Method of manufacturing an optical fiber preform

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PROBLEM TO BE SOLVED : To provide an optical fiber preform facilitating control of concentrations of rare earth elements, having a large effective cross section (A) and suppressing occurrence of nonlinear optical effects effectively in fiber amplifiers and fiber lasers and a method of producing an optical fiber preform suitable for production of the optical fiber.SOLUTION : A method of producing an optical fiber preform whose core is added with a rare earth element(s) comprises : a step of depositing glass fine particles based on silicon dioxide and containing no phosphorus in a quartz tube by the MCVD method; a step of adding a rare earth element and aluminum to the glass fine particles in the quartz tube by an immersion method; a step of heating the quartz tube while causing a phosphorus-containing gas to flow in the quartz tube to sinter the glass fine particles while adding phosphorus; and a step of heating the quartz tube added with the rare earth element, aluminum and phosphorus to collapse.