Long-distance remote comparison of ultrastable optical frequencies with 1e-15 instability in fractions of a second

TL;DR

This paper reports a groundbreaking remote optical frequency comparison over 50 km, achieving a fractional instability of 3e-15 in 0.1 seconds, surpassing previous methods and enabling rapid dissemination of ultra-stable laser frequencies.

Contribution

It introduces a fully optical, long-distance comparison technique using phase-stabilized fiber in a telecom network, achieving unprecedented short-term stability in remote optical frequency measurements.

Findings

Achieved 3e-15 fractional instability in 0.1 seconds.

Demonstrated remote comparison over 50 km with superior stability.

Enabled rapid dissemination of ultra-stable laser frequencies.

Abstract

We demonstrate a fully optical, long-distance remote comparison of independent ultrastable optical frequencies reaching a short term stability that is superior to any reported remote comparison of optical frequencies. We use two ultrastable lasers, which are separated by a geographical distance of more than 50 km, and compare them via a 73 km long phase-stabilized fiber in a commercial telecommunication network. The remote characterization spans more than one optical octave and reaches a fractional frequency instability between the independent ultrastable laser systems of 3e-15 in 0.1 s. The achieved performance at 100 ms represents an improvement by one order of magnitude to any previously reported remote comparison of optical frequencies and enables future remote dissemination of the stability of 100 mHz linewidth lasers within seconds.