The advent of telecommunications in 1870s completely revolutionized the world of communications. Metallic cables consisting of twisted wire cables, co-axial cables were the media of choice for many years. These could be used efficiently up to frequencies of 10MHz but the system performance degraded beyond this range. However, with the increasing demand for telephone services, it was necessary to find an alternative medium for telephony to cope up with the high demand. The development of low loss optical fibers gave a solution to this problem and their use revolutionized the speed of telecommunication. Optical fibers have become an unavoidable part of any high speed communication system due to its high information carrying capacity, high bandwidth and extremely low loss. The transmission performance of the optical communication systems is limited by various effects such as attenuation, dispersion, nonlinearity, scattering etc, which degrade the level of the signal. To compensate for all these limitations the signals have to be regenerated within the transmission link after some distance. While setting up the transmission link, it is to be ensured that the signal can be retrieved intelligibly at the receiving end. This can be done either by using optoelectronic repeaters or optical amplifiers. In optoelectronic repeaters the optical signal is first converted into an electric signal, then amplified in electric domain and finally converted back into optical signals. Regeneration by making use of repeater is a traditional way to compensate for loss and degradation along the transmission medium. Such regenerators become quite complex and expensive for dense wavelength division multiplexed (DWDM) lightwave systems. This process works well for moderate speed single wavelength operation but it can be fairly complex and expensive for highspeed multiwavelength systems. Moreover these so called opto-electronic repeaters once installed into the system can not be upgraded to higher bit rates. Thus a great deal of effort has been spent to develop all optical amplifiers. These devices operate in the optical domain to boost the power level of the signals. In the history of optical fiber communication systems, the advent of optical amplifier was an important milestone. Optical amplifiers can amplify the optical signals directly without requiring its conversion to the electric domain. The development of optical amplifiers started in early eighties and their use for long haul communication systems became widespread during late nineties. Optical amplifiers provided flexibility while upgrading the installed transmission links to higher bit rates. This flexibility of the bit rates allows overcoming the electrical bottleneck of an electric repeater, which was unable to transmit at high bit rates. The opto-electronic repeaters provided with maximum of 40-80 Gbps bit rate.