Disclosed are an optical fiber preform, a preparation method therefor, and a plasma deposition device. According to the method, by means of fluorine-doped sintering, a fluorine-doped distribution with an inner cladding layer gradient is formed, and the preparation process difficulty of viscosity matching between a core layer, an inner cladding layer and an optical cladding layer, especially viscosity matching on the boundary of the core layer and the optical cladding layer, can be solved; meanwhile, a constrained diffusion distribution of each layer of fluoride in a powder rod is realized, and the refractive index requirement of each layer is ensured; and the stress problem of a large-thickness fluorine-doped layer can be effectively solved by means of the synchronous implementation of fluorine-doped deposition and stress relief, and the phenomenon whereby the thicker the fluorine-doped layer, the more prone same is to cracking is avoided.
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