Propagation Characteristics Of Spatial Optical Solitons In Nonlocal Medium With Competing Nonlinearities

Spatial optical solitons are light beams that keep their shapes upon propagation because of the balance between diffraction and nonlinearity,which have potential applications in all-optical signal processing and optical interconnects due to their low power and particle-like nature on interactions.Compared with local solitons,solitons in nonlcal medium with competing nonlinearities have become a new hot topic in the field of solitons because of their many novel characteristics.So far,the studies of competitive nonlocal soliton are based on phenomenological models.In this paper,a model which is based on the molecular orientation effect and thermal effect in nematic liquid crystals is selected to investigate the solitons characteristics.In addition,ground-state soliton properties in competitive nonlocal media are analyzed by variational method.Moreover,the soliton propagation properties in competitive nonlocal media are obtained by numerical method.The main research content is as below:The first chapter,we mainly introduce the origin,basic concepts and characteristics of solitions,and focus on the nonlocal solitons ﹑ the related experimental reports of spatial solitons in nonlocal media﹑the research of spatial solitons in competitive nonlocal media.The second chapter,we obtain the NNLS equation in nonlocal nolinear media form Maxwell equation,and the equation of light in nematic liquid crystal.In addition,several numerical methods which are used to solve the schrodinger equation are intruduced,including the square operator iterative method algorithm,the improved square operator iterative method algorithm.In chapter 3,we found the parameters of ground state solitons based on the model of light transmission in nematic liquid crystal.We found the beam widthdecreasing with transmission constant,the beam power increasing with transmission constant.When the transmission constant is fixed,the beam with is increase with the thermal nonlinear coefficient,while the beam power decreases with thermal nonlinearity.The thermal effect changes the characteristics of the spatial solitons in the nematic liquid crystals.The thermal effect will cause the change of the anisotropic transverse direction of the material’s refractive index.The thermal effect leads to the transverse nonuniform distribution of the anisotropy of the refractive index.The effect of the thermal effect on the beam transmission is not isolated and is related to the nonlocality of the molecular orientation effect.The higher the nonlocal degree of the molecular orientation effect,the smaller the effect of heat effect on the beam propagation.In chapter4,we investigate the propagation of bright solitons and soliton pairs from the nonlocal medium to the nonlocal medium with competing nonlinearities by the numerical simulations.we find the nonlocal dipole solitons will split into two individual solitons,and the propagation of the nonlocal oscillating bound state which is composed by two out-of-phase solitons depends on the position of the interface.