Touch of glass

UK university team develops new production process for hollow-core optical fibres, which could lead to faster IT solutions. Siobhan Wagner reports

Researchers from Bath University have developed next-generation optical fibres that they claim could lead to faster and more powerful computing and telecommunications technologies.

The technology is the result of a change in the fabrication procedure which cuts the production time of hollow-core optical fibres from around a week to a day, reducing the overall cost.

Jonathan Knight from the Centre for Photonics and Photonic Materials at Bath’s Department of Physics said the development challenges both the conventional design and production of optical fibres.

‘We have a new design for the fibre, but to manufacture that design we needed to completely revise our fabrication procedure,’ he said.

In standard optical fibres, light travels in a small cylindrical core of glass running down the fibre length. Hollow-core fibres provide better performance, but fabricating the special kind of fibre needed to guide light down an air hole is difficult. Also, until now, the fibres worked for only a limited range of wavelengths.

The new procedure shows how a tiny change to these fibres — narrowing the wall of glass about the large central hole by just 100 nanometres (a 10 millionth of a metre) — broadens the range of wavelengths that can be transmitted. This was achieved by omitting some of the most difficult steps in the fabrication procedure.

The researchers began fabricating their fibre by slowly feeding a high purity tube of glass into a furnace at 2,000ºC. They then quickly pulled it out at the bottom.

‘When you do that, you end up with capillaries, which are about a millimetre in diameter but look the same in their cross section as the original tube — just a bit smaller,’ said Knight.

The team drew a few hundred capillaries and laid them down horizontally on a stacking jig, which holds them in place to form a 2D stack. A gap was left in the middle of the capillaries to form the hollow core. The stack was then pushed inside a second tube and that, too, was put in the furnace at 2,000ºC until it formed a fibre.

‘All the little holes that were in the original tubes became a microstructured cladding and the large hole we left became the core,’ said Knight.

Traditionally, hollow cores are created by inserting an extra tube in the middle of a fibre. Knight said the team discovered this extra tube decreased the performance of the fibres, by limiting the bandwithand increasing the dispersion of light.

The new fibre’s superiorperformance means it could have a significant impact in a wide range of fields. Knight said this will make it especially useful for the delivery of laser pulses, and his group is now working with a UK ultra-short pulse laser system producer. ‘We are interested in developing fibres that the company could put into its products to help improve the performance of its lasers,’ he said.

Future applications could include spectroscopy, biomedical and surgical optics, laser machining, the automotive industry and aerospace.

‘Using light rather than electrical circuits to carry information will make optical fibres many times more powerful and bring much closer the day when information technology will consist of optical devices rather than less efficient electronic circuits,’ said Knight.’