Spectrally resolved linewidth enhancement factor of a semiconductor frequency comb

The linewidth enhancement factor (LEF) has recently moved into the spotlight of research on frequency comb generation in semiconductor lasers. Here we present a novel modulation experiment that enables direct measurement spectrally resolved LEF laser comb. By utilizing phase-sensitive technique, are able to extract for each individual mode any type. We first investigate and verify this universally applicable technique using Maxwell–Bloch simulations. Following, experimental demonstration quantum cascade comb, confirming predicted key role dynamics.