Active optical fiber for ultrahigh-power laser and preparation method of active optical fiber

The invention relates to an active optical fiber for an ultrahigh-power laser and a preparation method thereof, and belongs to the technical field of active optical fibers and preparation methods thereof. Comprising a core layer, an inner cladding, an outer cladding and a protective layer which are sequentially arranged from inside to outside, the edge refractive index of the core layer is n < 10 >, the center refractive index of the core layer is n < 11 >, the edge refractive index n < 10 > of the core layer is larger than the center refractive index n < 11 > of the core layer, the refractive index of the inner cladding layer is n < 2 >, and the edge refractive index n < 10 > of the core layer is larger than the refractive index n < 2 > of the inner cladding layer; the core layer comprises silicon dioxide and rare earth doping elements, the rare earth doping elements comprise, by mole, 4%-10% of aluminum, 0.3%-1.0% of ytterbium and 4%-10% of phosphorus, and the concentration of the rare earth doping elements