| 摘要 |
PROBLEM TO BE SOLVED: To provide the double-clad fiber, in which exciting light injected into a first clad is efficiently coupled to a core and which hardly necessitates labor, time and costs for manufacturing, and an optical amplifier and fiber laser using it. SOLUTION: In this double-clad fiber, a first clad 2 is provided with two or more linear reflecting surfaces 4, and the directions of those reflecting surfaces 4 to a core 1 are changed at an optional place in the transmitting direction of light. The first clad 2 is provided with two or more linear reflecting surfaces 4, the first clad 2 is twisted around the rotation symmetrical axis X of the core 1, and whereby the direction of the reflecting surfaces 4 to the core 1 are changed at an optional place in the transmitting direction of light. The first clad 2 and the core 1, the first clad 2 and a second clad 3 or all of the first clad 2 and the core 1 and the second clad 3 are twisted around the rotation symmetrical axis X of the core 1, and whereby the directions of the reflecting surfaces 4 to the core 1 are changed at an optional place in the transmitting direction of light. Either of the double-clad fibers is used in the required place of a light amplifier. Either of the double-clad fibers is used in the transmittable optical fiber of a fiber laser while laser oscillating exciting light. |
