Investigation of moderate-to-strong turbulence effects on free space optics — A laboratory demonstration

The increasing demand for higher bandwidth is the motivation behind research studies in free space optical (FSO) communications. In particular, the impact of the atmospheric channel on the FSO link performance has been investigated for decades. Among known channel effects, turbulence is the one, which is thoroughly studied from theoretical and experimental point of views. However, due to limitation of laboratory equipment and channel length, only experimental works in the weak turbulence regime are reported. Therefore, in this paper a dedicated indoor controlled laboratory chamber is used to simulate the outdoor FSO communications for moderate-to-strong turbulence regimes. Instead of increasing the link distance, we generate high temperature gradients along the propagation path of 7 m by blowing cold air in a parallel direction to the laser beam. The performances of the on off keying intensity modulated FSO link is assessed by means of the Q-factor and the optical intensity distribution plots of received signals, thus giving an insight into the level of scintillation achieved in moderate to strong turbulence regimes.