| 摘要 |
PURPOSE:To eliminate easily the propagated light in the clad layer, by forming two clad layers and by adding the light absorbent to the outside clad layer and by making the refractive index of the outside clad layer higher than that of the inside clad layer. CONSTITUTION:The second clad layer 23 of the glass having the refractive index higher than that of quartz tube 24 is provided in quartz tube 24, and the first clad layer 22 of the glass having the refractive index higher than that of tube 24 and lower than that of the second clad layer 23 is provided inside the second clad layer 23, and the core of the glass having the highest refractive index is provided inside the first clad layer 22, and the additive which absorbs the introduced undesired transmission light is added into the second clad layer. By this constitution, undesired light beam 28 which does not make the critical angle in the interface between the core and the first clad layer is absorbed into the second clad layer 23. Core 21 is formed with the glass consisting of SiO2 and GeO2, and the first clad layer 22 is formed with the glass consisting of SiO2 and P2O5, and the second clad layer is formed with the glass consisting of SiO2, GeO2 and B2O3. |
