## 5 Performance of Terahertz Replicas Generation  
While increasing the OPC repetition rate can offer benefits in terms of higher data throughput as well as higher frequency range with excellent signal quality, it also presents challenges related to power consumption, synchronization, and cost in terms of components and the necessary infrastructure by building or upgrading the requested electro-optical mixing system. In our setup, we just change the OPC repetition rate to \(f_{s}=100\) GHz. This leads to the accomplishment of terahertz replica generation at mixing frequencies of up to \(10f_{s}+f_{IF}\approx 1\) THz at the SOA-MZI output in both empirical and virtual investigations. The implementation of the experimental repetition rate principle has outstanding performance in terms of increasing the power and mitigating the noise [46]. To assess how well the system performs when operating at 1 THz, we measure the bit BER indicator [51] of the up-mixed field loading for two types of data modulations, which are QPSK and 4096-quadrature amplitude modulation (QAM), as a function of the symbol rate; see Figure 9. To measure the BER, we employ a dedicated device known as a bit error rate tester (BERT). \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Standard Modulation**} & \multicolumn{2}{c}{**Differential Modulation [28]**} \\ \cline{2-5}  & **Simulation** & **Reality** & **Simulation** & **Reality** \\ \hline Frequency Limit (GHz) & 195.5 & 59 & 195.5 & 59 \\ \hline Conversion Gain (dB) & 13 & 30 & 25 & 34 \\ \hline EVM (\%) & 24 & 8.5 & 14 & 5.5 \\ \hline Data Rate (Gbit/s) & 5 & 5 & 5 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of SOA-MZI electro-optical mixer performances using standard and differential modulation approaches. Figure 9 displays the BER performance in opposition to symbol rates of the achievable up-mixed signal. The highest recorded BER is 0.0024, corresponding to a 32% EVM for the QPSK signal at the baud rate or symbol rate (SR) of 2.5 GSymb/s in the experimental work, while it is 0.0023 at 2.5 GSymb/s for the imitated study. In contrast, it registers at 0.00034 for the 4096-QAM signal, equating to a 4.5% EVM at 10 GSymb/s in the simulation study, while it is 0.0005 at 10 GSymb/s in the experimental work. It is noteworthy that we observe an increase in BER as the SR rises for both systems. The actual BER is very similar to the simulated one, affirming the robust performance of the terahertz replica generation systems. Additionally, the distinctive characteristics of the employed SOAs and their physical components, including bias current, also impact the quality of the modulated light, as reflected in the BER values. The maximum bit transmission rate is 5 and 120 Gbit/s by loading 4- and 4096-QAM data for up mixing operations, respectively. The electro-optical SOA-MZI system in our study faces several limitations that warrant further exploration in our future designs. One notable constraint lies in the nonlinear effects within SOAs, including gain saturation and XPM, in addition to the ASE noise, which can compromise signal quality and overall system performance. Additionally, the inherent bandwidth limitations of SOAs, particularly in the THz frequency range, pose challenges to achieving ultra-high data rates. The sensitivity of the system to temperature fluctuations, complexities in the alignment of the MZI, and potential integration issues with existing optical networks further contribute to the system's limitations. Addressing these challenges in future research could involve strategies to mitigate nonlinearities, broaden the bandwidth of SOAs, enhance temperature stability, simplify MZI alignment, and improve overall system integration, thereby advancing the feasibility and efficiency of THz communication systems based on the electro-optical SOA-MZI architecture. To achieve efficient mixing in a SOA-MZI system, a balance of both high and low nonlinearities is often sought.