Ultrahigh-Q on-chip silicon–germanium microresonators

Abstract

To date, integrated waveguides with the lowest losses have all relied at least in part on amorphous materials. In this work, we demonstrate fully crystalline, single-mode integrated microresonators comprising epitaxially grown S i 0.86 G e 0.14 waveguide cores with silicon claddings. This platform supports ultrahigh-quality-factor resonances, with Q reaching 1.71 ± 0.06 × 10 8 , corresponding to a loss rate of 0.39 ± 0.02 d B / m . This Q is nearly an order-of-magnitude improvement over that seen in prior integrated Si waveguides. Together with silicon’s strong Kerr nonlinearity, our results could unlock important new avenues for microwave photonics, optomechanics, and quantum transduction.