Perfect Diffraction with Bianisotropic Metagratings

TL;DR

This paper demonstrates that bianisotropic metagratings with four resonances can achieve near-perfect diffraction efficiency, enabling highly asymmetric light deflection with simple geometry and robustness to fabrication imperfections.

Contribution

The authors introduce a novel bianisotropic unit cell design supporting four resonances for perfect diffraction, combining theoretical analysis and experimental validation.

Findings

Achieved near-perfect diffraction efficiency with bianisotropic metagratings.

Demonstrated asymmetric light deflection with high efficiency using simple, sub-wavelength structures.

Showed robustness of optical properties against fabrication imperfections.

Abstract

One highly desirable function of a diffraction grating is its ability to deflect incident light into a specific diffraction order with near-perfect efficiency. While such asymmetry can be achieved in a variety of ways, e.g., by using a sawtooth (blazed) geometry, a recently emerged approach is to use a planar metagrating comprised of designer multi-resonant periodic units (metamolecules). Here we demonstrate that a bianisotropic unit cell supporting four resonances interfering in the far field can be used as a building block for achieving the prefect deflection. A coupled mode analysis shows that these modes provide a small number of orthogonal electromagnetic radiation patterns that are needed to suppress transmission/reflection into all but one diffraction order. Bianisotropy caused by a mirror symmetry breaking enables a normally incident wave to excite, through near-field couplings, two otherwise "dark" resonant modes. We design and experimentally realize bianisotropic metamolecules which are sub-wavelength in all three dimensions, and whose optical properties are desensitized to fabrication imperfections by their geometric simplicity. We show that optical beams tightly focused onto the metagratings with just a few unit cells can also be asymmetrically deflected with high efficiency, paving the way for compact broadband optical devices.