TILBA-ATMO: enhancing LEO-to-ground downlinks with 45-mode turbulence mitigation

Authors: Antonin Billaud, Clara Abbouab, Cédric Dautancourt, Julien Samaan, Guillaume Larché, Laure
Etchegoinberry, Claire Autebert, Guillaume Labroille, Pu Jian

Cailabs, Rennes, FRANCE

Abstract

This paper introduces an efficient high-throughput communication technology to address the proliferation of Low Earth Orbit (LEO) satellite networks due to the need for higher debit rates. The TILBA ATMO system can mitigate atmospheric turbulence, a common limitation for Free Space Optics (FSO) downlinks. This enables the use of fast detectors, fiber components and modulation schemes such as Erbium-Doped Fiber Amplifiers (EDFAs) and coherent modulation and detection which would otherwise be prohibited.
Cailabs’s approach is centered on the utilization of its core technology: Multi-Plane Light Conversion (MPLC) which
enables demultiplexing of any incoming turbulent beam into a set of single-mode fibers (SMF), which are followed by an active optical recombining stage. By dynamically adjusting phase shifters inside recombining stages, one can ensure that a constructive interference is generated, thus merging the demultiplexed turbulent channels into a unique SMF.
Optical Ground Stations (OGS) will be equipped with large telescopes (D> 40 cm), necessitating the mitigation of stronger turbulences (D/r0 >10), which leads to the use of higher spatial modes for collection and recombining.
This paper demonstrates the use of a TILBA-ATMO system, based on 45 Hermite-Gaussian (HG) modes MPLC, for
turbulence mitigation in realistic conditions with D/r0 = 7 and high turbulence speeds. The experimental results of the
system will be showcased for different turbulence conditions.