Research On All-fiber Sensor Based On Thin-core Fibe

Fiber optic sensing has been developed over the years to produce a variety of sensors based on different principles,such as fiber optic Surface Plasmon Resonance（SPR）sensors and Mach-Zehnder（M-Z）interferometric fiber optic sensors.With the advantages of small size,compact structure and fast response,fiber optic sensors are widely used in biological,chemical and medical fields.In this thesis,an all-fiber multiparameter measurement sensor with Multi-mode-Thin-core-Multi-mode（MTM）structure is designed based on fine core optical fiber.The SPR resonance principle is used to measure refractive index,temperature,curvature and humidity,and combined with the M-Z interference principle to measure refractive index,temperature and curvature,and the measured sensitivity values are substituted into the sensitivity coefficient matrix to achieve simultaneous dual-parameter measurements.The main work of the thesis is as follows.1.In this thesis,the multi-parameter sensing characteristics of all optical fiber sensor with MTM structure are studied by using SPR resonance principle.Firstly,FDTD Solutions and Matlab software were used to optimize the sensor structure,and the length of the sensing area was determined to be 15 mm and the thickness of the metal silver film was 40 nm.Based on the SPR resonance principle,the four parameters of refractive index,temperature,curvature and humidity were simulated to obtain the resonance spectra of the above parameters,and the variation trend of the resonance spectra was analyzed when the parameters changed.According to the simulation results of the sensor structure,the sensor was fabricated by optical fiber welding technology and plasma magnetron sputtering technology.According to the different parameters,different experimental testing systems are designed and built,and the four parameters are measured experimentally.The experimental results show that the refractive index sensitivity is 4888.77 nm/RIU,and the temperature wavelength sensitivity is-0.3215nm/℃,and the intensity sensitivity is 0.2016%/℃,and the curvature sensitivity is-7.98%/m^-1,and the humidity sensitivity was-0.593 nm/%RH.2.In order to solve the problem of temperature crosstalk of traditional optical fiber sensors,this thesis studies the interference spectrum measurement of these sensors according to the above structure and M-Z interference principle.Firstly,the working principle of M-Z interference is analyzed according to the sensor structure.Then the refractive index,temperature and curvature are calculated theoretically by Matlab software.Then,according to the different parameters measured,the corresponding experimental test system is built,and the three parameters are measured experimentally.The experimental results show that the refractive index sensitivity is-70.378 nm/RIU,the temperature sensitivity is 72.43 pm/℃,and the curvature sensitivity is-2.717 nm/m^-1.Then,the spectra of refractive index,temperature and curvature are processed by Fast Fourier Transform（FFT）,and the mode analysis is carried out.Finally,the principle and error analysis of the two-parameter measurement of the sensor are introduced,and two measurement matrices of refractive index and temperature,curvature and temperature are established.The two-parameter simultaneous measurement is realized,and the cross-sensitivity between parameters is eliminated.The resolution of the simultaneous measurement of refractive index and temperature is calculated asδn=3.28×10^-4 RIU,δT=3.33×10^-2℃.