| 摘要 |
In an optical fiber of this invention, the MFD is increased to effectively suppress the influence of nonlinear optical effects. A method of manufacturing the optical fiber effectively prevents bubble occurrence in a transparent preform, deformation of the preform, and flaws on the preform surface during the manufacture. The optical fiber has, from its center to the peripheral portion, a first core having a first refractive index n1, a second core having a second refractive index n2 (<n1), a first cladding having a third refractive index n3 (<n2), and a second cladding having a fourth refractive index n4 (>n3, <n2). The outer diameter of the second core is set to be 25 to 40 mum. Specifically, the refractive indices of the first and second claddings of the optical fiber preferably increase in the radial direction from the inner side thereof to the peripheral side thereof. This structure is obtained by adjusting the supply amount of a fluorine material in the manufacturing process of preform regions corresponding to first and second claddings such that the contents of fluorine decreases in the radial direction.
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