Information capacity of direct detection optical transmission systems

We show that the spectral efficiency of a direct detection transmission system is at most 1 bit/s/Hz less than the spectral efficiency of a system employing coherent detection with the same modulation format. Correspondingly, the capacity per complex degree of freedom in systems using direct detection is lower by at most 1 bit

Time varying ISI model for nonlinear interference noise

We show that the effect of nonlinear interference in WDM systems is equivalent to slowly varying inter-symbol-interference (ISI), and hence its cancellation can be carried out by means of adaptive linear filtering. We characterize the ISI coefficients and discuss the potential gain following from their cancellation.Comment: Submitted to the optical fiber communication conference (OFC), 201

Efficient and accurate modeling of multi-wavelength propagation in SOAs: a generalized coupled-mode approach

We present a model for multi-wavelength mixing in semiconductor optical amplifiers (SOAs) based on coupled-mode equations. The proposed model applies to all kinds of SOA structures, takes into account the longitudinal dependence of carrier density caused by saturation, it accommodates an arbitrary functional dependencies of the material gain and carrier recombination rate on the local value of carrier density, and is computationally more efficient by orders of magnitude as compared with the standard full model based on space-time equations. We apply the coupled-mode equations model to a recently demonstrated phase-sensitive amplifier based on an integrated SOA and prove its results to be consistent with the experimental data. The accuracy of the proposed model is certified by means of a meticulous comparison with the results obtained by integrating the space-time equations

Assessing the effects of mode-dependent loss in space-division multiplexed systems

Mode-dependent loss (MDL) is known to be a major issue in space-division multiplexed (SMD) systems. Its effect on performance is complex as it affects both the data carrying signal and the accumulated amplification noise. In this paper we propose a procedure for characterizing the MDL of SDM systems by means of standard measurements that are routinely performed on SDM setups. The figure of merit that we present for quantifying MDL incorporates the effect on the transmitted signal and the noise and is directly related to the spectral efficiency reduction

Asymptotic Probability Density Function of Nonlinear Phase Noise

The asymptotic probability density function of nonlinear phase noise, often called the Gordon-Mollenauer effect, is derived analytically when the number of fiber spans is very large. The nonlinear phase noise is the summation of infinitely many independently distributed noncentral chi-square random variables with two degrees of freedom. The mean and standard deviation of those random variables are both proportional to the square of the reciprocal of all odd natural numbers. The nonlinear phase noise can also be accurately modeled as the summation of a noncentral chi-square random variable with two degrees of freedom and a Gaussian random variable.Comment: 13 pages, 3 figure