Intensity modulation and direct detection (IM/DD) together with pulse amplitude modulation (PAM) is a cost-efficient solution for intra-datacenter links. However, sophisticated digital signal processing (DSP) is inevitable to reach the demanded high data rates for these short-reach applications. In this article, we compare different DSP schemes that enable rates of 200 Gb/s/λ and beyond. Those schemes include Tomlinson–Harashima precoding, partial response signaling, Viterbi equalization and post-filtering together with Volterra nonlinear equalization. Extensive experimental measurements are shown in which the DSP approaches are compared at gross rates between 180 Gb/s and 300 Gb/s. The experiments are done in C-band for fiber links of up to 2 km length. As modulation formats, PAM4, PAM6, and PAM8 are considered. Net bit rates well over 200 Gb/s are shown for all formats at a range of 1 km single mode fiber using a transmission system consisting of currently available commercial components. The optimum DSP configuration as well as the best modulation format varies along the investigated data rates. The best solution is shown to change from partial response PAM4 for lower rates to PAM6 and PAM8 at high bit rates.

中文翻译：

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用于使用 PAM 的高速短距离 IM/DD 系统的 DSP

强度调制和直接检测 (IM/DD) 以及脉冲幅度调制 (PAM) 是用于数据中心内链路的经济高效的解决方案。然而，复杂的数字信号处理 (DSP) 不可避免地要达到这些短距离应用所需的高数据速率。在本文中，我们比较了实现 200 Gb/s/λ 及更高速率的不同 DSP 方案。这些方案包括 Tomlinson-Harashima 预编码、部分响应信令、Viterbi 均衡和后滤波以及 Volterra 非线性均衡。显示了广泛的实验测量，其中 DSP 方法在 180 Gb/s 和 300 Gb/s 之间的总速率下进行了比较。实验是在 C 波段进行的，用于长达 2 公里的光纤链路。作为调制格式，考虑了 PAM4、PAM6 和 PAM8。使用由当前可用的商业组件组成的传输系统，在 1 公里单模光纤的范围内，所有格式的净比特率都显示出远远超过 200 Gb/s。最佳 DSP 配置以及最佳调制格式随调查的数据速率而变化。最佳解决方案显示为从较低速率的部分响应 PAM4 更改为高比特率的 PAM6 和 PAM8。