We investigate the spontaneous emission (SE) of self-assembled InAs quantum dots (QDs) embedded in GaAs ridge waveguides that lay on a low index substrate. In thin enough waveguides, the coupling to the fundamental guided mode is vanishingly small. A pronounced anisotropy in the coupling to non-guided modes is then directly evidenced by normal-incidence photoluminescence polarization measurements. In this regime, a measurement of the QD decay rate reveals a SE inhibition by a factor up to 4. In larger wires, which ensure an optimal transverse confinement of the fundamental guided mode, the decay rate approaches the bulk value. Building on the good agreement with theoretical predictions, we infer from calculations the fraction β of SE coupled to the fundamental guided mode for some important QD excitonic complexes. For a charged exciton (isotropic in plane optical dipole), β reaches 0.61 at maximum for an on-axis QD. In the case of a purely transverse linear optical dipole, β increases up to 0.91. This optimal configuration is achievable through the selective excitation of one of the bright neutral excitons.
References
For the sake of simplification, all simulations are performed by assuming that the refractive indices of the epoxy glue is equal to that of SiO2. This approximation does not impact the following discussion.
We have not determined if X = [110] or . However, this ambiguity does not impact the results discussed in the paper.
The QD ensemble located in the square pattern exhibits a decay rate . A theoretical evaluation of the photonic density of states experienced by an in-plane dipole embedded in the planar structure yields leading to a bulk decay rate .
