Shape deformation of nanoresonator: a quasinormal-mode perturbation theory

TL;DR

This paper introduces a new quasinormal-mode perturbation theory that accurately predicts how nanoresonator resonances evolve with shape deformations, enabling advanced design and understanding of optical properties.

Contribution

A novel extrapolation-based QNM perturbation theory that accurately models shape deformations in nanoresonators, surpassing previous material-focused theories.

Findings

Accurately predicts eigenfrequencies and modes for deformed nanoresonators.

Enables design of super-cavity modes and exceptional points.

Effective even for large deformations.

Abstract

When material parameters are fixed, optical responses of nanoresonators are dictated by their shapes and dimensions. Therefore, both designing nanoresonators and understanding their underlying physics would benefit from a theory that predicts the evolutions of resonance modes of open systems---the so-called quasinormal modes (QNMs)---as the nanoresonator shape changes. QNM perturbation theories (PTs) are one ideal choice. However, existing theories developed for material changes are unable to provide accurate perturbation corrections for shape deformations. By introducing a novel extrapolation technique, we develop a rigorous QNM PT that faithfully represents the electromagnetic fields in perturbed domain. Numerical tests performed on the eigenfrequencies, eigenmodes and optical responses of deformed nanoresonators evidence the predictive force of the present PT, even for large deformations. This opens new avenues for inverse design, as we exemplify by designing super-cavity modes and exceptional points with remarkable ease and physical insight.