Monolithic tantalum pentoxide microrings with intrinsic Q factors exceeding 4X10(6)

Abstract: Tantalum pentoxide (Ta2O5), as a silicon-photonic-compatible material platform, has garnered significant attention for high-performance integrated photonics due to its exceptional properties: a broad transparency window spanning from 0.28 um to 8 um, a moderate refractive index of 2.05 at 1550 nm, and an impressive nonlinear refractive index of 7.2X10^-19 m^2/W. Despite these advantages, achieving low-loss fabrication of monolithic microrings on the Ta2O5 platform remains challenging due to its inherent hardness and brittleness, which often result in rough sidewalls and significant scattering losses. In this work, we successfully demonstrated monolithic Ta2O5 microring resonators with exceptionally high intrinsic and loaded quality (Q) factors. This was accomplished through the innovative application of photolithography-assisted chemo-mechanical etching (PLACE) technology. By optimizing the coupling region between the microring and the bus waveguide, as well as meticulously controlling surface roughness during fabrication, we achieved near-critical coupling in the resulting microrings. The devices exhibited loaded Q factors of 2.74X10(6) in the telecom band without employing expensive electron-beam lithography, showing an intrinsic Q factor as high as 4.47X10(6) and a low propagation loss of only 0.0732 dB/cm - representing the highest results reported for strongly confined Ta2O5-based microring resonators to date. This work paves the way for the development of advanced photonic devices on the Ta2O5 platform with low manufacturing cost, including low-threshold microlasers, highly sensitive sensors, broad bandwidth supercontinuum sources, and optical frequency combs.