Topological photonic crystal fiber with multiple spin corner states.

Abstract

The photonic quantum Hall effect enables unidirectional wave propagation in artificial photonic structures. Corner states, induced by helical edge states at material interfaces, localize light in small volumes and exhibit strong compatibility with optical fiber guiding modes. However, existing corner states lack propagating characteristics due to their zero out-of-plane momentum (k_z) along the fiber axis. Here, we propose a strategy by transforming the scattering columns of crystal cells to create a hybrid structure combining topological and trivial regions. Through controlled splicing, we induce corner states with frequencies residing in the bulk bandgap at k_z > 0. Unlike the k_z = 0 case, multiple corner states emerge within the bandgap, attributed to the hybridization of TE and TM modes. Furthermore, analogous corner states are observed in higher-order topological bandgaps accompanied by edge states. Finally, we demonstrate that guided modes exhibit channel-selective properties for both left- and right-spinning light sources and characterize the fiber's optical properties. Our work bridges the photonic quantum Hall effect with optical fiber technology, paving the way for advanced topological fiber applications.