Pulse Cluster Dynamics in Passively Mode-Locked Semiconductor Vertical-External-Cavity Surface-Emitting Lasers

In recent years different setups based on external cavities have been developed, in order to enhance the performance of pulsed semiconductor mode-locked lasers, namely the peak power and width of the emitted pulses. Depending on the operating conditions and the cavity configuration, pulse cluster solutions emerge with a nonidentical temporal interpulse spacing, which limit the performance of such devices. In this work we present a system of multidelay differential equations to describe the dynamics of a passively mode-locked vertical-external-cavity surface-emitting laser with V-shaped cavity geometry, that allows for an effective modeling and detailed studies of parameter dependencies. We apply numeric integration as well as path-continuation methods to understand the underlying bifurcation scenarios and hence the parameter regions of stable operation. Our investigations indicate that pulse cluster solutions emerge along the fundamental periodic solution branch with a critical influence of the cavity round-trip time on the number of pulses in the cluster. We find regions of multistability of higher-order pulse clusters and predict how different types of dynamics can be favored by tuning the cavity geometry.