3D printing has potential to cut cost of optical silica fibres

Australian and Chinese engineers develop method for printing optical silica preforms that can be drawn into fibres

it’s no exaggeration to say that optical silica fibres are among the most important materials for the world economy. High-speed Internet depends on them, and therefore so do many of the financial transactions that underpin stock markets. However, making them is a labour-intensive and precise process.

The new technique, developed by a research team led by John Canning of the University of technology in Sydney, collaborating with Gang-Dean Peng’s team from University of New South Wales and colleagues from Harbin Engineering University and Yanshan University in China produces a preform from optical silica that can be drawn into fibres using a much simpler and cheaper procedure.

optical fibre
Researchers used a 3D printing method known as direct-light projection (DLP) to make silica fibre preforms. They fabricated preforms for a step index fibre (a) and a structured preform (b). These preforms were then placed in a draw tower (middle picture) to make the final optical fibre (right). The orange inset shows a cross section of a step index fibre. Image:John Canning, University of Technology in Sydney

“Making silica optical fibre involves the labour-intensive process of spinning tubes on a lathe, which requires the fibre’s core or cores to be precisely centered,” explained Canning. “With additive manufacturing, there’s no need for the fibre geometry to be centered. This removes one of the greatest limitations in fibre design and greatly reduces the cost of fibre manufacturing.”

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Canning and his collaborators describe their research in the Optical Society journal Optics Letters. The research builds on earlier work in which the team is a polymer material to demonstrate drawing fibres from a 3D-printed preform, but expanding technique to silica required considerable additional innovation: notably the need for a temperature of more than 1900°C to 3D print glass.

The team used a commercially available direct light projection 3D printer, which is normally used to polymerise photo-reactive monomers, and loaded it with silica nanoparticles along with monomer at greater than 50 per cent by weight. They then printed a cylindrical object hollow core, which they subsequently filled with a similar mix of the same monomer and silica nanoparticles, but in this case adding germanosilicate dopant to the mixture to increase the refractive index.

Having produced the preform, they then performed a heating step to remove the polymer binding agent, leaving the nanoparticles held together by intermolecular forces. Raising the temperature further fused the nanoparticles together into a solid structure. This could then be heated and pulled in a draw tower to create optical fibres.

Initial experimentation produced fibres that had high light-loss characteristics, but the team has identified cause of these losses and is working to address them.

“The new technique worked surprisingly well and can be applied to a range of glass material processing to improve other types of optical components,” said Canning. “With further improvements to limit the light losses, this new approach could potentially replace the conventional lathe-based method of making silica optical fibres. This would not only reduce fabrication and material costs but also lower labour costs because training and hazards are reduced.”