Differentiating absorptive and scattering losses in silicon nitride optical waveguide resonators

We present a methodology to distinguish between absorptive and scattering losses in SiN optical waveguide resonators by measuring the thermo-optic redshift in resonant wavelength and deducing absorption losses using thermal properties determined through the differential 3ω method. This information offers researchers valuable insights for improving device performance and optimizing fabrication processes. We demonstrate results on the effect of a 650oC thermal anneal on R=120um whispering-gallery mode microring resonators fabricated using N-rich PECVD SiN with n=1.92 at 800nm, which reduced total losses from 1.4dB/cm to 0.64dB/cm at 780nm and yielded an intrinsic-Q of 1.1 million, due primarily to decreased absorption losses.