Abstract
Phase-coherent transfer of optical frequencies over a long distance is required for diverse photonic applications, including optical clock dissemination and physical constants measurement. Several demonstrations were made successfully over fiber networks, but not much work has been done yet through the open air where atmospheric turbulence prevails. Here, we use an 18 km outdoor link to transmit multiple optical carriers extracted directly from a frequency comb of a 4.2 THz spectral width. In stabilization to a high-finesse cavity with a 1.5 Hz linewidth, the comb-rooted optical carriers are simultaneously transferred with collective suppression of atmospheric phase noise to −80 dBc Hz−1. Microwaves are also delivered by pairing two separate optical carriers bound with inter-comb-mode coherence, for example a 10 GHz signal with phase noise of −105 dBc Hz−1 at 1 Hz offset. Lastly, an add-on demonstration is given for multi-channel coherent optical communications with the potential of multi-Tbps data transmission in free space.
Highlights
Phase-coherent transfer of optical frequencies over a long distance is required for diverse photonic applications, including optical clock dissemination and physical constants measurement
Light propagation is greatly affected by atmospheric turbulence stochastically in forms of intensity scintillation and phase fluctuation[16], which significantly limits the practical range of coherent optical frequency transfer when the Doppler shift is not actively compensated[17,18,19]
We demonstrate a comb-rooted scheme of transferring multiple optical carriers concurrently over an 18 km open-air optical link
Summary
Phase-coherent transfer of optical frequencies over a long distance is required for diverse photonic applications, including optical clock dissemination and physical constants measurement. In stabilization to a high-finesse cavity with a 1.5 Hz linewidth, the comb-rooted optical carriers are simultaneously transferred with collective suppression of atmospheric phase noise to −80 dBc Hz−1. We demonstrate a comb-rooted scheme of transferring multiple optical carriers concurrently over an 18 km open-air optical link. Subsequent transfer of the comb-rooted optical carriers over the long open-air link is made to reveal that the atmospheric phase disturbance adheres to the weakturbulence model even with large Rytov variance[16], thereby the Doppler shift can be suppressed actively in the presence of intensity scintillation. The concurrent transfer of multiple comb-rooted optical carriers is intended for longdistance delivery of not just individual optical frequencies and microwaves that are synthesized by paring different optical carriers bound with high inter-comb-mode coherence
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
