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Data transmission hit 64Gbit/s with NRZ modulation

Posted: 28 Feb 2014 ?? ?Print Version ?Bookmark and Share

Keywords:VCSEL? IBM? NRZ? data?

A team of IBM researchers has set a data transfer achievement at 64Gbit/s over a 57m long multi-mode optical fibre, with a vertical-cavity surface-emitting laser (VCSEL). This speed was recorded 14 per cent faster than the previous record and about 2.5x faster than the capabilities of a typical commercial technology.

While most researchers thought that achieving higher transmission rates would require more complex types of modulation like PAM-4, a standard non-return-to-zero (NRZ) modulation was utilised in sending the data.

New York IBM T.J. Watson Research Centre researcher Dan Kuchta said, "Others have thought that this [NRZ] modulation wouldn't allow for transfer rates much faster than 32Gbit/s...this technology has at least one or two more generations of product life in it."

Following this achievement, it is expected that standard existing technology for sending data over short distances should be able to meet the growing needs of servers, data centres and supercomputers through the end of this decade.

To achieve such high speeds, the researchers used a combination of VCSEL developed at Chalmers University of Technology 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," Kuchta explained. "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 added.

"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 26GHz, the rate would be only about 44Gbit/s."

"What we're doing with equalisation is we're breaking the historical rule of thumb," Kuchta stated.

He also said that the fast speeds only worked for a distance of 57m, so this technology isn't designed for sending data across continents. Instead, it's most suitable for transmitting data within a building. About 80 per cent of the cables at data centres and most, if not all, of the cables used for typical supercomputers are less than 50m long.

Kuchta also mentioned that this technology is ready for commercialisation right now.

- Jean-Pierre Joosting
??EE Times Europe

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