## 4 Simulation Results and Discussion  
Figure 3 shows the eye diagrams of the channel with the worst compensation characteristics when 24 WDM channels are transmitted through each dispersion-managed link to which the dispersion map of Figure 2 is applied. The eye diagrams in Figure 3 are obtained when the launch power of the WDM channel is \(5\) dBm and the rRD of each fiber span is set to \(240\) ps/nm. Figure 3a is an eye diagram obtained in the case of applying the conventional dispersion map into a dispersion-managed link for comparing the compensation effect through the proposed dispersion maps of Figure 2. The conventional dispersion map does not intentionally change the cumulative dispersion profile over the transmission distance, but the cumulative dispersion profile is constant in all fiber spans, unlike the dispersion maps in Figure 2. That is, the eye diagram in Figure 3a is obtained from a dispersion-managed link where the rRD of each fiber span is uniformly applied at \(240\) ps/nm. By comparing the rest of the eye diagrams with Figure 3a, it can be confirmed that the reception quality is better than the conventional dispersion map through compensation of distortion due to chromatic dispersion and SPM when the proposed dispersion map is applied. In a pseudo-linear system where chromatic dispersion and SPM exists, optical pulse distortion occurs through the interaction of the two phenomena. That is, when the amplitude (intensity) of the optical pulse is changed due to chromatic dispersion, the nonlinear phase shift is generated according to the changed intensity, resulting in distortion of the optical pulse. Applying this mechanism to the eye diagram analysis shown in Figure 3, the eye diagram of Figure 3a shows that the conventional dispersion map does not sufficiently compensate for the amplitude and phase distortion caused by the interaction between  
Figure 3: The eye diagrams. the chromatic dispersion and SPM experienced by the optical pulse. On the other hand, although there are differences in degree, it can be confirmed that the proposed dispersion maps combined with midway-OPC help reduce the amplitude and phase fluctuation of the optical signal. It is confirmed that, under the same conditions, the application of the proposed dispersion map to the dispersion-managed link is more effective in compensating the distorted WDM channel than the case where the conventional dispersion map is applied. What is noticeable from Figure 3 is that the degree of compensation for the distorted WDM channel varies depending on the applied dispersion map into dispersion-managed link, that is, on the specific configuration of the dispersion map. Therefore, from now on, for each dispersion map, it is necessary to evaluate the compensation characteristics depending on the changes of the launch power of the WDM channel, rRD required to form the dispersion map, and TRD of the overall link. Figure 4 shows the rRD of the fiber span against the WDM channel launch power that can achieve 1 dB EOP for the worst channel, when WDM channels are transmitted through a dispersion-managed link configured with conventional dispersion map and with 'linear-GD: AD' of Figure 2f. It should be noted from Figure 4 that there is a lower limit on the launch power of the WDM channel that can achieve 1 dB EOP. It is judged that this is because when the launch power of the WDM channel is very small, the loss of the optical fiber can greatly affect the channel signals, and as a result, the compensation effect by the midway-OPC is reduced. What can be utilized from the results of Figure 4 is that the allowable range of the channel's launch power for each rRD must be limited to achieve an EOP of 1 dB or less through the dispersion-managed link configured with the dispersion map of Figure 2. We define this range as the power margin notated in Figure 4. That is, the power margin is the difference between the maximum and the minimum value of the launch power of the WDM channel that can obtain 1-dB EOP.