Alcatel breaks another world record in long-haul submarine optical transmission

Alcatel, world leader in intelligent optical networking, has achieved another world record in optical submarine optical transmission by transporting 3.65Tbps capacity (365x10Gbps) over 6 850km on a single fibre.

The unprecedented number of 365 wavelengths, each operating at 10Gbps over a distance equivalent to most transatlantic cable links, reinforces Alcatel`s leadership in submarine optical technology.

This breakthrough would allow the simultaneous transmission over a single optical fibre and across the Atlantic Ocean, of 45 million voice calls, or 552 CD-ROMs, or 35 Encyclopaedia Britannicas, or 16 high definition movies. It will enable operators and service providers to dramatically increase the capacity transported over a single fibre, thereby further optimising the cost of their networks.

The laboratory demonstration was achieved using wide bandwidth optical amplifiers and an advanced fibre map-an innovative assembly of fibres which optimises transmission quality over all wavelengths. The particular combination of fibres used allowed Alcatel researchers to squeeze wavelengths to a spacing of 22.2GHz between channels, less than half the International Standard of 50GHz, hence allowing the unprecedented number of 365 wavelengths.

Consequently, this gave a spectral efficiency (which measures how effectively one is using the bandwidth) of 0.45-bits/Hz-substantially better than today`s value of 0.2-bits/Hz. The remarkable combination of the high spectral efficiency with a large optical bandwidth of 66nm produced the high throughput achieved in this experiment.

This demonstration also significantly contributes to Alcatel`s objective of producing simpler and cheaper global networks by improving the integration between terrestrial and submarine systems. Indeed, it was achieved with NRZ modulation format (Non Return to Zero) for the information modulation instead of the more complex modulation formats normally utilized for submarine transmissions. NRZ format is commonly used in terrestrial networks-therefore this laboratory result opens a bridge between the technology used for submarine applications and those utilized for terrestrial applications.

"This world record confirms Alcatel as a key innovator in submarine network technology. Alcatel`s continuous breakthroughs in R&D allow the company to prepare next-generation solutions in order to provide its customers with the highest performance and lowest cost," said Bernard Le Mou"el, CTO of Alcatel`s Optics Group. "Furthermore, due to its end-to-end optics R&D and its complete technology portfolio, Alcatel is the sole supplier able to offer seamless solutions for terrestrial and submarine infrastructures."

The "fibre map" is like an Underground map of the types of fibre used in the end-to-end link. The fibre type is changed periodically along the link so that on average all the wavelengths travel at the same speed, or experience the same dispersion. (Dispersion: the fact that different wavelengths travel at different speeds in materials such as glass or water, results in rainbows from water droplets or as light passes through a prism.)

This is important for even a single channel contains a small spread of wavelengths and too much dispersion would result in pulses spreading out in time. Over 6 000 to 7 000 km the spreading could become so great that one pulse merges into the next. One cannot use fibre with no dispersion, for this creates interference between different channels; it occurs because with no dispersion the pulses in different wavelengths all travel together and get the maximum time to interact due to non-linear effects. Choosing a "fibre map" with different dispersive fibres avoids all the wavelengths from travelling together; the mixture (of positive and negative dispersions) results in close to zero average dispersion, which avoids too much individual pulse spreading.