光纤中的电磁对偶变换与导波的模式分析

讨论了麦克斯韦方程在各向同性均匀电介质中的电磁对偶变换不变性,定义了电磁混合比,求出了对偶场的充要条件.把上述不变性和充要条件应用于阶跃光纤,分析其导波模式,证明在非轴对称情况下,阶跃光纤中不存在具有色散的受导简正模.存在的解只有临界折射模(n=n₂时的特解).求出了它的分立频谱.受导简正模只存在于轴对称情况中.以上结论与实验事实不矛盾,并由此解释了基模的特性关键词：光纤光学光波导电磁对偶变换受导波

ELECTROMAGNETIC ADJOINT TRANSFORMATION AND MODE ANALYSIS FOR GUIDED WAVES IN AN OPTICAL FIBER

The adjoint transformation of electromagnetic fields for uniform isotropic dielectric is considered for guided waves in an optical fiber. The necessary and sufficient condition for two solutions to be a pair of partners is derived. The modes of guided waves are analyzed under this condition. It is proved that the dispersive normal modes do not exist in the case of non-axial symmetry. The guided modes in such cases are modes of critical refraction, which has a discrete spectrum. The dispersive normal modes exist in axial symmetrical cases. Theoretical predictions are comparable with the experiment data. The behaviour of the fundamental mode shows that it is a mode of critical refraction rather than a dispersive normal mode as is predicted by the theory.