## Experimental investigation of the equalization-enhanced phase noise in long haul 56 Gbaud DP-QPSK systems |

Optics Express, Vol. 20, Issue 13, pp. 13841-13846 (2012)

http://dx.doi.org/10.1364/OE.20.013841

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### Abstract

We experimentally demonstrate the impact of equalization-enhanced phase noise (EEPN) on the performance of 56 Gbaud dual-polarization (DP) QPSK long haul transmission systems. Although EEPN adds additional noise to the received symbols, we show that this reduces the phase variance introduced by the LO laser, and therefore should be considered when designing the carrier phase recovery (CPR) algorithms and estimating system performance. Further, we experimentally demonstrate the performance degradation caused by EEPN when a LO laser with a large linewidth is used at the receiver. When using a 2.6 MHz linewidth distributed feedback (DFB) laser instead of a ~100 kHz linewidth external-cavity laser (ECL) as a LO, the transmission distance is reduced from 4160 km to 2640 km due to EEPN. We also confirm the reduction of the phase variance of the received symbols for longer transmission distances showing its impact on the CPR algorithm optimization when a DFB laser is used at the receiver. Finally, the relationship between the EEPN-induced penalty versus the signal baud rate and the LO laser linewidth is experimentally evaluated, and numerically validated by simulations.

© 2012 OSA

## 1. Introduction

1. W. Shieh and K.-P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express **16**(20), 15718–15727 (2008). [CrossRef] [PubMed]

1. W. Shieh and K.-P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express **16**(20), 15718–15727 (2008). [CrossRef] [PubMed]

3. A. P. T. Lau, T. S. R. Shen, W. Shieh, and K.-P. Ho, “Equalization-enhanced phase noise for 100 Gb/s transmission and beyond with coherent detection,” Opt. Express **18**(16), 17239–17251 (2010). [CrossRef] [PubMed]

1. W. Shieh and K.-P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express **16**(20), 15718–15727 (2008). [CrossRef] [PubMed]

## 2. Equalization-enhanced phase noise

*k*

^{th}symbol

*k*

^{th}transmitted symbol. The phase shift

**16**(20), 15718–15727 (2008). [CrossRef] [PubMed]

3. A. P. T. Lau, T. S. R. Shen, W. Shieh, and K.-P. Ho, “Equalization-enhanced phase noise for 100 Gb/s transmission and beyond with coherent detection,” Opt. Express **18**(16), 17239–17251 (2010). [CrossRef] [PubMed]

10. G. Colavolpe, T. Foggi, E. Forestieri, and M. Secondini, “Impact of phase noise and compensation techniques in coherent optical systems,” J. Lightwave Technol. **29**(18), 2790–2800 (2011). [CrossRef]

## 3. Experimental setup

## 4. Experimental and simulation results

^{−3}(corresponding to the BER threshold of a forward error correction (FEC) with 7% overhead). This is because in a back-to-back configuration the DFB laser only induces larger phase shift variance compared to the ECL, and that variance can still be tolerated with the employed CPR algorithm [11] without introducing penalties.

^{−3}BER threshold). In contrast, the transmission distance of the ECL/DFB system is reduced to 2640 km, due to the large amount of EEPN in such high baud rate and long distance transmission. By comparing the DFB/ECL and the ECL/DFB systems, it is clear that in our 56 Gbaud DP-QPSK system rather than the phase recovery ability of the CPR algorithms, the EEPN-induced noise

13. X. Chen, A. Al Amin, and W. Shieh, “Characterization and monitoring of laser linewidths in coherent systems,” J. Lightwave Technol. **29**(17), 2533–2537 (2011). [CrossRef]

## 5. Summary

## References and links

1. | W. Shieh and K.-P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express |

2. | C. Xie, “Local oscillator phase noise induced penalties in optical coherent detection systems using electronic chromatic dispersion compensation,” in Proc. OFC'09, Paper. OMT4. |

3. | A. P. T. Lau, T. S. R. Shen, W. Shieh, and K.-P. Ho, “Equalization-enhanced phase noise for 100 Gb/s transmission and beyond with coherent detection,” Opt. Express |

4. | S. Oda, C. Ohshima, T. Tanaka, T. Tanimura, H. Nakashima, N. Koizumi, T. Hoshida, H. Zhang, Z. Tao, and J. C. Rasmussen, “Interplay between local oscillator phase noise and electrical chromatic dispersion compensation in digital coherent transmission system,” in Proc. ECOC'10, Paper. Mo.1.C.2. |

5. | M. Salsi, O. Bertran-Pardo, J. Renaudier, W. Idler, H. Mardoyan, P. Tran, G. Charlet, and S. Bigo, “WDM 200Gb/s single-carrier PDM-QPSK transmission over 12,000km,” in Proc. ECOC'11, Paper. Th.13.C.5. |

6. | P. J. Winzer, A. H. Gnauck, G. Raybon, M. Schnecker, and P. J. Pupalaikis, “56-Gbaud PDM-QPSK: coherent detection and 2,500-km transmission,” in Proc. ECOC'09, Paper. PD2.7. |

7. | M. G. Taylor, “Phase estimation methods for optical coherent detection using digital signal processing,” J. Lightwave Technol. |

8. | T. Pfau, S. Hoffmann, and R. Noe, “Hardware-efficient coherent digital receiver concept with feedforward carrier recovery for M-QAM constellations,” J. Lightwave Technol. |

9. | Q. Zhuge, B. Châtelain, C. Chen, and D. V. Plant, “Mitigation of equalization-enhanced phase noise using reduced-guard-interval CO-OFDM,” in Proc. ECOC'11 Paper. Th.11.B.5. |

10. | G. Colavolpe, T. Foggi, E. Forestieri, and M. Secondini, “Impact of phase noise and compensation techniques in coherent optical systems,” J. Lightwave Technol. |

11. | Q. Zhuge, M. E. Pasandi, X. Xu, B. Châtelain, Z. Pan, M. Osman, and D. V. Plant, “Linewidth-tolerant low complexity pilot-aided carrier phase recovery for M-QAM using superscalar parallelization,” in Proc. OFC'12, Paper. OTu2G.2. |

12. | K. Kikuchi and K. Igarashi, “Characterization of semiconductor-laser phase noise with digital coherent receivers,” in Proc. OFC'11, Paper. OML3. |

13. | X. Chen, A. Al Amin, and W. Shieh, “Characterization and monitoring of laser linewidths in coherent systems,” J. Lightwave Technol. |

**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: April 26, 2012

Revised Manuscript: May 23, 2012

Manuscript Accepted: May 24, 2012

Published: June 7, 2012

**Citation**

Qunbi Zhuge, Xian Xu, Ziad A. El-Sahn, Mohammad E. Mousa-Pasandi, Mohamed Morsy-Osman, Mathieu Chagnon, Meng Qiu, and David V. Plant, "Experimental investigation of the equalization-enhanced phase noise in long haul 56 Gbaud DP-QPSK systems," Opt. Express **20**, 13841-13846 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-13-13841

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### References

- W. Shieh and K.-P. Ho, “Equalization-enhanced phase noise for coherent-detection systems using electronic digital signal processing,” Opt. Express16(20), 15718–15727 (2008). [CrossRef] [PubMed]
- C. Xie, “Local oscillator phase noise induced penalties in optical coherent detection systems using electronic chromatic dispersion compensation,” in Proc. OFC'09, Paper. OMT4.
- A. P. T. Lau, T. S. R. Shen, W. Shieh, and K.-P. Ho, “Equalization-enhanced phase noise for 100 Gb/s transmission and beyond with coherent detection,” Opt. Express18(16), 17239–17251 (2010). [CrossRef] [PubMed]
- S. Oda, C. Ohshima, T. Tanaka, T. Tanimura, H. Nakashima, N. Koizumi, T. Hoshida, H. Zhang, Z. Tao, and J. C. Rasmussen, “Interplay between local oscillator phase noise and electrical chromatic dispersion compensation in digital coherent transmission system,” in Proc. ECOC'10, Paper. Mo.1.C.2.
- M. Salsi, O. Bertran-Pardo, J. Renaudier, W. Idler, H. Mardoyan, P. Tran, G. Charlet, and S. Bigo, “WDM 200Gb/s single-carrier PDM-QPSK transmission over 12,000km,” in Proc. ECOC'11, Paper. Th.13.C.5.
- P. J. Winzer, A. H. Gnauck, G. Raybon, M. Schnecker, and P. J. Pupalaikis, “56-Gbaud PDM-QPSK: coherent detection and 2,500-km transmission,” in Proc. ECOC'09, Paper. PD2.7.
- M. G. Taylor, “Phase estimation methods for optical coherent detection using digital signal processing,” J. Lightwave Technol.27(7), 901–914 (2009). [CrossRef]
- T. Pfau, S. Hoffmann, and R. Noe, “Hardware-efficient coherent digital receiver concept with feedforward carrier recovery for M-QAM constellations,” J. Lightwave Technol.27(8), 989–999 (2009). [CrossRef]
- Q. Zhuge, B. Châtelain, C. Chen, and D. V. Plant, “Mitigation of equalization-enhanced phase noise using reduced-guard-interval CO-OFDM,” in Proc. ECOC'11 Paper. Th.11.B.5.
- G. Colavolpe, T. Foggi, E. Forestieri, and M. Secondini, “Impact of phase noise and compensation techniques in coherent optical systems,” J. Lightwave Technol.29(18), 2790–2800 (2011). [CrossRef]
- Q. Zhuge, M. E. Pasandi, X. Xu, B. Châtelain, Z. Pan, M. Osman, and D. V. Plant, “Linewidth-tolerant low complexity pilot-aided carrier phase recovery for M-QAM using superscalar parallelization,” in Proc. OFC'12, Paper. OTu2G.2.
- K. Kikuchi and K. Igarashi, “Characterization of semiconductor-laser phase noise with digital coherent receivers,” in Proc. OFC'11, Paper. OML3.
- X. Chen, A. Al Amin, and W. Shieh, “Characterization and monitoring of laser linewidths in coherent systems,” J. Lightwave Technol.29(17), 2533–2537 (2011). [CrossRef]

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