Topological photonic crystals provide an important platform for robust light transport and light-field manipulation. To meet the demands for developing multifunctional and densely integrated photonic circuits, it is necessary to flexibly control light flow with multi-degrees of freedom while maintaining strong topological protection. In this work, we investigate multifunctional topological photonic crystals based on hybrid topological domain walls, which support valley-polarized chiral edge states (VCES). Based on hybrid domain walls, we design two types of compact topological photonic devices. By exploiting direction-selective coupling between valley edge states (VES) and VCES, we construct nonreciprocal coupled waveguides with a nonreciprocal transmission ratio of 10 dB and output-port isolation ratio of more than 30 dB. Moreover, through different configurations of the direction of external magnetic field, we construct a multi-channel selective routing device that enables the configurable transport of valley-polarized electromagnetic waves among multiple channels. Hybrid topological waveguides provide a foundation for designing novel photonic devices, offering the potential for realizing multifunctional integrated topological photonic networks in both classical and quantum regimes.
Hou et al. (Mon,) studied this question.