Cascaded Fiber-Optic Interferometers for Multi-Perimeter-Zone Intrusion Detection With a Single Fiber Used for Each Defended Zone

A new fiber-optic perimeter intrusion detection system employing only one single-mode fiber as a disturbance sensor for each perimeter zone is presented. A disturbance signal generated through interference between lights from two resonators, i.e., a linear laser cavity and an extended resonator, was used for determining intrusion for each defended zone. A single-mode fiber was used not only for sensing the intrusion-induced disturbance but also for transmission of pump and signal lights. Although many papers have reported multi-perimeter-zone intrusion detection systems, the study presents, for the first time, a system with a single-mode fiber used all along the perimeter that is in a line pattern and is sectioned into multiple defended zones. An outdoor test for a four perimeter-zone intrusion detection system was carried out with a short section of fiber attached on a netted fence in each defended zone. Experimental results demonstrated that there was no cross interference between any two defended-zone light circuits, and that a high alarm-upon-intrusion rate and a zero false alarm rate could be reached by using the presented detection algorithm.