Uplink Pre-Compensation for Ground-to-Space Optical Communications Using Downlink Tomographic Reconstruction

Uplink pre-compensation in ground-to-satellite optical links remains a problem, with an appropriate measurement of the wavefront error in the uplink path often not being available. We present a method that uses successive measurements of the readily accessible downlink beam to perform a tomographic reconstruction of the volume of atmosphere common to the downlink beam and the ground-station field-of-view. These measurements are done through the existing downlink wavefront sensor. From here, an estimate of the wavefront error along the uplink path can be obtained. We evaluate this method in simulation over representative atmospheric conditions and find good performance, especially for situations where the satellite point-ahead angle is many times greater than the atmosphere's isoplanatic angle. Compared to pre-compensation directly using the downlink phase, we find that this method estimates the uplink path with a residual mean-square wavefront error that is up to 8.6 times less. The hardware simplicity of this method makes it a promising solution for uplink pre-compensation implementations targeted at optical communications.