Provided is an optical fiber that is in particular suitable for Raman
amplification. An effective area at a wavelength of 1570 nm is in a range
of 35 .mu.m.sup.2 to 45 .mu.m.sup.2, an absolute value of a dispersion
slope at the wavelength is equal to or less than 0.04 ps/nm.sup.2 /km, and
a dispersion value at the wavelength is in a range of 5 ps/nm/km to 10
ps/nm/km. It is desirable that a refractive index profile contains at
least one annular region between a center core and a cladding region.
