Hysteresis Behavior of External Cavity Quantum Cascade Lasers in the Strong Feedback Regime

We experimentally investigate mode hops of a continuous-wave (cw) external cavity (EC) quantum cascade laser (QCL) in Littrow configuration, observing hysteresis for variations of either external cavity length, chip current, or grating angle. The results are compared with two different theoretical models. Simulation results suggest that hysteresis in EC-QCLs is caused by self-stabilization due to mode coupling.