To realize the refractive index dispersion accurately is essential for the design of optical devices. In this paper, we study hexagonal ZnO microrod cavities. We measure angle-resolved photoluminescence and use an iterative method to derive the refractive index dispersion near the band edge. Because of the large exciton binding energy in bulk ZnO, the photogenerated excitons are stable at room temperature. As a result, excitons could significantly affect the refractive index dispersion near the resonance energy. Thus, we construct a modified Lorentz oscillator model to extract the transverse and longitudinal exciton resonance energy and the damping term due to the scattering between LO-phonons and excitons at room temperature. The Rabi splitting energy and zero detuning point obtained by this method are reliable. The dispersion relations of polaritons measured by our angle-resolved photoluminescence agree well with the dispersion relation of polaritons, deduced by using the refractive index dispersion and optical parameters obtained by our theoretical model, thus, lending support to our theoretical model and the extracted parameters.
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