文章对上下行数据流分别使用差分相移键控(DPSK)和开关键控(OOK)不同的混合调制方式，通过比较下行采用不同调制码型，在没有色散补偿的情况下，实现了20 km、上下行10 Gbit/s对称速率的传输。结果表明，使用反向归零 (IRZ) 码的混合调制方式可以使下行数据流具有较高的消光比，上行数据流具有较好的色散容限，从而提高了传输系统的整体性能。

Different combined modulation modes of DPSK and OOK are separately employed for the upstream and downstream links. By comparison with different modulation formats in the downstream link, 20 km upstream and downstream transmission at a symmetric rate of 10 Gbit/s is realized without dispersion compensation, which shows that higher extinction ratio in the downstream link and better dispersion tolerance in the upstream link can be realized by employing the combined modulation with IRZ code so as to enhance the overall performances of the transmission system.