General and Reliable Azimuthal Alignment Algorithm for Low Loss Multicore Fiber Fusion Splicing

Abstract

Multicore fiber is a promising spatial division multiplexing technology to increase the transmission bandwidth of optical fiber links in any given available spatial cross section. To connect multicore fibers, similar to single-core fibers, fusion splicing is an indispensable tool. Since multicore fibers cannot be circularly symmetric, precise transverse and azimuthal alignment is crucial to minimize the insertion loss penalty that would originate from even small offsets in the core locations of the two fibers to be spliced together. In this paper, a novel azimuthal alignment algorithm for multicore fiber splicing is presented. Since it is based on side-view images, it can also determine the twist rates of both fibers to be spliced and take these twist rates into account when calculating the optimum azimuthal alignment angle at the very ends of the two fibers. In the case of fibers with markers, i.e., fibers that are not rotationally symmetric, the relative and absolute polarities of the two fiber ends are computed as well. We present the formulation of the azimuthal alignment algorithm and demonstrate its stability and versatility for a wide range of fibers with vastly different geometries, core numbers and twist rates, including an offset single-core fiber. In the case of 4-core fibers with markers, we achieve average splice losses of less than 0.03 dB regardless of the polarity, which is a substantial advantage in terms of real-world applicability in the field. For a twisted 7-core fiber, we demonstrate an accurate twist rate detection with standard deviation < 1.4/m (turns per meter).