Abstract
The capacity limits of fiber-optic communication systems in the nonlinear regime are not yet well understood. In this paper, we study the capacity of amplitude modulated first-order soliton transmission, defined as the maximum of the so-called time-scaled mutual information. Such definition allows us to directly incorporate the dependence of soliton pulse width to its amplitude into capacity formulation. The commonly used memoryless channel model based on noncentral chi-squared distribution is initially considered. Applying a variance normalizing transform, this channel is approximated by a unit-variance additive white Gaussian noise (AWGN) model. Based on a numerical capacity analysis of the approximated AWGN channel, a general form of capacity-approaching input distributions is determined. These optimal distributions are discrete comprising a mass point at zero (off symbol) and a finite number of mass points almost uniformly distributed away from zero. Using this general form of input distributions, a novel closed-form approximation of the capacity is determined showing a good match to numerical results. Finally, mismatch capacity bounds are developed based on split-step simulations of the nonlinear Schrdinger equation considering both single soliton and soliton sequence transmissions. This relaxes the initial assumption of memoryless channel to show the impact of both inter-soliton interaction and Gordon–Haus effects. Our results show that the inter-soliton interaction effect becomes increasingly significant at higher soliton amplitudes and would be the dominant impairment compared to the timing jitter induced by the Gordon–Haus effect.
Highlights
It is predicted that the capacity of data transfer network, mainly consists of optical fibers, will fall behind the data traffic demands in the near future [1]
The optimal probabilities of the nonzero mass points, (d) The maximum Time-scaled mutual information (MI) given based on the solution of (26) and the lower bounds on the time-scaled capacity of the original noncentral chi-squared distribution (NCX) channel achieved by using different input distributions, including, on-off keying (OOK), 4 pulse amplitude modulation (4-PAM) and the input distribution given in (a) to (c)
The optimized distributions are discrete with a mass point at zero corresponding to no soliton transmission as well as an almost uniform distribution of mass points spread in a range away from zero up to the peak amplitude constraint
Summary
It is predicted that the capacity of data transfer network, mainly consists of optical fibers, will fall behind the data traffic demands in the near future [1]. We investigate the capacity of the optical fiber channel when only a single discrete spectrum point is encoded and the data is mapped on the imaginary part of the corresponding eigenvalue. This is essentially equivalent to the amplitude modulated soliton communication in [26]. Taking into account a peak amplitude constraint imposed by bandwidth limitations, the capacity in bits/normalized time and its corresponding input distribution are estimated using the proposed AWGN model and an approximate analytical approach. Based on the mismatch capacity results, the impact of inter-soliton interaction and Gordon–Haus effects on the capacity of soliton communication systems is studied
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