Gain compression coefficient and above-threshold linewidth enhancement factor in InAs/GaAs quantum dot DFB lasers

摘要

We measure, for the first time, the gain compression coefficient and above-threshold linewidth enhancement factor(alpha parameter) in quantum dot (QD) distributed feedback lasers (DFB) by time-resolved-chirp (TRC)characterization. The alpha parameter is measured to be 2.6 at threshold and increases to 8 when the output power of theQD DFB is increased to 3 mW. The dependence of the above-threshold alpha parameter on the optical power is found tobe stronger than the optical gain compression effect alone can predict. The inhomogeneous gain broadening, gainsaturation at the ground states and carrier filling in the excited states in QDs are proposed to explain the results.