  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.
