提出了一种新的等效折射率方法，可以将光波导的两维折射率分布精确等效成一维折射率分布。从波动方程出发，通过严格的数学推导，得到了一维等效折射率分布的表达式。该等效折射率分布由二维光波导的模场分布和折射率分布决定。在此等效过程中，几乎无任何近似，因此具有比传统等效折射率方法(EIM)更高的精度，而且不受波导截止条件的限制，并适用于任意的折射率分布结构。以SOI(silicon-on-insulator)脊型光波导为例，给出新方法的一个具体等效实施过程，比较了新方法与传统等效折射率方法计算得到的等效模场分布及等效折射率，结果显示本文方法的有更高的计算精度。最后，文中给出了一个利用这种等效方法计算弯曲波导损耗的例子。新方法可以使对三维结构(截面为任意折射率分布)的模拟简化成二维模拟。

A new effective index method (EIM) is introduced to reduce a two-dimensional refractive index structure to a one-dimensional one accurately. The present EIM can be implemented for arbitrarily shaped waveguides. An explicit formula is obtained for the effective refractive index profile determined by the model filed and the cross-sectional refractive index of the original structure. In order to show how the present method is carried out, a silicon-on-insulator (SOI) rib waveguide is used in a numerical example. The effective model field distribution and the effective index profile are calculated with the present EIM. The bending loss of a SOI bent waveguide is also calculated with the present and conventional EIMs respectively. The numerical results show that the present method is much more accurate than the conventional EIM.