Modulation of the Multiple Bound States in the Continuum of the All-Dielectric Metasurface

Abstract

Based on the ideas of modulation of multiple BICs, ultrahigh Q-factor resonance has been realized by array of planar metasurfaces with H-shaped nanoholes, perforated on a Si3N4 photonic crystal slab surrounded by a silica medium. Multiple BICs of both at Γ BICs and off Γ BICs are obtained. Two BICs at the Γ point show up in the lower band of the visible light, and they can be tuned by the center position and hole size of each part of the H-shaped, the refractive index of the surrounding medium, and the lattice constant. In detail, they move apart from each other or shift together with a fixed distance, with the structure parameters changing. On the other hand, the off Γ BICs behave only in the form of monotonously shifting. The at Γ BICs transform from BICs to quasi-BICs obviously with the broken symmetry of the H-shaped nanohole; however, its influence on off Γ BICs is insignificant. BICs in both types are ultra-sensitive to the surrounding medium, and the Q-factor of the BICs reaches a value more than 106. The results here are helpful in the design of photonic filters and sensors.