Investigation of degrading effects and performance optimization in long-haul WDM transmission systems and reconfigurable networks

Optical signals experience various degrading effects in optical fiber transmission systems and reconfigurable networks. Among those the most important effects include chromatic dispersion, fiber nonlinearities, polarization-related impairments such as polarization mode dispersion (PMD) and polarization dependent loss (PDL), as well as their mutual or combined effects. Depending upon the signal nature (analog or digital, as well as different data formats) and system's structure (reconfigurable network or point-to-point transmission), the way to improve or optimize system performance may be different.; Recirculating fiber loop testbed is a powerful tool to investigate different perspectives in typical optically amplified long-haul or ultra-long-haul (ULH) systems by sending optical signals through a certain length fiber repeatedly. Most of the study in this dissertation is based on the testbed with different system parameters or configurations.; Polarization-related impairments became a big hurdle to high performance systems, especially when the data rate increases to >10-Gb/s/channel. Both PMD and PDL can induce statistical system fluctuations, and enhanced degradations will happen due to their interaction. Using a loop-synchronized polarization scrambling technique, we replicate a distributed long-haul link with accurate polarization statistics. Thus we are able to show experimentally two major degrading effects due to PMD and PDL: (i) combined effects of PMD and PDL, and (ii) degrading effects due to low frequency polarization scrambling in the presence of PDL.; The major part of this dissertation is performance optimization where we show different approaches to (i) overcome the limitations due to fiber dispersion and nonlinearities using pulse-width management for return-to-zero (RZ) systems, (ii) combat PMD and PDL effects by applying dynamic monitoring, optical compensation and electronic mitigation. The advanced methods of PMD emulation, including both the variable first-order emulator and all-order emulator with tunable statistics, have been presented with a further emphasis of experimental realization of importance Sampling.; Although external modulation is the dominating technique in long-haul systems, we also investigate the feasibilities of direct modulation into 10-Gb/s long-haul transmission systems and 40-Gb/s systems using asymmetric narrow-band optical filtering at the transmitter or the receiver.