A Sensing Demodulation System Using A Triangular Spectrum Fiber Bragg Grating

A sensing demodulation system, which is an essential part of a fiber Bragg grating(FBG) sensing system, is mainly based on the principles of tunable Fabry-Perot filter demodulation method and tunable light source demodulation method, and its performance is easily affected by the mechanical components and the stability of the light power. In this thesis, we propose a method for fabrication of triangular spectrum FBG(TS-FBG),and then fabricate the TS-FBG automatically according to the design results, then use it as an edge filter to achieve a sensing demodulation system which could detect the wavelength in the range of 1515~1525nm and the resolution of 3.6pm. This thesis includes:(1) The spectrum and temperature characteristics of the TS-FBG are analyzed. The TS-FBG is designed by using the Cross-Entropy Optimization(CEO) method, and the design results show that bandwidth of the TS-FBG is 10 nm, the maximum reflectivity is 97%, and the linearity is 6.813×10-4. An automatic method for fabrication of the TS-FBG is proposed, and then used to fabricate the TS-FBG according to the design results mentioned above. The experiment results show that the bandwidth of the TS-FBG obtained is 10 nm, the maximum reflectivity is 96.6%, and the edge spectrum shows a good linearity, which can meet the design results.(2) A sensing demodulation system using the TS-FBG is built and tested, and the testing results show that the range of demodulated wavelength is 1515~1525nm, and the wavelength resolution limitation is up to 3.6 pm, which can detects wavelength cheaply and accurately. With the help of negative temperature mechanism, the maximum wavelength shift of the TS-FBG is reduced to 35 pm in the range of-5~75℃, compared with 808 pm for an uncompensated, thus the temperature insensitivity of sensing demodulation system can be improved greatly.The meaning of the sensing demodulation system using a TS-FBG studied in this thesis is that not only broaden the range of detected wavelength and improve the demodulation accuracy, but also reduce the effect on the demodulation system coursed by the temperature, which has the important practical significance on the application of fiber Bragg grating sensing technology.