Qunbi Zhuge

Bio: Qunbi Zhuge is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Quadrature amplitude modulation & Transmission (telecommunications). The author has an hindex of 24, co-authored 180 publications receiving 2006 citations. Previous affiliations of Qunbi Zhuge include Ciena & Beijing University of Posts and Telecommunications.

Digital subcarrier multiplexing for fiber nonlinearity mitigation in coherent optical communication systems.

Abstract: In this work we experimentally investigate the improved intra-channel fiber nonlinearity tolerance of digital subcarrier multiplexed (SCM) signals in a single-channel coherent optical transmission system. The digital signal processing (DSP) for the generation and reception of the SCM signals is described. We show experimentally that the SCM signal with a nearly-optimum number of subcarriers can extend the maximum reach by 23% in a 24 GBaud DP-QPSK transmission with a BER threshold of 3.8 × 10−3 and by 8% in a 24 GBaud DP-16-QAM transmission with a BER threshold of 2 × 10−2. Moreover, we show by simulations that the improved performance of SCM signals is observed over a wide range of baud rates, further indicating the merits of SCM signals in baud-rate flexible agile transmissions and future high-speed optical transport systems.

Beyond 100 Gb/s: capacity, flexibility, and network optimization [Invited]

Abstract: In this paper, we discuss building blocks that enable the exploitation of optical capacities beyond 100 Gb∕s. Optical networks will benefit from more flexibility and agility in their network elements, especially from coherent transceivers. To achieve capacities of 400 Gb∕s and more, coherent transceivers will operate at higher symbol rates. This will be made possible with higher bandwidth components using new electro-optic technologies implemented with indium phosphide and silicon photonics. Digital signal processing will benefit from new algorithms. Multi-dimensional modulation, of which some formats are already in existence in current flexible coherent transceivers, will provide improved tolerance to noise and fiber nonlinearities. Constellation shaping will further improve these tolerances while allowing a finer granularity in the selection of capacity. Frequency-division multiplexing will also provide improved tolerance to the nonlinear characteristics of fibers. Algorithms with reduced computation complexity will allow the implementation, at speeds, of direct pre-compensation of nonlinear propagation effects. Advancement in forward error correction will shrink the performance gap with Shannon’s limit. At the network control and management level, new tools are being developed to achieve a more efficient utilization of networks. This will also allow for network virtualization, orchestration, and management. Finally, FlexEthernet and FlexOTN will be put in place to allow network operators to optimize capacity in their optical transport networks without manual changes to the client hardware.

Spectral Efficiency-Adaptive Optical Transmission Using Time Domain Hybrid QAM for Agile Optical Networks

Abstract: We report the transmission of time domain hybrid QAM (TDHQ) signals for agile optical networks. A continuous tradeoff between spectral efficiency and achievable distance by mixing modulation formats including QPSK, 8QAM, and 16QAM is demonstrated in two scenarios: 1) 28 Gbaud non-return-to-zero (NRZ) signal for fixed 50 GHz grid systems; 2) superchannel transmission at date rates of up to 1.15 Tb/s and spectral efficiencies of up to 7.68 b/s/Hz. The TDHQ signal is generated using high-speed digital-to-analog converters (DACs) at the transmitter, and low-complexity digital signal processing (DSP) is proposed for processing the TDHQ signals at the receiver. Moreover, the nonlinearity tolerance of hybrid QAM signals with different configurations is investigated.

Performance comparison of DML, EML and MZM in dispersion-unmanaged short reach transmissions with digital signal processing.

Abstract: In this paper, transmission performances of directly modulated laser (DML), electro-absorption modulated laser (EML) and Mach-Zehnder modulator (MZM) are experimentally compared in dispersion-unmanaged high-speed transmission systems with digital signal processing (DSP). We show that, although the DML based transmitter is often believed to be less favorable in C-band high-speed transmissions, it exhibits superior performance over the other two transmitters when either linear or nonlinear digital signal processing is adopted. By theoretical and experimental analysis, we reveal that the superiority of DML can be attributed to the compensation of fiber power fading by its inherent adiabatic chirp as well as the mitigation of chirp induced distortions by the linear or nonlinear equalization. Experimental results of 56Gb/s 4-level pulse amplitude modulation (PAM4) signals under various equalization schemes including linear feedforward equalization, simplified nonlinear Volterra equalization and partial response signaling are presented. Particularly, we show that for DML a 40km transmission distance can be achieved to satisfy the extended range-4 (ER4) Ethernet interconnect using a simplified Volterra equalizer, and a 20km transmission distance can be supported using a linear equalizer. In contrast, for MZM and EML, the achievable transmission distances are respectively 20km and 15km using the Volterra equalizer, respectively, and 15km and 10km using linear equalizer, respectively. Moreover, we show that even using the combination of the Volterra equalizer and partial response signaling, the transmission distances of MZM and EML based systems are limited to 30km and 20km.

Machine learning based linear and nonlinear noise estimation

Abstract: Operators are pressured to maximize the achieved capacity over deployed links. This can be obtained by operating in the weakly nonlinear regime, requiring a precise understanding of the transmission conditions. Ideally, optical transponders should be capable of estimating the regime of operation from the received signal and feeding that information to the upper management layers to optimize the transmission characteristics; however, this estimation is challenging. This paper addresses this problem by estimating the linear and nonlinear signal-to-noise ratio (SNR) from the received signal. This estimation is performed by obtaining features of two distinct effects: nonlinear phase noise and second-order statistical moments. A small neural network is trained to estimate the SNRs from the extracted features. Over extensive simulations covering 19,800 sets of realistic fiber transmissions, we verified the accuracy of the proposed techniques. Employing both approaches simultaneously gave measured performances of 0.04 and 0.20 dB of standard error for the linear and nonlinear SNRs, respectively.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Pattern Recognition and Machine Learning

Abstract: Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Status and Potential of Lithium Niobate on Insulator (LNOI) for Photonic Integrated Circuits

Abstract: Lithium niobate on insulator (LNOI) technology is revolutionizing the lithium niobate industry, enabling higher performance, lower cost and entirely new devices and applications. The availability of LNOI wafers has sparked significant interest in the platform for integrated optical applications, as LNOI offers the attractive material properties of lithium niobate, while also offering the stronger optical confinement and a high optical element integration density that has driven the success of more mature silicon and silicon nitride (SiN) photonics platforms. Due to some similarities between LNOI and SiN, established techniques and standards can readily be adapted to the LNOI platform including a significant array of interface approaches, device designs and also heterogeneous integration techniques for laser sources and photodetectors. In this contribution, we review the latest developments in this platform, examine where further development is necessary to achieve more functionalities in LNOI integrated optical circuits and make a few suggestions of interesting applications that could be realized in this platform. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Massive individual orbital angular momentum channels for multiplexing enabled by Dammann gratings

Abstract: Data transmission rates in optical communication systems are approaching the limits of conventional multiplexing methods. Orbital angular momentum (OAM) in optical vortex beams offers a new degree of freedom and the potential to increase the capacity of free-space optical communication systems, with OAM beams acting as information carriers for OAM division multiplexing (OAM-DM). We demonstrate independent collinear OAM channel generation, transmission and simultaneous detection using Dammann optical vortex gratings (DOVGs). We achieve 80/160 Tbit s−1 capacity with uniform power distributions along all channels, with 1600 individually modulated quadrature phase-shift keying (QPSK)/16-QAM data channels multiplexed by 10 OAM states, 80 wavelengths and two polarizations. DOVG-enabled OAM multiplexing technology removes the bottleneck of massive OAM state parallel detection and offers an opportunity to raise optical communication systems capacity to Pbit s−1 level. Dammann gratings are used to realize multiplexing based on the generation, transmission and detection of optical angular momentum (OAM). The OAM of optical vortex beams offers a new degree of freedom for multiplexing and hence the promise of higher data communication rates, but massive parallel detection of OAM states has proved challenging. Now, researchers in China, Australia and Singapore have used Dammann optical vortex gratings (DOVGs) to realize multiplexing of massive OAM channels with individual modulation and simultaneous detection capabilities. They achieved a data capacity of 80 Tbit s−1 by multiplexing 1600 channels using ten OAM states, 80 wavelengths and two polarizations. This DOVG-enabled OAM multiplexing technology removes the bottleneck of massive parallel detection of OAM states and has the potential to increase optical communication capacities to the Pbit s−1 level.