Xingwen Yi

University of Electronic Science and Technology of China, Hua-yang, Sichuan, China

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Publications (79)117.48 Total impact

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    ABSTRACT: One of the primary drawbacks of orthogonal frequency-division multiplexing (OFDM) is the large peak-to-average ratio (PAPR). It continues to contribute nonlinear degradations after it was introduced into optical fiber transmissions. However, phase-modulated OFDM can reduce the PAPR to the minimum, since its amplitude can be constant. In this paper, we conduct the theoretical and experimental study on the laser phase noise effect in phase-modulated coherent optical OFDM systems. Due to the laser phase noise, the phase transformation at the receiver is prone to errors due to phase wrapping. Consequently, we propose a mean-phase-compensation (MPC) method, which compensate for the mean phase offset for each OFDM symbol that has a Gaussian-distributed histogram. This method can avoid the problematic unwrapping function in phase transformation. We derive the closed-form expressions for the phase noise spreading and the corresponding signal-to-noise ratios (SNRs) based on the Wiener phase noise model. Unlike conventional coherent optical OFDM, the phase noise spreading to each OFDM subcarrier is decided by the reciprocal of the square of the subcarrier frequency, and the SNR can be improved by using a stronger PM modulation. We also discuss the SNR improvement by discarding a few affected subcarriers closing to dc. In a simulation, we demonstrate that our closed-form expressions are accurate. Finally, we experimentally verify our MPC method and our analysis.
    No preview · Article · Feb 2016 · IEEE Photonics Journal
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    ABSTRACT: We propose a training symbols-free polarization demultiplexing method by constructing a cost function (CCF-PDM) for coherent optical PDM-OFDM. This method is applicable for high-speed, wide-bandwidth OFDM signals, different subcarrier modulation formats and long-haul transmission. It shows comparable performance with that of conventional method but without overhead and converges fast. Since the neighboring subcarriers experience similar polarization effects, we set the initial matrix parameters by the neighboring subcarrier to reduce the number of iteration for the gradient algorithm and prevent swapping the data of the two orthogonal polarizations. We verify this method in experiment by transmitting 66.6-Gb/s PDM-OFDM signal with 4QAM subcarrier modulation over 5440km SSMF and 133.3-Gb/s PDM-OFDM signal with 16QAM subcarrier modulation over 960km SSMF respectively. We compare its performance with that of training symbols. We also analyze the convergence speed of this method.
    No preview · Article · Jul 2015 · Optics Express
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    ABSTRACT: We have recently demonstrated the improved phase noise tolerance in coherent optical OFDM by digital coherent superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitian symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. According to the concept of phase-conjugated twin wave, both approaches can also mitigate the fiber nonlinearity to the first order. We prove that both approaches can cancel the inter-carrier interference (ICI) due to phase noise to the second order, and we derive the reduced ICI power to the fourth order using the Wiener phase noise model. In simulation, we show the enhanced tolerance to the laser phase noise and fiber nonlinearity.
    No preview · Article · Jul 2015 · Photonic Network Communication
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    ABSTRACT: Optical spectral measurements are crucial for optical sensors and many other applications, but the prevailing methods, such as optical spectrum analysis and tunable laser spectroscopy, often have to make compromises among resolution, speed, and accuracy. Optical frequency combs are widely used for metrology of discrete atomic and molecular spectral lines. However, they are usually generated by optical methods and have large comb spacing, which limits the resolution for direct sampling of continuous spectra. To overcome these problems, this paper presents an original method to digitally generate an ultrafine optical frequency comb (UFOFC) as the frequency ruler for spectral measurements. Each comb line provides one sampling point, and the full spectrum can be captured at the same time using coherent detection. For an experimental demonstration, we adopted the inverse fast Fourier transform to generate a UFOFC with a comb spacing of 1.46 MHz over a 10-GHz range and demonstrated its functions using a Mach-Zehnder refractive index sensor. The UFOFC obtains a spectral resolution of 0.01 pm and response time of 0.7 μs; both represent 100-fold improvements over the state of the art and could be further enhanced by several orders of magnitude. The UFOFC presented here could facilitate new label-free sensor applications that require both high resolution and fast speed, such as measuring binding kinetics and single-molecule dynamics.
    No preview · Article · Jun 2015 · Light: Science & Applications
  • Xingwen Yi · Dengke Zeng · Xuemei Chen · Jing Zhang · Kun Qiu
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    ABSTRACT: We have recently demonstrated the improved phase noise tolerance in coherent optical OFDM by digital coherent superposition of optical OFDM subcarriers, which are phase-conjugated pairs with Hermitan symmetry. In this approach, we realized DCS of OFDM subcarriers in single polarization (or channel), denoted as SP-DCS-OFDM. In this paper, we show that another approach is in dual polarizations, or DP-DCS-OFDM. We prove that both approaches can reduce the ICI due to phase noise, including laser phase noise and nonlinear phase noise. We discuss their improved phase noise tolerance in simulation. We also discuss their difference in terms of complexity and performance.
    No preview · Article · Dec 2014
  • Xingwen Yi · Bo Xu · Jing Zhang · Yun Lin · Kun Qiu
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    ABSTRACT: Digital coherent superposition (DCS) of optical OFDM subcarrier pairs with Hermitian symmetry can reduce the inter-carrier-interference (ICI) noise resulted from phase noise. In this paper, we show two different implementations of DCS-OFDM that have the same performance in the presence of laser phase noise. We complete the theoretical calculation on ICI reduction by using the model of pure Wiener phase noise. By Taylor expansion of the ICI, we show that the ICI power is cancelled to the second order by DCS. The fourth order term is further derived out and only decided by the ratio of laser linewidth to OFDM subcarrier symbol rate, which can greatly simplify the system design. Finally, we verify our theoretical calculations in simulations and use the analytical results to predict the system performance. DCS-OFDM is expected to be beneficial to certain optical fiber transmissions.
    No preview · Article · Dec 2014 · Optics Express
  • Zhenming Yu · Xingwen Yi · Jing Zhang · Difu Zhao · Kun Qiu
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    ABSTRACT: We have recently demonstrated polarization demultiplexing in Stokes space (SS-PDM), which is susceptible to polarization-dependent loss (PDL). In this paper, we apply the method of PDL monitoring and compensation in Stokes space to enhance SS-PDM. It is applied for each subcarrier in the frequency domain after SS-PDM. Because each subcarrier has a much lower speed and narrower bandwidth, the polarization effects that it experiences can be treated as flat. This method can work for different modulation formats on orthogonal frequency-division multiplexing (OFDM) subcarriers and only needs a small number of samples for convergence. In simulation, when the PDL is less than 3.5 dB, it significantly improves the performance of SS-PDM and is comparable with the conventional channel estimation based on training symbols (TSs). We also conduct the experiments of 66.6-Gb/s coherent optical PDM-OFDM with 4QAM subcarrier modulation over 5440-km SSMF and 133.3-Gb/s coherent optical PDM-OFDM with 16QAM subcarrier modulation over 960-km SSMF, respectively. The experimental results show that this method improves the performance of SS-PDM significantly and can match the performance of channel estimation based on TSs. To the best of our knowledge, this is the first experimental validation of PDL monitoring and compensation in Stokes space.
    No preview · Article · Dec 2014 · Journal of Lightwave Technology
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    ABSTRACT: Digital coherent superposition (DCS) provides an approach to combat fiber nonlinearities by trading off the spectrum efficiency. In analogy, we extend the concept of DCS to the optical OFDM subcarrier pairs with Hermitian symmetry to combat the linear and nonlinear phase noise. At the transmitter, we simply use a real-valued OFDM signal to drive a Mach-Zehnder (MZ) intensity modulator biased at the null point and the so-generated OFDM signal is Hermitian in the frequency domain. At receiver, after the conventional OFDM signal processing, we conduct DCS of the optical OFDM subcarrier pairs, which requires only conjugation and summation. We show that the inter-carrier-interference (ICI) due to phase noise can be reduced because of the Hermitain symmetry. In a simulation, this method improves the tolerance to the laser phase noise. In a nonlinear WDM transmission experiment, this method also achieves better performance under the influence of cross phase modulation (XPM).
    Full-text · Article · Jun 2014 · Optics Express
  • Xingwen Yi · Xuemei Chen · Chao Li · Ming Luo · Qi Yang · Zhaohui Li · Kun Qiu
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    ABSTRACT: We experimentally demonstrate digital coherent superposition of optical OFDM subcarrier pairs with Hermitian symmetry to mitigate phase noise, including laser phase noise and cross-phase modulation in a WDM transmission.
    No preview · Conference Paper · Mar 2014
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    ABSTRACT: A novel superchannel transmission scheme is proposed where an optical comb source is used to carry the multiband signal and one subcarrier is reserved for regeneration as a local oscillator at the receiver end. By combining carrier tracking and carrier expanding, a 4 × 2 Tbit/s superchannel wavelength division multiplexed self-coherent transmission over a 320 km standard single mode fibre has been successfully demonstrated.
    No preview · Article · Jan 2014 · Electronics Letters
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    ABSTRACT: The overhead of cyclic prefix (CP) in coherent optical OFDM (CO-OFDM) tends to be too large for high-speed and long-haul optical fiber transmissions. We discuss and experimentally demonstrate a transmission of reduced guard interval OFDM (RGI-OFDM) with much reduced CP overhead based on digital sub-band demultiplexing. The proposed techniques are used to process a 66.7-Gb/s RGI-CO-OFDM signal (similar to 20-GHz bandwidth) after 5440-km fiber transmission. The experiments show that it can reduce the overhead from 36.7% to 12.5%. We also optimize the digital signal processing in the filter bank for a better performance.
    No preview · Article · Nov 2013 · IEEE Photonics Technology Letters
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    ABSTRACT: We propose a modified method of constant modulus algorithm (CMA) based on polarization demultiplexing in Stokes space for polarization demultiplexing (SS-PDM) in optical coherent receivers. SS-PDM can tolerate chromatic dispersion (CD) and polarization-dependent loss (PDL), but is sensitive to PMD. On the other hand, the CMA with high-order FIR filters could compensate for polarization-mode-dispersion (PMD) effectively, but suffers from the singularity problem which results from PDL. Therefore, we use the polarization rotation matrix estimated by SS-PDM to set the initial center taps of the CMA. The singularity problem of the CMA is avoided effectively in a much wider range of PDL and its convergence speed is also improved. We demonstrate this modified CMA in a simulation of 100-Gbit/s PDM-QPSK with PDL of 1, 3, and 5 dB, respectively. PDL is emulated by attenuating one polarization tributary before polarization multiplexing and the interaction between PDL and PMD is ignored. The singularity problem disappears as expected. Because the tolerance of PDL is affected by DGD, we further investigate the PDL tolerance under different DGD. Finally, we conduct the simulation of 100-Gbit/s PDM-QPSK with PDL of 3 dB over 3000 km SSMF and 4000 km SSMF separately. The convergence speed accelerates indeed compared with that of the conventional CMA.
    No preview · Article · Oct 2013 · Journal of Lightwave Technology
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    ABSTRACT: A technique is proposed to measure the high-resolution and wide-band characterization of amplitude, phase responses, and polarization property of optical components. This technique combines the optical spectrum stitching and optical channel estimation methods. Two kinds of fiber Bragg grating based Fabry-Perot cavities with ultrafine structures have been characterized based on this technique. By using 1024 point fast Fourier transform and a narrow linewidth, wavelength-tunable laser source, a frequency resolution of ∼10 MHz is realized with an optical measurement range beyond 250 GHz.
    Full-text · Article · Jul 2013 · Optics Letters
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    ABSTRACT: We propose an approach based on constant envelope modulation to mitigate fiber induced nonlinearities in CO-OFDM systems. The extensive simulation results demonstrate that the proposed scheme not only greatly mitigates the nonlinear sensitivity of CO-OFDM transmissions but also avoids the severe nonlinear tolerance degradation caused by inline dispersion compensation.
    No preview · Conference Paper · Jul 2013
  • Xiaoping Zhou · Xingwen Yi · Kun Qiu
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    ABSTRACT: It is desirable to remove the optical de-multiplexer in reconfigurable optical add/drop multiplexers (OADM) and use coherent receivers instead for channel selection. We set up a wavelength division multiplexed orthogonal frequency division multiplexed system with a raw bit rate of 66.7 Gb/s per channel and a transmission distance of 2,240 km. We show that the OADM can broadcast more than 64 WDM channels to a coherent balanced receiver and can select out a single channel with less than 1 dB of Q-factor degradation. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)
    No preview · Article · Jun 2013 · Optical Engineering
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    Tao Gui · Cai Li · Qi Yang · Xiao Xiao · Linghen Meng · Chao Li · Xingwen Yi · Chao Jin · Zhaohui Li
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    ABSTRACT: In coherent optical communication systems, the transmitter usually employs an optical in-phase and quadrature (IQ) modulator to perform electrical-to-optical up-conversion. However, some environmental factors, such as temperature and mechanical stress, strongly influence the stability. To stabilize the quality of the transmitted signal, auto bias control (ABC) is essential to keep modulator in optimum bias. In this paper, we present a novel method of ABC for the optical orthogonal frequency division multiplexing (O-OFDM) signal. In the proposed scheme, a small cosine/sine wave dither signal is added on to the I/Q baseband signal, respectively. Based on the power monitoring of the 1st and 2nd harmonics of the dither signal, the biases of the optical IQ modulator for O-OFDM system can be adjusted very precisely. The simulation and experimental results show good performance on locating the optimum bias voltages for the IQ modulator with high precision.
    Full-text · Article · Mar 2013 · Optics Express
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    Zhenming Yu · Xingwen Yi · Qi Yang · Ming Luo · Jing Zhang · Lei Chen · Kun Qiu
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    ABSTRACT: We propose a polarization demultiplexing method for coherent optical PDM-OFDM based on Stokes space, without inserting training symbols. The proposed approach performs well for different modulation formats of OFDM subcarrier, and shows comparable performances with that of conventional methods, but with a fast convergence speed and reduced overhead. The OFDM signal in the time domain cannot satisfy the conditions of SS-PDM accurately. Therefore, we first digitally convert the received OFDM signals to the frequency domain using fast Fourier transform (FFT). Each subcarrier of the OFDM signal has a much lower speed and narrower bandwidth, the polarization effects that it experiences can be treated as flat. Consequently, we can apply the polarization demultiplexing in Stokes space (SS-PDM) on per subcarrier basis. We verify this method in experiment by transmitting 66.6-Gb/s PDM-OFDM signal with 4QAM subcarrier modulation over 5440km SSMF and 133.3-Gb/s PDM-OFDM signal with 16QAM subcarrier modulation over 960km SSMF respectively. We also compare the results with those of training symbols. Finally, we analyze of the convergence speed of this method.
    Full-text · Article · Feb 2013 · Optics Express
  • Xingwen Yi · Qi Yang · Kun Qiu
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    ABSTRACT: We propose digital coherent superposition of optical OFDM subcarrier pairs with Hermitian symmetry to mitigate phase noise. Both in theory and simulation, we show that the inter-carrier-interference resulted from phase noise can be reduced.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: Fiber nonlinearity limits the use of coherent optical orthogonal frequency division multiplexing (CO-OFDM) to upgrade wavelength-division multiplexing (WDM) systems using legacy non-return-to-zero-on-off-keying (NRZ-OOK) channels. This letter proposes to compensate for the fiber nonlinearity of CO-OFDM with NRZ-OOK neighbors by combining digital signal processing (DSP)-based self-phase modulation (SPM) post-compensation with pilot-tone-based cross-phase modulation (XPM) compensation. The simulation results demonstrate that the optimum low-pass filter bandwidth for pilot-tone-based XPM compensation depends on the pilot-to-signal ratio value and launch optical power. Our method allows a 4-dB increase in the launch power for a 40-Gb/s single polarization CO-OFDM channel placed in the middle of six 10.7-Gb/s NRZ channels in a 50-GHz space and 1 200-km WDM system.
    No preview · Article · Nov 2012 · Chinese Optics Letters
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    ABSTRACT: With careful designs to combat fibre nonlinearity, 4 × 1.93 Tbit/s 8-PSK DFT-S OFDM transmission over 2240 km SSMF is experimentally demonstrated. The spectral efficiency within each superchannel is 5.6 bit/s/Hz.
    No preview · Article · Nov 2012 · Electronics Letters

Publication Stats

1k Citations
117.48 Total Impact Points

Institutions

  • 2009-2016
    • University of Electronic Science and Technology of China
      Hua-yang, Sichuan, China
  • 2014
    • Jinan University (Guangzhou, China)
      Shengcheng, Guangdong, China
  • 2009-2010
    • University of California, Davis
      • Department of Electrical and Computer Engineering
      Davis, California, United States
  • 2005-2009
    • University of Melbourne
      • Department of Electrical and Electronic Engineering
      Melbourne, Victoria, Australia