We measure the FM noise power spectral density of quantum-dot mode-locked lasers (QD-MLLs) and compare this to their measured linewidths as predictors of performance in a digital coherent system. We explain our observations in terms of the non-Lorentzian line shape of the source wherein linewidth is determined by the low frequency part of its FM noise. Investigation of system performance with simulations based on the measured phase sequences and back-to-back coherent transmission experiments show that QD-MLLs with linewidths of several megahertz can have comparable performance to that of a laser with only a few hundreds of kilohertz of Lorentzian linewidth, due to the non-white part of their FM noise. We show that spectral linewidths of lasers with similar spectral properties can underestimate their performance in coherent systems, regardless of the linewidth measurement technique used. We propose a “Lorentzian-equivalent linewidth” measure to characterize lasers with non-white FM noise and to estimate their impact in digital coherent optical systems. This measure is obtained from phase variations at frequencies higher than typical frequencies often used to characterize lasers with white FM noise and comparable to the system baud. The proposed measure is shown to be a better predictor of system performance than the measured linewidth, for lasers with non-white FM noise. The impact of non-white FM noise on the optimization of carrier phase recovery and system performance is also discussed.

中文翻译：

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用于数字相干光学系统的具有非白色调频噪声的激光器的相位噪声测量和性能

我们测量量子点锁模激光器 (QD-MLL) 的 FM 噪声功率谱密度，并将其与作为数字相干系统性能预测指标的测量线宽进行比较。我们根据源的非洛伦兹线形状来解释我们的观察，其中线宽由其 FM 噪声的低频部分决定。通过基于测量的相位序列和背靠背相干传输实验的模拟研究系统性能表明，具有几兆赫线宽的 QD-MLL 可以具有与只有几百千赫的洛伦兹线宽的激光器相当的性能，由于其 FM 噪声的非白色部分。我们表明，具有相似光谱特性的激光器的光谱线宽会低估它们在相干系统中的性能，无论使用何种线宽测量技术。我们提出了一种“洛伦兹等效线宽”措施来表征具有非白色调频噪声的激光器并估计它们在数字相干光学系统中的影响。该测量值是从频率高于典型频率的相位变化中获得的，典型频率通常用于表征具有 FM 白噪声的激光器，并且与系统波特率相当。对于具有非白色 FM 噪声的激光器，所提出的测量显示出比测量的线宽更好地预测系统性能。还讨论了非白调频噪声对载波相位恢复和系统性能优化的影响。我们提出了一种“洛伦兹等效线宽”措施来表征具有非白色调频噪声的激光器，并估计它们在数字相干光学系统中的影响。该测量值是从频率高于典型频率的相位变化中获得的，典型频率通常用于表征具有 FM 白噪声的激光器，并且与系统波特率相当。对于具有非白色 FM 噪声的激光器，所提出的测量显示出比测量的线宽更好地预测系统性能。还讨论了非白调频噪声对载波相位恢复和系统性能优化的影响。我们提出了一种“洛伦兹等效线宽”措施来表征具有非白色调频噪声的激光器，并估计它们在数字相干光学系统中的影响。该测量值是从频率高于典型频率的相位变化中获得的，典型频率通常用于表征具有 FM 白噪声的激光器，并且与系统波特率相当。对于具有非白色 FM 噪声的激光器，所提出的测量显示出比测量的线宽更好地预测系统性能。还讨论了非白调频噪声对载波相位恢复和系统性能优化的影响。对于具有非白色 FM 噪声的激光器，所提出的测量显示出比测量的线宽更好地预测系统性能。还讨论了非白调频噪声对载波相位恢复和系统性能优化的影响。对于具有非白色 FM 噪声的激光器，所提出的测量显示出比测量的线宽更好地预测系统性能。还讨论了非白调频噪声对载波相位恢复和系统性能优化的影响。