Four-wave mixing parametric oscillation and frequency comb generation at visible wavelengths in a silica microbubble resonator

TL;DR

This paper demonstrates dispersion engineering in a silica microbubble resonator to enable visible wavelength four-wave mixing and frequency comb generation with high quality factors, advancing applications in metrology and sensing.

Contribution

It introduces a novel fabrication technique for microbubble resonators with tailored dispersion properties to generate visible wavelength frequency combs via four-wave mixing.

Findings

Dispersion can be engineered by reducing wall thickness to shift zero dispersion wavelength.

Four-wave mixing observed at 765 nm with pump power of 3 mW.

A frequency comb with 14 lines is generated at visible wavelengths.

Abstract

Frequency comb generation in microresonators at visible wavelengths has found applications in a variety of areas such as metrology, sensing, and imaging. To achieve Kerr combs based on four-wave mixing in a microresonator, dispersion must be in the anomalous regime. In this work, we demonstrate dispersion engineering in a microbubble resonator (MBR) fabricated by a two-CO$_2$ laser beam technique. By decreasing the wall thickness of the MBR down to 1.4 $\mu$m, the zero dispersion wavelength shifts to values shorter than 764 nm, making phase matching possible around 765 nm. With the optical \textit{Q}-factor of the MBR modes being greater than $10^7$, four-wave mixing is observed at 765 nm for a pump power of 3 mW. By increasing the pump power, parametric oscillation is achieved, and a frequency comb with 14 comb lines is generated at visible wavelengths.