Finite element simulation of a perturbed axial-symmetric whispering-gallery mode and its use for intensity enhancement with a nanoparticle coupled to a microtoroid

TL;DR

This paper introduces an optical mode solver for a hybrid whispering gallery resonator and nanoparticle system, analyzing intensity enhancement effects and optimal nanoparticle sizes for bio-detection and field amplification.

Contribution

The paper develops a novel mode solver for asymmetric resonator-nanoparticle systems and studies their enhancement properties, including optimal nanoparticle sizes and resonance effects.

Findings

Optimal nanoparticle size for maximum enhancement

Far-from-resonance operation yields comparable enhancement to near-resonance

Plasmonic absorption degrades cavity quality near resonance

Abstract

We present an optical mode solver for a whispering gallery resonator coupled to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of the resonator. Such a hybrid resonator-nanoparticle is similar to what was recently used for bio-detection and for field enhancement. We demonstrate our solver by parametrically studying a toroid-nanoplasmonic device and get the optimal nano-plasmonic size for maximal enhancement. We investigate cases near a plasmonic resonance as well as far from a plasmonic resonance. Unlike common plasmons that typically benefit from working near their resonance, here working far from plasmonic resonance provides comparable performance. This is because the plasmonic resonance enhancement is accompanied by cavity quality degradation through plasmonic absorption.