Two-Stage Taper Enhanced Ultra-High $Q$ As $_{2}$S $_{3}$ Ring Resonator on LiNbO$_{3}$

A hybrid optics platform consisting of LiNbO
₃
waveguides vertically coupled to high-index-contrast As
₂
S
₃
waveguides can provide tight bend radii for ring resonators and strong tuning capability via electrical-optic effects in LiNbO
₃
substrate. A vertically integrated As
₂
S
₃
ring resonator having an ultranarrow free spectral range (FSR) of 0.0579 nm and side-coupled to a low-index Ti-diffused:LiNbO
₃
straight waveguide was designed and fabricated. Using improved design and fabrication processes, a low 1.2-dB/cm propagation loss in the ring with over 30 dB of extinction ratio was demonstrated on a fabricated 1.7-cm-long path ring resonator with a 400- μm radius, which corresponds to a calculated intrinsic quality factor-Q as high as 3.5 × 10
⁵
. To our knowledge, this is the highest Q factor reported for chalcogenide ring resonator planar waveguide devices.