Large-mode-area active optical fiber and preparation method thereof

The invention provides a large-mode-area active optical fiber, which comprises a fiber core, a first cladding, a second cladding and a third cladding, wherein the first cladding, the second cladding and the third cladding sequentially encircle the periphery of the fiber core; the effective refractive index of the second cladding is lower than the effective refractive indexes of the first claddingand the fiber core; a pump core area encircles the outer side of the third cladding; an external cladding encircles the outer side of the pump core area and comprises a layer of air vent holes or capillary bars doped with quartz glass; and the effective refractive index of the external cladding is lower than that of the pump core area. On the premise of ensuring a large mode area of the active optical fiber, the optical fiber suppresses amplified spontaneous radiation, improves the stability of the optical fiber, and ensures the quality of light beam. The invention also provides a preparationmethod of the active optical fiber. By adopting a liquid phase multi-point doping mode of gas-phase aluminum doping and rare-earth ions, continuous doping for many times can be flexibly controlled and realized, the size of a rare-earth doped core bar is greatly increased, and uniform doping of the rare-earth ions and aluminum is simultaneously realized.