APPARATUS FOR COATING OPTICAL FIBER

PROBLEM TO BE SOLVED: To provide an apparatus for coating an optical fiber in which a coating material is concentrically applied and the thickness of the coating material can be equalized. SOLUTION: A die for coating comprises an insert having high heat conductivity larger than 1 W/(cm.K). The insert is preferably made of diamond having a heat conductivity of 5-20 W/(cm.K). Since most of viscosity decrease of the coating material occurs in a part very close to the inside wall in the land region of the die, heat generated by the viscosity decrease of the coating material can efficiently be dissipated by using the insert of high heat conductivity. The insert also diminishes temperature difference between both side walls facing the fiber down to a negligible level when the fiber is off the center, and therefore enables a situation widely performed in drawing the fiber at low speed and consequently force making the fiber approach the center satisfactorily to be regained and recovered, respectively.