In the evolution of optical networks, spectral efficiency (SE) enhancement has been the most cost-efficient and thus the main driver for capacity increase for decades. As a result, the development of optical transport systems has been focused on the $C$ - and $L$ -bands, where silica optical fiber exhibits the lowest attenuation, and erbium-doped fiber amplifiers provide an efficient solution to compensate for the optical loss. With a gradual maturity in the SE growth, however, the extension of the optical bandwidth beyond the $C + L$ -band is expected to play a significant role in future capacity upgrades of optical networks and, thus, attract increasing research interests. In this article, we discuss the merits and challenges of ultrawideband optical transport systems and networks beyond conventional bands.

中文翻译：

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超宽带系统和网络：超越 C + L 波段

在光网络的发展过程中，频谱效率 (SE) 增强一直是最具成本效益的，因此是数十年来容量增加的主要驱动力。因此，光传输系统的发展一直集中在 $加元 - 和 $L$ - 波段，其中二氧化硅光纤的衰减最低，而掺铒光纤放大器提供了一种有效的解决方案来补偿光损耗。然而，随着 SE 增长的逐渐成熟，光带宽的扩展超出了 $C + L$ - 波段有望在未来光网络容量升级中发挥重要作用，从而吸引越来越多的研究兴趣。在本文中，我们讨论了超宽带光传输系统和网络超出常规频段的优点和挑战。