Experimental validation of phase-only pre-compensation over 494 m free-space propagation

It is anticipated that ground-to-geostationary orbit (GEO) laser communication will benefit from pre-compensation of atmospheric turbulence for laser beam propagation through the atmosphere. Theoretical simulations and laboratory experiments have determined its feasibility; extensive free-space experimental validation has, however, yet to be fulfilled. Therefore, we designed and implemented an adaptive optical (AO)-box which pre-compensates an outgoing laser beam (uplink) using the measurements of an incoming beam (downlink). The setup was designed to approximate the baseline scenario over a horizontal test range of 0.5 km and consisted of a ground terminal with the AO-box and a simplified approximation of a satellite terminal. Our results confirmed that we could focus the uplink beam on the satellite terminal using AO under a point-ahead angle of 28 mrad. Furthermore, we demonstrated a considerable increase in the intensity received at the satellite. These results are further testimony to AO pre-compensation being a viable technique to enhance Earth-to-GEO optical communication.