Vector coupled-mode analysis of coupling between two identical optical fiber cores

The vector coupled-mode analysis considering the exact HE(11) modes is applied to two single-mode coupled optical fiber cores, including the strongly guiding fibers. The accuracy of the conventional coupled-mode theory and the recently formulated new theory as applied to the two-core system is examined. Array modes of different polarization states are considered. It is shown that the full-wave coupled-mode calculations behave well in predicting the array-mode propagation constants beyond the weakly guiding regime and that the simpler conventional theory can provide satisfactory results when applied in the vectorial form.