NEC Achieves 50Tb Submarine Cable over 10,000km Distance

Photo: NEC (cropped)

NEC Corporation has demonstrated a transmission capacity of 50.9 terabits (Tb) per second on a single optical fiber, over a distance greater than 11,000km.

According to the company, this is the first time 50Tb have been achieved over 10,000km using C+L band erbium-doped fiber amplifiers (EDFA).

Achieving such a high capacity 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 explained.

NEC researchers developed a multilevel, linear and nonlinear constellation optimization algorithm, through which NEC obtained an optimized 32QAM (opt32) constellation that achieves close to Shannon capacity, and has a higher nonlinear capacity limit, which is more relevant to submarine transmission.

The opt32 modulation allowed NEC researchers to achieve an unprecedented spectral efficiency of 6.14 b/s/Hz over a trans-pacific distance.

In addition, C+L amplification is used to maximize the capacity per fiber pair. In order to deliver a record breaking capacity NEC’s researchers developed a patent-pending bi-directional amplifier design that reduces the effective noise figure and the device complexity.

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