Photorefractive Crystal Spatial Solitons In Self-deflection And Deformation

Screening photovoltaic soliton arised in the condition of applied external alternating electric field and bias electric field are studied. The numerical simulation shows there are three main factors that influence the deflection and deformation of screening photovoltaic bright and dark soliton occurred in the LiNbO3 crystal applied external bias electric field:the concentration of the crystal NA the dark radiation intensity Id and the bias electric field E0. When NA is greater, the degree of self-deflection and deformation of the bright soliton is larger,but opposite for dark soliton; the smaller the Id is, the more easily the space charge field induced by beam in the crystal is saturated, leading to the limited deformation for top of soliton (bright solitons) or the bottom (dark solitons); if the value of Eo gets larger, the degree of self-deflection and deformation of bright and dark solitons will be greater.Starting from the band transport model, we derive the space charge field of the photorefractive crystal applied external alternating electric field, it consists of local and non-local terms, the former decides the structure of soliton, the other determines the self-deflection effect of soliton. We get the envelope solutions of the screening bright and dark soliton by theoretical calculation, and find that when the external alternating electric field is synchronous with light modulation, the effective field of the external alternating electric field is in the same direction with the crystal axis, screening bright soliton will be formed in the crystal; when there has the phase difference ofπbetween them, the effective field of external alternating electric field has the opposite direction, there will form a screening dark soliton.We get the self-deflection characteristics of screening bright and dark solitons in the cystal applied with external alternating electric field by perturbation method:bright soliton will deflect along the opposite direction of the crystal axis,and it has a parabolic trajectory, the deflection distance is proportional to the three power of applied alternating electric field and light intensity modulation respectively. When the ratio of the soliton center intensity to the dark radiation is 10, the deflection distance of bright soliton will be max, while the dark soliton has no such phenomenon. Because the spatial frequency of the soliton center has linear motion as the soliton propagate, cross-sectional distribution of amplitude changes at the same time, the curve slope at deflection direction becomes larger, the curve in the opposite direction flattens, and numerical simulation gets the same conclusion.It is found that the self-deflection of dark solitons in the conditions of external alternating electric field and bias field is similar, they have a non-parabolic trajectory shifted toward the crystal axis. Their spatial frequency components will also change, leading to changes in the shape of soliton, the self-deflection and deformation will increase as the alternating electric field gets larger.