Topologically Enhanced Circular Dichroism from Metasurfaces

Circular dichroism (CD) is one of the most distinctive properties of chiral materials. In recent decades, chiral metasurfaces have been regarded as a promising framework to realize chiral optical devices with ultrathin thickness and compact footprints. Various efforts have been devoted to increase the CD response from such metasurfaces. Here we present a method to enhance the CD effect from metasurfaces utilizing a topological concept. Two multilayered photonic crystals with different topological invariants are adopted and put in contact leading to the appearance of a topological edge state and a distinct electromagnetic field concentration at the interface. By embedding L-shaped chiral metasurfaces into the interface, the CD response is observed to be obviously boosted. We find that due to the robustness feature of the topological edge state, the spectral position of the CD peak is fixed at the edge-state wavelength and is immune to structural variation of the metasurface array. Considering that the multilayered films are easy to fabricate, such a topological concept could act as a simple and feasible strategy for enhancing chiral optical response from nanoscales, and could find wide applications in realizing ultracompact polarization-selective optical components.