Enhancement of the thermo-optic phase modulation efficiency in silicon nitride waveguides by incorporating an...

Silicon nitride (SiN) has emerged as an essential material in silicon photonics due to its broadband transparency, low propagation loss, and high power handling capacity. Despite these advantages, implementing efficient phase modulators (PMs) in SiN waveguides remains challenging due to the low thermo-optic (TO) coefficient. Traditional SiN TO-PMs often require high driving power, hindering their integration into compact, low-power photonic integrated circuits (PICs). In this study, we propose a novel approach to enhance the TO effect of SiN waveguides by incorporating polymer planar waveguides with superior TO properties. By embedding a SiN strip within a polymeric planar waveguide, we have achieved a significant reduction in the modulation power required for the SiN PMs. Mach-Zehnder modulator with the embedded SiN strip demonstrated a P_π of 42.7 mW and a response time of 110 µs. This method simplifies fabrication, requiring only a single stepper lithography process without precise alignment between layers. This advancement paves the way for low-power, high-efficiency phase modulators in SiN photonics, with potential applications extending to the visible spectrum.