Enhanced thermo-optic tuning micro-ring resonator on silicon nitride platform

The rapid growth of integrated photonics for optical computing, LiDAR, and quantum information processing has established silicon nitride (SiN) as a leading platform due to its ultra-low optical loss and CMOS compatibility. However, its inherently low thermo-optic coefficient limits the efficiency of thermal modulation. Here, we first present a compact bi-material dual micro-ring resonator that integrates a small Si ring within a larger SiN ring to overcome this limitation. Localized heating in Si efficiently controls the optical phase while preserving the ultra-low propagation loss of SiN. The high thermo-optic coefficient of Si, nearly ten times that of SiN, enables strong and energy-efficient modulation. The device achieves a π-phase shift with only 45.2 mW of power, representing a 33.6% improvement over conventional SiN-only resonators, while maintaining comparable response time and excellent thermal stability. Fabricated entirely using standard CMOS-compatible processes without additional steps, it demonstrates high manufacturability and scalability. This architecture provides a practical, energy-efficient solution for phase control on the SiN platform and establishes a pathway toward dense, low-loss, and high-tuning efficiency photonic systems.