Reverse-emission-state-transition mode locking of a two-section InAs/InGaAs quantum dot laser

Reverse-emission-state-transition mode locking in a two-section InAs/InGaAs quantum dot laser is experimentally investigated and confirmed by simulations. Stable mode locking starts on the first excited state (λ=1207 nm) and then, with increasing gain current, a transition to stable simultaneous two-state mode locking on excited state and ground state (λ=1270 nm) takes place. This particular state-transition occurs already at 0 V reverse-bias and at moderate gain-section currents. It is attributed to the strong active region chirping of the gain medium and in particular to a photon pumping process in the saturable absorber section.