There is provided at low cost an optical fiber suitable for wavelength division
multiplex transmissions that has strengthened the tolerance to bending loss at
even smaller bending diameters. The present invention is an optical fiber whose
base material is silica glass and that has a two layer structure formed by a core
that has a substantially uniform refractive index and by a cladding that is located
outside the core and that has a substantially uniform refractive index, wherein
the optical fiber satisfies the following conditions (1) to (3): (1) an outer diameter
of the core is in a range of 4 to 8 m, and a relative refractive index difference
of the core is in a range of 0.4 to 0.8%; (2) chromatic dispersion at a wavelength
of 1550 nm is in a range of 2 to 15 ps/nm/km; and (3) effective area at a wavelength
of 1550 nm is 40 m2 or more.
