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

Amplified spontaneous emission measurements are investigated below threshol d in InAs quantum-dot lasers emitting at 1.22 mu m, The dot layer of the la ser was grown in a strained quantum well (QW) on a GaAs substrate. Ground s tate gain is determined from cavity mode Fabry-Perot modulation. As the inj ection current increases, the gain rises super-linearly while changes in th e index of refraction decrease, Below the onset of gain saturation, the lin ewidth enhancement factor is as small as 0.1, which is significantly lower than that reported for QW lasers.