Rigorous electromagnetic quasinormal-mode method made easy for users

TL;DR

This paper introduces an accessible, simplified method for computing electromagnetic quasinormal modes, combining numerical techniques with approximations, and demonstrates its practicality through an open-source package integrated into commercial software.

Contribution

It presents a new, user-friendly approach to calculating QNMs that bridges the gap between complex theory and practical application, with an open-source implementation.

Findings

Enables ultrafast QNM reconstructions using the new method.

Simplifies the computation process for users familiar with real-frequency methods.

Demonstrates practicality through an open-source package integrated into commercial software.

Abstract

Full-wave numerical methods based on quasinormal modes (QNMs) offer valuable physical insights and computational efficiency for analyzing electromagnetic resonators. However, despite their advantages, many researchers in electromagnetism continue to favor real-frequency domain or time-domain approaches, often using finite element or finite-difference time-domain methods. This preference stems from various factors, including the perception that QNM theory is still developing or requires advanced mathematical tools from complex analysis. In this work, we combine numerical techniques with accurate ap-proximations to simplify the computation of QNMs and enable ultrafast reconstructions us-ing QNM expansions. The result is a new approach that is straightforwardly accessible to users familiar with real-frequency methods. We demonstrate the practicality of our ap-proach through an open-source package [Doi: 10.5281/zenodo.18708748] implemented within a widely-used commercial photonics software.