Point-to-point stabilized optical frequency transfer with active optics

Benjamin P. Dix-Matthews, Sascha W. Schediwy, David R. Gozzard, Etienne Savalle, François-Xavier Esnault, Thomas Lévèque, Charles Gravestock, Darlene D'Mello, Skevos Karpathakis, Michael Tobar, Peter Wolf

Research output: Contribution to journalArticlepeer-review

47 Citations (Scopus)


Timescale comparison between optical atomic clocks over ground-to-space and terrestrial free-space laser links will have enormous benefits for fundamental and applied sciences. However, atmospheric turbulence creates phase noise and beam wander that degrade the measurement precision. Here we report on phase-stabilized optical frequency transfer over a 265 m horizontal point-to-point free-space link between optical terminals with active tip-tilt mirrors to suppress beam wander, in a compact, human-portable set-up. A phase-stabilized 715 m underground optical fiber link between the two terminals is used to measure the performance of the free-space link. The active optical terminals enable continuous, cycle-slip free, coherent transmission over periods longer than an hour. In this work, we achieve residual instabilities of 2.7 × 10−6 rad2 Hz−1 at 1 Hz in phase, and 1.6 × 10−19 at 40 s of integration in fractional frequency; this performance surpasses the best optical atomic clocks, ensuring clock-limited frequency comparison over turbulent free-space links.
Original languageEnglish
Article number515
Number of pages8
JournalNature Communications
Issue number1
Publication statusPublished - 1 Dec 2021


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