Edge states of bound photon pairs: Topology and interactions

We discuss bulk and edge states of bound photon pairs supported by the one-dimensional array of nonlinear optical cavities for the two scenarios: (i) dimer array consisting of identical cavities with the two types of tunneling constants and with on-site Kerr-type nonlinearity; (ii) simple array of identical cavities with both on-site nonlinearity and nearest neighbor nonlinear interaction. It is demonstrated that both structures can support interaction-induced edge states of bound photon pairs. We analyze the properties of such exotic states thus providing the insights into the emerging field of nonlinear topological photonics.