Random-bend loss in single-mode and parabolic-index multimode optical fiber cables

Excess losses of single-mode and multimode cabled optical fibers due to random bends of the Gaussian correlation function are discussed theoretically. By comparing theoretical results of various correlation functions to measured excess losses of the cabled fibers, it is verified that the correlation function of random bends of single-mode and multimode cabled fibers is estimated to be Gaussian. Using the estimated Gaussian correlation function, random-bend loss formulas of the single-mode and the graded-index multimode fiber cables are given. To use a cabled single-mode fiber over a wider wavelength region intended for a wavelength-division-multiplexing system, the relative refractive-index difference between core and cladding should be made larger to reduce the random-bend loss substantially. Cabling losses of graded-index multimode fibers depend strongly on the relative refractive-index difference and the diameter of the core.