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The objective of this study is to investigate optical technologies and techniques enabling 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.
Propagation of laser beams through turbulent media degrades the characteristics of the optical signal (i.e. phasefrontdistortion, scintillation, beam spreading, beam wandering). The degradation of the optical beam is significantly larger in the uplink than in the downlink, due to 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 phasefront 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 has been 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. 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 thevarious solutions shall be evaluated by simulations (i.e., atmospheric turbulence simulator tool). After a trade-off of the possible solutions (e.g., advanced wavefront 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 conclude on the preferred option(s) and the Contractor shall carry out a preliminary design of the required upgrades for implementation in future Optical Ground Stations supporting reliable high date rate optical links under strong atmospheric turbulence conditions.