Introductory Chapter: A Revisit to Optical Amplifiers

Abstract

The modern age of information may be regarded as the era of fastand high-bandwidth communication, which exploits fiber-optic communication system. Transmission of signals spanning distances of over thousands of kilometers essentially cause signal degradation. Due to varieties of loss mechanisms in the medium (the optical channel used for transmission), there happens gradual attenuation in the power of signals being transmitted, as those propagate through a communication channel. Clearly, the attenuation imposed by the medium remains a serious issue that affects light propagating ultra-long distances through a fiberoptic cable (the communication link). The degradation of signal must be overcome, which makes the utilization of the process of amplification (of signal) vital. Further, in order for the information carried by a signal to be detectable at the receiving end, there must be a minimum amount of threshold power, which the signal must possess. As such, optical amplifiers, which would incorporate optical fibers and/or waveguides, remain indispensable in fiber-optic communication systems owing to the limitations imposed by the transmission channels/systems. These limitations would arrive in the form of fiber loss and dispersion, which are usually overcome by exploiting varieties of amplifiers. In reality, loss and dispersion are related to each other [1], which can be well-understood upon giving a thought to a pulse shape—more broad a pulse becomes (causing dispersion), more will be the decrease in power (causing loss), and vice-versa.