The burgeoning demand for broadband services such as database queries, home shopping, video-on-demand, remote education, telemedicine and videoconferencing will push the existing networks to their limits. This demand was mainly fueled by the brisk proliferation of Personal Computers (PC) together with the exceptional increases in their storage capacity and processing capabilities and the widespread availability of the internet. Hence the necessity, to develop high-speed optical technologies in order to construct large capacity networks, arises. Two of the most popular multiplexing techniques available in the optical domain that are used in the building of such high capacity networks, are Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM). However merging these two techniques to form very high-speed hybrid WDM/OTDM networks brings about the merits of both multiplexing technologies. This thesis examines the development of one of the key components (picosecond optical pulses) associated to such high-speed systems. Recent analysis has shown that RZ format is superior to conventional NRZ systems as it is easier to compensate for dispersion and nonlinear effects in the fibre by employing soliton-like propagation. In addition to this development, the use of wavelength tunability for dynamic provisioning is another area that is actively researched on. Self-seeding of a gain switched Fabry Perot laser is shown to one of the simplest and cost effective methods of generating, transform limited optical pulses that are wavelength tunable over very wide ranges. One of the vital characteristics of the above mentioned pulse sources, is their Side Mode Suppression Ratio (SMSR). This thesis examines in detail how the pulse SMSR affects the performance of high-speed WDM/OTDM systems that employ self-seeded gain-switched pulse sources.