SINGLE-MODE OPTICAL FIBER AND ITS PRODUCTION METHOD

摘要

An interface region (20) is provided at the boundary between a core region (10) and a clad region (30). The refractive index of the interface region (20) decreases from the core region side toward the clad region side. The rate of change of relative index difference is found for the region where the relative index difference varies from 0.8x DELTA n to 0.3x DELTA n where DELTA n is the relative index difference of the core region (10), and normalized by the radius gamma of the core. The normalized rate of change (0.5x DELTA n)/(d/ gamma ) is used as an index for evaluation of the change of the refractive index. The lower limit of the allowable range of the normalized rate of change is determined to be 0.4%, and the upper limit thereof is determined to be 4.0%. The influence of the tailing of the profile of the refractive index and the strain in the optical fiber are reduced, thus providing a single-mode optical fiber through which low-loss optical transmission is possible.