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

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 Gamma BICs and off Gamma BICs are obtained. Two BICs at the Gamma 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 Gamma BICs behave only in the form of monotonously shifting. The at Gamma BICs transform from BICs to quasi-BICs obviously with the broken symmetry of the H-shaped nanohole; however, its influence on off Gamma 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 10(6). The results here are helpful in the design of photonic filters and sensors.