Xuebing Zhang

Bio: Xuebing Zhang is an academic researcher from Jinan University. The author has contributed to research in topics: Orthogonal frequency-division multiplexing & Quadrature amplitude modulation. The author has an hindex of 7, co-authored 19 publications receiving 293 citations. Previous affiliations of Xuebing Zhang include Hong Kong Polytechnic University.

Advanced modulation formats for 400-Gbps short-reach optical inter-connection

Abstract: Besides the long-haul optical networks covering over thousands of kilometers for backbone transmission, short reach optical networks (SR-ONs) are widely deployed in metro-area for aggregation and accessing. The SR-ONs include the metro optical transport networks (Metro-OTN), optical access networks or other optical inter-connection systems with even shorter distance. As predicted, the growing bandwidth demanding from SR-ONs will be much more than that from the long-haul optical networks in the near future. Besides, there are tremendous amounts of optical terminals and end-users in SR-ONs compared with the long-haul transmission systems and thus will induce large cost and huge energy consumption. So, the power and cost efficiency should be the key consideration for SR-ONs besides the transmission performance. To improve the power and cost efficiency in SR-ONs, advanced modulations and detection techniques based on low power, low cost and integrated optical modulators should be utilized. In this paper, different advanced modulation formats have been discussed. 56Gbps PAM4, 112Gbps poly-binary and 100Gbps DMT that can be used to realize 400-Gbps SR-ONs for different applications have also been demonstrated respectively. In addition, low-cost and low-power opto-electronic components suitable for SR-ONs, the impairments induced by all kinds of defects and bandwidth limitation of opto-electronic components and the corresponding compensation techniques based on DSP algorithms have also been discussed in the experiments.

Experimental demonstration of 110-Gb/s unsynchronized band-multiplexed superchannel coherent optical OFDM/OQAM system

Abstract: In this paper, we experimentally demonstrate the first 110-Gb/s multi-band superchannel coherent optical orthogonal frequency-division multiplexing based on offset quadrature amplitude modulation (OFDM/OQAM) system. Unlike the conventional orthogonal band-multiplexed OFDM system, no timing or frequency synchronization is required for the OFDM/OQAM system. We further investigate the influence of guard band, and find that very trivial guard band spacing (<20MHz) is required without any sensitivity performance or spectral efficiency degradation. Thus, the newly designed scheme would significantly reduce the implementation constrains for the band-multiplexed superchannel coherent optical OFDM system.

Transmission of 100-Gb/s DDO-OFDM/OQAM over 320-km SSMF with a single photodiode

Abstract: In this paper, we propose a novel approach to simultaneously receive multi-band 100-Gb/s direct-detection optical signal with only one polarization and one conventional 40-GHz photodiode. The modulation format of orthogonal frequency-division multiplexing based on offset quadrature amplitude modulation (OFDM/OQAM) is selected to provide signal spectrum with high side-lobe suppression ratio, which can effectively reduce the electrical sub-band frequency interference. The whole 100-Gb/s OFDM/OQAM signal is comprised of 6 sub-bands with 16- and 32-QAM formats loading. Only one guard band is required to accommodate the overlapped 6-band signal-to-signal beat interference (SSBI). The receiver bandwidth is mainly limited by the digital storage oscilloscope (DSO) of 33 GHz. The transmission distance over standard single mode fiber (SSMF) is up to 320 km.

Experimental Demonstration of 429.96-Gb/s OFDM/OQAM-64QAM Over 400-km SSMF Transmission Within a 50-GHz Grid

Abstract: We experimentally demonstrate a 429.96-Gb/s signal transmission over a 400-km standard single-mode fiber within the 50-GHz grid and successfully achieve spectral efficiency as high as 8.63 bit/s/Hz. Orthogonal frequency-division multiplexing/ offset quadrature amplitude modulation with 64-quadrature amplitude modulation is se- lected as the modulation format to provide a "perfect" rectangular spectrum that effi- ciently reduces the channel crosstalk. No timing or frequency alignment is required for the subbands to form the superchannel.

Single photodiode direct detection system of 100-Gb/s OFDM/OQAM-64QAM over 80-km SSMF within a 50-GHz optical grid

Abstract: We propose a novel guard-band-shared direct-detection (GBS-DD) scheme to improve the receiver spectrum efficiency (SE). The 100-Gb/s signal is modulated by 2 sub-bands, which are assigned onto two orthogonal polarizations. The central wavelengths of the two sub-bands are set as 10.84-GHz frequency space. The two sub-bands are then received simultaneously using a single conventional photodiode (PD) of 40-GHz bandwidth. Only one optical pilot carrier is inserted to beat with the 2 sub-bands on the two polarizations. When the 2 sub-band signal entering into the receiver, the signal-to-signal beat interference (SSBI) terms fall and overlap in the same guard band. As a consequence, the bandwidth usage of the PD is enhanced from 1/2 to 2/3. The 100-Gb/s signal is modulated using orthogonal frequency-division multiplexing based on offset quadrature-amplitude-modulation of 64-quadrature amplitude modulation (OFDM/OQAM-64QAM), and transmitted over 80-km standard single mode fiber (SSMF) within a 50-GHz optical grid. It is shown that the proposed GBS-DD scheme can be implemented by the current commercial optical/electrical devices.

Experimental study of PAM-4, CAP-16, and DMT for 100 Gb/s Short Reach Optical Transmission Systems

Abstract: Advanced modulation formats combined with digital signal processing and direct detection is a promising way to realize high capacity, low cost and power efficient short reach optical transmission system. In this paper, we present a detailed investigation on the performance of three advanced modulation formats for 100 Gb/s short reach transmission system. They are PAM-4, CAP-16 and DMT. The detailed digital signal processing required for each modulation format is presented. Comprehensive simulations are carried out to evaluate the performance of each modulation format in terms of received optical power, transmitter bandwidth, relative intensity noise and thermal noise. The performance of each modulation format is also experimentally studied. To the best of our knowledge, we report the first demonstration of a 112 Gb/s transmission over 10km of SSMF employing single band CAP-16 with EML. Finally, a comparison of computational complexity of DSP for the three formats is presented.

Beyond 100-Gb/s Transmission Over 80-km SMF Using Direct-Detection SSB-DMT at C-Band

Abstract: For short-reach links, direct detection offers the advantages of low cost and low complexity. Discrete multitone (DMT) is a promising format due to its high spectral efficiency, flexibility and tolerance to chromatic dispersion (CD). In this study, we experimentally demonstrate a beyond 100-Gb/s DMT transmission over 80-km single mode fiber (SMF) without CD compensation. Using dual-drive Mach–Zehnder modulator-assisted single-sideband modulation, CD-induced power fading is eliminated after direct detection. Trellis coder modulation (TCM) is used to increase the Euclidean distance of the constellation points and nonlinearity equalization (NLE) is employed to mitigate system nonlinearities. Both TCM and NLE algorithms have contributions to improve the system performance. The experimental results show that high capacities up to 122, 110 and 105 Gb/s are achieved with bit error rate at 4.5 × 10−3 for back to back, 40- and 80-km SMF transmissions, respectively. The required OSNR after 80-km SMF transmission is 34.2 dB. To the best of our knowledge, this study reports the lowest required OSNR and highest capacity for C-band direct-detection transmission over 80-km SMF.

Volterra and Wiener Equalizers for Short-Reach 100G PAM-4 Applications

Abstract: Unlike ultralong coherent optical systems that seriously suffer from fiber nonlinearities, short-reach noncoherent systems such as data center interconnections, which utilize small, cheap, and low-bandwidth components, are sensitive to nonlinearities that are mainly produced by devices responsible for electrical signal amplification, modulation, and demodulation. One of the most promising schemes for these applications is the four-level pulse amplitude modulation format combined with intensity modulation and direct detection; however, it can be significantly degraded by linear and nonlinear intersymbol interference. Linear and nonlinear signal degradation can efficiently be handled by different types of equalizers. In many cases, the straightforward linear equalizer cannot lower the error rate at the acceptable level. Therefore, much stronger equalizers based on nonlinear models such as the Volterra series are proposed. Volterra filter that can also be orthogonalized by the Wiener model is well described in the existing literature, and, in this paper, we investigate the most critical points related to high-speed Volterra filter design and implementation. Several experiments are carried out in order to indicate filter requirements/complexity, acquisition, and stability. We also provide a simple guidance for filter complexity reduction and useful hints for channel acquisition.

A Survey of Optical Carrier Generation Techniques for Terabit Capacity Elastic Optical Networks

Abstract: Elastic optical networks (EON) have been proposed to meet the network capacity and dynamicity challenges. Hardware and software resource optimization and re-configurability are key enablers for EONs. Recently, innovative multi-carrier transmission techniques have been extensively investigated to realize high capacity (Tb/s) flexible transceivers. In addition to standard telecommunication lasers, optical carrier generators based on optical frequency combs (OFC) have also been considered with expectations of reduced cost and inventory, improved spectral efficiency, and flexibility. A wide range of OFC generation techniques have been proposed in the literature over the past few years. It is imperative to summarize the state of the art, compare and assess these diverse techniques from a practical perspective. In this survey, we identify salient features of optical multicarrier generators, review and compare these techniques both from a physical and network layer perspective. OFC demultiplexing/filtering techniques have also been reviewed. In addition to transmission performance, the impact of such sources on the network performance and real-world deployment strategies with reference to cost, power consumption, and level of flexibility have also been discussed. Field trials, integrated solutions, and flexibility demonstrations are also reported. Finally, open issues and possible future directions that can lead to real network deployment are highlighted.

Alternative Decoding Methods for Optical Communications Based on Nonlinear Fourier Transform

Abstract: Long-haul optical communications based on nonlinear Fourier Transform have gained attention recently as a new communication strategy that inherently embrace the nonlinear nature of the optical fiber. For communications using discrete eigenvalues ${\boldsymbol{\lambda }} \in {\mathbb{C}^ + }$ , information are encoded and decoded in the spectral amplitudes ${\boldsymbol{q}}({\boldsymbol{\lambda }}) = {\boldsymbol{b}}({\boldsymbol{\lambda }})/({\frac{{{\boldsymbol{da}}({\boldsymbol{\lambda }})}}{{{\boldsymbol{d\lambda }}}}})$ at the root ${{\boldsymbol{\lambda }}_{{\rm{rt}}}}$ where ${\boldsymbol{a}}({{{\boldsymbol{\lambda }}_{{\rm{rt}}}}}) = 0$ . In this paper, we propose two alternative decoding methods using ${\boldsymbol{a}}({\boldsymbol{\lambda }})$ and ${\boldsymbol{b}}({\boldsymbol{\lambda }})$ instead of ${\boldsymbol{q}}({\boldsymbol{\lambda }})$ as decision metrics. For discrete eigenvalue modulation systems, we show that symbol decisions using ${\boldsymbol{a}}({\boldsymbol{\lambda }})$ at a prescribed set of ${\boldsymbol{\lambda }}$ values perform similarly to conventional methods using ${\boldsymbol{q}}({\boldsymbol{\lambda }})$ but avoid root searching, and, thus, significantly reduce computational complexity. For systems with phase and amplitude modulation on a given discrete eigenvalue, we propose to use ${\boldsymbol{b}}({\boldsymbol{\lambda }})$ after for symbol detection and show that the noise in $\frac{{{\boldsymbol{da}}({\boldsymbol{\lambda }})}}{{{\boldsymbol{d\lambda }}}}$ and ${{\boldsymbol{\lambda }}_{{\rm{rt}}}}$ after transmission is all correlated with that in ${\boldsymbol{b}}({{{\boldsymbol{\lambda }}_{{\rm{rt}}}}})$ . A linear minimum mean square error estimator of the noise in ${\boldsymbol{b}}({{{\boldsymbol{\lambda }}_{{\rm{rt}}}}})$ is derived based on such noise correlation and transmission performance is considerably improved for QPSK and 16-quadratic-amplitude modulation systems on discrete eigenvalues.