Objective:The objective of this activity is to demonstrate reliable high data rate optical transmission through the atmosphere (>100Gbps) in a scenario representative (in terms of link attenuation and optical turbulence) of an optical link between a telecom satellite and an Optical Ground Station for elevation angles down to 5deg. Targeted Improvements:Improve the service quality and availability of high data rate optical links through the atmosphere (e.g., direct to Earth optical downlinks, optical feeder links) due to strong atmospheric turbulence effects for elevations angles down to 5deg / scintillation index >1 Description:Propagation of laser beams through turbulent media degrades the characteristics of the optical signal (i.e., phase-front distortion, scintillation, beam spreading, beam wandering). The degradation of the optical beam is significantly larger in the uplink than in the downlink, dueto fact that the turbulence is much closer to the ground transceiver than to the space transceiver. Countermeasures on the transmitted and the received optical communications beams are necessary in order to improve the link quality (i.e., BER), and to increase the link availability and the link communications time (i.e., reduce the minimum elevation angle). Adaptive Optics is typically used to correct the atmospheric induced phase-front distortions on the (received) optical downlink, and hence, to increase the coupling efficiency into a single mode fibre, or equivalently, the mixing efficiency with an optical local oscillator. Such countermeasure hasbeen experimentally proven for weak and medium turbulence (typically for elevation angles > 20-30deg). However, to maximize the link quality, the link availability and the link communications time, countermeasures to compensate for strong atmospheric turbulence (elevation angles down to 5deg) in the downlink are to be developed and demonstrated. Furthermore, the expected improvements of turbulence countermeasures for the (transmitted) optical uplink are first to be demonstrated (e.g., wave-front pre-distortion, transmitter diversity) for typical elevation angles > 20-30deg. In this activity, the Contractor shall investigate optical technologies and techniques that enable reliable high data rate optical links under strong atmospheric turbulence conditions (i.e., scintillation index >>1, which typically corresponds to elevation angles down to 5deg). For the evaluation of the feasibility and the scalability of the investigated options, the Contractor is to consider ground receiver aperture diameters up to 1meter and ground transmitter aperture diameters up to 50cm. To support the assessment, the performances of the various solutions shall be preliminary evaluated by simulations (i.e., atmospheric turbulence simulator tool). After a trade-off of the possible solutions (e.g., advanced wave-front sensors and high spatial resolution correction actuators less sensitive to scintillation effects, novel large area / high bandwidth / low noise detectors, adaptive number of WDM channels, etc.), the Contractor shall select the preferred option(s) for demonstration in a scenario representative (in terms of link attenuation and optical turbulence) of a high data rate optical link (>100Gbps) between a telecom satellite and an Optical Ground Station for elevation angles down to 5deg. System scalability shall be implemented by means of wavelength division multiplexing (WDM). The performances of the optical link shall be tested for a sufficiently long time period (e.g., 12 months) under different atmospheric turbulence conditions (to assess day time / night time turbulence changes and seasonalturbulence variations).