An optical fiber for an optical network is disclosed. The optical fiber includes a core having a core region having a first refractive index N.sub.1, and a refractive index depressed region surrounding the core region and having a second refractive index N.sub.2 that is lower than the first refractive index. A clad surrounds the core and having a third refractive index N.sub.4. The optical fiber has a zero-dispersion wavelength that is not less than 1555 nm and positioned in a wavelength range which does not exceed L-band. The optical fiber has negative dispersion values in C-band and positive dispersion values in L-band.