FIELD: physics.
SUBSTANCE: invention relates to lasers and optical amplifiers and is intended to improve characteristics of waveguides. Disclosed is a waveguide for a single-mode fibre laser, comprising an active fibre and a passive fibre, wherein the active fibre has an octahedron cross-section with a central part in the form of a strand doped with luminescent ions of a rare-earth element, and a polymer shell with a layer of quartz glass doped with fluorine. Passive quartz glass fibre is doped with fluorine and has a polymer cladding, wherein the refraction index of the passive fibre is less than the refraction index of the cladding of the active fibre by 3×10-3, at that, on the preselected section of the waveguide, the passive fibre in the sections at the beginning and at the end of the section has a large diameter and in the middle section a small diameter, and the active fibre in the sections at the beginning and at the end of the section has a small diameter and in the middle section a large diameter, wherein the active fibre is configured to accommodate a portion of a larger diameter between portions of a smaller diameter of the passive fibre to form optical and mechanical contact in the middle portions of the fibres, which are flat.
EFFECT: high efficiency of pumping energy delivery from the passive fibre to the active fibre and reduced signal loss.
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