The ever-growing machine-to-machine traffic in data centers has stimulated the increase of transceiver data rate from 25 Gb/s/λ to 100 Gb/s/λ and beyond. It is believed that advanced modulation formats and digital-to-analog converters (DACs) will be employed in next generation short-reach transceivers. Digital pre-emphasis techniques are widely employed in DAC-based transceivers to compensate for the high frequency roll-off due to the RF and optoelectronics components in optical transceivers. However, digital pre-emphasis essentially reduces the magnitude of the signal low frequency components for a flat frequency response, which unavoidably increases quantization error, reducing the overall signal-to-noise ratio. This trade-off between SNR and bandwidth conflicts with the high SNR requirement of advanced modulation formats such as the Nyquist-shaped pulse amplitude modulation (PAM). To mitigate the quantization error induced SNR degradation, we show that analog pre-emphasis filters can be used in conjunction with digital pre-emphasis for improved system performance. To understand the impact of the analog pre-emphasis filter on system performance, we analyze the relationship between the flatness of the system frequency response and the SNR degradation due to digital pre-emphasis, and demonstrate 1.1-dB increase of receiver sensitivities, for both 64-Gb/s and 128-Gb/s intensity-modulation direct detection (IM-DD) PAM4 signals, respectively employing a directly modulated laser (DML) and an electroabsorption modulator (EAM).

中文翻译：

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模拟和数字预加重对带宽受限光收发器信噪比的影响

数据中心不断增长的机器对机器流量刺激了收发器数据速率从 25 Gb/s/λ 增加到 100 Gb/s/λ 及更高。据信，下一代短距离收发器将采用先进的调制格式和数模转换器 (DAC)。数字预加重技术广泛用于基于 DAC 的收发器，以补偿由于光收发器中的 RF 和光电子组件而导致的高频滚降。然而，数字预加重本质上降低了信号低频分量的幅度以获得平坦的频率响应，这不可避免地增加了量化误差，降低了整体信噪比。SNR 和带宽之间的这种权衡与诸如奈奎斯特形脉冲幅度调制 (PAM) 等高级调制格式的高 SNR 要求相冲突。为了减轻量化误差引起的 SNR 退化，我们展示了模拟预加重滤波器可以与数字预加重结合使用，以提高系统性能。为了了解模拟预加重滤波器对系统性能的影响，我们分析了系统频率响应的平坦度与数字预加重导致的 SNR 劣化之间的关系，并证明了两者的接收器灵敏度均增加了 1.1 dB 64-Gb/s 和 128-Gb/s 强度调制直接检测 (IM-DD) PAM4 信号，分别采用直接调制激光器 (DML) 和电吸收调制器 (EAM)。为了减轻量化误差引起的 SNR 退化，我们展示了模拟预加重滤波器可以与数字预加重结合使用，以提高系统性能。为了了解模拟预加重滤波器对系统性能的影响，我们分析了系统频率响应的平坦度与数字预加重导致的 SNR 劣化之间的关系，并证明了两者的接收器灵敏度均增加了 1.1 dB 64-Gb/s 和 128-Gb/s 强度调制直接检测 (IM-DD) PAM4 信号，分别采用直接调制激光器 (DML) 和电吸收调制器 (EAM)。为了减轻量化误差引起的 SNR 退化，我们展示了模拟预加重滤波器可以与数字预加重结合使用，以提高系统性能。为了了解模拟预加重滤波器对系统性能的影响，我们分析了系统频率响应的平坦度与数字预加重导致的 SNR 劣化之间的关系，并证明了两者的接收器灵敏度均增加了 1.1 dB 64-Gb/s 和 128-Gb/s 强度调制直接检测 (IM-DD) PAM4 信号，分别采用直接调制激光器 (DML) 和电吸收调制器 (EAM)。