MULTIMODE FIBER OPTIC INTRUSION DETECTION SYSTEM

摘要

A method and system of intrusion detection for a multimode fiber optic cable (12). A signal is launched into the cable (12) to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the cable (12). A small portion of the higher order signal modes arriving at the remote end (28) of the cable (12) is sampled and monitored for transient changes in the mode field power distribution, which changes with physical disturbance of the cable (12). When changes characteristic of fiber intrusion are detected, an alarm activates. Attempt to access optical fibers in a communication cable can be sensed and alarmed. The active signal of a multimode optical fiber (12) is monitored for signal degradation and transient power disturbance patterns that could indicate fiber damage or physical intrusion. Using adaptive filtering, normal background disturbances from heating/cooling systems, motors, fans and other building systems can be filtered out.