Contents 1. Introduction
Space division multiplexing (SDM) technology is expected to become one of the key transmission strategies for future optical communication systems [1]. Researchers all over the world have been intensively investigating a wide variety of optical fibers for SDM transmission, and in the last 10 years SDM optical fibers have been confirmed to offer transmission over thousands of kilometers or speeds over Peta-bit/s. In Japan, the collaborative study group called EXtremely Advanced Transmission (EXAT) [1] was established in 2008; it has led several national projects on SDM technology. This paper reviews the progress made in both single-mode and few-mode multi-core fibers (SM- and FM-MCFs) research in Japan since 2010. It should be noted that while many remarkable results have been achieved using other SDM fibers (e.g. coupled core MCF), SDM sub-systems, and SDM transmission systems have been established all over the world, this paper focuses on the non-coupled type MCFs developed as part of the EXAT initiative.
