Giant Faraday rotation in high- Q all-dielectric magneto-optical metasurfaces embedded in photonic crystal cavities

The pursuit of high-efficiency and ultrathin magneto-optical devices remains a critical challenge in modern integrated photonics, particularly for developing compact nonreciprocal devices essential for optical isolation and quantum information processing. While all-dielectric magneto-optical metasurfaces, which show strong light–matter interaction and lower optical loss, have been demonstrated to enhance magneto-optical effects, the absolute Faraday rotation value achieved thus far remains insufficient for practical applications. Here, we report a hybrid structure that synergistically combines dielectric metasurfaces with photonic crystal to overcome these limitations. By introducing Mie resonators and magneto-optical films as defect layers into a one-dimensional photonic crystal, 60% transmittance and giant Faraday rotation ( θ F =41°) at 1468.93 nm with an ultrahigh quality factor ( Q >10 5 ) can be achieved simultaneously. The extraordinarily large Faraday rotation originates from the coupling between a waveguide mode in the photonic crystal and the electric quadrupolar mode of Mie resonators. Our work establishes, to our knowledge, a new design paradigm for magneto-optical and active photonic devices, opening avenues for free-space optical isolators, magnetically tunable metasurfaces, and quantum photonic interface applications.