Minimizing modes interaction based on time interleaving method in mode division multiplexing systems

Abstract

Efforts for higher transmission capacity have a significant attention in mode division multiplexing (MDM) systems. However, modes interaction is the main issue that degrades the performances of MDM systems and limits transmission distance. In this work, a new approach for minimizing the interaction of the modes in m-ary quadrature amplitude modulation (mQAM) MDM systems based on time interleaving method is analytically modeled and numerically demonstrated. In the proposed approach, mQAM symbols of modes are initially shaped and then time-interleaved (TI) by producing an optical delay between them. The symbols shaping is performed by adding a Mach–Zehnder modulator (MZM) after the mQAM modulator in the transmitter side. Sequentially, modes interference is lowered by inserting an optical delay between the more overlapping modes such as the degenerated modes. The performance of proposed system is studied by deriving an analytical model to estimate nonlinear phase noise (NPN) induced due to various fiber impairments. Moreover, the effect of the proposed technique is numerically investigated by examining the performances of two-mode and five-mode transmission systems. Each mode carries a sinusoidal-enveloped 4QAM signal at a rate of 20Gsymbol/s. The results reveal that the nonlinear phase noise (NPN) is significantly mitigated when the time delay between interleaved modes is equal to half the symbol period. For five modes TI-4QAM MDM system, the NPN is lowered by nearly 72%, 75.5%, and 73% for LP01, LP11a, and LP21a, respectively whereas the transmission reach is lengthened greater than 270% for different excited modes as compared with conventional 4QAM MDM system.