Microdeformation losses of single-mode fibers with step-index profiles

In this paper, we consider the coupling between the guided mode and the cladding modes of a single-mode fiber due to deformations such as microbends of the fiber axis and random core diameter fluctuations. Expressions for the coupling losses are presented for fibers with step-index profiles, and the autocorrelation functions of the microdeformations are assumed Gaussian, characterized by the rms deviation and the correlation length of the random function. In the case of a step-index fiber the results are compared with results found from the theories of Petermann and Marcuse [1], [2] which differ substantially for large correlation lengths. Microbending losses are shown only to differ slightly from the results of Petermann. Both microbending losses and losses due to random core diameter fluctuations differ substantially from Marcuse´s results, because of different approximations of the cladding mode fields.