While frequency combs are mostly connected to short pulse emission, it is not the only way to generate a comb. Quantum or interband cascade lasers for example show a completely different behavior. Here, we give an overview of this exciting phenomena including theory and experiments.
Starting from the desired modal field we solve for the supporting waveguide refractive index structure within a semiconductor diode laser. Specifically we analyze the problem of maximizing far-field on-axis intensity and discuss the practical aspects of waveguide design.
We show that the linewidth broadening factor of a mid-infrared interband cascade laser operated above the lasing threshold is around 2.0, which does not increase with increasing pump current. The linewidth broadening factor is extracted from the self-mixing interferometry technique.