Coupled-cavity semiconductor lasers under current modulation: Small-signal analysis

The modulation characteristics such as the power response and the chirp (dynamic line broadening) of single-frequency coupled-cavity semiconductor lasers are analyzed theoretically. The model is based on the small-signal analysis of a set of generalized rate equations and neglects the lateral variations of the optical field and the carrier density in the two cavity sections. When the controller section is biased below threshold in a three-terminal device the modulation response is not significantly affected by the intercavity coupling. By contrast, new features arise when both sections are biased above threshold. It is found that the chirp can be significantly reduced by a proper combination of the bias levels and the modulation splitting between the two sections. The chirp reduction also depends on the strength of the intercavity coupling and its phase, and the best performance is achieved for the case of in-phase coupling. The calculated results are in qualitative agreement with the reported experimental data and are useful as a guide to optimize the performance of a coupled-cavity device.