Coherent frequency transfer over long-haul and shared optical fiber links employing distributed Raman amplification

In this work we report the results of a study on phase-coherent transfer of narrow linewidth optical frequencies in single-mode fiber links employing bi-directional distributed Raman amplification (DRA). Both co- and counter-propagating amplification pump schemes have been investigated and with optimized input parameters, a coherent optical frequency at 1542 nm was transferred on a 305 km fiber. We also describe the optical frequency transfer on a 94-km long metro fiber link in presence of two ITU WDM telecom data channels with the help of DRA, allowing for an attained fractional frequency instability of 3·10^-19 at 1000 s for the transferred frequency signal.