BENDING LOSSES OF COATED SINGLE-MODE FIBERS - A SIMPLE APPROACH

On the base of a modified fiber geometry model, a new approach for the bending losses of coated optical single-mode fibers is developed, which results in a simple formula. An improved condition for the peak locations is given, that allows for the wavefront curvature of the leaky mode in the bent fiber, since it is derived by wave optics. Simple explicit relations for both the peak spacings and the peak-to-trough ratio are given. Their asymptotic forms for small bend radii are independent of the fundamental-mode parameters. An interpretation of oscillations in the bend-loss curves in terms of a thin-film filter effect of the triple-layer structure on the lateral leaky-mode radiation fully explains the behavior, especially the loss increase in the peaks compared to the case of an infinite cladding. The agreement with numerical and experimental results of other authors is excellent.