Characterisation techniques for special optical fibres
Special optical fibres are introduced with the emphasis on rare-earth-doped fibres and fibres with crystal-like properties. Characterisation techniques for these types of fibre are discussed and several applications are described. In particular, optical time-domain reflectometry is used to demonstrate a distributed temperature sensor based on the temperature dependence of the absorption in rare-earth-doped fibres. Further, energy transfer between ytterbium and erbium is characterised and an erbium fibre laser sensitised with ytterbium is demonstrated. Finally, techniques for the creation of crystal-like properties in optical fibres are developed and second-order nonlinear phenomena in these fibres are analysed both experimentally and theoretically.