Disclosed is an optical transmission line having a length L of 30 km to 150
km, preferably 30 km to 70 km, an absolute value of a dispersion not
smaller than 8 ps/nm/km at a wavelength of 1.55 .mu.m at every point of
the optical transmission line, a maximum accumulated dispersion not larger
than 7.5.times.L (ps/nm) at a wavelength of 1.55 .mu.m, and a dispersion
for the entire optical transmission line of -5 to +5 ps/nm/km at a
wavelength of 1.55 .mu.m. The optical transmission line is formed by, for
example, combination of a positive dispersion optical fiber and a negative
dispersion optical fiber.
