Cascaded multiplexed optical link on a telecommunication network for frequency dissemination

TL;DR

This paper demonstrates a cascaded optical link system integrated with telecommunication networks for ultra-stable frequency dissemination, achieving high stability over long distances and enabling remote optical clock synchronization.

Contribution

It introduces a novel cascaded optical link setup with integrated telecommunication infrastructure for stable frequency transfer, including autonomous repeater stations and bidirectional multiplexing.

Findings

Fractional frequency instability of 3×10^-15 at 1 second

Achieved 5×10^-20 instability over 20 hours

Integrated 150 km links with existing Internet fiber infrastructure

Abstract

We demonstrate a cascaded optical link for ultrastable frequency dissemination comprised of two compensated links of 150 km and a repeater station. Each link includes 114 km of Internet fiber simultaneously carrying data traffic through a dense wavelength division multiplexing technology, and passes through two routing centers of the telecommunication network. The optical reference signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The repeater station operates autonomously ensuring noise compensation on the two links and the ultra-stable signal optical regeneration. The compensated link shows a fractional frequency instability of 3 \times 10-15 at one second measurement time and 5 \times 10-20 at 20 hours. This work paves the way to a wide dissemination of ultra-stable optical clock signals between distant laboratories via the Internet network.