基于MZM的RZ/CSRZ-DQPSK信号产生的新方法

差分相移键控(DPSK)和差分正交相移键控(DQPSK)对光纤非线性具有很高的容忍度,且灵敏度高,在高速、高频谱效率系统中具有优越性。提出了一种基于双驱动马赫-曾德尔调制器(MZM)的差分正交相移键控归零码(RZ-DQPSK)和差分正交相移键控载波抑制归零码(CSRZ-DQPSK)信号产生的新方法。利用一个双驱动MZM实现DQPSK调制,另一个MZM实现波形切割,生成RZ/CSRZ-DQPSK信号。给出了详细的理论推导过程。该方法简化了高速RZ/CSRZ-DQPSK光信号的产生过程,减少了调制器个数。仿真结果表明,CSRZ-DQPSK信号载波频率分量被抑制,具有比RZ-DQPSK信号更紧凑的频谱结构,采用平衡相干检测接收方法接收到的信号有清晰的眼图。

New method for generation of RZ/CSRZ-DQPSK signals based on MZM

Differential phase-shift keying(DPSK) and differential quadrature phase-shift keying(DQPSK) have attracted significant attentions for its advantages of receiver sensitivity and tolerance to fiber nonlinearity in high speed and high spectral efficiency optical transmission system.A novel scheme,using dual-drive Mach-Zehnder modulator(MZM) for generation of return-to-zero DQPSK(RZ-DQPSK) signal and carrier-suppressed return-to-zero DQPSK(CSRZ-DQPSK) signal,was proposed.It needed one MZM to generate DQPSK signal and another to curve RZ/CSRZ pulse out of the NRZ-phase modulated signal.An exact analytical solution for this method was derived.The proposed method simplified the generation of RZ/CSRZ-DQPSK signal and was expected to be more cost-effective due to the reduction in requirement of modulator.Simulation results show that CSRZ-DQPSK has a more compact spectrum than that of RZ-DQPSK because of carrier suppression.The received signal has a clear eye diagram under balanced coherent detection.