| 摘要 |
PURPOSE:To produce the titled preform having good dimensional accuracy in a simple process without requiring a mandrel, by preparing a porous glass rod for a core, forming a porous glass body for a clad on the surface thereof, dehydrating the resultant composite porous glass preform and heating the dehydrated preform at a high temperature. CONSTITUTION:A gas 5 consisting of oxygen, hydrogen and glass raw materials for a core, e.g. SiCl4, GeCl4, etc., is introduced into a burner 4 for the core to deposit fine glass particles 22 formed in the burner flame on the tip of a rotating starting member 23 and produce a cylindrical porous glass rod 21 for the core. A gas 7 consisting of oxygen, hydrogen and glass raw material for a clad having a lower refractive index than that of the glass raw materials for the core is introduced into a burner for the clad to form fine glass particles 24 for the clad in the flame. The fine glass particles 24 for the clad are then deposited on the above-mentioned glass rod 21 for the core to form a porous glass body 25 for the clad and produce a composite porous glass preform 26, which is then dehydrated in a high-temperature atmosphere containing a dehydrating agent, e.g. chlorine based gas, etc., and heated at a high temperature to produce the aimed transparent glass preform. |
