Nonlinear optical effects of ultrahigh-Q silicon photonic nanocavities immersed in superfluid helium

TL;DR

This study investigates nonlinear optical effects in ultrahigh-Q silicon nanocavities immersed in superfluid helium at cryogenic temperatures, revealing temperature-dependent bistability and high photon storage capacity.

Contribution

First experimental demonstration of optical nonlinearities in silicon nanocavities at cryogenic temperatures within superfluid helium, highlighting temperature effects on cavity behavior.

Findings

Observation of blue-shifted bistability crossing the helium lambda point

Restoration of symmetric Lorentzian spectra at lower temperatures

Achievement of a stored photon number of about 40,000

Abstract

Photonic nanocavities are a key component in many applications because of their capability of trapping and storing photons and enhancing interactions of light with various functional materials and structures. The maximal number of photons that can be stored in silicon photonic cavities is limited by the free-carrier and thermo-optic effects at room temperature. To reduce such effects, we performed the first experimental study of optical nonlinearities in ultrahigh-Q silicon disk nanocavities at cryogenic temperatures in a superfluid helium environment. At elevated input power, the cavity transmission spectra exhibit distinct blue-shifted bistability behavior when temperature crosses the liquid helium lambda point. At even lower temperatures, the spectra restore to symmetric Lorentzian shapes. Under this condition, we obtain a large stored intracavity photon number of about 40,000, which is limited ultimately by the local helium phase transition. These new discoveries are explained by theoretical calculations and numerical simulations.