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Coherent optical transmission systems can be modeled as a four-dimensional (4D) signal space resulting from the two polarization states, each with two quadratures. Recently, nonlinear analytical models have been proposed capable of capturing the impact of Kerr nonlinearity on 4D constellations. None of these addresses the inter-channel nonlinear interference (NLI) imposed by arbitrary modulation formats in multi-channel wavelength division multiplexed (WDM) systems. In this paper, we introduce a general nonlinear model for multi-channel WDM systems that is valid for arbitrary modulation formats, even asymmetric ones. The proposed model converges to the previous models, including the EGN model, in the special case of polarization multiplexed systems. The model focuses on the cross-phase modulation (XPM) nonlinear term that lies at the heart of the NLI in multi-channel WDM systems operating on standard high dispersion single-mode fiber. We show that strategic mappings of the modulation format's coordinates to the polarization states can reduce the NLI undergone by these formats.
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Nonlinear GN model for coherent optical communications systems with hybrid fiber spans
The nonlinear Gaussian-noise (GN) model is a useful analytical tool for the estimation of the impact of distortion due to Kerr nonlinearity on the performance of coherent optical communications systems with no inline dispersion compensation. The original nonlinear GN model was formulated for coherent optical communications systems with identical single-mode fiber spans. Since its inception, the original GN model has been modified for a variety of link configurations. However, its application to coherent optical communications systems with hybrid fiber spans, each composed of multiple fiber segments with different attributes, has attracted scarcely any attention. This invited paper is dedicated to the extended nonlinear GN model for coherent optical communications systems with hybrid fiber spans. We review the few publications on the topic and provide a unified formalism for the analytical calculation of the nonlinear noise variance. To illustrate the usefulness of the extended nonlinear GN model, we apply it to coherent optical communications systems with fiber spans composed of a quasi-single-mode fiber segment and a single-mode fiber segment in tandem. In this configuration, a quasi-single-mode fiber with large effective area is placed at the beginning of each span, to reduce most of the nonlinear distortion, followed by a single-mode fiber segment with smaller effective-area, to limit the multipath interference introduced by the quasi-single-mode fiber to acceptable levels. We show that the optimal fiber splitting ratio per span can be calculated with sufficient accuracy using the extended nonlinear GN model for hybrid fiber spans presented here.
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- Award ID(s):
- 1910140
- PAR ID:
- 10194739
- Date Published:
- Journal Name:
- 2020 29th Wireless and Optical Communications Conference (WOCC)
- Page Range / eLocation ID:
- 1 to 6
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/WOCC48579.2020.9114952
