Perfect diffraction metagratings supporting bound states in the continuum and exceptional points

TL;DR

This paper demonstrates how tailored metagratings operating near bound states in the continuum and exceptional points can precisely control diffraction and wavefronts, enabling high efficiency and selectivity for optical applications.

Contribution

It introduces a novel design of metagratings that leverage BICs and EPs to achieve unprecedented control over diffraction, combining spectral selectivity with efficient wavefront shaping.

Findings

Achieved perfect diffraction efficiency near BICs and EPs.

Enabled spectral filtering and wavefront control using metagratings.

Demonstrated potential for sensing and optical filtering applications.

Abstract

Resonance coupling in non-Hermitian systems can lead to exotic features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been widely employed to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineering spatial wavefronts have remained elusive. Here, we show that, by operating a suitably tailored metagrating around a BIC and EPs, it is possible to achieve an extreme degree of control over coupling to different diffraction orders in metasurfaces. We stack subwavelength metallic slit arrays on a metal-insulator-metal waveguide, enabling a careful control of the coupling between localized and guided modes. By periodically tuning the coupling strength from weak to strong, we largely tailor the overall spectrum and enable the emergence of singular features, like BICs and EPs. Perfect unitary diffraction efficiency with large spectrum selectivity is achieved around these singular features, with promising applications for arbitrary wavefront shaping combined with filtering and sensing.