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Low-Complexity Nonlinear Tomlinson-Harashima Precoding Based on Absolute-Term for ZR Inter-DCI

IEEE PHOTONICS TECHNOLOGY LETTERS 2025年第1期37卷 17-20页

作者： Chen, Zhuo Zhang, Jie Liang, Zipeng Dai, Xiaoxiao Yang, Qi Wang, Liang Deng, Lei Cheng, Mengfan Liu, Deming Huazhong Univ Sci & Technol Sch Opt & Elect Informat Wuhan 430074 Peoples R China Jinyinhu Lab Wuhan 430040 Peoples R China

Due to the sensitivity to cost and power consumption, the intensity modulation direct detection (IM/DD) transmission system attracts significant interest in inter-data center interconnections. In medium reach IM/DD transmission systems, chromatic dispersion caused power fading effect appears to be a major performance limiting problem for double sideband (DSB) signal. Tomlinson-Harashima Precoding (THP) is an effective method for compensating for the dispersion at the transmitter side. By incorporating nonlinear kernels into the transfer function, the nonlinear THP can compensate both the dispersion and the nonlinear distortion of the signal and improve the performance of the system. However, the added nonlinear kernels will significantly increase the complexity. To reduce the complexity of nonlinear THP, we propose a low-complexity absolute-term kernel based nonlinear THP scheme. Compared with the conventional Volterra kernel based THP scheme, the proposed methods can reduce the number of multipliers by 50%-60% without performance degradation. We successfully demonstrate a 70-km 40-Gbaud and a 90-km 30-Gbaud DSB PAM-4 C-band IM/DD transmission over dispersion-uncompensated links.

关键词： Kernel Decoding Complexity theory C-band Optical attenuators Optical receivers Optical transmitters Dispersion Decision feedback equalizers Precoding Data center interconnection dispersion Tomlinson-Harashima precoding intensity modulation direct detection

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Machine Learning-Assisted Mitigation of Optical Multipath Interference in PAM4 IM-DD Transmission Systems

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PHOTONICS 2025年第4期12卷 310-310页

作者： Cui, Wenxin Huo, Jiahao Zhu, Jin Tao, Jianlong Qin, Peng Zhang, Xiaoying Bai, Haolin Univ Sci & Technol Beijing Sch Comp & Commun Engn Beijing 100083 Peoples R China

This paper aims to mitigate multipath interference (MPI) in intensity modulation with direct detection (IM-DD) systems using machine learning techniques, specifically for four-level pulse amplitude modulation (PAM4) systems. We propose a machine learning-assisted MPI mitigation scheme, called KNN-aided SVM+RF-M. In this scheme, KNN-aided SVM serves as a soft decision algorithm that adapts the decision threshold to signal amplitude fluctuations, improving the decision accuracy for MPI-affected PAM4 signals. By replacing the original hard decision in the RF-M algorithm with KNN-aided SVM, we mitigate the error transfer problem inherent in RF-M. MPI mitigation is then achieved through MPI estimation and noise value cancellation methods applied to signals after soft decision processing. Our proposed scheme is validated in a 28 GBaud PAM4-DD transmission system, and the simulation results show that our proposed scheme can improve SIR tolerance by 2 dB and receiver sensitivity by about 1 dB at the 7% HD-FEC threshold compared to the original RF-M scheme.

关键词： machine learning support vector machine K-nearest neighbor intensity modulation direct detection multipath interference four-level pulse amplitude modulation

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Feedforward Neural Network Enabled Optical Multi-Path Interference Mitigation for High-Speed IM-DD Transmissions

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2024年第19期42卷 6749-6759页

作者： Qiu, Yongfeng Xiang, Meng Xiang, Junjiang Yang, Hailin Lin, Di Li, Jianping Fu, Songnian Qin, Yuwen Guangdong Univ Technol Inst Adv Photon Technol Sch Informat Engn Guangzhou 510006 Peoples R China Guangdong Prov Key Lab Informat Photon Technol Guangzhou 510006 Peoples R China

The performance of high-speed intensity modulation direct detection (IM-DD) transmission can be severely degraded by the optical multipath interference (MPI), due to the repeated reflections from polluted fiber connectors. Here, we propose a data-driven MPI mitigation scheme, utilizing a feedforward neural network (FNN) with the capability of powerful nonlinear mapping, after both the temporal and frequency domain MPI model are numerically investigated. Our simulation results reveal that, when the 28 Gbaud PAM-4 signals are transmitted over standard single mode fiber (SSMF), the proposed FNN can effectively mitigate the MPI and improve the transmission performance, under conditions of variable signal-interference ratios (SIRs) and various laser linewidths. Compared with recently reported non-data-driven MPI mitigation schemes, the FNN enabled MPI mitigation scheme can increase the SIR tolerance by 1.5, 1.8, and 0.8 dB, under conditions of 100 kHz, 1 MHz, and 10 MHz laser linewidth, respectively, in case the KP4-FEC threshold is considered. Meanwhile, we thoroughly study the simplification of the FNN enabled MPI mitigation scheme relying on the multiple-symbol-output (MSO) structure and weight pruning, leading to a computational complexity reduction by 32.4%, in comparison with non-data-driven MPI mitigation schemes. Finally, the performance of full-size FNN and simplified FNN enabled MPI mitigation is experimentally evaluated for the 28 Gbaud PAM-4 signals transmission over 10.81 km SSMF, observing a 2.2 and 0.9 dB improvement of SIR tolerance at the KP4-FEC threshold, respectively.

关键词： Feedforward neural network intensity modulation direct detection optical multipath interference signal-to-interference Feedforward neural network intensity modulation direct detection optical multipath interference signal-to-interference

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Cost-Effective 40-Gbaud THP PS-PAM-4 C-Band IM/DD Transmission for 50-km Inter-DCI Utilizing 2-bit DAC

IEEE PHOTONICS JOURNAL

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IEEE PHOTONICS JOURNAL 2024年第3期16卷 1页

作者： Chen, Zhuo Liang, Zipeng Wu, Junyu Lu, Weiqi Chang, Xinyu Dai, Xiaoxiao Yang, Qi Liu, Chen Cheng, Mengfan Deng, Lei Liu, Deming Shieh, William Huazhong Univ Sci & Technol Sch Opt & Elect Informat Wuhan 430074 Peoples R China Westlake Univ Sch Engn Hangzhou 310010 Peoples R China Jinyinhu Lab Wuhan 430040 Peoples R China

Data center interconnections are cost-sensitive. We propose and demonstrate a cost-effective C-band intensity modulation direct detection (IM/DD) transmitter for extended range (ER) inter-datacenter interconnects utilizing only a 2-bit digital-to-analog converter (DAC). Tomlinson-Harashima precoding (THP) is used in transmitter DSP to compensate for dispersion-induced impairments. Due to the uniform distribution of signal levels after THP encoding, a high-resolution DAC is required to generate electrical signals. The hardware cost of the transmitter can be significantly reduced by compressing the physical number of bits (PNOB) of the DAC to 2 bits. We quantize the signal to 4 levels and utilize up-sampling and noise shaping to greatly reduce the in-band quantization noise. The in-band signal to noise ratio (SNR) can be increased to 23 dB. We experimentally demonstrate a cost-effective 40-Gbaud probabilistic shaping PAM-4 C-band IM/DD transmission over 50-km utilizing only a 2-bit DAC in the transmitter without any optical dispersion compensation. The performance of the proposed scheme is proximate to the common case of using an 8-bit DAC. It has a BER gap of about 2 x 10(-3) only when the received optical power (ROP) is higher than -6 dBm.

关键词： Data center interconnection digital-to-analog converter tomlinson-harashima precoding intensity modulation direct detection

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Optical Multi-Path Interference Mitigation for PAM4-IMDD Systems Using Balanced Coding

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2024年第17期42卷 5918-5927页

作者： Lian, Kunjian Xu, Zengquan Qiao, Meng Li, Zongkai Wang, Jintao Liu, Jie Wang, Dawei Sun Yat sen Univ Guangdong Prov Key Lab Optoelect Informat Proc Chi Guangzhou 510275 Peoples R China Sun Yat Sen Univ Sch Elect & Informat Technol Guangzhou 510275 Peoples R China

The optical multipath interference (MPI) effect is detrimental to the widely deployed intensity modulation direct detection (IMDD) systems. Here, we develop a balanced coding scheme-minimum running digital sum (MRDS), applied at the transmitter, shaping the signal's spectrum to suppress the low-frequency carrier-carrier beat noise. Thus, it helps mitigate MPI with a much smaller power penalty. Compared to other reported methods, it requires only simple operations with low computational complexity at the expense of small overhead. Simulation and experimental results confirm the coding scheme can effectively improve the bit error rate (BER) performance of a high baudrate four-level pulse amplitude modulation (PAM4) IMDD system under various signal-to-interference ratio (SIR), received optical power (ROP), and laser linewidth. Assisted with the cascade of feed-forward equalization (FFE), post filtering (PF), and maximum likelihood sequence estimation (MLSE), the MRDS coding performs the best among all the compared MPI mitigation methods in an experimental 30 Gbaud PAM4-IMDD system.

关键词： Optical fibers Optical reflection Optical receivers Adaptive optics Optical crosstalk Noise Symbols intensity modulation direct detection multipath interference balanced codes

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Silicon Photonic Phase-Diverse Receiver Enabling Transmission of >Net 250 Gbps/? Over 40 km for High-Speed and Low-Cost Short-Reach Optical Communications

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2023年第12期41卷 3680-3687页

作者： Hu, Yixiang Li, Xueyang Mao, Deng Alam, Md Samiul Berikaa, Essam Zhang, Jinsong Bernal, Santiago Samani, Alireza Mousa-Pasandi, Mohammad E. O'Sullivan, Maurice Plant, David V. McGill Univ Dept Elect & Comp Engn Montreal PQ H3A 0E9 Canada Peng Cheng Lab Shenzhen Peoples R China Ciena Corp Ottawa ON K2K 0L1 Canada

The fast growth of data traffic in short-reach optical communications drives the demand for high-speed and low-cost optical modules. Here we demonstrate a silicon photonic (SiP) phase-diverse receiver based on our recently proposed asymmetric self-coherent detection (ASCD) scheme with Mach-Zehnder interferometers (MZI). The SiP MZI-ASCD receiver has a hardware-efficient architecture and recovers complex double-sideband signals via the beatings between a signal portion and a delayed signal portion from an asymmetric MZI using only 2 single-ended photodiodes and 2 analog-to-digital converters. The removal of the local oscillator in the direct detection receiver enables low-cost uncooled lasers, whereas the phase diversity closes the gap with coherent detection in terms of electrical spectral efficiency (ESE). Using a SiP MZI-ASCD receiver with a 15 ps delay, we detect a 60 Gbaud single-polarization 16-QAM signal transmitted over 40 km of single-mode fiber (SMF) below 20% overhead (OH) SD-FEC threshold of 2 x 10(-2) with a net bit rate of 200 Gbps and a record net ESE of 5.86 b/s/Hz per wavelength per polarization. Using a SiP MZI-ASCD receiver with a different delay of 7.5 ps, transmission of single-polarization 16-QAM DSB signal up to 80 Gbaud over 40 km is achieved below 24% OH SD-FEC threshold of 4.5 x 10(-2) with a record net bit rate of 258 Gbps and a net ESE of 5.31 b/s/Hz per wavelength per polarization.

关键词： Coherent detection integrated receivers intensity modulation direct detection phase diversity self-coherent detection short-reach optical communications silicon photonics

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400 Gbps/λ PAM-4 data transmission over FSO link by employing space division multiplexing for data center interconnects using LG modes enabled VCSELs

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OPTICAL AND QUANTUM ELECTRONICS 2023年第3期55卷 1-12页

作者： Raza, Aadil Iqbal, Saeed Iqbal, Muhammad Mirza, Jawad Ghafoor, Salman Atieh, Ahmad COMSATS Univ Islamabad CUI Dept Phys Islamabad Pakistan Barani Inst Informat Technol Dept Comp Sci Rawalpindi Pakistan Natl Univ Technol NUTECH Dept Comp Sci Islamabad Pakistan SEECS Photon Res Grp Islamabad Pakistan Natl Univ Sci & Technol NUST SEECS Islamabad Pakistan Optiwave Syst Inc Ottawa ON K2E 8A7 Canada

In this paper, a high-speed short-reach free space optical (FSO) transmission system is proposed for data center interconnect (DCI). This system supports the transmission of 400 Gbps over a single wavelength by employing spatial vertical cavity surface emitting lasers. Space division multiplexing along with polarization division multiplexing of the Laguerre-Gaussian (LG) modes (LG(00) and LG(01)) are exploited to achieve higher capacity over FSO channel. intensity modulation direct detection scheme is used in the proposed system for cost-efficiency. Least mean square equalization is applied to the received data signals to mitigate the FSO channel's impairments. The performance of the proposed system is evaluated by observing the bit error ratio (BER) for weak, moderate and strong turbulences at different weather dynamics. The effects of polarization induced crosstalk and aperture misalignment induced crosstalk on BER degradation are also investigated. FSO channel lengths of 700 m, 500 m and 150 m are achieved for weak, moderate and strong turbulences, respectively. The receiver sensitivities at forward error correction limit of 3.8 x 10(-3 )for each FSO channel length are compared with back to back configuration. A penalty of 2.5 dB is observed for strong turbulence whereas 2 dB and 0.6 dB penalties are obtained for moderate and weak turbulences, respectively. The proposed FSO-DCI could be used to provide high aggregate transmission capacity of 800 Gbps and 1.6 Tbps for future DCI by adding more LG modes or other wavelengths.

关键词： Free space optical communication Pulse amplitude modulation Space division multiplexing intensity modulation direct detection Data center interconnect Bit error ratio

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Hardware-Efficient Duobinary Neural Network Equalizers for 800 Gb/s IM/DD PAM4 Transmission Over 10 km SSMF

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2023年第12期41卷 3783-3790页

作者： Bluemm, Christian Liu, Bo Li, Bing Rahman, Talha Hossain, Md Sabbir-Bin Schaedler, Maximilian Schlichtmann, Ulf Kuschnerov, Maxim Calabro, Stefano Huawei Munich Res Ctr Opt & Quantum Commun Lab D-80992 Munich Germany Tech Univ Munich Chair Elect Design Automat D-80333 Munich Germany

In this article, we discuss challenges and options for scaling IM/DD transceivers towards 800 Gbps. Our focus is CWDM4 PAM4 transmission and our target distance is 10 km in O-band, which is a most urgent use case for next generation optical short reach systems like data centre interconnects and networks. At this reach and rate, chromatic dispersion (CD) becomes the main challenge. Its mitigation is essential and primarily done with digital signal processing. State of the art techniques, however, make transceivers quickly too complex. We show upon measurement results how neural network equalization can meet Volterra equalization performance with 30% less hardware multiplier complexity. When also applying magnitude weight pruning, an additional 43% reduction is possible without performance loss across all CWDM4 lanes. If needed, an added MLSE stage can further push performance in both cases. In any of these configurations, a key enabler against strong CD penalties is duobinary training, which is applicable to all feed-forward equalization architectures.

关键词： Chromatic dispersion mitigation digital signal processing intensity modulation direct detection neural network equalizer

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170 Gbaud On-Off-Keying SiP Ring Resonator Modulator-based Link for Short-Reach Applications

170 Gbaud On-Off-Keying SiP Ring Resonator Modulator-based L...

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Silicon Photonics Conference (SiPhotonics)

作者： Ostrovskis, Armands Salgals, Toms Koenigsmann, Michael Farid, Azra Marinins, Aleksandrs Kruger, Benjamin Pittala, Fabio Scott, Ryan P. Haisch, Hansjoerg Zhang, Lu Yu, Xianbin Puerta, Rafael Spolitis, Sandis Schatz, Richard Gallo, Katia Gruen, Markus Louchet, Hadrien Yamaguchi, Kazuo Bobrovs, Vjaceslavs Pang, Xiaodan Ozolins, Oskars Riga Tech Univ Inst Telecommun LV-1048 Riga Latvia Riga Tech Univ Commun Technol Res Ctr LV-1048 Riga Latvia Keysight Technol Deutschland GmbH D-71034 Boblingen Germany Keysight Technol Inc Santa Clara CA USA Zhejiang Univ Coll Informat Sci & Elect Engn Hangzhou Peoples R China Zhejiang Lab Hangzhou Peoples R China Ericsson AB Ericsson Res Stockholm Sweden KTH Royal Inst Technol Dept Appl Phys S-10691 Stockholm Sweden Keysight Technol Tokyo Japan RISE Res Inst Sweden S-16440 Kista Sweden

We demonstrate a record 170 Gbaud on-off keying C-band silicon photonics ring resonator modulator-based transmitter with performance below the 6.7% overhead HD-FEC threshold after optical back-to-back and transmission... 详细信息

ISBN: (纸本)9798350394054;9798350394047

关键词： silicon photonics ring resonator modulators on-off keying short-reach communication intensity modulation direct detection

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A modified Volterra equalizer for compensation distortion in C-band DML-based short reach limited-bandwidth system with 80-Gb/s PAM-4 signals

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OPTICS COMMUNICATIONS 2022年 513卷 128105-128105页

作者： Xi, Yu Bi, Meihua Miao, Xin Hu, Weisheng Hangzhou Dianzi Univ Sch Commun Engn Xiasha Gaojiaoyuan 2rd St Hangzhou 310018 Zhejiang Peoples R China Shanghai Jiao Tong Univ Dept Elect Engn State Key Lab Adv Opt Commun Syst & Networks 800 Dongchuan Rd Shanghai 200240 Peoples R China

In this paper, we investigate the system model of intensity modulation with direct detection (IM/DD)-based high-speed short-reach link with directly modulation laser (DML) and bandwidth-limitation optics devices. And, based on this model, we propose a modified Volterra equalizer to compensate distortion by constructing second-order feature vectors for support vector machine (SVM) trainer in this high-capacity and limited bandwidth system. Owing to high-dimensional mapping characteristics of SVM, for our scheme, only a single classification hyperplane is needed to be trained to achieve satisfactory equalization performance for the multi classification tasks of PAM-M, which would reduce the calculation complexity. Moreover, the 80-Gb/s PAM-4 per wavelength transmission experiment with 10-G optics in 20-km standard single mode fiber (SSMF) DML system is conducted and utilized to manifest the feasibility and effectiveness of our scheme. The results show that our scheme can reach the HD-FEC threshold and achieve outstanding performance than commonly used equalizers.

关键词： intensity modulation direct detection directly modulation laser Channel equalization Support vector machine Volterra

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