Abstract

We propose and demonstrate the use of subcarrier/polarization-interleaved training symbols for channel estimation and synchronization in polarization-division multiplexed (PDM) coherent optical orthogonal frequency-division multiplexed (CO-OFDM) transmission. The principle, the computational efficiency, and the frequency-offset tolerance of the proposed method are described. We show that the use of subcarrier/polarization interleaving doubles the tolerance to the frequency offset between the transmit laser and the receiver’s optical local oscillator as compared to conventional schemes. Using this method, we demonstrate 43-Gb/s PDM CO-OFDM transmission with 16-QAM subcarrier modulation over 5,200-km of ultra-large-area fiber.

© 2011 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), http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-2-841 .
    [CrossRef] [PubMed]
  2. S. L. Jansen, I. Morita, T. C. W. Schenk, and H. Tanaka, “121.9-Gb/s PDM-OFDM Transmission With 2-b/s/Hz Spectral Efficiency Over 1000 km of SSMF,” J. Lightwave Technol. 27(3), 177–188 (2009).
    [CrossRef]
  3. T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Trans. Wirel. Comm. 45(12), 1613–1621 (1997).
  4. X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
    [CrossRef]
  5. S. L. Jansen, I. Morita, T. C. W. Schenk, and H. Tanaka, “Long-haul transmission of 16 x 52.5 Gbits/s polarization-divisionmultiplexed OFDM enabled by MIMO processing (Invited),” J. Opt. Netw. 7(2), 173–182 (2008).
    [CrossRef]
  6. X. Liu and F. Buchali, “A Novel Channel Estimation Method for PDM-OFDM Enabling Improved Tolerance to WDM Nonlinearity,” in Proc. Optical Fiber Commun. Conf. (OFC) 2009, Paper OWW5, http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2009-OWW5 .
  7. X. Liu, F. Buchali, and W. Robert, “Tkach, “Improving the Nonlinear Tolerance of Polarization-Division-Multiplexed CO-OFDM in Long-Haul Fiber Transmission,” J. Lightwave Technol. 27(16), 3632–3640 (2009).
    [CrossRef]
  8. C. J. Youn, X. Liu, S. Chandrasekhar, Y.-H. Kwon, J.-H. Kim, J.-S. Choe, K.-S. Choi, and E. S. Nam, “An Efficient and Frequency-Offset-Tolerant Channel Estimation and Synchronization Method for PDM CO-OFDM Transmission,” in Proc. European Conf. Optical Commun. 2010, Paper P4.06.
  9. S. L. Jansen, I. Morita, T. C. W. Schenk, N. Takeda, and H. Tanaka, “Coherent Optical 25.8-Gb/s OFDM Transmission Over 4160-km SSMF,” J. Lightwave Technol. 26(1), 6–15 (2008).
    [CrossRef]
  10. S. Chandrasekhar, X. Liu, B. Zhu, and D. W. Peckham, “Transmission of a 1.2-Tb/s 24-Carrier No-Guard-Interval Coherent OFDM Superchannel over 7200-km of Ultra-Large-Area Fiber,” in Proc. European Conf. Optical Commun. 2009, post-deadline paper PD2.6.
  11. D. S. Millar, S. Makovejs, V. Mikhailov, R. I. Killey, P. Bayvel, and S. J. Savory, “Experimental Comparison of Nonlinear Compensation in Long-Haul PDM-QPSK Transmission at 42.7 and 85.4 Gb/s,” in Proc. European Conf. Optical Commun. 2009, Paper 9.4.4.
  12. X. Liu, S. Chandrasekhar, B. Zhu, P. J. Winzer, A. H. Gnauck, and D. W. Peckham, “Transmission of a 448-Gb/s Reduced-Guard-Interval CO-OFDM Signal with a 60-GHz Optical Bandwidth over 2000 km of ULAF and Five 80-GHz-Grid ROADMs,” in Proc. Optical Fiber Commun. Conf. (OFC) 2010, post-deadline paper PDPC2. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2010-PDPC2
  13. X. Liu, S. Chandrasekhar, B. Zhu, P. J. Winzer, A. H. Gnauck, and D. W. Peckham, “448-Gb/s Reduced-Guard-Interval CO-OFDM Transmission Over 2000 km of Ultra-Large-Area Fiber and Five 80-GHz-Grid ROADMs,” J. Lightwave Technol. 29(4), 483–490 (2011).
    [CrossRef]
  14. ITU-T Recommendation G.975.1, 2004, Appendix I.9.

2011 (1)

2009 (2)

2008 (3)

2007 (1)

X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
[CrossRef]

1997 (1)

T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Trans. Wirel. Comm. 45(12), 1613–1621 (1997).

Bao, H.

Buchali, F.

Chandrasekhar, S.

Cox, D. C.

T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Trans. Wirel. Comm. 45(12), 1613–1621 (1997).

Gnauck, A. H.

Hong, Z.

X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
[CrossRef]

Hu, X.

X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
[CrossRef]

Huang, Y.

X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
[CrossRef]

Jansen, S. L.

Liu, X.

Morita, I.

Peckham, D. W.

Robert, W.

Schenk, T. C. W.

Schmidl, T. M.

T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Trans. Wirel. Comm. 45(12), 1613–1621 (1997).

Shieh, W.

Takeda, N.

Tanaka, H.

Tang, Y.

Winzer, P. J.

Zhu, B.

ETRI J. (1)

X. Hu, Y. Huang, and Z. Hong, “Residual Synchronization Error Elimination in OFDM Baseband Receivers,” ETRI J. 29(5), 596–606 (2007).
[CrossRef]

IEEE Trans. Wirel. Comm. (1)

T. M. Schmidl and D. C. Cox, “Robust Frequency and Timing Synchronization for OFDM,” IEEE Trans. Wirel. Comm. 45(12), 1613–1621 (1997).

J. Lightwave Technol. (4)

J. Opt. Netw. (1)

Opt. Express (1)

Other (6)

X. Liu and F. Buchali, “A Novel Channel Estimation Method for PDM-OFDM Enabling Improved Tolerance to WDM Nonlinearity,” in Proc. Optical Fiber Commun. Conf. (OFC) 2009, Paper OWW5, http://www.opticsinfobase.org/abstract.cfm?URI=OFC-2009-OWW5 .

C. J. Youn, X. Liu, S. Chandrasekhar, Y.-H. Kwon, J.-H. Kim, J.-S. Choe, K.-S. Choi, and E. S. Nam, “An Efficient and Frequency-Offset-Tolerant Channel Estimation and Synchronization Method for PDM CO-OFDM Transmission,” in Proc. European Conf. Optical Commun. 2010, Paper P4.06.

S. Chandrasekhar, X. Liu, B. Zhu, and D. W. Peckham, “Transmission of a 1.2-Tb/s 24-Carrier No-Guard-Interval Coherent OFDM Superchannel over 7200-km of Ultra-Large-Area Fiber,” in Proc. European Conf. Optical Commun. 2009, post-deadline paper PD2.6.

D. S. Millar, S. Makovejs, V. Mikhailov, R. I. Killey, P. Bayvel, and S. J. Savory, “Experimental Comparison of Nonlinear Compensation in Long-Haul PDM-QPSK Transmission at 42.7 and 85.4 Gb/s,” in Proc. European Conf. Optical Commun. 2009, Paper 9.4.4.

X. Liu, S. Chandrasekhar, B. Zhu, P. J. Winzer, A. H. Gnauck, and D. W. Peckham, “Transmission of a 448-Gb/s Reduced-Guard-Interval CO-OFDM Signal with a 60-GHz Optical Bandwidth over 2000 km of ULAF and Five 80-GHz-Grid ROADMs,” in Proc. Optical Fiber Commun. Conf. (OFC) 2010, post-deadline paper PDPC2. http://www.opticsinfobase.org/abstract.cfm?URI=NFOEC-2010-PDPC2

ITU-T Recommendation G.975.1, 2004, Appendix I.9.

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Figures (5)

Fig. 1
Fig. 1

Illustration of PDM CO-OFDM subcarriers allocation. (a) The previous synchronization and channel estimation method using CDP-TSs. A is symbol with all subcarriers filled. (b) The proposed synchronization and channel estimation method using SI-DP TSs. (t1, t2, t3) are training symbols, and dn is n-th payload symbol. E(O) is a symbol whose even (odd) subcarriers are filled.

Fig. 2
Fig. 2

Experimental setup of a 43-Gb/s PDM-OFDM-16QAM system using the proposed channel estimation and synchronization method. Insets: (a) Offline digital signal processing at the transmitter; (b) OFDM frame structure; and (c) Offline digital signal processing at the receiver. AWG: arbitrary waveform generator. PBC: polarization beam combiner. OC: optical coupler. SW: acousto-optic switch.

Fig. 3
Fig. 3

Measured timing metric using the proposed synchronization method. (a) X-polarization components,(b) Y-polarization components, (c) PDM components

Fig. 4
Fig. 4

Subcarrier index correction versus frequency offset using (a) The previous methods5, 6 and(b) The proposed method.

Fig. 5
Fig. 5

(a) Measured Q2 factor as a function of signal launch power after 3,200-km transmission; (b) Measured Q2 factor as a function of the transmission distance with the signal launch power fixed at −6 dBm.

Equations (6)

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[ t 1 x t 2 x   ​ t 3 x t 1 y t 2 y t 3 y ] = [ E O E E E O ]
ε = f o f f s e t Δ f s c = 1 2 π arg [ n = 0 N 1 r * ( n ) r ( n + N ) ]
ε = 1 π arg [ n = 0 N / 2 1 r * ( n ) r ( n + N / 2 ) ]
[ a ( k )     b ( k ) c ( k )     d ( k ) ] = { [ r 2 x ( k ) / O ( k )     r 3 x ( k ) / O ( k ) r 2 y ( k ) / O ( k )     r 3 y ( k ) / O ( k ) ]           if   k = k o d d , [ r 3 x ( k ) / E ( k )     r 2 x ( k ) / E ( k ) r 3 y ( k ) / E ( k )     r 2 y ( k ) / E ( k ) ]         if     k = k e v e n    
M x ( y ) ( d ) = | n = 0 N / 2 1 r x ( y ) * ( d + n ) r x ( y ) ( d + n + N / 2 ) | 2 / | n = 0 N / 2 1 r x ( y ) * ( d + n ) r x ( y ) ( d + n ) | 2
M x + y ( d ) = | n = 0 N / 2 1 r x * ( d + n ) r x ( d + n + N / 2 ) + n = 0 N / 2 1 r y * ( d + n ) r y ( d + n + N / 2 ) | 2 | n = 0 N / 2 1 r x * ( d + n ) r x ( d + n ) + n = 0 N / 2 1 r y * ( d + n ) r y ( d + n ) | 2

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