Hyperparametric effects in a whispering-gallery mode rutile dielectric resonator at liquid helium temperatures

TL;DR

This paper reports the first observation of hyperparametric effects, including amplification and oscillations, in a rutile whispering-gallery mode resonator at cryogenic temperatures, leading to a single-mode frequency comb.

Contribution

It introduces the first demonstration of hyperparametric phenomena in a dielectric rutile resonator at 4.2 K, with a novel explanation involving intrinsic material nonlinearity.

Findings

Observation of low power drive level sensitivity

Generation of a single-mode frequency comb at 19.756 GHz

Explanation of effects via a model involving material nonlinearity

Abstract

We report the first observation of low power drive level sensitivity, hyperparametric amplification, and single-mode hyperparametric oscillations in a dielectric rutile whispering-gallery mode resonator at 4.2 K. The latter gives rise to a comb of sidebands at 19.756 GHz. Whereas, most frequency combs in the literature have been observed in optical systems using an ensemble of equally spaced modes in microresonators or fibers, the present work represents generation of a frequency comb using only a single-mode. The experimental observations are explained by an additional 1/2 degree-of-freedom originating from an intrinsic material nonlinearity at optical frequencies, which affects the microwave properties due to the extremely low loss of rutile. Using a model based on lumped circuits, we demonstrate that the resonance between the photonic and material 1/2 degree-of-freedom, is responsible for the hyperparametric energy transfer in the system.