Patent ID: 7139476

Claim:
An apparatus for detecting and locating a disturbance, comprising: at least one light source; an optical system comprising at least one optical waveguide, the optical waveguide having at least one detection zone defining a length, wherein a disturbance to be detected and located can occur at a place that can be near one or another of respective ends of the detection zone; wherein the optical system is configured to carry signals along at least two counter-propagating optical channels extending in opposite directions along said length of the detection zone such that the disturbance produces a phase variation between polarization components, originating at the place of the disturbance; at least one beam separator coupled to the optical system, wherein the beam separator develops at least two beams coupled into said two counter-propagating optical channels, respectively; at least one polarization sensitive beam combiner operative selectively to combine polarization components of said at least two beams traveling along the optical waveguide, the polarization sensitive beam combiner being coupled to the optical waveguide so as to act upon at least one of said two counter-propagating optical channels, where said at least one of said two counter-propagating optical channels is propagating in a direction that is one of toward the detection zone and away from the detection zone; at least one polarization sensitive detector coupled to the optical waveguide; a data processing unit coupled to the polarization sensitive detector, the data processing unit being operable to localize the place of the disturbance to a point along said length, between said ends of the detection zone, from a difference in time of propagation of the phase variation in said opposite directions.