Bending Effects in Finite-Cladding Single-Mode Slab Waveguides

A new approach to the physical description and quantification of bend loss in arbitrarily bent single-mode fibers is based on the coupling of the fundamental mode to cladding modes solely due to curvature change along the fiber. Using a slab model, it is shown that there is an optimum bend design criterion based on the rate of change of curvature that can reduce bend loss to almost arbitrarily low levels regardless of curvature, provided only that the fiber coating index value is sufficiently smaller than that of the cladding index. With a finite coating, the propagation of the field around the bend is influenced by both the refractive index of the coating and its bulk absorption.