RARE EARTH ELEMENT DOPED OPTICAL FIBER AND MANUFACTURING METHOD THEREOF

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PROBLEM TO BE SOLVED : To provide a rare earth element doped optical fiber for which photo-darkening is suppressed and a manufacturing method thereof. SOLUTION : A glass particle layer 3 is formed by depositing glass fine particles on an inner surface of a quartz tube 1. The glass particle layer is heated to form a glass layer 6 and is collapsed to form a core base material. On this occasion, a rare earth element is doped into the glass particle layer 3, or a rare earth element is reduced by introducing chlorine gas into a reaction tube after the glass particle layer is formed, or both are performed so as to satisfy that "the concentration of the rare earth element in a core in the core base material after the collapse has at least a maximum value at a position between an outer peripheral surface of the core body and the core center, and the concentration decreases toward the core center therefrom and reaches a lowest point at the core center, and a ratio of the concentration at the core center to the maximum value of the concentration is 5% to 95%". COPYRIGHT : (C)2012, JPO&INPIT