Reverse excited state / ground state dynamics in mode-locked two-section quantum dot semiconductor lasers

In this contribution reverse emission state transition of a two-section quantum dot laser at a saturable absorber bias of zero volt (short circuit) is presented where lasing and mode-locking starts first on the energetically higher first excited-state (ES) and then, with increasing gain current, additional lasing and mode-locking on the energetically lower ground-state (GS) takes place. A huge coexistence regime as well as temporal simultaneity of both GS and ES mode-locking is experimentally confirmed. At the onset of two-state mode-locking shorter pulse widths are found for the GS as compared to the ES at the same gain current. A considerable shortening of the ES pulse widths is observed when GS mode-locking starts. These state-resolved emission dynamics are confirmed by time-domain travelling-wave equation modeling. Finally, by electrically shortening the saturable absorber via an external variable resistor, a resistor Self-Electro-Optical Devices (SEED) configuration is exploited and tailored emission state control is achieved.