1. Concept

By the mid-1990s, it was clear that optical fibers offered tremendous potential for transmission, thanks to the very high carrier frequency of the signals they propagate (200 THz for a wavelength of 1.5 μm) and their very low losses (less than 0.4 dB/km over a 60 THz band, from 1,250 to 1,650 nm wavelengths). Fiber optic transmission systems are expected to have capacities in the Tbit/s range, and reach into the hundreds and even thousands of kilometers with the advent of optical amplifiers.

To realize this potential, however, a number of parasitic phenomena linked to propagation in the fiber must be combated:

• These include linear effects such as chromatic dispersion. The latter is responsible for a temporal broadening of pulses that can mix "1s" (presence of a pulse) and "0s" (absence of a pulse). This effect can...