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  • 1. Jacobsen, G.
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Li, J.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Zhang, Y.
    Phase noise influence in coherent optical OFDM systems with RF pilot tone: Digital IFFT multiplexing and FFT demodulation2012In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 33, no 3, p. 217-226Article in journal (Refereed)
    Abstract [en]

    We present a comparative study of the influence of dispersion induced phase noise for CO-OFDM systems using Tx channel multiplexing and Rx matched filter (analogue hardware based); and digital FFT multiplexing/ IFFT demultiplexing techniques (software based). An RF carrier pilot tone is used to mitigate the phase noise influence. From the analysis, it appears that the phase noise influence for the two OFDM implementations is very similar. The software based system provides a method for a rigorous evaluation of the phase noise variance caused by Common Phase Error (CPE) and Inter-Carrier Interference (ICI) and this, in turns, leads to a BER specification. Numerical results focus on a CO-OFDM system with 1 GS/s QPSK channel modulation. Worst case BER results are evaluated and compared to the BER of a QPSK system with the same capacity as the OFDM implementation. Results are evaluated as a function of transmission distance, and for the QPSK system the influence of equalization enhanced phase noise (EEPN) is included. For both types of systems, the phase noise variance increases significantly with increasing transmission distance. An important and novel observation is that the two types of systems have very closely the same BER as a function of transmission distance for the same capacity. For the high capacity QPSK implementation, the increase in BER is due to EEPN, whereas for the OFDM approach it is due to the dispersion caused walk-off of the RF pilot tone relative to the OFDM signal channels. For a total capacity of 400 Gbit/s, the transmission distance to have the BER < 10-4 is less than 277 km. For an RF pilot located in the center of the OFDM band in a CO-OFDM implementation with n-level PSK channel modulation the current results suggest that the walk-off effect is equivalent to the EEPN impact in a single channel n-level PSK system with the same capacity. This observation is important for future design of coherent long-range systems since it shows that there is a free choice between CO-OFDM and a high capacity nPSK implementation at least as long as the phase noise influence is concerned.

  • 2. Jacobsen, G.
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Sergeyev, S.
    Zhang, Y.
    Phase noise influence in long-range coherent optical OFDM systems with delay detection, IFFT multiplexing and FFT demodulation2012In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 33, no 4, p. 289-295Article in journal (Refereed)
    Abstract [en]

    We present a study of the influence of dispersion induced phase noise for CO-OFDM systems using FFT multiplexing/IFFT demultiplexing techniques (software based). The software based system provides a method for a rigorous evaluation of the phase noise variance caused by Common Phase Error (CPE) and Inter-Carrier Interference (ICI) including - for the first time to our knowledge - in explicit form the effect of equalization enhanced phase noise (EEPN). This, in turns, leads to an analytic BER specification. Numerical results focus on a CO-OFDM system with 10-25 GS/s QPSK channel modulation. A worst case constellation configuration is identified for the phase noise influence and the resulting BER is compared to the BER of a conventional single channel QPSK system with the same capacity as the CO-OFDM implementation. Results are evaluated as a function of transmission distance. For both types of systems, the phase noise variance increases significantly with increasing transmission distance. For a total capacity of 400 (1000) Gbit/s, the transmission distance to have the BER < 10-2 for the worst case CO-OFDM design is less than 800 and 460 km, respectively, whereas for a single channel QPSK system it is less than 1400 and 560 km.

  • 3.
    Jacobsen, Gunnar
    et al.
    Acreo AB, Electrum 236, Kista, Sweden.
    Kazovsky, L. G.
    Stanford University, USA.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Zhang, Y.
    Tianjin University, China.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Phase noise influence in optical OFDM systems employing RF pilot tone for noise cancellation2011In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 32, no 2Article in journal (Refereed)
    Abstract [en]

    For coherent and direct-detection Orthogonal Frequency Division Multiplexed (OFDM) systems employing radio frequency (RF) pilot tone phase noise cancellation the influence of laser phase noise is evaluated. Novel analytical results for the common phase error and for the (modulation dependent) inter carrier interference are evaluated based upon Gaussian statistics for the laser phase noise. In the evaluation it is accounted for that the laser phase noise is filtered in the correlation signal detection. Numerical results are presented for OFDM systems with 4 and 16 PSK modulation, 200 OFDM bins and baud rate of 1 GS/s. It is found that about 225 km transmission is feasible for the coherent 4PSKOFDM system over normal (G.652) fiber.

  • 4. Jacobsen, Gunnar
    et al.
    Lidon, Maria Sol
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    Influence of pre-and post-compensation of chromatic dispersion on equalization enhanced phase noise in coherent multilevel systems2011In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 32, p. 257-261Article in journal (Refereed)
    Abstract [en]

    In this paper we present a comparative study of the equalization enhanced phase noise (EEPN) for preand post-compensation of chromatic dispersion in high capacity and high constellation systems. This is - to our knowledge - the first detailed study in this area for precompensation systems. Our main results show that the local oscillator phase noise determines the EEPN influence in post-compensation implementations whereas the transmitter laser determines the EEPN in pre-compensation implementations. As a result of significance for the implementation of practical longer-range systems it is to be emphasized that the use of chromatic dispersion equalization in the optical domain - e.g. by the use of dispersion compensation fibers - eliminates the EEPN entirely. Thus, this seems an efficient solution for such systems operating at high constellations in the future.

  • 5. Jacobsen, Gunnar
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    EEPN and CD study for coherent optical nPSK and nQAM systems with RF pilot based phase noise compensation2012In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 20, no 8, p. 8862-8870Article in journal (Refereed)
    Abstract [en]

    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.

  • 6. Jacobsen, Gunnar
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    Receiver implemented RF pilot tone phase noise mitigation in coherent optical nPSK and nQAM systems2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 15, p. 14487-14494Article in journal (Refereed)
    Abstract [en]

    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.

  • 7. Jacobsen, Gunnar
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Zhang, Yimo
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Error-rate floors in differential n-level phase-shift-keying coherent receivers employing electronic dispersion equalisation2011In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 32, p. 191-193Article in journal (Refereed)
    Abstract [en]

    A model for the phase noise influence in differential n-level phase shift keying (nPSK) systems and 2nlevel quadrature amplitude modulated (2nQAM) systems employing electronic dispersion equalization and quadruple carrier phase extraction is presented. The model includes the dispersion equalization enhanced local oscillator phase noise influence. Numerical results for phase noise error-rate floors are given for dual polarization (DQPSK, Dl6PSK and D64PSK) system configurations with basic baud-rate of 25 GS/s. The transmission distance in excess of 1000 km requires local oscillator lasers with sub-MHz linewidth.

  • 8. Jacobsen, Gunnar
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Sergeyev, Sergey
    Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 10, p. 12351-12362Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Digital Dispersion Equalization and Carrier Phase Estimation in 112-Gbit/s Coherent Optical Fiber Transmission System2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coherent detection employing multilevel modulation format has become one of the most promising technologies for next generation high speed transmission system due to the high power and spectral efficiencies. With the powerful digital signal processing (DSP), coherent optical receivers allow the significant equalization of chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise (PN) and nonlinear effects in the electrical domain. Recently, the realizations of these DSP algorithms for mitigating the channel distortions in the transmission system are the most attractive investigations. 

    The CD equalization can be performed by the digital filters developed in the time and the frequency domain, which can suppress the fiber dispersion effectively. The PMD compensation is usually performed in the time domain with the adaptive least mean square (LMS) and constant modulus algorithms (CMA) equalization. Feed-forward and feed-back carrier phase estimation algorithms are employed to mitigate the phase noise from the transmitter and local oscillator lasers. The fiber nonlinearities are compensated by using the digital backward propagation methods based on solving the nolinear Schrodinger (NLS) equation and the Manakov equation. 

    In this dissertation, we present a comparative analysis of three digital filters for chromatic dispersion compensation, an analytical evaluation of carrier phase estimation with digital equalization enhanced phase noise and a brief discussion for PMD adaptive equalization. To implement these investigations, a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent transmission system is realized in the VPI simulation platform. With the coherent transmission system, these CD equalizers have been compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations and their computational complexity. Meanwhile, the bit-error-rate (BER) floor in carrier phase estimation using a one-tap normalized LMS filter is evaluated analytically, and the numerical results are compared to a differential QPSK detection system.

  • 10.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    DSP based Chromatic Dispersion Equalization and Carrier Phase Estimation in High Speed Coherent Optical Transmission Systems2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coherent detection employing multilevel modulation formats has become one of the most promising technologies for next generation high speed transmission systems due to the high power and spectral efficiencies. Using the powerful digital signal processing (DSP), coherent optical receivers allow the significant equalization of chromatic dispersion (CD), polarization mode dispersion (PMD), phase noise (PN) and nonlinear effects in the electrical domain. Recently, the realizations of these DSP algorithms for mitigating the channel distortions in the coherent transmission systems are the most attractive investigations.

    The CD equalization can be performed by the digital filters developed in the time and the frequency domain, which can suppress the fiber dispersion effectively. The PMD compensation is usually performed in the time domain with the adaptive least mean square (LMS) and constant modulus algorithms (CMA) equalization. Feed-forward and feed-back carrier phase estimation (CPE) algorithms are employed to mitigate the phase noise (PN) from the transmitter (TX) and the local oscillator (LO) lasers. The fiber nonlinearities are compensated by using the digital backward propagation methods based on solving the nonlinear Schrödinger (NLS) equation and the Manakov equation.

    In this dissertation, we present a comparative analysis of three digital filters for chromatic dispersion compensation, a comparative evaluation of different carrier phase estimation methods considering digital equalization enhanced phase noise (EEPN) and a brief discussion for PMD adaptive equalization. To implement these investigations, a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent transmission system with post-compensation of dispersion is realized in the VPI simulation platform. In the coherent transmission system, these CD equalizers have been compared by evaluating their applicability for different fiber lengths, their usability for dispersion perturbations and their computational complexity. The carrier phase estimation using the one-tap normalized LMS (NLMS) filter, the differential detection, the block-average (BA) algorithm and the Viterbi-Viterbi (VV) algorithm is evaluated, and the analytical predictions are compared to the numerical simulations. Meanwhile, the phase noise mitigation using the radio frequency (RF) pilot tone is also investigated in a 56-Gbit/s NRZ single polarization QPSK (NRZ-SP-QPSK) coherent transmission system with post-compensation of chromatic dispersion. Besides, a 56-Gbit/s NRZ-SP-QPSK coherent transmission system with CD pre-distortion is also implemented to analyze the influence of equalization enhanced phase noise in more detail.

  • 11.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Mitigation of EEPN in long-haul n-PSK coherent transmission system using modified optical pilot carrier2013In: Asia Communications and Photonics Conference, ACP 2013, Optical Society of America, 2013Conference paper (Refereed)
    Abstract [en]

    We present the compensation of the equalization enhanced phase noise (EEPN) in the long-haul n-level phase shift keying (n-PSK) coherent optical transmission system, by employing a scheme of phase modulated optical pilot carrier.

  • 12.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Zhang, Y.
    Analysis of carrier phase extraction methods in 112-Gbit/s NRZ-PDM-QPSK coherent transmission system2012In: 2012 Asia Communications And Photonics Conference (ACP), IEEE , 2012, p. AS1C.2-Conference paper (Refereed)
    Abstract [en]

    We present a comparative analysis on three carrier phase extraction approaches, including a one-tap normalized least mean square method, a block-average method, and a Viterbi-Viterbi method, in coherent transmission system considering equalization enhanced phase noise.

  • 13.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Li, J.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Variable-step-size LMS adaptive filter for digital chromatic dispersion compensation in PDM-QPSK coherent transmission system2009In: 2009 International Conference on Optical Instruments and Technology: Optical Systems and Modern Optoelectronic Instruments, SPIE - International Society for Optical Engineering, 2009, p. 75062I-Conference paper (Refereed)
    Abstract [en]

    High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments. Digital filters in coherent optical receivers can be used to mitigate the chromatic dispersion entirely in the optical transmission system. In this paper, the least mean square adaptive filter has been developed for chromatic equalization in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent optical transmission system established on the VPIphotonics simulation platform. It is found that the chromatic dispersion equalization shows a better performance when a smaller step size is used. However, the smaller step size in least mean square filter will lead to a slower iterative operation to achieve the guaranteed convergence. In order to solve this contradiction, an adaptive filter employing variable-step-size least mean square algorithm is proposed to compensate the chromatic dispersion in the 112-Gbit/s coherent communication system. The variable-step-size least mean square filter could make a compromise and optimization between the chromatic dispersion equalization performance and the algorithm converging speed. Meanwhile, the required tap number and the converged tap weights distribution of the variable-step-size least mean square filter for a certain fiber chromatic dispersion are analyzed and discussed in the investigation of the filter feature.

  • 14.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Forzati, M.
    Acreo AB, Electrum 236, Kista, Sweden.
    Mårtensson, J.
    Acreo AB, Electrum 236, Kista, Sweden.
    Mussolin, M.
    University of Padova, Italy.
    Li, J.
    Acreo AB, Electrum 236, Kista, Sweden.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Y.
    Tianjin University, Tianjin, China.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Frequency-domain chromatic dispersion equalization using overlap-add methods in coherent optical system2011In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 27, no 2Article in journal (Refereed)
    Abstract [en]

    The frequency domain equalizers (FDEs) employing two types of overlap-add zero-padding (OLA-ZP) methods are applied to compensate the chromatic dispersion in a 112-Gbit/s non-return-to-zero polarization division multiplexed quadrature phase shift keying (NRZ-PDM-QPSK) coherent optical transmission system. Simulation results demonstrate that the OLA-ZP methods can achieve the same acceptable performance as the overlap-save method. The required minimum overlap (or zero-padding) in the FDE is derived, and the optimum fast Fourier transform length to minimize the computational complexity is also analyzed.

     

  • 15.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Acreo AB.
    Zhang, Yimo
    Phase noise mitigation in coherent transmission system using a pilot carrier2011In: Optical Transmission Systems, Subsystems, and Technologies IX / [ed] Xiang Liu, SPIE - International Society for Optical Engineering, 2011Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the phase noise elimination employing an optical pilot carrier in the high speed coherent transmission system considering the equalization enhanced phase noise (EEPN). The numerical simulations are performed in a 28-Gsymbol/s quadrature phase shift keying (QPSK) coherent system with a polarization multiplexed pilot carrier. The carrier phase estimation is implemented by the one-tap normalized least mean square (NLMS) filter and the differential phase detection, respectively. Simulation results demonstrate that the application of the optical pilot carrier is very effective for the intrinsic laser phase noise cancellation, while is less efficient for the EEPN mitigation.

  • 16. Xu, Tianhua
    et al.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Sergeyev, S.
    Friberg, Ari T.
    Liu, T.
    Zhang, Y.
    Analysis of chromatic dispersion compensation and carrier phase recovery in long-haul optical transmission system influenced by equalization enhanced phase noise2017In: Optik (Stuttgart), ISSN 0030-4026, E-ISSN 1618-1336, Vol. 138, p. 494-508Article in journal (Refereed)
    Abstract [en]

    The performance of long-haul coherent optical fiber transmission system is significantly affected by the equalization enhanced phase noise (EEPN), due to the interaction between the electronic dispersion compensation (EDC) and the laser phase noise. In this paper, we present a comprehensive study on different chromatic dispersion (CD) compensation and carrier phase recovery (CPR) approaches, in the n-level phase shift keying (n-PSK) and the n-level quadrature amplitude modulation (n-QAM) coherent optical transmission systems, considering the impacts of EEPN. Four CD compensation methods are considered: the time-domain equalization (TDE), the frequency-domain equalization (FDE), the least mean square (LMS) adaptive equalization are applied for EDC, and the dispersion compensating fiber (DCF) is employed for optical dispersion compensation (ODC). Meanwhile, three carrier phase recovery methods are also involved: a one-tap normalized least mean square (NLMS) algorithm, a block-wise average (BWA) algorithm, and a Viterbi-Viterbi (VV) algorithm. Numerical simulations have been carried out in a 28-Gbaud dual-polarization quadrature phase shift keying (DP-QPSK) coherent transmission system, and the results indicate that the origin of EEPN depends on the choice of chromatic dispersion compensation methods, and the effects of EEPN also behave moderately different in accordance to different carrier phase recovery scenarios.

  • 17.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101). Acreo AB, Sweden.
    Jacobsen, Gunnar
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Li, J.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101). Acreo AB, Sweden.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Digital compensation of chromatic dispersion in 112-Gbit/s PDM-QPSK system2009In: Optical Transmission Systems, Switching, and Subsystems VII, SPIE - International Society for Optical Engineering, 2009, p. 763202-Conference paper (Refereed)
    Abstract [en]

    High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments. Coherent optical receivers using digital signal processing techniques can mitigate the fiber impairments in the optical transmission system, including the chromatic dispersion equalization with digital filters. In this paper, an adaptive finite impulse response filter employing normalized least mean square algorithm is developed for compensating the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent communication system, which is established in the VPI simulation platform. The principle of the adaptive normalized least mean square algorithm for signal equalization is analyzed theoretically, and at the meanwhile, the taps number and the tap weights in the adaptive finite impulse response filter for compensating a certain fiber chromatic dispersion are also investigated by numerical simulation. The chromatic dispersion compensation performance of the adaptive filter is analyzed by evaluating the behavior of the bitor-rate versus the optical signal-to-noise ratio, and the compensation results are also compared with other present digital filters.

  • 18.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    Tianjin University, China.
    Analytical estimation of phase noise influence in coherent transmission system with digital dispersion equalization2011In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, no 8, p. 7756-7768Article in journal (Refereed)
    Abstract [en]

    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

  • 19.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Jacobsen, Gunnar
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Li, Jie
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Zhang, Yimo
    Carrier phase estimation methods in coherent transmission systems influenced by equalization enhanced phase noise2013In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 293, p. 54-60Article in journal (Refereed)
    Abstract [en]

    We present a comparative study on three carrier phase estimation algorithms, including a one-tap normalized least mean square (NLMS) method, a block-average method, and a Viterbi-Viterbi method in the n-level phase shift keying coherent transmission systems considering the equalization enhanced phase noise (EEPN). In these carrier phase estimation methods, the theoretical bit-error-rate floors based on traditional leading-order Taylor expansion are compared to the practical simulation results, and the tolerable total effective linewidths (involving the transmitter, the local oscillator lasers and the EEPN) for a fixed bit-error-rate floor are evaluated with different block sizes, when the fiber nonlinearities are neglected. The complexity of the three carrier phase estimation methods is also discussed. We find that the carrier phase estimation methods in practical systems should be analyzed based on the simulation results rather than the traditional theoretical predictions, when large EEPN is involved. The one-tap NLMS method can always show an acceptable behavior, while the step size is complicated to optimize. The block-average method is efficient to implement, but it behaves unsatisfactorily when using a large block size. The Viterbi-Viterbi method can show a small improvement compared to the block-average method, while it requires more computational complexity.

  • 20.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    Tianjin University, China.
    Digital chromatic dispersion compensation in coherent transmission system using a time-domain filter2010In: 2010 Asia Communications and Photonics Conference and Exhibition, ACP 2010, Shanghai, 2010, p. 132-133Conference paper (Refereed)
    Abstract [en]

    We demonstrate the chromatic dispersion equalization employing a time-domain filter in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent system. The required tap number of the filter is analyzed from anti-aliasing and pulse broadening. The dynamic range of the filter is evaluated by using different number of taps. ©2010 IEEE.

  • 21.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Tianjin University, Peoples R China; UCL, England.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Acreo Swedish ICT AB, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jie
    Sergeyev, Sergey
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Zhang, Yimo
    Analytical BER performance in differential n-PSK coherent transmission system influenced by equalization enhanced phase noise2015In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 334, p. 222-227Article in journal (Refereed)
    Abstract [en]

    Long haul high speed optical transmission systems are significantly distorted by the interplay between the electronic chromatic dispersion (CD) equalization and the local oscillator (LO) laser phase noise, which leads to an effect of equalization enhanced phase noise (EEPN). The EEPN degrades the performance of optical communication systems severely with the increment of fiber dispersion. LO laser linewidth, symbol rare, and modulation format. In this paper, we present an analytical model for evaluating the performance of bit-error-rate (BER) versus signal-to-noise ratio (SNR) in the n-level phase shift keying (n-PSK) coherent transmission system employing differential carrier phase estimation (CPE), where the influence of EEPN is considered. Theoretical results based on this model have been investigated for the differential quadrature phase shift keying (DQPSK). the differential 8-PSK (D8PSK), and the differential 16-PSK (D16PSK) coherent transmission systems. The influence of EEPN on the BER performance in term of the fiber dispersion, the LO phase noise, the symbol rate, and the modulation format are analyzed in detail. The BER behaviors based on this analytical model achieve a good agreement with previously reported BER floors influenced by EEPN. Further simulations have also been carried out in the differential CPE considering EEPN. The results indicate that this analytical model can give an accurate prediction for the DQPSK system, and a leading-order approximation for the D8PSK and the D16PSK systems.

  • 22.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, Gunnar
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Jie
    Sergeyev, Sergey
    Zhang, Yimo
    Influence of Digital Dispersion Equalization on Phase Noise Enhancement in Coherent Optical System2012In: 2012 Asia Communications And Photonics Conference (ACP), IEEE , 2012, p. AS1C.3-Conference paper (Refereed)
    Abstract [en]

    The phase noise enhancement due to digital dispersion equalization is investigated, which indicates that the phase noise from transmitter laser can also interact with the dispersion depending on the choice of digital dispersion compensation methods.

  • 23.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Vanin, Evgeny
    Acreo AB, Electrum 236, Kista, Sweden.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Zhang, Yimo
    Tianjin University, China.
    Chromatic dispersion compensation in coherent transmission system using digital filters2010In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 18, no 15, p. 16243-16257Article in journal (Refereed)
    Abstract [en]

    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

  • 24.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics (Closed 20120101), Optics (Closed 20120101).
    Digital compensation of chromatic dispersion in 112-Gbit/s PDM-QPSK system2009In: 2009 Asia Communications and Photonics Conference and Exhibition, ACP 2009, 2009, p. 5377275-Conference paper (Refereed)
    Abstract [en]

    Coherent optical receivers with digital filters can mitigate the impairments in optical transmission system. In this paper, an adaptive filter employing NLMS algorithm is developed for chromatic dispersion compensation in a 112-Gbit/s PDM-QPSK coherent communication system. The performance of the adaptive filter is analyzed by comparing with present digital filters .

  • 25.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jacobsen, Gunnar
    Acreo AB, Electrum 236, Kista, Sweden.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Li, Jie
    Acreo AB, Electrum 236, Kista, Sweden.
    Wang, Ke
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Friberg, Ari T.
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Normalized LMS digital filter for chromatic dispersion equalization in 112-Gbit/s PDM-QPSK coherent optical transmission system2010In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 283, no 6, p. 963-967Article in journal (Refereed)
    Abstract [en]

    High bit rates optical communication systems pose the challenge of their tolerance to linear and nonlinear fiber impairments. Coherent optical receivers using digital signal processing techniques can mitigate the fiber impairments in the optical transmission system, including the chromatic dispersion equalization with digital filters. In this paper, an adaptive finite impulse response filter employing normalized least mean square algorithm is developed for compensating the chromatic dispersion in a 112-Gbit/s polarization division multiplexed quadrature phase shift keying coherent communication system, which is established in the VPI Simulation platform. The principle of the adaptive normalized least mean square algorithm for signal equalization is analyzed theoretically, and at the meanwhile, the taps number and the tap weights in the adaptive finite impulse response filter for compensating a certain fiber chromatic dispersion are also investigated by numerical simulation. The chromatic dispersion compensation performance of the adaptive filter is analyzed by evaluating the behavior of the bit-error-rate versus the optical signal-to-noise ratio, and the compensation results are also compared with other present digital filters.

  • 26.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, J.
    Djupsjöbacka, A.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jacobsen, G.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Quasi real-time 230-Gbit/s coherent transmission field trial over 820 km SSMF using 57.5-Gbaud dual-polarization QPSK2013In: Asia Communications and Photonics Conference, ACP 2013, Optical Society of America, 2013Conference paper (Refereed)
    Abstract [en]

    We demonstrate 230-Gbit/s (57.5-Gbaud) polarization-multiplexed QPSK coherent transmission over 820 km field-installed SSMF with quasi real-time DSP, without resorting to ETDM. BER performance well below FEC error-free threshold (2×10-3) at 231-1 PRBS length was achieved.

  • 27.
    Xu, Tianhua
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Tianjin University, China.
    Li, J.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Acreo Swedish.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Djupsjöbacka, A.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Zhang, Y.
    Bayvel, P.
    Field trial over 820 km installed SSMF and its potential Terabit/s superchannel application with up to 57.5-Gbaud DP-QPSK transmission2015In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 353, p. 133-138, article id 20166Article in journal (Refereed)
    Abstract [en]

    In this paper, we report the result of a field trial of 56-Gbaud (224-Gbit/s) and 57.5-Gbaud (230-Gbit/s) dual-polarization quadrature phase shift keying (DP-QPSK) coherent optical transmission over 820 km installed standard single mode fiber (SSMF). Offline digital signal processing (DSP) was applied for signal recovery and bit-error-rate (BER) counting in our field trial experiments, and BER performance well below the 7% overhead hard-decision forward error correction (FEC) error-free threshold (4.5×10-3) at 231-1 pseudo random bit sequence (PRBS) pattern length has been achieved, with the best achievable BERs of 2×10-4 (56-Gbaud) and 3×10-4 (57.5-Gbaud), respectively. In parallel a 1.15-Tbit/s (5×230-Gbit/s) quasi-Nyquist spaced wavelength division multiplexing (WDM) superchannel transmission over the same 820 km optical field link (FL) was also investigated through numerical simulations based on the same 57.5-Gbaud DP-QPSK signal using 1% roll-off Nyquist pulse shaping with 60-GHz channel spacing, and the results indicate that the BER performance well below the 7% overhead hard-decision FEC error-free threshold (4.5×10-3) for the 1.15-Tbit/s DP-QPSK superchannel transmission can be achieved.

  • 28. Zhang, H.
    et al.
    Wang, S.
    Gong, Y.
    Liu, T.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Jia, D.
    Zhang, Y.
    A quantitative robustness evaluation model for optical fiber sensor networks2013In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213, Vol. 31, no 8, p. 1240-1246Article in journal (Refereed)
    Abstract [en]

    Optical fiber sensor networks (OFSNs) are facing the problem of a lack of systematic evaluation criteria to assess network performance. In this paper, a universal quantitative robustness evaluation model for OFSNs is proposed. The model defines robustness as the mathematical expectation of the monitoring coverage ratio, which has taken into account the performance under all possible network states and the probability of each state. This model is applied to four basic network topologies including line, ring, star and bus topologies, and their mathematical expressions of robustness are derived by analyzing all possible states in detail. Further simulation gives a quantitative comparison among these topologies, proving that the ring and star topologies are optimal for the monitoring of strip-shaped and square regions, respectively. Finally, two influencing factors, the attenuation coefficient and the threshold, are investigated for their impact on the robustness of the network.

  • 29. Zhang, Hongxia
    et al.
    Chen, Xinwei
    Ye, Wenting
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics.
    Jia, Dagong
    Zhang, Yimo
    Mitigation of the birefringence dispersion on the polarization coupling measurement in a long-distance high-birefringence fiber2012In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 23, no 2, p. 025203-Article in journal (Refereed)
    Abstract [en]

    Due to the birefringence dispersion, the polarization coupling parameter measurement in high-birefringence fiber decreases obviously with the fiber length, especially for long-distance fibers. In this paper, two methods for mitigating the birefringence dispersion in a long-distance fiber are proposed. The first method is a spectral-domain measurement method. The experimental setup and results are described in detail. The other method is a time-domain numerical dispersion compensation algorithm to amend the coupling strength calculation equation. It is based on the fact that the interferogram envelope area is constant even with the existence of birefringence dispersion. The experimental result shows that the time-domain algorithm has high accuracy, and the absolute deviation is less than 1%. The two methods are validated to mitigate the birefringence dispersion in the long-distance high-birefringence fiber effectively.

  • 30. Zhang, Hongxia
    et al.
    Liu, Kun
    Jia, Dagong
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Material Physics.
    Liu, Tiegen
    Peng, Gangding
    Jing, Wencai
    Zhang, Yimo
    Improved low concentration gas detection system based on intracavity fiber laser2011In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 82, no 2, p. 023104-Article in journal (Refereed)
    Abstract [en]

    The improvement of a low concentration gas detection system based on the intracavity fiber laser is proposed in this paper. The sensitivity of the system is deduced based on Lambert-Beer law. The optimized system was established with the gas cell made elaborately. In order to apply the wavelength sweeping technique, the fiber Bragg grating reflector was substituted by the wavelength independent Faraday rotation reflector. The sensitivity of the system for acetylene detection is reduced to less than 100 ppm by using the average of three absorption spectra. The acetylene detection coefficients of variation with different concentrations are measured. The gas measurement system is validated to detect low concentration gas effectively.

  • 31. Zhang, Hongxia
    et al.
    Xu, Tianhua
    KTH, School of Information and Communication Technology (ICT), Optics and Photonics, Optics.
    Jia, Dagong
    Jing, Wencai
    Liu, Kun
    Zhang, Yimo
    Effects of angular misalignment in interferometric detection of distributed polarization coupling2009In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, no 9, p. 095112-Article in journal (Refereed)
    Abstract [en]

    White light interferometry is used to measure the distributed polarization coupling (DPC) in polarization-maintaining fibers (PMFs). By using a scanning Michelson interferometer to compensate the optical path difference (OPD) induced by the modal birefringence of PMFs, both the coupling strength and positions of the coupling points can be acquired. In ideal DPC measurement, the two reflective mirrors on the fixed and scanning arms of the Michelson interferometer are normal to each other. But in practice, the movable reflective mirror cannot be aligned normally to the fixed mirror exactly, which leads to an angular misalignment. The angular misalignment causes a variation of the OPD, which will reduce the fringe visibility. The theoretical simulation is investigated correspondingly. Consequently, the angular error leads to the miscalculation of the polarization coupling intensity. Based on the experimental results, a revised coupling strength calculation equation is proposed to minimize the influence of angular misalignment.

1 - 31 of 31
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