Focused ion beam polishing based optimization of high-Q silica microdisk resonators

Abstract Whispering gallery mode (WGM) microdisk resonators are promising optical devices that confine light efficiently and enable enhanced nonlinear optical effects. This work presents a novel approach to reduce sidewall roughness in SiO 2 microdisk resonators using focused ion beam (FIB) polishing. The microdisks, with varying diameter ranging from 5 to 20 μ m are fabricated using a multi-step fabrication scheme. However, the etching process introduces significant sidewall roughness, which increases with decreasing microdisk radius, degrading the resonators’ quality. To address this issue, a FIB system is employed to polish the sidewalls, using optimized process parameters to minimize Ga ion implantation. White light interferometry measurements reveal a significant reduction in surface roughness from 20 nm to 7 nm for a 5 μ m diameter microdisk, leading to a substantial enhancement in the scattering quality factor (Qss) from 3 × 10 2 to 2 × 10 6 . These findings demonstrate the effectiveness of FIB polishing in improving the quality of microdisk resonators and open up new possibilities for the fabrication of advanced photonic devices.