Analysis of Hybrid Optical Amplifiers for Dense Wavelength Division Multiplexing (DWDM) Systems Using Adequate Channel Spacing

The evolved multimedia services and the increase in the number of worldwide internet users have raised the demand for high capacity networks; this in turn evolved the optical transmission system. In today’s era, the accepted solution for transmission capacity for increasing transmission capacity is by using the wavelength division multiplexing (WDM) to keep the required level of system’s performance over longer transmission distance. Adversely this kind of multichannel system along with linear effects like optical attenuation and chromatic dispersion is more sensitive to fibre non-linearity which results in signal distortion and thus causes dramatic degradation in the performance of the system. Primarily, the effect that puts the limitation on distance of transmission is optical signal attenuation. To compensate this optical signal attenuation, one of the way is to by making use of signal repeaters and the other is by amplifying the optical signal. For WDM systems the former solution was not the best choice because it requires de-multiplexing, conversion, processing and regenerating the signals of all the 16 channels; thus, it was quite complex and expensive. Simultaneously when optical signals were being amplified their power also gets increased during transmission without any conversion. Thus, this method is way simpler and cheaper than those using repeaters. Optical Amplifiers used in WDM transmission are Semiconductor optical amplifiers (SOAs), doped fiber amplifier (DFAs), Raman amplifiers(RAs). But the major drawback of SOAs is that they produce large amount of ASE and serious signal distortion that is caused through their gain dynamics. Irrespective of SOA case DFA provides signal amplification with less signal impairments, but their frequency is highly dependent on the gain spectrum because of the doped material. Also, SOAEDFA are being attractive now-a-days as they have high on-off ratio and thus increase the transmission distance. Moreover most of the noiseless amplifications are provided by the Raman amplifiers; in such cases the gain spectrum can be changed by varying the number of pumps and their frequencies to achieve higher gain. Thereby it causes the need of powerful pump which is not much reasonable. For combining the benefits and to compensate the ABSTRACT