Li Jingchi, An Shaohua, Su Yikai
Opt Lett. 2020 Nov 15;45(22):6178-6181. doi: 10.1364/OL.410473.
We propose and experimentally demonstrate a joint equalization scheme to recover a zero-guard band dual-single sideband (dual-SSB) four-level pulse amplitude modulation (PAM4) signal in a system with moderate bandwidth limitation. In the joint equalization scheme, a multiple-input multiple-output feedforward equalizer (MIMO-FFE) is first used to mitigate the residual crosstalk resulting from non-ideal optical filtering. Then, a modified post filter (PF) is placed after the MIMO-FFE to suppress the MIMO-FFE-enhanced low-frequency noise, whereas the known inter-symbol interference introduced by the modified PF is further eliminated with the maximum likelihood sequence estimation algorithm. Based on the proposed scheme, we experimentally demonstrate a 112-Gb/s zero-guard band dual-SSB PAM4 signal transmission over an 80-km single mode fiber with the averaged bit error ratio of two sidebands below 3.8×10. We also achieve, to the best of our knowledge, a record electrical spectral efficiency of 7.1 b/s/Hz for single polarization direct detection systems using a dual-SSB PAM4 or dual-SSB 16-quadrature amplitude modulation format.
我们提出并通过实验证明了一种联合均衡方案，用于在具有适度带宽限制的系统中恢复零保护带双单侧边带（dual-SSB）四电平脉冲幅度调制（PAM4）信号。在联合均衡方案中，首先使用多输入多输出前馈均衡器（MIMO-FFE）来减轻由非理想光学滤波导致的残余串扰。然后，在MIMO-FFE之后放置一个改进的后置滤波器（PF），以抑制MIMO-FFE增强的低频噪声，而由改进的PF引入的已知符号间干扰则通过最大似然序列估计算法进一步消除。基于所提出的方案，我们通过实验证明了在80公里单模光纤上112-Gb/s零保护带dual-SSB PAM4信号传输，两个边带的平均误码率低于3.8×10。据我们所知，我们还实现了使用dual-SSB PAM4或dual-SSB 16正交幅度调制格式的单偏振直接检测系统创纪录的7.1 b/s/Hz的电频谱效率。
