Robust generation of intrinsic C points with magneto-optical bound states in the continuum.

C points, 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 a low factor and high sensitivity to structural geometry, rendering them fragile and susceptible to perturbations and disorders. We report magneto-optical (MO) bound states in the continuum (BICs) with a symmetry-preserved planar photonic crystal.