提出了一种全新的基于相位强度级联调制器和色散补偿光纤(DCF)的四进制幅移键控(4-ASK)非归零码(NRZ)到归零码(RZ)格式转换方案。理论分析了新格式转换器的工作原理，并进行了20 Gb/s的四进制幅移键控NRZ到RZ的格式转换实验研究。结果表明，该方案能将四进制幅移键控NRZ信号转换为四进制幅移键控RZ信号，转换过程不改变信号波长，且转换后信号脉宽较窄、时间抖动较原信号小，该码型转换器还可以应用于多波长幅移键控信号的码型转换。

A novel non-return-to-zero (NRZ) to return-to-zero (RZ) format converter for quaternary amplitude shift keying (4-ASK) signal is proposed based on phase-intensity modulators and one dispersion compensating fiber (DCF) module. The operation principle of the proposed converter is described theoretically. 20-Gb/s NRZ-4-ASK signal to RZ-4-ASK signal conversion is also experimentally demonstrated. The results show that 20-Gb/s NRZ-4-ASK signal could be successfully converted to RZ-4-ASK signal without wavelength shift and the pulse width of the converted signal is narrow. The timing-jitter of the converted signal is lower than the original one. The format converter could also be applied to multi-wavelength amplitude shift keying conversion.