在自聚焦饱和非线性光折变正方晶格中心通过光诱导一个负缺陷态,研究了输入光束宽度与晶格波导尺寸可比拟时,二阶涡旋光束正对缺陷点垂直入射下的传输性能.数值仿真表明,在晶格深度与光强大小相匹配的情况下,输入光束演变形成类四极子的强度分布,且束缚在负缺陷处,值得注意的是,这四点的相位不再保持二阶涡旋状,而是对角相位相同,相邻点相位相反.若改变晶格深度与光强大小的比值都无法形成稳定的局域态.

In this paper,we study the transmission performance of the normal launched charge-2 vortex beam in the self-focusing saturated nonlinear photorefractive crystal which has an optically induced negative defect state in the center,where the width of the input beam can be compared with the lattice waveguide.Numerical simulation shows that,when the depth of the lattice can match with the light power,the input beam evolves into a similar quadrupole,and all the energy is kept in the defect site.What is more important,it′s phase doesn′t keep the initial spiral structure.But the diagonal points have the same phase,while the adjacent points have opposite phase.If we change the ratio of the depth of lattice and the power of the input beam,stable local solitons will not exist.