We experimentally demonstrate a 56-Gb/s vestigial sideband (VSB) modified duobinary (MDB) 4-level pulse amplitude modulation (PAM4) signal transmission over an 80-km single-mode fiber (SMF) in an intensity-modulation and direct-detection (IM/DD) system without optical dispersion compensation. Compared to the conventional PAM4 signal without pulse shaping, the MDB PAM4 signal exhibits a higher spectral efficiency (SE) due to the modified duobinary precoding. Moreover, if VSB modulation is employed to mitigate the chromatic dispersion (CD)-induced power fading, the VSB MDB PAM4 signal suffers less image interference resulting from VSB filtering and direct detection (DD), thanks to its lower components at the carrier frequency. A proof-of-concept experiment is performed, in which the performances of the conventional VSB PAM4 signal, the VSB Nyquist PAM4 signal, and the VSB MDB PAM4 signal are investigated and compared comprehensively. The experimental results show that only the VSB MDB PAM4 signal can reach the bit error ratio (BER) below the 20% soft-decision forward error correction (SD-FEC) threshold of $2.4\times 10^{-\mathrm {2}}$ at the 56-Gb/s rate after the 80-km SMF transmission, due to the mitigated image interference.

中文翻译：

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具有减轻图像干扰的 IM/DD 系统中的 VSB 修正双二进制 PAM4 信号传输

我们通过实验证明了 56 Gb/s 残留边带 (VSB) 修正双二进制 (MDB) 4 级脉冲幅度调制 (PAM4) 信号在 80 公里单模光纤 (SMF) 上的强度调制和直接传输。没有光色散补偿的检测 (IM/DD) 系统。与没有脉冲整形的传统 PAM4 信号相比，由于改进的双二进制预编码，MDB PAM4 信号表现出更高的频谱效率 (SE)。此外，如果采用 VSB 调制来减轻色散 (CD) 引起的功率衰减，由于 VSB MDB PAM4 信号在载波频率上的分量较低，因此 VSB 滤波和直接检测 (DD) 导致的图像干扰较少。进行了概念验证实验，其中常规 VSB PAM4 信号的性能，VSB Nyquist PAM4 信号和 VSB MDB PAM4 信号进行了综合研究和比较。实验结果表明，只有VSB MDB PAM4信号才能达到低于$2.4\times 10^{-\mathrm {2}}的20%软判决前向纠错（SD-FEC）阈值的误码率（BER）由于减轻了图像干扰，在 80 公里 SMF 传输后以 56 Gb/s 的速率传输。