Adaptive optics LEO uplink pre-compensation with finite spatial modes

Adaptive optics pre-compensation of free-space optical com-munications uplink from ground to space is complicated by the "point ahead angle" due to spacecraft velocity and the finite speed of light, as well as anisoplanatism of the uplink beam and the wavefront beacon. This Letter explores how pre-compensation varies with the number of spatial modes applied and how it varies with a beacon at the point-ahead angle versus a downlink beacon. Using a w0 =16 cm Gaus-sian beam propagating through a modified Hufnagel-Valley model as an example, we find pre-compensation perfor-mance plateaus beyond similar to 100 applied modes regardless of integrated turbulence strength, and that a point ahead beacon provides a 1-4 dB gain in median received power and an order-of-magnitude reduction in scintillation over a downlink beacon at wavelengths typical of optical commu-nications. Modeling tailored to specific scenarios should be conducted to determine whether implementing a resource -intensive point ahead beacon is the optimum path to meeting link requirements. (c) 2023 Optica Publishing Group https://doi.org/10.1364/OL.482550