Femtosecond Time Synchronization of Optical Clocks Off a Flying Quadcopter

Published: April 18, 2019


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.
Citation: Nature Communications
Pub Type: Journals


optical clocks, time transfer, optical two-way time-frequency transfer, frequency combs
Created April 18, 2019, Updated September 04, 2019