Disclosed is a nonlinear dispersion-shifted optical fiber, wherein a
charomatic dispersion at a wavelength of 1550 nm is equal to a set value
required for optical signal processing utilizing a nonlinear phenomenon, a
dispersion slope at a wavelength of 1550 nm falls within a range of 0.001
to 0.1 ps/nm.sup.2 /km, a margin of fluctuation of the charomatic
dispersion in a longitudinal direction of the optical fiber at a
wavelength of 1550 nm falls within a range of 0.01 to 3 ps/nm/km, and a
nonlinear constant n.sub.2 /A.sub.eff at a wavelength of 1550 nm is not
smaller than 15.times.10.sup.-10 /W.
