Nonlinear mechanisms of filamentation in broad-area semiconductor lasers

There are three nonlinear mechanisms that can lead to filamentation in broad-area semiconductor lasers: gain-saturation-induced changes in the refractive index through the linewidth-enhancement factor, self-focusing due to heat-induced index changes, and self-defocusing through intensity-dependent index changes in the cladding layer. We present a theoretical model to analyze these mechanisms and their relative roles in destabilizing the laser output. We find that there exists a critical value for the linewidth-enhancement factor below which broad area lasers are stable for wide stripe widths (as wide as 250 μm) and high pumping levels (as high as 20 times threshold). We also find that broad-area lasers are less susceptible to filamentation through self-defocusing and show how an intensity-dependent index in the cladding layer may be used to suppress filamentation caused by the linewidth-enhancement factor