The invention relates to a method of manufacturing an active optical fibre having a cladding and a doped core, as well as the active optical fibre equipped with the cladding and the doped core. The active optical fibre according to the invention is adapted to conduct and generate radiation having a wavelength λ and is provided with a cladding and a core containing at least one active dopant, characterised in that the core comprises elongate elements made of a first type of glass having a first refractive index n1 and elongate elements of a second type of glass having a second refractive index n2, oriented along the optical fibre and forming a compact bundle, wherein transverse dimensions of the elongate core elements are smaller than ⅕ of the wavelength λ. Such optical fibres are used in laser generation and in amplification techniques.