WDM transmission using semiconductor optical amplifiers

It has recently been shown that SOAs can be used effectively in WDM transmission systems when the crosstalk is either avoided by operating in a nearly-linear regime, or when it is suppressed by using a holding beam (reservoir channel). Either way, the ultimate capacity of a SOA-amplified transmission line is limited by the noise figure and saturation output power of the amplifier, key parameters which have seen considerable progress in recent years. For optimal results, attention has to be given to the gain of the SOAs in the amplifier chain, which has to be matched to the span loss, and to the amplifier spacing. An overview is given of a number of recent WDM transmission experiments that used SOAs as the in-line amplifiers.