Correlations between axial and lateral emission of coupled quantum dot–micropillar cavities

Abstract

We report on optical studies of coupled quantum dot--micropillar cavities using a ${90}^{\ensuremath{\circ}}$ excitation-and-detection scheme. This specific configuration allows us to excite the micropillar structures either in the axial direction or in the lateral direction and to simultaneously detect emission from both directions. That enables us to reveal correlations between emission into the cavity mode and the leaky modes in the regime of cavity quantum electrodynamics. In particular, we can access and distinguish between axial cavity emission and lateral emission consisting of emission of quantum dots into the leaky modes and losses due to sidewall scattering, respectively. In the multiemitter regime, this technique provides direct access to the respective loss channels and reveals a strong increase of sidewall losses in the low-diameter regime below about 3.0 $\ensuremath{\mu}\mathrm{m}$. Beyond that, in the single-emitter regime, we observe an anticorrelation between quantum dot emission coupled into the cavity mode and into the leaky modes which is controlled by light-matter interaction in the weak coupling regime. This anticorrelation is absent in the strong coupling regime due to the presence of entangled light-matter states. Moreover, excitation-power-dependent studies demonstrate that the intensity ratio between axial and lateral emission increases strongly above the lasing threshold due to enhanced directionality of emission into the lasing mode. In fact, theoretical studies confirm that this intensity ratio is an additional indicator of laser action in high-$\ensuremath{\beta}$ microlasers for which the onset of lasing is difficult to identify by the input-output characteristics.