Engineering and enhancement of non-reciprocal effects in BIC-supporting metasurfaces

We theoretically demonstrate strong enhancement of non-reciprocal magneto-optical (MO) cross-polarization coupling in metasurfaces mediated by quasi-bound states in the continuum (q-BICs). We do so by utilizing n-doped InSb micropillar metasurfaces under an external magnetic field in the polar Kerr configuration. q-BIC-driven MO responses follow the resonant absorption features that are further tuned by structural tilting. Tilts parallel to the incidence, yield an enhanced MO Brewster-like effect, while non-parallel tilts introduce reciprocal geometric coupling that can be isolated to reveal a strongly enhanced purely MO, non-reciprocal response. These results highlight q-BICs as an efficient route to amplify non-reciprocal effects in MO metasurfaces.