Two-state passive mode-locking of quantum dot semiconductor lasers: Classical state scenario and novel reverse state dynamics

We present both experimental and theoretical investigations of the so-called reverse emission state dynamics in a two-section InAs/InGaAs Quantum Dot (QD) laser. In contrast to the classical state scenario, we demonstrate by properly designing the laser cavity and the QD active region, a reversal of the emission state transition: At a certain gain current Excited-state (ES) lasing and mode-locking (ML) starts first and then, with increasing gain current, a transition to simultaneous ES and ground-state (GS) ML takes place. This enables a novel approach to wavelength-switching of the mode-locked pulses over a range of 63 nm: the realization of a two-section QD laser with a resistor Self-Electro-optic Effect Device (SEED) configuration. These results are reviewed together with the state-of-the-art realization of InAs/InGaAs two-section QD lasers operating in two-state ML regime.