Space data highway networks are currently being deployed to provide high data rate connectivity to non-fibre-connected areas around the world and to prepare the incoming growth of Internet Of Things market. Among other solutions, GEO optical feeder links are seen as the backbone of the future globalized very high data rate satellite-based telecommunication networks. The FEEDELIO experiment developed for ESA in April 2019 demonstrated the relevance of angular decorrelation models to assess the statistical characteristics of the pre-compensated uplink irradiance that is deeply affected by anisoplanatism. Based on the conclusion drawn from this experiment, we present the results of a preliminary design study of an Adaptive Optics (AO) pre-compensated optical feeder links ground station. Exploiting end-to-end simulations under relevant turbulence conditions, time-correlated fading statistics are investigated to provide typical fading durations for AO pre-compensated optical channel, taking into account the impact of point-ahead mispointing errors.

The future of very high throughput optical links between the ground and GEO satellites depends on the ability to overcome turbulence channel disruptions caused by the optical propagation through the atmosphere. Pre-compensation by adaptive optics has been identified as a game changer, as it could theoretically provide for the uplink the additional margin necessary to secure the link budget. Several experimental activities have been reported to investigate the practical increase that can be expected from AO pre-compensation, demonstrating very promising results. Due to the proximity of the line of sight from ground and the strong variability of turbulence conditions these results would benefit from a confirmation on a more representative line of sight. The line of sight between ESA's Optical Ground Station and the top of Mount Teide provides an unprecedented opportunity to provide this confirmation in a relevant environment. We report here the results of the first experimental demonstration of uplink pre-compensation performed on this line of sight in April 2019. The increase of average optical power is demonstrated and compared to expected performance. The influence of anisoplanatism is demonstrated and quantified; consequences on the future of GEO feeder links are inferred.

To concurrently cope with the scarcity of RF frequency bands, the growing capacity demand and the required lower cost of the ground segment, Very High Throughput Satellites systems must rely on new technical solutions. Optical feeder links are considered as a promising alternative to surpass classical RF technology, offering assets inherent to optical technologies (large bandwidth, no frequency regulation, low beam divergence, components availability). Nevertheless the potential of this technology shall not conceal the remaining challenges to be overcome to make it relevant for operational missions: clouds, turbulence, power generation and high efficiency modulations. VERTIGO (Very High Throughput Satellite Ground Optical Link) is a 3-year H2020 project funded by the European commission and started mid-2019 focusing on the optical link itself regardless of site diversity aspect and aiming at demonstrating in ground demonstrations required technologies to implement very high capacity optical feeder links. In this paper we present the current status and perspectives of the project.

Free-space optical (FSO) communication technologies constitute a solution to cope with the bandwidth demand of future satellite-ground networks. They may overcome the RF bottleneck and attain data rates in the order of Tbit/s with only a handful of ground stations. Here, we demonstrate single-carrier Tbit/s line-rate transmission over a free-space channel of 53.42 km between the Jungfraujoch mountain top (3700 m) in the Swiss Alps and the Zimmerwald Observatory (895 m) near the city of Bern, achieving net-rates of up to 0.94 Tbit/s. With this scenario a satellite-ground feeder link is mimicked under turbulent conditions. Despite adverse conditions high throughput was achieved by employing a full adaptive optics system to correct the distorted wavefront of the channel and by using polarization-multiplexed high-order complex modulation formats. It was found that adaptive optics does not distort the reception of coherent modulation formats. Also, we introduce constellation modulation – a new four-dimensional BPSK (4D-BPSK) modulation format as a technique to transmit high data rates under lowest SNR. This way we show 53 km FSO transmission of 13.3 Gbit/s and 210 Gbit/s with as little as 4.3 and 7.8 photons per bit, respectively, at a bit-error ratio of 1 ∙ 10−3. The experiments show that advanced coherent modulation coding in combination with full adaptive optical filtering are proper means to make next-generation Tbit/s satellite communications practical.