## 6 Simulation Results and Analysis
Similarly, when \(\lambda_{SR}=35\) dB,\(\rho=0.9\), the SOP values before and after the introduction of RIS are about 2.15 \(\times\) 10\({}^{-6}\) and 8.00 \(\times\) 10\({}^{-8}\), respectively, they differ by two orders of  
magnitude. Therefore, it is further demonstrated that the addition of RIS in mixed systems proves especially potent in effectively decreasing SOP as \(\rho\) increases. Figure 4 shows how \(\lambda_{SR}\) and the system SOP are related before and after RIS was introduced with different values of average interference noise ratio in the mixed RF/FSO system. The simulation results show that the SOP of the system decreases monotonically as \(\lambda_{SR}\) increases. Regardless of the presence or absence of RIS, with an increase in the average interference noise ratio, there is a concurrent decrease in the SOP. Furthermore, the RIS can significantly reduce the SOP when the average interference noise ratio remains constant. When \(\lambda_{SR}=35\) dB and the average interference noise ratio is 2 dB, the system SOP before and after the introduction of RIS in the system is about 9.12 \(\times\)\(10^{-7}\) and 8.14 \(\times\)\(10^{-8}\), respectively. Similarly, when \(\lambda_{SR}=35\) dB, the average interference noise ratio is 4 dB, the system SOP values before and after the introduction of RIS in the system are about 2.85 \(\times\)\(10^{-7}\) and 2.25 \(\times\)\(10^{-8}\), respectively. Therefore, when the RIS is employed in the mixed RF/FSO system, the SOP is obviously lower and the system has better secrecy performance. Figure 3: Simulation diagram of SOP under different energy conversion efficiency \(\rho\) with or without RIS. Figure 2: Simulation diagram of SOP under different time switching factors \(\lambda\) with or without RIS. Figure 5 presents the correlation between \(\lambda_{SR}\) and in the RIS-aided mixed RF/FSO system SOP under the influence of different reflecting elements N. Figure 5 shows that the system SOP decreases gradually as \(\lambda_{SR}\) increases. When \(\lambda_{SR}=35\) dB, and the number of reflecting elements \(N\) is varied as 4, 6, and 8, respectively, the corresponding system SOP values are about \(1.07\times 10^{-7}\), \(2.75\times 10^{-8}\), and \(7.05\times 10^{-9}\), respectively. The SOP value of the system at N = 8 is significantly lower than those at N = 4 and 6. This is because a higher number of reflecting elements indicates that more reflecting elements are jointly involved in receiving and reflecting the interfering signals, which can reduce the quality of the eavesdropper communication to a greater extent and increase the effectiveness of interference. Therefore, an appropriate increase in N in the RIS-aided mixed RF/FSO system can improve its security performance. Figure 6 shows the correlation between \(\lambda_{SR}\) and the RIS-aided mixed RF/FSO system SOP for different distances of \(J-R^{\prime}\) as well as \(R^{\prime}-E\). As \(\lambda_{SR}\) increases, the mixed system SOP decreases with decreasing \(d_{JR^{\prime}}\) and \(d_{R^{\prime}E}\). When \(\lambda_{SR}=35\) dB, the SOP values of the system are about 5.01 \(\times\)\(10^{-6}\) and 3.31 \(\times\)\(10^{-6}\) for \(d_{JR^{\prime}}=10\) m,\(d_{R^{\prime}E}=10\) m and \(d_{JR^{\prime}}=5\) m,\(d_{R^{\prime}E}=5\) m, respectively. When the link distances are increased simultaneously, the greater the loss of interference signal in the link, and the worse  
Figure 4: Simulation diagram of SOP with different average interference noise ratio with or without RIS. Figure 5: Simulation diagram of SOP under different number of RIS reflecting elements N in the RIS-aided mixed RF/FSO system. When the distances between the two sections are relatively small, the interference signal transmission loss is small which enhances the interference effect, consequently reducing the SOP. Therefore, a proper reduction of the link distances before and after reflection in the RIS-aided mixed RF/FSO system can effectively improve the system's secrecy performance.