Nonlinear Dynamics in Semiconductor Lasers - Abstract

Columbo, Lorenzo

Dynamics of a broad-band Quantum Cascade Laser. From chaos to coherent dynamics and mode-locking

We study the multi longitudinal mode dynamics of broadband mid-IR and THz Quantum Cascade Laser (QCLs), using a time domain traveling wave model based on a set of effective semiconductor Maxwell-Bloch equations. The model includes key ingredients describing the radiation-semiconductor medium interaction such as an asymmetric, frequency dependent gain/refractive index and a phase-amplitude coupling (linewidth enhancement factor). The analytical determination of the traveling wave (TW) single mode solutions and their threshold allow us to identify favorable parameters for multimode nontrivial behaviors relatively close to threshold. Our numerical simulations show that TW instabilities lead to chaotic emission or regular regimes where the laser exhibits pulsed emission. In latter case one or more self-formed pulses travel in the laser cavity depending on the initial conditions (pulse multistability). On the fundamental side, we also show that very short carriers lifetime (1-10 ps) dominated by non-radiative phonon scattering characteristic of QCLs makes their dynamical behavior close to the lasing threshold as general as that described by a modified complex Ginzburg Landau equation. On the applicative side, our results which are in very good agreement with recent experimental evidences on the dynamics of ultra-broadband QCLs [1], may shine some light on the physical mechanism at the origin of frequency combs generation in the mid-IR and THz spectral regions with important implications in the field of high precision spectroscopy in biomedicine, environmental monitoring, etc.. [1] H. Li et al., Opt. Express 23, 33270 (2015).