| 摘要 |
PURPOSE: Provided is a rod-in-tube optical fiber preform, which permits drawing of optical fiber having desired properties without using any additional heating step before a fiber drawing step, and provides solutions to problems of additional cost, stress induction and increased breakability. CONSTITUTION: The overclad optical fiber preform(10) is suitable to be set in the inlet of a vertical optical fiber drawing furnace having an inside high-temperature zone. The preform(10) comprises a core rod(18), an outer overclad tube(20) having an opened terminal formed to be introduced into the inlet of the drawing furnace and a tube axis, and a fixed plug(22) secured to the vicinity of the terminal. The core rod(18) is disposed in the inner part of the outer overclad tube(20) in the axial direction, so that the bottom end of the rod(18) is prevented from moving downwardly by the plug(22), when the terminal end of the tube(20) is introduced into the inlet and dropped into the high-temperature zone of the furnace.
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