Nanoparticle doping – a method of fabrication of highly efficient rare-earth-doped silica fibres for fibre lasers

Silica optical fibres doped with rare-earths ions are key components of photonics devices like fibre lasers and fibre amplifiers operating in near-infrared spectral region. Since rare earths in silica glass cause clustering and phase separation, the silica glass matrix must be modified, e.g. by alumina. Since starting materials of such components are available only in solid state, conventional chemical vapor deposition methods (like the MCVD method) used for telecom fibre production and based on starting materials in gaseous (or liquid) state had to be modified. This paper deals with “nanoparticle-doping” method by which high-quality thulium-doped and holmium-doped preforms for specialty optical fibre drawing can be prepared. An easy implementation of the nanoparticle-doping method into established technologies belongs to its strong points. High dopant concentration up to 10 mol% of alumina and thousands of ppm of rare earths (and high alumina/rare-earth ratio up to 50/1) distributed homogeneously in preforms (fibres) in macro-, micro- and nano- scale can be achieved by the proposed way. Fibre lasers based on such fibres exhibited low threshold, high slope efficiency (up to 64 % in case of thulium-doped fibre lasers and 80% in case of holmium-doped fibre lasers) and high output power (Watts in case of thulium-doped fibre lasers and tens of Watts in case of holmium-doped fibre lasers).