Modeling passive mode-locking in vertical-external-cavity surface-emitting semiconductor lasers

In this paper, a novel theoretical description of passive mode-locking in electrically-driven VECSELs is developed. Results reveal that the onset of mode locking depends on the interplay of three different effects namely, contrast in saturation fluences, spot area ratio, and balance between intensities at the active medium and absorber. Thus, the standing wave effect in the vertical cavities can be used to improve the mode-locking performance. In order to favor mode locking, emitter and absorber have to be tightly coupled in order to saturate the latter in their mutual dynamical interplay.