Free-space optics communications employing elliptical-Aperture multimode diversity reception under anisotropic turbulence

We experimentally demonstrate an elliptical-Aperture multimode diversity receiver to mitigate the impairment from anisotropic turbulence, which is emulated by employing an electrically-controlled heater. The anisotropy gradually decreases as the flow-level of the introduced airflow from fans increases. In contrast to circular-Aperture reception, the elliptical-Aperture multimode diversity receiver can effectively resist beam wander under anisotropic turbulence, reducing outage probability from 14.63% to 0.38% for detecting a dual-polarization 30-Gbaud QPSK signal. Without the aid of an adaptive optics system, this work demonstrates the feasibility of realizing an anisotropic-Turbulence-resistant FSO link using multimode and multi-Aperture diversity reception employing digital coherent combining techniques.