Coupling of Photorefractive Solitons

Abstract

A comprehensive theory for coupled soliton pairs in photorefractive materials is presented for incoherent and coherent soliton pairs in various different configurations and types of photorefractive crystals. The two beams need to have the same polarization, wavelength and should be mutually incoherent for the coupled soliton pairs to be realized. There exist diverse realizations of the soliton pairs like bright-bright, dark-dark, grey-grey and bright-dark etc. A theory for coupled spatial solitons in photovoltaic photorefractive crystals is illustrated first. The space charge field is obtained and the conditions under which the system reduces to studying open circuit photovoltaic and closed circuit photovoltaic spatial soliton pairs is elucidated. Subsequently, a theory for coupled spatial soliton pairs in non photovoltaic photorefractive crystals is illustrated. This theory, in turn is shown to reduce to the system studying screening soliton pairs and centrosymmetric soliton pairs under appropriate conditions. Coupled soliton pairs can be either incoherently coupled or coherently coupled depending upon the mutual phase relationship between the two light beams and both of these are studied in detail. Lastly, a novel soliton pair known as Gaussian or quasi soliton pair is investigated in photorefractive materials. The condition for existence of a vast set of such Gaussian or quasi soliton pairs is delineated along with the pertinent parameter space. The properties and dynamical evolution characteristics of such Gaussian solitons pairs are studied in detail. Relevant examples have been provided to illustrate the results.