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Multi-Zone Fiber-Optic Intrusion Detection System With Active Unbalanced Michelson Interferometer Used for Security of Each Defended Zone

A new fiber-optic system with an active unbalanced Michelson interferometer (AUMI) was designed for multi-zone perimeter intrusion detection by employing only two single-mode fibers for each sensing zone. A pump laser at the monitor site was used to remotely pump the erbium-doped fibers located, respectively, at the two arms of the AUMI for each sensing zone. Configured into a fiber laser cavity, the AUMI served as an optical switch that would modulate the optical power when one arm of the AUMI was perturbed by intrusion to induce a phase offset variation. In the study, an armored cable with a length of 200 meters in total was divided into four sections each guarding a perimeter zone. The experimental results showed that the AUMI system correctly responded to perturbations induced by footstepping on a fiber cable buried underground, vibrating a netted fence, or knocking a window. A high alarm-upon-intrusion rate and zero false alarm rate could be reached by using the presented detection algorithm.