In this paper we study statistical properties of nonlinear impairments enhancement due to linear mode coupling in few mode optical fibers. Previously we have shown that strong linear mode coupling leads to the enlargement of nonlinear distortions, but in the case of the weak linear mode coupling this phenomenon shows itself in the stochastic manner. Therefore we use simulations based on numerical solving of the generalized coupled nonlinear Schrödinger equations to plot distribution histograms of the difference between rms of nonlinear impairments in the case of presence and in the case of absence of the weak linear mode coupling for different mean lengths of coupling fiber sections, different values of signal power, and modulation formats. Presented results show that distribution plotted for the fundamental mode has higher dispersion than the same one for the first- or second-order modes. In mode division multiplexed systems it means that channel using fundamental mode as a carrier is more affected to nonlinear impairments enhancement than mode channels of higher orders. Nonlinear impairments may sufficiently decrease the effectiveness of linear coupling compensation for all the mode channels.
In this paper we propose to evaluate the possibility of applying the method known as differential transformation of signals to reduce the dynamic range of optical signals for mitigation of impairments caused by Kerr-nonlinearities. The essence of this method is as follows. The channel signal is the difference between the original signal and its extrapolated values. We have simulated nonlinear propagation of proposed signal and original signal to define nonlinear impairments reduction due to signal compression. Presented results show that differential transformation of signal allows to sufficiently mitigate envelope distortions caused by self-phase modulation and cross-phase modulation.
In this paper we consider nonlinear impairments of mode division multiplexed signals with QAM modulation in optical fibers with linear mode coupling of spatial modes. We simulate simultaneous propagation of fundamental mode and two first-order vortex modes in standard single mode fiber at 850 nm and propagation of fundamental mode and first- and second-order vortices in step-index fiber with enlarged core at 1550 nm. Simulation results shows that in strong coupling regime linear coupling lead to sufficient increasing of nonlinear impairments, but QAM-modulated signal is more robust to this effect than OOK modulated signal.
We considered interaction of PMD and Kerr-nonlinearities in the two-channel WDM system to derive conditions of signal improvement due to such interaction. We presented statistics of eye-diagram opening and investigated properties of fiber links providing this kind of signal improvement.
This paper presents results of investigation on interaction of PMD and Kerr-nonlinearities in long-haul fiber links. It is shown that PMD may significantly reduce impairments caused by nonlinear effects. There are shown dependences on the input polarization, peak pulse power, PMD coefficient and used line codes.
This paper presents results of investigation on cross-phase modulation effect and influence of polarization effects on it. It
is shown that fast polarization scrambling can effectively reduce impairments caused by cross-phase modulation in the
case of NRZ signal.
This paper presents results of numerically solved model of fiber link including Kerr-nonlinearities,
dispersive effects and polarization-mode dispersion. Different types of Gaussian pulses are modeled
at step-index and non-zero dispersion shifted fibers.
We present a solution of the synthesis for reflective optical filters designed for WDM-systems. Filter is based on multilayer dielectric structures with apodized (modulated) refractive index profile. The method of synthesis provides calculation of the uniform quarter-wave filter-prototype. The calculation of the prototype is executed with relation, which join given spectrum characteristics with constructive parameters of the filter. On the base of calculated filterprototype
the filter with bilateral Gaussian apodization of a refractive index profile, possessing given spectral properties is formed.