WDM and optical amplifier (Wavelength Division Multiplexing)

Wavelength Division Multiplexing (WDM) is the basic technology of optical networking. It is a technique for using a fibre (or optical device) to carry many separate and independent optical channels. The principle is identical to that used when we tune our television receiver to one of many TV channels. Each channel is transmitted at a different radio frequency and we select between them using a “tuner” which is just a resonant circuit within the TV set. Of course wavelength in the optical world is just the way we choose to refer to frequency and optical WDM is quite identical to radio FDM. Another way of envisaging WDM is to consider that each channel consists of light of a different colour. Thus a WDM system transmits a “rainbow”. Actually at the wavelengths involved the light is invisible but it's a good way of describing the principle. For long distance communication to achieve error free reception use of repeaters is essential Repeaters are costly. Here we are using the combination of the optical amplifiers namely Raman and EDFA. By using the combination of these amplifiers with proper gain adjustment we can achieve the greater distance at which repeater can be placed which causes substantial advantage in reducing the no. of spans thereby reducing the whole cost for communication setup. Optical Amplifiers amplifies the optical signal Noise and distortion also amplified by it.