Research And Security Application On High-performance Long Distance Phase-sensitive Optical Time-domain Reflectometer System

Phase-sensitive optical time domain reflectometer is an effective tool allowing fully distributed monitoring of vibrations along the fiber cables with distinguished advantages of not only anti-electromagnetic interference, resistance to corrosion,but also multi-point detection, long sensing distance and high sensitivity, thus it has great potential in many security applications, such as safety monitoring of pipelines, airports, borderlines and other long-distance perimeters.In order to further improve the Φ-OTDR system’s performance and put it into practical use, this paper does the following works from the perspective of theory and its application in engineering:(1) Proceeding from the principle of Rayleigh backscattering, this paper studies on Φ-OTDR sensing mechanism, list out the system’s key performance indicators: sensing distance, spatial resolution, response frequency, signal-to-noise ratio, and analysis their impact factor;(2) Considering the limitations of just using Raman amplification or heterodyne detection to improve the Φ-OTDR system’s performance, this paper presents a scheme combining Raman amplification with heterodyne detection. It uses heterodyne detection to increase the conversion gain and signal-to-noise ratio of Rayleigh backscattering light, meanwhile uses Raman amplification to compensate Rayleigh backscattering light’s transmission loss. The scheme can realise a novel high-performance Φ-OTDR system whose sensing distance up to 103 km, for the longest distance reported so far, the spatial resolution of 15.7m, SNR up to 7.89 dB. And in the pipeline gouge experiment it has good effect of resolution;(3) According to Internet of Things’ technology framework, security monitoring system based on Φ-OTDR can be divided into three layers: Φ-OTDR hardware as the sensing layer; network layer for the TCP/IP, RS-232, user defined communication protocols, etc.; application layer for the alarm service. At the network layer, this paper designs two kinds of communication protocols to provide services for application layer: structure and data frames forms, and their underlying transport protocol can be TCP or RS-232, and so on. By using software modular programming with the MFC framework based on stream Socket and Socket API, this paper achieves the communication module, which makes Φ-OTDR security monitoring system with communicaiton features such as alarm message sent, real-time data transmission;(4) For security applications this paper design an application integration solution involved in Φ-OTDR monitoring system, audio broadcasts and video cameras. In forming defensive area of partitioning and mapping sensor cable along the perimeter, the alarm area number was sent to the alarm center over the network when the invasion happened. The alarm center makes the relevant video camera rotate to capture current activities and corresponding audio broadcast to issue alarm sounds according to the alarm area number, which produce a rapid response intelligent system. In the early stages of engineering application, this paper uses protocol converters to accept Φ-OTDR system’s alarm signal, and light up the corresponding LEDs. The test on mining of oil pipeline demonstrate the system have functions of partial map, local alerts and network communication.