中文摘要：

给出了中心对称光折变晶体中屏蔽孤子的高阶空间电荷场．当高阶项可以忽略时，这个电荷场就变为早前在中心对称光折变晶体中研究的屏蔽孤子的空间电荷场．研究了中心对称光折变晶体中屏蔽孤子的高阶非线性波动方程．在适当的条件下，这个非线性波动方程能够展示明暗空间光孤子．这类晶体不同于非中心对称晶体，其非线性折射率的改变来源于二次电光效应，而不是一般的线性电光效应．应用光束传播的方法，对这些孤子的稳定性进行了讨论．表明在小的微扰下这类孤子是稳定的，不会发生分裂．

英文摘要：

The space-charge field with a higer-order nonlinearity in biased centrosymmetric photorefractive media is presented. When the higer-order term can be neglected, this space-charge field is that studied previously in biased centrosymmetric photorefractive media. The nonlinear wave equation with a higerorder nonlinearity is investigated in biased centrosymmetric photorefractive media, which Can exhibit bright and dark spatial solitons under appropriate conditions. The nonlinear change in the refractive index in centrosymmetric photorefractive media resulted from the quadratic electro-optic effect, rather than the linear electro-optic effect in noncentrosymmetrie media. The stability of th~se spatial solitons is discussed using beam propagation methods, and it has been found that optical spatial solitons in biased centrosymmetrie photorefractive media are stable against small perturbations in amplitude not broken up.