Numerical approach to field fluctuations and spectral lineshape in InGaAsP laser diodes

This paper reports on a numerical approach to model the field fluctuations, spectral lineshape and linewidth in semiconductor lasers. The approach is based on numerical solution of the laser rate equations augmented by Langevin noise sources that account for fluctuations in the lasing field. The paper newly examines contributions of intensity and frequency noises to the spectral characteristics of the lineshape and its linewidth over a wide range of injection current. The model is applied to InGaAsP lasers emitting in a wavelength of 1.5 mum as the most representative light sources in optical communication systems. Accuracy of approximated models of calculating linewidth from low-frequency components of the frequency noise is checked. Effect of non-linear gain suppression on the lineshape is also explored. The spectral lineshape promotes and the linewidth decreases as the laser is injected far from the near-threshold region. The lineshape changes mainly with changes in the frequency noise spectrum while the linewidth is sensitive to variation in the low-frequency levels of both intensity and frequency noises. Copyright (C) 2004 John Wiley Sons. Ltd.