| 摘要 |
PROBLEM TO BE SOLVED: To prevent generation of breakage at both ends of an optical fiber bundle, caused by elongation of the length of a parent conduit in order to improve the yield of a conduit. SOLUTION: Plural number of triple optical fibers 3 are housed, together with fused glass in a jacket pipe 2 arranged within a high pressure furnace 1 and are heated by a heating device, so that a temperature at the both ends of the triple optical fibers 3 is lowered by 5-20 deg.C compared with a temperature at the optical part of the same. Whereupon, first the triple optical fibers at the central part are fused, air bubbles generating at that time are pushed away towards the both ends, and the inside of the jacket pipe 2 is in the evacuated state. Then, the air bubbles are finally discharged from the both ends of the triple optical fiber bundle into the jacket pipe 2, and the air bubbles are will not be contained in the obtained parent conduit.
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