| 摘要 |
PURPOSE:To easily produce an optical fiber, etc., at a good yield even if the difference in the coefft. of expansion between a core and a clad is large. CONSTITUTION:After a first melt is poured from an injection port 2a and is filled in casting molds 4, 6 at a proper temp., a second melt is poured to partially fill the casting mold 2. The volume of the melts shrink and the second melt flows into the center of the first melt when the temps. of these melts fall. A base material 12 of a step index type is thus obtd. A heater is thereafter disposed around the base material 12 exposed by separating the central part casting mold 4 to the left and right to heat the base material without cooling the base material 12 down to room temp. The lower casting mold 6 is pulled downward after proper heating. A fiber preform of a desired diameter is obtd. by the softening by arising the temperature of the base material 12. Since this fiber preform is small in diameter, the crack, etc., occurring in the difference in the coefft. of expansion when the first and second melts are vitrified hardly arise. |
