Femtosecond Time Synchronization of Optical Clocks Off a Flying Quadcopter

Published

April 18, 2019

Author(s)

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

Abstract

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

Keywords

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

Citation

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 October 7, 2025)