| 摘要 |
PURPOSE:To reduce residual air bubbles and to decrease an optical loss by incorporating dopant having lowering activity of the vitrescence temp. on to the piled layer of the base plate. CONSTITUTION:On to the base plate A, fine particles of glass are piled by flame piling method and piled layers B, C are formed successively. When the piled up layer C is vitrescent transparently by doping with Ge and Ti, the difference of the refractive index is produced between the core layer C' and the clad layer B'. Namely, an optimum vitrescence temp. (Tc) of the piled layer C are different from each other to be Tc<Ta, and in the case of forming the piled layer C, other than the main dopant of Ge and Ti effective for increasing the refractive index, the other auxiliary dopant capable of lowering the vitrescence temp. of the piled layer are simultaneously doped. Consequently, the optimum vitrescence temp. of the formed piled-layer C is changed from Tc to Tc- T and is dropped lower than Tc. By this means, the residual air bubbles are reduced and the reduction of the optical loss is attained. |
