| 摘要 |
PURPOSE:To control the concentration distribution of a dopant easily and accurately in preparing a base material for optical fibers by the vapor phase axial deposition method, by using a raw material gas containing a radioisotope of the dopant in addition to the raw material gas containing the dopant for controlling the refractive index. CONSTITUTION:Bubblers 1, 2 and 3 containing SiCl4, <65>GeCl4 and <68>Gecl4respectively are controlled by valves 11, 12 and 13, 21, 22 and 23, and 31, 32 and 33 to feed the SiCl4 and <68>GeCl4 at first to a burner 4 and cause a high-temperature hydrolytic reaction in an oxyhydrogen flame to form SiO2 and <68>GeO2. A fine glass powder containing the <68>GeO2 is then stuck to the lower end of a seed rod 6, which is then pulled upward while rotated to grow a porous preform 7 in the axial direction thereof. The concentration distribution of the <68>GeO2 in the preform 7 is then sensed by a radiation sensor 91, and necessary adjustment is carried out based on the sensed results. The raw material gas of the <68>GeCl 4 is then changed over to the raw material of the <65>GeCl4. |
