Amplifiers are the modules used generally in long haul networks to manage loss in a DWDM network. Here the signal is directly amplified without conversion of optical signal into electrical signal .
Optical Amplifiers amplify input light through stimulated emission, the same mechanism that is used by lasers but only difference is that amplifiers doesn’t need feedback circuitry. It’s main ingredient is the optical gain realized when the amplifier is pumped (electrically or optically ) to achieve population inversion. The optical gain, in general, depends not only on the frequency (or wavelength) of the incident signal, but also on the local signal intensity at any point inside the amplifier.
There are mainly two types of amplifiers used in DWDM network and they are EDFA(Erbium doped fiber Amplifier ) and Raman Amplifier.
EDFA:
Erbium doped fiber amplifiers makes use of rare-earth elements (Er3+ ) as a gain medium by doping the fiber core during the manufacturing process .Erbium-doped fiber amplifiers (EDFAs) is widely used because they operate in the wave- length region near 1.55 μm .In EDFA,pumping at a suitable wavelength provides gain through population inversion. The gain spectrum depends on the pump- ing scheme as well as on the presence of other dopants, such as germania and alumina, within the fiber core. Efficient EDFA pumping is possible using semiconductor lasers operating near 0.98- and 1.48-μm wavelengths. Most EDFAs use 980-nm pump lasers as such lasers are commercially available and can provide more than 100 mW of pump power. Pumping at 1480 nm requires longer fibers and higher powers because it uses the tail of the absorption band ,
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