Making fast pipes faster

26 May 2011

In March, two separate research groups from Japan presented breakthroughs in terabit data transmission at the Optical Fiber Communications (OFC) conference in Los Angeles.

Dayou Qian of NEC claimed to have achieved a data-transmission rate of 101.7 Tbps through 165 kilometres of fiber. According to New Scientist:

He did this by squeezing light pulses from 370 separate lasers into the pulse received by the receiver. Each laser emitted its own narrow sliver of the infrared spectrum, and each contained several polarities, phases and amplitudes of light waves to code each packet of information.

At the same conference, the National Institute of Information and Communications Technology in Tokyo said it had achieved a total throughput of 109 Tbps by using a fiber with seven light-guiding cores (today’s optical fibers just use one such core), with each core running 15.6 Tbps.

"We introduced a new dimension, spatial multiplication, to increasing transmission capacity," Jun Sakaguchi told New Scientist.

Well, stand back.

Earlier this week, Nature Photonics published research from a group of German, Swiss and UK scientists who managed to achieve data speeds of 26 Tbps over 50 kilometers of single-mode fiber – on just a single laser. (The 100+ Tbps demos at OFC used multiple lasers.)

The secret? They used OFDM (the same modulation-scheme technology that powers LTE, Wimax and the 802.11a/g/n flavors of Wi-Fi) to generate 325 optical frequencies within a narrow spectral band of laser wavelengths, according to ABC News.

Dr Juerg Leuthold from the Karlsruhe Institute of Technology bills it as the fastest line rate ever achieved using a single light source.

As is always the case with new optical speed records, the speeds don’t translate into anything close to commercial deployment for a long time, not least because they don’t cover a lot of distance (although NICT says its hundred-terabit multicore fiber technology will likely find a home first in massive data centers used by the likes of Google and Amazon).

That’s probably as well, as the world’s core network operators are still working their way up to 100G waves in their optical systems. And the frequent exabyte predictions from Cisco Systems notwithstanding, we’re probably still at least half a decade away from requiring 26 Tbps worth of capacity per laser.

However, it’s worth mentioning that one of the key breakthroughs in the OFDM-powered 26-terabit demo isn’t the speed so much as the energy efficiency gains that come with using just one laser to achieve it, according to Professor Ben Eggleton, director of the Centre for Ultrahigh bandwidth Devices for Optical Systems at Sydney University, who told ABC News that as broadband data usage increases – which in Australia will be driven by the rollout of the NBN – so will energy consumption:

Professor Eggleton says the internet consumes vast amounts of energy; eating up about 2 per cent of Australia's energy budget.

"[Energy consumption] is growing at the same rate that internet traffic is growing. It's doubling every 18 months, which means that in 10 years we've got a real crisis," he said.

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