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Femtosecond synchronization of optical clocks over free-space links



Jean-Daniel Deschenes, Laura C. Sinclair, Fabrizio R. Giorgetta, William C. Swann, Esther Baumann, Hugo Bergeron, Michael A. Cermak, Nathan R. Newbury


The use of optical clocks/oscillators in future ultra-precise navigation, gravitational sensing, and relativity experiments will require time comparison and synchronization over terrestrial or satellite free-space links. Here we demonstrate full synchronization of two optical oscillators across a free-space link. The time deviation between synchronized oscillators is below 1 fs over timescales from 0.1 s to 6500 s, despite atmospheric turbulence, beam interruptions, and kilometer-scale path length variations. Over 50 hours, the time offset is below ±20 fs. Our approach relies on the two-way reciprocity of a single spatial-mode optical link, valid to below 225 attoseconds across a turbulent 4-km path. This fs-level of time-frequency transfer should enable optical networks using state-of-the-art optical clocks/oscillators.
Physical Review X


Deschenes, J. , Sinclair, L. , Giorgetta, F. , Swann, W. , Baumann, E. , Bergeron, H. , Cermak, M. and Newbury, N. (2015), Femtosecond synchronization of optical clocks over free-space links, Physical Review X, [online], (Accessed May 21, 2024)


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Created December 10, 2015, Updated October 12, 2021