Research On The Distributed Optical Fiber Vibration Sensing System Based On ?-OTDR

The distributed optical fiber sensing system uses optical fiber as the sensing medium,and utilizes changes in the characteristics of the transmitted light in the optical fiber to implement monitoring of external physical quantities.Due to its long-distance sensing,full-scale continuity,and strong anti-interference capabilities,it has been widely used in civil engineering,electric power,communication and other industries.Based on phase-sensitive optical time domain reflectometer(?-OTDR),this dissertation conducts simulation and experimental and research on fiber optic vibration monitoring and vibration monitoring of dry-type hollow reactors.This dissertation briefly describes the basic principles of distributed optical fiber sensing technology,summarizes the current research status of ?-OTDR system,and starts from the Rayleigh scattering of light,theoretically analyzes the sensing mechanism of?-OTDR technology and the key performance of the system The index its influencing factors and improvement methods are systematically analyzed,which laid the theoretical foundation for the experiments and modeling simulation in the subsequent chapters.This dissertation builds a distributed vibration monitoring system based on ?-OTDR,and introduces the devices and parameters in the experiment.The experimental system constructed successfully monitors vibration on a variety of optical fibers and custom-made dry-type hollow reactors with laid optical fibers.The effects of factors such as the type of optical fiber and the frequency and amplitude of the electrical signal applied on the piezoelectric ceramic in the experiment were investigated.The results show that the detected light intensity of the vibration position was not found to change significantly with the voltage and frequency of the applied sine wave signal.,single-mode fiber is more suitable for ?-OTDR system.In addition,this dissertation proposes a method combining ?-OTDR technology and Raman amplification technology to build a more simplified long-distance distributed vibration monitoring system,which successfully detects vibration on 45 km fiber.Finally,due to the limitation of experimental conditions,the related problems of ?-OTDR were further studied by modeling.The ?-OTDR was modeled based on the relationship Rayleigh scattered light power and phase,and the problems of renew and phase ambiguity of vibration signals were simulated.The demodulation method of Coherent Optical Time Domain Reflectometry(COTDR)is applied to ?-OTDR,and the normalized cross-correlation calculation and peak detection method as a new demodulation method of ?-OTDR system is validated.This work has a certain reference value for the performance optimization of long-distance distributed optical fiber vibration sensing system.