Numerical investigation of four-wave mixing in DWDM systems with high-order QAM modulation formats

Abstract

The wavelength-division multiplex (WDM) systems represent the key technology for future optical networks. Next step for achieving the improvement of transmission system and growth of capacity is employment of high-order modulation formats. This paper provides an insight into the numerical investigation on one of the most detrimental degradation effect in multichannel systems – four-wave mixing (FWM) and its impact on transmitted signals which used novel types of high-order square and star quadrature amplitude modulation (QAM) formats, respectively. This type of nonlinear effect causes inter- and intra-channel crosstalk interference, what are the worst cases of all possible channel impairments, because all spectral properties of transmitted signal are mixed together resulting to the decreasing system performance. Our investigation is based on finding the precise solution of coupled nonlinear Schrödinger’s equations (CNLSE) for DWDM system with channel spacing according to the ITU-T standardization. For solving CNLSE, it was created numerical model through mathematical method referred as split-step Fourier method (SSFM). The investigation is oriented especially on QAM formats, different kinds of optical fibers which are typically used in today’s networks and various types of system parameters such as value of channel spacing, input power and number of channels. The obtained results are discussed and analyzed with the aim of finding the most optimal and suitable properties of DWDM transmission system.