Analysis of two‐core single‐mode optical fibers for subscriber lines

Abstract

AbstractMulticore optical fiber, consisting of several cores in the same clad, has been developed for use as optical fiber cable for subscriber lines, by which high‐density cable can be realized. One of the problems of multicore fiber is crosstalk between adjacent cores. In this paper, a two‐core single‐mode optical fiber, which is the basic structure of the multifiber, is analyzed and an optimum refractive index profile for desired crosstalk and possible high density is discussed. In the analysis, comparison was made between step‐type, W‐type, α‐power and inverse α‐power index profiles, considering the mode field diameter which is an important parameter for a single‐mode optical fiber. The results show that: (1) under the same mode field diameter, the crosstalk for α‐power or for inverse α‐power refractive index profile has little difference with that for the step‐type profile; (2) by the use of the W‐type refractive index profile, high density becomes possible. Based on these results, the design and evaluation of the multifiber can be carried out. To analyze the coupled fiber with a radially inhomogeneous refractive index profile, the point matching method and homogeneous multilayer division method are combined. Although scalar approximation is made in the method, in the case of a weak waveguide, the relative error of coupling coefficients was found to be less than 0.1% even for strong coupling.