Skew evaluation using two-dimensional refractive-index profile in single-mode fiber ribbons

The skew of fiber ribbons must be small for high bitrate parallel optical transmission systems. Accurate skew evaluation using fiber parameters is important for this purpose. A simple method, based on the calculus of variations, is proposed for evaluating the skews of fiber ribbons. This method employs only one mode field (LP₀₁ mode) of an ideal step-index fiber as a trial function and a two-dimensional (2-D) refractive index profile. The measured skews of a 16-fiber ribbon composed of fibers with different parameters are compared with calculated values and are found to be in good agreement. The influence on the skew of several refractive index profile deviations (including asymmetric profile deviations) are evaluated using the proposed method. It is found that the asymmetric core profile has a large influence on skew whereas that of the asymmetric core-cladding boundary is relatively small.