Abstract
Nonlinear Fourier transform (NFT) based transmission technique relies on the integrability of the nonlinear Schrodinger equation (NLSE). However, the lossless NLSE is not directly applicable for the description of light evolution in fibre links with lumped amplification such as Erbium-doped fibre amplifier (EDFA) because of the nonuniform loss and gain evolution. In this case, the path-averaged model is usually applied as an approximation of the true NLSE model including the fibre loss. However, the inaccuracy of the lossless path-average model, even though being small, can also result in a notable performance degradation in NFT-based transmission systems. In this paper, we extend the theoretical approach, which was first proposed for solitons in EDFA systems, to the case of NFT-based systems to constructively diminish the aforementioned performance penalty. Based on the quantitative analysis of distortions due to the use of path-average model, we optimise the signal launch and detection points to minimise the models mismatch. Without loss of generality, we demonstrate how this approach works for the NFT systems that use continuous NFT spectrum modulation (vanishing signals) and NFT main spectrum modulation (periodic signals). Through numerical modelling, we quantify the corresponding improvements in system performance.
Highlights
A PPLICATION of Nonlinear Fourier transform (NFT) [1] for fibre-optic communication, dating back to the celebrated work of Hasegawa and Nyu [2], has attracted a great deal of interest in recent years
In this work we demonstrate how to improve the performance of NFT-based systems using specific properties of the perturbation theory developed for nonlinear Schrodinger equation (NLSE) in the case of Erbium-doped fibre amplifier (EDFA) system
As the periodic NFT spectrum is discrete, the latter situation is different from the nonlinear inverse synthesis (NIS) method, and the similarity in the improvement of performance for both cases demonstrates the generality of the path-average approach
Summary
A PPLICATION of NFT [1] for fibre-optic communication, dating back to the celebrated work of Hasegawa and Nyu [2], has attracted a great deal of interest in recent years. The basic concept of NFT is the possibility to decompose the solution of the NLSE (the master model describing the light evolution in the fibre), into noninteracting “nonlinear modes” evolving inside the NFT domain in a simple linear manner This property makes the parameters of these modes to be promising candidates to carry the data along the fibre, the idea which lies behind the most of the NFTbased techniques [4]. In a real-world transmission we always have features that are at odds with the integrable NLSE model, to name the most important two: optical noise and fibre loss [17] The former is usually studied and incorporated into the integrable model using a perturbation approach [3], [16], resulting in the slightly-perturbed stochastic evolution of modulated NFT spectrum.
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