Quasinormal modes of Floquet media slabs

TL;DR

This paper develops a theoretical framework combining photonic quasinormal modes and time-varying media to enable efficient analysis and design of dynamically controlled optical devices with specific scattering properties.

Contribution

It introduces a QNM-based approach for slabs with time-periodic permittivity, providing a reduced-order model for analyzing resonant features in time-modulated media.

Findings

Efficient computation of scattered fields in time-modulated systems

Insight into modulation coupling with resonant modes

Strategies for selective modal excitation and suppression

Abstract

Exploiting non-Hermitian wave-matter interactions in time-modulated media to enable the dynamic control of electromagnetic waves requires advanced theoretical tools. In this article we bridge concepts from photonic quasinormal modes (QNMs) and time-varying metamaterials providing the foundation for designing dynamic optical devices with prescribed scattering properties. Establishing the QNM framework for slabs with time-periodic permittivity, and solving the associated nonlinear eigenvalue problem, allows us to derive the QNM expansion capturing the resonant features of the system. This reduced-order model enables highly efficient computation of scattered fields while revealing insight into how modulation couples to resonant modes, creating tailored gain-loss engineering. Our approach is validated through numerical experiments on time-modulated systems, and we design strategies to engineer tailored excitations selectively amplifying or suppressing specific modal contributions.