A new way to process fibre optic signals has been demonstrated by UCL researchers, which they say could double the distance at which data travels error-free through sub-marine cables. The technology is also being tested on other fibre communications systems that support home and office networking.
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 it is corrupted or distorted while travelling, it can also help to increase the useful capacity of fibres. The UCL technology is used 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 99 percent of all sub-marine data, and demand is rising with increased use of the internet, which can't be matched by the fibres' current capacity. Changing the receivers is far cheaper and easier than re-laying cables.
Currently, to cope with increased demand, more data is being sent using the existing fibre infrastructure with different frequencies of light creating the data signals. But the large number of light signals being sent can interact with each other and distort, causing the data to be received with errors.
A study published in Scientific Reports and sponsored by the EPSRC (Engineering and Physical Sciences Research Council) demonstrates 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 Dr Robert Maher, of University College London Electronic & Electrical Engineering, said: "By eliminating the interactions between the optical channels, we are able to almost double the distance signals can be transmitted error-free, from 3,190km to 5,890km, which is the largest increase ever reported for this system architecture."
He said: "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 us to undo the distortion by sending the data channels back on a virtual digital journey at the same time."
The researchers used a "16QAM super-channel" made of a set of frequencies which could be coded using amplitude, phase and frequency to create a high-capacity optical signal. The super-channel was then detected using a high-speed "super-receiver", and new signal processing techniques developed by the team enabled the reception of all the channels together and without error.
The researchers now plan to test their new method on denser super-channels commonly used in digital cable TV (64QAM), cable modems (256QAM) and Ethernet connections (1024QAM).
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