Research On Spatial Solitons Induced By Shifting In Centrosymmetric Photorefractive Crystal

Photorefractive space solitons have the characteristics of being generated in low power,short time and stable propagation.They have a large application value in the optical fiber communication,optical waveguide and other related areas.The spatial solitons have been a hot topic for researchers.In this paper,we will translate the centrosymmetric photorefractive crystal potassium tantalate niobate in the experiment to produce spatial solitons and analyze it in theory.In view of this,the main work of this paper is as follows:Firstly,the correlative study of photorefractive spatial solitons is reviewed and the progress of research on the spatial solitons in centrosymmetric photorefractive crystals is introduced emphatically.Secondly,the structural characteristics,physical properties and related applications of potassium tantalate niobate are introduced.Potassium tantalum niobate crystal has strong secondary electro-optical effect at room temperature;After pressurized,the crystal changes from the optical isotropic body into anisotropic body and the refractive index ellipsoid changes from a sphere into an ellipsoid.Based on this,the expression of the refractive index of the cubic phase potassium tantalum niobate with different axial bias is deduced and the change of the optical axis of the crystal is deduced.The mathematical expressions of the refractive index and the refractive index ellipsoid equation under the axial bias are analyzed emphatically.The changes of the refractive index elliptic equation and the refractive index ellipsoid equation are analyzed before and after the application of the electric field.Thirdly,the photorefractive effect of the crystal is enhanced by the relative translation of the crystal under biased conditions.The propagation characteristics of space solitons in potassium niobate tantalum crystals are studied experimentally.(1)The influence of external electric field on beam propagation shape is observed.The experimental results show that when the external electric field is applied to the crystal,the beam will appear a short self-focusing phenomenon,then returned to the self-defocusing state;When the crystal is applied with different voltage,the self-focusing degree of the beam will be enhanced with the increasing of the voltage value.(2)Using the control variable method to carry out the external electric field.The experimental results show that:It is possible to produce stable photorefractive space solitons in the crystal by translating only with the external electric field.(3)The effect of the translation condition on the beam propagation shape is observed.The experimental results show that:Under the condition of external electric field,the translation can cause the self-focusing phenomenon of the light beam in the crystal and has the tendency of self-trapped into bright space solitons;The speed of crystal movement is greater,the self-focusing of the beam is stronger.From the appearance point of view,with the greater the speed of movement,the beam will become more and more fine.If the crystal is translated at a specific speed,the voltage applied to it is changed,and the propagation behavior of the beam has a similar effect.Finally,according to the literature and related theory,the theoretical model of the space charge field in the centrosymmetric photorefractive crystal under the translation mechanism is constructed.Based on the model,the reason of the formation of the spatial solitons phenomenon is analyzed theoretically.The wave equation of beam propagation under the new model theory is numerically solved.The propagation behavior and evolution of the beam at different translation speeds are simulated.