Research On Optical Fiber Refractive Index Array Sensor Based On Microwave Demodulation Technology

Refractive index is an important parameter for liquid properties,fiber-optic refractive index sensor has attracted more and more attention because of its strong to electromagnetic interference and miniaturization,and it has been widely used in the fields of biomedicine,chemical safety and environmental monitoring.Aiming at the problems of complex structure and poor integration of optical fiber refractive index sensor,a fiber refractive index array sensor is developed in this thesis,the array can implement multi-function and solve cross-sensitive.This thesis built a microwave demodulation system based on optical carrier microwave measurement technology,and used the system to implement the refractive index sensing.The main contents of this thesis include:(1)The microwave measurement technology of optical carrier is analyzed in this thesis,and verify the feasibility of the technology by simulation.On the basis of theoretical research and simulation,a demodulation system for refractive index array sensors is built.(2)Used the denoising algorithm for signal processing and analyzed the performance of the system.The two methods of cumulative average and wavelet transform are used to denoise the demodulated signal,compared before and after denoising signal,cumulative average and wavelet transform have a good effect on noise suppression.(3)Used the microwave demodulation system to solve the fiber refractive index array sensor and the liquid refractive index experiment was done.In this thesis proposed a self-calibration structure to improve the demodulation performance and produced a self-calibration sensor.The refractive index sensor is based on Fresnel reflection,the parallel multiplexing of the sensor array is realized by a 1×8 optical fiber splitter,so that the 8 channel simultaneous measurement of refractive index sensor is realized.The experimental results show that the sensitivity of the refractive index sensor can reach 4.228 mV/RIU,linearity is about 0.989,and has good stability and repeatability.Because the demodulation technique proposed in this thesis is based on intensity demodulation,so it is vulnerable to the fluctuation of the light source and the vibration of the sensing fiber,a self-calibration structure is proposed in this thesis.The self-calibration structure is to make a sensor with two reflecting surfaces,a reference surface and a reflecting surface.By dividing the two reflection intensity can eliminate the fluctuation,the experiment results show that the refractive index resolution of the sensor is improved from 0.052% to 0.015%,linearity increased from 0.9888 to 0.9996.