The invention is to provide an optical transmission link suitable for a high speed and high bit rate wavelength division multiplex transmission. An optical transmission link 1 is composed of a non-linearity diminishing optical fiber F.sub.1, a dispersion adjusted transmission optical fiber F.sub.2, and an optical fiber F.sub.3 for diminishing and adjusting a dispersion slope. The mode field diameter of the non-linearity diminishing optical fiber F.sub.1 is made into 12 m or more. The dispersion slope is made small to be nearly zero with the mode field diameter of the dispersion adjusted transmission optical fiber F.sub.2 set to 10 m or more, and the dispersion produced at the non-linearity diminishing optical fiber F.sub.3 is adjusted to be small. At the optical fiber F.sub.3 for diminishing and adjusting a dispersion slope, the dispersion slope of the entire optical transmission link 1 is adjusted to nearly zero. The refractive index profile of the fibers F1 and F2 is made into a segment type, and the refractive index profile of the optical fiber F3 for diminishing and adjusting a dispersion slope is made W-shaped. The absolute value of dispersion at any point position in the lengthwise direction of the optical transmission link 1 is made greater than 0.5 ps/nm/km, thereby suppressing the generation of four-wavelength mixture.