## 1 Introduction  
Free space optical (FSO) communication has obvious advantages in terms of data transmission rate, spectrum license, bandwidth availability, and cost-effectiveness, but atmospheric turbulence and attenuation, building jitter and the deviation of receiving equipment pose a significant challenge to long-distance communication over the FSO link [1, 2]. In contrast, radio frequency (RF) communication is not sensitive to atmospheric turbulence, but its spectrum resources are limited. The advantages of these two types of communications can be integrated by using relay technology where a mixed RF/FSO system can be formed that combines RF communication with FSO communication to achieve long-distance transmission. As the RF links are broadcast, there are security risks where an eavesdropper can eavesdrop on the transmitted information. Therefore, physical layer security (PLS) is currently a prominent topic [3], and especially the research on security performance in mixed RF/FSO systems is one of the hotspots [4]. For example, there are studies on relay gain schemes. [PERSON] et al. investigated the different gain schemes at the relay mixed RF/FSO systems with an eavesdropper in the RF link, analyzing their secrecy outage probability (SOP) and average secrecy capacity (ASC) [5]. On this basis, [PERSON] et al. also analyzed the influence of atmospheric turbulence and other related factors on the system secrecy performance, deriving both asymptotic and lower bound expressions for the SOP and ASC [6]. Channelstate information has also been studied. [PERSON] et al. analyzed the mixed RF/FSO system secrecy outage performance with imperfect channel state information [7], and the authors in [8] also considered four transmitting antenna selection schemes on this basis to enhance the mixed RF/FSO system secrecy performance. PLS can also be enhanced by jamming with the communication of eavesdropper. Considering an eavesdropper user in the RF link, our team studied simultaneous wireless information and power transfer (SWIPT) structure that was introduced in the relay to control energy harvesting and information transmission. The collected energy was used to emit interference signals to reduce the receiving rate of the eavesdropper, which improved the communication system's secrecy performance [9]. The PLS performance of the eavesdropper based on the wireless-powered friendly jammer transmitting interference signals was studied in [10]. In recent years, an electromagnetic device with controllable electromagnetic characteristics has been proposed, namely reconfigurable intelligent surface (RIS) [11]. By introducing RIS into a mixed RF/FSO system, the performance of the system can be significantly enhanced. For example, [PERSON] et al. in [12] deployed the RIS as a transmitter or reflector to send signals, respectively, and the proposed RF/FSO system using RIS offered 20-25 dB gain with respect to a conventional RF/FSO system. [PERSON] et al. investigated the RIS, and the results illustrated that increasing the RIS- reflecting elements in RF and FSO links could significantly reduce the outage probability (OP) and average bit error rate of the system [13]. In [14], the system performance of intelligent reflecting surface (IRS)-aided RF/FSO communication network was studied, and the influence of factors such as the number of IRS elements, pointing error, atmospheric turbulence, and other factors on system OP and average bit error rate were analyzed. [PERSON] et al. employed a signal space diversity technique to enhance the spectral efficiency and the diversity order of distributed RIS-assisted dual-hop mixed RF/FSO systems [15]. [PERSON] et al. used the RIS in the FSO link segment of a mixed system to form the optical RIS, and the performance of the mixed communication system assisted by it was analyzed in [16]. In [17], [PERSON] et al.