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Coherent Optical Phase Transfer across Turbulent Open Air Paths with 10^-17 instability at 1- second



Laura C. Sinclair, Hugo Bergeron, William C. Swann, Jean-Daniel Deschenes, Nathan R. Newbury


We demonstrate carrier-phase optical two-way time-frequency transfer (carrier-phase OTWTFT) across a turbulent air path. Through the two-way exchange of optical pulse trains from phase- stabilized frequency combs, carrier-phase OTWTFT continuously tracks the relative phase between two distant optical oscillators, i.e. cavity-stabilized lasers, operated at different carrier frequencies with a phase/timing precision of 9 mrad (7 attoseconds) at = 1 second averaging periods despite atmospheric fading and atmospheric phase noise across the 4-km free space link. The corresponding modified Allan deviation is 1.2x10^-17/t_avg^(3/2) from 1 ms to ~ 3 s, reaching 6x10^-20 at 850 seconds. This performance at one second is a 20-fold improvement over previous OTWTF that did not exploit the additional information in the carrier phase. At this level, carrier-phase OTWTF can distribute the stability of the next-generation optical clocks/oscillators without penalty. Moreover, the measurement effectively extends the sub- second mutual coherence time of the cavity-stabilized lasers to arbitrarily long coherence times, enabling future correlated spectroscopy between distant atomic clock samples for high precision clock comparisons.
Physical Review Letters
Created January 29, 2018, Updated September 4, 2019