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Performance enhanced probabilistically shaped PAM4 signal based on nonlinear differential coding for IM/DD system

OPTICAL FIBER TECHNOLOGY 2022年 71卷

作者： Liu, Tianyi Ma, Jie Lu, Jia Liu, Jianfei Zeng, Xiangye Wang, Yang Hebei Univ Technol Sch Elect & Informat Engn Tianjin 300401 Peoples R China Tianjin Key Lab Elect Mat & Devices Tianjin 300401 Peoples R China

In this paper, the probabilistically shaped pulse amplitude modulation (PS-PAM) signal is proposed in intensity modulation and direct detection (IM/DD) system. For the traditional shaping scheme with constant composition distribution matcher (CCDM), there are several problems that high-precision algorithm for long block coding, the loss of information rate for short block coding. In addition, it can increase nonlinear interference. In order to reduce computational complexity and alleviate the influence of nonlinear interference on the system, the nonlinear differential coding (NLDC) scheme is used to realize PS, which can be better integrated with the costeffective optical access network. This paper evaluates seven shaping spectrums obtained by different NLDC coding coefficients. As the coding coefficient increases, the performance of the system gradually improves. Moreover, this paper proposed the machine learning includes neural network (NN) and improved K-means clustering algorithm at the receiver. The results show that the PS-PAM4 signal is significantly better than the ordinary PAM4 signal in improving the channel bandwidth tolerance and signal transmission rate. Under the same data rate, using NLDC can save 5.8 GHz bandwidth for the system. For the bandwidth-limited system, the PS-PAM4 signal can obtain 19Gbit/s bit rate gain compared with the ordinary PAM4 signal. Compared with the typical shaping scheme using CCDM, this scheme can achieve 2.2 GHz band tolerance gain and 5Gbit/s rate gain in nonlinear fiber channel.

关键词： Intensity modulation and direct detection Probabilistic shaping nonlinear differential coding Neural network K-means clustering algorithm

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Performance analysis of spectrally shaped DDO-OFDM based on nonlinear differential coding and real-valued precoding

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OPTICS COMMUNICATIONS 2023年第1期542卷

作者： Ma, Jie Song, Ruoling Lu, Jia Liu, Jianfei Liu, Tianyi Luo, Mingming Hebei Univ Technol Sch Elect & Informat Engn Tianjin 300401 Peoples R China Univ Technol China Tianjin Key Lab Elect Mat & Devices Tianjin 300401 Peoples R China Hebei Prov Key Lab Adv Laser Technol & Equipment Tianjin 300401 Peoples R China

This paper presents a cost-effective spectrally shaped quadrature amplitude modulation (SS-QAM) signal in bandwidth limited direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems. The concatenation of the nonlinear differential coding (NLDC) and real-valued precoding sequentially implements spectral-shaping and multi-carrier modulation. Real-value discrete cosine transform (DCT) and discrete Hartley transform (DHT) are used to realize the uniform distribution of the fluctuation signal-to-noise ratio (SNR) and reduce the peak-to-average power ratio (PAPR). To broaden the flexibility of constellation mapping and improve the fine granularity of signals, six modulation formats are analyzed and evaluated in DDO-OFDM systems. Results show that SS-QAM is superior to uniformly distributed QAM in terms of reducing bit error rate (BER) and increasing normalized generalized mutual information (NGMI). Compared to the uniform 25/36/49/64/81/100 QAM OFDM signal, when the transmission distance is 20 km, SS-25/36/49 QAM signal can achieve error free transmission and SS-64/81/100 QAM can achieve 0.9971/1.0037/1.0255 Q-factor improvement and 0.0009/0.0014/0.0015 NGMI gain. When the transmission distance is 50 km, SS -25/36/49/64/81/100 QAM can achieve 0.4182/0.5169/0.9311/0.9988/1.0216/1.1487 Q-factor improvement and 0.0004/0.0008/0.0031/0.0043/0.0066/0.0083 NGMI gain. When the transmission distance is 80 km, SS -25/36/49/64/81/100 QAM can achieve 0.4754/0.7486/1.181/1.2012/1.2302/1.3904 Q-factor improvement and 0.0015/0.0046/0.0108/0.0152/0.0172/0.0205 NGMI gain. In addition, the Q-factor and NGMI gain increases as the fiber length increases, which verifies that the presented scheme is robust to the nonlinear effect.

关键词： DDO-OFDM nonlinear differential coding Spectral shaping Real-valued precoding

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Spectral shaped PAM4 signal based on nonlinear differential coding for AOWC system with Self-pumping structure

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OPTICAL FIBER TECHNOLOGY 2022年第0期73卷

作者： Liu, Tianyi Lu, Jia Ma, Jie Wang, Yang Liu, Jianfei Hebei Univ Technol Sch Elect & Informat Engn Tianjin 300401 Peoples R China Tianjin Key Lab Elect Mat & Devices Tianjin 300401 Peoples R China Hebei Prov Key Lab Adv Laser Technol & Equipment Tianjin 300401 Peoples R China

Spectral shaped 4-level pulse amplitude modulation (PAM4) signal based on nonlinear different coding (NLDC) is proposed in an all-optical wavelength conversion (AOWC) system with self-pumping structure. Laser-driven Mach-Zehnder modulator generates multiple spectra and forms self-pumping structure by selecting signal and pump light, which can ignore the laser phase conversion noise. However, uniform PAM4 signal is severely distorted by nonlinear effects of the practical bandwidth-limited and power-limited AOWC systems. In order to effectively reduce nonlinear interference and fully evaluate the performance of the AOWC systems with selfpumping structure, the PAM4 signal based on NLDC is proposed and demonstrated in two AOWC systems based on parallel pump and vertical pump structures. Compared with the uniform PAM4 signal, the bit error rate (BER) of converted light with NLDC can be reduced by two orders of magnitude, two pump structures can reach 3.496 x 10-5 and 2.85 x 10-4, respectively. The two structures can obtain bandwidth tolerance gains of 3.45 GHz and 3.7 GHz, respectively. When the bandwidth is 18 GHz, this scheme can obtain more than 10Gbit/s data rate gain. In addition, NLDC can make PAM4 signal insensitive to the injection current of semiconductor optical amplifier, which proves that the proposed scheme has high tolerance to the nonlinear effect and is suitable for high-capacity AOWC system.

关键词： Self -pumping All -optical wavelength conversion Spectral shaping nonlinear differential coding

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