Signals travel through fibers over large distances with attenuation. Then the optical amplifiers are needed in the CWDM (corse wavelength divsion multiplexing) and DWDM (dense wavelength divsion multiplexing). Optical amplifiers are devices that can amplify optical signals directly without the need to convert them to electrical signals. EDFA (erbium doped fibre amplifier) is the most common optical amplifiers.

... Read more »