Numerical Study Of Spatial Solitons In Photorefractive Crystal

Spatial solitons evolve from a nonlinear change in the refractive index of a material induced by the light intensity distribution. When the combined effects of the refractive nonlinearity and the beam diffraction exactly compensate each other, the beam propagates without change in shape and the photorefractive (PR) spatial solitons form. For the PR spatial solitons can be formed at mW power levels and their wide potential application in many fields such as all-optical switch, optical waveguide, optical signal processing and optical communications, they have attracted considerable research interest. In the thesis, we study the theory of one dimensional PR solitons and their properties such as dynamical evolutions, interactions and self-bending, and investigate numerically by using the finite-difference method. The main work is developed in the following way:1. Review the history and current status of research of four basic types of the PR spatial solitons, and compared with the Kerr solitons, we introduce the characteristic and applications of PR spatial solitons.2. The forming mechanism of the SP spatial solitons is educed by the Kukhtarev-Vinetskii model. The numerical integral solutions of bright and dark solitons are given in a PR crystal, and the closed-form solutions are given in the low-amplitude case. Then, to illustrate our results, we use the strontiurn barium niobate(SBN) crystal, give the numerical solution of the bright and dark solitons and the relationship between the solitons intensity and their full-width half-maximun(FWHM).3. Use the finite-difference method, the dynamical evolution of the screening solitons are numerically simulate with the result that the screening solitons can propagate stably in the crystal. Considering the absorption coefficient, we numerically study the loss effect and high-order solitons evolution in low-amplitude case, the numerical result indicates that the high-order solitons tend to experience larger cycles of compression and expansion.4. Using the finite-difference method, we numerically study the stable property of solitons. The result is that PR solitons are stable against small perturbations, when the perturbation is large, the solitons will not retain its shape. 5. Numerical investigations of the interactions among bright screening-photovoltaic solitons are performed in detail by using the finite-difference method. The numerical results show that a number of variables such as the soliton initial separation and phases can determine the interaction forces of solitons. The numerical study indicates that two in-phase solitons attract each other, and soliton fusions do occur at certain interaction length. The distance of the soliton fusions increases monotonously with the initial separation of the two interacting solitons. On the other hand, two beams of the out-of-phase, the solitons repel each other with a decreasing monotonously with the initial separation. When the relative phase of the two solitons is in the ranges of (0,Ï€) and (-Ï€,0), energy transfer will accompany the interactions. Moreover, interactions among multiple solitons are also investigated.6. Considering the diffusion effects, the self-bending process is occurred in the biased PR media. Using perturbation analysis, we found that the center of the optical beam moves on a parabolic trajectory.