| 摘要 |
PROBLEM TO BE SOLVED: To realize periodic transmission peak characteristics having an equal interval by providing two pieces of chirped gratings whose periods are gradually changed in parallel. SOLUTION: Diffraction grating patterns being on a mask are transcribed on the core 1 of an optical fiber 1 in which Ge is doped in order to raise a refractive index by a phase photomask method. Since neutral oxygen defects of parts which are irradiated with a light by using, for example, an excimer laser having a wavelength 240 nm as a light source are optically changed into defects called as Ge-E' centers, the refractive index is change. As a result, semipermanent diffraction gratings are formed in the core 1. A diffraction grating area 1 and a diffraction grating area 2 are totally equivalent structures and the diffraction grating is made to be a chirped structure in which periods are directively changed, for example, from 0.523 μm to 0.510 μm over from the left to the right. The total length of the diffraction grating areas is 5.6 mm. Thus, fiber gratings having transmission peaks of not smaller than 15 lines having 0.1 nm interval are obtained. |
