Observation of robust intrinsic C points generation with magneto-optical bound states in the continuum

TL;DR

This paper demonstrates the creation of robust, intrinsic C points with high-Q factors in a planar photonic crystal using magneto-optical bound states in the continuum, enabling controllable chiral light manipulation.

Contribution

It introduces a novel magneto-optical BIC approach that maintains symmetry and robustness, overcoming limitations of previous methods.

Findings

Achieved intrinsic C points with high Q factors in a planar photonic crystal.

Demonstrated magnetic field-controlled switchable C point handedness.

Revealed Zeeman splitting induces MO BICs and quasi-BICs with circular eigenstates.

Abstract

C points, characterized by circular polarization in momentum space, play crucial roles in chiral wave manipulations. However, conventional approaches of achieving intrinsic C points using photonic crystals with broken symmetries suffer from low Q factor and are highly sensitive to structural geometry, rendering them fragile and susceptible to perturbations and disorders. In this letter, we report the realization of magneto-optical (MO) bound states in the continuum (BICs) using a symmetry-preserved planar photonic crystal, achieving intrinsic at-{\Gamma} C points that are robust against variation in structural geometry and external magnetic field. MO coupling between two dipole modes induces Zeeman splitting of the eigenfrequencies, leading to MO BICs and quasi-BICs with circular eigenstates for high-Q chiral responses. Furthermore, switchable C point handedness and circular dichroism are enabled by reversing the magnetic field. These findings unveil a new type of BICs with circular eigenstates and on-demand control of C points, paving the way for advanced chiral wave manipulation with enhanced light-matter interaction.