Study For Distributed Fiber Optic Strain Monitoring System

Distributed fiber optic sensor can meet the requirements of long-distance and continuous monitoring, be easy to achieve the remote sensing and controlling, obtain the parameter information of monitoring body completely. It is suitable to monitor the variety of large structure body. Based on the advantage and funded by the project "Eleventh Five-Year" National Key Technology R&D Program (2006BAC04B03) and the Geological Survey Project of CGS (1212010641008), the dissertation studied on the Brillouin distributed fiber optic sensing technique and developed the fiber optic strain monitoring system.In general, Brillouin scattering would occur when light transmitted in the fiber. The Brillouin frequency shift will change when the fiber materials are affected by the temperature or strain. The dissertation introduced the theory of the Brillouin scattering, and illustrated the relations between the Brillouin frequency shift and strain and temperature.According to the principle of BOTDR, we used the optical coherent detection method between the backward Brilliouin scattering light and the local reference light which generated by the microwave electro-optic modulator to develop the BOTDR monitoring system. The dissertation contrasted various detection schemes of the backward Brilliouin scattering light, identified the design of the distributed fiber optic strain monitoring system. Based on that, the author studied on the calculation of parameters of the monitoring system and the design and achievement of the hardware and software intensively, developed the BOTDR monitoring system.Through the calibration and simulation test in the lab, the performance of monitoring system was verified. In the correct experiment of fiber strain monitoring influenced by temperature, used statistics analysis method to acquire the function relation of the fiber strain measuring influenced by the environment temperature, provided theory guide for the data processing of the actual BOTDR monitoring project.In Deng Jia Wu Chang landslide in Wushan in Chongqing, The distributed fiber optic strain field monitoring experiment was carried on. The approach to monitoring landslide, such as the fiber type choosing, the fiber embedment craft, the fiber network arrangement principle and so on, was explored and practiced. Put forward the approach to monitoring landslide with FBG and BOTDR and practiced in Canlian landslide in Wushan, further discussed the possibility and advantage of BOTDR combining with FBG to monitor landslide.