Suppression of spatial hole burning and pulse stabilization for actively modelocked quantum cascade lasers using quantum coherent absorption

We theoretically study of an actively modelocked quantum cascade laser in which we incorporate quantum coherent absorption by interleaving quantum coherent absorbing periods with gain periods. We show that this absorption suppresses the spatial hole burning that is responsible for pulse instability. As a consequence, the laser produces a stable train of single-peak soliton-like pulses with pulse durations less than 1.25 ps over a broad range of pump powers. We also show that the laser self-starts from initial quantum noise.