In the present invention, there is provided an amplification module, particularly for cladding-pumped optical devices, comprising a coil (7) with a wound, double-sheathed active optical fiber (6) and at least one fixing means (8) for fastening the fiber to the coil. Said double-sheathed active optical fiber (6) has non-circular cross section of the inner sheath (2). The cross section of the inner sheath (2) of the double-sheathed active optical fiber (6) has changing orientation relative to the coil (7) lateral jacket. The invention further provides a process for producing the above-described amplification module, wherein a double-sheathed active optical fiber (6) with non-circular cross section of the inner sheath (2) is twisted prior winding onto a coil (7) or during winding onto the coil (7) and subsequently it is fixed to the coil (7) by at least one fixing means (8). The proposed invention can be advantageously used in various engineering fields, particularly in laser systems of high output for material treating or for medicinal laser systems