Optimizing driving conditions of a MQW EA modulator for soliton generation

A detailed analysis of the pulses generated with a multiple quantum well (MQW) electroabsorption (EA) modulator used as a soliton source is performed. The pulse temporal and spectral shape are simulated and a good agreement is obtained with the experimental results. An irregular holed spectrum shape is observed under certain operating conditions and its existence is attributed to parasitic phase modulation. This type of spectrum could be observed even for pulses having a time bandwidth τΔν product below 0.4 which makes them usually considered as nearly transform limited. However it is not the case. The influence of the pulse spectral shape on transmission performances is investigated by means of a realistic simulation of soliton pulse propagation at 10 Gb/s. It is shown that for 9000 km propagation distance and for pulses presenting this irregular spectral shape a signal degradation occurs as the timing jitter is above 10 ps and the quality factor Q is below 2, which results in an increase of the transmission bit error rate. In order to avoid the generation of this kind of pulses when operating a MQW modulator as a soliton source, a mapping is realized giving the adequate voltages to apply to the diode for acceptable soliton generation