Photorefractive spatial solitons

Since they have been predicted and observed six years ago, photorefractive spatial solitons have attracted substantial research interest. Photorefractive solitons bring about several new fundamental aspects related to solitons in general. Perhaps the single most important aspect is being the first system in which (2+1)D solitons were demonstrated. This has enabled the study of interactions between 2D solitons in a full 3D medium, which has revealed a fundamentally new property of interacting solitons: conservation of angular momentum when the solitons are bound to each other in a spiraling configuration. Another key property of the photorefractive nonlinearity that has had a major impact on soliton research, is its non-instantaneous nature. This has allowed us to generate a new type of "self-trapped" light beams: Incoherent Solitons, which are made of partially spatially incoherent light or of temporally and spatially incoherent white light. In this review, we start from the formation mechanism of photorefractive spatial solitons, and especially focus on the bright screening solitons. We then describe the waveguides induced by these solitons, and use this understanding to explain and demonstrate soliton interactions (collisions), which are probably the most fascinating features of all solitons in nature, because they shows how a soliton (a self-trapped wavepacket) is related to a real particle. Then, we describe Incoherent Solitons and end by discussing several ideas on how to utilize the photorefractive solitons for useful applications.