Systematic Engineering of Waveguide-Resonator Coupling for Silicon Microring/Microdisk/Racetrack Resonators: Theory and Experiment

A systematic engineering of waveguide-resonator coupling for optimum phase matching and field-overlap is proposed to achieve critical coupling and strong over-critical coupling for microring, micro racetrack and microdisk resonators on silicon-on-insulator (SOI) platform. The impact of the waveguide-resonator dimensions, their spacing and interaction length on the strength of the coupling are investigated. We show that by optimization of the dimension of the waveguide-resonator structure, the coupling strength can be engineered to be insensitive to fabrication errors. Based on our optimization techniques, critical coupling to low
Q
resonators (
Q
~ 10
⁴
) as well as ultra-high
Q
resonators (
Q
~ 3.1 x 10
⁶
) is experimentally demonstrated.