# Experimental Demonstration of Terahertz-Wave Signal Generation for 6G Communication Systems
## 3 Experimental Setup for THZ Signal Generation
The second scenario extends the transmission over 30 km of single-mode fiber (SMF), introducing realistic channel impairments, such as dispersion, attenuation, and potential nonlinear effects. Despite these challenges, the EVM results demonstrate that the system maintains acceptable performance levels, with only a marginal increase compared to the BtB case. This indicates the robustness of the proposed scheme over long-distance fiber links and underscores its potential for practical deployment in fiber-based THz communication systems. Figure 13: EVM versus optical received power for QPSK THz signal over BtB transmission. The third scenario combines a short-range wireless link of 1 m with the 30 km fiber transmission, forming a hybrid wireless-fiber configuration. This setup aims to evaluate the system's capability to handle combined wireless and optical channel impairments, such as free-space path loss and fiber dispersion. Preliminary results suggest that while the EVM slightly increases in this hybrid scenario, it still remains within the acceptable limits for reliable QPSK demodulation. This hybrid approach demonstrates the flexibility of the system in supporting integrated wireless and fiber networks, which is a vital consideration for future high-capacity, flexible communication infrastructures. Overall, these three scenarios comprehensively assess the system's resilience and performance under different transmission conditions, providing valuable insights into its suitability for real-world applications. Further analysis of the constellation diagrams and EVM trends across varying power levels and link configurations could offer deeper understanding of the system's limitations and optimization pathways. It is important to note that the distance of the wireless channel is constrained by the limited space in the indoor laboratory. The second scenario investigates the performance of the generated THz signal after transmission over a 30 km span of SMF, as illustrated in Figure 14. This assessment aims to evaluate the signal integrity and robustness in a realistic transmission environment, which is essential for practical communication systems. The results demonstrate that the transmitted signal experiences only a slight power penalty of approximately 0.3 dB compared to the BtB configuration, where no transmission loss occurs. This minimal power degradation suggests that the system retains high signal quality over extended fiber links, indicating effective preservation of the signal's amplitude and phase characteristics. Such a small power penalty is indicative of low insertion loss and minimal dispersion or nonlinear effects impacting the signal during propagation. Additionally, this finding highlights the potential for deploying this THz generation and transmission scheme in real-world fiber-optic networks, where maintaining signal strength and quality over long distances is critical. Further analysis of the received signal's spectral and phase stability post-transmission could provide deeper insights into the system's resilience, paving the way for practical high-capacity THz communication links in future wireless networks. Notably, at the QPSK threshold value of 37%, the received power registers at \(-13.8\) dBm. These findings aligned with the results obtained in the simulation phase  
Figure 14: EVM versus optical received power for QPSK THz signal over 30 km SMF transmission. (Figure 8), which also indicated that the power penalty between the BtB and SMF transmission is negligible. The third scenario assesses the performance of the generated THz signal using a hybrid transmission that combines 30 km of SMF with a 1-m RF wireless channel. The results presented in Figure 15 indicate that the optical received power reaches \(-8.5\) dBm at the QPSK threshold value of 37%. As seen from this Figure, the required power (\(-8.5\) dBm) of 1 m RF channel transmission is high compared to BtB transmission (\(-13.8\) dB) due to the losses in the wireless channel.