130 research outputs found
Signal-noise interaction in nonlinear optical fibers: a hydrodynamic approach
We present a new perturbative approach to the study of signal-noise
interactions in nonlinear optical fibers. The approach is based on the
hydrodynamic formulation of the nonlinear Schr\"odinger equation that governs
the propagation of light in the fiber. Our method is discussed in general and
is developed in more details for some special cases, namely the
small-dispersion regime, the continuous-wave (CW) signal and the solitonic
pulse. The accuracy of the approach is numerically tested in the CW case.Comment: Revised version, submitted to Optics express, 15 pages, 6 figure
Why Noise and Dispersion may Seriously Hamper Nonlinear Frequency-Division Multiplexing
The performance of optical fiber systems based on nonlinear
frequency-division multiplexing (NFDM) or on more conventional transmission
techniques is compared through numerical simulations. Some critical issues
affecting NFDM systems-namely, the strict requirements needed to avoid burst
interaction due to signal dispersion and the unfavorable dependence of
performance on burst length-are investigated, highlighting their potentially
disruptive effect in terms of spectral efficiency. Two digital processing
techniques are finally proposed to halve the guard time between NFDM symbol
bursts and reduce the size of the processing window at the receiver, increasing
spectral efficiency and reducing computational complexity.Comment: The manuscript has been submitted to Photonics Technology Letters for
publicatio
Numerical Methods for the Inverse Nonlinear Fourier Transform
We introduce a new numerical method for the computation of the inverse
nonlinear Fourier transform and compare its computational complexity and
accuracy to those of other methods available in the literature. For a given
accuracy, the proposed method requires the lowest number of operationsComment: To be presented at the Tyrrhenian International Workshop on Digital
Communications (TIWDC) 201
A Novel Detection Strategy for Nonlinear Frequency-Division Multiplexing
A novel decision feedback detection strategy exploiting a causality property
of the nonlinear Fourier transform is introduced. The novel strategy achieves a
considerable performance improvement compared to previously adopted strategies
in terms of Q-factor.Comment: The work has been submitted to the Optical Fiber Communication (OFC)
Conference 201
Decision-Feedback Detection Strategy for Nonlinear Frequency-Division Multiplexing
By exploiting a causality property of the nonlinear Fourier transform, a
novel decision-feedback detection strategy for nonlinear frequency-division
multiplexing (NFDM) systems is introduced. The performance of the proposed
strategy is investigated both by simulations and by theoretical bounds and
approximations, showing that it achieves a considerable performance improvement
compared to previously adopted techniques in terms of Q-factor. The obtained
improvement demonstrates that, by tailoring the detection strategy to the
peculiar properties of the nonlinear Fourier transform, it is possible to boost
the performance of NFDM systems and overcome current limitations imposed by the
use of more conventional detection techniques suitable for the linear regime
Non-parametric Estimation of Mutual Information with Application to Nonlinear Optical Fibers
This paper compares and evaluates a set of non-parametric mutual information
estimators with the goal of providing a novel toolset to progress in the
analysis of the capacity of the nonlinear optical channel, which is currently
an open problem. In the first part of the paper, the methods of the study are
presented. The second part details their application to several
optically-related channels to highlight their features.Comment: This work has been submited to IEEE International Symposium on
Information Theor
On the error probability evaluation in lightwave systems with optical amplification
We review the time domain, frequency domain, and Fourier series Karhunen–Loéve series expansion (KLSE) methods for exact BER evaluation in intensity- and phase-modulated direct-detection optically amplified systems.We compare their complexity and computational efficiency, and discuss the most relevant implementation issues. We show that the method based on a Fourier series expansion has the simplest implementation and requires the minimum number of eigenvalues to converge to the exact BER value for various kind of optical filters. For this method, we also introduce an equivalent form of the moment generating function, that avoids the singularity for eigenvalues equal to zero, and derive an alternative expansion where signal and noise are expanded on the same orthonormal basis
Scope and Limitations of the Nonlinear Shannon Limit
The concept and significance of the so called nonlinear Shannon limit are reviewed and their relation to the channel capacity is analyzed from an information theory point of view. It is shown that this is a limit (if at all) holding only for conventional detection strategies. Indeed, it should only be considered as a limit to the information rate that can be achieved with a given modulation/detection scheme. By virtue of some simple examples and theoretical results, it is also shown that, using the same approximated models commonly adopted for deriving the nonlinear Shannon limit, the information rate can be arbitrarily increased by increasing the input power. To this aim, the validity of some popular approximations to the output distribution is also examined to show that their application outside the scope for which they were devised can lead to pitfalls. To the best of our belief, the existence of a true nonlinear Shannon limit has still not been demonstrated, and the problem of determining the channel capacity of a fiber-optic system in the presence of Kerr nonlinearities is still an open issue
Digital signal processing for compensating fiber nonlinearities
Successful compensation of nonlinear distortions due to fiber Kerr nonlinearities relies on the availability of an accurate channel model. Some models obtained by approximate solutions of the nonlinear Schrödinger equation and the backpropagation method are taken into account. It turns out that backpropagation is not the optimal processing technique and in some cases is outperformed by simpler processing techniques
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