Strong polarization mode coupling in microresonators

TL;DR

This paper investigates strong polarization mode coupling in silicon nitride microresonators, revealing how avoided crossings significantly alter dispersion and impact frequency comb generation, with potential for dispersion engineering.

Contribution

It demonstrates the strong coupling between TE and TM modes in Si3N4 resonators and explores how these interactions affect dispersion and frequency combs, proposing both mitigation and utilization strategies.

Findings

Strong polarization mode coupling causes resonance shifts.

Couplings lead to broad anomalous dispersion windows.

Mode crossings can be used for dispersion engineering.

Abstract

We observe strong modal coupling between the TE00 and TM00 modes in Si3N4 ring resonators revealed by avoided crossings of the corresponding resonances. Such couplings result in significant shifts of the resonance frequencies over a wide range around the crossing points. This leads to an effective dispersion that is one order of magnitude larger than the intrinsic dispersion and creates broad windows of anomalous dispersion. We also observe the changes to frequency comb spectra generated in Si3N4 microresonators due polarization mode and higher-order mode crossings and suggest approaches to avoid these effects. Alternatively, such polarization mode-crossings can be used as a novel tool for dispersion engineering in microresonators.