Third-harmonic generation in silica wedge resonators

TL;DR

This paper demonstrates third-harmonic generation in small silica wedge microresonators with tunable emission, achieved through dispersion engineering and thermal control, advancing nonlinear optics in integrated microcavities.

Contribution

It introduces a method for efficient third-harmonic generation in small silica wedge resonators with tunability via thermo-optical and Kerr effects, and validates phase matching with couple-mode theory.

Findings

Successful third-harmonic generation in silica wedge microresonators.

Tunable third-harmonic emission through thermal and Kerr effects.

Suppression of four-wave mixing by operating in normal dispersion regime.

Abstract

Whispering-gallery-mode microcavities are known to have 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 operate in the normal dispersion regime preventing frequency comb generation by suppressing infrared cascading four-wave mixing. This allows for a clean third harmonic generation at phase-matched visible optical modes. Tunability of the third-harmonic emission is obtained due to a combination of the thermo-optical and Kerr effects. An additional thermal control of the phase matching condition allows for optimizing third-harmonic generation, and agreement between this process and couple-mode theory is demonstrated.