Fujitsu optical connector may cut server connectivity costs

Connector eliminates need for costly polishing.

Fujitsu Laboratories and Furukawa Electric have developed an optical connector that could reduce connectivity costs for servers.

The connector precisely aligns multiple fibers to make optical interconnects. While the companies did not go into detail, they said savings can be achieved because the technology eliminates the need for expensive, high-precision polishing at connection points.

The jointly developed connector can carry data at speeds of 25Gbps (gigabits per second), but could be faster in the future.

It reduces the cost of connecting optical fibers by more than half, Fujitsu said. The manufacturer believes the technology could deliver large cost benefits to data centers.

The connector incorporates a spring mechanism that bends the optical fibers slightly to make up for small differences in their lengths. The mechanism pulls back the fibers so they line up precisely when being plugged into a multi-fiber connector. When used with a housing accommodating four connectors that Fujitsu and Furukawa developed in 2011, the setup can link up to 96 optical fibers. The companies will present the research that led to the new connector's development at the SPIE Photonics West conference in San Francisco this week.

Aside from possible savings, the optical connector was designed to exhibit lower noise and higher speed than conventional electrical wiring connections. It could accelerate data transmission between boards and improve server performance, the company said.

The high-bandwidth connections provided by optics are faster than traditional electrical wiring technology used in most computers. However, the cost of using optical transceivers and fibers can be five to 10 times the cost of using copper, according to a Corning white paper.

Last year, Corning and Intel showed off MXC, an optical interconnect that can carry 25Gbps on each of its 64 fibers over a distance of 300 meters. That's a total bandwidth of 1.6 terabits per second over a single cable."We take a different approach," said Tsuyoshi Yamamoto, senior director of Fujitsu Labs' Photonic Devices Laboratory. "Our connector mates fiber facets directly in physical contact. The MXC connectors have a microlens array at the mating face and obtain optical coupling through air gaps.

"The physical contact connection provides the lowest connecting loss without reflection loss from air gaps. In couplings using microlens, the connection loss increases but the position tolerance is larger. We put a high priority on the low-loss connecting and take this approach."

Another feature of the Fujitsu-Furukawa connector is that laser processing is used on fiber tips so that fibers in different cables can be flush without any gaps between them. The laser processing is supposed to be as good as costly, multiple polishing steps to bring about a desired shape in the filament ends. "Finding a fiber facet formation method suitable for a physical contact connection was the most difficult problem in this development," said Tsuyoshi Aoki, a researcher in the Photonic Devices Laboratory.

"We attempted many conditions and many methods. Finally, we found by chance that laser processing realizes this. We think that we solved one of the issues for deploying optical interconnects to servers."

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