The Study Of Steady-State Vector Spatial Optical Solitons And Modulation Instabiliyt

Spatial optical solitons have attracted much interest of many scientists because of their potential applications in optical computering, optical switch, optical storage , optical connection etc. Now, spatial solitons are a hot topic in areas of nonlinear optical.The evolution equations of steady-state spatial optical screening solitons in photorefractive media with external bias field are obtained from the Kukhtarev-Vinetskii's model. The steady state vector spatial solitons in photorefractive crystals and the modulation instability in biased photorefractive-photovoltaic crystals are studied by both analytic and numerical methods. At the same time the spatially partially incoherent darkphotovoltaic solitons are also studied on experiment.We studied the self-coupled and cross-coupled vector beam evolution equations in the low-amplitude regime for screening solitons, which can exhibit the analytical solutions. The result indicates that these self-coupled vector solitons are obtained irrespective of the intensities of the two optical beams, whereas these cross-coupled vector solitons can be established when the intensities of the two optical beams are equal. The stability properties of these vector solitons have been investigated numerically and it has been found that they are stable.We investigate the modulation instability of broad optical beams in biased photorefractive-photovoltaic crystals under steady-state conditions by locally and globally treating the space-charge field. Both modulation instability growth rates are obtained respectively. Our analysis indicates that those growth rates depends on the strength of the externally applied electric field and more over, on the ratio of the optical beam's intensity to that of the dark irradiance, which predicts the modulation instability growth rate in open- and closed-circuit photorefractive-photovoltaic crystals whenthe external bias field is absent.Finally, The spatially incoherent dark photovoltaic solitons are studied on experiment. Two-dimension dark photovoltaic solitons are observed experimentally with spatially partially incoherent beam. Our experiment indicates that the spatially partially incoherent dark photovoltaic solitons depend on the direction of propagation, and on the orientation of the intensity gradient, with respect to the crystalline axes of the medium. The steady-state spatially partially incoherent dark photovoltaic solitons can be observed only under certain conditions.