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

TL;DR

This paper demonstrates that focused ion beam polishing significantly reduces sidewall roughness in silica microdisk resonators, greatly enhancing their quality factors and advancing the fabrication of high-performance photonic devices.

Contribution

It introduces a novel FIB polishing method to improve the surface quality and optical performance of silica microdisk resonators, addressing fabrication-induced roughness issues.

Findings

Surface roughness reduced from 7 nm to 20 nm

Quality factor improved from 3×10^2 to 2×10^6

FIB polishing effectively enhances microdisk resonator performance

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\textsubscript{2} microdisk resonators using focused ion beam (FIB) polishing. The microdisks, with varying diameter ranging from 5 to 20 $\mu$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 7 nm to 20 nm for a 5 $\mu$m diameter microdisk, leading to a substantial enhancement in the scattering quality factor (Qss) from $3\times 10^2$ to $2\times 10^6$. 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.