Variations of linewidth enhancement factor and linewidth as a function of laser geometry in (AlGa)As lasers

A quantitative analysis of the laser geometry dependence of the linewidth enhancement factor alpha and linewidth Delta f in GaAs/AlGaAs lasers is presented. Analytical expressions for the refractive index change and alpha are presented. Variations of alpha and Delta f depending on active layer thickness and laser length are estimated by using the expressions and previous experimental data of absorption spectra. Considering small variations in the reported experimental data depending on laser type, it is shown that the calculated values of alpha agree well with the experimental data. The magnitude of alpha decreases gradually with the decrease of active layer thickness and laser length. Since the change of active layer thickness affects only alpha , neglecting small variations of other terms in the linewidth expression, the reduction of active layer thickness is suggested to be a practical method for the reduction of linewidth.>