| 摘要 |
PURPOSE:To obviate the decrease in the refractive index of a stress imparting part and the decrease in the insertion loss and to make stable production of the above coupler by adding fluorine to the clad part to provide the refractive index nearly equal to the refractive index of B2O3 to the clad part. CONSTITUTION:The fluorine is added to the SiO2 glass of the clad part 14b by which the refractive indices of the clad part 14b and the stress imparting part 15 added with the B2O3 are nearly equaled. The coefft. of thermal expansion of the clad part 14b added with the fluorine does not increase as compared with the coefft. of thermal expansion of the SiO2 glass and, therefore, the difference in the coefft. of thermal expansion between the clad part 14b and the stress imparting part 15 is prevented from decreasing. The need for adding an additive for adjusting the refractive index such as GeO2 to the stress imparting part 15 of the base material for the optical fiber is, therefore, eliminated. The polarization maintaining optical fiber type optical coupler of a low insertion loss is economically produced with good reproducibility at a high yield. |
