Patent ID: 7206469

Claim:
A method for securing a telecommunications optical fiber against intrusion comprising: providing a telecommunications optical fiber having a transmit end and a receive end; providing for the optical fiber a transmitter of optical pulses at the transmit end and a receiver of the transmitted optical pulses at the receive end such that data can be transmitted along the fiber in a telecommunications system; detecting manipulation of the optical fiber causing movement of a portion thereof along the length thereof by; injecting polarized light pulses into an end of the optical fiber, detecting at an end of the optical fiber a series of received light signals which have been transmitted along the fiber and which include reflected and/or backscattered components; comparing in a polarimeter at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes of polarization of the received light signals relative to the previously received light signals; analyzing the changes in polarization to determine any changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; and generating an alarm in response to the detection of any such changes which are indicative of manipulation of the optical fiber causing movement of a portion thereof along the length thereof; wherein the changes in polarization are detected by splitting the received light signals into at least first and second paths and using the first path to detect an amplitude of the light in the path when linearly polarized and using the second path to detect an amplitude of the light in the path when circularly polarized.