| 摘要 |
PURPOSE:To manufacture a polarization-maintaining fiber having excellent characteristics, in high reproducibility, by inserting stress-imparting glass rods in the longitudinal grooves applied to the outer circumference of a core glass rod to be used as the preform, inserting the core glass rod into a quartz tube, and carrying out the melt-spinning of the composite. CONSTITUTION:The glass core 15 having high refractive index is covered with the glass rod 17 having a glass portion 16 having lower refractive index than the core 15. A pair of grooves 18 having axial symmetry are applied to the outer circumference of the glass rod 17. The groove 18 has the shape and dimension to accept the stress-imparting rod 19 with close clearance, and has preferably polished surface. A stress-imparting glass rod 19 (having higher thermal expansion coefficient than the quartz glass to be used as the sheath) is inserted in each groove 18, and the assembly is inserted in a quartz glass tube 20. The composite is subjected to the melt-spinning preferably evacuating the space in the quartz glass tube 20 to obtain a polarization-maintaining fiber 21 having a pair of stress-imparting parts 23 at both sides of the core part 22. |
