The Research On Locating Fiber Perimeter Sensor

Fiber perimeter senor can be divided into two types: Regional and Locat ing. The topic of this thesis is fiber perimeter sensor based on Mach-Zehnde r Interferometer.Firstly, a general review of the fiber-optic perimeter sensor is given.Then, different design schemes of locating fiber-optic preimeter sensor are introduced and analyzed. Currently, fiber-optic interferometer is the most mature distributed locating fiber-optic preimeter sensor. OTDR is also a potentially alternative. But OTDR is more complex and more expensive. There are mainly two schemes based on fiber-optic interferometer, one is based on Sagnac, the other is based on Mach-Zehnder. The hardware of the latter is simpler and more mature. What really matters is the signal processing. The system discribed in this thesis is based on Mach-Zehnder interferometer, which can be used for intrusion detecting and the spot can also be located by the cross-correlation algorithm. Main contents of the thesis are as follows:(1)the designing of the hardware system.The hardware is based on Mach-Zehnder interferometer, which includes duplex fiber cable, laser, coupler, isolator, photoelectric detection module, acquisition card and so on. When there is a vibration signal, there will be phase modulation which can be detected.(2)the designing of the software system.The Software part is the most importent part of the whole system. The process is as follows: firstly, the total variation was calculated, the intrusion can be detected by compared with a threshold of the total variation. Then the signal is compressed and denoised by wavelet transform. At last, the spot is located by cross-correlation algorithm.In real tests, for 1km fiber, the locating accuracy of the system is ±20m.