Submarine cables get simpler, faster

Uhm, what do they mean?

You don't need to convert the signal to amplify it, there are optical amplifiers now.

Are they talking about dispersion? I'm not sure if that's even a problem at dispersion compensated fibers (you take one fiber with "positive" dispersion, and a matching fiber with "negative" dispersion and put them in series so the effects cancel each other out).

So what have they actually achieved?

Eh? According to wikipedia (yeah, I know...):

"The current laboratory fiber optic data rate record, held by Bell Labs in Villarceaux, France, is multiplexing 155 channels, each carrying 100 Gbit/s over a 7000 km fiber.[26] Nippon Telegraph and Telephone Corporation has also managed 69.1 Tbit/s over a single 240 km fiber (multiplexing 432 channels, equating to 171 Gbit/s per channel).[27] Bell Labs also broke a 100 Petabit per second kilometer barrier (15.5 Tbit/s over a single 7000 km fiber)."

http://en.wikipedia.org/wiki/Optical_fiber

So okay that was in a lab but where does the need for repeaters come in /at all/?

There's nothing new here

And it's misleading. The big problem to go any significant distance is attenuation and that's a fundamental problem that doesn't go away with a fancy product name :-)

Attenuation a problem?

Hi Terranesia,

attenuation sure is basic, but can be reduced by using better fibre quality, and (the fibre permitting) the initial signal can be strengthened. Remember those old telegraph lines across the Atlantic used several hundred Volts. Not sure what optical signal strength this Ciena kit can operate with (really not my field), but if they really can lay a cable that's just a cable and has no added repeaters, it'll doubtless save some money. Also remember those repeaters have to be powered, which adds running cost.

Attenuation is a problem

Hi Alan Brown, Rustident Spaceniak

Attenuation is the problem that limits how long the cable can be. Multiple vendors now offer the DSP that means the dispersion of a cable to be compensated (equalised) allowing thousands of kilometers with no inline dispersion compensation. Loss on the other hand limits you at best to several hundreds of kilometers before an optical amplifier is needed if you wanted to do something like a cable link from an island to a mainland. Crossing something like the Atlantic requires an optical amplifier every 50km or so due to noise considerations. There's no way around it.

Since the Atlantic was mentioned - if you assume something like 6500km of a cable route between Cornwall and New York and a state of the art loss of about 0.15dB/km you still have 1000dB of attenuation which is 100 orders of magnitude. To convert from optical to electrical I need to detect a signal of about 10 microWatts in NY. Therefore I would need to launch something like 10 to the power of 95 Watts to overcome the fibre attenuation. Give that our sun is outputting about about 10 to the power of 26 Watts you can see how big the attenuation problem is and how the DSP can't address that problem. We can probably argue about an order of magnitude or two in my above hand waving, but we're not going to find the missing 70 or so orders.

If we are just confining ourselves to shorter island hopping systems, then the cable is on the continental shelf and and still needs plenty of steel armouring to protect against drag fishing nets, anchors and so forth. This completely dominates the weight of the cable compared to any in-line repeater housings, so again the article is misleading.

EDFA

Erbium doped fibre amplifier

magically turns green LED light, powered by simple auxiliary DC feed in the cable, into noiseless laser amplification of even densely packed IR carrier beams (wavelength division multiplexing), independently of the modulation scheme - upgrade both ends to 200GB/s, whatever, and you're done. .