Microbending losses of single-mode, step-index and multimode, parabolic-index fibers

We present formulas for the microbending losses of fibers that are caused by random deflections of the fiber axis. We consider single-mode (or almost single-mode), step-index fibers and multimode, parabolic-index fibers and compare their losses. Loss formulas for the single-mode fiber are derived from coupled-mode theory using radiation modes. Simple empirical approximations of the general formulas are also presented. The losses of the parabolic-index, multimode fiber have been derived earlier. The losses of both fiber types are compared by assuming either that each fiber samples the spatial Fourier spectrum of the distortion function at the same spatial frequency, or by comparing typical fibers of each type with each other regardless of any similarity between them. It is found that the multimode, parabolic-index fiber has lower losses if it supports a sufficient number of guided modes.