Linear and Nonlinear Light Propagation in Lithium Niobate Waveguide Arrays

Abstract

We investigate both linear and nonlinear behaviour of light in one-dimensional waveguide arrays, which are fabricated by titanium in-diffusion in lithium niobate crystals. Copper ions are in-diffused to increase the photorefractive effect of the waveguide. When the input power of a narrow light beam excites only one channel (width about 4 μm), discrete diffraction (both normal and anomalous) is observed because of evanescent coupling of the adjacent waveguides. When the input light power is increased, the nonlinear index changes induced by the photovoltaic effect suppress linear coupling, resulting in the formation of discrete soliton or gap solitons. We observe bright staggered gap solitons that are formed due to the balance between anomalous diffraction and the self-defocusing nonlinearity of our sample. For a theoretical description the bandgap structures of the waveguide array are calculated using Floquet-Bloch analysis.