Theoretical optimization of mid-infrared interband cascade lasers for amplitude modulated frequency comb generation

Frequency comb generation in mid-infrared interband cascade lasers (ICLs) promises to lead to rapid and low-power-consumption chemical sensing of multiple species or broadband lines in the 3-5 μm atmospheric window. We present a complete electron-wavevector-resolved model of the ICL frequency combs based on the Maxwell-Bloch formalism that intrinsically includes the group velocity dispersion (GVD) from the active core. Using a version of this model validated against the available experimental data, we provide a resolution of several longstanding puzzles in this field. We find that the presence of a fast gain component due to the transfer of electrons from the electron injector reservoir does not preclude the generation of pulses, provided the recovery time of the saturable absorber (SA) section of the two-section devices is sufficiently short. However, the generation of single pulses and phase-locked AM combs appears difficult in the conventional design because of the accumulation of holes over successive round trips. A modified design with the reduced density of states in the hole injector is proposed to overcome this problem. Detailed simulations as a function of the injection current density, SA length and lifetime, waveguide GVD, and other parameters are presented in order to guide the future experimental implementation.