Securitized Optical Fiber Communication and Sensor Systems Using Mode-Selective Couplers

In this paper, we report the results of testing a securitized hybrid sensing/communication system. A long-period grating sensor operating in the 1550 nm range along a bidirectional communication link at 1310 nm is securitized against intrusion by launching visible light at 650 nm through a splitter. The arising few-mode interference pattern changes are monitored and the responses to a variety of deformations on the fiber link are investigated. It is shown that the intrusion sensing channel is activated by even the weakest deformations imposed on the fiber with no losses on the channel being incurred. Analysis of the intermodal pattern changes make it possible to discern the types of deformations imposed on the sensor-communication channel.