## Improved two-stage equalization for coherent Pol-Mux QPSK and 16-QAM systems |

Optics Express, Vol. 20, Issue 26, pp. B141-B150 (2012)

http://dx.doi.org/10.1364/OE.20.00B141

Acrobat PDF (1260 KB)

### Abstract

We report a two-stage blind frequency domain equalization method for long-haul coherent polarization-multiplexed (pol-mux) systems using quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16-QAM). In the first stage, blind CD parameter prediction is conducted prior to a CD equalizer. This supports flexible path switching in optical networks. In the second stage, a frequency-domain multi-modulus algorithm (MMA) equalizer is used to cope with the residual fiber impairments and perform polarization de-multiplexing. Compared with the conventional constant modulus algorithm (CMA), MMA shows advantages including better steady state performance and a faster convergence rate. Furthermore, all the estimation and equalization algorithms are implemented in the frequency domain which potentially provides the least complexity for the pol-mux optical coherent systems. The proposed algorithm is experimentally demonstrated with an 800-km 10 Gbaud coherent optical pol-mux system. For QPSK signal, the proposed method achieves error-free transmission and shows superior convergence speed against CMA, and for 16-QAM signals, the proposed MMA outperforms CMA with more than 1-dB improvement in Q-value.

© 2012 OSA

## 1. Introduction

1. J. Yu and X. Zhou, “Ultra-high-capacity DWDM transmission system for 100G and beyond,” IEEE Commun. Mag. **48**(3), S56–S64 (2010). [CrossRef]

2. P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol. **28**(4), 547–556 (2010). [CrossRef]

4. T. Pfau, S. Hoffmann, and R. Noé, “Hardware-efficient coherent digital receiver concept with feedforward carrier recovery for M-QAM constellations,” J. Lightwave Technol. **27**(8), 3042–3049 (2009). [CrossRef]

5. S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express **16**(2), 804–817 (2008). [CrossRef] [PubMed]

7. B. Spinnler, “Equalizer design and complexity for digital coherent receivers,” IEEE Sel. Top. in Quantum Electron. **16**(5), 1180–1192 (2010). [CrossRef]

8. R. Kudo, T. Kobayashi, K. Ishihara, Y. Takatori, A. Sano, and Y. Miyamoto, “Coherent optical single carrier transmission using overlap frequency domain equalization for long-haul optical systems,” J. Lightwave Technol. **27**(16), 3721–3728 (2009). [CrossRef]

9. A. V. Tran, C. Zhu, C. C. Do, S. Chen, T. Anderson, D. Hewitt, and E. Skafidas, “8×40-Gb/s optical coherent pol-mux single carrier system with frequency domain equalization and training sequences,” IEEE Photon. Technol. Lett. **24**(11), 885–887 (2012). [CrossRef]

10. M. S. Faruk and K. Kikuchi, “Adaptive frequency-domain equalization in digital coherent optical receivers,” Opt. Express **19**(13), 12789–12798 (2011). [CrossRef] [PubMed]

5. S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express **16**(2), 804–817 (2008). [CrossRef] [PubMed]

8. R. Kudo, T. Kobayashi, K. Ishihara, Y. Takatori, A. Sano, and Y. Miyamoto, “Coherent optical single carrier transmission using overlap frequency domain equalization for long-haul optical systems,” J. Lightwave Technol. **27**(16), 3721–3728 (2009). [CrossRef]

11. S. Yamanaka, T. Kobayashi, A. Sano, H. Masuda, E. Yoshida, Y. Miyamoto, T. Nakagawa, M. Nagatani, and H. Nosaka, “11 × 117 Gb/s PDM 16-QAM Transmission over 1440 km with a spectral efficiency of 6.4 b/s/Hz using high-speed DAC,” in European Conference and Exhibition on Optical Communication (ECOC), paper We.8.C.1 (2010).

13. X. Zhou, J. Yu, M.-F. Huang, Y. Shao, T. Wang, P. Magill, M. Cvijetic, L. Nelson, M. Birk, G. Zhang, S. Ten, H. B. Matthew, and S. K. Mishra, “Transmission of 32-Tb/s capacity over 580 km using RZ-shaped PDM-8QAM modulation format and cascaded multimodulus blind equalization algorithm,” J. Lightwave Technol. **28**(4), 456–465 (2010). [CrossRef]

## 2. Two-stage NDA SC-FDE system design

### 2.1 Receiver DSP architecture

5. S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express **16**(2), 804–817 (2008). [CrossRef] [PubMed]

16. S. Zhang, P. Y. Kam, C. Yu, and J. Chen, “Decision-aided carrier phase estimation for coherent optical communications,” J. Lightwave Technol. **28**(11), 1597–1607 (2010). [CrossRef]

### 2.2 Blind CD compensation

### 2.3 Frequency domain blind equalization

**16**(2), 804–817 (2008). [CrossRef] [PubMed]

10. M. S. Faruk and K. Kikuchi, “Adaptive frequency-domain equalization in digital coherent optical receivers,” Opt. Express **19**(13), 12789–12798 (2011). [CrossRef] [PubMed]

18. J. J. Shynk, “Frequency-domain and multirate adaptive filtering,” IEEE Sig. Proc. Mag. **9**(1), 14–37 (1992). [CrossRef]

*N*× 1 FD input vector,

*IFFT*bracket, and

18. J. J. Shynk, “Frequency-domain and multirate adaptive filtering,” IEEE Sig. Proc. Mag. **9**(1), 14–37 (1992). [CrossRef]

10. M. S. Faruk and K. Kikuchi, “Adaptive frequency-domain equalization in digital coherent optical receivers,” Opt. Express **19**(13), 12789–12798 (2011). [CrossRef] [PubMed]

**16**(2), 804–817 (2008). [CrossRef] [PubMed]

20. J. Yang, J.-J. Werner, and G. A. Dumont, ““The multimodulus blind equalization and its generalized algorithms,” IEEE J. Sel. Areas on Commun. **20**(5), 997–1015 (2002). [CrossRef]

## 3. Experimental results and discussion

^{5}samples for each polarization stored for off-line processing.

## 4. Conclusions

## Acknowledgments

## References and links

1. | J. Yu and X. Zhou, “Ultra-high-capacity DWDM transmission system for 100G and beyond,” IEEE Commun. Mag. |

2. | P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol. |

3. | I. Fatadin, D. Ives, and S. J. Savory, “Blind equalization and carrier phase recovery in a 16-QAM coherent optical system,” J. Lightwave Technol. |

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

5. | S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express |

6. | M. Kuschnerov, M. Chouayakh, K. Piyawanno, B. Spinnler, E. de Man, P. Kainzmaier, M. S. Alfiad, A. Napoli, and B. Lankl, “Data-aided versus blind single-carrier coherent receivers,” IEEE Photon. J. |

7. | B. Spinnler, “Equalizer design and complexity for digital coherent receivers,” IEEE Sel. Top. in Quantum Electron. |

8. | R. Kudo, T. Kobayashi, K. Ishihara, Y. Takatori, A. Sano, and Y. Miyamoto, “Coherent optical single carrier transmission using overlap frequency domain equalization for long-haul optical systems,” J. Lightwave Technol. |

9. | A. V. Tran, C. Zhu, C. C. Do, S. Chen, T. Anderson, D. Hewitt, and E. Skafidas, “8×40-Gb/s optical coherent pol-mux single carrier system with frequency domain equalization and training sequences,” IEEE Photon. Technol. Lett. |

10. | M. S. Faruk and K. Kikuchi, “Adaptive frequency-domain equalization in digital coherent optical receivers,” Opt. Express |

11. | S. Yamanaka, T. Kobayashi, A. Sano, H. Masuda, E. Yoshida, Y. Miyamoto, T. Nakagawa, M. Nagatani, and H. Nosaka, “11 × 117 Gb/s PDM 16-QAM Transmission over 1440 km with a spectral efficiency of 6.4 b/s/Hz using high-speed DAC,” in European Conference and Exhibition on Optical Communication (ECOC), paper We.8.C.1 (2010). |

12. | A. H. Gnauck, P. J. Winzer, C. R. Doerr, and L. L. Buhl, “10 × 112-Gb/s PDM 16-QAM transmission over 630 km of fiber with 6.2-b/s/Hz spectral efficiency,” in Optical Fiber Communication Conference (OFC), paper PDPB8 (2009). |

13. | X. Zhou, J. Yu, M.-F. Huang, Y. Shao, T. Wang, P. Magill, M. Cvijetic, L. Nelson, M. Birk, G. Zhang, S. Ten, H. B. Matthew, and S. K. Mishra, “Transmission of 32-Tb/s capacity over 580 km using RZ-shaped PDM-8QAM modulation format and cascaded multimodulus blind equalization algorithm,” J. Lightwave Technol. |

14. | C. Zhu, A. V. Tran, S. Chen, L. B. Du, T. Anderson, A. J. Lowery, and E. Skafidas, “Dual-stage frequency domain equalization for long-haul coherent polarization-multiplexed QPSK and 16-QAM systems,” in European Conference on Optical Communication (ECOC), paper We.1.A.2 (2012). |

15. | T. Nakagawa, M. Matsui, T. Kobayashi, K. Ishihara, R. Kudo, M. Mizoguchi, and Y. Miyamoto, “Non-data-aided wide-range frequency offset estimator for QAM optical coherent receivers,” in Optical Fiber Communication Conference (OFC), paper OMJ1 (2011). |

16. | S. Zhang, P. Y. Kam, C. Yu, and J. Chen, “Decision-aided carrier phase estimation for coherent optical communications,” J. Lightwave Technol. |

17. | F. N. Hauske, Z. Zhang, C. Li, C. Xie, and Q. Xiong, “Precise, robust and least complexity CD estimation,” in Optical Fiber Communication Conference (OFC), paper JWA32 (2011). |

18. | J. J. Shynk, “Frequency-domain and multirate adaptive filtering,” IEEE Sig. Proc. Mag. |

19. | B. Porat, |

20. | J. Yang, J.-J. Werner, and G. A. Dumont, ““The multimodulus blind equalization and its generalized algorithms,” IEEE J. Sel. Areas on Commun. |

**OCIS Codes**

(060.1660) Fiber optics and optical communications : Coherent communications

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

(060.4510) Fiber optics and optical communications : Optical communications

**ToC Category:**

Subsystems for Optical Networks

**History**

Original Manuscript: August 23, 2012

Manuscript Accepted: November 10, 2012

Published: November 28, 2012

**Virtual Issues**

European Conference on Optical Communication 2012 (2012) *Optics Express*

**Citation**

Chen Zhu, An V. Tran, Simin Chen, Liang B. Du, Trevor Anderson, Arthur J. Lowery, and Efstratios Skafidas, "Improved two-stage equalization for coherent Pol-Mux QPSK and 16-QAM systems," Opt. Express **20**, B141-B150 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-26-B141

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### References

- J. Yu and X. Zhou, “Ultra-high-capacity DWDM transmission system for 100G and beyond,” IEEE Commun. Mag.48(3), S56–S64 (2010). [CrossRef]
- P. J. Winzer, A. H. Gnauck, C. R. Doerr, M. Magarini, and L. L. Buhl, “Spectrally efficient long-haul optical networking using 112-Gb/s polarization-multiplexed 16-QAM,” J. Lightwave Technol.28(4), 547–556 (2010). [CrossRef]
- I. Fatadin, D. Ives, and S. J. Savory, “Blind equalization and carrier phase recovery in a 16-QAM coherent optical system,” J. Lightwave Technol.27(15), 3042–3049 (2009). [CrossRef]
- T. Pfau, S. Hoffmann, and R. Noé, “Hardware-efficient coherent digital receiver concept with feedforward carrier recovery for M-QAM constellations,” J. Lightwave Technol.27(8), 3042–3049 (2009). [CrossRef]
- S. J. Savory, “Digital filters for coherent optical receivers,” Opt. Express16(2), 804–817 (2008). [CrossRef] [PubMed]
- M. Kuschnerov, M. Chouayakh, K. Piyawanno, B. Spinnler, E. de Man, P. Kainzmaier, M. S. Alfiad, A. Napoli, and B. Lankl, “Data-aided versus blind single-carrier coherent receivers,” IEEE Photon. J.2(3), 387–403 (2010). [CrossRef]
- B. Spinnler, “Equalizer design and complexity for digital coherent receivers,” IEEE Sel. Top. in Quantum Electron.16(5), 1180–1192 (2010). [CrossRef]
- R. Kudo, T. Kobayashi, K. Ishihara, Y. Takatori, A. Sano, and Y. Miyamoto, “Coherent optical single carrier transmission using overlap frequency domain equalization for long-haul optical systems,” J. Lightwave Technol.27(16), 3721–3728 (2009). [CrossRef]
- A. V. Tran, C. Zhu, C. C. Do, S. Chen, T. Anderson, D. Hewitt, and E. Skafidas, “8×40-Gb/s optical coherent pol-mux single carrier system with frequency domain equalization and training sequences,” IEEE Photon. Technol. Lett.24(11), 885–887 (2012). [CrossRef]
- M. S. Faruk and K. Kikuchi, “Adaptive frequency-domain equalization in digital coherent optical receivers,” Opt. Express19(13), 12789–12798 (2011). [CrossRef] [PubMed]
- S. Yamanaka, T. Kobayashi, A. Sano, H. Masuda, E. Yoshida, Y. Miyamoto, T. Nakagawa, M. Nagatani, and H. Nosaka, “11 × 117 Gb/s PDM 16-QAM Transmission over 1440 km with a spectral efficiency of 6.4 b/s/Hz using high-speed DAC,” in European Conference and Exhibition on Optical Communication (ECOC), paper We.8.C.1 (2010).
- A. H. Gnauck, P. J. Winzer, C. R. Doerr, and L. L. Buhl, “10 × 112-Gb/s PDM 16-QAM transmission over 630 km of fiber with 6.2-b/s/Hz spectral efficiency,” in Optical Fiber Communication Conference (OFC), paper PDPB8 (2009).
- X. Zhou, J. Yu, M.-F. Huang, Y. Shao, T. Wang, P. Magill, M. Cvijetic, L. Nelson, M. Birk, G. Zhang, S. Ten, H. B. Matthew, and S. K. Mishra, “Transmission of 32-Tb/s capacity over 580 km using RZ-shaped PDM-8QAM modulation format and cascaded multimodulus blind equalization algorithm,” J. Lightwave Technol.28(4), 456–465 (2010). [CrossRef]
- C. Zhu, A. V. Tran, S. Chen, L. B. Du, T. Anderson, A. J. Lowery, and E. Skafidas, “Dual-stage frequency domain equalization for long-haul coherent polarization-multiplexed QPSK and 16-QAM systems,” in European Conference on Optical Communication (ECOC), paper We.1.A.2 (2012).
- T. Nakagawa, M. Matsui, T. Kobayashi, K. Ishihara, R. Kudo, M. Mizoguchi, and Y. Miyamoto, “Non-data-aided wide-range frequency offset estimator for QAM optical coherent receivers,” in Optical Fiber Communication Conference (OFC), paper OMJ1 (2011).
- S. Zhang, P. Y. Kam, C. Yu, and J. Chen, “Decision-aided carrier phase estimation for coherent optical communications,” J. Lightwave Technol.28(11), 1597–1607 (2010). [CrossRef]
- F. N. Hauske, Z. Zhang, C. Li, C. Xie, and Q. Xiong, “Precise, robust and least complexity CD estimation,” in Optical Fiber Communication Conference (OFC), paper JWA32 (2011).
- J. J. Shynk, “Frequency-domain and multirate adaptive filtering,” IEEE Sig. Proc. Mag.9(1), 14–37 (1992). [CrossRef]
- B. Porat, A Course in Digital Singal Processing (Wiley, 1997).
- J. Yang, J.-J. Werner, and G. A. Dumont, ““The multimodulus blind equalization and its generalized algorithms,” IEEE J. Sel. Areas on Commun.20(5), 997–1015 (2002). [CrossRef]

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