Revisiting Bianisotropic Photonics with Coupled-Mode Theory

Metasurfaces have been extensively studied using homogenization techniques, which leverage the subwavelength nature of meta-atoms to model their electromagnetic response. While these approaches are effective in the microwave regime, they face challenges at optical frequencies due to weaker mode confinements and larger sizes of the meta-atoms compared to the wavelength. Coupled-mode theory has emerged as a powerful phenomenological model to describe resonant behavior in photonic structures. In this work, we explore the connection between coupled-mode theory and the bianisotropic homogenization models. By analyzing the interplay between the mode coupling strength and bianisotropic effects, we establish a direct relationship between resonant mode interactions and metasurface scattering properties. Our findings provide new insights into the physics of photonic metastructures and offer a unified perspective for modeling their electromagnetic behavior.