Authors: Zhou, HH; Li, Y; Lu, D; Yue, L; Gao, C; Liu, YY; Hao, RB; Zhao, ZX; Li, W; Qiu, JF; Hong, XB; Guo, HX; Zuo, Y; Wu, J
OPTICS EXPRESS
Volume: 27 Issue: 8 Pages: 11385-11395 Published: APR 15 2019 Language: English Document type: Article
DOI: 10.1364/OE.27.011385
Abstract:
With the rapid development of cloud services, data-center applications and the Internet of Things, short-reach communications have attracted much more attention in recent years. 4-level pulse amplitude modulation (PAM4) is a promising modulation format to provide both high data rate and relatively low cost for short-reach optical interconnects. In this paper, a joint clock recovery and feed-forward equalization algorithm (CR-FFE) is proposed to simultaneously eliminate the inter-symbol interference (ISI) and track large sampling clock offset (SCO) in PAM4 transmission. The algorithm estimates timing error according to the difference between two tap coefficients of fractionally spaced equalizers, thus solving the problem of incompatible prerequisites between clock recovery and channel equalization. A 10GHz directly modulated laser (DML) based 50-Gbit/s PAM4 transmission experiment is implemented to investigate the performance of the proposed algorithm. Experimental results show that the proposed CR-FFE algorithm can resist SCO up to 1000ppm after 40 km standard single-mode fiber (SSMF) transmission under the 2x10(-2) SD-FEC BER threshold, which is dramatically improved comparing with that of 20 ppm in traditional CR cascaded by FFE algorithm. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
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