Dual-Layer Cross-Coupled Tunable Resonator System in a Three-Dimensional Si₃N₄ Photonic Integration Platform

With a three-dimensional Si₃N₄ integration, we demonstrate a dual-layer cross-coupled resonator system where an S-bend waveguide is coupled with a racetrack microring resonator loaded with a sub-microring. The device has a compact structure and provides more design freedom. The transfer matrix method is used to model the device. The resonance spectrum is significantly affected by the coupling coefficient between the waveguide and the resonator, generating versatile resonance features. A group of devices with a varying coupling length are implemented, exhibiting an evolution trend consistent with the simulation results. The resonance wavelength can be thermo-optically tuned by the micro-heater placed above the resonator. The three-dimensional Si₃N₄ platform enables dense integration of high-performance devices, opening new avenues for future compact, high-density, and cost-effective photonic integrated circuits.