High-Q Multiple Fano Resonances with Near-Unity Modulation Depth Governed by Nonradiative Modes in All-Dielectric Terahertz Metasurfaces.

Reducing radiative losses for a high quality factor resonance based on the concept of nonradiative states including anapole mode and bound states in the continuum mode has been attracting extensive attention. However, a high quality factor resonance is obtained at the expense of its modulation depth. Here, an asymmetric metasurfaces structure consisted of silicon double D-shaped resonator arrays that can support both an anapole mode and two bound states in the continuum modes in terahertz band is proposed, which has not only ultrahigh quality factor but also near-unity modulation depth. A resonance derived from anapole mode with stronger electromagnetic field enhancement and higher quality factor can be achieved by increasing the gap of resonator. Meanwhile, two Fano resonances governed by bound states in the continuum modes can be identified, and their quality factors can be easily tailored by controlling the asymmetry of resonator. Such an all-dielectric metasurfaces structure may give access to the development of the terahertz sensors, filters, and modulators.