Extreme Diffraction Control in Metagratings Leveraging Bound States in the Continuum and Exceptional Points

Abstract

Coupled resonances in non‐Hermitian systems can lead to exotic optical features, such as bound states in the continuum (BICs) and exceptional points (EPs), which have been recently emerged as powerful tools to control the propagation and scattering of light. Yet, similar tools to control diffraction and engineer spatial wavefronts have remained elusive. Here, it is shown that, by operating a metagrating around BICs and EPs, it is possible to achieve an extreme degree of control over coupling to different diffraction orders. Subwavelength metallic slit arrays stacked on a metal‐insulator‐metal waveguide, enabling a careful control of the coupling between localized and guided modes are explored. By tuning the coupling strength from weak to strong, the overall spectral response can be tailored and the emergence of singular features, like BICs and EPs can be enabled. Perfect unitary diffraction efficiency with large spectrum selectivity is achieved around these singular features, with promising applications for selective wavefront shaping, filtering, and sensing.

Coexistence of Surface Lattice Resonances and Bound states In the Continuum in a Plasmonic Lattice

“…Our results show that by using GR-like modes, the lossy flaw in plasmonic systems can be mitigated, thus providing ultra-high-quality factors even with metallic components. A similar result was recently reported for 1D plasmonic gratings [40].…”

Emerging Planar Nanostructures Involving Both Local and Nonlocal Modes

“…Strong or weak couplings between LSPRs and guided modes can be realized by tailoring the system parameters such as the height or period of the metallic meta-atoms. Underpinned by these rich coupling mechanisms, the complex frequency and the spatial properties of the eigenmodes can be engineered at will, which inspires many novel effects, such as exceptional points (EPs), BICs, − and unidirectional lossless surface plasma propagations …”

Design Strategies and Applications of Dimensional Optical Field Manipulation Based on Metasurfaces

“…[55] Deng et al investigated the coupling between the localized modes and guided modes, and an extreme degree of control over different diffraction orders was achieved with a giant dispersion. [56] Recently, Yang et al realized significant improvement in third harmonic generation based on magnetic resonances induced BIC mode, [57] which efficiently suppresses the far-field fundamental radiation due to its high-Q factor nature. [58,59] Compared with the conventional designs with local resonances, the guided mode can also be employed to improve the Q factor of metasurfaces within an ultra-thin surface.…”