Equalization of negative-exponential fading in saturated semiconductor optical amplifiers

In this paper, we discuss the mitigation of negative-exponential fading in Optical Wireless Communication (OWC) systems. The mitigation technique involves the utilization of a semiconductor optical amplifier (SOA) whose gain saturates in normal link operation, but which also provides a power-dependent varying gain when the link experiences a fade. The unbalanced SOA operation serves towards the equalization of the signal power at its output and as a result the link fades become less severe and of reduced duration. Our analytical results predict that the fade probability can be reduced by over 90% under negative-exponential fading conditions, while the scintillation index at the SOA output is also reduced by 75% if an optimal level of received power, and therefore gain saturation, is observed. Finally, our results show that the average duration of fades can also be reduced by a significant percentage of 68% for the same level of gain saturation in the SOA.