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Femtosecond Time Synchronization of Optical Clocks Off a Flying Quadcopter



Hugo Bergeron, Laura C. Sinclair, William C. Swann, Isaac H. Khader, Kevin C. Cossel, Michael A. Cermak, Jean-Daniel Deschenes, Nathan R. Newbury


Optical clock networks promise advances in global navigation, time distribution, coherent sensing, relativity experiments, dark matter searches and other areas1-12. Such networks will need to compare and synchronize clocks over free-space optical links. Optical two-way time- frequency transfer (O-TWTFT) has synchronized clocks to 10^-19 in frequency and <1 fs in time across turbulent free-space links, but between fixed terminals where complete reciprocity in time-of-flight across the single-mode link underwrites the performance. The addition of motion leads to breakdown in this time-of-flight reciprocity and therefore degrades O-TWTFT. Here, we show the inclusion of velocity-dependent effects into comb-based O-TWTFT allows for essentially penalty-free operation with velocity. Over turbulent km-scale paths, using a quadcopter-mounted retroreflector or swept delay line at velocities up to ±24 m/s, we synchronize clocks to 10^-17 at 100 s in frequency, despite 10^-7 Doppler shifts, and to <1 fs in time deviation, despite 50-ps breakdown in time-of-flight reciprocity.
Nature Communications


optical clocks, time transfer, optical two-way time-frequency transfer, frequency combs


Bergeron, H. , Sinclair, L. , Swann, W. , Khader, I. , Cossel, K. , Cermak, M. , Deschenes, J. and Newbury, N. (2019), Femtosecond Time Synchronization of Optical Clocks Off a Flying Quadcopter, Nature Communications (Accessed September 21, 2023)
Created April 17, 2019, Updated October 12, 2021