Competence Center for Specialty Optical Fibers

While satellite-based internet connectivity has been a recent hot topic, most of the global internet traffic passes through intercontinental Silica-based fibre-optic cables that span many thousands of kilometres. The unrelenting growth in demand for internet bandwidth and the need for redundancy means significantly more undersea cables are required [1]. Such cables, based on current silica-based fibres, are expensive to manufacture, to install, and to operate. Despite the transmission losses of Silica-based fibres being very low – ~0.15 dB/km and very close to the intrinsic material loss of ~0.12 dB/km – the signal strength after ~100 km of propagation is very weak [2]. Multiple amplifiers are therefore embedded into the cables to repeatedly boost the signal, with each fibre requiring its own chain of dedicated amplifiers. Significant electrical power is also needed to power the amplifiers, adding to the cost [3]. A promising alternative to Silica-based fibres are fibres based on fluoride glasses like Zirconium fluoride-ZrF4, Barium fluoride-BaF2, Lanthanum fluoride-LaF3, Aluminium fluoride-AlF3, and Sodium fluoride-NaF (ZBLAN) glass. The theoretical intrinsic loss of ZBLAN is 20 times lower at ~0.006 dB/km [4]. This means that a fully developed ZBLAN-based fibre-optic cable would only require amplifiers every ~2000 km. Some connections, such as between Australia and New Zealand, can therefore be amplifier-free, which significantly reduces the cost while allowing near-limitless scalability. While ZBLAN development is ramping up rapidly, several major challenges must be overcome to achieve its full potential. One such challenge is the tendency for ZBLAN glass to form microcrystals during the heating process of fibre fabrication. Such crystals induce scatter within the fibre, resulting in higher losses. Earlier studies using parabolic flights have suggested that gravity plays a significant role in crystal formation, with crystallisation suspected to be reduced in micro-gravity conditions [5]. To further study this phenomenon and take advantage of this, Flawless Photonics developed a space-compatible miniaturised fibre draw system, which was installed on the International Space Station (ISS). This automated production system allowed the fabrication of different fibre compositions with different parameters. It requires minimal interaction by astronauts. In this 2024 mission, multiple lengths of ZBLAN fibres were fabricated. The total length fabricated was almost 12 km, with the longest continuous length of fibre being 1141 m. The fibres produced were successfully returned to Earth and more than 2 km of fibre were analysed by multiple institutions across the globe.