This paper describes the overview of special issues for the research and development on space-divisionmultiplexing transport systems that consist of scalable transmission node and novel transmission fibers. The topics of this issues covers network node architecture, integrated optical switching system with lowpower optical amplification, optical wiring and interconnection, high-core-count multicore fiber, and long-haul transmission performances verification with the capacity over 1 Pbit/s.

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The difficulty in greater enhancement of fiber capacity motivates our introduction of spatial division multiplexing. Since using multiple fibers/cores/modes on a link increases the complexity of switching operations, more efficient optical node architectures must be developed. In this paper, we present a classification of switching capabilities at the nodes, in terms of space and wavelength, and show two node architectures based on different switching classes: subsystem-modular optical cross-connect nodes and fiber cross-connect nodes. We did numerical simulations on two topologies of different sizes and cost analysis for the results and concluded that both node architectures can substantially reduce the node hardware scale, which clarifies that efficient switching for spatial division multiplexing can be achieved.

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consumption technologies for space-division multiplexing optical amplification and switching repeater nodes are required in this context. Here, we review technologies for low power consumption

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Space division multiplexing (SDM) technology is becoming more attractive because it offers large transmission capacity of a multiple of the spatial channel count. An SDM network with multi-core fibers (MCFs) provides a degree of freedom of spatial switching in addition to wavelength selective switching. Thus, wavelength routing devices for SDM networks also have to be developed. This paper reviews recent work on N-in-1 wavelength selective switch (WSS) devices suitable for SDM networks. The devices are based on the spatial and planar optical platform, which utilizes the advantages of free-space and waveguide optics.

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Technologies for space division multiplexing are rapidly progressing to support the ultra-high density transmission systems. Though developments of these technologies are started for core network systems, requirements adopting these technologies are also arising for using in optical nodes. This paper summarizes optical connecting technologies utilized in optical nodes such as optical connectors and Fanin/ Fan-out devices.

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Multi-core fibers (MCFs) and few-mode fibers (FMFs) are expected as a good candidate for overcoming the capacity limit of a current optical communication system. This paper reviews the classification and recent works of MCFs, FMFs and few-mode multi-core fibers for space division multiplexing transmission. In addition, design concept and characteristics of a single-mode 37-core fiber, which has largest core number so far, are presented. Here, tradeoff requirements such as core count, Aeff, inter-core crosstalk, and cladding diameter are discussed.

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Digital coherent technologies enabled the use of spectral-efficient modulation formats with forward error correction codes as well as the waveform equalization for overcoming the transmission distance limit due to polarization mode dispersion and chromatic dispersion. Currently, transmission capacity over a single-mode fiber (SMF) reached 100 Tb/s in laboratory experiments, but it is close to the physical limitation restricted by the fiber nonlinearity and fiber fuse. Space division multiplexing (SDM) techniques are indispensable for breaking the capacity limit of standard SMF. In particular, dense SDM (DSDM) technology, which is defined as SDM with spatial multiplicity of ≥ 30, has been extensively studied for realizing optical transport networks with the scalability beyond 1 Pb/s capacity. In this paper, DSDM technologies including a system concept and its recent progress are discussed for realizing Pbit/ s-class capacity transmission systems. We also describe the world first 1 Pb/s unidirectional inlineamplified transmission experiment over 205.6 km of single-mode 32 core fiber.

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