One of the big advantages of fiber optics is its capability for long distance high speed communications. Attenuation at long wavelengths is low. Fibers can be fusion spliced with virtually no loss. High-powered lasers and fiber amplifier regenerators mean long distances are easily obtained.
However over very long distances, new factors in fiber performance become important. Chromatic dispersion, the dispersion caused by light of different wavelengths, and polarization mode dispersion, caused by the polarization in fibers, become factors limiting fiber links. Even the variation of fiber attenuation with wavelength can become an issue. All 3 may need testing on long distance networks to ensure proper link performance.