Counterintuitive Reversal of Circular Dichroism via Controllable Plasmonic Guided Mode Resonance in Diatomic Metasurfaces

Chiral metasurfaces, featuring customizable chiroptical response, have shown great potential across diverse applications, including optical sensing, chiral emission, and light spin detection. However, most previous studies have focused on chiroptical response stemming from the resonance of nanoresonators or their coupling. Here, the great capability of controlling nonlocal resonance for achieving versatile manipulation of circular dichroism (CD) is demonstrated. A counterintuitive sign reversal of CD is realized by modulating the collective interference of the plasmonic guided mode resonances (GMRs) within diatomic metasurfaces. The designed metasurfaces, composed of two nanoresonators, can effectively couple both orthogonal linear-polarized components of circularly polarized light to the same GMR. Through a simple adjustment of the spacing of nanoresonators to modulate the interference between GMRs, continuous variation and sign reversal of CD are achieved. Importantly, due to the fact that the modulation of GMRs does not impact the chiral resonant modes of the nanoresonators, the significant advantages of the designed metasurfaces in achieving chiral optical encryption are experimentally demonstrated. This work introduces an effective approach for the continuous manipulation of CD without altering the structural geometric chirality. It provides novel insights into exploring chiroptical mechanisms and holds promise for applications in chiral sensing and light spin detection.