Measurement of the linewidth enhancement factor α of semiconductor lasers

Abstract

A theory of the amplitude and phase modulation characteristic of a single mode semiconductor laser is presented. In this model the amplitude modulation couples through the complex susceptibility of the gain medium to the phase. We show that this coupling constant can be obtained by a high-frequency modulation experiment. This measured coupling constant is used to infer the linewidth enhancement factor α as discussed by Henry, and Vahala and Yariv. Experiments confirmed the model and we measured a linewidth enhancement factor ‖α‖=4.6±1.0 for a GaAlAs buried optical guide laser.