Research On Design And Performance Optimization Of Distributed Optical Fiber Vibration Monitoring System

With the rapid development of optical fiber technology and optical communication technology,optical cables have been deeply integrated into the process of national construction as a basic resource.Human factors such as manual excavation,large mechanical operations,and accidental cutting and breaking by maintenance personnel have become the main cause and potential threat of abnormal vibration or external damage of optical cables.The distributed optical fiber vibration sensing system based on φ-OTDR is based on the optical fiber itself as the sensing element,without external sensors and other transmission networks,with low cost,anti-electromagnetic interference,fast response,long-distance detection and other advantages.It can realize the long-distance distributed vibration detection of the line by using the existing optical fiber,and become an effective monitoring means of optical cable channel breakage,complex optical cable identification,and has also been effectively developed and promoted in the power system,oil pipeline,perimeter security and other fields.However,the traditional(p-OTDR system still has shortcomings in noise reduction processing,efficient demodulation,and diversified applications.Therefore,it is of great significance to study the distributed optical fiber vibration monitoring system based on φ-OTDR,optimize and improve the performance of the sensing system,and expand the application scope to ensure the safe operation of optical fiber lines and promote the large-scale application of distributed optical fiber sensing technology.In this paper,a φ-OTDR signal-to-noise ratio improvement scheme based on FBG narrow bandwidth filtering is proposed.The multi-channel optical cable identification research based on φ-OTDR was carried out,and the real-time identification of 4-channel optical cable was realized.The real-time φ-OTDR monitoring integrated software is designed,which can display the real-time interface,abnormal alarm and storage functions.The main work content is as follows:(1)This paper analyzes the relevant theories of φ-OTDR system in detail,a distributed optical fiber vibration monitoring system based on heterodyne coherent detection and IQ demodulation and its comprehensive processing software are designed.A distributed optical fiber vibration monitoring prototype is developed.The system computer software can display the vibration signal curve in real time and alarm the abnormal position,and the system monitoring length can reach 40km under laboratory conditions.(2)Aiming at the problem that the power optical cable network is complex and cannot accurately identify the optical cable,a solution based on the time division multiplexing and frequency matching technology of optical switch is proposed,which realizes the vibration monitoring and rapid identification of the 4-channel optical cable.(3)A signal-to-noise ratio improvement scheme of φ-OTDR system based on FBG narrowband filtering is proposed,and an efficient filtering structure of small signal return light of φ-OTDR system is designed.Compared with the traditional DWDM filtering scheme,the signal-tonoise ratio is improved by more than 3dB,and the performance of distributed optical fiber vibration monitoring system is optimized.