Patent ID: 8736826

Claim:
A method of monitoring a length of single-mode optical fiber for physical disturbance along its length, comprising the steps of: (i) at a first location, launching into the fiber polarized light having at least two different predetermined launch states of polarization (L a ,L b ) whose respective Stokes vectors (s La , s Lb ) are linearly independent of each other; (ii) at a second location downstream from the first location, receiving the light from the fiber; (iii) analyzing the received light using at least two different analyzer states of polarization that are characterized by respective Stokes vectors that are linearly-independent of each other; (iv) detecting the analyzed light to provide corresponding electrical detection signals and deriving therefrom corresponding digital detection signals; (v) deriving from the digital detection signals one or more representations ([s a (t 1 ), s b (t 1 )], [s a (t 2 ), s b (t 2 )]; M(t 1 ,t 2 ); c(t 1 ,t 2 ); C(t 1 ), C(t 2 )) of a change in the polarization coupling properties (R) of the fiber between a first time (t 1 ) and a second time (t 2 ); (vi) computing from said one or more representations at least one measure of change in polarization coupling properties of the fiber, said at least one measure being substantially independent of said launch states and said analyzer states; and (vii) determining with reference to preselected criteria of reportable physical disturbances whether or not said at least one measure indicates a reportable physical disturbance along said length of fiber.