NEC Corporation has successfully conducted the very first transmission capacity of 50.9 terabits on a single optical fiber - over a distance of more than 11,000 kilometres.

To accomplish the task, the company used C+L band erbium-doped fiber amplifiers, known as EDFA. They helped to boost the fiber's capacity distance product to 570 petabits per second-kilometer.

The company is working towards pushing up the ‘benchmark' capacity of 50Tb across trans-Pacific distances, in order to increase the reach of ultra high-capacity submarine cable segments.

“Achieving such a high capacity, even with extremely wide bandwidth EDFAs, requires efficient use of the bandwidth at a level that is close to the Shannon limit, the fundamental spectral efficiency limit of optical communications,” the company says in a statement.

The Shannon limit is the estimated maximum transfer rate of any communications medium. The company says there are ways to design systems to get close to that limit in a linear regime, but this does not always work with nonlinear regimes. This is due to performance gaps.

In order to solve the problem, NEC researchers developed what they call a ‘multileveal, linear and nonlinear constellation optimization algorithm' - essentially something that can reach the Shannon limit, but can also reacher a higher nonlinear capacity limit.

The company says the new modulation format is easier to implement as there is no iterative decoding or non-uniform coding. This is what allowed the company to exceed the maximum efficiency.

C+L amplification can maximize the capacity per fiber pair. The company also developed a bi-directional amplifier design that reduces effective noise figure and device complexity.