Modulation format identification (MFI) is widely used in elastic optical networks, such as optical performance monitoring and signal compensation. We propose an MFI scheme, through extraction of the amplitude probability distribution feature of the received signals and an analysis of the relative entropy, which is also known as the Kullback–Leibler divergence (KL). The modulation formats (MFs) can be distinguished via calculation of the KL value. Through this method, four commonly used transmission formats were investigated, namely, polarization-division multiplexing (PDM)-QPSK/16QAM/32QAM and 64QAM. A simulation transmission model was created, and the results were analyzed. The simulation results show that the MFs investigated can be distinguished when the optical signal-to-noise ratio (OSNR) is less than or equal to the corresponding theoretical 7% forward error correction (FEC) limit (bit error ratio = 3.8 × 10 − 3). In addition, two important factors, i.e., fiber nonlinearity and sample size, were investigated in relation to the proposed method. The results show that the method exhibits a certain tolerance to fiber nonlinearity and can be used to identify the MF at the FEC threshold even when the sample number is 1000. Furthermore, the experimental verifications were conducted to ensure the practicality of the proposed method.

中文翻译：

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基于相对熵的相干光通信系统调制格式识别

调制格式识别（MFI）广泛应用于弹性光网络，如光性能监测和信号补偿。我们提出了一种 MFI 方案，通过提取接收信号的幅度概率分布特征和分析相对熵，也称为 Kullback-Leibler 散度（KL）。调制格式 (MF) 可以通过计算 KL 值来区分。通过这种方法，研究了四种常用的传输格式，即偏振分复用（PDM）-QPSK/16QAM/32QAM和64QAM。建立了仿真传输模型，并对结果进行了分析。仿真结果表明，当光信噪比 (OSNR) 小于或等于相应的理论 7% 前向纠错 (FEC) 限制（误码率 = 3.8 × 10 -）时，可以区分所研究的 MF。 3）。此外，研究了与所提出的方法相关的两个重要因素，即光纤非线性和样本大小。结果表明，该方法对光纤非线性具有一定的容忍度，即使样本数为1000，也可用于识别FEC阈值下的MF。此外，还进行了实验验证，以确保所提出方法的实用性。对所提出的方法进行了研究。结果表明，该方法对光纤非线性具有一定的容忍度，即使样本数为1000，也可用于识别FEC阈值下的MF。此外，还进行了实验验证，以确保所提出方法的实用性。对所提出的方法进行了研究。结果表明，该方法对光纤非线性具有一定的容忍度，即使样本数为1000，也可以用于识别FEC阈值下的MF。此外，还进行了实验验证，以确保所提出方法的实用性。