New record set for data-transfer speeds

Researchers have set a new record for data transmission over a multimode optical fibre - sending data at a rate of 64 gigabits per second.
Researchers at the International Business Machines Corporation (IBM) sent data at a rate of 64 gigabits per second (Gb/s) over a cable 57-metres-long using a type of laser called a vertical-cavity surface-emitting laser (VCSEL).
The achieved rate was about 14 per cent faster than the previous record and about 2.5 times faster than the capabilities of today's typical commercial technology, researchers said.
The achievement demonstrated that the standard, existing technology for sending data over short distances should be able to meet the growing needs of servers, data centers and supercomputers through the end of this decade, they said.

To achieve such high speeds, the researchers used the VCSEL lasers developed at Chalmers University of Technology in Sweden and custom silicon-germanium chips developed at IBM Research.
"The receiver chip is a unique design that simultaneously achieves speeds and sensitivities well beyond today's commercial offerings," said researcher Dan Kuchta of the IBM TJ Watson Research Center in New York.

"The driver chip incorporates transmit equalisation, which widens the bandwidth of the optical link. While this method has been widely used in electrical communication, it hasn't yet caught on in optical communication," he said.
"Researchers typically rely on a rule of thumb that says the usable data-transfer rate is about 1.7 times the bandwidth," Kuchta explained.

"That means that with the VCSEL laser, which has a bandwidth of about 26 GHz, the rate would be only about 44 Gb/s," he added.
The fast speeds only worked for a distance of 57 metres, so this technology is not designed for sending data across continents. Instead, it's most suitable for transmitting data within a building, Kuchta said.