Topological waveguide crossing between pseudo-spin-valley-locked domain-wall states

Pseudo-spin and valley are two significant degrees of freedom in topological photonics, which enable the realization of robust boundary states and consequently tremendous fabrication-tolerant photonic devices. As integration density increases in photonic chips, low-crosstalk waveguide crossings become critical for maintaining overall performance. With conventional waveguide crossings susceptible to defect-induced backscattering, topology can provide a viable solution to this issue. Here, we experimentally demonstrate a topological waveguide crossing based on pseudo-spin-valley-locked domain-wall states. By combining two unidirectional spin-polarized domain-wall channels supporting states with distinct valley degrees of freedom, our system can intrinsically suppress both backscattering and interchannel crosstalk (