Bend Loss, Tapering, and Cladding-Mode Coupling in Single-Mode Fibers

A new approach to the physical description and quantification of total bend loss in arbitrarily bent single-mode fiber is based on the coupling of the fundamental mode to cladding modes caused by curvature change. A criterion is derived that limits the maximum allowable rate of change of curvature to reduce bend loss to almost arbitrarily low levels regardless of the maximum curvature, provided only that the coating index is sufficiently smaller than the cladding index. This criterion is less demanding for pre- tapered fibers or fibers with a thinner cladding.