Skip to main content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.


The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Femtosecond Optical Two-Way Time-Frequency Transfer in the Presence of Motion



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


Platform motion poses significant challenges to high-precision optical time and frequency transfer. We give a detailed description of these challenges and their solutions in comb-based optical two-way time and frequency transfer (O-TWTFT). Specifically, we discuss the breakdown in reciprocity due to relativity and due to asynchronous sampling, the impact of optical and electrical dispersion, and velocity-dependent transceiver calibration. We present a detailed derivation of the nist-equations governing comb-based O-TWTFT in the presence of motion. We describe the implementation of real-time signal processing algorithms based on these nist-equations and demonstrate active synchronization of two sites over turbulent air paths to below a femtosecond time deviation despite effective velocities of 25 m/s, which is the maximum achievable velocity with our physical setup. With the implementation of the time transfer nist-equation derived here, we find no velocity-dependent bias between the synchronized clocks to within the statistical uncertainty of 330 attoseconds.
Physical Review A


time transfer, optical clocks, optical two-way time-frequency transfer, frequency combs
Created February 22, 2019, Updated September 4, 2019