The invention relates to a hard cladding rare-earth-doped
optical fiber and a preparation method thereof. The hard cladding rare-earth-doped
optical fiber comprises a core layer, a
quartz cladding and a
fluorine-doped cladding which are arranged from inside to outside in the radial direction, wherein the core layer is doped with
rare earth ions; and the
refractive index of the
fluorine-doped cladding is gradually increased from inside to outside in the radial direction. The part playing a light limiting role in the
fluorine-doped
quartz layer of the hard cladding
optical fiber is mainly the part closest to the
quartz cladding, so that in the embodiment, the fluorine-doped quartz layer is optimized, that is, the fluorine-doped cladding is designed into a form that the
refractive index of the fluorine-doped cladding is gradually increased from inside to outside in the radial direction, and during manufacturing, high-concentration
doping is carried out on the innermost side to ensure that the
fluorine doping concentration meets the requirement, so that the light limiting requirement of the optical
fiber can be met, and meanwhile, the
fluorine doping amount is gradually reduced towards the outer side instead of carrying out high-concentration
doping on the whole fluorine-doped cladding, so that the manufacturing difficulty of the fluorine-doped tube can be reduced.