Introduction Before the introduction of optical amplifiers, reach extension was achieved via repeaters or regenerators. A regenerator is also called optical-electrical-optical (OEO) device since it converts the optical signal to an electrical signal, processes this signal (re-amplify, reshape and retime) and then converts back to an optical signal so that the signal can then cover longer distances. This process is not only expensive but also restricts the useable optical bandwidth due to the limitations of the electronics. The introduction of optical amplifiers in the 1990s conquered the regenerator technology and opened doors to the WDM technology. There are various types of optical amplifiers depending on the technique of amplifying, namely SOA (semiconductor optical amplifier), EDFA and Raman amplifier. In this paper we delve in deeper into the SOA technology and look into its form-factor independent niche application with 100G LR4 Ethernet for metro networks. Fundamentals of SOA A semiconductor optical amplifier (SOA) has been used in an arrayed of applications such as wavelength conversion, signal regeneration, pulse reshaping and power limiting. Because it is capable of high integration and volume manufacturing, it has been very popular when operation demand space and power efficiency. SOA has been deployed in wide spectrum of high-speed applications from long-haul to metro and access optical networks. SOA is commercially available in different formfactors according to the application and requirements. Figure 1 Stimulated Emission The basic working principle of a SOA is the same as a semiconductor optical laser based on stimulated emission except that it does not have any feedback from reflection. Figure 1 explains the process of stimulated emission. The transmission medium is first excited with an external current such that the electron jumps to its higher energy level. An incoming photon of a specific frequency then interacts with the excited electron forcing it to drop back to its natural lower energy level. The energy lost during this process creates a new photon with identical phase, frequency, polarization, and direction of the incident photon.
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