Linewidth enhancement factor of a type-II interband-cascade laser

Experimental results using the amplified spontaneous emission spectroscopy of a type-II interband-cascade laser are presented. Using the Hakki-Paoli method, the optical gain spectra of the laser are extracted for the wavelength of 3.13μm at various subthreshold current levels. A group index of around 3.33 is determined from Fabry-Pérot modal spacing. The change in refractive index with increased bias current is obtained from the peak wavelength shifts of the Fabry-Pérot spectrum. A low value of 0.71 for the linewidth enhancement factor at the lasing wavelength near threshold is found.