RARE-EARTH ADDED FLUOROPHOSPHATE FIBER

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PROBLEM TO BE SOLVED : To provide an optical fiber of non-quartz-based glass in which a fiber loss is low, and which can fusion-bond on a vertical cut face to a quartz fiber, and also can be used as an amplification medium of an L-band optical amplifier practical in a low nonlinearity. SOLUTION : This optical fiber is a fluorophosphate fiber having a double clad at one core and surrounding it, with an added rare earth to at least core glass, when refractive indexes of a core, a first clad and a second clad are n1, n2 and n3, a relationship of n3≥n1>n2 holds true, and the refractive indexes of a quartz glass-made fiber to be connected, the core, and first clad glass are identical within 0.2% and a yield temperature of glass is equal to or more than 450°C. The outside second clad has a cross-sectional area which occupies 70% or more with respect to a fiber cross-sectional area, and has a composition not containing an alkaline earth. COPYRIGHT : (C)2009, JPO&INPIT