Dynamics and stability of complex-coupled DFB lasers with absorptive gratings

The basic influence of the saturable nature of absorptive gratings in complex-coupled DFB lasers are investigated, using a simplified model with an extended set of rate equations. It is demonstrated that the coupling coefficient depends on the bias condition and affects all essential laser properties like the static frequency shift, the P-I characteristic and modulation response. In addition, stability problems, like bistable behavior or pulsations, may occur in these devices. Therefore, design rules and approximate criteria for stable laser operation are derived.