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8-strand multi-core fiber will boost optical interconnects

31 Mar 2015

Sumitomo Electric development claims to be “highest-density” multi-core fiber-optic cable.

Sumitomo Electric Industries has developed a multi-core optical fiber (MCF) including 8 cores within in the standard 125-μm cladding suitable for optical interconnects, and realized an ultra-high-density fiber optic cable with, what the company claims is “the highest core density ever reported”.

To cope with growing data traffic in short-reach interconnects used for parallel processing in supercomputers and resource disaggregation in data centers, novel optical interconnect technologies for broadband high-density transmission are now being intensively researched and developed. (In a disaggregated design computing, memory, storage, communication elements of a server are physically separated, which makes for more logical resource allocation, eases repair or upgrade, and enables more efficient use of the resources).

At the same time, multi-core optical fiber has been also intensively researched and developed, with cable companies also trying seven-core and three-core designs to accommodate many fibers side-by-side. Sumitomo Electric’s MCF, which made its debut at this month’s OFC expo in Los Angeles, is billed as a “next-generation” optical fiber that can support and enable ultra-high-capacity transmission systems.

Of the competition, the company says, “Most of the previously-reported MCF developments have required the fiber’s cladding diameter to be thicker than the standard 125μm diameter optical fibers to increase core count while allowing good optical properties with each core and suppressing core-to-core crosstalk. In the specification of its new 8-core fiber, Sumitomo Electric notes, “a cladding diameter larger than 125μm is not preferable for the short-reach transmissions where tight bends are easily applied to the fiber”.

A company statement added, “We have developed, for the first time, a MCF with a cladding diameter of 125μm, equivalent to the standard optical fibers and it includes eight cores with low core-to-core crosstalk. Our MCF also has optical characteristics comparable to the standard single-mode fiber specified for 1.3μm wavelength band where signal distortion can be suppressed. Having such features, the 125μm cladding achieves the mechanical reliability equivalent to that of the standard optical fibers, and can be integrated into various technologies that use standard optical fibers, such as cabling and connecting technologies.

"The core count of eight has been desirable since full-duplex (2x) 100Gbit/s (4x25Gbit/s) signals can be transmitted over a single MCF with transceiver technology designed for conventional 25Gbit/s signals. Furthermore, our MCF’s optical characteristics suit silicon photonics technology, which allows highly integrated optical devices operable at the 1.3μm band."

12-core cable; 96 fibers

Sumitomo also announced that it has fabricated a 12-core MCF cable using the new 8-fiber MCFs, meaning that 96 cores are included within an outer diameter of 3mm. here, the core density was more than two times higher than those of earlier-reported multiple fiber optic communication cables, the company claims:

“We also evaluated the transmission characteristics in the 1.3μm band of a 1.1km-long MCF cable. The evaluation test using 100G Ethernet transceiver showed that the MCF cable can ensure error-free transmission for 800 Gbit/s (8 cores x 4 wavelengths x 25 Gbit/s) signals, which is eight times higher than conventional SSMF cables. The results of the transmission experiment indicate that the developed MCF cable has the transmission capacity of 9.6 Tbit/s (based on 12 fibers x 8 cores x 4 wavelengths x 25Gbit/s). Sumitomo Electric concluded, “improvements in transceivers can further enhance the MCF’s transmission capacity.”

About the Author

Matthew Peach is a contributing editor to optics.org.

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