Zero-energy edge states and solitons in strained photonic graphene

Photonic graphene is a form of graphene in optic platforms that is important for fabrication of photonic topological insulators, which may lead to novel techniques to realize various types of light manipulation. Among a plethora of schemes to reform photonic graphene to meet the desired specifications, the significance of strain operations has not received sufficient attention. Here, we theoretically and numerically report zero-energy edge states in strained photonic graphene. After applying strain, photonic graphene can be regarded as a stack of Su-Schrieffer-Heeger chains, which can be considered to be a convincing cause of the appearance of zero-energy edge states. In addition, the topological origin is analyzed based on the tight-binding method, and we find that the Zak phase is pi when there is a zero-energy edge state. In reference to the dispersive nature of zero-energy edge states, the self-action effect of nonlinearity is introduced to balance the dispersive broadening of these states to form both bright and dark zero-energy edge solitons. We believe that the results obtained may provide deeper understanding of the role of strain in two-dimensional lattices and may find potential applications in fabricating future on-chip on-demand photonic devices.