Coupled spiral-shaped microdisk resonators with non-evanescent asymmetric inter-cavity coupling.

We study coupled spiral-shaped microdisk resonators with non-evanescent asymmetric inter-cavity coupling via seamlessly jointed notches. Our finite-difference time-domain numerical simulations reveal that the throughput-port transmissions are reciprocal between counterclockwise (CCW) and clockwise (CW) traveling-wave modes, while the drop-port transmissions and modal field distributions are input-port dependent. By introducing a slight mismatch in radii between two coupled microdisks while preserving their seamlessly jointed notches, we are able to show selectively enhanced extinction ratio for one of the split modes while suppressing the other. Our experiments using coupled spiral-shaped microdisk resonators in silicon nitride-on-silica suggest split resonances with an extinction ratio of ~20 dB using identical coupled microdisks, and an enhanced resonance extinction ratio of ~24 dB using slightly mismatched coupled microdisks. The non-evanescent coupling preserves high-Q resonances.