Dual Topological Textures from Chiral Bound States in the Continuum: Simultaneous Generation of Merons and Skyrmions in Momentum Space

We numerically and theoretically demonstrate the simultaneous generation of polarization dependent high-order merons and skyrmions constructed by degenerate chiral Bound states in the continuum (BICs) in a magneto optical (MO) photonic crystal (PhC) slab with C 6 v symmetry. Under an external magnetic field, the degenerate BICs split into chiral eigen modes, giving rise to momentum-space topological textures characterized by non-zero orbital angular momentum (OAM) and skyrmion numbers. Meanwhile, the cross-polarized components of transmitted light give rise to skyrmionic textures that fully map the Poincaré sphere under circularly polarized illumination that carry quantized OAM charges. A rectified Hamiltonian and a non-reciprocal Temporal coupled-mode theory model (TCMT) are proposed to explain these innovative phenomena convincingly. These textures exhibit remarkable robustness against various perturbations. Our work establishes a versatile platform for generating and manipulating topological textures with potential applications in robust optical information processing and metrology.