## 4 Results and Discussion  
This section elaborates the simulation results of the proposed system. Optisystem Ver.13 simulation software is used to carry out the simulations, which contains most of the components used for the design of a practical optical communication system. The performance metric of BER, specified by the number of error bits per transmitted ones, is performed at the receiver end in Optisystem by using a clock recovery module, followed by a data recovery component. The Optisystem makes use of the sequence length and makes several iterations to estimate the BER values. The threshold of \(10^{-3}\) is used in this work as mentioned by a dotted line in the figures containing results. The BERs of eye diagrams are found to be higher than the considered threshold value before Nonlinearities compensation, but is much lower (BER < \(10^{-5}\)) with application of the proposed compensation technique. In order to discuss pre-FEC BER, the optical transmission system interfaces on series of packet transport routers support monitoring the condition of an optical network by using pre-FEC BER. In the Optisystem, BER is estimated using a Gaussian algorithm with transmission of a short sequence of bits. After the bit recovery, the BER test set calculates the error bits and use the transmitter channel information to produce the BER. Figure 6 describes the flow chart for connection among analytical and simulation models. Figure 7 presents the BER performance of the system against the effective non-linear area of the optical fiber. The simulations are conducted for different channel spacings used for the proposed WDM system. The results show that the performance of the system against RIrNLs improves with the increase in area and is optimum at 80 \(\upmu\)m\({}^{2}\) effective area. Similarly, Figure 8 presents the OSNR results for different channel spacings, as the effective  
area is varied. The simulation results are plotted for a 32-channel WDM system, with an aggregate data rate of 100 Gbps. Figure 6: Proposed flow chart to how analytical and simulation models are linked. Figure 7: BER results for a range of Nonlinear effective area at 50, 25 and 12.5 GHz channel spacings (32 channels). Figure 9 includes the results for BER versus effective area for different number of channels. The plot indicates that RIrNLs increase with the number of channels, for a fixed channel spacing of 50 GHz. However, the proposed system provides low BER values, even for 32 channels after the mitigation of RIrNLs effects. Moreover, the projected model examines simulation results in up to 500 km of fiber length as shown in Figure 10. The results also show that the proposed model has the ability to support multi channels for up to 500 km of optical path covered, by treating RIrNLs. Figure 8: OSNR versus nonlinear effective area for 32 number of channels, 100 Gbps aggregate data rate, considering different channel spacing values. Figure 9: BER versus nonlinear effective area for 4, 8, 16 and 32 channels (50 GHz channel spacing). The system performance will degrade with a reduced channel spacing. For this purpose, an additional analysis has been performed and results have been included in the paper for Dense-WDM spacings of 12.5 GHz and 25 GHz. Since each channel carries data bandwidth of 3.16 GHz, further reduction in channel spacing causes severe distortion and very high BER. The results section has been updated with the results for 12.5 GHz and 25 GHz channel spacings for 32 number of total channels. The results for receiver sensitivity are shown in terms of received optical power. The BER threshold of \(10^{-3}\) has been considered to analyze the receiver sensitivity. The laser frequency for first channel is 193.1 THz, which corresponds to the wavelength of 1552.5 nm. For 32 number of channels with 25 GHz spacings, the range for the WDM system is from 193.1 THz to 193.875 THz.