Third-harmonic generation in silica wedge resonators

Abstract

Whispering-gallery-mode microcavities are known to have a high optical quality factor, making them suitable for nonlinear optical interactions. Here, third-harmonic generation is observed using a relatively small radius wedge silicon oxide optical microcavity. The small radii wedge microdisks can be dispersion-tailored to obtain either normal or anomalous group velocity dispersion. In our case, we operated in the normal dispersion regime preventing frequency comb generation by suppressing IR cascading four-wave mixing. This approach allowed for a clean third-harmonic generation at phase-matched visible optical modes. Tunability of the third-harmonic emission was obtained due to a combination of thermo-optical and Kerr effects. An additional thermal control of the phase-matching condition allows the optimization of the third-harmonic generation, and an agreement between this process and the couple-mode theory was demonstrated.