Glass powder doping of nanocrystal-doped fibres Challenges and results

Incorporating new optical materials as nanocrystals into glass fibres for new functionalities has recently become a hot research topic. Our team (funded by the European FET Open project NCLAS) investigates the introduction of nanoscale laser crystallites into the core of optical fibres using the glass powder doping method. Active Y2O3:Pr3+ nanocrystals (NCs) were prepared via different synthesis methods, and structurally and spectroscopically characterized. After modification of technological parameters, the optimised NCs have been proposed as a luminescence centres to embed into germanate and silicate glass hosts. Glasses were analysed in terms of optical (transmission, refractive index matching to NCs) and thermal (thermal stability, viscosity, thermal expansion coefficient) parameters. Crystallisation issues during fibre drawing were particularly investigated. In a first step, glass powder-NCs mixing techniques and fibre preform preparation were developed. It was shown that temperature cycle profiles including dwell time and heating/cooling ramp rates influenced the glass-NCs properties and can lead to glass crystallisation or NCs dissolution. The sintering investigations pointed out the melting temperature limits to preserve active NCs in the glasses. In germanate glasses, Y2O3:Pr3+ dissolution was noticed at 800 degrees C. In the case of the silicate glass compositions these regions vary from 700 degrees C to 1050 degrees C. The results allowed to select optical fibre drawing conditions performed by the powder-in-tube method. Their distribution uniformity is not yet sufficient, requiring further optimisation of the drawing kinetics.

Automated summary

Incorporating new optical materials as nanocrystals into glass fibres for new functionalities is a hot research topic. This study investigates the introduction of nanoscale laser crystallites into the core of optical fibres and analyzes the structural and spectroscopic characteristics of these nanocrystals. The optical and thermal parameters of the glasses are analyzed and the drawing conditions of the optical fibres are selected. However, further optimization of the fibre drawing process is needed to improve its distribution uniformity.