An optical fiber includes a core region and a cladding region formed on an outer circumference of the core region. The cladding region includes a plurality of holes arranged around the core region and has a refractive index lower than a refractive index of the core region. A zero dispersion wavelength of the optical fiber is shorter than 1150 nanometers. The optical fiber propagates a light having a wavelength longer than 1000 nanometers exclusively in a fundamental mode of LP.sub.01 mode. An effective core area of the optical fiber is equal to or smaller than 12.0 .mu.m.sup.2 at a wavelength of 1064 nanometers.