Combined Symbol-Pattern-Dependent Adaptive Equalization and Sequence Detection for Coherent Optical Fiber Communications
Yi Cai, Hung‐Chang Chien, Meng Xiang, Wei Wang, Fan Li, Zihe Hu, Mingyi Gao, Chenxu Jiang, Zhongxing Tian, Hansheng Xu, Kaisheng Zhang, Jiaojie Shen, Ji Ting Huang
Abstract
The key idea of this work is to treat the symbol- pattern-dependent inter-symbol-interference (ISI) that is avoided in conventional single-symbol modulation systems as useful symbol correlation, incorporate the feature of the symbol correlation into both adaptive equalization and sequence detection and thus, upgrade the system to a multi-symbol-oriented pattern-dependent equalization and detection regime. Specifically, we propose an adaptive equalization scheme sharing a pattern-dependent look- up-table with a maximum likelihood sequence estimation process to facilitate tolerance and mitigation on symbol-pattern-dependent ISI. The proposed scheme can be applied to various transmission systems with linear or nonlinear pattern-dependent ISI, such as bandwidth constrained systems with severe linear ISI, or high-power long-distance transmission systems with fiber nonlinearity induced self-phase modulation. In exemplary coherent transmission systems with digital narrow filtering before digital to analog conversion at transmitter, we experimentally demonstrate effective demodulation and detection of a polarization-division-multiplexing quaternary- phase-shift-keying signal with a constrained 3-dB transmitter bandwidth down to 1/8 of thesignal baud rate.