Hollowed-out optical fibres promise big boost for internet infrastructure

Optical fibres, the cornerstone technology for high-speed data transfer, can be given a significant performance boost by hollowing out their centre, researchers from Southampton University have discovered.

 Optical fibres, which are made of silica glass, have long been the transmission medium of choice for high-speed optical communications as well as for other uses such as sensing oil and gas installations, structural monitoring for railways and bridges and medical endoscopes.

Due to scattering of the light inside the glass, a fraction of the transmitted power is lost, a process known as attenuation. This power loss worsens as the wavelength of light is shortened. This higher transmission loss through the fibre poses a serious limitation to the performance of all applications that require shorter wavelengths.

Researchers have now demonstrated that guiding light through air-filled fibres offers a potential way to overcome this attenuation limit set by the glass’s scattering.

They created three different hollow-core fibres, with losses comparable to or lower than that achieved in solid glass fibres around technologically relevant wavelengths of 660, 850, and 1060 nanometres.

The lower attenuation in a fibre that guides light through air offers the potential for advances in quantum communications, data transmission, and laser power delivery, the team believe.

Professor Francesco Poletti, from Southampton University, said: “Many alternative glass types and waveguide technologies have been investigated since the 1970s to try to solve this problem, all to no avail.”

“Our findings show that hollow-core fibres have the potential to outperform the current optical fibres at various wavelengths used in optical technology today. Not only do they have lower attenuation, they can also withstand higher laser intensities, such as those needed to melt rocks and drill oil wells, as well as produce more efficient lasers for manufacturing.”

The hollow-core fibres can also transmit undistorted laser pulses with peak power levels so high that they would be unusable if transmitted by standard glass fibres, and preserve the polarisation of light needed to produce more accurate sensors and imaging endoscopes.

The hollow-core fibres have been in development for a decade and work by confining light in the central void thanks to thin glass membranes surrounding the core.

Their first fibres had attenuations of 5dB, or around 30 per cent of light transmission, for every metre of fibre. Continuous development has allowed the team to produce fibres that improve this by a factor of 10,000 by achieving an attenuation of only 5dB every 10 kilometres.

Professor Poletti continued: “The technology we are developing has the potential to underpin the development of faster data centres with shorter delays for the end user, more accurate gyroscopes for interplanetary missions, more efficient laser-based manufacturing, to name but a few.”

The team believes their new cables could enable faster, more reliable internet infrastructure with larger bandwidth than the current cables allow.