In this paper, we describe recent progress in space-division multiplexed (SDM) transmission, and our proposal and demonstration of dense space-division multiplexing (DSDM), which offers the possibility of ultra-high capacity SDM transmission systems with high spatial density and spatial channel count of over 30 per fiber. We introduce the SDM transmission matrix, which cross indexes the various types of multi-core multi-mode transmissions according to the type of light propagation in optical fibers and how the spatial channels are handled in the network. For each category in the matrix, we present the latest advances in transmission studies, and evaluate their transmission performance by spectral and spatial efficiencies. We also expound on technologies for multi-core and/or multi-mode transmission including optical fiber, signal processing, spatial multi/demultiplexer, and amplifier, which will play key roles in configuring DSDM transmission systems, and review the first DSDM transmission experiment over a 12 core × 3 mode fiber.

Dense Space-Division Multiplexed Transmission Systems Using Multi-Core and Multi-Mode Fiber

In this paper, we review recent progress on space division multiplexed (SDM) transmission and our proposal of dense SDM (DSDM) with more than 30 spatial channels toward capacities beyond petabit/s. Furthermore, we discuss the requirements for realizing long-haul DSDM transport systems using multicore and/or multimode fiber, including power and space efficient amplification schemes, the use of fibers with large effective areas and transmission lines with low intercore crosstalk, low differential mode delay (DMD), and low mode dependent loss (MDL). Graded index heterogeneous 12-core × 3-mode fiber with low crosstalk, low DMD, and low MDL, parallel multiple-input and multiple-output signal processing, low mode dependent gain Erbium-doped fiber amplifiers, and MDL equalization technologies are significant as regards extending the reach of multicore and multimode transmission. We review our long-distance transmission experiment on polarization-division multiplexed 16-quadrature amplitude modulation signaling over 12-core × 3-mode fiber.

Dense Space Division Multiplexed Transmission Over Multicore and Multimode Fiber for Long-haul Transport Systems

This paper describes ultra-high capacity long haul optical transmission technologies based on multicore fibers (MCFs) with space-division multiplexing. First, we discuss the factors limiting the total capacity and the attainable distance of MCF, and show that the transmission distances are severely limited by crosstalk (XT) between adjacent cores. Next, we discuss a propagation-direction interleaving (PDI) technique to suppress XT. In PDI, adjacent cores have different propagation directions, and thus, bidirectional transmission is realized by a single MCF. We discuss spectral efficiency and attainable distance of several MCFs and show that three-fold reach extension is possible by using PDI in 12-core fiber with dual-ring structure. We also describe a long haul transmission experiment on a 12-core DRS fiber with PDI.

Crosstalk-Managed High Capacity Long Haul Multicore Fiber Transmission With Propagation-Direction Interleaving

We propose the optimum design of high spatial density few-mode multicore fiber (MCF) for repeated space-division multiplexed (SDM) transmission. Numerical analyses reveal that a hexagonally arranged six-mode seven-core structure is potentially better than the other possibility, the six-mode multicore structure, in terms of realizing high spatial density and low mode-dependent loss (MDL) characteristics at the splice point; its benefits will enable us to construct long-haul dense SDM transmission links. We fabricate a 171  μ m cladding six-mode seven-core fiber and successfully demonstrate low loss, differential mode delay (DMD), crosstalk, and splice-induced MDL characteristics while maintaining the relative core multiplicity factor of more than 50. Finally, we demonstrate repeated optical 12 × 12 MIMO transmission of more than 100 km using our six-mode MCF and erbium doped fiber amplifier (EDFA).

Six-Mode Seven-Core Fiber for Repeated Dense Space-Division Multiplexing Transmission

We report the design and fabrication of a compact multi-core fiber fan-in/fan-out using a grating coupler array on the SOI platform. The grating couplers are fully-etched, enabling the whole circuit to be fabricated in a single lithography and etching step. Thanks to the apodized design for the grating couplers and the introduction of an aluminum reflective mirror, a highest coupling efficiency of −3.8 dB with 3 dB coupling bandwidth of 48 nm and 1.5 dB bandwidth covering the whole C band, together with crosstalk lower than −32 dB are demonstrated.

/pdf/on-chip-grating-coupler-array-on-the-soi-platform-for-fan-in-51eubfwcer.pdf

On-chip grating coupler array on the SOI platform for fan-in/fan-out of MCFs with low insertion loss and crosstalk

We propose a low-loss fan-out for 12-core multicore fiber, which achieves physical-contact connection between coupled cores by accurately arranging fibers and optimizing the conditions for physical contact, and demonstrate a physical contact connection with a low average insertion loss of 0.64 dB and a high return loss of over 55 dB for 12 cores.

S. Yanagi

Papers

Low-loss Physical-contact-type Fan-out Device for 12-core Multicore Fiber