Gain and linewidth enhancement factor in InAs quantum-dot laser diodes

Amplified spontaneous emission measurements are investigated below threshold in InAs quantum-dot lasers emitting at 1.22 μm. The dot layer of the laser was grown in a strained quantum well (QW) on a GaAs substrate. Ground state gain is determined from cavity mode Fabry-Perot modulation. As the injection current increases, the gain rises super-linearly while changes in the index of refraction decrease. Below the onset of gain saturation, the linewidth enhancement factor is as small as 0.1, which is significantly lower than that reported for QW lasers.