The new method has the potential to reduce the costs of long-distance fiber optic communications since the signals would not have to be electronically boosted on their journey, which is important when the cables are buried underground or on the ocean floor.
Since the technique can correct transmitted data if it is damaged or distorted during transmission, it could also help increase the usable capacity of the fibers. This is done right at the end of the link, at the receiver, without having to introduce new components into the link itself. Increasing capacity in this way is important because optical fibers carry 99% of all data, and demand is increasing with greater internet usage. This demand cannot be met by the current capacity of the fibers, and replacing receivers is much cheaper and easier than re-rotating the cables.
To cope with this increased demand, more information is being sent using the existing fiber optic infrastructure with different light frequencies, creating data signals. The large number of light signals being sent can interact with each other and become distorted, causing errors in the received data.
The study, published in Scientific Reports and sponsored by the EPSRC, reports a new way to improve transmission distance by reducing interactions between different optical channels as they travel side-by-side over an optical cable.
One of the biggest global challenges we face is how to maintain communications with the booming demand for the Internet - overcoming the capacity limits of fiber optic cables is a big part of the solution to that problem.
Professor Polina Bayvel
The study's author, Dr. Robert Maher (UCL Electronic & Electrical Engineering), said: "By eliminating interactions between optical channels, we are able to double the distance signals that can be transmitted without errors, from 3,190 kilometers to 5,890 kilometers, which is the largest reported increase for this system architecture. The challenge is to design a technique to simultaneously capture a group of optical channels, known as a super-channel, with a single receiver. This allows us to eliminate distortion by sending the data channels back on a virtual digital path at the same time.".
The researchers used a 16QAM super-channel made up of a set of frequencies that could be encoded 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 novel signal processing techniques developed by the team, enabling the reception of all channels simultaneously and without error. The researchers will test their new method on denser super-channels commonly used in digital cable television (64QAM), cable modems (256QAM), and Ethernet connections (1024QAM).
