Optical coupling of fundamental whispering gallery modes in bi-spheres

TL;DR

This paper investigates the optical coupling of fundamental whispering gallery modes in identical microspheres, revealing complex multi-resonance behaviors that challenge traditional coupled-mode theory predictions.

Contribution

It provides an exact multi-sphere Mie theory analysis showing that coupled fundamental modes produce complex responses rather than simple split modes.

Findings

Coupled modes lead to multi-resonance optical responses.

Field distributions deviate from coupled-mode theory predictions.

Traditional bonding and anti-bonding modes are not observed as expected.

Abstract

What will happen if two identical microspheres, with fundamental whispering gallery modes excited in each of them, become optically coupled? Conventional wisdom based on coupled-mode arguments says that two new modes, bonding and anti-bonding, with two split frequencies would be formed. In this paper we demonstrate, using exact multi-sphere Mie theory, that in reality an attempt to couple two fundamental modes of microspheres would result in a complex multi-resonance optical response with the field distribution significantly deviating from predictions of coupled-mode type theories.