Efficient and compact thermo-optic phase shifter in silicon-rich silicon nitride

The design, fabrication, and characterization of low-loss ultra-compact bends in high-index (n=3.1 at λ=1550nm) plasma-enhanced chemical vapor deposition silicon-rich silicon nitride (SRN) were demonstrated and utilized to realize efficient, small footprint thermo-optic phase shifter. Compact bends were structured into a folded waveguide geometry to form a rectangular spiral within an area of 65×65µm², having a total active waveguide length of 1.2 mm. The device featured a phase-shifting efficiency of 8mW/π and a 3 dB switching bandwidth of 15 KHz. We propose SRN as a promising thermo-optic platform that combines the properties of silicon and stoichiometric silicon nitride.