Dressed Linewidth Enhancement Factors in Small Semiconductor Lasers

We show that the linewidth of a semiconductor-based small laser, when operated above the threshold, might not directly reflect the permittivity variation induced by carriers in the gain material. In fact, the linewidth may be significantly dressed by responses of modal amplitudes to emitting sources if the small cavity is dispersive, lossy, leaky, spectrally-sharp in gain, but not necessarily intricately-structured. This dressing effect might reduce linewidth enhancements. Despite a large material linewidth enhancement factor, the source-amplitude response could still keep the enhancement effect mild.