Optical frequency transfer via 146 km fiber link with 10^{-19} relative accuracy

TL;DR

This paper demonstrates ultra-precise optical frequency transfer over 146 km fiber with near-theoretical stability and an uncertainty below 10^{-19}, advancing long-distance frequency standard dissemination.

Contribution

It presents a highly stable optical frequency transfer method over long fiber links with unprecedented accuracy and stability, approaching fundamental limits.

Findings

Fractional instability of 3*10^{-15} at 1 s over 146 km

Relative uncertainty below 1*10^{-19} after 30,000 seconds

Noise contributions are two orders of magnitude lower in short fiber tests

Abstract

We demonstrate the long-distance transmission of an ultra-stable optical frequency derived directly from a state-of-the-art optical frequency standard. Using an active stabilization system we deliver the frequency via a 146 km long underground fiber link with a fractional instability of 3*10^{-15} at 1 s, which is close to the theoretical limit for our transfer experiment. The relative uncertainty for the transfer is below 1*10^{-19} after 30 000 seconds. Tests with a very short fiber show that noise in our stabilization system contributes fluctuations which are two orders of magnitude lower, namely 3*10^{-17} at 1 s, reaching 10^{-20} after 4000 s.