New technique doubles error free transmission distance for subsea optical cables

A team of researchers has demonstrated new way to process fibre optic signals that could double the distance at which data travels error-free through transatlantic sub-marine cables.

The UCL research reveals that the new method has the potential to reduce the costs of long-distance optical fibre communications as signals wouldn't need to be electronically boosted on their journey, which is important when the cables are buried underground or at the bottom of the ocean.

As the technique can correct the transmitted data if they are corrupted or distorted on the journey, it could also help to increase the useful capacity of fibres. This is done right at the end of the link, at the receiver, without having to introduce new components within the link itself.

Increasing capacity in this way is important as optical fibres carry 99percent of all data and demand is rising with increased use of the internet, which can't be matched by the fibres' current capacity, and changing the receivers is far cheaper and easier than re-laying cables.

To cope with this increased demand, more information is being sent using the existing fibre infrastructure with different frequencies of light creating the data signals. The large number of light signals being sent can interact with each other and distort, causing the data to be received with errors.

The study reports a new way of improving the transmission distance, by undoing the interactions that occur between different optical channels as they travel side-by-side over an optical cable.

Study author Robert Maher said that by eliminating the interactions between the optical channels, they are able to double the distance signals can be transmitted error-free, from 3190km to 5890km, which is the largest increase ever reported for this system architecture.

Maher added that the challenge is to devise a technique to simultaneously capture a group of optical channels, known as a super-channel, with a single receiver. This allows them to undo the distortion by sending the data channels back on a virtual digital journey at the same time.

The study is published in Scientific Reports.