The Optical Low Coherence Reflectometry Applied In The Fiber Bragg Grating Sensing

FBG(Fiber Bragg Grating)is one of the most common optical element in modern optical fiber sensing field, and nowadays widely used in the structure health monitoring of large construction. Usually the characterization of the linear variation between center wavelength of FBG reflectance spectrum(Bragg wavelength) and the external Physical quantity such as strain were used to realize FBG sensing, The detection methods mianly include reflectance spectrum method, filter method and interferometry. OLCR(Optical Low Coherence Reflectometry) can also measure the FBG reflectance spectrum and realize the sensor demodulation as a new optical detection technology. Moreover, when external variables are more complicated, for example, the FBG is under non-uniform stress, the OLCR system can demodulate and achieve the FBG reflectance. When combined with the peeling algorithm, this way can reconstruct the non-uniform strain distribution of FBG. Obviously, the OLCR technology provide an important means for the detection of FBG. In this paper, the main research work is as follows:Firstly, this paper summarized and analyzed the research status of FBG sensing and demodulation technology, the application of OLCR technology in the detection of FBG, and also cleared the research content and target. On the basis of optical transmission theory, this paper discussed the FBG sensing principle and established the strain sensing model. Then this paper presented the principle and method of FBG strain demodulation and reconstruction.Secondly, based on the OLCR working theory, this paper described the detection method for FBG with OLCR. Especially combined with the peeling algorithm, this way can reconstruct the non-uniform strain distribution. Futher more, this paper designed and built the OLCR-FBG dynamic scanning detection system with balanced detection structure and high precision translation stage to improve the performance of system. And the OLCR-FBG system is mainly composed of the detailed hardware module, the software control program based on Lab VIEW and processing algorithm which were all developed by myself. The system achieves good man-machine interface.Finally, this paper completed the OLCR-FBG system performance test. The achieved interference signals tested in the balanced and unbalanced detection structure indicated that the signals were amplified and the noise were well suppressed with the balanced structure. The higher accuracy air-bone translation stage weakens the influence of vibration, and ensures the better reliability of the datas than the step into translation stage. In the end, the tuning mechanism of cantilever beam was designed and maked for the FBG strain test, the equal strength beam for FBG homogeneous strain and the rectangular beam for inhomogeneous strain. The homogeneous strain experiment obtained well FBG reflectance spectrum. The repeatability of Bragg wavelength is less than 10 pm, and the maximum error is less than 20 uε in the homogeneous strain detection. Finally in the FBG inhomogeneous strain experiment, we built the relationship between FBG reflectance spectrum and different linear strain. The results showed that this paper initially realized the reconstruction of FBG inhomogeneous strain, and the strain trend to be basically correct.