Analysis of frequency chirp of self-injected nanostructure semiconductor lasers

The frequency chirp of a self-injected quantum dot (QD) semiconductor laser is studied through the chirp-to-powerratio. By taking into account the carrier dynamics in the nanostructures, the effects of the optical feedback conditions as wellas of the linewidth enhancement factor are investigated with a semi-analytical rate equation model. On the one hand, underthe long delay case, the simulations show the occurrence of a detrimental parasitic ripple both in the amplitude and thefrequency responses. On the other hand, in the short cavity regime, the calculations reveal that the modulation properties canbe nicely purified regarding the amplitude and the phase of the delayed field. To this end, substantial improvements in termsof the modulation bandwidth, the relaxation frequency and the frequency chirp are pointed out. Finally, the simulations alsoshow that the linewidth enhancement factor constitutes a severe constraint in the self-injected QD lasers independent of thecavity regime.