Research On FsFBG High-temperature Sensing Technology Based On Fiber Laser

Temperature monitoring is an important method to ensure the performance of equipment,safe production,and avoiding interference with the measurement of other parameters.Remote temperature detection in complex and extreme environments has been a research hotspot.The femtosecond Fiber Bragg Grating(fsFBG)has the characteristics of anti-interference,fast response and corrosion resistance,which stands out from other temperature sensors.The key issues of remote high-temperature detection using fsFBG are signal acquisition and wavelength-center demodulation with high signal-to-noise ratio(SNR),high power and narrow linewidth.To achieve high temperature detection in complex environments,this thesis designs and develops a fiber laser type high temperature sensing system based on the temperature sensitive mechanism and high temperature resistance of fsFBG,using fsFBG as a temperature sensitive element and a wavelength feedback device,and designs a wavelength demodulation system using the principle of tunable FP filter.The main research contents are as follows:Firstly,from the necessity of temperature sensing measurement in complex environment,the fiber grating temperature sensor was emphatically introduced,the current situation of domestic and international researches were analyzed.Focused on the high temperature stable measurement,the detection scheme based on fsFBG as the temperature sensitive element was determined,and the fsFBG signal acquisition and demodulation system was also studied.Secondly,starting from the fundamental theory of fsFBG,the reflectance spectral characteristics and center-wavelength variation relationship with temperature were deduced.Comparative analysis of the current main active signal acquisition methods,a fiber laser-type fsFBG signal acquisition method was used to solve problems of passive systems such as low SNR,large line-width and low power.Real system was built through device selection and optimized to realize fsFBG signal output.Thirdly,according to the acquired fsFBG signal characteristics and demodulation requirements,by comparing and analyzing advantages and disadvantages of mainstream demodulation methods,we designed the fsFBG signal demodulation system based on a tunable FP filter,and realized the digital signal circuit design with an FPGA as the main control chip,external integrated wavelength decoding,photoelectric conversion,data acquisition and transmission,power supply drive,internal integrated circuit drive,and peak-seeking algorithm.Finally,an experimental platform was built to verify the results of the fsFBG signal acquisition and demodulation system.The fiber laser-based fsFBG signal acquisition system achieves a linewidth of 27.6 pm,wavelength stability error of 3.25 pm,output power of 2 dBm,and SNR of 65 dB with the linewidth compression of over 94%and the power gain of 30 dB compared with the passive system.the temperature-wavelength sensitivity is 15.3 pm/? in a range 255?1002?.The fsFBG signal demodulation system based on the tunable FP filter has been verified to achieve a maximum standard wavelength demodulation error of-8.6 pm and a maximum temperature demodulation error of 3.51%.