Design Of High-temperature Fiber Grating Sensor Demodulating System

Harsh surroundings are widely existed in industry,national defense,aviation area,this includes high temperature,pressure,strong radiation and electromagnetic interference,et al.How to realize precise,transient physical quantity sensing and measurement in harsh condition is a big problem.Fibergrating sensorsa new sensor which has the merits of passivity,anti-electromagnetic interference,low insert loss,good wavelength selectivity and can realize long haul and distributed sensing that provide an opportunity for solving the above problem.The traditional fabrication of fiber Bragg gratings(FBG)is based on UV laser writing technology,the induced refractive index strongly depends on the photosensitivity of the fiber,which is readily erased when the temperature is more than 350 ?,limiting its sensing applications in hash environment.Therefore,the need for a high-temperature resisting “extreme” FBG is urgent.Femtosecond laser(fs)have been proven to induce perpetual index changes in any transparent dielectrics that has nothing to do with the photosensitivity.This technology brings new vitality for the fabrication of high temperature resisting FBG.This paper is based on the method of femtosecond laser(fs)micro-machining and aimed at fabricating high temperature resisting FBG to solve the harsh environment sensing problems,and a simultaneous measurement of FBG sensing demodulation system is designed by combining with the existing wavelength demodulation technology and Lab VIEW.The main work of the paper is listed as bellows:(1)Discussed the coupled mode theory of fiber gratings,the temperature and strain sensing mechanism of FBGs.Alsosome typical demodulation methodis introduced,especially the principles of the FBGA module.(2)A FBG temperature monitoring system software based on FBGA demodulation module is developed in Lab VIEW platform.The software can achieve the following functions: data acquiring,waveform graphical displaying,sensor finding peaks,sensor wavelength-temperature fitting,data saving and temperature alarming.(3)An experiment system with high precision has been created for the grating inscription,including a femtosecond pulse output system,a dynamic grating fabrication system,a spectrum recording system and an annealing test system.Then,two kinds of high-temperature fiber Bragg gratings(FBGs)was fabricated on the SMFby using the phase mask method and point by point system.Through the annealing experiment,the temperature sensitivity and high temperature stability of the grating was investigated.The experimental results show that the sensor has a very high temperature stability under 900?,and the sensitivity coefficient can achieve 12.7 pm/? in the range of 100-900?.