Semiconductor optical amplifiers in negative-exponential fading: regenerators and pre-amplifiers

In this study, the authors discuss the mitigation of negative-exponential fading in optical wireless communication systems. The mitigation technique involves the utilisation of a semiconductor optical amplifier (SOA) that, depending on the link arrangement, acts either as regenerator or pre-amplifier. As a regenerator, the SOA gain saturates during normal link operation and increases when the link experiences a fade. This unbalanced SOA operation serves towards the equalisation of the signal power at its output and fades become less severe and of reduced duration. The analytical results predict that the fade probability is reduced by over 90% and the scintillation index is improved by 75% for an optimal level of the received power. Moreover, the average duration of fades is also reduced by 68% for the same power level. As a pre-amplifier, the SOA modifies the noise statistics at the receiver and provides a static sensitivity increase of at least 10 dB at 10 Gb/s, depending on the bit-error-rate (BER) target. The analytical results show that this sensitivity improvement imparts a reduction of one order of magnitude on the average BER, of at least 94% on the outage probability and of at least 78% on the average duration of fades.