Design of a high phase-shift efficiency wide-tuning silicon nitride filter

Silicon nitride photonic integrated circuits with ultra-low loss are widely used in applications such as telecommunications and optical sensing. However, the radiation loss increases rapidly as the radius is reduced, resulting in large-sized silicon nitride photonic integrated circuits. The weak thermo-optical effect limits the high-efficiency, low-power consumption applications. In this paper, a stepped index waveguide structure is studied to reduce the bending loss by enhancing the mode confinement. A bend with a radius of 30μm is designed using Ansys MODE. Polymer with a high thermo-optic coefficient is used as the cladding of the silicon nitride waveguide to improve the tuning performance of the phase shifter. The grooves around the waveguide also acts as an adiabatic trench to increase the efficiency of the thermal electrode. A π phase shift under thermal tuned power of 7.5mW is achieved with a 300μm long silicon nitride waveguide. Finally, a cascaded silicon nitride micro-ring resonator with radius of 50μm is designed to achieve an efficient filter with a wide tuning range of 116nm. This scheme provides a novel approach for high-density, wide-tunable and miniaturized devices in silicon nitride photonic integrated circuits.