Gain optical fiber with double-clad fluoride and its preparation method

A gain optical fiber with a double-clad fluoride, comprising a fiber core, a D-shaped inner cladding, an outer cladding, and a polymer coating, wherein the fiber core, the D-shaped inner cladding, and the outer cladding each are a fluoride glass material, and the polymer coating is a fluorinated ethylene propylene copolymer,

• a raw material composition of the fluoride glass material of the fiber core is ZrF4—BaF2—LaF3—YF3—AlF3—LiF—PbF2—ErF3—NH4HF2, a raw material composition of the fluoride glass material of the D-shaped inner cladding is ZrF4—BaF2—LaF3—YF3—AlF3—LiF—NH4HF2, and a raw material composition of the fluoride glass material of the outer cladding is ZrF4—BaF2—LaF3—YF3—AlF3—NaF—NH4HF2,
• glass transition temperatures of a material of the fiber core, the D-shaped inner cladding, the outer cladding, and the polymer coating increase in turn,
• the fiber core and the D-shaped inner cladding are prepared by a suction injection method, and the D-shaped inner cladding is polished into a D-shaped structure, and the outer cladding is prepared by a core insertion casting method to form an optical fiber preform with a D-shaped double-clad fluoride and draw an optical fiber.