Self-written waveguides in photosensitive materials

We present an overview of the physics of self-written waveguides created in photosensitive optical materials, including the experimental observations and the corresponding theoretical models for describing the growth of both bright and dark self-written beams. We discuss in more details the properties of self-written waveguides created in photosensitive polymers, which have been discovered in the recent experimental and theoretical studies. The self-writing process is essentially a nonlinear phenomenon, since the temporal dynamics depends on the optical exposure. Under appropriate conditions, permanent large changes in the refractive index are induced along the propagation direction of an optical beam, so that optical channels, or "filaments", appear as waveguides becoming "frozen" in a photosensitive material. We describe the growth of individual filaments as well as the interaction of several filaments, also making a comparison between the physics of self-written waveguides and the concept of spatial optical solitons in self-focusing nonlinear media.