Valley Hall edge solitons in honeycomb lattice with an armchair-type domain wall

Thanks to the topological protection, photonic topological edge states can move along the edges of photonic crystals without radiating into the bulk or reflecting when encountering disorders or defects. The valley Hall effect helps obtain topological edge states without breaking the time-reversal symmetry but breaking the inversion symmetry of the system, which means that the valley Hall edge state is independent of the magnetic field. Thus, with two inversion symmetry-broken photonic lattices, a domain wall that supports valley Hall edge states can be established. Generally, the zigzag-type domain wall is likely to support topological valley Hall edge states. However, in this work we investigate the valley Hall edge state on the armchair-type domain wall in a honeycomb lattice and demonstrate that armchair-type valley Hall edge states can also circumvent sharp corners with tiny reflection. The armchair-type domain wall, with the refractive index change being staggered, supports not only the bright but also the dark valley Hall edge solitons, and even the vector valley Hall edge solitons. Our results deepen the understanding of topological valley Hall edge states on different types of domain walls and may find applications in developing techniques of manipulating light fields for fabricating on-chip optical functional devices.