Influence of the fiber index profile on vectorial fiber modes and application to tapered fiber devices

The correspondence between the scalar modes LP and the nearly degenerate true vectorial modes in circular two-layer fibers is well established. For example, LP₂₁ corresponds to a combination of EH₁₁ and HE₃₁, while LP₀₂ is composed only of HE₁₂. For the multilayer fibers, inversion of the correspondences for certain modes can occur. We illustrate this inversion for a three-layer fiber. We propose a method permitting to distinguish the hybrid modes HE_νμ and EH_νμ in such fibers and we show the possibility of major taper-induced power coupling between these modes in SMF-28 fiber.