Merging Exceptional Points Enabled Higher‐Order Bound States in the Continuum

ABSTRACT Bound states in the continuum (BICs) are nonradiative modes within the continuum, offering unique opportunities for wave control in open systems. While most BICs carry a unity charge, higher‐order BICs can enrich light–matter interaction through complex singularity structures and nontrivial topology. However, to date, such higher‐order BICs have only been realized in systems with higher rotational symmetry or higher energy bands, limiting practical implementation. Here, we propose a new mechanism to realize higher‐order topological BICs through mode coupling in a photonic crystal slab with only C 4 ​ symmetry. By merging four pairs of exceptional points, we obtain a Dirac BIC with a topological charge of −3, exhibiting highly anisotropic radiation suppression and enhanced Q factors along specific directions over a broad wavevector range. This work provides a controllable route to engineer higher‐order BICs in simple planar devices, offering new freedoms for charge manipulations, higher‐dimensional topologies, and structured light generation.