Bifurcation-Cascade Diagrams of an External-Cavity Semiconductor Laser: Experiment and Theory

We report detailed experimental bifurcation diagrams of an external-cavity semiconductor laser. We have focused on the case of a DFB laser biased up to 1.6 times the threshold current and subjected to feedback from a distant reflector. We observe bifurcation cascades resulting from the destabilization of external-cavity modes that appear successively when the feedback is increased, and explain, in light of the Lang and Kobayashi (LK) model, how the cascading is influenced by various laser operating parameters (current, delay, and feedback phase) and experimental conditions. The semiquantitative agreement between experiments and simulations validates over a large range of operating parameters, the LK model as a tool for reproducing the salient aspects of the dynamics of a DFB laser subjected to external optical feedback.