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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 14, Iss. 1 — Jan. 9, 2006
  • pp: 58–62
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Simple PMD-insensitive OSNR monitoring scheme assisted by transmitter-side polarization scrambling

Guo-Wei Lu, Man-Hong Cheung, Lian-Kuan Chen, and Chun-Kit Chan  »View Author Affiliations


Optics Express, Vol. 14, Issue 1, pp. 58-62 (2006)
http://dx.doi.org/10.1364/OPEX.14.000058


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Abstract

Recently, degree of polarization (DOP) of light has been utilized as a parameter to monitor optical signal-to-noise-ratio (OSNR). However, in the presence of polarization-mode dispersion (PMD), when using DOP to determine OSNR, OSNR is always underestimated due to the depolarization effect induced by PMD. In this paper, we propose and experimentally demonstrate a simple PMD-insensitive OSNR monitoring technique based on DOP measurement. By the assistance of the transmitter-side polarization scrambling, the in-service OSNR parameter can be accurately derived from the measured maximum DOP value within the polarization scrambling period, which is immune to PMD effect. The monitoring performance is experimentally evaluated by statistical method at OSNR of 25 dB. Experimental results show that OSNR monitoring with about 1-dB standard deviation can be achieved in a 10-Gb/s NRZ-OOK system with DGD varying from 0 to 80 ps.

© 2006 Optical Society of America

1. Introduction

Optical signal-to-noise-ratio (OSNR) has been vigorously pursued as an important performance parameter in future high-speed (≥10 Gb/s) reconfigurable optical networks. Several polarization-assisted methods have been proposed to monitor OSNR in an in-band manner [1–6

1. Alan Eli Willner, S.M.R. Motaghian Nezam, Lianshan Yan, Zhongqi Pan, and Michelle C. Hauer, “Monitoring and control of polarization-related impairments in optical fiber systems,” IEEE J. Lightwave Technol. 22, 106–125 (2004). [CrossRef]

]. Among them, the monitoring scheme based on degree of polarization (DOP) measurement offers many noteworthy advantages as it is simple, insensitive to chromatic dispersion, scalable to higher bit-rate systems, and obviates high-speed electronics [1–2

1. Alan Eli Willner, S.M.R. Motaghian Nezam, Lianshan Yan, Zhongqi Pan, and Michelle C. Hauer, “Monitoring and control of polarization-related impairments in optical fiber systems,” IEEE J. Lightwave Technol. 22, 106–125 (2004). [CrossRef]

]. However, as DOP is affected by both OSNR and polarization-mode dispersion (PMD) [7–8

7. Mats Petersson, Henrik Sunnerud, Bengt-Erik Olsson, and Magus Karlsson, “Optical performance monitoring using degree of polarization in presence of polarization-mode dispersion,” in Proceedings of European Conference on Optical Communication, paper Tu3.6.2 (2004).

], OSNR will be underestimated in the presence of PMD when DOP is chosen as the monitored parameter for OSNR. It would be highly desirable to develop PMD-insensitive monitoring schemes. Recently, a PMD-insensitive DOP-based OSNR monitoring scheme has been proposed and experimentally demonstrated [7

7. Mats Petersson, Henrik Sunnerud, Bengt-Erik Olsson, and Magus Karlsson, “Optical performance monitoring using degree of polarization in presence of polarization-mode dispersion,” in Proceedings of European Conference on Optical Communication, paper Tu3.6.2 (2004).

][9

9. Mats Skold, Bengt-Erik Olsson, Henrik Sunnerud, and Magnus Karlsson, “PMD-insensitive DOP-based OSNR monitoring by spectral SOP measurements,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2005), paper OThH3.

]. But intricate data processing and a narrow tunable filter (~0.1 nm) are needed to derive the PMD-induced DOP by spectral state-of-polarization (SOP) measurement, and it is only suitable for high-bit-rate (≥40 Gb/s) or narrow-pulse systems.

In this paper, we demonstrate that, by applying a polarization scrambler at the transmitter side, OSNR can be easily and accurately monitored using a conventional DOP analyzer. This proposed method makes the DOP-based OSNR monitoring technique more practical for deployment in real systems with non-negligible PMD. Using a 10-Gb/s non-return-to-zero on-off keying (NRZ-OOK) system, we demonstrate that, at OSNR=25 dB/0.1nm, OSNR can be accurately monitored irrespective of the PMD varying from 0 to 80 ps with <0.6 dB estimation mean deviation, and about 1-dB standard deviation. The high-order PMD involved in the system is assumed to be negligible in this paper.

2. Operation principle

Fig. 1. Experimental configuration for the proposed PMD-insensitive DOP-based OSNR monitoring scheme.

DOP=DOPOSNR×DOPPMD
(1)

In our proposed scheme, the use of the transmitter-side polarization scrambler is to make the input SOP of the signal cover the whole Poincaré-sphere within one scrambling period. When the SOP of the signal is launched at 45° in Jones space (i.e. γ = 0.5) with respect to the two PSPs of the transmission link, the DOP measured at the receiver will be the minimum. On the other hand, when the SOP of the signal aligns with one of the PSPs (i.e. γ = 0) of the transmission link, the DOP measured at the receiver will be the maximum and the PMD-induced DOP will approach 1 (DOPPMD≈1), corresponding to the case when there is no effective DGD. The maximum DOP is dependent on OSNR only (DOPmaxDOPOSNR), while the minimum DOP value is dependent on both the OSNR and PMD. Thus, the OSNR can be derived from the measured maximum DOP value at the receiver side within one scrambling period by the following equation:

OSNR(dB0.1nm)=10log[(DOPmax1DOPmax)(NEBf0.1)]
(2)

3. Experiment and results

Fig. 2. Histograms for the measured OSNR data with DGD of (a)(d) 10 ps, (b)(e) 40 ps, and (c)(f) 70 ps by the conventional DOP-based method (left) and the proposed DOP-based method (right).

4. Summary

Fig. 3. The measured OSNR by the proposed method (●) and the conventional method (■) with DGD varying from 0 to 80 ps. The measured OSNR values were illustrated by the estimation mean with error bars.
Fig. 4. The measured OSNR by the proposed method under different OSNR conditions with DGD varying from 0 to 80 ps.

Acknowledgments

The work described in this paper was supported in part by a research grant from Hong Kong Research Grants Council under Project CUHK4110/05E.

References and links

1.

Alan Eli Willner, S.M.R. Motaghian Nezam, Lianshan Yan, Zhongqi Pan, and Michelle C. Hauer, “Monitoring and control of polarization-related impairments in optical fiber systems,” IEEE J. Lightwave Technol. 22, 106–125 (2004). [CrossRef]

2.

D. C. Kilper, “Optical performance monitoring,” IEEE J. of Lightwave Technol. 22, 294–304 (2004). [CrossRef]

3.

C.Y. Joun, K.J. Park, J.H. Lee, and Y.C. Chung, “OSNR monitoring technique based on orthogonal delayed-homodyne method,” IEEE Photon. Technol. Lett. 14, 1467–1471 (2002).

4.

Man-Hong Cheung, Lian-Kuan Chen, and Chun-Kit Chan, “A PMD-insensitive OSNR monitoring scheme based on polarization-nulling with off-center narrowband filtering,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2004), paper FF2.

5.

J.H. Lee, D.K. Jung, C.H. Kim, and Y.C. Chung, “OSNR monitoring technique using polarization-nulling method,” IEEE Photon. Technol. Lett. 13, 88–90 (2001). [CrossRef]

6.

Mats Petersson, Henrik Sunnerud, Magnus Karlsson, and Bengt-Erik Olsson, “Performance monitoring in optical networks using stokes parameters,” IEEE Photon. Technol. Lett. 16, 686–688 (2004). [CrossRef]

7.

Mats Petersson, Henrik Sunnerud, Bengt-Erik Olsson, and Magus Karlsson, “Optical performance monitoring using degree of polarization in presence of polarization-mode dispersion,” in Proceedings of European Conference on Optical Communication, paper Tu3.6.2 (2004).

8.

Chongjin Xie and Daniel C. Kilper, “Influence of polarization scattering on polarization-assisted OSNR monitoring in dense WDM systems with NZ-DSF and Raman Amplification”, in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2005), paper JWA40.

9.

Mats Skold, Bengt-Erik Olsson, Henrik Sunnerud, and Magnus Karlsson, “PMD-insensitive DOP-based OSNR monitoring by spectral SOP measurements,” in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2005), paper OThH3.

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(260.5430) Physical optics : Polarization

ToC Category:
Fiber Optics and Optical Communications

Citation
Guo-Wei Lu, Man-Hong Cheung, Lian-Kuan Chen, and Chun-Kit Chan, "Simple PMD-insensitive OSNR monitoring scheme assisted by transmitter-side polarization scrambling," Opt. Express 14, 58-62 (2006)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-1-58


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References

  1. Alan Eli Willner, S.M.R. Motaghian Nezam, Lianshan Yan, Zhongqi Pan, Michelle C. Hauer, "Monitoring and control of polarization-related impairments in optical fiber systems," IEEE J. Lightwave Technol. 22, 106-125 (2004). [CrossRef]
  2. D. C. Kilper, "Optical performance monitoring," IEEE J. of Lightwave Technol. 22, 294-304 (2004). [CrossRef]
  3. C.Y. Joun, K.J. Park, J.H. Lee, and Y.C. Chung, "OSNR monitoring technique based on orthogonal delayed-homodyne method," IEEE Photon. Technol. Lett. 14, 1467-1471 (2002).
  4. Man-Hong Cheung, Lian-Kuan Chen, Chun-Kit Chan, "A PMD-insensitive OSNR monitoring scheme based on polarization-nulling with off-center narrowband filtering," in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2004), paper FF2.
  5. J.H. Lee, D.K. Jung, C.H. Kim, and Y.C. Chung, "OSNR monitoring technique using polarization-nulling method," IEEE Photon. Technol. Lett. 13, 88-90 (2001). [CrossRef]
  6. Mats Petersson, Henrik Sunnerud, Magnus Karlsson, and Bengt-Erik Olsson, "Performance monitoring in optical networks using stokes parameters," IEEE Photon. Technol. Lett. 16, 686-688 (2004). [CrossRef]
  7. Mats Petersson, Henrik Sunnerud, Bengt-Erik Olsson, and Magus Karlsson, "Optical performance monitoring using degree of polarization in presence of polarization-mode dispersion," in Proceedings of European Conference on Optical Communication, paper Tu3.6.2 (2004).
  8. Chongjin Xie, Daniel C. Kilper, "Influence of polarization scattering on polarization-assisted OSNR monitoring in dense WDM systems with NZ-DSF and Raman Amplification", in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2005), paper JWA40.
  9. Mats Skold, Bengt-Erik Olsson, Henrik Sunnerud, and Magnus Karlsson, "PMD-insensitive DOP-based OSNR monitoring by spectral SOP measurements," in Optical Fiber Communication Conference, OSA Technical Digest (Optical Society of America, Washington DC, 2005), paper OThH3.

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