Fiber Raman amplification for metrological transfer of phase-coherent optical frequencies

We analyze the benefits of distributed Raman amplification in metrology transfer of phase-coherent ultra-narrowband optical frequencies in a long fiber link (200 km with additional 16 dB loss), providing high-gain bi-directional amplification with limited impact on phase noise, attaining a fractional frequency instability of 3 × 10
^-
19 over 1000 s.