Quantum cascade lasers with optical feedback: Regular multimode dynamics

We study the dynamics of a Quantum Cascade Laser subject to strong optical feedback in the framework of the Lang-Kobayashi model. In particular, we demonstrate that the continuous wave instability may lead to coherent multimode oscillations that indicate spontaneous phase-locking among external cavity modes. We recently predicted that this unique behavior is linked to the absence of relaxation oscillations in unipolar semiconductor lasers, which are characterized by a fast carriers recombination time (class-A lasers). These theoretical evidences may help understanding the mechanisms possibly leading to spontaneous mode-locking and pulse generation in QCLs.