Realizing lossless metasurfaces with true chirality necessitates three-dimensional structures, posing fabrication challenges. While 3D metallic nanostructures have been explored, they suffer from high losses. Photonic bound states in the continuum (BICs), particularly in dielectrics, offer loss tailoring, but applications have been limited to planar structures. This research introduces a novel nanofabrication approach enabling height control of individual resonators in all-dielectric metasurfaces, allowing efficient control of resonance features. Out-of-plane symmetry breaking in quasi-BIC metasurfaces is achieved, demonstrating a maximally chiral all-dielectric quasi-BIC metasurface selectively responding to specific circular polarization based on structural handedness. This opens new avenues for all-dielectric BICs, chiral nanophotonics, and applications like optical angular momentum generation and holographic metasurfaces.

Lucca Kühner, Fedja J. Wendisch, Alexander A. Antonov, Johannes Bürger, Ludwig Hüttenhofer, Leonardo de S. Menezes, Stefan A. Maier, Maxim V. Gorkunov, Yuri Kivshar, Andreas Tittl