Double-Layer Cross-Coupled Silicon Nitride Multi-Ring Resonator Systems

We demonstrate a double-layer Si₃N₄ multi-ring resonator system, where an S -bend waveguide is cross-coupled with a ring cavity loaded with two sub-ring resonators. The device performance is analyzed by using the transfer matrix method. The alignment-error-induced device performance variations are also discussed. The measured spectra coincide well with the simulated results. The device has high tuning flexibility and more design freedom with two sub-rings placed above the ring cavity. The spectrum profile can also be tuned by changing the cross-coupling coefficient. A heater placed above the resonator can shift the resonant wavelength effectively.