分析了由两种光调制结构产生的高阶调相非归零码的码间跃变图案，并以此来研究码间跃变图案与光滤波性能间的关系。串行调制器方案下，部分跃变图案为曲线型，而在并行调制器方案下，所有的码间跃变图案本征均为直线型。可以证明，码间跃变图案特性对光滤波特性存在重要影响。在串行调制器方案下，光滤波可以导致明显的跃变图案依赖性。相对而言，并行调制方案有更小的眼睁开代价，因此具有更好的窄带滤波容忍性。最后，研究了在解调器参数优化下接收机灵敏度随光滤波带宽的变化曲线。

The inter-symbol-transition (IST) patterns of multi-level non-return-to-zero phase-shift-keying (NRZ-PSK) signals generated by two kinds of optical modulator implementations are analyzed to reveal the underlying relationship between IST patterns and optical filtering performance. In the tandem modulator implementations, some IST patterns are curved, and in the parallel implementations, all IST patterns are inherently straight lines. It′s proved that these IST patterns characteristics play a significant role in determining optical filtering performance. In the tandem implementations, optical filtering can lead to obvious IST pattern dependent signal distortion. As a comparison, the parallel implementations have less filtering-induced eye-opening penalty and consequently better tolerance against narrow filtering. Finally, the receiver sensitivity as a function of optical filter bandwidth for differential optical detection is studied together with the optimization of the demodulator parameter.