Abstract
Exciting multiple high Q-factor Fano resonances in all-dielectric metamaterials has become an effective means of designing high performance optical devices. In this paper, we present an all-dielectric metamaterial in the near infrared region by depositing silicon material on the silica substrate and etching two square air holes in the middle of each meta-molecule. Combining with the bound states in the continuum (BIC) theory, four sharp Fano profiles with the modulation depth nearly 100% are excited, in which the maximum Q-factor can exceed 104. The toroidal dipole (TD) also characterizes our metamaterial. By verifying the square inverse law satisfied by Q-factor and combining the electromagnetic field distribution characteristics, the excitation mode of the Fano resonance is expounded. In addition, by turning the polarization direction of the incident light, the Fano resonance at λ = 1238.5 nm can be turned on or off, which performs perfect characteristics for an optical switch. Utilizing the narrow linewidth and significant near-field constraints of the Fano resonances, an optical refractive index sensor can be obtained with the sensitivity of ~ 287.5 nm/RIU and maximum figure of merit (FOM) of ~ 389 RIU-1. It is believed that the proposed system can further enhance the development of high-performance biosensors, nonlinear optics, and optical switches.
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