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Proceedings Paper

Benefits of digital backpropagation in coherent QPSK and 16QAM fibre links
Author(s): Carsten Behrens; Robert I. Killey; Seb J. Savory; Ming Chen; Polina Bayvel
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Paper Abstract

We investigate the transmission performance, with and without digital backpropagation, in wavelength-division-multiplexed- (WDM) transmission systems using polarisation-division-multiplexed (PDM) differentially-encoded quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (16QAM). We consider transmission at 56GBd, 28GBd, 14GBd and 7GBd per WDM-channel while varying the channel spacing from 100GHz to 12.5GHz to maintain constant spectral efficiency per modulation format. The symmetrical split-step method based on the Manakov equation was employed to backpropagate the central WDM-channel with the help of receiver based digital signal processing. Performance of digital backpropagation was found to decrease with reduced symbol-rate, owing to the smaller proportion of the overall spectrum which is backpropagated in these cases. At higher symbol-rates digital backpropagation is up to 0.5dB more effective for 16QAM than for the QPSK format, which we attribute to the increased influence of intra-channel nonlinearities for formats with multiple intensity values leading in turn to a higher benefit when intra-channel effects are compensated for. Improvement in launch power @ BER=3x10-3 amounts to 1.9dB for 56GBd QPSK and 2.4dB of 56GBd 16QAM.

Paper Details

Date Published: 18 February 2011
PDF: 6 pages
Proc. SPIE 7988, Optical Transmission Systems, Switching, and Subsystems VIII, 79880S (18 February 2011); doi: 10.1117/12.888669
Show Author Affiliations
Carsten Behrens, Univ. College London (United Kingdom)
Robert I. Killey, Univ. College London (United Kingdom)
Seb J. Savory, Univ. College London (United Kingdom)
Ming Chen, Huawei Technologies (Germany)
Polina Bayvel, Univ. College London (United Kingdom)

Published in SPIE Proceedings Vol. 7988:
Optical Transmission Systems, Switching, and Subsystems VIII
Yikai Su; Ernesto Ciaramella; Xiang Liu; Naoya Wada, Editor(s)

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