Study On The Distributed Fiber Bragg Grating Sensing System

At present, single FBG (Fiber Bragg Grating) sensor technique has been developed rapidly. However a large number of sensors are needed for structures' monitoring and controling in large-scale projects. For example at least 5000 sensors are necessary to monitor an airplane's construction. Therefore single FBG sensor can not fulfill these practical needs. Now people start to pay more attention to the distributed FBG sensing system.Firstly, we give theoretical model of FBG sensor in this paper. Based on numerical calculation, the influence of FBG parameters on the grating's frequency spectrum properties are studied in detail, and the temperature sensing principles of FBG are investigated experimentally by naked single-mode FBG whose wavelength is 1549 ran. It is found that variations of Bragg wavelength are linear with variations of temperature. The experimental results are agreement with theoretical analys.Secondly, the condition of signal resolution for FBG distributed sensors is introduced, the mathematical expressions of the multi-point temperature sensing are given. We also analyze the system multiplexing capacity dominated by optical source bandwidth. Through temperature sensing experiment with the FBG array, which is consisted of three FBGs (whose Bragg wavelength are 1549 ran, 1550 nm and 1551 nm.), no crosstalk conditions in the experimental system are concluded, and as much as 39 FBGs can be utilized. By using the method of taking the loss to simulate the distance, the effect of distance on the distributed sensing system is considered experimentally. And it is shown that the reliable transmission distance is 50 km in the experimental system.Finally, FBG sensor network technology and some methods of FBG wavelength demodulation are described. Based on a tunable F-P filter, a kind of parallel demodulation system is designed. The hardware part of the demodulation system includes the photoelectric signal test circuit, the signal processing circuit, and the voltage scanning circuit of tunable F-Pfilter. In the end some improvable methods of the designed system are pointed out.