Ultra-Narrowband Circular Dichroism in Chiral Nanopore Arrays Based on Bound States in the Continuum: Implications for Ultrasensitive Detection of Chiral Molecules

Narrow-band (UN) circular dichroism (CD) is important in the fields of chiral molecular sensing, negatively refractive materials, and polarization-resolved imaging. However, designing chiral structures with strong, ultra UN, and dynamically tunable CD spectra remains challenging. In this paper, bound states in the continuum (BICs) and magneto-optical (MO) materials are introduced into chiral nanopores, and hexagonal chiral nanopore arrays (HCNAs). The simulation results show that the HCNAs generate two ultra UN CD signals in the infrared band when the structural symmetry is broken by introducing perturbation. The CD intensities of HCNAs can be considerably enhanced and dynamically adjusted when an external magnetic field is applied. The CD enhancing mechanism of HCNAs is explained by quantum optical models, the electric field, and current distributions of HCNAs. By altering the geometrical characteristics of HCNAs, the impacts of various structural parameters on the CD signals of HCNAs were discussed. In addition, the sensing properties of HCNAs for ambient refractive index and chiral molecules were evaluated, and the figure of merit (FOM) of HCNAs can reach 23,398. These results aid in developing ultra UN chiral sensor systems and provide opportunities for enhancing CD signals. This CD signal with high amplitude and ultranarrow bandwidth provides good application prospects for the ultrasensitive detection of chiral molecules.