UC San Diego Researchers Break Fibre Transmission Record

Researchers in the US claim to have developed a new method that increases the maximum data transmission rates of a fibre optic cable, potentially paving the way for faster broadband speeds in the future.

A team of photonic experts at the researchers the University of California, San Diego (UCSD) were able to boost the maximum power (and therefore distance) at which signals can be transmitted through fibre.

Using current techniques, transmissions deteriorate once a power threshold is reached due to signal distortions known as “crosstalk”, caused by the different channels of information interfering with each other. This means the signal is unrecognised by the receiver at the end of the connection and electronic generators must be used to extend reach, hampering speeds.

Fibre speeds

“With fibre optics, after a certain point, the more power you add to the signal, the more distortion you get, in effect preventing a longer reach.” Explained Nikola Alic, a research scientist from the Qualcomm Institute. “Our approach removes this power limit, which in turn extends how far signals can travel in optical fibre without needing a repeater.”

To remedy this, researchers deployed “frequency combs” that predicted such crosstalk in advance, allowing the receiver at the end of the fibre link to reverse the distortion. Using this technique, the team successfully decipher a signal even after it travelled along a record 12 kilometres of fibre cable using only standard amplifiers and no repeaters.

Experiments involved three or five optical channels, but the researchers say it could be used in systems with far more. For example, most modern fibre cables use more than 32 such channels.

Change the channel

“Crosstalk between communication channels within a fiber optic cable obeys fixed physical laws. It’s not random,” added Stojan Radic, a professor in the Department of Electrical and Computer Engineering at UCSD and senior author of the study. “We now have a better understanding of the physics of the crosstalk. In this study, we present a method for leveraging the crosstalk to remove the power barrier for optical fibre.”

The development could have an impact on broadband, landline, cellular and cable services where much attention has been paid towards improving the ‘last mile’ speeds of networks.

For example, BT hopes to provide speeds of at least 500Mbps on a copper connection to much of the UK within the next decade, while providers like CityFibre, TalkTalk and Sky are working on extending fibre to the home to enable 1Gbps speeds for businesses and consumers.

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