| With the development of technology and economy,China has built a lot of transmission pipelines(such as gas pipeline,oil pipelines,electric pipeline),transport systems(such as subways and trains)and bridges,etc.It is necessary to monitor health status of these long-distance infrastructures.Compared with traditional sensor,?-OTDR with coherent detection is sensitive to the vibration event around the fiber.In this dissertation,multipoint vibrations along the fiber in ?-OTDR system with coherent detection have been deeply analyzed and evaluated.First of all,we introduce the principle of Rayleigh back scattering and ?-OTDR,and explain the key features of ?-OTDR.Secondly,we optimize the performance of EDFA via the simulation and experiment.Finally,the problem caused by multiple vibrations in ?-OTDR sensor with coherent detection is studied.By analyzing the one-dimensional impulse response of Rayleigh scattering in single-mode fiber,the relationship between Rayleigh scattering and phase changes caused by fiber vibrations is derived,and the influence of coherent detection is proved by simulation and experiment. |
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