The demand from satellite operators for ever increasing capacity during these years has led to the emergence of VHTS (Very High Throughput Satellites) system solutions. Such satellites exhibit as a minimum several times the capacity of conventional satellites and possibly up to Terabit per second and beyond. One of the main challenges associated to the implementation of these very high capacity systems is to feed the satellite in an efficient way to limit the cost of the system, in particular that of the ground segment. While RF bands are facing saturation and are submitted to strict frequency regulation, leading to a large number of ground stations, optical feeder links are considered as a promising technology to meet the future VHTS system requirements while strongly reducing the ground segment. Nevertheless, optical feeder links are still facing some implementation uncertainties, beyond the obvious issue of nebulosity which can be alleviated through site diversity approach. While several feeder link architectures are envisaged leading to significant implementation differences, atmospheric propagation impairments and their mitigation techniques together with high power generation and management as well as efficient modulation use are of primary importance in the design and sizing of the optical feeder link. During past years several experimentations on ground or in-flight have demonstrated part of these concepts and subsystems necessary to implement such high capacity systems. Simultaneous combination of all these concepts in comprehensive demonstrations has however not been implemented yet. This paper recalls the main drivers of satellite systems design based on optical feeder links and introduces the H2020 VERTIGO project that is specifically addressing the topic of the GEO-ground optical link and the associated technological challenges (high optical power generation, high efficiency waveforms, atmospheric impairments mitigation techniques).