Waveguides Induced by Screening-Photovoltaic Solitons in Biased Photorefractive--Photovoltaic Crystals

We investigate theoretically waveguides induced by screening-photovoltaic solitons in biased photorefractive--photovoltaic crystals. We show that the number of guided modes in a waveguide induced by a bright screening-photovoltaic soliton increases monotonically with the increasing intensity ratio of the soliton, which is the ratio between the peak intensity of the soliton and the dark irradiance. On the other hand, waveguides induced by dark screening-photovoltaic solitons are always single mode for all intensity ratios and the confined energy near the centre of a dark screening-photovoltaic soliton increases monotonically with the increasing intensity ratio. When the bulk photovoltaic effect is neglectable, these waveguides are those
induced by screening solitons. When the external field is absent, these waveguides predict those induced by photovoltaic solitons.