Metrological transfer of phase-coherent optical frequencies over long distances employing Distributed Raman Amplification

In this paper we analyze Distributed Raman Amplification (DRA) for phase-coherent optical links, showing the promising features as well as the existing limits for such a new technique. After the demonstration of an optical frequency transfer on 200 km in single fiber span in our experiment, with a frequency instability of 3×10^-19 at 100-1000 s, we present an analysis aimed in particular at extending the technique on significantly longer hauls and at overcoming detrimental nonlinear effects.