Level-crossing and modal structure in microdroplet resonators

TL;DR

This paper reports the fabrication and experimental mapping of whispering-gallery modes in a liquid-core, liquid-clad microdroplet resonator, revealing complex modal structures including mode crossings and standing interference patterns.

Contribution

It introduces a novel liquid microdroplet resonator with detailed experimental characterization of its modal structure and mode crossings.

Findings

More than half of the droplet's modes have degenerate sibling modes.

The resonator exhibits a rich modal structure with high-order transverse modes.

Mode crossings lead to standing interference patterns.

Abstract

We fabricate a liquid-core liquid-clad microcavity that is coupled to a standard tapered fiber, and then experimentally map the whispering-gallery modes of this droplet resonator. The shape of our resonator is similar to a thin prolate spheroid, which makes space for many high-order transverse modes, suggesting that some of them will share the same resonance frequency. Indeed, we experimentally observe that more than half of the droplet's modes have a sibling having the same frequency (to within linewidth) and therefore exhibiting a standing interference-pattern.