Microbending Loss in Optical Fibers

For the full potential of presently available optical fibers to be realized, care will have to be taken to minimize any perturbations that affect the fiber's transmission. One such perturbation is random bends in the axis of the fiber. Gloge1 and Marcuse 2 have shown t h a t such bends need not be of large amplitude to cause losses of a few decibels per kilometer. We have found this "microbending loss" to be common in multifiber structures. The worst of these structures add as much as 500 d B / k m to the loss of the fibers. Although several decibel-perkilometer added loss is more typical, the effect clearly poses a danger to system performance unless proper steps are taken to minimize it. The following experimental study of microbending loss shows how it can be reduced by means of coatings and increased fiber numerical aperture.