One Million Q-Factor SiGe-on-Si Ring Resonator in the Mid-Infrared

The mid-infrared (MIR) wavelength range (3 - 15 μm) is attractive for applications in several fields, particularly in sensing due to the strong fundamental absorption lines exhibited by numerous molecules [1]. MIR integrated photonics is gaining interest in the quest for compact, efficient and cost-effective sensors. CMOS-compatible Group-IV platforms based on silicon and germanium can provide the required performances to achieve this quest [2]. One crucial integrated photonic structure on these platforms is a compact resonator with high light confinement, characterised by its quality factor (Q-factor). Integrated SiN-on-SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> [3] and SOI [4] resonators reaching one million Q-factor have been demonstrated. However, these platforms are limited to the lower end of the MIR spectrum (< 3.8 μm) due to absorption by the SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf>. Demonstrations on platforms that can operate at longer MIR wavelengths, such as graded-index SiGe-on-Si [5], SiGe-on-Si [6], Ge-on- Y2o3 [7] have so far struggled to reach Q-factors above 250 000. In this work, we demonstrate a significant improvement in the performance of integrated SiGe-on-Si ring resonators, reaching a record Q-factor of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> at λ = 4.42 μm.