Mode splitting in side emission from vertical-cavity surface-emitting lasers

We present side-emission (luminescence) data from vertical-cavity surface-emitting lasers which show cavity-induced effects on the emission spectrum. In particular, the heavy-hole luminescence spectrum contains two peaks when pumped in such a way as to excite electron-hole pairs well inside the cavity region, where coupling to free-space modes is minimized, and only one peak when pumped near the edge of the cavity (near a cleaved facet), where coupling to free-space modes is maximized. This splitting;an be distinguished as a cavity-induced effect with little ambiguity from other factors present in semiconductor quantum-well radiation, such as the light- and heavy-hole splitting. A fit to the data using Lorentzian line shapes gives a vacuum-field Rabi splitting of roughly 34 meV, which is consistent with theoretical calculations and with other reports on this phenomenon. We therefore conclude that the two peaks in the spectrum are due to Rabi oscillation in the cavity, and that they represent an actual change in the energy configuration of the quantum well.