| 摘要 |
PROBLEM TO BE SOLVED: To provide a preform for a single mode optical fiber which is suitable for a system using an optical amplifier and which has a small dispersion of a polarization mode, and to provide a single mode optical fiber. SOLUTION: The preform for a single mode optical fiber has a core having the center refractive index n1 and a clad having the refractive index n0 around the core. The refractive indices of the core and the clad have the relation of n1>n0. When the max. refractive index n2 in the part of the core where the refractive index increases in the radial direction from the center to the outside and the change rate P of the refractive index in the radial direction passing the core axis have the relation of P(θ)=(n2(θ)-n0)/(n1-n0)/(n1-n0)×100(%), wherein P(θ) and n2(θ) are values of P and n2 respectively, in the direction at an angleθfrom the axial center of the core, the max. change rate Pd (the difference between the max. and the min.) of the change rate P of the refractive index around the preform is <=30%. The center refractive index n1 of the core and the max. refractive index n2 have the relation of n1<n2 or n1>n2. |
