## 4 Results and Discussion  
To verify this work's goals, system tracing and evaluation are presented in this section. Figure 3a-g represents the optical spectra for signals processed through the proposed cross-seeding system, as indicated in Figure 2. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **Parameter** & **Value(s)** & **Unit** \\ \hline \multirow{4}{*}{CW Laser} & First Wavelength & 193.025 & THz \\  & Wavelength spacing & 25 & GHz \\  & Launching power & 0 & dB \\ \multirow{2}{*}{Sine Generator} & Frequency & 6.25 & GHz \\  & DS Bit rate & 10 & Gb/s \\ Bidirectional optical fiber & Length & 25 & Km \\ \multirow{2}{*}{ONU Transmitter} & Attenuation & 0.2 & dB/Km \\  & US Bit rate & 2.5 & Gb/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The main parameters for the proposed DWDM-PON system components. Figure 3: _Cont._  
Figure 3a represents 16 DS channels with a channel spacing of 12.5 GHz starting from (\(\uplambda_{\text{1-1}}\) = 193.019 THz) to (\(\uplambda_{\text{8-2}}\) = 193.206 THz). These channels resulted from the eight CW light sources, each with 0 dB, after being forced to the MZM with a 6.25 GHz sine wave generator, as indicated in point (a) (Figure 2) and Table 1.  
After being demultiplexed, the even and odd DS channels are modulated through IM with the NRZ format, each with 10 Gb/s. Finally, these channels are applied to DS MUX to provide the cross-seeding odd and even spectra ready to be transmitted through FF1 and FF2, respectively. These spectra are presented in Figure 3b,c and are considered to correspond to the system signals' trace at points (b) and (c) in Figure 2.  
Figure 3d represents the spectrum of a chosen odd DS channel spectrum (i.e., \(\uplambda_{\text{1-1}}\) = 193.019 THz as an example for the odd channels) after transmitting 25 km through FF1 and after being demultiplexed at point (d) in Figure 2 before an ONU receiver. Figure 3f represents this channel after transmitting back through the retransmitting path (US path) with a record of 2.5 Gb/s (i.e., point (e) in Figure 2). One needs to remember (as in Figure 2) that the retransmitting path (US path) includes a CLS module, MUX, transmitting through FF2 (not in FF1, which is used in the DS path and is the core of the cross-seeding technique that eliminates RB), and, finally, DeMUX to reach a point (e) Figure 2.  
Figure 3: System trace and evaluation (**a**); 16 DS channels with channel spacing 12.5 GHz; (**b**) eight DS odd channels before transmitting through feed fiber 1 (FF1); (**c**) eight DS even channels before transmitting through FF2; (**d**) the DS odd channel \(\uplambda_{\text{1-1}}\) before the optical network unit (ONU) (**e**); the DS even \(\uplambda_{\text{1-2}}\) channel before the ONU (**f**); the US odd channel \(\uplambda_{\text{1-1}}\) after the US path (**g**); the US even channel \(\uplambda_{\text{1-2}}\) after the US path. A similar analysis is done by choosing the even DS channel \(\lambda_{1\text{-}2}\) = 193.031 THz as an example for the even channels. Figure 3e,g shows this channel spectrum after transmitting the DS path through FF2 and then returning using US path through FF1. These spectra correspond to the system trace at points (f) and (g) in Figure 2.  
Finally, Figure 4 represents the eye diagrams for the selected odd and even channels after the retransmitting path (i.e., points (e) and (g) in Figure 2). Figure 4a,b represents the eye diagram evaluation for the previously chosen odd and even channels that are presented in Figure 3f,g (i.e., \(\lambda_{1\text{-}1}\) and \(\lambda_{1\text{-}2}\)) while Figure 4c,d represents the eye diagram representation for the extra chosen channels (i.e., \(\lambda_{8\text{-}1}\) and \(\lambda_{8\text{-}2}\)).