Research On Fiber Bragg Grating Demodulating System And Novel Sensing Method

Fiber Bragg grating (FBG) has potential value in many fields because of its capability of responding to a wide variety of measurands, such as strain and temperature. Since the immunity from the fluctuation of the light source as well as the losses of the fiber link, fiber Bragg grating sensors have attracted increasing attention. Nowadays, with the development of the FBG, the research focus has changed to demodulating technology and new sensing methods, and the key factor for the application of FBG sensors is how to measure a small shift of Bragg wavelength accurately.In this dissertation, the sensing theory of FBG is introduced firstly, and some typical demodulation methods are also analyzed. According to the tunable fiber Fabry-Perot filter method, a fiber Bragg grating demodulating system with the DSP chip is developed, and the impact of peristalsis, temperature drift and hysteresis of the filter is eliminated with the linear interpolation calibration method. The design of circuit and the development of software system are introduced detailedly in this thesis. The circuit is composed of power-supply section, signal-acquisition section, power-driver section of the Fabry-Perot filter, data-transmission section and Micro-controller section; and the software system includes controlling program of the circuit and monitoring software in the PC.Finally, with the mechanism of wavelength-sweeping, a remote FBG sensing system based on the self-heterodyne technology is proposed and experimentally demonstrated. The system is able to detect the FBG placed170km away, offering a signal-to-noise ratio of33dB without amplification. Applying this system to remote temperature detection, the measurement accuracy is1℃.