“There were three ways we could go,” he recalled, “continue with coax, use waveguides or move to fibre. It was very apparent that optical fibre was going to be the winner.” The first subsea optical cable came into use in 1985; a 140Mbit/s link between the UK and Belgium, laid following trials of the technology across a Scottish loch. Since then, fibre optic technology has leapt ahead. “The line rate has gone from 144Mbit/s to 155, 622, 2.5Gbit/s and 10G,” said Barnes. “Today, we supply technology that supports 100G per wavelength, with Gbres capable of supporting more than 100 wavelengths.” But the rapid increase in line rate – eight generations – has not been accompanied by a similar improvement in 14 April 2015 www.newelectronics.co.uk I t might seem like submarine communication is a relatively new fangled idea, but no; the Grst cable to link the UK and the US came into operation around 1860, carrying telegraphy. Since those heady days, submarine cables have been the way to link callers on different continents and, more recently, to carry the vast amounts of data spawned by the internet. While communication satellites are available, they handle much less than 10% of all trafGc. But it is only in the last 30 years or so that submarine cables have come into their own and the reason is Gbre optics. Before that, all data travelled over coaxial cable. Those of a certain age will recall the difGculty of making a transatlantic call and the message that ‘all circuits are busy; please try again later’. The reason was that coaxial cable had a maximum bandwidth of 45Mbit/s, equating to around 6000 voice calls. The cable was already more than 40mm in diameter and increasing the bandwidth would have required it to be even larger, leading to greater cost and handling issues. Today’s Gbre optic cables – less than 20mm in diameter – can handle up to 200million voice circuits per Gbre pair and they may have up to eight Gbre pairs. Even with that capacity, submarine Gbre optic cables are coming under pressure as the volume of data spirals. Xtera is one of the leading companies in the Geld. Stuart Barnes, general manager of the company’s UK operations, is a submarine communications veteran, having cut his teeth at STC Submarine Cables in Greenwich. He said that, by 1980, it was obvious that coaxial cable had run out of steam. “We were trying to squeeze the last drop of performance from the technology,” he recalled. Meanwhile, work was well underway at STC’s Research Labs in Harlow into the use of Gbre optics for communications – work that would win Dr Charlie Kao the Nobel Prize in Physics 2009 ‘for groundbreaking achievements concerning the transmission of light in Gbres for optical communication’. It made sense, in Barnes’ opinion, to see whether that work could be used in the submarine world. Xtera is deploying a new optical amplifier to increase the bandwidth of EDFA repeaters to 55nm 14 Pushing towards the limits Submarine fibre optic cables have enabled modern international communications, but can photonics help to alleviate bandwidth problems? By Graham Pitcher.
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Transcript
“There were three ways we could go,” he recalled,
“continue with coax, use waveguides or move to fibre. It was
very apparent that optical fibre was going to be the winner.”
The first subsea optical cable came into use in 1985; a
140Mbit/s link between the UK and Belgium, laid following
trials of the technology across a Scottish loch.
Since then, fibre optic technology has leapt ahead. “The
line rate has gone from 144Mbit/s to 155, 622, 2.5Gbit/s
and 10G,” said Barnes. “Today, we supply technology that
supports 100G per wavelength, with Gbres capable of
supporting more than 100 wavelengths.”
But the rapid increase in line rate – eight generations –
has not been accompanied by a similar improvement in
14 April 2015 www.newelectronics.co.uk
It might seem like submarine communication is a
relatively new fangled idea, but no; the Grst cable to
link the UK and the US came into operation around
1860, carrying telegraphy.
Since those heady days, submarine cables have been
the way to link callers on different continents and, more
recently, to carry the vast amounts of data spawned by the
internet. While communication satellites are available, they
handle much less than 10% of all trafGc.
But it is only in the last 30 years or so that submarine
cables have come into their own and the reason is Gbre
optics. Before that, all data travelled over coaxial cable.
Those of a certain age will recall the difGculty of making a
transatlantic call and the message that ‘all circuits are busy;
please try again later’. The reason was that coaxial cable
had a maximum bandwidth of 45Mbit/s, equating to around
6000 voice calls. The cable was already more than 40mm in
diameter and increasing the bandwidth would have required
it to be even larger, leading to greater cost and handling
issues. Today’s Gbre optic cables – less than 20mm in
diameter – can handle up to 200million voice circuits per
Gbre pair and they may have up to eight Gbre pairs.
Even with that capacity, submarine Gbre optic cables are
coming under pressure as the volume of data spirals.
Xtera is one of the leading companies in the Geld. Stuart
Barnes, general manager of the company’s UK operations, is
a submarine communications veteran, having cut his teeth
at STC Submarine Cables in Greenwich.
He said that, by 1980, it was obvious that coaxial cable
had run out of steam. “We were trying to squeeze the last
drop of performance from the technology,” he recalled.
Meanwhile, work was well underway at STC’s Research
Labs in Harlow into the use of Gbre optics for
communications – work that would win Dr Charlie Kao the
Nobel Prize in Physics 2009 ‘for groundbreaking
achievements concerning the transmission of light in Gbres
for optical communication’. It made sense, in Barnes’
opinion, to see whether that work could be used in the
submarine world.
Xtera is deploying a
new optical
amplifier to increase
the bandwidth of
EDFA repeaters to
55nm
14
Pushingtowards the limits
Submarine fibre optic cables have
enabled modern international
communications, but can photonics
help to alleviate bandwidth problems?
By Graham Pitcher.
ampliGer technology. “There have only been two generations
of optical repeater,” Barnes pointed out, “regenerative and
then the optically ampliGed repeater.”
Regenerative systems required ‘three Rs’ in each
repeater – reamplifying, reshaping and retiming the signal.
“It was an optical to electrical to optical process,” he
explained. Each device was spaced roughly 50km apart on a
transatlantic cable and built using discrete components on
rigid boards. Not only did they have to deal with the data
passing through, they also had to withstand the high
pressure of being on the seabed, which brought mechanical
issues into play.
Tony Frisch, senior vp of Xtera’s repeater business unit
www.newelectronics.co.uk 14 April 2015
and another subsea veteran, added: “There were about 10
ICs per Gbre pair in the regenerator, along with four lasers –
two for each direction – two integrated receivers and a few
discrete components. All these were mounted on
specialised boards. And we also needed to handle Gbres,
electrical connections and power.”
One thing common to cables now and then is power.
Barnes said: “You need 25kV DC to power a long
transoceanic cable and half of that power is lost in the
cable.” Frisch added: “We still push about 1A through the
cable and still need several kV, depending on the length of