Abstract

Semiconductor lasers based upon self-assembled quantum dots (QDs) are a promising source for applications in optical networks. Their charge-carrier confinement in all three spatial dimensions results in a range of special attributes such as ultra low threshold current, high material gain, small line width and weak temperature dependence when compared to conventional quantum well lasers [1]. When operated under proper conditions, QD based laser can not only emit light from the QD ground state (GS) but also from the first excited state (ES). The relatively slow QD carrier dynamics give rise to an incomplete gain clamping of the ES population, which consequently allows for simultaneous two-state lasing. This phenomenon, not to be confused with multi-mode lasing, is so far unique among all lasers. Moreover, some material systems exhibit a decline or even complete quenching of the GS intensity after the onset of ES lasing [2]. All optical switching of GS and ES lasing and an optically induced hysteresis via injection into the GS of such quenched devices have been experimentally observed and recently reported [3]. We numerically investigate the dynamics of such devices under external optical injection into the ground state using a model, that is based upon semiconductor-Bloch-equations and includes microscopically calculated charge-carrier scattering rates.

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