Optical fiber

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PROBLEM TO BE SOLVED : To obtain an excitation mode of basic mode, and to ensure that the gain of signal light in higher-order mode is equal to or higher than the gain in basic mode. SOLUTION : In an optical fiber having a step refractive type index distribution mainly composed of silica glass and having a core and a cladding, when a concentration of a rare earth element in a range of radius a3 from the center of core is denoted by d1, and the concentration of a rare earth element in a range of radius a2 from the radius a3 of the core is denoted by d2, it is ensured that the gain in the higher-order mode of signal light propagating through the optical fiber is equal to or higher than the gain in the basic mode by selecting the value of d1/d2 suitable for the value of a2/a1. COPYRIGHT : (C)2014, JPO&INPIT