| 摘要 |
PURPOSE:To obtain an optical fiber with a small loss in a longer wavelength zone by forming the 1st clad of an optical fiber with high purity SiO2, making the refractive index of the 2nd ellipsoidal clad higher than that of the 1st clad, and forming the 3rd clad having a lower refractive index than the 2nd clad. CONSTITUTION:For example, the core 1 is formed with GeO2-SiO2, the 1st clad 2 with high purity SiO2, the 2nd ellipsoidal clad 3 with GeO2+B2O3+SiO2, and the 3rd clad 4 with SiO2. The refractive index difference DELTAn1 between the core 1 and the 2nd clad 3 is about 0.5%, and that DELTAn2 between the 2nd clad 3 and the 1st clad 2 is about 0.1%. The thickness of the clad 2 is made larger than the radius of the core 1, the refractive index of the clad 2 is made lower than that of the core 1, and the refractive index of the clad 3 is made lower than that of the core 1 and higher than that of the clad 2. The 3rd clad 4 having a lower refractive index than the clad 3 is formed at the outside of the clad 3. Thus, a constant polarization type optical fiber with a small loss even in a longer wavelength zone is obtd. |
