Digital nonlinear compensation for next-generation optical communication systems using advanced modulation formats

Digital backward propagation (DBP) is an effective way to enable the simultaneous compensation of both linear and nonlinear fiber impairments, which cause severe impacts on present optical transmission systems using high spectral-efficient techniques for the growing capacity demand. The principle of DBP is to apply split-step Fourier method (SSFM) to solve the inverse nonlinear Schrödinger equation (NLSE) onto the received distorted complex signal of full information based on coherent detection with a digital signal processing (DSP) module. However, DBP performance must be traded off for computational complexity. Requiring many calculation steps for high accuracy, the conventional SSFM algorithm is inefficient and thus not feasible especially in real-time hardware implementations. This work focuses on DBP performance and the possibilities to enhance hardware efficiency for systems using DBP. In addition to the conventional DBP algorithm, logarithmic DBP and correlated DBP methods are introduced. The performance of different DBP algorithms is compared and the influence of system parameters is analyzed. In this thesis, advanced modulation formats of current optical communication systems, such as differential phase shift keying (DPSK) and higherorder quadrature amplitude modulation (QAM), are chosen for the numerical investigations. The impact of fiber nonlinear effect without DBP compensation is presented for various bit rates, fiber types and link designs. Especially the performance degradation caused by the Gordon-Mollenauer effect in DPSK-systems is discussed.