Performance Analysis and Experimental Investigation of Physical-Layer Security in OCDMA-Based Hybrid FSO/Fiber Wiretap Channel

In this paper, optical code division multiple access (OCDMA) based hybrid free-space optical (FSO)/fiber wiretap channel is proposed, and the physical-layer security is analyzed theoretically, using the conditional secrecy outage probability as the performance metric. Taking into account the background noise, multiple-access interference, shot noise, and thermal noise, the closed expression of the conditional secrecy outage probability is obtained. Under the condition that the eavesdropper intercepts information on the fiber link and the minimum conditional secrecy outage probability is zero, the safe transmission distance and interception distance of the system are defined and studied. Furthermore, a 10-Gb/s experimental system of OCDMA-based hybrid FSO/fiber wiretap channel is built for the first time. The bit error rates of the legitimate user and eavesdropper are measured as well as the interception distance of the system.