Cutting costs in optical fibres
Hollow-core optical fibres can be manufactured in a day rather than a week by changing their structure, reducing the overall cost of fabrication, according to scientists at Bath University, UK. They believe this could lead to faster and more powerful optical telecommunications, laser machining, and cheaper generation of X-ray or ultra-violet light for use in biomedical and surgical optics.
Rodrigo Amezcua Correa, post-doctoral researcher on the project at Bath, explains, ‘[Traditional] state-of-the art hollow-core fibres are formed using a 2D array of circular capillaries stacked around a thin-walled core tube. Additional solid rods are inserted into the interstitial holes (formed between three capillaries that touch each other) to create the required strands of glass, joined and supported by thin silica webs in the final fibre’. The 2D-pattern of capillaries around the core traps and guides light.
The process developed at Bath reduces the number of fabrication steps by eliminating the core tube and extra glass in the interstitial holes. Instead the core is created by omitting seven capillaries, and the structure is inflated using pressure.
‘Inflation leaves bigger strands at the interstitial sites, joined by thinner webs to create the photonic bandgap,’ adds Correa.
‘Omitting the core tube results in a core wall thickness just half that of the struts in the cladding, suppressing the surface modes. Our new fibres can [therefore] guide light over broader wavelength ranges and reduce the dispersion and dispersion slope by a factor of almost two, the lowest yet reported for hollow core photonic bandgap fibres. We want to extend this design for fibres with larger and smaller cores sizes.’
The research has been conducted as part of a collaborative industry-academic EU Framework 6 project – NextGenPCF – to create a hollow-core optical fibre gas sensor for methane detection in mines and landfill sites.
Correa says, ‘Hollow-core photonic bandgap fibres are a relatively new technology. They have a greater damage threshold, and reduced nonlinearity and dispersion properties [than standard optical fibres], allowing exciting propagation of light’.
Professor Jonathan Knight from the Centre of Photonics and Photonic Materials at Bath adds, ‘In standard optical fibres, light travels in a small cylindrical core of glass running down the fibre length. The glass limits [performance] in many ways. For example, [it] can be damaged if there is too much light [and the material] causes short pulses of light to spread out in a blurring effect that makes them less defined. Fibres in which light travels in air down a hollow core hold great promise’.