Abstract: The present invention is related to a chromatic dispersion compensating module which realizes signal transmission at a high bit rate by its simple constitution, and an optical transmission system comprising the same. The chromatic dispersion compensating module according to the present invention comprises a chromatic dispersion compensator which compensates for the chromatic dispersion of an optical fiber transmission line at a predetermined wavelength, and a temperature controller which controls the temperature of the chromatic dispersion compensator in such a manner to set the chromatic dispersion of the chromatic dispersion compensator at a desired value. By this constitution, the dispersion compensation control in correspondence with the chromatic dispersion fluctuation in the optical fiber transmission line caused by the temperature fluctuation and the like is made possible.

Abstract: The present invention relates to an optical transmission line enabling WDM communications in a wide signal light wavelength band centered at a wavelength of 1.55 &mgr;m, in which nonlinear optical phenomena are less likely to occur; and an optical fiber constituting a part of the optical transmission line. The optical fiber has a dispersion D (unit: ps/nm/km) and a dispersion slope S (unit: ps/nm2/km) satisfying the conditions of −83≦D≦−18 and 0.0050×D≦S≦0.0025×D; and, as characteristics with respect to light having a wavelength of 1.55 &mgr;m, an effective area of 15 &mgr;m2 or more and a bending loss of 50 dB/m or less when wound at a diameter of 20 mm.