Two-Way Optical Frequency Comparisons Over 100km Telecommunication Network Fibers

TL;DR

This paper demonstrates ultra-high resolution optical frequency comparisons over 100 km telecommunication fibers using two-way transfer, achieving remarkable stability and uncertainty levels suitable for intercontinental optical clock comparisons.

Contribution

It introduces a bi-directional scheme with a single fiber and a real-time two-way comparison over parallel fibers, advancing high-precision frequency transfer over existing telecommunication networks.

Findings

Relative stability of 7×10^-18 at 1 s with bi-directional scheme

Achieved fractional uncertainty of 2×10^-20 in frequency comparison

Real-time comparison over 100 km fibers with high stability

Abstract

By using two-way frequency transfer, we demonstrate ultra-high resolution comparison of optical frequencies over a telecommunication fiber link of 100 km operating simultaneously digital data transfer. We first propose and experiment a bi-directional scheme using a single fiber. We show that the relative stability at 1 s integration time is 7 10^18 and scales down to 5 10^21. The same level of performance is reached when an optical link is implemented with an active compensation of the fiber noise. We also implement a real-time two-way frequency comparison over a uni-directional telecommunication network using a pair of parallel fibers. The relative frequency stability is 10^15 at 1 s integration time and reaches 2 10^17 at 40 000 s. The fractional uncertainty of the frequency comparisons was evaluated for the best case to 2 10^20. These results open the way to accurate and high resolution frequency comparison of optical clocks over intercontinental fiber networks.