4. Optical amplification

Amplification is an essential function in transmission, and major research efforts have been devoted over the last thirty years to the development of optical amplifiers. The solid-state amplifier, which has been the subject of much work since the early 1970s, has not seen much development as an amplifier inserted into a transmission system, apart from a few demonstrations in the 1.3 μm window, where there are no industrially available doped-fiber amplifiers.

On the other hand, its characteristics make it ideal for use in all aspects of optical signal processing (multiplexing and demultiplexing, regeneration, wavelength conversion, etc.), where non-linear effects (cross-gain modulation, cross-phase modulation) are required.

The doped-fiber amplifier first appeared at the end of the 1980s, and very quickly became an industry standard: today,...