An optical communication system has a configuration in which an optical transmission
line is laid between a repeater (transmitter) and another repeater (receiver).
The optical transmission line is formed by fusion-splicing a first optical fiber
on the upstream side and a second optical fiber on the downstream side. The first
optical fiber has a transmission loss of 0.25 dB or less, and an effective area
of 80 m2 or above (preferably 100 m2 or above),
at a wavelength of 1550 nm, which is the wavelength of signal light. The second
optical fiber is connected to the downstream end of the first optical fiber and
has positive dispersion regions and negative dispersion regions which are alternately
arranged along the longitudinal direction and whose chromatic dispersions at a
wavelength of 1550 nm are positive and negative, respectively.
