Improve The Performance Of Distributed Fiber §¶-otdr Security Systems

Along with rapid development of the technology and economy, the residential safety is required more and more highly, a variety of security systems are constantly emerging. In this paper, a novel security systems based on theΦ-OTDR (phase-sensitive optical time-domain reflectometer,) distributed optical fiber sensing technology is proposed. The technology achieves the purpose of sensing by coherent addition of amplitudes of the light backscattered from different parts of the fiber which arrive simultaneously at the photodetector. As a practical matter, theΦ-OTDR can detect perturbations much too weak to be perceived with a conventional OTDR system. Compared with ordinary sensing system, distributed fiber-optic sensing system has many advantages. Conventional sensors such as shock sensors, sound sensors, infrared sensors, magnetic sensors etc can only be used individually in small-scale, and often have a poor concealment, the distributed fiber sensing technology make use of the optical fibers along the path as the sensitive components to carry out large-scale monitoring, The sensor cable is buried under ground and has a very good concealment. The biggest advantage of distributed fiber sensing system is its low cost; a commercial distributed optical fiber sensor system can replace at least 1,000 point sensors. The subject has a strong practical value and innovative,Φ-OTDR technology is reported in recent years, there are few researchers on this domain. The author has done a great deal of pioneering research on three aspects: reducing the system costs, extending the sensing distance, and the practical research.The detailed work of the thesis is listed as follow:(1) Starting with the theory of OTDR, the theory ofΦ-OTDR distributed optic-fiber sensing system was discussed.(2) AnΦ-OTDR distributed optic-fiber sensing system based on a DFB laser and a special FRP encapsulated fiber cable was proposed. The system can locate the intrusion point, within a distance range of 8km, with the best spatial resolution of 100m.(3) AnΦ-OTDR distributed optic-fiber sensing system based on a fiber laser with high power and narrow linewidth was proposed and constructed. Using the self-designed EDFA, the sense distance had been extended to 32km.(4) A long-distanceΦ-OTDR distributed optic-fiber sensing system based on Raman amplification was designed, achieving the sensing distance 62km (which is the longest to the best of our knowledge).(5) Studying the wavelet signal processing algorithms to reduce the noise in the alarm signal and the algorithm had been applied on the DSP .Intrusion alarm system software was designed and developed on LabVIEW.