Lucent calculates upper limits of optical fibre

Scientists from Lucent Technologies' Bell Labs research division reported Thursday that optical fibre can theoretically send far more data than has ever been expected.

But to some observers, the announcement -- that optical fibre can support 100Tbps, or 100 trillion binary digits per second (the equivalent of 20 billion one-page e-mails) -- may actually underestimate the power of optical fibre.

"Every time people think there's a limit, either in the number of wavelengths they can get on a fibre or the speed of a single wavelength, somebody figures out a way to get around it," said Dave Passmore, an analyst at The Burton Group Corp. in Midvale, Utah.

"It may be that even this ultimate limit is surmountable. Ingenuity may find a way," Passmore said.

Passmore compared Bell Labs' findings with the ongoing proclamations of the limits of copper wires. "For a long time, people said that 9.6Kbps was all you could get, and then 14.4Kbps. Now we're up to 56Kbps, and folks may figure out ways to pack even more bits than that. You never know."

Partha Mitra, a physicist at Bell Labs who worked on the study, agreed, saying that the study findings are only an estimate and that actual speeds will vary, depending on the kind of fibre being used.

"The number is not set in stone," Mitra said, "but we've put a reasonably round number on it. It's not going to be 1,000Tbps, and it's not going to be 50Tbs. But if it were 150, I wouldn't be terribly surprised. The point is that we haven't had a number like this before."

Mitra added that the 100Tbps estimate is contingent on other parts of the technological equation falling into place.

"We'll have to have better modulation schemes and better electronics, such as coherent detection or multilevel detection," Mitra said. "With the current schemes, you're limited to 1 bit per second per hertz."

Currently, most commercial-grade optical fibres transmit less than 2Tbps, and some lab tests have proved speeds as fast as 10Tbps.

"This paper highlights the fundamental understanding of the ultimate capacity of fibre," Alastair Glass, CTO of Lucent's optical networking division, said in a statement. "It says that we are still a long way from the fundamental limits in current commercial systems."

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