We have developed a technique to control the polarization dependence of quantum dot (QD)-semiconductor optical amplifiers (SOAs) using vertically stacked self-assembled InAs QDs with moderately thick intermediate layers. By increasing the number of stacking layers, the transverse magnetic polarization component of electroluminescence (EL) from the cleaved edge surface of the SOA has been enhanced dramatically. Broadband and almost isotropic EL with a polarization difference of less than 1.2 dB has been demonstrated in a 1.3 μm optical communication band for nine-layer stacked QDs in the active region of the SOA.

We studied polarization anisotropy observed in photoluminescence from closely stacked InAs/GaAs quantum dots (QDs). As the number of stacked layers was increased, the anisotropy in the (001) plane became drastically larger and the [001]-polarization component became larger than the [110] component when observed from the [ 110] direction. However, the polarization intensity of the [ 110] component remained stronger than that of the [001] component in the stacked QDs. Such varied polarization anisotropies depending on the observation direction have been found to result from the valence-band mixing in the vertically coupled electronic states. #

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