Ultra-High-Q Racetrack Resonators on Thick SOI Platform Through Hydrogen Annealing Smoothing

Abstract

We implemented a hydrogen annealing based post-processing technique as a tool to improve the sidewall roughness of 3 μm thick silicon-on-insulator (SOI) waveguides and demonstrated ultra-high- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factors on racetrack resonators leveraging on the propagation loss reduction achieved through the smoothing process. The designed racetracks are based on a combination of rib waveguides and strip-waveguide-based Euler bends. We measured intrinsic quality factors of 14×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> for a racetrack with a footprint of ∼5.5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 10.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> for a smaller racetrack with footprint of ∼1.48 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The estimated propagation loss for the rib waveguides was ∼2.7 dB/m, representing a ×3 reduction respect to the previously measured losses of 3 μm thick SOI rib waveguides treated with thermal oxidation smoothing. Overall, the post-processing technique allowed to significantly reduce the sidewall roughness without altering the geometry of the waveguides, unlike in sub-micron scale SOI platforms, making it an attractive solution for applications demanding ultra-low losses.