Abstract
In recent years, short-reach optical links have attracted much more attention and have come to constitute a key market segment due to the rapid development of data-center applications and cloud services. Four-level pulse amplitude modulation (PAM4) is a promising modulation format to provide both a high data rate and relatively low cost for short-reach optical links. However, the direct detector and low-cost components also pose immense challenges, which are unforeseen in coherent transmission. To compensate for the impairments and to truly meet data rate requirements in a cost-effective manner, various digital signal processing (DSP) technologies have been proposed and investigated for short-reach PAM4 optical links. In this paper, an overview of the latest progress on DSP equalization technologies is provided for short-reach optical links based on PAM4 modulation. We not only introduce the configuration and challenges of the transmission system, but also cover the principles and performance of different equalizers and some improved methods. Moreover, machine learning algorithms are discussed as well to mitigate the nonlinear distortion for next-generation short-reach PAM4 links. Finally, a summary of various equalization technologies is illustrated and our perspective for the future trend is given.
Highlights
Driven by upcoming services such as the Internet of Things (IoT), 4K/8K video applications, virtual reality (VR) and big data, the global internet protocol (IP) traffic has grown explosively in recent years [1]
Various equalization technologies based on digital signal processing (DSP) have been investigated for short-reach links over the years [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53]. Conventional equalizers, such as the feed-forward equalizer (FFE) or decision feedback equalizer (DFE), are employed to compensate for the linear impairments induced by limited bandwidth and chromatic dispersion (CD) [26,27,28], while the equalizer based on the Volterra series is utilized to mitigate nonlinear distortion [29,30,31,32]
We have reviewed various equalization technologies for short-reach PAM4 optical links
Summary
Driven by upcoming services such as the Internet of Things (IoT), 4K/8K video applications, virtual reality (VR) and big data, the global internet protocol (IP) traffic has grown explosively in recent years [1]. Various equalization technologies based on digital signal processing (DSP) have been investigated for short-reach links over the years [26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53] Conventional equalizers, such as the feed-forward equalizer (FFE) or decision feedback equalizer (DFE), are employed to compensate for the linear impairments induced by limited bandwidth and CD [26,27,28], while the equalizer based on the Volterra series is utilized to mitigate nonlinear distortion [29,30,31,32]. To deal with these impairments in practical implementation, the principles of conventional.
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