Hybrid TDM/WDM-Based Fiber-Optic Sensor Network for Perimeter Intrusion Detection

A distributed fiber-optic sensor system is proposed and demonstrated for long-distance intrusion-detection, which employs the hybrid time/wavelength division multiplexing architecture. The sensing elements are single-mode telecommunication fiber which can be hanged on the fence and hedge or buried along the monitored perimeter. The pulsed light generated by the superluminescent diode was filtered by the filter which has multichannel (m=6), and then amplified by erbium-doped fiber amplifiers. A 1×(n+1) (n=20) splitter of which every port has a fiber delay coil except the first port splits the amplified light. The fiber delay coils have different lengths, which generate different delay time and produce n time zones. By utilizing the m channel dense wave-length division multiplexing modules, every fiber sensing unit (OSU)-based unbalance Mach-Zehnder Sagnac interferometer technology occupy a time zone and a wavelength. By utilizing 20 time zones and 6 wavelengths, the system contains up to 120 OSUs, of which the distributed sensing distance is from 0 to 500 m. So, the whole sensing distance of this system could reach 60 km. The system has been demonstrated to stably run over six months with the false alarm rate of less than 4%.