Network Integrity Systems, Inc.

Joseph Giovanni

Cary R Murphy

Mark K Bridges

David E Vokey

Daniel M Goertzen

Some or all of the optical fibers of a single-mode or multi-mode cable are monitored for intrusion by transmitting through the fibers a signal which can be analyzed for changes in its characteristics which are indicative of movement as a prelude to an intrusion event. To avoid independent monitors of all of the fibers, in some cases the same light signal is looped through a plurality of the fibers in series by passive jumpers. Switches can be used to disconnect out those fibers which are compromised. As an alternative a plurality of separate monitoring signals can be provided each associated with its own sensor where unique combinations of the signals are transmitted through separate fibers allowing a higher number of fibers to be monitored than the number of signals.

Monitoring individual fibers of an optical cable for intrusion

Intrusion detection for a multimode fiber optic cable uses a light signal launched into the fiber through the low ratio leg of a tap coupler to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the cable. A small portion of the higher order signal modes at the remote end is monitored for transient changes in the mode field power distribution which are characteristic of fiber intrusion to activate an alarm. The active signal of a multimode optical fiber is monitored for both signal degradation and transient power disturbance patterns that could indicate fiber damage or physical intrusion. A translator can be provided in an existing optical fiber system in which the data signals are translated in wavelength and/or launch conditions to optimize the monitoring signals in an otherwise non-optimized system.

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Conover, NC, United States of America

Joseph Giovanni