Alternate-mark-inversion (AMI) has been used in the past to improve the transmission performance of binary intensity modulation formats. In this work, we improved the tolerance of O-band 4-level pulse amplitude modulation (PAM4) transmission to channel impairments through the adoption of an AMI scheme. Improvements in receiver sensitivity were shown in both semiconductor optical amplifier (SOA) and bismuth-doped fibre amplifier (BDFA) equipped links. We confirmed the capability of 4-level AMI to extend the reach in the O-band, which was achieved through the mitigation of nonlinear and dispersive effects. We experimentally demonstrated a 4.28-dB Q-factor improvement for transmission over 60 km of SMF-28e. To offer an insight to the mechanisms leading to the improved tolerance to transmission impairments, we presented numerical simulations that illustrate the underlying method of action of AMI4.

中文翻译：

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用于O波段频谱范围扩展的4级交替标记反转

过去已经使用交替标记反转（AMI）来提高二进制强度调制格式的传输性能。在这项工作中，我们通过采用AMI方案，提高了O波段4级脉冲幅度调制（PAM4）传输对信道损伤的容忍度。配备半导体光放大器（SOA）和掺铋光纤放大器（BDFA）的链路均显示出接收器灵敏度的提高。我们确认了4级AMI可以扩展O波段的覆盖范围，这是通过减轻非线性和色散效应实现的。我们通过实验证明了SMF-28e超过60公里传输的Q因子提高了4.28 dB。为了深入了解导致对传输损伤的耐受性提高的机制，