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Valley-contrast physics has gained considerable attention, particularly forrealizing photonic topological insulators (PTIs) that support reflection-freevalley-polarized edge modes (VPEMs) in the absence of inter-valley scattering.It is an open question whether similar robust states can exist in the absenceof topological valley phase, i.e., nonvanishing Berry curvature at the valleys.We show that a C6\u{psion}-symmetric triangular photonic crystal (PhC)inherently exhibits uniform distribution of spatially varying phase vortices,which support a local (limited) version of valley Hall effect (LVHE), where thevalley polarization is location defined as opposed to being fixed throughoutthe bulk. We then demonstrate that defect regions with sublattice asymmetry inotherwise a symmetric PhC lead to wave localization and splitting of photonsaccording to their valley index, thus enabling VPEMs along a line defectwaveguide. We fabricate our device on a silicon-on-insulator (SOI) slab andcharacterize it at near-infrared frequencies showing robust transmissionthrough sharp bends comparable to valley PTIs. Our results present a newperspective to creating valley edge states and outline a new waveguidingmechanism applicable to electromagnetics as well as plasmonics, mechanics andacoustics.

Valley polarized edge states beyond inversion symmetry breaking