Fiber-Optic Multizone Intrusion Detection System Based on Fabry–Perot Interferometers With Fiber Bragg Gratings

This article introduces a new type of fiber-optic multi-perimeter zone (PZ) intrusion detection system with a sensing fiber (SF) sandwiched between a pair of fiber Bragg gratings (FBGs) to form a fiber Fabry–Perot interferometer (FFPI) for each PZ. These FFPIs are cascaded into a line by using only an optical fiber contained in a fiber cable and defend, respectively, multiple PZs. These FFPIs operate at different optical wavelengths, corresponding to the laser lights emitted from a wavelength-division-multiplexing (WDM) source at the monitoring station. The reflected light from each FFPI carries a signal equivalent to the disturbance on the SF. After the reflected lights from all PZs are detected by corresponding photodetectors (PDs) at the monitoring station, these signals would be processed to determine which PZ is disturbed by intruders. In outdoor experiments, we have measured the performance of this new type of intrusion detection system with four PZs. We observed a 100% alarm rate for whichever PZ to be invaded and zero false alarm rates for all of the PZs when they are not invaded, in which case they could be tapped or lightly disturbed by humans or small animals or disturbed by environmental effects, such as sound noise, wind, and rain.