Over 3 Million Q-Factor Compact Bend-Coupled Silicon Microdisk Resonator for High-Performance Microwave Photonic Filtering and Frequency Identification

Microdisk resonator (MDR), as a common class of optical resonators, has emerged as a cornerstone of integrated photonics due to its ultracompact footprint and high light-confining capacity. In this work, a silicon photonic bend-coupled MDR with an ultrahigh Q-factor and a compact footprint is proposed, in which the bus waveguide is engineered to satisfy the strict phase-matching condition for the fundamental whispering gallery mode (WGM), while selectively suppressing the higher order WGMs. The proposed bend-coupled MDR features an ultrahigh Q-factor of $3.3\times 10$ ${}^{\mathbf {6}}$ and a large free spectral range of 2.67 nm. Leveraging the ultrahigh-Q bend-coupled MDR, widely tunable microwave photonic filtering and high-accuracy microwave frequency identification are experimentally implemented. The demonstrated microwave photonic filter achieves breakthrough performance with a narrow passband of 59 MHz and a wide frequency tuning range of 50 GHz. Concurrently, the photonics-assisted microwave frequency identification system exhibits a wide measurement range of 40 GHz, ranging from 6 to 46 GHz, a high measurement accuracy of 14.5 MHz, and a high-frequency resolution of 80 MHz. The proposed ultrahigh-Q bend-coupled MDR paves a way for revolutionizing large-scale and high-density photonic integrated circuits, enabling wideband microwave photonic signal processing, ultraprecision metrology and scalable quantum photonic networks.