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 necessa ry and sufficient condition for two solutions to be a pair of partners is d erived. 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-ax ial symmetry. the guided modes in such cases are modes of critical refracti on, which has a discrete spectrum. The dispersive normal modes ey-ist in ax ial symmetrical cases. Theoretical predictions are comparable with the expe riment 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.