Fiber-Optic Perimeter Intrusion Detection by Employing a Fiber Laser Cavity in Each Defensed Zone

A fiber laser cavity was employed for the first time in fiber-optic multi-zone perimeter intrusion detection system. A length of four-core armored fiber cable was configured into multiple sections with each defensing a perimeter zone. For each defensed perimeter zone, only three single-mode fibers of the four-core fiber cable were employed for intrusion detection. Two of them were used for constructing a Michelson interferometer, which sensed the disturbance excited by intruders, whereas, the other one carried light between the sensing site and the receiver site. The most distinctive part of the proposed system lies in the use of a fiber laser cavity with the Michelson interferometer serving as an end mirror for intrusion detection at each perimeter zone. Experimental results showed that upon intrusion, a 100% alarm rate could be reached by properly setting the thresholds of three intrusion parameters for alarm and that the properly set thresholds could reliably trigger alarms upon intrusion under various weather conditions.