| 摘要 |
A refractory dielectric body is heated with a plasma torch at conditions which do not result in substantial removal of a surface portion of the body, yet which are sufficient to reduce both surface and bulk impurities. Typically, the body is solid, e.g., a rod as opposed to a tube, and is treated with the plasma in the absence of simultaneous deposition of material onto the body. Advantageously, an isothermal plasma torch is utilized, and the torch advantageously produces an oxygen or oxygen-containing plasma. The invention is useful for reducing chlorine impurities by at least about 30% to a depth of at least about 10 mu m, with accompanying reduction of hydroxyl impurities. The invention thus provides a useful method for reducing the concentration of impurities that contribute to imperfections during the process of drawing fiber from an optical fiber preform, without requiring substantial removal of the surface of the preform.
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