Nonlocality in Thin Gratings from Evanescent Mode Coupling

Le résumé fourni par la source

Recent advances in subwavelength photonic structures have stimulated growing attention to nonlocality that extends beyond a single unit cell. While flat optical devices such as metasurfaces are commonly described using local electromagnetic models, where each slit is assumed to respond independently to the incident field, subwavelength structures allow evanescent diffraction channels to couple multiple slits and generate spatially nonlocal responses. In this work, we show that a mode–coupling factor derived from coupled mode theory governs the transmission of thin perfect electric conductor gratings. The imaginary part arises from evanescent diffraction channels whose slow convergence over neighboring slits reveals long–range nonlocal coupling. Therefore, the retrieved anisotropic effective permittivity tensor provides a homogenized description of thin gratings with inherent nonlocality. This framework paves the way for understanding and engineering strongly anisotropic nonlocal responses in flat optics and other subwavelength photonic structures.

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