Transition regions in planar $W$ optical fibers

Transition regions at the interfaces of single- and dual-mode regimes have been investigated for some configurations of planar $W$ optical fibers based on numerical solution of the dispersion equation. It is shown that the sizes of the transition regions under consideration at the cutoff frequencies of the fundamental, first odd, and second even modes depend strongly on the geometric and optical parameters of $W$ optical fibers. These circumstances should be taken into account when choosing parameters of $W$ optical fibers in order to ensure in them a stable single-mode or multimode regime, necessary field concentration, and efficient filtering of leaky modes.