High-Q Silicon Nitride Few-Mode Microdisk Resonators

High-Q silicon nitride microdisk resonators (MDRs) with fewer resonant modes are proposed and experimentally demonstrated. The proposed MDRs consist of microdisks and optimized bent bus waveguides. The introduction of asymmetric directional couplers (DCs) successfully destroys part of high-order modes resonance and enhances that of TE1 and TE2 radial modes so that the spectral purity of the MDRs is improved. In this way, guided-modes propagate in MDRs with low loss and > 106 Q-factors are obtained. The maximum measured loaded Q-factor and intrinsic Q-factor is
$4.7\times 10 ^{6}$
and
$5.9\times 10 ^{6}$
, respectively. The minimum wavelength interval between two notches is 0.68 nm. The proposed few-mode MDRs are realized with one step silicon nitride etching process provided by a multiproject wafer foundry and they have broad application prospects in integrated microwave photonic systems, sensing, and other fields.