Reduction of dynamic linewidth in single-frequency semiconductor lasers

Carrier density oscillations and frequency chirping of pulse code modulated single frequency semiconductor lasers are shown to be greatly reduced by use of a small current step in the leading edge of the drive pulse. For a 100 km single mode fibre link the dispersion power penalty at 1.55 μm resulting from dynamic line broadening is predicted to be reduced from 3.7 to 1.0 dB by use of the modified current pulse.