Arbitrary Polarization Generation in Magneto-optical Metasurfaces Enabled by Bound States in the Continuum

TL;DR

This paper presents a magneto-optical metasurface that enables continuous, active tuning of light polarization states at normal radiation by manipulating bound states in the continuum with an external magnetic field.

Contribution

It introduces a novel magneto-optical metasurface platform that achieves dynamic polarization control without structural changes, expanding capabilities for photonic devices.

Findings

Continuous polarization tuning at normal radiation achieved.

Magnetic field controls polarization singularities migration.

Full Poincaré sphere coverage demonstrated.

Abstract

The generation of arbitrary polarization states of light is essential for optical communication and photonic information processing. Photonic crystal and metasurface platforms supporting bound states in the continuum (BICs) provide a powerful route for polarization engineering through tailoring the radiation from the resonant modes. However, existing approaches typically rely on static structural symmetry breaking or off-normal radiation, which limits continuous polarization tuning of vertical radiation. Here, we demonstrate a magnetooptical metasurface that generates arbitrary polarization states of light at normal radiation. By applying an external magnetic field with variable rientation, a symmetry-protected BIC is transformed into a quasi-BIC whose radiation polarization can be continuously tuned. The magneto-optical perturbation drives the controlled migration of polarization singularities in momentum space, allowing the emitted states to continuously span the entire Poincar\'e sphere without structural modification. This approach establishes a compact platform for actively tunable polarization sources and polarizationencoded photonic devices.