Spectral Engineering With CMOS Compatible SOI Photonic Molecules

Photonic systems based on microring resonators have a fundamental constraint given by the strict relationship among free spectral range, total quality factor QT, and resonator size, intrinsically making filter spacing, photonic lifetime, and footprint interdependent. Here, we break this paradigm employing CMOS-compatible silicon-on-insulator photonic molecules based on coupled multiple inner ring resonators. The resonance wavelengths and their respective linewidths are controlled by the hybridization of the quasiorthogonal photonic states. We demonstrate photonic molecules with doublet and triplet resonances with spectral splitting only achievable with single-ring orders of magnitude larger in footprint. In addition, this splitting is potentially controllable based on the coupling (bonds) between resonators. Finally, the spatial distribution of the hybrid states allows up to sevenfold QT enhancement.