The state-of-the-art silica glass optical fibres can carry light signals over tens of kilometres with very low optical loss and provide high-capacity communication networks. However, their brittleness, low stretchability and energy intensiveness make them less suitable for local short-range applications and devices such as automotive, digital home appliances, fabrics, laser surgery, endoscopy and implantable devices based on optical fibres. The sustainable solution to these may be found within biopolymer-based optical fibres.
Schematic illustration of a light coupled optical fibre and photographs of methylcellulose-based optical fibers under ambient light and UV light. Image credit: Ville Hynninen and Nonappa
'The wide availability of cellulosic raw materials provides an excellent opportunity to unravel the hidden potential of renewable materials for practical applications through sustainable fibre processing routes,' says Associate Professor Nonappa, whose research team at Tampere University is developing biopolymer-based optical fibres for short-distance applications.
Conventionally, the polymer or plastic optical fibres are used for short-distance applications, but their processing may involve relatively high temperatures and the use of hazardous chemical treatment.
'By using methylcellulose hydrogel, we have shown that optical fibres can be produced at room temperature using a simple extrusion method without any chemical crosslinkers. The resulting fibres are highly transparent, mechanically robust, flexible and show low optical loss,' Nonappa states.
Biopolymer-based optical fibres suitable for multifunctional sensors
In addition to pure light signal transmission, the methylcellulose optical fibres can be feasibly modified and functionalized.
'The hydrogel matrix allows straightforward addition of various molecules and nanoparticles without compromising the mechanical properties or light propagation abilities of the fibres making them suitable for multifunctional sensors', says doctoral researcher Ville Hynninen, the first author of the paper.
For example, incorporating an extremely low mass fraction of protein-coated gold nanoclusters produced luminescent optical fibres, and acted also as a fibre-based toxic metal ion sensor.
Overall, the presented results and the abundance of cellulosic derivatives and raw materials encourage further research and optimization of cellulose-derived optical components and devices.
Source: Aalto University