  We describe the application of Raman Optical-fiber Amplification (ROA) for
the phase coherent transfer of optical frequencies in an optical fiber link.
ROA uses the transmission fiber itself as a gain medium for bi-directional
coherent amplification. In a test setup we evaluated the ROA in terms of on-off
gain, signal-to-noise ratio, and phase noise added to the carrier. We
transferred a laser frequency in a 200 km optical fiber link with an additional
16 dB fixed attenuator (equivalent to 275 km of fiber on a single span), and
evaluated both co-propagating and counter-propagating amplification pump
schemes, demonstrating nonlinear effects limiting the co-propagating pump
configuration. The frequency at the remote end has a fractional frequency
instability of 3e-19 over 1000 s with the optical fiber link noise
compensation.
