  We report direct observation of the strong exciton-photon coupling in ZnO
tapered whispering gallery (WG) microcavity at room temperature. By scanning
excitations along the tapered arm of ZnO tetrapod using micro-photoluminescence
spectrometer with different polarizations, we observed a transition from the
pure WG optical modes in the weak interaction regime to the excitonic polariton
in the strong coupling regime. The experimental observations are well described
by using the plane wave model including excitonic polariton dispersion
relation. This provides a direct mapping of the polariton dispersion, and thus
a comprehensive picture for coupling of different excitons with differently
polarized WG modes.
