Demonstration of Adaptive Optical Pre-Compensation in Horizontal Tests

Though long anticipated, adaptive optical (AO) pre-compensation is now experiencing a surge in interest thanks to technological advances and the identification of a real-world application with the advent of satellite laser communication as a viable alternative to radio-frequency. Here, we present an overview of our activities to date in pre-compensation, from the development of our AO system in laboratory experiments using artificial turbulence [1], to the integration into a transportable "AO-box" and testing in first proof-of-principle experiments over horizontal links using real turbulence [2] to the verification in horizontal tests of pre-compensation under large point-ahead-angles beyond the estimated isoplanatic range [3]. We describe the concept and realization of our experimental setup which provides simultaneous bidirectional correction of the incoming beam (post-compensation) and outgoing beam (pre-compensation). We then detail the transfer of this setup into two optical terminals representing a "ground terminal" and "satellite terminal". We describe the results of the horizontal measurement campaigns which have been undertaken to date in which a 7.1 dB increase in the received intensity was demonstrated under a small PAA over 0.5 km and in which a decline in the received laser power over increasingly large point-ahead-angle was demonstrated over a 1.0 km test range. We conclude with the current outlook for pre-compensation technology and indicate future planned experiments.