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• Photonic Bandgap Hollow Core Fibers (PBG-HCFs) have been investigated. • High-performance HCFs with practical single mode (SM) properties has been realized.. • Furthermore, we have successfully developed HCF mechanical-splice and HCF cables. Hollow core fibers (HCF) are innovative optical fibers having the potential to break the limits of conventional optical fibers. Examples of innovation are ultra-low loss potential, ultra-low nonlinearity, resistance against harsh conditions, and long interaction lengths with gases confined to the core. In addition, ultra-low latency characteristics have attracted much attention in recent years, particularly amongst financial trading communication systems. For the first time in the world, we have succeeded in developing a high-performance HCF with practical single mode (SM) properties realized by a resonant couple phenomenon, to apply the HCF in the low latency transmission. Furthermore, we have successfully developed HCF connectors and HCF cables to realize the actual low latency transmissions. These development results will be reported. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the current situations of optical fibers used for terrestrial and submarine transmission systems as well as up-to-date R&D on these fibers. The current fibers include standard single mode fibers (SMFs), non-zero dispersion shifted fibers (NZ-DSFs), and dispersion managed lines (DMLs). Even though these fibers show quite high and matured properties, the internet traffic is continuously growing, and around 2015–2020, it is expected that the current transmission fibers would become inadequate. To prepare for the future ultra high-capacity transmission, there are three important R&D directions for transmission fibers. (1) Reducing non-linearity by means of enlarging Aeff and/or reducing attenuation loss. It is very important in the case of transmission systems using new multi-level signal formats. (2) Expanding the transmission band more than the current C- and/or L-Band by utilizing new transmission fibers. For example, holey fibers (HFs), which have an endlessly single mode (ESM) property, are one of the interesting candidates of the new transmission fibers. (3) Using Space Division Multiplexing (SDM) by using multi-core fibers. The multi-core fiber literally multiples the core number within a fiber dimension, which enables multiple transmission capacity per one fiber. In addition to the developments of transmission fibers, component fibers have also been studied and developed. Examples of R&D on these component fibers will be also discussed in the latter part of this paper. [ABSTRACT FROM AUTHOR]