| 摘要 |
PURPOSE:To produce a transparent material having controlled refractive index distribution, at a low cost, by immersing a porous material in a solution containing a compound having different refractive index from that of the material, allowing the compound to diffuse in the porous material, drying the product, and sintering and densifying the material. CONSTITUTION:A porous material is immersed in a solution containing a compound having a refractive index different from that of the raw material, and the compound is allowed to diffuse in the raw material to form the concentration distribution of said compound from the surface to the center. After drying the raw material impregnated with the compound, the material is sintered by slowly raising the temperature to obtain a densified transparent material having continuous refractive index distribution from the center toward the circumferential part and suitable as an optical fiber preform. The porous raw material is a dry gel prepared from a metallic alkoxide by a sol-gel method or its sintered product. The above compound effective to increase the refractive index is the hydrolyzed liquid, etc. of the alkoxide, chloride or acetate of Al, Ti, Zr, Ge, Si, Tl, Ga, Gd, Pb, etc., and the compound to decrease the index is e.g. boric acid, phosphoric acid, hexafluorosilicic acid, etc.
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