Field propagation with nearly constant Gaussian beam parameters in unbiased self-defocusing photorefractive media

Optical devices, where light controls light, are of interest to the computing and communications industries due to their potential to vastly improve information capacity and processing speed. One such device is an optical logic gate, based on the interactions of low divergence fields in photorefractive media. Presently, bright solitons in self-focusing photorefractive media offer one attractive possibility. A wide variety of other low divergence fields have also been outlined in recent literature, however, no theoretical model of a single bright soliton propagating in unbiased selfdefocusing photorefractive media is currently available. Evidence is presented of self-defocusing photorefractive media as an intensity dependent Gradient-Index (GRIN) lens with a negative power. Using this model, we outline conditions for the change in the complex beam parameter, and consequently the area and wavefront curvature, of the Gaussian beam to be minimised as it propagates through the selfdefocusing media. This is the first instance where self-defocusing photorefractive media has been modelled as an intensity dependent GRIN lens, and where a low divergence field propagating through unbiased self-defocusing media with a constant complex Gaussian beam parameter has been described.