| 摘要 |
PURPOSE:To equalize the bulk densities of fine grain layers and to produce the preform having a stabilized specific refractive index between the core and clad by monitoring the surface temp. of the fine glass grain deposit and controlling the amt. of a gas to be supplied into the burner. CONSTITUTION:A rod 1 is rotated, plural burners 3 and 4 are traversed in the axial direction of the rod 1, and a gas is supplied at a specified flow rate to deposit fine quartz glass grains. The temp. of the surface layer 21 of the grains formed by the preceding burner 3 is measured by a radiation thermometer 31, etc., and the temp. of the surface layer 22 of the fine glass grains formed by the succeeding burner 4 is measured. The amt. of the gas to be supplied to the preceding burner 3 is adjusted in each traverse so that both temps. are equalized, and the bulk density of the entire grain layer is uniformized. The fine glass grain layer is placed in a heating furnace and dehydrated, then the furnace is filled with a high-temp. gaseous fluorine atmosphere to vitrify the layer, and a fluorine-doped Si layer is obtained. As a result, an optical fiber preform in which the refractive index in the clad is not fluctuated is obtained. |
