made.Depending on the different measured parameters,the sensor was protected by package of refractive index,curvature and strain to prevent breakage.Experimental measurement devices with different parameters were designed and built to verify the feasibility of optimal structure and the repeatability of interference spectrum.The experimental results show that the maximum refractive index sensitivity is-202.74 nm/RIU,the maximum air temperature sensitivity is 0.2478 nm/℃,the maximum water bath temperature sensitivity is0.2035 nm/℃,the maximum curvature sensitivity is-18.806 nm/m^-1,and the maximum strain sensitivity is-2.48 pm/με.Fast Fourier transform was performed on the transmission spectra of different parameters to perform mode analysis.Finally,the measurement matrix was established,and the water bath temperature and refractive index,air temperature and curvature,air temperature and strain were measured at the same time,and the crosstalk of temperature on each parameter was eliminated.