The reliability of future free-space optical communication (FSOC) links between satellites and the ground namely depends on accurate characterization of atmospheric turbulence along the optical path, which is critical for both performance prediction and the development of effective mitigation strategies. We present and validate two complementary approaches to extract, in real time, optical turbulence (OT) and wind information from adaptive optics telemetry acquired with a single Shack-Hartmann wavefront sensor during satellite downlinks, complemented with data from an external weather station. The first method provides fast and robust estimates of integrated OT parameters, while the second extends the SCO-SLIDAR framework to reconstruct detailed refractive index structure parameter (Cn2) and wind profiles along the line of sight. The consistency between the two approaches is demonstrated through laboratory validation with a turbulence emulation bench and real-world application to data collected at the FEELINGS optical ground station. These results pave the way for automated OT characterization at FSOC sites, while also highlighting current limitations posed by underlying assumptions, such as Taylor's frozen-flow hypothesis.

Adaptive optics can be used to mitigate the effects of atmospheric turbulence on imaging systems, but the correction is only partial, and deconvolution is often required to improve the resolution. This results in entire optical/digital systems, which are traditionally designed sequentially, i.e. , the adaptive optics system is optimised first, and the restoration algorithms are designed a second time. Studies on optical/digital systems have shown that jointly optimizing the whole system is a better alternative. We propose to extend these co-design strategies to the design of an adaptive optics-assisted imaging system. We derive a simple criterion that takes into account the source properties and the entire optical/ digital system performance. To illustrate its interest, we use it to optimize the wavelength distribution between the wavefront sensor and the imaging camera. In addition, we explore the potential of using multiple imaging channels operating at different wavelengths as a means of making an imaging system robust to turbulence strength and source magnitude variations. Later, any parameter of the optical/digital system, if not the entire system itself, could be optimized this way.

This article focuses on a laboratory demonstration of a predictive control law in an adaptive optics-assisted free-space communication link from a LEO satellite to the ground. The considered predictive control law is a linear quadratic Gaussian (LQG) law, used with an enhanced turbulent phase evolution model, a Zernike-based vector auto-regressive (VAR) model. Previous works in our team at ONERA have shown that VAR LQG control brings significant improvement in terms of coupling efficiency (CE) performance in a single-mode fiber (SMF), in numerical simulations. Additionally, to our best knowledge, no experimental validation of predictive control for LEO-to-ground free-space communication links has been performed yet. The goal of this work is thus twofold. First, we assess the experimental performance in controlled conditions of VAR LQG control and compare it to the output of an end-to-end simulation developed in parallel, with the aim of controlling and understanding the different error terms that can lead to discrepancies between both results. The CE performance with VAR LQG control is also compared to the CE performance with other classic and predictive control laws. To obtain a global understanding of the gain in performance with VAR LQG, we also include robustness studies of the input parameters. Second, the validated numerical tool allows simulations of more representative systems with realistic turbulence profiles, and their performance with VAR LQG. This is applied to telecom links as well as satellite observation. Ultimately, this work paves the way to on-sky validations on optical ground stations (OGS) such as ONERA's FEELINGS OGS.

Future free-space optical communication links be-tween the ground and satellites will require systematic on-site monitoring of atmospheric turbulence to ensure reliable operation. To address this need, ONERA’s FEELINGS optical ground station has been equipped with a real-time turbulence monitoring pipeline, capable of retrieving refractive index structure parameter and wind profile information along the line of sight during optical links. The pipeline is first validated under controlled turbulent conditions before being applied to measurements collected during GEO-feeder links with the TELEO payload in September 2024. The retrieved turbulence conditions are then compared with numerical weather prediction simulations and used to assess the expected link performance.

Structured illumination microscopy (SIM) is one of the most versatile super-resolution techniques. Yet, its application to high-resolution live imaging has been mainly limited to fluorescent and stationary specimens. Here, we present advancements in SIM to jointly tackle all the challenges of imaging living samples, i.e., obtaining super-resolution over an undistorted wide-field while dealing with sample motion, multiple scattering, sample-induced optical aberrations, and low signal-to-noise ratio. By using adaptive optics to compensate for optical aberrations and a reconstruction algorithm tailored for moving and thick tissue, we successfully apply SIM to in vivo retinal imaging and demonstrate structured illumination ophthalmoscopy with optical sectioning and resolution improvement for in vivo imaging of the human retina.

For the PROVIDENCE project, the joint exploitation of high resolution images provided by a multi-meter telescope, a fine space scene model, and low resolution information from a network of small-diameter telescopes is being analyzed.

Now that the first generation of adaptive optics dedicated to bidirectional ground-to-GEO optical links has been successfully tested, in-depth analysis of experimental performance is needed for current system optimization and future model-based concepts fine-tuning. Here we first present the principle of our ground station digital twin AOSIM and how it compares very well to experimental data obtained from bidirectional ground-to-GEO links between ONERA’s OGS FEELINGS and ADS GEO Payload TELEO; then we show some example of ways we used AOSIM for optimizing our current system with regard to Shack-Hartmann Wavefront Sensor and control matrix; and finally, we discuss perspectives in using AOSIM for fine-tuning of AO next generation concepts, through the example of optimal Point-Ahead-Angle pre-compensation of the uplink.

The performance of future high-throughput feeder links highly depends on the statistical properties of the optical propagation channel. The TELEO payload, equipped with high-frequency irradiance metrology, offers the possibility of fine characterization of uplink irradiance statistical properties in the presence of adaptive optics pre-compensation. The unique metrology equipment on the FEELINGS ground station allows for documenting the performance of the adaptive optics (AO) loop jointly with the downlink injection efficiency while inferring a spatio-temporal distribution of propagation channel characteristics (both Cn(2) and wind profiles). This work focuses on analyzing the statistical properties of received power measurements onboard and on the ground for September 2024 optical link sessions, comparing them to a performance model that exploits the statistical properties of the adaptive optics loop residuals fed with propagation channel monitoring outputs. The attenuation distributions on both uplink and downlink are analyzed jointly, detailing the main contributors to the error budget. Deviations from the models are discussed.

TELEO is the Airbus Defence and Space demonstrator dedicated to in-orbit testing of cross atmospheric optical uplink and downlink, designed and implemented in the frame of the CNES DYSCO project. The payload, equipped with high-frequency irradiance metrology, offers the possibility of fine characterization of uplink irradiance statistical properties in the presence of adaptive optics pre-compensation. Connected to optical ground station with high-frequency metrology of irradiance and injected power, the overall system is unique to consolidate know-how on optical link budget. This work presents In-Orbit Demonstration (IOD) results and then focuses on a comparison between Airbus OneWave software output with IOD data from FrOGS beacon, from FEELINGS pre-compensated uplink, from FEELINGS corrected downlink.