ИСТИНА

This work focuses on dielectric metasurfaces supporting high-Q resonances associated with bound states in the continuum (BIC) — modes that belong to the radiation spectrum but do not radiate [1]. In realistic systems, symmetry breaking transforms ideal BIC into quasi-BIC with finite but extremely high quality factors, making them accessible to external excitation [2]. BIC in all-dielectric metasurfaces enable ultra-high-Q resonances, making them a powerful platform for enhancing light–matter interactions. Such metasurfaces are particularly advantageous due to their minimal absorption losses compared to plasmonic structures. While the configuration based on symmetric quadrumers in silicon demonstrates the excitation of high-Q quasi-BIC via translational lattice perturbation [3], magneto-optical (MO) effects were not considered in that context, despite the relative simplicity of fabrication. The originality of this work lies in applying this lattice-scaling approach to a magnetic dielectric material, Bi-substituted yttrium iron garnet (Bi:YIG), for enhancing MO effects such as Faraday rotation. In previous studies, quasi-BIC were implemented in magneto-optical metasurfaces based on asymmetric nanodisks with a displaced air hole — a geometry that is more challenging to fabricate [4]. It was shown that such structures help to enhance the Faraday rotation up to 0.7° due to the excitation of high-Q quasi-BIC resonances. In studying metasurface based on a quadrumer voids in Bi:YIG layer with lattice-period-induced symmetry breaking, the Faraday rotation reaches Θ = –2.66° for a 210 nm thick of the magnetic material. The structure, deposited on a gold (Au) substrate (fig. 1), is numerically analyzed using the finite-difference time-domain (FDTD) method. The simulations reveal a resonance at a wavelength of 844 nm for a lattice period of 767 nm, confirming the presence of high-Q quasi-BIC modes responsible for the observed MO enhancement.