Femtosecond laser induced structural modifications in lithium niobate for integrated optical applications

Ultrashort laser pulses have found widespread applications for precise ablation within the past years. However, these laser sources can also be used for volume structuring of transparent materials. This allows to obtain e.g. a localized refractive index modification within the bulk material as required for photonic components. In this paper we will summarize the different structural modifications which can be induced in lithium niobate (LiNbO3) using ultrashort pulses. LiNbO3 is one of the most important and versatile materials for various photonic applications due to its outstanding electrooptic, nonlinear and photorefractive properties. The origin of the induced modifications as well as the physical mechanisms responsible for the resulting refractive index changes will be discussed. Another focus will be on the use of these structures for optical waveguides. As an application example efficient frequency conversion within a waveguide in periodically poled LiNbO3 (PPLN) will be highlighted