Influence of self-sustained pulsation in semiconductor lasers on optical transmission system

Degradations in semiconductor lasers caused by defects, such as dark lines or dark spots in an active region, sometimes introduce self-sustained pulsations. In this paper, dynamic properties of a modulated self-sustained pulsation InGaAsP/InP semiconductor laser are presented and the influence on the optical transmission system is described. In high-speed pulse modulation above the pulsation frequency, output waveforms showed a marked pattern effect. When the pulsing semiconductor laser is modulated below the pulsation frequency, the laser output had relatively large noise which had flat noise spectra. Therefore, error-rate characteristics were influenced by this noise. These results show that the self-sustained pulsations in semiconductor lasers sometimes cause transmission characteristics degradation on the optical transmission system. Therefore, careful attention should be paid to this matter.