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Mitsubishi breaks long distance Terabits record

Companies could enjoy cheaper international telephone calls and broadband data connections following optical network enhancements achieved in Japan.

Mitsubishi Electric Corporation has succeeded in sending data at 1.3 terabits per second down a fibre-optic cable 8,400 kilometres in length.

While the speed does not represent an overall speed record, it is a record for the distance, which is equivalent to that from Tokyo to Southern California, the path that fibre-optic cables between Japan and the US often run.

The achievement could be replicated by operators across the world, including those that transport data and voice calls between UK and US companies.

Getting more data to travel along a fibre-optic cable is extremely important for the cable operators.

The high cost of laying undersea cables and keeping them in working order adds to the price telecommunication carriers pay to use the cables.

If more data can be sent along a single fibre, the construction and running costs can be shared between more customers and the price to each customer can be reduced.

One of the standard technologies employed commercially on such cables is dense wavelength division multiplexing (DWDM), a system that allows multiple beams of light to travel along the fibre at the same time without interfering with each other.

Researchers at Mitsubishi Electric used DWDM to group 65 signals together, each giving data speeds of 20 gigabits per second bps. This initiative achieved the total speed of 1.3 terabits per second.

To be able to send the data over the distance tested the engineers worked to refine the amplifiers used in the system, said Takashi Mizuochi, manager of the lightwave transmission team at Mitsubishi Electric's research centre in Kanagawa outside Tokyo.

At intervals along the route of the fibre, amplifiers must be placed to boost the light signal and clean up any interference with the signal.

First, the team improved the amplifiers to produce a stronger light beam that can travel up to 75 kilometres without the need for amplification. Current systems can only manage gaps of around 45 kilometres before an amplifier station is needed, said Mizuochi.

Secondly, the team expanded the bandwidth of the amplifiers so that they would be able to handle more channels. The new amplifiers have a 36-nanometer bandwidth compared to a 30-nanometer bandwidth on normal amplifiers, thus allowing around 10 more channels to be carried down the fibre.

With the 8,400-kilometre barrier broken, Mizuochi is turning his attention to longer distances.

"Now we are trying to expand the distance to 9,000 kilometres," he said.

Why this distance? A transpacific fibre cable often runs in a ring with different paths being taken by the northern and southern halves of the ring. The northern half covers a distance of 9,000 kilometres, he said.

Mitsubishi Electric plans to disclose more details about the transmission system during a presentation at the Optical Fibre Communication Conference scheduled to be held in Anaheim, California, on 20 March.

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