Loss Analysis of Single-Mode Fiber Splices

Light transmission losses of single-mode fiber splices depend on the alignment accuracy of the fiber ends relative to each other. 1 We assume that the fibers are immersed in index-matching fluid to minimize reflection losses at the fiber ends. Most troublesome are transverse misalignments (offsets) and angular misalignments (tilts). Fiber splices are surprisingly tolerant of longitudinal misalignment. We begin our discussion by showing that the fields of single-mode, step-index fibers are very nearly gaussian in shape. This observation holds with even more assurance for parabolic-index fibers, because the modes of the infinitely extended parabolic-index medium are themselves gaussian and are changed only slightly by the truncation of the index profile at the core boundary. Once it is established that fiber modes may be closely approximated by gaussian field distributions, the evaluation of splice losses reduces to the computation of transmission losses between misaligned gaussian beams. 2,3 We present formulas for relating the width of the gaussian field distribution to the fiber parameters. An implicit relation for all types of 703