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

TL;DR

This paper addresses the challenges of high-precision optical time-frequency transfer in moving platforms, providing theoretical derivations, algorithms, and experimental validation demonstrating femtosecond synchronization despite motion.

Contribution

It introduces a comprehensive theoretical framework and real-time algorithms for comb-based optical two-way time-frequency transfer in moving environments, achieving sub-femtosecond synchronization.

Findings

Active synchronization below 1 femtosecond over turbulent air paths.

No velocity-dependent bias within 330 attoseconds.

Effective motion compensation in optical time transfer demonstrated.

Abstract

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 equations governing comb-based O-TWTFT in the presence of motion. We describe the implementation of real-time signal processing algorithms based on these 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 with our physical setup. With the implementation of the time transfer equation derived here, we find no velocity-dependent bias between the synchronized clocks to within at two-sigma statistical uncertainty of 330 attoseconds.