Time Synchronization over a Free-Space Optical Communication Channel
Isaac Khader, Hugo Bergeron, Laura C. Sinclair, William C. Swann,, Nathan R. Newbury, and Jean-Daniel Desch\^enes

TL;DR
This paper demonstrates real-time two-way time synchronization over a 4 km turbulent free-space optical channel using a repurposed digital communication system, achieving sub-picosecond accuracy.
Contribution
It introduces a novel application of FSO communication for precise time transfer, achieving high accuracy over turbulent air paths.
Findings
Fractional frequency deviation below 10^-15
Time deviation below 1 picosecond
Peak-to-peak wander of 16 ps over 8 hours
Abstract
Free space optical (FSO) communication channels are typically used to transmit high-speed data between sites over the air. Here we repurpose an FSO digital communication system and use it directly for two-way time transfer. We demonstrate real-time synchronization between two sites over a turbulent air path of 4 km using binary phase modulated CW laser light. Under synchronization, the two sites exhibit a fractional frequency deviation below and a time deviation below 1 picosecond at averaging times of seconds to hours. Over an 8-hour period the peak to peak wander is 16 ps.
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Taxonomy
TopicsAdvanced Frequency and Time Standards · Quantum optics and atomic interactions · Network Time Synchronization Technologies
