Backscattering-Induced Kerr Solitons in Ring Quantum Cascade Lasers

Ring quantum cascade lasers have recently gained considerable attention, showing ultrastable frequency comb and soliton operation, and thus opening a way to integrated spectrometers in the mid-infrared and terahertz fingerprint regions. Thanks to a self-consistent Maxwell-Bloch model, we demonstrate, in excellent agreement with the experimental data, that a small but finite coupling between the counter-propagating waves arising from distributed backscattering is essential to stabilize the soliton solution.