The demand for the transport of vast amounts of information in long-haul optical communication has driven the research into spatial-division multiplexing. A promising subcategory of spatial-division multiplexing, mode-division multiplexing employing few-mode fibers, uses the modes for transmitting parallel streams of information. Despite the complexity escalation due to mode-multiplexers and additional digital signal processing (DSP) to unravel the inter-modal effects, mode-division multiplexed systems show in early studies energy saving potential compared to parallel single-mode-based systems. However, dealing with multiple modes has shown so far the occurrence of the undesirable effect of mode-dependent loss (MDL). In the extreme case, losses may affect selectively certain modes causing system outage. Current approaches to reduce the MDL focus either on improving the design of single inline components or balancing the modal gains and losses throughout the optical link. Although both approaches aid to improve the system performance, significant amount of MDL remains in the system. By means of simulations and experiments, this thesis describes an innovative approach to further improve the system tolerance towards MDL. The approach combines an improvement in the optical domain and the use of alternative DSP schemes. For the former enhancement, the impact of mode coupling on MDL is first studied with simulations. With three- and six-spatial-mode transmission, it is shown that inducing strong mode coupling along the fiber or using mode scramblers helps to increase the tolerance towards MDL. Next, the use of alternative receiver DSP schemes such as near maximum-likelihood (ML) detection and their combination with different levels of mode coupling is evaluated. It is demonstrated that strongly coupled modes and ML techniques greatly improve the performance of MDL-impaired systems. At this point, the complexity of such algorithms is also computed and analyzed. Finally, experiments with fiber supporting six spatial modes in single and multiple wavelength-division multiplexing channels are described. The experiments clearly show performance degradation caused by MDL, which is improved through a near-ML detector.     «

The demand for the transport of vast amounts of information in long-haul optical communication has driven the research into spatial-division multiplexing. A promising subcategory of spatial-division multiplexing, mode-division multiplexing employing few-mode fibers, uses the modes for transmitting parallel streams of information. Despite the complexity escalation due to mode-multiplexers and additional digital signal processing (DSP) to unravel the inter-modal effects, mode-division multiplexed sy...     »