Abstract
In long haul optical fiber communication networks, whichcan span thousands of kilometers, bandwidth is at a premium due to the relatively low availability of optical fibers when compared with network traffic demands. Therefore, these networks require the highest performance in the physical layer, with transceivers that are capable of extracting all the available capacity from each optical fiber. Digital coherent transmitters and receivers, which enhance optical transmission systems by using digital signal processing, are essential for achieving this goal. This tutorial discusses the digital signal processing techniques that are used in the design of high performance coherent modems to compensate for adverse channel effects such as fiber impairments and optoelectronic device non-idealities.
Highlights
Color versions of one or more of the figures in this article are available online at https://ieeexplore.ieee.org.Manuscript received July 19, 2021.I N little over a decade, coherent optical fiber communications have gone from the research laboratory to extensive commercial deployment
Coherent optical transmission systems were extensively investigated in the latter half of the 20th century, it was the introduction of digital signal processing (DSP) [1] that enabled this extensive deployment in optical networks
Probabilistic constellation shaping – a technique which improves the linear signal to noise ratio (SNR) tolerance and possibly allows fine tuning of spectral efficiency (SE) – has been incorporated in commercial systems only in the last few years. In this tutorial paper, we provide an up-to-date summary of DSP algorithms for coherent optical fiber communication; focusing on the high performance and flexibility that is crucial for long haul transmissions systems
Summary
Color versions of one or more of the figures in this article are available online at https://ieeexplore.ieee.org. By linearly mapping signals between the optical and digital domains, these digital coherent transceivers are able to compensate for channel impairments, such as chromatic dispersion, which had previously limited the achievable data rate and transmission reach of direct detection systems. In contrast to short reach interconnects, the coherent transceivers used in long haul links must be extremely high performance; extracting all the available capacity from any given optical fiber. It is this type of transmission link that requires a performance oriented DSP design and will be the subject of this tutorial.
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