Abstract

In this paper, we verify the effectiveness of the last-stage long memory filter (LMF) in mitigating the long-memory response (LMR) of hardware, i.e. the transmitter and receiver. Based on the experimental results, we draw the following conclusions: 1) LMF can effectively mitigate the LMR impact, such as transmitter reflections, and its efficiency is more significant for high-order QAM signals. 2) Using LMF, a partially-correlated pattern exhibits similar performance to that of an uncorrelated pattern both in back-to-back and after 320-km standard single mode fiber (SSMF) transmission. Moreover, a simple solution to the computational complexity of LMF, effective-tap (ET) LMF, is proposed and demonstrated.

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References

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  1. A. Sano, T. Kobayashi, S. Yamanaka, A. Matsuura, H. Kawakami, Y. Miyamoto, K. Ishihara, and H. Masuda, “102.3-Tb/s (224x548-Gb/s) C- and extended L-band all-Raman transmission over 240 km using PDM-64QAM single carrier FDM with digital pilot tone,” in the Proceedings of OFC’2012, paper PDP5C3 (2012).
  2. X. Zhou, L. E. Nelson, R. Isaac, P. D. Magill, B. Zhu, D. W. Peckham, P. Borel, and K. Carlson, “4000 km transmission of 50GHz spaced, 10x494.85-Gb/s hybrid 32-64QAM using cascaded equalization and training-assisted phase recovery,” in the Proceedings of OFC’2012, paper PDP5C6 (2012).
  3. J. Yu, Z. Dong, H.-C. Chien, X. Xiao, Z. Jia, and N. Chi, “30-Tb/s (3×12.84-Tb/s) signal transmission over 320km using PDM 64-QAM Modulation,” in the Proceedings of OFC’2012, paper OM2A4 (2012).
  4. W.-R. Peng, H. Takahashi, T. Tsuritani, and I. Morita, “DAC-free generation and 1200-km transmission of 41-GBd PDM-64QAM using a single I/Q modulator,” in Proceedings of OECC’2012, paper PDP1–3 (2012).
  5. W.-R. Peng, H. Takahashi, T. Tsuritani, and I. Morita, “50-GHz-spaced, 8x499-Gb/s WDM transmission over 720-km SSMF using per-channel 41.6-GBd PDM-64QAM,” in Proceedings of ACP’2012, paper AF4C.1 (2012).
  6. D. Chang, F. Yu, Z. Xiao, Y. Li, N. Stojanovic, C. Xie, X. Shi, X. Xu, and Q. Xiong, “FPGA verification of a single QC-LDPC code for 100 Gb/s optical systems without error floor down to BER of 10−15” in Proceedings of OFC’2011, paper OTuN2 (2011).
  7. S. Haykin, Adaptive Filter Theory, 4th ed. (Prentice-Hall, 2002), Chap 5.
  8. M. J. Ready and R. P. Gooch, “Blind equalization based on radius directed adaptation,” in Proceedings of IEEE ICASSP’1990, pp.1699–1702 (1990).
    [CrossRef]
  9. T. Pfau, S. Hoffmann, and R. Noe, “Hardware-efficient coherent digital receiver concept with feed-forward carrier recovery for M-QAM constellations,” J. Lightwave Technol.27(8), 989–999 (2009).
    [CrossRef]
  10. ITU-T Recommendation G.975.1, Appendix I.9 (2004).

2009 (1)

J. Lightwave Technol. (1)

Other (9)

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

A. Sano, T. Kobayashi, S. Yamanaka, A. Matsuura, H. Kawakami, Y. Miyamoto, K. Ishihara, and H. Masuda, “102.3-Tb/s (224x548-Gb/s) C- and extended L-band all-Raman transmission over 240 km using PDM-64QAM single carrier FDM with digital pilot tone,” in the Proceedings of OFC’2012, paper PDP5C3 (2012).

X. Zhou, L. E. Nelson, R. Isaac, P. D. Magill, B. Zhu, D. W. Peckham, P. Borel, and K. Carlson, “4000 km transmission of 50GHz spaced, 10x494.85-Gb/s hybrid 32-64QAM using cascaded equalization and training-assisted phase recovery,” in the Proceedings of OFC’2012, paper PDP5C6 (2012).

J. Yu, Z. Dong, H.-C. Chien, X. Xiao, Z. Jia, and N. Chi, “30-Tb/s (3×12.84-Tb/s) signal transmission over 320km using PDM 64-QAM Modulation,” in the Proceedings of OFC’2012, paper OM2A4 (2012).

W.-R. Peng, H. Takahashi, T. Tsuritani, and I. Morita, “DAC-free generation and 1200-km transmission of 41-GBd PDM-64QAM using a single I/Q modulator,” in Proceedings of OECC’2012, paper PDP1–3 (2012).

W.-R. Peng, H. Takahashi, T. Tsuritani, and I. Morita, “50-GHz-spaced, 8x499-Gb/s WDM transmission over 720-km SSMF using per-channel 41.6-GBd PDM-64QAM,” in Proceedings of ACP’2012, paper AF4C.1 (2012).

D. Chang, F. Yu, Z. Xiao, Y. Li, N. Stojanovic, C. Xie, X. Shi, X. Xu, and Q. Xiong, “FPGA verification of a single QC-LDPC code for 100 Gb/s optical systems without error floor down to BER of 10−15” in Proceedings of OFC’2011, paper OTuN2 (2011).

S. Haykin, Adaptive Filter Theory, 4th ed. (Prentice-Hall, 2002), Chap 5.

M. J. Ready and R. P. Gooch, “Blind equalization based on radius directed adaptation,” in Proceedings of IEEE ICASSP’1990, pp.1699–1702 (1990).
[CrossRef]

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Figures (8)

Fig. 1
Fig. 1

(a) Long-memory filter (LMF) at the last stage of receiver equalizer (after carrier recovery circuit) for mitigating the long-memory response (LMR) impact. (b) Proposed effective-tap LMF (ET-LMF) for reducing the LMF’s computational complexity.

Fig. 2
Fig. 2

Experimental setup to verify the last-stage long-memory filtering (LMF) gain. ECL: external cavity laser, AWG: arbitrary waveform generator, PDM: polarization-division-multiplexing, EDFA: Erbium-doped fibre amplifier, SSMF: standard single mode fibre, OBPF: optical bandpass filter, BW: bandwidth, CD: chromatic dispersion, CMA: constant modulus algorithm, RDA: radius directed algorithm, BPS: blind phase search.

Fig. 3
Fig. 3

(a). Eight-level signal generation from 215−1 PRBSs in Matlab. We consider the following two patterns: i) uncorrelated pattern with D1 = 4096, D2 = 8192, D3 = 16384, and ii) partially-correlated pattern with D1 = 169, D2 = 96, D3 = 69, which is the pattern used in our previous demonstration [4]. Digital reflection would only be applied for results in Fig. 4. Figure 3(b). Output spectra of the generated 64QAM signal with the uncorrelated and partially-correlated data patterns.

Fig. 4
Fig. 4

(a) BER versus OSNR for 11.2-GBd single-polarized 4, 16, 64QAM signals with and without LMF. Note that only uncorrelated patterns are used in this study. (b) Upper rows: recovered constellations without and with LMF, bottom row: absolute values of the LMF tap coefficient versus tap index (integers running from −400 to + 400) after equalizations.

Fig. 5
Fig. 5

BER versus OSNR for the 11.2-GBd single-polarized 64QAM signals that use uncorrelated pattern. Digital reflection is inserted at the transmitter in order to demonstrate the refection compensation ability of LMF. Results with partially-correlated pattern are also depicted. UCP: uncorrelated pattern, PCP: partially-correlated pattern.

Fig. 6
Fig. 6

Q vs. launch power for 11.2-GBd PDM-64QAM signals after 320-km transmission. The LMF length is reduced to 401 tap for PDM signals here. UCP: uncorrelated pattern, PCP: partially-correlated pattern.

Fig. 7
Fig. 7

Effective-tap (ET) LMF example: 11.2-GBd, 320-km-transmitted PDM-64QAM (UCP) at the −7-dBm launch power. (a) Identifying the effective taps for ET-LMF equalization. (b) ET-LMF gain and required tap number vs. threshold γ.

Fig. 8
Fig. 8

Simulation results of BER versus OSNR. 11.2-GBd single-polarized 64QAM signals with three different patterns of Matlab, UCP, and PCP are compared.

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