A mid-infrared Brillouin laser using ultra-high-Q on-chip resonators

TL;DR

This paper reports the development of ultra-high-Q on-chip microresonators in the mid-infrared, enabling the first demonstration of Brillouin lasing with low threshold and narrow linewidth, advancing integrated mid-infrared photonics.

Contribution

The authors created ultra-high-Q mid-infrared resonators with innovative fabrication, achieving over 30 times higher Q-factor and demonstrating on-chip Brillouin lasing for the first time.

Findings

Q-factor of 38 million achieved, surpassing previous records

First on-chip mid-infrared Brillouin laser demonstrated

Lasing threshold of 91.9 μW with narrow linewidth

Abstract

Ultra-high-Q optical resonators have facilitated recent advancements in on-chip photonics by effectively harnessing nonlinear phenomena providing useful functionalities. While these breakthroughs, primarily focused on the near-infrared region, have extended interest to longer wavelengths holding importance for monitoring and manipulating molecules, the absence of ultra-high-Q resonators in this region remains a significant challenge. Here, we have developed on-chip microresonators with a remarkable Q-factor of 38 million, surpassing previous mid-infrared records by over 30 times. Employing innovative fabrication techniques, including the spontaneous formation of light-guiding geometries during material deposition, resonators with internal multilayer structures have been seamlessly created and passivated with chalcogenide glasses within a single chamber. Major loss factors, especially airborne-chemical absorption, were thoroughly investigated and mitigated by extensive optimization of resonator geometries and fabrication procedures. This allowed us to access the fundamental loss performance offered by doubly purified chalcogenide glass sources, as demonstrated in their fiber form. Exploiting this ultra-high-Q resonator, we successfully demonstrated Brillouin lasing on a chip for the first time in the mid-infrared, with a threshold power of 91.9 {\mu}W and a theoretical Schawlow-Townes linewidth of 83.45 Hz, far surpassing carrier phase noise. Our results showcase the effective integration of cavity-enhanced optical nonlinearities into on-chip mid-infrared photonics.