PROBLEM TO BE SOLVED: To provide a multi-core optical fiber which is high in mechanical reliability for achieving lateral irradiation in a long range, and for obtaining desired light quantity distribution in a longitudinal direction, and for achieving manufacturing with simple working.SOLUTION: A multi-core optical fiber 1H includes, at its top end, a top end working section 11 in which a plurality of groove sections 12, 13 and so on going around its periphery with cross-sections almost V-shaped are formed. The groove sections 12 and 13 and so on include: vertical faces 12a, 13a and so on formed almost vertically to cores 1d on which at least a portion of the plurality of cores 1d are opened and inclined faces 12b, 13b and so on configured to reflect the rays of light emitted from the cores 1d opened on the first faces to the outside of a multi-core optical fiber 1H. The respective groove sections 12, 13, and so on are formed so that at least a portion of the cores 1d can be opened, the cores 1d which being arranged at the more central side of the multi-core optical fiber 1H than the cores 1d opened on the vertical faces of the groove sections adjacent to the groove sections at the rear end side of the top end working section 11 among the plurality of cores 1d.COPYRIGHT: (C)2012,JPO&INPIT【課題】長い範囲の側方照射を実現し、かつ長手方向に所望の光量分布が得られ、しかも簡易な加工で作製でき、機械的な信頼性が高いマルチコア光ファイバを提供する。【解決手段】マルチコア光ファイバ1Hは、その先端において、その周囲を周回する断面略V字形状の溝部12,13,…が複数形成された先端加工部11を備え、溝部12,13,…は、コア1dに対して略垂直に形成され、複数のコア1dの少なくとも一部が開口する垂直面12a,13a,…と、この第1面に開口したコア1dから出射した光をマルチコア光ファイバ1Hの外側に向けて反射する傾斜面12b,13b,…とを有し、各溝部12,13,…は、複数のコア1dのうち、先端加工部11の後端側において当該溝部に隣接する溝部の垂直面に開口したコア1dよりもマルチコア光ファイバ1Hの中心側に配置されたコア1dの少なくとも一部を開口するように形成されている。【選択図】図11
