Zheng Lingchen, Shao Sizhu, Ding Jianfeng, Zhang Lei, Fu Xin, Yang Lin
Opt Express. 2018 Nov 26;26(24):32014-32025. doi: 10.1364/OE.26.032014.
We propose an analytical model to investigate the intrinsic frequency chirp with the method of 4-level pulse-amplitude-modulation (PAM-4) optical modulation by driving a single dual-drive silicon optical modulator. With the analytical model, we calculate the chirp parameters of this PAM-4 generation numerically. The intensity and phase of output signal changes with the PAM levels' switching, which results in the frequency chirp. We find that the modulator operating at different quadrature points (Q and Q) will have different frequency chirp behavior. The Q modulator has mainly negative chirp parameters while Q modulator has mainly positive chirp parameters. We characterize the eye diagrams and BER of the optical PAM-4 signals generated by the Q and Q modulator at the modulation rates of 25 Gbaud and 32 Gbaud, respectively, for both back-to-back and 2 km transmission in single mode fiber. The BER results show the Q modulator has a small power penalty attribute to the positive fiber dispersion, which is suited for the short-distance transmission in data center application.
我们提出了一种分析模型，通过驱动单个双驱动硅光调制器，采用四电平脉冲幅度调制（PAM-4）光调制方法来研究固有频率啁啾。利用该分析模型，我们对这种PAM-4产生的啁啾参数进行了数值计算。输出信号的强度和相位随PAM电平的切换而变化，这导致了频率啁啾。我们发现，在不同正交点（Q和Q）工作的调制器会有不同的频率啁啾行为。Q调制器的啁啾参数主要为负，而Q调制器的啁啾参数主要为正。我们分别对在25 Gbaud和32 Gbaud调制速率下，由Q和Q调制器产生的光PAM-4信号在单模光纤中的背对背和2 km传输情况下的眼图和误码率进行了表征。误码率结果表明，由于正的光纤色散，Q调制器具有较小的功率代价，这适用于数据中心应用中的短距离传输。
