OPTICAL FIBER, LASER DEVICE USING THE SAME, AND METHOD FOR MANUFACTURING OPTICAL FIBER

To provide an optical fiber that can change the outer diameter of light with a desired mode, a laser device using the optical fiber, and a method for manufacturing an optical fiber.SOLUTION: An optical fiber 10 includes: a first core 11; a first clad 21 surrounding the outer peripheral surface of the first core 11, the first clad having a lower index of refraction than that of the first core 11; a second core 12 surrounding the outer peripheral surface of the first clad 21, the second core having a higher index of refraction than that of the first clad 21; and a second clad 22 surrounding the outer peripheral surface of the second core 12, the second clad having a lower index of refraction than that of the first clad 21, the outer diameter of the second clad 22 being uniform in a longer direction. The optical fiber further includes a first optical fiber part as a part in a longer direction and a second optical fiber part as another part in a longer direction, the second optical fiber part leading to one side of the first optical fiber part. The difference of the relative index of refraction to the first clad 21 of the first core 11 and the second core 12 in the second optical fiber part is smaller than the difference of the relative index of refraction in the first optical fiber part.SELECTED DRAWING: Figure 3 【課題】所望のモードの光の外径を変化させ得る光ファイバ、これを用いたレーザ装置、及び光ファイバの製造方法を提供する。【解決手段】第１コア１１と、第１コア１１の外周面を囲い第１コア１１より屈折率が低い第１クラッド２１と、第１クラッド２１の外周面を囲い第１クラッド２１より屈折率が高い第２コア１２と、第２コア１２の外周面を囲い第１クラッド２１より屈折率が低い第２クラッド２２と、を有し、第２クラッド２２の外径が長手方向において一定である光ファイバ１０は、長手方向の一部分である第１光ファイバ部分と、長手方向の他の一部分であり第１光ファイバ部分の一方側に連続する第２光ファイバ部分と、を含み、第２光ファイバ部分における第１コア１１及び第２コア１２の第１クラッド２１に対する比屈折率差は、第１光ファイバ部分におけるこの比屈折率差より小さい。【選択図】図３