Alcatel-Lucent pushes subsea fiber speeds past 30 Tbps

John C. Tanner

Alcatel-Lucent pushes subsea fiber speeds past 30 Tbps

July 16, 2013

ITEM: It’s fiber-speed record-breaking time again, with Alcatel-Lucent announcing Tuesday that Bell Labs researchers have successfully transmitted 31 Tbps on a single subsea optical fiber at a distance of over 7,200 km.

The fiber wasn’t actually underwater – it was at Alcatel-Lucent’s Innovation City campus in Villarceaux near Paris. But AlcaLu is billing it as “the highest-ever capacity for undersea data transmission on a single fiber”.
Which is more or less true, depending what you compare it to. Last year, for example, NEC and Verizon achieved optical speeds of 21.7 Tbps over a 1,503-km cable.
On the other hand, earlier this year, researchers at the University of Southampton in England demonstrated optical transmission speeds of 73.7 Tbps – which is 99.7% of the speed of light itself.
To be fair, though, the Southampton team didn’t use standard glass fiber but an all-new kind of fiber made mostly of air.
No, really:
This new design enables low loss (3.5 dB/km), wide bandwidth (160nm), and latency that blows the doors off normal optic fiber — light, and thus the data, really is travelling 31% faster down this new hollow fiber. To achieve the transmission rate of 73.7 terabits per second, the researchers used wave division multiplexing (WDM), combined with mode division multiplexing, to transmit three modes of 96 channels of 256Gbps. Mode division multiplexing is a new technology that seems to involve spatial filtering — rotating the signals with a polarizer, so that more of fiber can be used
However, that technology is more likely to be utilized for short-distance apps like inside data centers, not subsea cables spanning thousands of kilometers.
And as AlcaLu points out, 31 Tbps is around three-times the capacity you can currently get on a state-of-the-art subsea fiber.
Here’s how they did it (from the press release):
The experiment leveraged Bell Labs’ pioneering work in 200 Gigabit per second (Gbps) single-carrier data channels. At such speeds and distances signal distortions and noise make data recovery very challenging. To counter this problem, in this new test Bell Labs researchers made use of innovative detection techniques and harnessed an array of technologies in modulation, transmission, and signal processing twinned with advanced error correcting coding.
The experiment used 155 lasers, each operating at a different frequency and carrying 200 Gbit/s over a 50 GHz frequency grid to dramatically enhance the performance of current WDM (Wavelength Division Multiplexing) systems, which are today being deployed with speeds up to 100G.
And there you have it.
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John C. Tanner
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