Optical amplifiers(OA) compensate for the attenuation ofoptical fibers by increasing the level of the input signal by a certain factor. They are used for long transmission distances in wide- area communications.
Optical amplifiers can operate with or without opto-electrical light conversion. OA amplifiers with opto-electrical light conversion have an O/E converter at the input which converts the optical signal into an electrical signal which is then electronically amplified. At the amplifier output, there is again an electro-optical reconversion of the electrical signal into a light signal.
The second group works without electro-optical light conversion and amplifies the optical signal directly. Since at ultra-fast bit rates of 50 Gbit/s and more the switching functions can no longer be realized by opto-electrical methods, purely optical switching methods are required for these applications. These amplifiers are fiber amplifiers in which the optical fiber is doped with rare earths such as erbium (Er), ytterbium( Yb), thulium (Tm) or neodymium( Nd) and which have several cladding glasses for light amplification. The different doping elements have an effect on the emitting wavelengths. For example, material doped with erbium radiates at 1,550 nm, ytterbium at wavelengths between 1,020 nm and 1,050 nm, and thulium at 1,500 nm. These all-optical amplifiers include the semiconductor-based Semiconductor Optical Amplifier( SOA), the Raman amplifier, and the doped fiber-optic EDFA amplifier.
In the case of optical amplifiers, a distinction is made between the optical power amplifier, which amplifies the power of the laser and is located upstream of the transmission link, the optical line amplifier, which compensates for the attenuation of long optical fiber links and must be used every 60 km to 120 km, and the preamplifier, which is located at the end of the optical transmission link and adapts the light signal for the optical decoder.