中文摘要：

分析了磁光薄膜中同时激发的多个频率的静磁波对导波光的衍射作用过程，以三频为例推导了三级近似的耦合模方程，对于两频磁光作用的理论计算与实验基本一致．对于三频磁光作用，数值分析结果表明：对于主衍射效率（Principle Diffraction Efficiency，PDE），小信号时只需考虑一级磁光作用．在超出小信号范围且PDE达到峰值之前，第三级磁光作用对PDE影响很小，只需考虑前两级磁光作用．小信号时，得到了PDE的近似解析表达式，在一定的频率间隔范围内与耦合方程的一级近似解较为符合．

英文摘要：

The process of multiple diffractions of guided optical waves （GOWs） with multifrequency magnetostatic forward volume waves （MSFVWs） exited simultaneously in magneto optic （MO） film waveguides was analyzed. The coupled-mode equations for the case of three MSFVW signals were presented in third-order MO coupling approximation, and the theoretical calculations were consistent with the experiments for two-frequency MO interaction case. It was shown by numerical calculation for three-frequency MO interaction case that only the first order MO interaction needs to be taken into account to calculate the principle diffraction efficiencies {PDEs） in small signal limit. When beyond the limit the third order MO interaction has little effects on PDEs before PDEs reach the peak values and the coupled-mode equations can be simplified in second-order MO coupling approximation to calculate the PDEs. For small signal, the approximate analytic expression of PDEs was obtained, the results of which were agree with the numerical results of coupled-mode equations in the first order approximation.