As data transmission demands grow with increasing users and complex applications, long-haul optical transmission links face greater pressure. Researchers have explored two approaches to address this: increasing bandwidth efficiency by transmitting more bits per unit frequency and expanding the exploitable bandwidth within fibre optic links. The first method, which involves using more complex modulation formats, has reached limitations due to stricter signal-to-noise ratio (SNR) thresholds. Consequently, bandwidth expansion has become the primary strategy for increasing data transmission capacity. This thesis investigates the use of Ultra-Wide Band (UWB) systems, specifically utilizing the C, L, and S bands, to expand usable bandwidth to around 20 THz, compared to the 5 THz available in the C band.