Soutenance de thèse de Joana TORRES

Soutenance de thèse de Joana TORRES, doctorante dans le groupe Imagerie et Information du Laboratoire Charles Fabry, le 10 décembre 2025 à 14h30 dans l'Auditorium de l'Institut d'optique graduate school à Palaiseau, sur le thème : "High-performance adaptive optics control in strong turbulence scenarios for free space optical communications". 

Abstract: "As demand for global connectivity increases, satellite internet has become critically important. However, current systems are limited by  connections between the satellites and Earth with Radio Frequency communications links. Free Space Optical Communications (FSOC) links offer significant greater bandwidth, better power efficiency, greater security, and the potential to support ‘Quantum Encryption’ techniques for totally secure communications.  However, optical links are limited by the effects of atmospheric turbulence which reduces link efficiency and causes outages (fades). In astronomy, turbulence mitigation is performed using adaptive optics (AO), however the requirement to track quickly moving satellites in low earth orbit, observe at low elevation angles, and operate at any time of the day adds significant challenges. In particular, stronger turbulence causes scintillation across the telescope aperture and limits the performance of the adaptive optics wavefront sensor.

These issues are addressed in this thesis where the use of high-performance control algorithms is introduced. These are based on ‘Linear Quadratic Gaussian’ (LQG) control to enhance the correction of adaptive optics systems in optical communications.  Minimum variance LQG control has been used in astronomy and proposed for satellite tracking to provide significant AO performance gains. For the first time, such algorithms are applied in the context of low elevation links for FSOC and tested in simulations in which scintillation is correctly accounted. Here, the design and implementation of the controller is explained, together with the way future controllers might account for the strong scintillation seen in FSOC. The results show excellent performance with dramatic improvement on coupling efficiency and stability of the link. Finally, the results are set in context given the requirements and performance metrics used in FSOC. The impact on the field is explained, including on nascent Quantum Key Distribution networks, where it is shown that the algorithms significantly increase the Secure Key Rate."