Design of Ultrathin Faraday Rotators Based on All-Dielectric Magneto-Optical Metasurfaces at the Telecommunication Band

Magneto-optical (MO) interactions offer a direct route to nonreciprocal optical devices but are intrinsically weak in the optical domain, posing a major challenge in the downsizing of MO functional devices. In this study, we present a design strategy for ultrathin MO Faraday rotators based on all-dielectric metasurfaces supporting high-quality factor quasi-bound states in the continuum (QBIC) modes. Light trapping in QBIC modes induced by band folding significantly enhances MO interactions in a controllable manner, enabling a technologically relevant 45° Faraday rotation with an MO metasurface that is only a few hundred nanometers thick. The design also incorporates electromagnetically induced transparency via spectrally overlapping resonant modes to achieve high light transmittance reaching 80%. This approach not only enables a compact yet practical MO Faraday rotator but also holds promises for advancing free-space magnetic sensors and MO modulators.