Adaptive Optics for Daytime Deep-Space Optical Communications

To facilitate faster data transfer between astronomical equipment in space and base stations on Earth, optical communications links can be deployed. Among the design challenges faced when designing deep space communications are: very low power of received signals, the effect atmospheric turbulence on propagating signals, and strong presence of background light from the Sun, which varies over the course of the day. To cope with these challenges, deep space optical communications require adaptive optics (AO) systems to maximize the number of received signal photons, as well as exceptionally narrow bandwidth optical filters to remove background noise from received signals.

During the project, a spectral and spatial filtering system has been designed, optimized and prototyped in the laboratories of Fraunhofer IOSB. Firstly, through preliminary studies, the most promising technologies for spectral and spatial filtering have been identified. After performing simulations for a broad parameter space for each type of filter, it was decided that the laboratory demonstrator should be based on a Fabry-Pérot etalon coupled with a bandpass filter and a Shack-Hartmann wavefront sensor. A breadboard demonstrator has been implemented to validate the performances of the proposed technologies in the laboratory.

The demonstrator has delivered performance improvements in the range of 2.5 to 34 with respect to tip/tilt-only correction. These results are promising and show that daytime AO using signal photons for wavefront sensing could allow for much smaller detectors to be used for communications.

This work has been supported by the European Space Agency under contract numbers 4000125644/18/D/MB and 4000126965/19/D/MB.