Optical Two-way Time-frequency Transfer Across Partially Reciprocal Free-space Links
Martha I. Bodine, William C. Swann, Isaac H. Khader, Esther Baumann, National Institute of Standards and Technology; Jean-Daniel Deschenes, Université Laval, Canada; Nathan R. Newbury, National Institute of Standards and Technology
Location: Regency B
Optical two-way time-frequency transfer (OTWTFT) has enabled femtosecond-level synchronization of optical clocks across free-space links and phase comparisons at the 10-19 level. To achieve this level of performance, OTWTFT relies on the reciprocity of a bi-directional single-spatial mode free-space link to suppress picosecond-level or greater timing fluctuations caused by atmospheric turbulence. Over link distances of a few kilometers, optical transit times are on the order of microseconds; consequently, the turbulent features of the atmosphere are effectively frozen in time, and the reciprocity of the bi-directional link is near perfect. However, as link distance increases or as the uplink and downlink paths become physically separated due to relative motion of the two clock sites, link reciprocity begins to break down, potentially degrading the precision of OTWTFT. Here, we explore the effects of partial reciprocity on OTWTFT, which should pave the way for future optical time transfer in the presence of significant relative platform motion and over distances of tens of kilometers or even greater.