A Study Of Partially Coherent Solitons In Photorefractive Media

Photorefractive spatial solitons form when the diffraction of the beam is exactly balanced by self-focusing due to the photorefractive material nonlinearity. And solitons are localized wave entities that propagate in nonlinear while maintaining a constant shape. Photorefractive spatial solitons at mW power levels were observed and two-dimensional spatial solitons can propagate stably in photorefractive material, so they are one of the significant subjects in nonlinear optics. In recent years, incoherent spatial solitons were observed in photorefractive media. This findings have changed our traditional understanding of soliton phenomenon, and let to many new research topics. By using incoherent optical source, it will improve the development of the application of soliton-based communication systems.Starting from the physical process of photorefractive effect, we explain in detail the self-trapping mechanism of steady-state photorefractive spatial solitons. Then we show the experimental results of partially coherent solitons and introduce the approaches which describe partially coherent wave propagation in nonlinear media. We derive the evolution equations of steady-state partially coherent screening solitons with external bias field and the numerical integral solutions of the bright solitons in a photorefractive crystal are given. The partially coherent beam can been described as the superposition of all the coherent component, the diffraction behavior of the coherent components propagating in photorefractive crystal are numerically studied through the finite-difference method. The results show that the diffraction processes have something to do with the beams' envelope. The angle with respect to the z axis can affect the deflection of the beam. But coherent components can propagate stably in nonlinear photorefractive crystal. And then discuss the coherent length which is described the coherent properties when the screening solitons is formed. The result shows that the coherent length is a constant, only have to do with coherent degree.Otherwise, by solving the nonlinear propagation equations of partially coherent beams in logarithmically photorefractive media, we obtain an exact analytical solution. The coherent components propagation undergo periodic oscillation. Then we discuss the propagation states of partially coherent beam: the stationary propagation and periodically oscillatory propagation. The evolution properties of the coherent characteristics are also discussed in detail, the results show that the coherent length has the same expression with screening soliton.