| 摘要 |
PURPOSE:To reduce the bulk density of a porous preform, to facilitate the OH group removal, and to decrease the volatilization of dopants, by hydrolyzing glass powder with an oxyhydrogen flame comprising a large amount of steam at a reduced gas temperature. CONSTITUTION:H2 and steam are fed into the third layer 102 of the four-layer burner 10 to form the oxyhydrogen flame 34 comprising a large amount of steam and to reduce the gas temperature. The size of the glass particles 36 is reduced to give the porous preform 26 of low bulk density, which is then vitrified by the heater 28 in the H2 atmosphere together with OH group removal. The low bulk density of the porous preform permits easy removal of the OH groups, and the low gas temperature reduces the volatilization due to the disproportionation of dopants, particulaply GeO2. According to the method, the high-quality basic material 30 for optical fiber with a low OH group content can be obtained. |
