给出了一种全光双跳自由空间光通信(FSO)系统的基本结构，建立了包含大气损耗、大气湍流和瞄准误差的复合衰落信道模型，考虑背景噪声和放大器自发辐射噪声对系统性能的影响，推导了在全部信道状态信息时，采用副载波强度调制全光中继系统的中断概率和误码率闭合表达式，对比分析了全光双跳FSO与直传链路的中断概率以及信噪比、源节点发射的光子数、光自由度等参数对系统中断概率及误码率的影响。仿真结果表明，全光双跳放大转发中继能够明显改善系统的性能。

The fundamental structure of all-optical dual-hop free-space optical communication (FSO) system is presented and the composite fading channel model which includes atmospheric loss, atmospheric turbulence and pointing errors is established. In the full channel state information relaying, subcarrier intensity modulation is adopted. The closed-form expressions for outage probability and bit-error rate (BER) of dual-hop FSO systems are derived, based on the effects of background noise and amplified spontaneous emission noise. Then the outage probability of dual-hop FSO system is compared with that of the direct link. The effects of the parameters, such as signal-to-noise ratio, the average transmitted photon count of the source node (SN) and optical degree-of-freedom, on the outage probability and bit-error rate are also researched. The results show that all-optical dual-hop relaying can significantly improve the performance of the systems.