Propagação de feixes ópticos de correlação em atmosfera turbulenta

Abstract

The turbulent mixing of air at different temperatures turns the refractive index of air in the atmosphere into a randomly varying quantity. Together with scattering by fog, this fluctuation figures among the greatest obstacles in information transmission through free-space optics. In this thesis, a passive method is introduced that attenuates the distortions created by the atmosphere through the use of correlation beams: entities which describe photon correlations and propagate formally as regular beams. The correct choice of correlation mitigates some of the most severe aberrations and allows for information coding immune to the fluctuations up to good approximation. The models are demonstrated via Monte Carlo simulations and through an experiment in which turbulence is generated in the lab with a turbulence emulating chamber and the correlation beam is created using spontaneous parametric down-conversion. One of the correlation beam's spatial properties, parity, is shown to be particularly robust against the fluctuations and an experimental proposal is presented that exploits this capability. Investigations are done concerning other implications of a robust correlation beam, which indicate at least one drawback: a reduction in the overall signal collected by a receiver.