Optical Propagation through Atmospheric Turbulence for Space Links

In future satellite links, Free Space Optics (FSO) systems can be of paramount importance in accomplishing the growing need for high-speed connectivity. Indeed, Radio Frequency (RF) or microwaves technologies are strongly constrained by physical and hardware limitations, particularly considering deep-space missions, whereas FSO systems could attain the high capacity values typical of optical fiber links, e.g., various hundreds of Gbit/s. However, it is to be highlighted that simply transferring terrestrial systems to space is not feasible. In fact, designing optical links for space is a challenging task, because of the very long distance and the effect of the atmosphere, both adding severe penalties. In this context, we provide here an overview of the key elements that characterize the channel model. A particular care must be paid to the optical beam propagation in the atmosphere, which works as inhomogenous and turbulent medium. We also introduce the key technologies that can be exploited to mitigate these effects and their expected performance. These are key elements to be considered in the design and realization of future FSO links.