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1.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • EEPN and CD study for coherent optical nPSK and nQAM systems with RF pilot based phase noise compensation
  • 2012
  • record:In_t: Optics Express. - 1094-4087. ; 20:8, s. 8862-8870
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A radio frequency (RF) carrier can be used to mitigate the phase noise impact in n-level PSK and QAM systems. The systems performance is influenced by the use of an RF pilot carrier to accomplish phase noise compensation through complex multiplication in combination with discrete filters to compensate for the chromatic dispersion (CD). We perform a detailed study comparing two filters for the CD compensation namely the fixed frequency domain equalizer (FDE) filter and the adaptive least-mean-square (LMS) filter. The study provides important novel physical insight into the equalization enhanced phase noise (EEPN) influence on the system bit-error-rate (BER) versus optical signal-to-noise-ratio (OSNR) performance. Important results of the analysis are that the FDE filter position relative to the RF carrier phase noise compensation module provides a possibility for choosing whether the EEPN from the Tx or the LO laser influences the system quality. The LMS filter works very inefficiently when placed prior to the RF phase noise compensation stage of the Rx whereas it works much more efficiently and gives almost the same performance as the FDE filter when placed after the RF phase noise compensation stage.
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2.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • Receiver implemented RF pilot tone phase noise mitigation in coherent optical nPSK and nQAM systems
  • 2011
  • record:In_t: Optics Express. - 1094-4087. ; 19:15, s. 14487-14494
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • In this paper, a novel method for extracting an RF pilot carrier signal in the coherent receiver is presented. The RF carrier is used to mitigate the phase noise influence in n-level PSK and QAM systems. The performance is compared to the use of an (ideal) optically transmitted RF pilot tone. As expected an electronically generated RF carrier provides less efficient phase noise mitigation than the optical RF. However, the electronically generated RF carrier still improves the phase noise tolerance by about one order of magnitude in bit error rate (BER) compared to using no RF pilot tone. It is also found, as a novel study result, that equalization enhanced phase noise - which appears as correlated pure phase noise, amplitude noise and time jitter - cannot be efficiently mitigated by the use of an (optically or electrically generated) RF pilot tone.
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3.
  • Jacobsen, Gunnar, et al. (creator_code:aut_t)
  • Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation
  • 2013
  • record:In_t: Optics Express. - : Optical Society of American (OSA). - 1094-4087. ; 21:10, s. 12351-12362
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We propose - as a modification of the optical (RF) pilot scheme -a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within 1/2 orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper.
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4.
  • Kakkar, Aditya, et al. (creator_code:aut_t)
  • Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation
  • 2015
  • record:In_t: Optics Express. - 1094-4087. ; 23:9, s. 11221-11226
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.
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5.
  • Lu, Yang, et al. (creator_code:aut_t)
  • Multi-channel collision-free reception for optical interconnects
  • 2018
  • record:In_t: Optics Express. - : OPTICAL SOC AMER. - 1094-4087. ; 26:10, s. 13214-13222
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A multi-channel reception scheme that allows each node to receive an arbitrary set of wavelengths simultaneously (i.e., collision-free) is proposed for optical interconnects. The proposed scheme only needs to use a few receivers and fixed-wavelength filters that are designed based on error-control coding theory. Experiments with up to four channel collision-free reception units are carried out to demonstrate the feasibility of the proposed scheme.
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6.
  • Xu, Tianhua, 1984-, et al. (creator_code:aut_t)
  • Analytical estimation of phase noise influence in coherent transmission system with digital dispersion equalization
  • 2011
  • record:In_t: Optics Express. - 1094-4087. ; 19:8, s. 7756-7768
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We present a novel investigation on the enhancement of phase noise in coherent optical transmission system due to electronic chromatic dispersion compensation. Two types of equalizers, including a time domain fiber dispersion finite impulse response (FD-FIR) filter and a frequency domain blind look-up (BLU) filter are applied to mitigate the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying (PDM-QPSK) transmission system. The bit-error-rate (BER) floor in phase estimation using an optimized one-tap normalized least-mean-square (NLMS) filter, and considering the equalization enhanced phase noise (EEPN) is evaluated analytically including the correlation effects. The numerical simulations are implemented and compared with the performance of differential QPSK demodulation system. (C) 2011 Optical Society of America
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7.
  • Xu, Tianhua, 1984-, et al. (creator_code:aut_t)
  • Chromatic dispersion compensation in coherent transmission system using digital filters
  • 2010
  • record:In_t: Optics Express. - 1094-4087. ; 18:15, s. 16243-16257
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We present a comparative analysis of three popular digital filters for chromatic dispersion compensation: a time-domain least mean square adaptive filter, a time-domain fiber dispersion finite impulse response filter, and a frequency-domain blind look-up filter. The filters are applied to equalize the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying transmission system. The characteristics of these filters are compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations, and their computational complexity. In addition, the phase noise tolerance of these filters is also analyzed. (C) 2010 Optical Society of America
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8.
  • Zafra, Sebastian Ortega, et al. (creator_code:aut_t)
  • Phase noise tolerance study in coherent optical circular QAM transmissions with Viterbi-Viterbi carrier phase estimation
  • 2014
  • record:In_t: Optics Express. - 1094-4087. ; 22:25, s. 30579-30585
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • We present a performance evaluation of a non-conventional approach to implement phase noise tolerant optical systems with multilevel modulation formats. The performance of normalized Viterbi-Viterbi carrier phase estimation (V-V CPE) is investigated in detail for circular m-level quadrature amplitude modulation (C-mQAM) signals. The intrinsic property of C-mQAM constellation points with a uniform phase separation allows a straightforward employment of V-V CPE without the need to adapt constellation. Compared with conventional feed-forward CPE for square QAM signals, the simulated results show an enhanced tolerance of linewidth symbol duration product (Delta vT(s)) at a low sensitivity penalty by using feed-forward CPE structure with C-mQAM. This scheme can be easily upgraded to higher order modulations without inducing considerable complexity.
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9.
  • Zhang, Lu, et al. (creator_code:aut_t)
  • Digital mobile fronthaul employing differential pulse code modulation with suppressed quantization noise
  • 2017
  • record:In_t: Optics Express. - : Optical Society of America. - 1094-4087. ; 25:25, s. 31921-31936
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A differential pulse code modulation (DPCM) based digital mobile fronthaul architecture is proposed and experimentally demonstrated. By using a linear predictor in the DPCM encoding process, the quantization noise can be effectively suppressed and a prediction gain of 7~8 dB can be obtained. Experimental validation is carried out with a 20 km 15-Gbaud/λ 4-level pulse amplitude modulation (PAM4) intensity modulation and direct detection system. The results verify the feasibility of supporting 163, 122, 98, 81 20-MHz 4, 16, 64, 256 QAM based antenna-carrier (AxC) containers with only 3, 4, 5, 6 quantization bits at a sampling rate of 30.72MSa/s in LTE-A environment. Further increasing the number of quantization bits to 8 and 9, 1024 quadrature amplitude modulation (1024 QAM) and 4096 QAM transmission can be realized with error vector magnitude (EVM) lower than 1% and 0.5%, respectively. The supported number of AxCs in the proposed DPCM-based fronthaul is increased and the EVM is greatly reduced compared to the common public radio interface (CPRI) based fronthaul that uses pulse code modulation. Besides, the DPCM-based fronthaul is also experimentally demonstrated to support universal filtered multicarrier signal that is one candidate waveform for the 5th generation mobile systems.
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