Topological Diffraction from Grating with Space Variant Chirality

Light-matter interactions in a chiral structure can induce strong polarization selectivity. Specifically, an optical activity in a form of polarization rotation and a circular dichroism may be controlled by the mirror symmetry breaking of the unit-cell geometry. We design and experimentally investigate plasmonic metasurfaces with a spatially varying chiral geometry and demonstrate how this architecture may lead to a geometric Berry phase. Our designed structure produces a polarization-dependent diffraction of nearly linear states. We experimentally examine the diffraction orders and show that they are topological in nature. Moreover, the influence of various geometrical factors is also investigated.