Modeling of quasi-supercontinuum laser linewidth and derivatives characteristics of InGaAs quantum dot broadband laser

We present the development of theoretical model based on multi-population rate equation to assess the broadband lasing emission in addition to the derivative optical gain and chirp characteristics from the supercontinuum InGaAs/GaAs self-assembled quantum-dot (QD) interband laser. The model incorporates the peculiar characteristics such as inhomogeneous broadening of the QD transition energies due to the size and composition fluctuation, homogeneous broadening due to the finite carrier lifetime in each confined energy states, and the presence of continuum states in wetting layer. We showed that the theoretical model agrees well with the experimental data of broadband QD laser. From the model, the broadband lasing characteristics can be ascribed to the large dispersion of QD with varying energy sub-bands and the change of de-phasing rate. These interesting characteristics can be attributed to the carrier localization in different dots that result in a system without a global Fermi function and thus an inhomogeneously broadened gain spectrum. Furthermore, our simulation results predict that the linewidth enhancement factor (α = 2) from the ground state (GS) in this new class of semiconductor lasers is slightly larger but in the same order of magnitude as the values obtained in conventional QD lasers. The calculated gain spectrum shows similar magnitude order of material differential gain (̃10^-16 cm²) and material differential refractive index (̃10^-20 cm³) as compared to conventional QD lasers. The comparable derivative characteristics of broadband QD laser shows its competency in providing low frequency chirping as well as a platform for monolithic integration operation.