## 400 Gbit/s 256 QAM-OFDM transmission over 720 km with a 14 bit/s/Hz spectral efficiency by using high-resolution FDE |

Optics Express, Vol. 21, Issue 3, pp. 2632-2641 (2013)

http://dx.doi.org/10.1364/OE.21.002632

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### Abstract

We demonstrate 400 Gbit/s frequency-division-multiplexed and polarization-division-multiplexed 256 QAM-OFDM transmission over 720 km with a spectral efficiency of 14 bit/s/Hz by using high-resolution frequency domain equalization (FDE) and digital back-propagation (DBP) methods. A detailed analytical evaluation of the 256 QAM-OFDM transmission is also provided, which clarifies the influence of quantization error in the digital coherent receiver on the waveform distortion compensation with DBP.

© 2013 OSA

## 1. Introduction

2. X. Liu, S. Chandrasekhar, T. Lotz, P. Winzer, H. Haunstein, S. Randel, S. Corteselli, B. Zhu, and D. W. Peckham “Generation and FEC-decoding of a 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation achieving 11.15-b/s/Hz intrachannel spectral efficiency and 800-km reach,” OFC2012, PDP5B.3.

2. X. Liu, S. Chandrasekhar, T. Lotz, P. Winzer, H. Haunstein, S. Randel, S. Corteselli, B. Zhu, and D. W. Peckham “Generation and FEC-decoding of a 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation achieving 11.15-b/s/Hz intrachannel spectral efficiency and 800-km reach,” OFC2012, PDP5B.3.

## 2. Experimental setup for 400 Gbit/s 256 QAM-OFDM transmission

_{2}H

_{2}frequency-stabilized fiber laser [4

4. K. Kasai, A. Suzuki, M. Yoshida, and M. Nakazawa, “Performance improvement of an acetylene (C_{2}H_{2}) frequency-stabilized fiber laser,” IEICE Electron. Express **3**(22), 487–492 (2006). [CrossRef]

_{0}. As a result, ten optical sidebands separated at 2.59 GHz were generated from the multi-carrier generator. Then, each of the fivesidebands from the MZM was modulated using an IQ modulator (IQM) with an OFDM signal generated by an arbitrary waveform generator (AWG) at a sampling rate of 12 Gsample/s. The AWGs generated the OFDM baseband signals using a fast Fourier transform (FFT) and FDE [5

5. A. Al Amin, S. L. Jansen, H. Takahashi, I. Morita, and H. Tanaka, “A hybrid IQ imbalance compensation method for optical OFDM transmission,” Opt. Express **18**(5), 4859–4866 (2010). [CrossRef] [PubMed]

7. Y. Koizumi, K. Toyoda, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “512 QAM transmission over 240 km using frequency-domain equalization in a digital coherent receiver,” Opt. Express **20**(21), 23383–23389 (2012). [CrossRef] [PubMed]

_{0}. This signal was used as the pilot tone signal required for the optical phase tracking of the local oscillator (LO) under optical PLL operation [8

8. K. Kasai, J. Hongo, M. Yoshida, and M. Nakazawa, “Optical phase-locked loop for coherent transmission over 500 km using heterodyne detection with fiber lasers,” IEICE Electron. Express **4**(3), 77–81 (2007). [CrossRef]

12. K. Toyoda, Y. Koizumi, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “Marked performance improvement of 256 QAM transmission using a digital back-propagation method,” Opt. Express **20**(18), 19815–19821 (2012). [CrossRef] [PubMed]

^{−3}was improved by 1 dB with the FDE improvement.

## 3. Experimental result

^{−3}after 320, 640, and 720 km transmissions were 2, 5, and 15 dB, respectively. In Fig. 12(b), BER obtained without and with the FDE improvement (N = 1 and 16, respectively) are plotted. The transmission distance with a BER below the FEC threshold (2 x 10

^{−3}) was extended from 560 to 720 km as a result of the improvement in the FDE as shown in Fig. 5, where BER at the OSNR of 29.3 dB was reduced to 1.0 x 10

^{−3}with the FDE improvement. The present result corresponds to an SE-product of 10,080 km·bit/s/Hz.

## 4. Numerical simulation and discussion

^{−4}as a result of the increased OSNR. This indicates that it is important to increase the ENOB of the A/D converter to improve the distortion compensation with DBP in our high spectral efficiency transmission [13].

## 5. Conclusion

## References and links

1. | P. J. Winzer, “Modulation and multiplexing in optical communication systems,” IEEE LEOS Newsletter |

2. | X. Liu, S. Chandrasekhar, T. Lotz, P. Winzer, H. Haunstein, S. Randel, S. Corteselli, B. Zhu, and D. W. Peckham “Generation and FEC-decoding of a 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation achieving 11.15-b/s/Hz intrachannel spectral efficiency and 800-km reach,” OFC2012, PDP5B.3. |

3. | T. Omiya, K. Toyoda, M. Yoshida, and M. Nakazawa, “400 Gbit/s frequency-division-multiplexed and polarization-multiplexed 256 QAM-OFDM transmission over 400 km with a spectral efficiency of 14 bit/s/Hz,” OFC2012, OM2A.7. |

4. | K. Kasai, A. Suzuki, M. Yoshida, and M. Nakazawa, “Performance improvement of an acetylene (C |

5. | A. Al Amin, S. L. Jansen, H. Takahashi, I. Morita, and H. Tanaka, “A hybrid IQ imbalance compensation method for optical OFDM transmission,” Opt. Express |

6. | Y. Koizumi, K. Toyoda, M. Yoshida, and M. Nakazawa, “1024 QAM (60 Gbit/s) single-carrier coherent optical transmission over 150 km,” Opt. Express |

7. | Y. Koizumi, K. Toyoda, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “512 QAM transmission over 240 km using frequency-domain equalization in a digital coherent receiver,” Opt. Express |

8. | K. Kasai, J. Hongo, M. Yoshida, and M. Nakazawa, “Optical phase-locked loop for coherent transmission over 500 km using heterodyne detection with fiber lasers,” IEICE Electron. Express |

9. | T. Yamazaki, T. Tanabe, F. Kannari, Y. Shida, and S. Fushimi, “Fiber delivery of ultrashort optical pulses preshaped on the basis of a backward propagation solver,” Jpn. J. Appl. Phys. 1, Regul. Pap. Short Notes |

10. | C. Paré, A. Villeneuve, P.-A. Bélanger, and N. J. Doran, “Compensating for dispersion and the nonlinear Kerr effect without phase conjugation,” Opt. Lett. |

11. | M. Tsang, D. Psaltis, and F. G. Omenetto, “Reverse propagation of femtosecond pulses in optical fibers,” Opt. Lett. |

12. | K. Toyoda, Y. Koizumi, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “Marked performance improvement of 256 QAM transmission using a digital back-propagation method,” Opt. Express |

13. | B. Schmauss, C. Lin, and R. Asif, “Progress in digital backward propagation,” ECOC2012, Th.1.D.5. |

**OCIS Codes**

(060.1660) Fiber optics and optical communications : Coherent communications

(060.2330) Fiber optics and optical communications : Fiber optics communications

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: November 29, 2012

Revised Manuscript: January 14, 2013

Manuscript Accepted: January 14, 2013

Published: January 28, 2013

**Citation**

Tatsunori Omiya, Masato Yoshida, and Masataka Nakazawa, "400 Gbit/s 256 QAM-OFDM transmission over 720 km with a 14 bit/s/Hz spectral efficiency by using high-resolution FDE," Opt. Express **21**, 2632-2641 (2013)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-3-2632

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### References

- P. J. Winzer, “Modulation and multiplexing in optical communication systems,” IEEE LEOS Newsletter23(1), 4–10 (2009).
- X. Liu, S. Chandrasekhar, T. Lotz, P. Winzer, H. Haunstein, S. Randel, S. Corteselli, B. Zhu, and D. W. Peckham “Generation and FEC-decoding of a 231.5-Gb/s PDM-OFDM signal with 256-iterative-polar-modulation achieving 11.15-b/s/Hz intrachannel spectral efficiency and 800-km reach,” OFC2012, PDP5B.3.
- T. Omiya, K. Toyoda, M. Yoshida, and M. Nakazawa, “400 Gbit/s frequency-division-multiplexed and polarization-multiplexed 256 QAM-OFDM transmission over 400 km with a spectral efficiency of 14 bit/s/Hz,” OFC2012, OM2A.7.
- K. Kasai, A. Suzuki, M. Yoshida, and M. Nakazawa, “Performance improvement of an acetylene (C2H2) frequency-stabilized fiber laser,” IEICE Electron. Express3(22), 487–492 (2006). [CrossRef]
- A. Al Amin, S. L. Jansen, H. Takahashi, I. Morita, and H. Tanaka, “A hybrid IQ imbalance compensation method for optical OFDM transmission,” Opt. Express18(5), 4859–4866 (2010). [CrossRef] [PubMed]
- Y. Koizumi, K. Toyoda, M. Yoshida, and M. Nakazawa, “1024 QAM (60 Gbit/s) single-carrier coherent optical transmission over 150 km,” Opt. Express20(11), 12508–12514 (2012). [CrossRef] [PubMed]
- Y. Koizumi, K. Toyoda, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “512 QAM transmission over 240 km using frequency-domain equalization in a digital coherent receiver,” Opt. Express20(21), 23383–23389 (2012). [CrossRef] [PubMed]
- K. Kasai, J. Hongo, M. Yoshida, and M. Nakazawa, “Optical phase-locked loop for coherent transmission over 500 km using heterodyne detection with fiber lasers,” IEICE Electron. Express4(3), 77–81 (2007). [CrossRef]
- T. Yamazaki, T. Tanabe, F. Kannari, Y. Shida, and S. Fushimi, “Fiber delivery of ultrashort optical pulses preshaped on the basis of a backward propagation solver,” Jpn. J. Appl. Phys. 1, Regul. Pap. Short Notes42(12), 7313–7317 (2003).
- C. Paré, A. Villeneuve, P.-A. Bélanger, and N. J. Doran, “Compensating for dispersion and the nonlinear Kerr effect without phase conjugation,” Opt. Lett.21(7), 459–461 (1996). [CrossRef] [PubMed]
- M. Tsang, D. Psaltis, and F. G. Omenetto, “Reverse propagation of femtosecond pulses in optical fibers,” Opt. Lett.28(20), 1873–1875 (2003). [CrossRef] [PubMed]
- K. Toyoda, Y. Koizumi, T. Omiya, M. Yoshida, T. Hirooka, and M. Nakazawa, “Marked performance improvement of 256 QAM transmission using a digital back-propagation method,” Opt. Express20(18), 19815–19821 (2012). [CrossRef] [PubMed]
- B. Schmauss, C. Lin, and R. Asif, “Progress in digital backward propagation,” ECOC2012, Th.1.D.5.

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