Instabilities for quantum-cascade lasers under self-phase modulation

Theoretical analysis of lasing instability in quantum-cascade lasers was carried out. A mid-infrared quantum-cascade laser structure with triple resonance levels was chosen as the prototype of the lasing medium with high Kerr nonlinearity from optical transitions. The self-phase modulation effect induced by Kerr nonlinearity was found to possibly change the unstable frequency domain significantly, i.e., not only broaden the unstable domain but also drive it from single-mode to multi-mode. The instability mechanisms of quantum-cascade lasers include one like the coherent multi-mode Rishen-Nummedal-Graham-Haken instability and the spatial-hole-burning-induced single-mode instability.