Patent ID: 7142736

Claim:
An apparatus for detecting and locating disturbances, comprising: at least one light source; an optical system with at least one optical waveguide, the optical waveguide having at least one detection zone at which a disturbance can occur and affect optical signals from the light source when traveling through the waveguide, in the detection zone, along counter-propagating optical channels; at least one beam separator between the light source and the optical system, wherein the beam separator couples at least two beams into the optical waveguide for each of the at least two counter-propagating optical channels; at least one polarization controller operable to manage optical properties of said counter-propagating optical channels, the polarization controller adjusting optical properties for at least one of the optical signals when propagating toward the detection zone; at least one detector coupled to the optical waveguide and responsive to the optical signals after traversing the detection zone; a data processing unit coupled to the detector, the data processing unit being operable to localize a place of the disturbance in the detection zone from a difference between times at which effects of the disturbance appear at the detector; and, a feedback control coupled to the optical system and to at least one said polarization controller, wherein the feedback control and the polarization controller are configured to maximize a signal-to-noise ratio and to minimize a polarization contribution to said difference between times, by at least one of: seeking a predetermined relationship between polarization phase transformations along the counter-propagating optical channels, maximizing a peak swing in intensity at a point of interference of the beams, and varying an input state of polarization for one of testing and adjusting a balance between said polarization transformations for the counter-propagating channels.