The main areas of research were related to experimentation in the use of various impurities in optical fibres to achieve specified parameters of the generated radiation. The composition of the material of active fibre lightguides includes ions of elements possessing optical transitions, and additional impurities correcting the refractive index and the spectral characteristics of the material. The creation of fibre lasers required the development of special optic fibres with a double cladding. The active medium of a fibre laser is a single-mode quartz core doped with an active rare-earth impurity, as well as impurities that form the profile of the refractive index. A fibre laser consists of the following main structural elements: a pumping source, a fibre amplifier —— active fibre doped with active matter, in which radiation is generated, and a resonator. Active fibre lightguides as a radiation amplification medium have a number of features in comparison with traditional laser crystals and glasses.