Incoherent spatial solitons

One of the most important recent advances in nonlinear science is the discovery of incoherent or partially coherent solitons. Until very recently, all soliton experiments (in all branches of physics) were conducted using coherent wavepackets or beams. In 1996 however, self-trapping of a quasi-monochromatic partially coherent beam was demonstrated for the first time in biased photorefractives. In general, incoherent spatial solitons are multimode self-trapped entities, which are possible in materials with non-instantaneous nonlinearities. Unlike in the case of coherent solitons, the phase across a partially coherent soliton beam is known to vary randomly in space/time. Soon thereafter, the theory describing this new family of solitons was developed. More specifically three different (albeit equivalent) approaches were introduced. These are: the coherent density method, the self-consistent multimode theory, and the approach describing the propagation of the mutual coherence function.