Reconfigurable Giant Nonreciprocity at Near-Normal Incidence via Phase-Change Magneto-Optical Metagratings

Abstract

Breaking Lorentz reciprocity in thermal radiation typically requires extreme grazing angles, suffering from severe geometric projection losses and state volatility. Here, we propose a dynamic, non-volatile, nonreciprocal absorber integrating a phase-change (Formula presented.) (Formula presented.) (Formula presented.) (GST) grating atop a magneto-optical InAs waveguide. Leveraging the transverse magneto-optical response in the Voigt configuration and precise momentum matching, the metagrating achieves strong nonreciprocal absorption contrast ((Formula presented.)) at a near-normal incidence angle of (Formula presented.) under a moderate magnetic field. The device enables continuous spectral steering via incident angle and magnetic field, alongside non-volatile digital latching of the nonreciprocal state via GST switching. Through non-Hermitian perturbation theory, we unveil that nonreciprocity quenching during the phase transition originates synergistically from spatial field redistribution and loss-induced damping. Our findings provide a robust, non-volatile platform for advanced thermal emission control.