The performance and integrity of optical fiber based devices and systems are often critically dependent on the optical coupling between interconnected fibers. In this paper, we discuss the optical characteristics of the interconnected joint when two dissimilar fibers are fusion-spliced together, and compare different approaches to estimate the optical coupling loss. We treat the total optical splice loss as a combination of the mode-field (MF) mismatch loss and the transition taper loss. We describe the spectral characteristics of mode-field mismatch loss and the taper loss between an erbium-doped fiber (EDF) and SMF28 fiber both experimentally and analytically. In addition, we outline some advanced techniques for fusion-splicing of large mode area (LMA) fibers and microstructured fibers. Finally, we compare two types of splicers using arc-discharge fusion and filament fusion technologies, and describe an automated splicing system with some examples.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.