Stabilized free-space optical frequency transfer

TL;DR

This paper demonstrates actively stabilized free-space optical frequency transfer over 150 m and 600 m links, achieving high stability suitable for optical clock signals, with potential applications in satellite communication and fundamental physics tests.

Contribution

It presents the first active stabilization of optical frequency transfer over free-space links up to 600 m with high stability, addressing atmospheric turbulence effects.

Findings

Achieved fractional frequency stability of 8.9e-18 at 1 s over 600 m.

Stability improves to 1.3e-18 at 64 s integration time.

Signal deep-fading limits transfer distance due to atmospheric turbulence.

Abstract

The transfer of high-precision optical frequency signals over free-space links, particularly between ground stations and satellites, will enable advances in fields ranging from coherent optical communications and satellite Doppler ranging to tests of General Relativity and fundamental physics. We present results for the actively stabilized coherent phase transfer of a 193 THz continuous wave optical frequency signal over horizontal free-space links 150 m and 600 m in length. Over the 600 m link we achieved a fractional frequency stability of 8.9e-18 at one second of integration time, improving to 1.3e-18 at an integration time of 64 s, suitable for transmission of optical atomic clock signals. The achievable transfer distance is limited by deep-fading of the transmitted signal due to atmospheric turbulence. We also estimate the expected additional degradation in stability performance for frequency transfer to Low Earth Orbit.