Magnetically Reconfigurable Mode Strong Coupling Toward Tunable Nanophotonic Sensing Devices.

Dynamic sensing is an important goal in nanophotonics, yet many tunable sensing platforms still rely on structural reconfiguration or material-property switching, which can limit operational stability, integration simplicity, and real-time controllability. Here, we present a magneto-optical metasurface that enables tunable strong coupling for reconfigurable refractive-index sensing through noncontact magnetic-field control without altering the device geometry. The system supports strong coupling between a structural quasi-bound state in the continuum (q-BIC) induced by symmetry breaking and a magneto-structurally induced q-BIC, termed the MS-BIC, giving rise to upper and lower hybrid branches whose spectral positions and Rabi splitting can be actively controlled by an external static magnetic field. For effective refractive indices of the analyte-loaded porous environment ranging from n = 1.01 to 1.15, the upper and lower branches exhibit sensitivities of about 479 and 461 n m / R I U , respectively, whereas the lower branch reaches a figure of merit as high as 915 R I U - 1 . Moreover, magnetic-field tuning introduces multiple addressable resonance features under a fixed analyte condition, providing redundant observables for cross-validated and noise-robust sensing. These results establish magnetically reconfigurable strong-coupling metasurfaces as a promising platform for high-performance refractive-index sensing in nanophotonic systems.