Buried fiber intrusion detection sensor with minimal false alarm rates

A novel design approach for a highly reliable buried intrusion detection sensor is described. The design involves the use of a low cost depolarized Sagnac fiber interferometer with a 'sensing loop' consisting of a delay line and buried fiber segment. The intrusion sensor is configured for an 'all fiber' remote deployment where active components (source, receiver, demodulator) are located separately and connected to the sensor through an insensitive fiber tether. A robust and cost effective buried sensor 'mat' design was developed. This design enabled high sensitivity as well as ease of deployment. Sensors were built and evaluated. Test results indicate an effective design.