Abstract

We propose a novel recursive-algorithm based maximum a posteriori probability (MAP) detector in spectrally-efficient coherent wavelength division multiplexing (CoWDM) systems, and investigate its performance in a 1-bit/s/Hz on-off keyed (OOK) system limited by optical-signal-to-noise ratio. The proposed method decodes each sub-channel using the signal levels not only of the particular sub-channel but also of its adjacent sub-channels, and therefore can effectively compensate deterministic inter-sub-channel crosstalk as well as inter-symbol interference arising from narrow-band filtering and chromatic dispersion (CD). Numerical simulation of a five-channel OOK-based CoWDM system with 10Gbit/s per channel using either direct or coherent detection shows that the MAP decoder can eliminate the need for phase control of each optical carrier (which is necessarily required in a conventional CoWDM system), and greatly relaxes the spectral design of the demultiplexing filter at the receiver. It also significantly improves back-to-back sensitivity and CD tolerance of the system.

© 2009 OSA

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References

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  1. W. Shieh, H. Bao, and Y. Tang, “Coherent optical OFDM: theory and design,” Opt. Express 16(2), 841–859 (2008).
    [CrossRef] [PubMed]
  2. A. Lowery, and J. Armstrong, “Adaptation of orthogonal frequency division multiplexing to compensate impairments in optical transmission systems,” European Conference on Optical Communication, paper 4.2.1 (2008).
  3. F. C. G. Gunning, T. Healy, X. Yang, and A. D. Ellis, “0.6Tbit/s capacity and 2bit/s/Hz spectral efficiency at 42.6Gsymbol/s using a single DFB laser with NRZ coherent WDM and polarization multiplexing,” European Conference on Lasers and Electro-Optics (E-CLEO), paper C18–5-FRI (2007).
  4. F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
    [CrossRef]
  5. J. Zhao, and A. D. Ellis, “Performance improvement using a novel MAP detector in coherent WDM systems,” European Conference on Optical Communication (2008), paper Tu.1.D.2.
  6. J. Proakis, Digital Communication, 4th Edition, McGraw-Hill, 2001.
  7. M. Cavallari, C. R. S. Fludger, and P. J. Anslow, “Electronic signal processing for differential phase modulation formats,” in Proc. Optical Fiber Communication Conference (2004), paper TuG2.
  8. J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
    [CrossRef]
  9. A. D. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005).
    [CrossRef]

2008 (1)

2007 (1)

J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
[CrossRef]

2006 (1)

F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
[CrossRef]

2005 (1)

A. D. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005).
[CrossRef]

Bao, H.

Chan, C. K.

J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
[CrossRef]

Chen, L. K.

J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
[CrossRef]

Ellis, A. D.

F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
[CrossRef]

A. D. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005).
[CrossRef]

Gunning, F. C. G.

F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
[CrossRef]

A. D. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005).
[CrossRef]

Healy, T.

F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
[CrossRef]

Shieh, W.

Tang, Y.

Zhao, J.

J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
[CrossRef]

IEEE Photon. Technol. Lett. (3)

F. C. G. Gunning, T. Healy, and A. D. Ellis, “Dispersion tolerance of coherent WDM,” IEEE Photon. Technol. Lett. 18(12), 1338–1340 (2006).
[CrossRef]

J. Zhao, L. K. Chen, and C. K. Chan, “Joint maximum likelihood sequence estimation for chromatic dispersion compensation in ASK-DPSK modulation format,” IEEE Photon. Technol. Lett. 19(1), 73–75 (2007).
[CrossRef]

A. D. Ellis and F. C. G. Gunning, “Spectral density enhancement using coherent WDM,” IEEE Photon. Technol. Lett. 17(2), 504–506 (2005).
[CrossRef]

Opt. Express (1)

Other (5)

A. Lowery, and J. Armstrong, “Adaptation of orthogonal frequency division multiplexing to compensate impairments in optical transmission systems,” European Conference on Optical Communication, paper 4.2.1 (2008).

F. C. G. Gunning, T. Healy, X. Yang, and A. D. Ellis, “0.6Tbit/s capacity and 2bit/s/Hz spectral efficiency at 42.6Gsymbol/s using a single DFB laser with NRZ coherent WDM and polarization multiplexing,” European Conference on Lasers and Electro-Optics (E-CLEO), paper C18–5-FRI (2007).

J. Zhao, and A. D. Ellis, “Performance improvement using a novel MAP detector in coherent WDM systems,” European Conference on Optical Communication (2008), paper Tu.1.D.2.

J. Proakis, Digital Communication, 4th Edition, McGraw-Hill, 2001.

M. Cavallari, C. R. S. Fludger, and P. J. Anslow, “Electronic signal processing for differential phase modulation formats,” in Proc. Optical Fiber Communication Conference (2004), paper TuG2.

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Figures (6)

Fig. 1.
Fig. 1.

Principle of MAP detection in CoWDM systems

Fig. 2.
Fig. 2.

Simulation model

Fig. 3.
Fig. 3.

(a) Signal spectral power density, and eye diagrams of Ch 3 for (b) ϕ=π/2 and (c) ϕ=π. The relative phases of channels are (0 ϕ 0 ϕ 0).

Fig. 4.
Fig. 4.

Required normalized OSNR versus ϕ for Ch 1–3 (Ch 1: circles; Ch 2: triangles; Ch 3: squares). The relative phases of channels are (a) (0 ϕ 0 ϕ 0) and (b) (0 ϕ 2ϕ 3ϕ 4ϕ). Dotted, dashed and solid lines represent the cases using hard decision, DD-based MAP, and coherent-detection based MAP, respectively.

Fig. 5.
Fig. 5.

Required normalized OSNR versus (a) 3-dB bandwidth of 2nd-order Gaussian-shaped AWG with 20GHz FSR; (b) fiber length. Dotted, dashed and solid lines represent the cases using hard decision, DD-based MAP, and coherent-detection based MAP respectively.

Fig. 6.
Fig. 6.

Performance of MAP detector as a function of quantization resolution under DD (dashed) and coherent detection (solid). The relative phases of sub-channels are (0 π/2 π 3π/2 2π).

Equations (5)

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bi,k=argmaxai,kP(ai,kRi,k)
bi,k=argmaxai,kΣSi,k{ai,k}P(Ri,kSi,k)
bi,k=argmaxai,kΣAi,k{ai,k}Pi,k(Ai,k)
Pi,k(Ai,k)=P(ri1,k+1,ri,k+1,ri+1,k+1Ai,k).Σai1,k1Σai,k1Σai+1,k1Pi,k1(Ai,k1)
Pi,k (Ai,k)=P(ri1,k+1o,ri,k+1o,ri+1,k+1o,ri1,k+1q,ri,k+1q,ri+1,k+1qAi,k)· Σai1,k1 Σai,k1 Σai+1,k1 Pi,k1 (Ai,k1)

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