Coupling coefficients in gain-coupled DFB lasers: inherent compromise between coupling strength and loss

A theoretical analysis of the gain-coupling coefficient for distributed feedback (DFB) lasers with first-order, rectangular, gain, or loss gratings is presented. For the structure with gain grating, the dependence of the gain-coupling coefficient on the modal gain has been taken into account for the first time. In both structures, an inherent compromise between coupling strength and extra modal loss is found. The results show that significant gain-coupling coefficient values are feasible.<>