Efficient frequency conversion by combined photonic–plasmonic mode coupling

Abstract

Due to its strong nonlinear susceptibility tensor components, zinc oxide (ZnO) provides highly efficient frequency conversion when excited with near-infrared pulses. Three-photon absorption offers an alternative to conventional ultraviolet sources for sub-bandgap excitation of ZnO. In this work, plasmonic nanoantennas are used to enhance coupling of infrared light into photonic ZnO resonators. The nanoantennas provide a strong field localization, which allows for a more efficient second- and third-harmonic generation within the ZnO film, as well as an immensely increased spontaneous photoluminescence emission due to interband absorption. The results demonstrate that the combination of plasmonic nanoantennas with photonic microresonators leads to a strongly enhanced nonlinear light-matter-interaction in thin ZnO films.