Modal gain and internal optical mode loss of a quantum dot laser

The modal gain spectra and internal optical mode loss of a semiconductor la ser structure containing a single layer of InGaAs quantum dots have been me asured independently and directly as a function of current density. The qua ntum dot gain exhibits no obvious polarization dependence. The maximum moda l gain of (11 +/- 4) cm(-1) obtained from the ground state of a single laye r of quantum dots is in this case insufficient for lasing operation since t he internal optical mode loss measured on the same sample is (11 +/- 4) cm( -1). As expected laser emission is not observed from the dot ground state, but from the excited dot state or from the wetting layer depending on devic e length. (C) 2000 American Institute of Physics. [S0003-6951(00)00428-9].