| 摘要 |
PURPOSE:To make the fluorine content uniform and to reduce unevenness in refractive index, by forming a porous preform for a clad on the surface of a vitreous substrate for a core, treating the preform with gaseous fluorine, and converting the substrate and the resulting porous preform contg. fluorine into transparent glass. CONSTITUTION:A porous preform 3 for a clad is formed on the surface of a quartz glass rod 1 for a core by feeding H2, O2, SiCl4 and BF3 to the 1st burner 2 and by moving the rod 1 upward while rotating. H2, O2 and CF4 are then fed to the 2nd burner 4 to treat the preform 3 with reactive gaseous fluorine. The rod 1 and the resulting porous preform 3 contg. fluorine united in a body 5 are converted into transparent glass by heating in a helium atmosphere. |
