High Sensitivity $\varphi$ -OTDR Over Long Distance With Polarization Multiplexed Codes

Newly introduced polarization diversity probing codes are suggested to enhance the sensitivity and bandwidth performance of differential phase-sensitive distributed OTDR systems. This was recently demonstrated by means of short-length specialized fibers with a backscattering induced by equally spaced Fiber Bragg Gratings inserted in the fiber itself. The work summarized in this letter aims to extend the polarization-diversity probing technique to widely spread standard single mode fibers (SSMF) used for telecommunications, by solely exploiting the Rayleigh backscattering. Conditions to achieve perfect phase estimation along such fibers are first detailed. An experimental validation highlights the ability to detect and localize, over 25km of SSMF, multiple low-energy perturbations within a 475Hz-bandwidth.