US Patent 8731357 Optical fiber

An optical fiber includes a core section and a cladding section. A k value expressed by k=4Aeff/(πMFD2) is 1.08 or larger, Aeff being an effective area and MFD being a mode field diameter, at a wavelength of 1550 nm, a chromatic dispersion is in a range from +19.0 ps/nm/km to +21.9 ps/nm/km, and MFD is in a range from 10.3 μm to 13.0 μm. The inequality, r1<r2<r3, is established, R=r3/r2 is larger than 1.0 and equal to or smaller than 5.4, and a relative refractive index difference Δ12 of the maximum value N2 with respect to the minimum value N1 is 0.05% or higher, r1 and r2 being radial positions respectively with minimum and maximum value N1 and N2 of a refractive index in the core section and r3 being a radius of the core section.