Impact of nonlinear effects on the performance of 120 Gb/s 64 QAM optical system using adaptive control of cascade of amplifiers

Several approaches have been proposed in order to solve the adaptive control of optical amplifier operating point problem (ACOP). These approaches aim to adjust the gain of each amplifier in a cascade of amplifiers. Some previous results show that it is possible to decrease the noise added by the amplifiers by using these strategies. However, the configurations found by these approaches may degrade the quality of the transmission due to nonlinear effect, because the amplifiers may operate with a high output power. Therefore, the goal of this work is to analyze the impact of the nonlinear effects in the solutions found by these approaches by evaluating the BER of a system that uses a very sensitive modulation in terms of OSNR (64QAM). We tested LossComp, WAdGC and AsHB approaches in a system with 40 channels, using 50GHz fixed grid and considering high and low system input powers. The results showed that for all analyzed approaches the system quality of transmission is affected by the nonlinear effects, and the effect is worse in those with higher amplifier output powers.