Wang Li, Jiang Hexun, He Huan, Luo Fengguang, Tang Ming
Opt Lett. 2021 Apr 1;46(7):1526-1529. doi: 10.1364/OL.417598.
Fractional Fourier transform (FrFT) training sequences (TSs) have been proposed to superimpose with signals to achieve time synchronization and polarization mode dispersion (PMD) estimation simultaneously before equalization. The feasibility of the proposed scheme is verified by experiment of a 30 GBaud/s PDM quadrature phase shift keying (QPSK) system. Without sacrificing spectrum efficiency, the proposed PMD estimation is robust against amplifier spontaneous emission (ASE) noise and has steady performance in a wide PMD range from 0 ps to 108 ps. The root mean square error (RMSE) of PMD is 5.6 ps by experimental verification. Further, the PMD estimated before equalization is utilized to adjust the numbers of taps in a subsequently tap-varied equalizer, which achieves feedforward adaptive equalization (FFD-AEQ). The number of the AEQ taps is adjusted to an optimal value with the prior-PMD information estimated by FrFT TSs. The experimental results show that the tap-varied AEQ has 52.6% power consumption decrease compared to the tap-fixed AEQ with 13 taps.
分数傅里叶变换（FrFT）训练序列（TSs）已被提出与信号叠加，以便在均衡之前同时实现时间同步和偏振模色散（PMD）估计。通过一个30 GBaud/s偏振复用正交相移键控（QPSK）系统的实验验证了该方案的可行性。在不牺牲频谱效率的情况下，所提出的PMD估计对放大器自发辐射（ASE）噪声具有鲁棒性，并且在从0 ps到108 ps的宽PMD范围内具有稳定的性能。通过实验验证，PMD的均方根误差（RMSE）为5.6 ps。此外，在均衡之前估计的PMD被用于调整随后的抽头可变均衡器中的抽头数量，从而实现前馈自适应均衡（FFD-AEQ）。利用FrFT TSs估计的先验PMD信息将AEQ抽头数量调整到最优值。实验结果表明，与具有13个抽头的固定抽头AEQ相比，抽头可变AEQ的功耗降低了52.6%。
