## 5 Simulation Results
### SNR Analysis  
In the conventional m \(\times\) n mesh-based HONoC, it is proved formally that the worst-case SNR is among the 1 st, 2 nd and 3 rd longest paths and the best SNR performance is achieved when m = n [19]. For fair comparison, symmetric mesh topologies are chosen for evaluations. Figure 11 shows worst-case SNR for the 1 st, 2 nd and 3 rd longest paths according to the SOA gain when every link contains an SOA and the network size is \(8\times 8\), \(16\times 16\), \(24\times 24\) and \(32\times 32\), respectively. When the SOA gain is 0 dB, the SNR values are the same as that for non-SOA HONoCs. The SNR gradually improves as the SOA gain increases, whereas it decreases at a certain threshold of the SOA gain. Furthermore, the SNR decreases further than that of the conventional HONoC without SOAs if the SOA gain increases even more. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Loss** & **Value (dB)** & **Loss** & **Value (dB)** \\ \hline \(L_{In,W}\) & 0.50 & \(L_{E,W}\) & 0.38 \\ \(L_{In,E}\) & 0.88 & \(L_{E,N}\) & 0.50 \\ \(L_{In,N}\) & 0.88 & \(L_{E,S}\) & 1.00 \\ \(L_{In,S}\) & 0.63 & \(L_{E,Ej}\) & 0.63 \\ \(L_{W,E}\) & 0.38 & \(L_{N,S}\) & 0.38 \\ \(L_{W,N}\) & 1.00 & \(L_{N,Ej}\) & 0.50 \\ \(L_{W,S}\) & 0.50 & \(L_{S,N}\) & 0.38 \\ \(L_{W,Ej}\) & 0.88 & \(L_{S,Ej}\) & 0.88 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Loss value in \(5\times 5\) Crux router. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Reference** \\ \hline Waveguide crossing loss & –0.12 dB & [12] \\ Propagation loss per cm & –0.274 dB/cm & [15] \\ Power loss of CSE in OFF state & –0.04 dB & [13] \\ Power loss of CSE in ON state & –0.5 dB & [9] \\ Power loss of PSE in OFF state & –0.005 dB & [9] \\ Power loss of PSE in ON state & –0.5 dB & [9] \\ Crossing crosstalk coefficient & –45 dB & [27] \\ Crosstalk coefficient of PSE in OFF state & –20 dB & [28] \\ Crosstalk coefficient of PSE in ON state & –25 dB & [28] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Loss and crosstalk coefficient values. Figure 12 shows the worst-case SNR of the SOA-enabled HONoC and that of the conventional HONoC according to the mesh size in an m \(\times\) m mesh. When the network size is larger than \(12\times 12\), the noise power exceeds the signal power in the mesh-based HONoC. In addition, the SNR decreases drastically as the network size increases. However, in our proposed architecture, the SNR of the 1 st, 2 nd and 3 rd longest paths are 1.19 dB, 0.89 dB and 0.28 dB when the network size is \(24\times 24\). When the network size is \(32\times 32\), the worst-case SNR is -1.05 dB and the SNR degradation is not large even if the network size is further increased. As the worst-case SNR determines the feasibility and the scalability of the HONoC, the proposed architecture shows a great advantage over the conventional HONoC architecture. Figure 13 shows the SNR improvement in an average basis for the 1 st, 2 nd and 3 rd longest paths with respect to the maximum hop count without SOAs, \(h\). The number of SOAs is proportional  
Figure 11: Worst-case SNR for SOA-enabled HONoC according to the SOA gain for different network sizes: (**a**) \(8\times 8\); (**b**) \(16\times 16\); (**c**) \(24\times 24\); and (**d**) \(32\times 32\). Figure 12: SNR comparison for the 1 st, 2 nd and 3 rd longest paths between SOA-enabled HONoC and conventional HONoC (without SOAs) in accordance with the mesh size. to the mesh size and is inversely proportional to \(h\). When the mesh size is smaller and \(h\) is larger, the amplification of the optical signal is relatively small. On the contrary, the amplification of the introduced crosstalk noise occurs frequently when the mesh size is larger and \(h\) is smaller. Therefore, the SNR improvement is closely related to the mesh size as well as \(h\), which determines the number of SOAs in the optical signal path.