Abstract
We address the properties of nonlinear-Fourier-transform (NFT)-based fiber-optic communications systems and, particularly, study how the presence of noise deteriorates the performance of these systems. Similarly to the case of linear Fourier modes evolving independently under the action of chromatic dispersion alone, NFT-based systems employ so-called ``nonlinear modes,'' forming a nonlinear spectrum, as data carriers, and these nonlinear modes evolve independently in an uncoupled manner under the joint action of nonlinearity and dispersion. However, the influence of amplified-spontaneous-emission (ASE) noise on these nonlinear modes is still relatively poorly studied. In this paper, dealing with a continuous nonlinear spectrum, we scrutinize the properties of the effective noise emerging in the nonlinear Fourier domain. We also show that in the transmission stages, where the signal peak power is relatively high (e.g., at the receiver, in back-to-back transmission, or at short distances), the performance of an NFT system is mostly degraded not by the inline ASE noise, but by the imperfections of the digital sampling and the forward and backward NFT algorithms, i.e., by the NFT processing noise.
Highlights
Optical-fiber systems are nowadays arguably the most significant part of the global telecommunication network, carrying the bulk of the world’s data traffic [1,2] and serving as a fundamental component of information and communication science and technology [3,4,5]
This OFDMtype modulation of the NF spectrum has been widely used [15,16,29,53], and was addressed theoretically in Ref. [43]. Such a spectral shape is convenient for nonlinear frequency-division multiplexing (NFDM) transmission because r(ξ ) in Eq (8) is a band-limited function, such that its linear Fourier transform (FT) has a finite extent; the latter is important when forming well-localized bursts in the true time domain to preclude the overlapping of symbols and detrimental effects resulting from intersymbol interference
We study the properties of the inline ASE noise and the numerical or processing error translated into the NF domain, for a NFDM transmission system that employs a continuous NF spectrum combined with orthogonal frequency-division multiplexing (OFDM)-type modulation
Summary
Optical-fiber systems are nowadays arguably the most significant part of the global telecommunication network, carrying the bulk of the world’s data traffic [1,2] and serving as a fundamental component of information and communication science and technology [3,4,5]. While in the current generation of optical transmission lines the dispersive signal spreading can be compensated by means of digital signal processing (DSP) at the receiver and/or the transmitter, the mitigation of noise and nonlinearity remain the paramount subjects in the development of efficient high-capacity optical transmission systems [3,4,5]. One of the most recent methods of combating nonlinear signal impairments is a technique often referred to as eigenvalue communications or nonlinear frequency-division multiplexing [13,14]. This technique involves the transmission of information
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