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We design and investigate a 10 Gb/s single user hybrid fiber-free space optical (FSO)-fiber experimental system based on optical code division multiple access (OCDMA). The receiving eye diagrams of legitimate user and eavesdropping user are measured, and the reliability and security of the hybrid system are analyzed through the eye diagrams. In order to analyze the security of the hybrid system, a tunable attenuator is used to simulate the eavesdropping situation of eavesdropping user at different position of fiber links. When analyzing the reliability of the system through the eye diagrams of legitimate user under different turbulence effects and different received power, we can see that the system can achieve reliable transmission with low-power reception only under weak turbulence. In the case of middle and strong turbulence, some measures must be taken to ensure the reliable transmission of the system. When analyzing the security of the system, the eye diagrams of eavesdropping user under the different turbulence effects and different eavesdropping distance are measured. It can be seen from the eye diagrams that the eye diagram in the second 20km optical fiber is worse, because Eve's eavesdropping signal in the second section of fiber is affected by the turbulence in FSO channel. The experimental results show that the hybrid fiber-FSO-fiber system based on OCDMA can achieve reliable transmission to ensure reliability, and also shows the good security through the poor eavesdropping.
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