| 摘要 |
PROBLEM TO BE SOLVED: To provide a coated optical fiber which can maintain good transmission characteristics at low temperature even when the fiber includes a glass fiber having poor bending strength. SOLUTION: The coated optical fiber 1 consists of, successively from the center, the glass fiber 11, a primary layer 12 and a secondary layer 13. The glass fiber 11 essentially comprises quartz glass with addition of impurities such as Ge and F elements in a specified distribution and has a core region having a high refractive index and a clad region having a low refractive index. Each of the primary layer 12 and the secondary layer 13 is made of, for example, a UV-curing resin. The resin of the primary layer 12 has 0.03 to 0.10 kg/mm2 Young's modulus at normal temperature. The tear strength of the primary layer 12 at 0 deg.C is 1.0 to 7.0 kg/mm. The adhesion strength between the glass fiber 11 and the primary layer 12 at 0 deg.C is 100 to 800 g/cm.
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