## Simultaneous and independent multi-parameter monitoring with fault localization for DSP-based coherent communication systems |

Optics Express, Vol. 18, Issue 23, pp. 23608-23619 (2010)

http://dx.doi.org/10.1364/OE.18.023608

Acrobat PDF (1096 KB)

### Abstract

Digital signal processing (DSP)-based coherent communications have become standard for future high-speed optical networks. Implementing DSP-based advanced algorithms for data detection requires much more detailed knowledge of the transmission link parameters, resulting in optical performance monitoring (OPM) being even more important for next generation systems. At the same time, the DSP platform also enables new strategies for OPM. In this paper, we propose the use of pilot symbols with alternating power levels and study the statistics of the received power and phase difference to simultaneously and independently monitor the carrier frequency offset between transmitter and receiver laser, laser linewidth, number of spans, fiber nonlinearity parameters as well as optical signal-to-noise ratio (OSNR) of a transmission link. Analytical predictions are verified by simulation results for systems with full chromatic dispersion (CD) compensation per span and 10% CD under-compensation per span. In addition, we show that by monitoring the changes in the statistics of the received pilot symbols during network operation, one can locate faults or OSNR degradations along a transmission link without additional monitoring equipments at intermediate nodes, which may be useful for more efficient dynamic routing and network management.

© 2010 OSA

## 1. Introduction

1. Z. Q. Pan, C. Y. Yu, and A. E. Willner, “Optical performance monitoring for the next generation optical communication networks,” Opt. Fiber Technol. **16**(1), 20–45 (2010). [CrossRef]

*et al.*[3

3. Y. Cao, S. Yu, J. Shen, W. Gu, and Y. Ji, “Frequency Estimation for Optical Coherent MPSK System Without Removing Modulated Data Phase,” IEEE Photon. Technol. Lett. **22**(10), 691–693 (2010). [CrossRef]

*et al.*[4

4. T. Duthel, G. Clarici, C. R. S. Fludger, J. C. Geyer, C. Schulien, and S. Wiese, “Laser Linewidth Estimation by Means of Coherent Detection,” IEEE Photon. Technol. Lett. **21**(20), 1568–1570 (2009). [CrossRef]

5. A. P. T. Lau and J. M. Kahn, “Signal design and detection in presence of nonlinear phase noise,” J. Lightwave Technol. **25**(10), 3008–3016 (2007). [CrossRef]

6. K. P. Ho and J. M. Kahn, “Electronic compensation technique to mitigate nonlinear phase noise,” J. Lightwave Technol. **22**(3), 779–783 (2004). [CrossRef]

7. A. P. T. Lau, S. Rabbani, and J. M. Kahn, “On the Statistics of Intrachannel Four-Wave Mixing in Phase-Modulated Optical Communication Systems,” J. Lightwave Technol. **26**(14), 2128–2135 (2008). [CrossRef]

8. E. Ip and J. M. Kahn, “Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation,” J. Lightwave Technol. **26**(20), 3416–3425 (2008). [CrossRef]

9. E. F. Mateo and G. F. Li, “Compensation of interchannel nonlinearities using enhanced coupled equations for digital backward propagation,” Appl. Opt. **48**(25), F6–F10 (2009). [CrossRef] [PubMed]

*N*and the dispersion map (as supposed to just accumulated CD) of the link. Furthermore, as shown in Fig. 1(a) , dynamic routing in practical terrestrial networks will still result in variations of link parameters such as

*N*from time to time. To evaluate the performance impact with imperfect knowledge of the link, Fig. 1(b) shows the resulting

*Q*-factor using BP with incorrect parameter values for a 1600 km system with 20 spans and 10% CD under-compensation per span. The modulation format is 200 Gb/s polarization-multiplexed Non Return-to-Zero (NRZ)-16-quadrature amplitude modulation (QAM) and the specifications of other link parameters are shown in Table 1 (in Section 3). The oversampling rate is 2 and the

*ξ*parameter of the BP algorithm described in [8

8. E. Ip and J. M. Kahn, “Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation,” J. Lightwave Technol. **26**(20), 3416–3425 (2008). [CrossRef]

*Q*-factor corresponding to algorithms that only compensate for CD is also shown as reference. From the figures, it can be seen that when the number of spans used in BP is smaller than the actual value by 3, the performance improvements by using BP is noticeably reduced. On the other hand, over-estimating

*N*will be equivalent to BP with multi-span step size, which increases computational complexity [8

8. E. Ip and J. M. Kahn, “Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation,” J. Lightwave Technol. **26**(20), 3416–3425 (2008). [CrossRef]

*γ*needs to be monitored with good accuracy at the receiver in order to fully optimize the performance of BP. Various approaches have been proposed to measure the nonlinear coefficients of short fibers utilizing the effect of self-phase modulation (SPM) [10

10. K. S. Kim, R. H. Stolen, W. A. Reed, and K. W. Quoi, “Measurement of the nonlinear index of silica-core and dispersion-shifted fibers,” Opt. Lett. **19**(4), 257–259 (1994). [CrossRef] [PubMed]

11. T. Kato, Y. Suetsugu, M. Takagi, E. Sasaoka, and M. Nishimura, “Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light,” Opt. Lett. **20**(9), 988–990 (1995). [CrossRef] [PubMed]

12. L. Prigent and J. P. Hamaide, “Measurement of Fiber Nonlinear Kerr Coefficient by four-Wave-Mixing,” IEEE Photon. Technol. Lett. **5**(9), 1092–1095 (1993). [CrossRef]

13. C. Xu and X. Liu, “Postnonlinearity compensation with data-driven phase modulators in phase-shift keying transmission,” Opt. Lett. **27**(18), 1619–1621 (2002). [CrossRef]

15. M. Mayrock and H. Haunstein, “Monitoring of Linear and Nonlinear Signal Distortion in Coherent Optical OFDM Transmission,” J. Lightwave Technol. **27**(16), 3560–3566 (2009). [CrossRef]

*N*may be given by upper layer protocols from the control plane but it may not be available sometimes. To this end, Tanimura et al. [16] studied the use of semi-blind sequences for optimizing the nonlinear equalization parameters in BP given an almost perfect prior knowledge of the transmission link. However, a thorough investigation on the monitoring of fiber nonlinear coefficients and number of spans are much needed for practical implementations of advanced DSP algorithms like BP in a dynamic network environment.

## 2. Simultaneous and independent multi-parameters monitoring using pilot symbols

### 2.1. System model

*N*spans of single-mode fiber (SMF) with length

*T*and alternating power levels

*T*will be chosen such that inter-symbol interference (ISI) and pulse shape distortion induced by chromatic dispersion (CD) and polarization-mode dispersion (PMD) is negligible. In addition, as the symbol rate of pilot sequence is much lower than that of data transmission, pulse distortion caused by filters designed for 25 GSym/s transmission and beyond should be negligible as well. Let

*i*

^{th}span respectively which are zero-mean complex circularly symmetric Gaussian random processes with power spectral density where

*v*is the carrier frequency,

*h*is the Planck constant.

*t*can be expressed as where the approximation is valid for high OSNR. The variance of the received signal power

*N*spans of fibers is given bywhich contains ASE-induced phase noise

*θ*is the relative phase of the transmitter (Tx) and receiver (Rx) laser at

*t*= 0. For high OSNR, the ASE-induced phase noise can be approximated as with zero mean and variance

*N*, OSNR as well as the nonlinear coefficients of the link from the statistics of the received power and phase difference. It should be noted that for the purpose of implementing advanced DSP algorithms like BP, it suffices to monitor the nonlinear parameter

### 2.2. Simultaneous and independent multi-parameter monitoring

*N*, fiber nonlinear coefficient and OSNR of the link. With Eqs. (2), (5), (8), (12)-(16) and some algebraic manipulations, one obtain

*N*. Subsequently, the fiber nonlinear parameter

## 3. Simulation Results and Discussions

*N*,

4. T. Duthel, G. Clarici, C. R. S. Fludger, J. C. Geyer, C. Schulien, and S. Wiese, “Laser Linewidth Estimation by Means of Coherent Detection,” IEEE Photon. Technol. Lett. **21**(20), 1568–1570 (2009). [CrossRef]

*N*,

*N*, OSNR and

*N*generally agrees with their true values for

*N*≤ 22. The slight inaccuracies for

*N*> 22 may be caused by accumulated CD, frequency offset, laser linewidth, or a combination of them. Although the estimation errors gradually increase with

*N*, the errors are limited to 1 span for a system containing around 25 spans. The OSNR monitoring accuracies shown in Fig. 5(b) for both dispersion maps with fiber nonlinearity are within 0.1 dB. The OSNR monitoring results are independent of the two dispersion maps and intra-channel nonlinearities. Figure 5(c) shows the estimated

*N*= 15. Although estimation errors can be observed for both dispersion maps, the errors are limited to 0.4 dB and 0.6 dB (or equivalently 0.51 and 0.78

## 4. Receiver-based fault localization using statistics of received pilot symbols

19. Y. G. Wen, V. W. S. Chan, and L. Z. Zheng, “Efficient fault-diagnosis algorithms for all-optical WDM networks with probabilistic link failures,” J. Lightwave Technol. **23**(10), 3358–3371 (2005). [CrossRef]

*et al.*[22

22. A. V. Sichani and H. T. Mouftah, “Limited-perimeter vector matching fault-localization protocol for transparent all-optical communication networks,” IET Communications **1**(3), 472–478 (2007). [CrossRef]

23. M. Khair, B. Kantarci, J. Zheng, and H. T. Mouftah, “Optimization for Fault Localization in All-Optical Networks,” J. Lightwave Technol. **27**(21), 4832–4840 (2009). [CrossRef]

*i*

^{th}span, the increase in the ASE noise power of the

*i*

^{th}amplifier

*i*. However, the induced change in the variance of phase difference

*i*. Intuitively, this is because ASE noise introduced earlier in the transmission link undergoes more fiber nonlinear effects and accumulates more nonlinear phase noise. Therefore, by monitoring

## 5. Conclusions

## Acknowledgments

## References and links

1. | Z. Q. Pan, C. Y. Yu, and A. E. Willner, “Optical performance monitoring for the next generation optical communication networks,” Opt. Fiber Technol. |

2. | S. Zhang, |

3. | Y. Cao, S. Yu, J. Shen, W. Gu, and Y. Ji, “Frequency Estimation for Optical Coherent MPSK System Without Removing Modulated Data Phase,” IEEE Photon. Technol. Lett. |

4. | T. Duthel, G. Clarici, C. R. S. Fludger, J. C. Geyer, C. Schulien, and S. Wiese, “Laser Linewidth Estimation by Means of Coherent Detection,” IEEE Photon. Technol. Lett. |

5. | A. P. T. Lau and J. M. Kahn, “Signal design and detection in presence of nonlinear phase noise,” J. Lightwave Technol. |

6. | K. P. Ho and J. M. Kahn, “Electronic compensation technique to mitigate nonlinear phase noise,” J. Lightwave Technol. |

7. | A. P. T. Lau, S. Rabbani, and J. M. Kahn, “On the Statistics of Intrachannel Four-Wave Mixing in Phase-Modulated Optical Communication Systems,” J. Lightwave Technol. |

8. | E. Ip and J. M. Kahn, “Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation,” J. Lightwave Technol. |

9. | E. F. Mateo and G. F. Li, “Compensation of interchannel nonlinearities using enhanced coupled equations for digital backward propagation,” Appl. Opt. |

10. | K. S. Kim, R. H. Stolen, W. A. Reed, and K. W. Quoi, “Measurement of the nonlinear index of silica-core and dispersion-shifted fibers,” Opt. Lett. |

11. | T. Kato, Y. Suetsugu, M. Takagi, E. Sasaoka, and M. Nishimura, “Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light,” Opt. Lett. |

12. | L. Prigent and J. P. Hamaide, “Measurement of Fiber Nonlinear Kerr Coefficient by four-Wave-Mixing,” IEEE Photon. Technol. Lett. |

13. | C. Xu and X. Liu, “Postnonlinearity compensation with data-driven phase modulators in phase-shift keying transmission,” Opt. Lett. |

14. | M. N. Petersen and M. L. Nielsen, “Experimental and theoretical demonstration of launch power optimisation using subcarrier fibre nonlinearity monitor,” Electron. Lett. |

15. | M. Mayrock and H. Haunstein, “Monitoring of Linear and Nonlinear Signal Distortion in Coherent Optical OFDM Transmission,” J. Lightwave Technol. |

16. | T. Takahito, |

17. | A. P. T. Lau and J. M. Kahn, “Design of inline amplifier gains and spacings to minimize the phase noise in optical transmission systems,” J. Lightwave Technol. |

18. | T. Tanimura, |

19. | Y. G. Wen, V. W. S. Chan, and L. Z. Zheng, “Efficient fault-diagnosis algorithms for all-optical WDM networks with probabilistic link failures,” J. Lightwave Technol. |

20. | J. H. Park, J. S. Baik, and C. H. Lee, “Fault-localization in WDM-PONs,” in Optical Fiber Communication/National Fiber Optic Engineers Conference (OFC/NFOEC), 2006, Paper JThB79. |

21. | S. S. Ahuja, S. Ramasubramanian, and M. Krunz, “Single-Link Failure Detection in All-Optical Networks using Monitoring Cycles and Paths,” IEEE/ACM Transactions on Networking, |

22. | A. V. Sichani and H. T. Mouftah, “Limited-perimeter vector matching fault-localization protocol for transparent all-optical communication networks,” IET Communications |

23. | M. Khair, B. Kantarci, J. Zheng, and H. T. Mouftah, “Optimization for Fault Localization in All-Optical Networks,” J. Lightwave Technol. |

**OCIS Codes**

(060.0060) Fiber optics and optical communications : Fiber optics and optical communications

(060.1660) Fiber optics and optical communications : Coherent communications

(060.4370) Fiber optics and optical communications : Nonlinear optics, fibers

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: September 27, 2010

Revised Manuscript: October 21, 2010

Manuscript Accepted: October 21, 2010

Published: October 26, 2010

**Citation**

Thomas Shun Rong Shen, Alan Pak Tao Lau, and Changyuan Yu, "Simultaneous and independent multi-parameter monitoring with fault localization for DSP-based coherent communication systems," Opt. Express **18**, 23608-23619 (2010)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-23-23608

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### References

- Z. Q. Pan, C. Y. Yu, and A. E. Willner, “Optical performance monitoring for the next generation optical communication networks,” Opt. Fiber Technol. 16(1), 20–45 (2010). [CrossRef]
- S. Zhang, et al., “Novel ultra wide-range frequency offset estimation for digital coherent optical receiver,” in Optical Fiber Communication/National Fiber Optic Engineers Conference, (OFC/NFOEC), 2010, Paper OWV3.
- Y. Cao, S. Yu, J. Shen, W. Gu, and Y. Ji, “Frequency Estimation for Optical Coherent MPSK System Without Removing Modulated Data Phase,” IEEE Photon. Technol. Lett. 22(10), 691–693 (2010). [CrossRef]
- T. Duthel, G. Clarici, C. R. S. Fludger, J. C. Geyer, C. Schulien, and S. Wiese, “Laser Linewidth Estimation by Means of Coherent Detection,” IEEE Photon. Technol. Lett. 21(20), 1568–1570 (2009). [CrossRef]
- A. P. T. Lau and J. M. Kahn, “Signal design and detection in presence of nonlinear phase noise,” J. Lightwave Technol. 25(10), 3008–3016 (2007). [CrossRef]
- K. P. Ho and J. M. Kahn, “Electronic compensation technique to mitigate nonlinear phase noise,” J. Lightwave Technol. 22(3), 779–783 (2004). [CrossRef]
- A. P. T. Lau, S. Rabbani, and J. M. Kahn, “On the Statistics of Intrachannel Four-Wave Mixing in Phase-Modulated Optical Communication Systems,” J. Lightwave Technol. 26(14), 2128–2135 (2008). [CrossRef]
- E. Ip and J. M. Kahn, “Compensation of Dispersion and Nonlinear Impairments Using Digital Backpropagation,” J. Lightwave Technol. 26(20), 3416–3425 (2008). [CrossRef]
- E. F. Mateo and G. F. Li, “Compensation of interchannel nonlinearities using enhanced coupled equations for digital backward propagation,” Appl. Opt. 48(25), F6–F10 (2009). [CrossRef] [PubMed]
- K. S. Kim, R. H. Stolen, W. A. Reed, and K. W. Quoi, “Measurement of the nonlinear index of silica-core and dispersion-shifted fibers,” Opt. Lett. 19(4), 257–259 (1994). [CrossRef] [PubMed]
- T. Kato, Y. Suetsugu, M. Takagi, E. Sasaoka, and M. Nishimura, “Measurement of the nonlinear refractive index in optical fiber by the cross-phase-modulation method with depolarized pump light,” Opt. Lett. 20(9), 988–990 (1995). [CrossRef] [PubMed]
- L. Prigent and J. P. Hamaide, “Measurement of Fiber Nonlinear Kerr Coefficient by four-Wave-Mixing,” IEEE Photon. Technol. Lett. 5(9), 1092–1095 (1993). [CrossRef]
- C. Xu and X. Liu, “Postnonlinearity compensation with data-driven phase modulators in phase-shift keying transmission,” Opt. Lett. 27(18), 1619–1621 (2002). [CrossRef]
- M. N. Petersen and M. L. Nielsen, “Experimental and theoretical demonstration of launch power optimisation using subcarrier fibre nonlinearity monitor,” Electron. Lett. 41(5), 268–269 (2005). [CrossRef]
- M. Mayrock and H. Haunstein, “Monitoring of Linear and Nonlinear Signal Distortion in Coherent Optical OFDM Transmission,” J. Lightwave Technol. 27(16), 3560–3566 (2009). [CrossRef]
- T. Takahito, et al., “Semi-Blind Nonlinear Equalization in Coherent Multi-Span Transmission System with Inhomogeneous Span Parameters,” in Optical Fiber Communication/National Fiber Optic Engineers Conference, (OFC/NFOEC), 2010, Paper OMR6.
- A. P. T. Lau and J. M. Kahn, “Design of inline amplifier gains and spacings to minimize the phase noise in optical transmission systems,” J. Lightwave Technol. 24(3), 1334–1341 (2006). [CrossRef]
- T. Tanimura, et al., “Digital clock recovery algorithm for optical coherent receivers operating independent of laser frequency offset,” in 34th European Conference on Optical Communication (ECOC), (2008), Paper Mo.3.D.2.
- Y. G. Wen, V. W. S. Chan, and L. Z. Zheng, “Efficient fault-diagnosis algorithms for all-optical WDM networks with probabilistic link failures,” J. Lightwave Technol. 23(10), 3358–3371 (2005). [CrossRef]
- J. H. Park, J. S. Baik, and C. H. Lee, “Fault-localization in WDM-PONs,” in Optical Fiber Communication/National Fiber Optic Engineers Conference (OFC/NFOEC), 2006, Paper JThB79.
- S. S. Ahuja, S. Ramasubramanian, and M. Krunz, “Single-Link Failure Detection in All-Optical Networks using Monitoring Cycles and Paths,” IEEE/ACM Transactions on Networking, 17, 1080–1093 (2009).
- A. V. Sichani and H. T. Mouftah, “Limited-perimeter vector matching fault-localization protocol for transparent all-optical communication networks,” IET Communications 1(3), 472–478 (2007). [CrossRef]
- M. Khair, B. Kantarci, J. Zheng, and H. T. Mouftah, “Optimization for Fault Localization in All-Optical Networks,” J. Lightwave Technol. 27(21), 4832–4840 (2009). [CrossRef]

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