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

The modal gain spectra and internal optical mode loss of a semiconductor laser structure containing a single layer of InGaAs quantum dots have been measured independently and directly as a function of current density. The quantum dot gain exhibits no obvious polarization dependence. The maximum modal gain of (11 +/- 4) cm(-1) obtained from the ground state of a single layer of quantum dots is in this case insufficient for lasing operation since the 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 device length. (C) 2000 American Institute of Physics. [S0003-6951(00)00428-9].