Dynamically Tunable Ultranarrow-Band Circular Dichroism of Chiral Nanorods Based on Continuous Domain-Bound States

Narrow-band circular dichroism of the chiral metasurface has been widely used in chiral molecules and circular polarization detection. However, it is still a challenge to further improve the quality factor of their CD and realize the dynamic regulation of their CD. In this paper, based on bound states in the continuum (BICs) and lithium niobate materials with electro-optical (EO) properties and nonlinear optical properties, we design an all-dielectric swastika-shaped chiral nanorod metasurface (SCNM). The simulation results show that when the structural parameter perturbation is introduced, the SCNMs generate three strong ultranarrow-band (UNB) CD signals in the infrared band, with the narrowest half-peak width (fwhm) reaching 0.22 nm and the Q-factors exceeding 104. The electric fields of the SCNMs indicate that the three UNB CD signals originated from Fano resonance in the chiral nanorods with BIC characteristics. The influence laws of different structural parameters on the CD signals of the SCNMs were further analyzed, and the dynamic regulation of the UNB CDs was achieved by controlling the applied electric field. In addition, the sensing characteristics and second-harmonic generation and regulation properties of SCNMs were evaluated. These findings not only contribute to the design of ultranarrow-band chiral nanodevices but also provide new opportunities for the generation and regulation of ultranarrow-band second-harmonic CD.