Distributed Raman optical amplification in phase coherent transfer of optical frequencies

TL;DR

This paper demonstrates the use of Raman Optical-fiber Amplification (ROA) for phase coherent transfer of optical frequencies over long fiber links, achieving high stability and analyzing amplification schemes and nonlinear effects.

Contribution

It introduces the application of ROA in phase coherent optical frequency transfer, evaluating its performance and limitations over 200 km fiber links.

Findings

Achieved fractional frequency instability of 3e-19 over 1000 seconds.

Compared co-propagating and counter-propagating pump schemes, identifying nonlinear effects.

Demonstrated effective phase coherent transfer using ROA with noise compensation.

Abstract

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.