Bound state in the continuum and polarization-insensitive electric mirror in a low-contrast metasurface

Abstract

High-contrast refractive indices are pivotal in dielectric metasurfaces for inducing various exotic phenomena, such as the bound state in the continuum (BIC) and electric mirror (EM). However, the limitations of high-index materials are adverse to practical applications, thus, low-contrast metasurfaces offering comparable performance are highly desired. Here, we present a low-contrast dielectric metasurface composed of radial anisotropic cylinders, which are SiO2 cylinders doped with a small amount of WS2. The cylinder exhibits unidirectional forward superscattering resulting from the overlap of the electric and magnetic dipole resonances. When a near-infrared plane wave incident normally, the metasurface consisting of the superscattering constituents manifests a polarization-insensitive EM. In contrast, when subjected to an in-plane incoming wave, the metasurface generates a symmetry-protected BIC characterized by an ultrahigh Q factor and nearly negligible out-of-plane energy radiation. Notably, the EM response of the metasurface exhibits robustness to deviation in the number and thickness of WS2 layers. Our work highlights the doping approach as an efficient strategy for designing low-contrast functional metasurfaces, thereby shedding new light on the potential applications in photonic integrated circuits and on-chip optical communication.