High-Q LiNbO₃ microtoroid resonators

The first LiNbO₃ microtoroid resonators with high quality factor are produced by gravity-assisted surface tension reshaping. The original microdisk is produced by selective ion implantation and chemical etching. It is transformed into the microtoroid by thickening its rim through stretching the melted surface region by gravity force. The used thermal treatment process not only produces atom-scale smooth surface, but also enhances the optical confinement of the resonant modes. The resonant mode characteristics of the microtoroid resonators are calculated by the full-vectorial mode solver using the finite-element method and are used to explain the temperature tuning mechanisms. The 20-μm-diameter LiNbO₃ microtoroid has the intrinsic quality factor of 5.9 × 10⁴ and the tuning rate of 24.3 pm/°C. When the microtoroid temperature increases, the resonant wavelength shifts toward the long wavelength side. Numerical simulation results successfully confirm the action of thermo-optic effect and thermal expansion effect in the temperature tuning process. The high- Q LiNbO₃ microtoroid resonators facilitate the efficiency enhancement of nonlinear-optic devices.