Perimeter security system based on fiber optic disturbance sensor

The design and field test of a perimeter security system based on fiber optic disturbance sensor was described. The system consisted of fiber optic disturbance sensor and control computer. The fiber optic disturbance sensor was in Mach-Zehnder interferometer configuration using single mode fiber cable, which made the system relatively low cost. A digital Phase Generated Carrier (PGC) demodulation technique was used to eliminate phase drifts in the interferometric sensor. The demodulator was based on Field Programmable Gate Array(FPGA) and Digital Signal Processor(DSP). A prototype system with 1Km sensing cable was constructed and tested. The sensing cable was bound on the fence to detect disturbance generated by intruder. The test result verified that this sensor was sensitive to intrusion behavior. Typical disturbance signal was recorded when intrusion behavior was going on. There was obvious characteristic in the recorded signal. Intrusion behavior generated non-stable random signal, which had many amplitude peaks. And the frequency was below 500Hz. This was helpful for recognition algorithms development. Wind in the test field also generated low frequency background noise and increased recognizing difficulties.