Exploiting virtual three-dimensional asymmetry for planar intrinsic chirality

Intrinsic chirality at optical wavelengths often relies on 3D nanofabrication or loss engineering. Here, we realize strong intrinsic chirality in a simple planar, single-height metasurface by exploiting substrate-induced virtual 3D asymmetry. Hybridized electric- and magnetic-dipole resonances yield optical chirality, and an in-plane perturbation guided by a nonlocal mode that reveals its critical role in intrinsic chirality tunes cross-polarized transmission phases to maximize circular dichroism (CD). Simulations predict CD = 0.97 near 935 nm, and fabricated devices exhibit a pronounced CD resonance, with peaks of 0.57 and 0.62 under frontside and backside illuminations, validating intrinsic chirality and the planar metasurface strategy.