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Overfitting effect of artificial neural network based nonlinear equalizer: from mathematical origin to transmission evolution

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Science China(Information Sciences) 2020年第6期63卷 67-79页

作者： Zheng YANG Fan GAO Songnian FU Ming TANG Deming LIU Wuhan National Laboratory for Optoelectronics School of Optical and Electronic InformationHuazhong University of Science and Technology Alibaba Infrastructure Service Alibaba Group

Overfitting effect of artificial neural network(ANN) based nonlinear equalizer(NLE) leads to a trap of bit error ratio(BER) overestimation in optical fiber communication system, especially when the performance is evaluated by the commonly-used pseudo-random binary sequence(PRBS). First, we mathematically investigate the PRBS generation and Gray code mapping rules, in comparison with the use of Mersenne Twister random sequence(MTRS). Under the condition of a symbol erasure channel, we identify that ANN can recognize both the PRBS generation and symbol mapping rules, by increasing the weights of NLE at specific positions, whereas the MTRS is currently safe owing to the limited input length of current ANN based NLE. Then, we design four channel models of fiber optical transmission to experimentally examine various impairments on the evolution of overfitting effect. When both the additive white Gaussian noise(AWGN) channel and the bandwidth limited channel are considered, the mitigation of overfitting becomes possible by the use of pruned PRBS(P-PRBS) training set with removing the generation and mapping rules determined input symbols. However, as for both the chromatic dispersion(CD) uncompensated channel and the CD managed channel, the overfitting effect becomes serious, because both CD and fiber nonlinearity induced inter-symbol interference(ISI) is beneficial for ANN to identify the PRBS symbol rules. Finally,possible solutions to mitigate the overfitting effect are summarized.

关键词： artificial neural network nonlinear equalizer pseudo-random binary sequence overfitting

Flexible rotation of transverse optical field for 2D self-accelerating beams with a designated trajectory

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Opto-Electronic Advances 2021年第3期4卷 45-52页

作者： Lei Zhu Xuesong Zhao Chen Liu Songnian FU Yuncai Wang Yuwen Qin Wuhan National Laboratory for Optoelectronics and School of Optical and Electronic InformationHuazhong University of Science and TechnologyWuhan 430074China School of Information Engineering Guangdong University of Technologyand Guangdong Provincial Key Laboratory of Photonics Information TechnologyGuangzhou 510006China

Self-accelerating beams have the unusual ability to remain diffraction-free while undergo the transverse shift during the free-space propagation.We theoretically identify that the transverse optical field distribution of 2D self-accelerating beam is determined by the selection of the transverse Cartesian coordinates,when the caustic method is utilized for its trajectory design.Based on the coordinate-rotation method,we experimentally demonstrate a scheme to flexibly manipulate the rotation of transverse optical field for 2D self-accelerating beams under the condition of a designated trajectory.With this scheme,the transverse optical field can be rotated within a range of 90 degrees,especially when the trajectory of 2D self-accelerating beams needs to be maintained for free-space photonic interconnection.

关键词： self-accelerating beams optical field caustic

Optical true time delay pool-based beamforming and limited feedback for reconfigurable intelligent surface-empowered cloud radio access networks

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Science China(Information Sciences) 2021年第10期64卷 88-102页

作者： Huan HUANG Xiaowen WANG Chongfu ZHANG Jie PENG Muchuan YANG Songnian FU Deming LIU Kun QIU School of Information and Communication Engineering Zhongshan InstituteUniversity of Electronic Science and Technology of China School of Electronic Information University of Electronic Science and Technology of ChinaZhongshan Institute School of Information Engineering Guangdong University of Technology School of Optical and Electronic Information Huazhong University of Science and Technology

Introducing reconfigurable intelligent surfaces(RISs) greatly improves the wireless propagation environment. Limited to feedback overheads and computing power, the low-complexity precoding and the cost-effective beamforming implementation are urgently demanded in RIS-empowered millimeter-wave cloud radio access networks(mmWave C-RANs). Herein, an optical true time delay pool-based hybrid beamforming(OTTDP-based HBF) scheme, enabling centralized analog beamforming control, is proposed for RIS-empowered mmWave C-RANs. By using codebook quantization techniques, we develop a non-iterative limited feedback(NI-LF) precoding algorithm for the RIS-empowered mmWave C-RAN using the proposed OTTDP-based HBF. In the NI-LF precoding algorithm, the complex joint optimization problem of hybrid precoding and phase-shifting of RIS is equivalently formulated as a maximum ratio transmission(MRT)problem and a sparse reconstruction problem. For an active antenna unit(AAU) equipped with eight antennas, a designed example of the proposed OTTDP is presented. furthermore, for a RIS-empowered mmWave C-RAN at 28 GHz, the received signal-to-noise ratio(SNR) curves obtained via different precoding schemes are compared and discussed. Compared with the precoding without RIS, the proposed NI-LF precoding by using different codebooks to quantize the phase-shifting of the RIS respectively achieves 20.56, 19.55, and18.93 dB performance improvement for the user located near the 49-element RIS. Moreover, performance degradations due to limited feedback are analyzed. The computational complexity and overhead of the proposed NI-LF precoding algorithm are also given and discussed.

关键词： reconfigurable intelligent surface optical true time delay millimeter-wave cloud radio access network limited feedback

Rayleigh backscattering noise in single-fiber Ioopback duplex WDM-PON architecture

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Frontiers of Optoelectronics 2012年第4期5卷 435-438页

作者： Duan LIU Songnian FU Ming TANG Ping SHUM Deming LIU National Engineering Laboratory of Next Generation Intemet Access System School of Optical&Electronic InformationHuazhong University of Science and TechnologyWuhan 430074China

This paper investigated the impact of Rayleigh backscattering （RB） noise in the proposed wavelength- division-multiplexed （WDM） single-fiber loopback access network. RB noise＇s impacts on the downstream and upstream service were discussed in details. It was found that the receiver sensitivity was less sensitive when the seeding-light power was below - 12.6 dBm. And for the uplink RB noise, a higher reflective semiconductor optical amplifier （RSOA）＇s bias current results in lower receiver sensitivity.

关键词： passive optical network （PON） reflectivesemiconductor optical amplifier （RSOA） Rayleigh back-scattering （RB）

Negative refraction mediated by bound states in the continuum

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Photonics Research 2021年第8期9卷 1592-1597页

作者： ZHANYUAN ZHANG FEIFEI QIN YI XU Songnian FU YUNCAI WANG YUWEN QIN Department of Electronic Engineering College of Information Science and TechnologyJinan UniversityGuangzhou 510632China Advanced Institute of Photonics Technology School of Information Engineeringand Guangdong Provincial Key Laboratory of Information Photonics TechnologyGuangdong University of TechnologyGuangzhou 510006China

Negative refraction might occur at the interface between a two-dimensional photonic crystal(Ph C)slab and a homogeneous medium,where the guiding of the electromagnetic wave along the third dimension is governed by total internal reflection.Herein,we report on the observation of negative refraction in the Ph C slab where the vertical guiding is enabled by a bound state in the continuum and essentially beyond the light cone.Such abnormal refraction and guiding mechanism are based on the synchronous crafting of spatial dispersion and the radiative lifetime of Bloch modes within the radiative continuum.Microwave experiments are provided to further validate the numerical proposal in an all-dielectric Ph C platform.It is envisioned that the negative refraction observed beyond the light cone might facilitate the development of optical devices in integrated optics,such as couplers,multiplexers,and demultiplexers.

关键词： refraction continuum radiative

10 Gb/s classical secure key distribution based on temporal steganography and private chaotic phase scrambling

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Photonics Research 2024年第2期12卷 321-330页

作者： ZHENSEN GAO ZHITAO DENG LIHONG ZHANG XULIN GAO YUEHUA AN ANBANG WANG Songnian FU ZHAOHUI LI YUNCAI WANG YUWEN QIN School of Information Engineering Guangdong University of TechnologyGuangzhou 510006China Pengcheng Laboratory Shenzhen 518062China Key Laboratory of Photonic Technology for Integrated Communication and Sensing Ministry of EducationGuangzhou 510006China School of Optoelectronic Engineering Guangdong Polytechnic Normal UniversityGuangzhou 510665China School of Electrical and Information Technology Sun Yat-sen UniversityGuangzhou 510006China

Secure distribution of high-speed digital encryption/decryption keys over a classical fiber channel is strongly pursued for realizing perfect secrecy communication systems.However,it is still challenging to achieve a secret key rate in the order of tens of gigabits per second to be comparable with the bit rate of commercial fiber-optic systems.In this paper,we propose and experimentally demonstrate a novel solution for high-speed secure key distribution based on temporal steganography and private chaotic phase scrambling in the classical physical layer.The encryption key is temporally concealed into the background noise in the time domain and randomly phase scrambled bit-by-bit by a private chaotic signal,which provides two layers of enhanced security to guarantee the privacy of key distribution while providing a high secret key rate.We experimentally achieved a record classical secret key rate of 10 Gb/s with a bit error rate lower than the hard-decision forward error correction(HD-FEC)over a 40 km standard single mode fiber.The proposed solution holds great promise for achieving high-speed key distribution in the classical fiber channel by combining steganographic transmission and chaotic scrambling.

关键词： chaotic distribution phase

Distributed Brillouin frequency shift extraction via a convolutional neural network

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Photonics Research 2020年第5期8卷 690-697页

作者： YIQING CHANG HAO WU CAN ZHAO LI SHEN Songnian FU MING TANG Wuhan National Laboratory for Optoelectronics(WNLO)&National Engineering Laboratory for Next Generation Internet Access System School of Optical and Electronic InformationHuazhong University of Science and TechnologyWuhan 430074China

Distributed optical fiber Brillouin sensors detect the temperature and strain along a fiber according to the local Brillouin frequency shift(BFS),which is usually calculated by the measured Brillouin spectrum using Lorentzian curve fitting.In addition,cross-correlation,principal component analysis,and machine learning methods have been proposed for the more efficient extraction of BFS.However,existing methods only process the Brillouin spectrum individually,ignoring the correlation in the time domain,indicating that there is still room for improvement.Here,we propose and experimentally demonstrate a BFS extraction convolutional neural network(BFSCNN)to retrieve the distributed BFS directly from the measured two-dimensional data.Simulated ideal Brillouin spectra with various parameters are used to train the BFSCNN.Both the simulation and experimental results show that the extraction accuracy of the BFSCNN is better than that of the traditional curve fitting algorithm with a much shorter processing time.The BFSCNN has good universality and robustness and can effectively improve the performances of existing Brillouin sensors.

关键词： neural network individual

Linear shallow neural network to accelerate transmitter dispersion eye closure quaternary(TDECQ) assessment

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Science China(Information Sciences) 2024年第4期67卷 337-338页

作者： Junjiang XIANG Zejun CHEN Yijun CHENG Hailin YANG Xuancheng HUO Meng XIANG Gai ZHOU Yuwen QIN Songnian FU Institute of Advanced Photonics Technology School of Information EngineeringGuangdong University of Technology School of Optical and Electronic Information Huazhong University of Science and Technology Key Laboratory of Photonic Technology for Integrated Sensing and Communication Ministry of Education of ChinaGuangdong University of Technology Guangdong Provincial Key Laboratory of Information Photonics Technology Guangdong University of Technology

To support the ever-emerging capacity requirement of datacenter interconnection(DCI) applications, transmitter dispersion eye closure quaternary(TDECQ) has been proposed by IEEE802.3 standard [1], which is specifically employed for the four-level pulse amplitude modulation(PAM-4) signals. However, the traditional scheme of TDECQ assessment needs several iterative operations,

关键词： IEEE Standards

Distributed curvature sensing based on a bending loss-resistant ring-core fiber

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Photonics Research 2020年第2期8卷 165-174页

作者： LI SHEN HAO WU CAN ZHAO LEI SHEN RUI ZHANG WEIJUN TONG Songnian FU MING TANG Wuhan National Laboratory for Optoelectronics(WNLO)&National Engineering Laboratory for Next Generation Internet Access System School of Optical and Electronic InformationHuazhong University of Science and TechnologyWuhan 430074China State Key Laboratory of Optical Fiber and Cable Manufacture Technology Yangtze Optical Fiber and Cable Joint Stock Limited Company(YOFC)R&D CenterWuhan 430073China

A theoretical and experimental study on curvature sensing using a Brillouin optical time-domain analyzer based on the ring-core fiber(RCF)is reported.The Brillouin gain spectrum of the RCF is investigated,and the Brillouin frequency shift(BFS)dependence on temperature and strain is calibrated.We theoretically analyze the fiber bending-induced BFS and peak Brillouin gain variation for the RCF through a numerical simulation method,and the RCF is revealed to have a high curvature sensitivity.Distributed curvature sensing is successfully demonstrated,with the bending radius ranging from 0.5 to 1.5 cm,corresponding to a BFS variation from 32.90 to7.81 MHz.The RCF takes advantage of great bending loss resistance,and the maximum macrobending loss at the extreme bending radius of 0.5 cm is less than 0.01 d B/turn.Besides,the peak Brillouin gain of the RCF is discovered to vary significantly in response to fiber bending,which is expected to be another parameter for distributed curvature determination.The results imply that the RCF is a promising candidate for highly sensitive distributed curvature measurement,especially in sharp bending circumstances.

关键词： fiber bending curvature