## 7 Conclusions  
This paper investigated how integrating RIS into the mixed RF/FSO system's interference link affects its physical layer security performance. We analyzed the system's security outage probability (SOP) and the average secrecy capacity (ASC) theoretically, and then Monte Carlo simulations were employed to verify the correctness of the theoretical expressions. The time switching factor, energy conversion efficiency, and average interference noise ratio, as well as the number of reflecting elements, fading severity parameter, and link distances before and after RIS reflection were mainly studied, and an analysis of their effects on the secrecy performance was conducted. The findings indicate that the system's SOP decreased when the time switching factor, energy conversion efficiency, and average interference noise ratio were increased with or without RIS assistance. When the time switching factor, energy conversion efficiency, and average interference noise ratio were fixed, the RIS-aided mixed system's SOP was significantly lower than that of the mixed system without RIS assistance. The improvement of secrecy performance achieved by introducing RIS in the mixed system was more significant as the time switching factor and energy conversion efficiency increased. Therefore, using RIS to assist reflection interference against eavesdropping in a mixed RF/FSO  
Figure 10: Simulation diagram of the ASC under different fading severity parameters \(m\) of RIS in the RIS-aided mixed RF/FSO system. Figure 9: Simulation diagram of ASC with different RIS reflections before and after of link distances \(d_{JR^{\prime}},d_{R^{\prime}E}\) in the RIS-aided mixed RF/FSO system. system could considerably decrease the SOP and improve the system's physical layer security performance. Furthermore, there was an impact of RIS-related parameters on system secrecy performance. With the increase in the number of RIS-reflecting elements, a higher intensity of interference signals could be reflected, which reduced the eavesdropper receiver side rate to a greater extent and decreased the SOP. The increase in the fading severity parameter improved the fading quality of the interfering link, thus providing better system secrecy performance. With an increase in the number of reflecting elements, the reduction in the SOP of the mixed system became more pronounced with an increase in the fading severity parameter. To reduce the interference signal transmission loss to improve the interference effect, the link distances before and after the reflection could be reduced properly, which would decrease the SOP of the system. Similarly, increasing the number of reflecting elements and fading severity parameters, as well as decreasing the link distances before and after reflection, would also increase the ASC of the system. In engineering applications, the appropriate number of reflecting elements, fading severity parameter, and link distances before and after reflection could be selected based on the actual performance requirements and flexible implementation cost considerations. In summary, the quality of eavesdropper communication was degraded and the mixed RF/FSO system physical layer security performance was considerably improved under the effect of RIS-assisted reflected interference signals. This provides a feasible solution for future research on physical layer security to improve security performance, and actively explores the breakthroughs of RIS in hardware as well as application so that it can be adapted to more application scenarios and have a greater function and effect. Conceptualization, [PERSON] ([PERSON]) and [PERSON] ([PERSON]); methodology, [PERSON] ([PERSON]); software, [PERSON] ([PERSON]); validation, [PERSON] ([PERSON]). [PERSON].