High-Q Racetrack Resonators based on Silicon Multimode Waveguides

Abstract

This thesis investigates silicon photonic racetrack resonators based on multimode waveguides. The resonators aim at achieving a relatively large free spectral range (FSR) of larger than 1 nm and an ultra- high Q factor of larger than 1 million. To achieve these goals, the resonator structure was devised and designed using numerical simulations. The resonator structure includes Euler bends, tapered waveguides, and a directional coupler region. The resonators were realized using a commercial foundry service, and their characteristics were measured and analyzed. To obtain precise characteristics, the measurement was carried out considering the self-heating effect. For the analysis, a theoretical model based on the temporal coupled-mode theory (TCMT) was employed. The best resonator exhibited a Q factor of approximately 1.99×106 and an FSR of 1.502 nm. Due to back scattering mechanisms in the resonators, dips in the transmission spectra of the resonators split, which were successfully fitted using the theoretical model. Furthermore, the relationships of the fitting parameters like the coupling efficiency of the resonators to the coupling region length were analyzed. Based on the relationships, critically-coupled resonators could be designed and realized in the future. The investigated resonators may be useful for microwave and nonlinear-optical devices requiring resonators with an ultra-high Q.