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

TL;DR

This paper reports the development of fully crystalline silicon-germanium microresonators with ultrahigh quality factors exceeding 10^8, promising advancements in integrated photonics applications such as frequency combs and quantum transduction.

Contribution

The work introduces epitaxially grown SiGe microresonators with record-high Q factors, significantly improving integrated silicon photonics performance.

Findings

Achieved Q > 10^8 for both polarization modes.

Maximum Q of approximately 1.71×10^8 for TM mode.

Low optical loss of about 0.39 dB/m.

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 $1.71\pm0.06 \times 10^8$ for the transverse magnetic (TM) polarization mode, corresponding to a loss of $0.39\pm0.02$ 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.