Fiber‐Optic Amplifiers

To improve optical communication systems, two principal ways have been studied, that is to achieve the most important goals to maximize the transmission capacity in terms of the product of achievable fiber bandwidth and length. One technique is to work on the increase of receiver responsivity, for example by the development of coherent‐optic transmission systems. Another technique is to amplify the absolute optical power without leaving the fiber, so as to obtain an optical amplification within the transmission link. Optical amplifiers can be introduced after the transmitter laser as booster‐amplifiers along the fiber link as inline‐amplifier and as pre‐amplifier in front of the receiver. This chapter talks about erbium doped fiber amplifiers (EDFAs) and fiber Raman amplifiers. Regarding the coupling direction, the Raman amplifier works in reverse and thus amplifier noise problems at the receiver are avoided.