| 摘要 |
PURPOSE:To obtain optical fiber having a large difference of specific refractive index between a core and a clad by adjusting a bulk density of a core corresponding part at the outermost peripheral part to be higher than the bulk density of internal part, and heat-treating a heaped body in an atmosphere contg. F-contg. gas for a certain period in a stage for making the heaped body transparent by heating. CONSTITUTION:O2 and H2 are ejected by feeding the gas from a feeding port 4 and 5, respectively, using a multicore tube burner 3A, 3B. At the same time, SiCl4 as feed gas, GeCl4 as dopant gas, etc. are fed through a feeding port 7 together with Ar gas as carrier gas. A reaction is thus caused, and simultaneously, shielding Ar gas is fed through a feeding port 6, causing successive deposition of fine glass particles from a tip end of a starting base material 8 toward an axial direction. Thus, a bulk density of a core corresponding part at an outermost peripheral part is adjusted to a larger bulk density than that of the internal part by elevating a surface temp. Then, obtd. soot base material is heated, if necessary in an atmosphere contg. Cl2, then heated for at least a specified period at 1,150+ or -150 deg.C in an atmosphere contg. F-contg. gas. Thus, F is added easily to only a clad corresponding part. |
