Topological polarization singularities induced by non-Hermitian Dirac points
Jun Wang, Jie Liu, Peng Hu, Qiao Jiang, Dezhuan Han
Abstract
In a Hermitian photonic system, a Dirac point can split into a pair of exceptional points (EPs) or even form a ring of EPs when non-Hermiticity is introduced. Herein, we present a type of non-Hermitian Dirac point situated in the complex plane of eigenfrequency. When differential loss is present, the Dirac point exhibits dual behavior: first, it splits into a pair of EPs with opposite chirality in the band structure; second, it induces a pair of circularly polarized states (C points) with opposite handedness in the far-field radiation. Furthermore, the breaking of the corresponding mirror symmetries allows independent control of these Dirac-point-induced C points, enabling the merging of two C points and the generation of unidirectional guided resonances. Our results demonstrate a clear relationship between branch-point singularities and polarization singularities, providing a new mechanism for generating unidirectional emission. This can be beneficial for band engineering and polarization manipulation.