Patent ID: 7693359

Claim:
A method for detecting movement of an optical fiber comprising: providing a optical fiber having a first end and a second end; detecting movement of a portion of the fiber along the length thereof by: injecting polarized light into one end of the optical fiber; detecting at one end of the fiber a series of received light signals which have been transmitted along the fiber; comparing 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; and 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; wherein the changes in polarization are detected by splitting the received light signals into a plurality of paths including first and second paths and using the first path to detect an amplitude of the light in the path when polarized in a linear direction and using the second path to detect an amplitude of the light in the path when polarized in a circular direction; wherein the splitter is selected such that the state of polarization (SOP) of the signals in the separate paths are NOT maintained relative to an absolute reference as would be required in a standard polarimeter.