Scalable fabrication of erbium-doped high-Q silica microtoroid resonators via sol-gel coating

This study explores sol-gel methods for fabricating erbium-doped silica microtoroid resonators, addressing the limitations of conventional doping techniques and enhancing device scalability. We develop a reproducible sol-gel process that yields defect-free films for photonic applications, and detail common defects and troubleshooting strategies. Two fabrication methods are compared: traditional film deposition on substrates and the direct coating of prefabricated resonators. The latter enables the fabrication of larger resonator diameters (up to 450 {\mu}m) without buckling, while achieving a high-Q factor and a low lasing threshold of 350 {\mu}W. These erbium-doped resonators exhibit multi-mode laser oscillations at 1550 nm, revealing the sol-gel method's potential for realizing scalable, gain-doped photonic devices.