Robust valley polarized states beyond topology

Abstract Valley-contrast physics has gained considerable attention, particularly for realizing photonic topological insulators (PTIs) that support reflection-free valley-polarized edge modes (VPEMs) in the absence of inter-valley scattering. It is an open question whether similar robust states can exist in the absence of topological order. We propose a new approach to VPEMs based on a line defect in a topologically-trivial, C6υ-symmetric photonic crystal (PhC). The VPEMs result from opposing orbital angular momenta (OAM) due to a local valley Hall effect (LVHE), where the valley polarization is locally defined as opposed to being fixed throughout the bulk of the PhC. We fabricate our device on a silicon-on-insulator (SOI) slab and characterize it at near-infrared frequencies showing robust transmission through sharp bends. Our results present a new perspective to the existence of gapless chiral edge (kink) states and outlines a new waveguiding mechanism applicable to the electromagnetic spectrum as well as other wave systems including plasmonics, mechanics and acoustics.