Azimuth-dependent chiroptical response in dielectric achiral metasurfaces

Dielectric chiral metasurfaces have attracted tremendous attention for their potential applications on next-generation planar photonic and biophotonic devices. However, most chiral metasurfaces are generally composed of complex chiral meta-atom structures, and few design schemes are developed to dynamically tune the chiroptical response. Here, we experimentally demonstrated an effective strategy to design achiral metasurfaces based on the extrinsic chirality of all-dielectric nanodisks arranged in a square array. We found there are two characteristic lattice modes corresponding to the coupling of nanodisk meta-atoms, and the azimuth-induced asymmetric distribution of electromagnetic fields leads to an obvious CD signal. Intriguingly, the azimuth-dependent CD signals exhibit fourfold rotational symmetry that is strongly dependent on the lattice symmetry. Meanwhile, the CD response can be modulated by simply changing azimuth of the nanodisks without fabricating two opposite chiral structures. Our work provides a simple design strategy for chiral metasurfaces based on the geometrically simplest 2D planar achiral meta-atoms and highlights the generation mechanism as well as adjustable ability of the chirality, which may promise various practical applications on on-chip azimuth and horizontal sensors.