Contents I. Introduction
Since the first demonstration [1], spatial solitons attracted very broad research activities, from both the fundamental and the applied points of view. In fact photorefractive solitons can be good candidates for realizing self-written and self-optimized integrated circuits [2], [3] through soliton waveguiding, if electro-optical materials with very slow dielectric relaxations are used as host media [4]. Among all, lithium niobate seems to be the best material for realizing soliton-based integrated circuits [5]–[7]: in fact its ultraslow dielectric relaxation allows to write soliton channels and used them as waveguides for very long time after formation, even months [5]. Thus, spatial solitons in lithium niobate can be considered almost quasi-permanent structures.
