Abstract

The self action of a narrow laser beam propagating near the edge of a lithium niobate waveguide array with defocusing nonlinearity and a semi-infinite periodic refractive index modulation in the transverse direction was investigated. The formation of surface gap solitons or nonlinear Tamm states was observed. The self-trapping of light was observed in the nonlinear regime above a certain threshold power when the propagation constant was shifted into the gap of the photonic transmission spectrum. A light localization occurred in the form of nonlinear surface modes exhibiting a staggered phase structure. A half-period vertical shift of the interference fringes corresponding to a phase jump in the horizontal beam direction was observed in each lattice site.