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  • 1. Jacobsen, G.
    et al.
    Xu, T.
    Popov, Sergei
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Sergeyev, S.
    Phase noise influence in coherent optical DnPSK systems with DSP based dispersion compensation2014In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 35, no 1, p. 57-61Article in journal (Refereed)
    Abstract [en]

    We present a comparative study of the influence of dispersion induced phase noise for n-level PSK systems. From the analysis, we conclude that the phase noise influence for classical homodyne/heterodyne PSK systems is entirely determined by the modulation complexity (expressed in terms of constellation diagram) and the analogue demodulation format. On the other hand, the use of digital signal processing (DSP) in homodyne/intradyne systems renders a fiber length dependence originating from the generation of equalization enhanced phase noise. For future high capacity systems, high constellations must be used in order to lower the symbol rate to practically manageable speeds, and this fact puts severe requirements to the signal and local oscillator (LO) linewidths. Our results for the bit-error-rate (BER) floor caused by the phase noise influence in the case of QPSK, 16PSK and 64PSK systems outline tolerance limitations for the LO performance: 5 MHz linewidth (at 3-dB level) for 100 Gbit/s QPSK; 1 MHz for 400 Gbit/s QPSK; 0.1 MHz for 400 Gbit/s 16PSK and 1 Tbit/s 64PSK systems. This defines design constrains for the phase noise impact in distributed-feed-back (DFB) or distributed-Bragg-reflector (DBR) semiconductor lasers, that would allow moving the system capacity from 100 Gbit/s system capacity to 400 Gbit/s in 3 years (1 Tbit/s in 5 years). It is imperative at the same time to increase the analogue to digital conversion (ADC) speed such that the single quadrature symbol rate goes from today's 25 GS/s to 100 GS/s (using two samples per symbol).

  • 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.
    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.

  • 3. 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.

  • 4.
    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.

  • 5. 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.

  • 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
    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.

  • 7.
    Leong, Miu Yoong
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO. Acreo Swedish ICT, Stockholm, Sweden .
    Jacobsen, Gunnar
    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, S.
    Receiver sensitivity in optical and microwave, heterodyne and homodyne systems2014In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 35, no 3, p. 221-229Article in journal (Refereed)
    Abstract [en]

    In this paper, we analyze the sensitivities of coherent optical receivers and microwave receivers. We derive theoretical limits of signal-to-noise ratio and bit error rate. By applying a generic approach to a broad range of receivers, we can compare their performance directly. Other publications have considered some of these receivers. However, their diverse nature obscures the big picture. Using our results as a unifying platform, previous publications can be compared and discrepancies between them identified.

  • 8.
    Leong, Miu Yoong
    et al.
    KTH, School of Engineering Sciences (SCI). Acreo.
    Larsen, K. J.
    Jacobsen, Gunnar
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Zibar, D.
    Sergeyev, S.
    Popov, S.
    BCH Codes for Coherent Star DQAM Systems with Laser Phase Noise2017In: Journal of optical communications, ISSN 0173-4911, E-ISSN 2191-6322, Vol. 38, no 1, p. 47-56Article in journal (Refereed)
    Abstract [en]

    Coherent optical systems have relatively high laser phase noise, which affects the performance of forward error correction (FEC) codes. In this paper, we propose a method for selecting Bose-Chaudhuri-Hocquenghem (BCH) codes for coherent systems with star-shaped constellations and M-ary differential quadrature amplitude modulation (DQAM). Our method supports constellations of any order M which is a power of 2, and includes differential M-ary phase shift keying as a special case. Our approach is straightforward, requiring only short pre-FEC simulations to parameterize a statistical model, based on which we select codes analytically. It is applicable to pre-FEC bit error rates (BERs) of around 10-3. We evaluate the accuracy of our approach using numerical simulations. For a target post-FEC BER of 10-5, codes selected with our method yield BERs within 2× target. Lastly, we extend our method to systems with interleaving, which enables us to use codes with lower overhead.

  • 9.
    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.

     

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