5. Optical amplifiers

The function of an optical amplifier is to generate gain directly in the optical domain, i.e. without converting the optical signal into an electrical signal and then converting the amplified electrical signal into an optical signal. This type of amplifier is generally independent of the electrical signal (analog, digital, frequency, bit rate, etc.) that modulates the optical carrier.

There are three main types of optical amplifier:

• rare-earth-doped fiber amplifiers ;

• fiber amplifiers using the Raman effect;

• semiconductor optical amplifiers.

Their operating principles and main features are described below (see § ...