High-order mode suppression in a high-Q disk resonator with metal patterning

High-quality (Q) resonators are essential for efficient light confinement and manipulation in silicon photonics. Conventional microring resonators (MRRs) and microdisk resonators (MDRs) face challenges, such as high losses due to sidewall roughness in MRRs or interference from excessively high-order modes in MDRs. To overcome these challenges, we propose a novel, to the best of our knowledge, MDR design that integrates a patterned nickel (Ni) metal layer on top of a conventional MDR. This metal layer leverages the optical absorption properties of metal to selectively suppress high-order modes, resulting in a microresonator with a high-Q factor comparable to a conventional MDR and simultaneously a clean spectral response similar to that of a conventional MRR. Experimental results show that the patterned MDR with a radius of 20 μm achieves a maximum extinction ratio of 31 dB and a Q factor of 1.5 × 10⁵, which is two orders of magnitude higher than the Q factor of an MRR of identical size fabricated using the same process. This novel MDR design combines a high-Q factor with a clean spectral response, offering significant potential for applications that require high-Q resonators in chip-scale photonic systems.