Ultrahigh-Q on-chip silicon-germanium microresonators for quantum transduction

As an entirely monocrystalline photonics platform, SiGe/Si is a promising has exceptionally low losses in both microwave [1] optical [2] and domains, with internal optical quality factors reaching 170M at room temperature and 150M at 4K. Using pulse-probe technieqes, we find that SiGe/Si waveguides display strong nonlinear effects at cryogenic temperatures. Strong free-carrier dispersion and bistability effects arise due to long free-carrier lifetimes. Moreover, the long lifetimes and free-carrier dispersion can both be modulated through the application of a DC electric field to the chip, which sweeps out charge carriers. Together with silicon’s intrinsically high c (3) tensor, this active control over nonlinearities could lead SiGe to applications like electro-optic modulation [3], optical logic, Kerr comb generation, and quantum transduction [4].



[1] Schilling et al, Optica 9, 284 (2022)

[2] Sandberg et al, Appl. Phys. Lett. 118, 124001 (2021)

[3] Timurdogan et al., Nature Photonics 11, 200 (2017).

[4] Orcutt et al, Quant. Sci. Tech. 5, 034006 (2020)