Laser power delivery through atmospheric turbulence to photovoltaic (PV) cells, e.g., for remote powering of UAVs, has unique requirements on adaptive beam control. In contrast to directed energy applications or laser communications, where the goal is to concentrate as much power as possible on a target or a receiver aperture, respectively, efficient power conversion with PV cells requires a uniform irradiance over the PV converter area. To minimize the loss of optical energy, the beam shape and size should be matched to the area the PV converter. This should be realized even if the distances between the transmitter and the PV converter are varying over time.
In this paper we present techniques for power beaming with adaptive fiber array transmitters. Control of piston, tip, and tilt phases within each sub-aperture allows for adaptive beam shaping and for mitigation of distortions caused by atmospheric-turbulence using light returning from an array of small retro-reflector interspersed with the PV cells as feedback signal for a stochastic parallel gradient descent (SPGD) controller. We will discuss several approaches to optimize the beam shape at the PV converter and present experimental results from proof-of-principle experiments on an atmospheric propagation path.