Full-Vectorial Mode Coupling in Optical Fibers

Optical full-vectorial modes have closely attracted much attention because of their unique optical features and thus may develop the fundamental researches and new functionalities of light. Beyond the conventional linear polarization modal coupling, we thoroughly investigate the inherent polarization-dependence and polarization-isolation features for full-vectorial mode coupling in optical fibers, as well as the coupling crosstalk in view of the modal degeneracy. We present the general full-vectorial coupling mechanism and numerically simulate the full-vectorial mode coupling for both fiber directional and grating-assisted coupling cases. Furthermore, we give the detailed analyses of coupling crosstalk based on the unified three-mode coupling model. Apart from lifting the modal degeneracy, significantly, the crosstalk can also be reduced by weakening the coupling coefficient and meanwhile increasing the coupling length. This extended full-vectorial mode coupling mechanism may provide theoretical guidance on exploiting new all-fiber-based polarization-sensitive passive elements to control full-vectorial fields and modal polarization states.