The influence of resonator structure on the linewidth enhancement factor of semiconductor lasers

The phenomenon of intensity-phase coupling in semiconductor lasers is studied in the linear regime in terms of an effective linewidth enhancement factor. The circumstances under which the longitudinal laser structure of a distributed feedback laser may influence this coupling are determined. For the case of uniform gain and carrier density no effect is expected from a periodic or quasi-periodic corrugation. However, when the gain layer is corrugated or a periodic gain is otherwise implemented, the influence may be considerable. It is shown that the degree of gain coupling between right- and left-travelling waves and the specific mechanism by which variations in the carrier density influence this coupling are of key importance. It is found that depending on the degree and nature of the gain coupling the effective linewidth enhancement factor may be considerably reduced or enhanced