Grating optical fiber, and optical fiber base material suitable for grating

摘要

A grating optical fiber comprises a core, a first clad layer formed around the core, and a second clad layer formed around the first clad. Germanium is doped in the core, while germanium and fluorine are doped in the first clad layer. Gratings are formed on both the core and the first clad layer. The difference between the indexes of refraction between the first and second clad layers is smaller than the difference between the indexes of refraction between the core and the first clad layer.