Ultrahigh-$Q$ on-chip silicon-germanium microresonators

Abstract

We demonstrate fully crystalline, single-mode ultrahigh quality factor integrated microresonators comprising epitaxially grown Si${}_{0.86}$Ge${}_{0.14}$ waveguide cores with silicon claddings. These waveguides support resonances with internal $Q>10^8$ for both polarization modes, a nearly order-of-magnitude improvement over that seen in prior integrated Si photonics platforms. The maximum $Q$ is $1.71\pm 0.06\times 10^8$ for the transverse magnetic (TM) polarization mode, corresponding to a loss of $0.39\pm 0.02$ dB/m. Together with silicon's strong Kerr nonlinearity and low losses in the optical, microwave and acoustic regimes, our results could lead to the Si${}_{1-x}$Ge${}_x$/Si architecture unlocking important new avenues for Kerr frequency combs, optomechanics, and quantum transduction.