Observation of nonlinear surface waves in modulated waveguide arrays

The study of surface waves in periodic photonic structures such as photonic crystals or optical lattices is attracting increasing attention. Their basic properties have many similarities to the physics of electrons localized at crystalline surfaces, which were first discussed by Tamm [1] and Shockley [2]. The direct observations of such states have been performed only in photonic systems [3,4], such as periodic waveguide arrays. It was found that strong surface localization is possible when the edge waveguide is modified and the defect strength exceeds a certain threshold, in agreement with original predictions by Tamm [1]. Such a surface defect can also be induced through optical nonlinearity, resulting in the formation of surface lattice solitons [5¿11]. On the other hand, it was recently demonstrated that arrays of periodically curved waveguides can support a novel type of linear surface modes without any surface defects [12,13].