Measurement of differential gain and linewidth enhancementfactor ofInGaAs vertical cavity surface emitting laser

Abstract
The differential gain of an InGaAs/GaAs vertical cavity surface emitting laser (VCSEL) has been obtained through measurement of the subthreshold spectral linewidth. The results are in close agreement with a theoretical model for a VCSEL operating at the peak of the gain spectrum. The linewidth enhancement factor has been measured to be ~0.7 at low bias currents again in agreement with theory.