Emission-line width and $\alpha$-factor of 850-nm single-mode vertical-cavity surface-emitting lasers based on InGaAs/AlGaAs quantum wells

The emission-line width for 850-nm single-mode vertical-cavity surface-emitting lasers based on InGaAs/AlGaAs quantum wells is studied. The width of the emission line for a laser with a 2-$\mu$m oxide current aperture attains it minimum ($\sim$110 MHz) at an output power of 0.8 mW. As the optical output power is further increased, anomalous broadening of the emission line is observed; this is apparently caused by an increase in the $\alpha$-factor as a result of a decrease in the differential gain in the active region under conditions of increased concentration of charge carriers and of high internal optical losses in the microcavity. The $\alpha$-factor is estimated using two independent methods.