Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

TL;DR

This paper demonstrates a two-way optical phase comparison technique over a multiplexed fiber network, achieving ultra-stable frequency transfer by passively cancelling fiber noise, with potential for complex future applications.

Contribution

It introduces a passive two-way optical phase comparison method that cancels fiber noise without active stabilization, enhancing frequency transfer stability over metropolitan networks.

Findings

Achieved 1E-21 stability in optical frequency comparison.

Successfully performed on a 47 km fiber in a metropolitan network.

Demonstrated passive noise cancellation advantages.

Abstract

We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this technique, the fiber noise was passively cancelled, and we compared two optical frequencies at the ultimate 1E-21 stability level. The experiment was performed on a 47 km fiber that is part of the metropolitan network for Internet traffic. The technique relies on the synchronous measurement of the optical phases at the two ends of the link, that is made possible by the use of digital electronics. This scheme offers several advantages with respect to active noise cancellation, and can be upgraded to perform more complex tasks.