对称膜系的特征矩阵具有单层膜特征矩阵的性质.尽管对称膜系的透射带和反射带的等效折射率分别为实数和虚数,其实都是数学上的而不是物理上的等效.完全可利用等效折射率理论,讨论对称膜系在全波段上的光谱特性. The characteristic matrix of a symmetric membrane system has the property of a monolayer film characteristic matrix, and although the equivalent refractive indices of the transmission band and the reflection band of a symmetric film system are real and imaginary, respectively, it is actually a mathematical rather than a physical equivalent. The equivalent refractive index theory can be fully used to discuss the spectral characteristics of a symmetric membrane system over the entire wavelength band.