To expand the transmission capacity of coherent fiber optic communication systems, ultra-wideband (UWB) wavelength division multiplexing (WDM), are being investigated. In this chapter, we first introduce a transmission scheme that utilizes a Fast—than—Nyquist rate in a multi-band optical transmission system. Then, the performance of a UWB WDM transmission system that covers the widely used C + L band as well as the additional O-, E-, and S-bands is investigated. The transmission system is established and the channel effects are discussed. In addition, an optimization scheme for compensating the spectral power tilt caused by SRS in the S + C + L band system, which utilizes a Raman amplifier and the partition particle swarm optimization (PPSO) algorithm, is demonstrated. Finally, ultra-wideband transmission of 480, 50 GHz spaced channels with PDM 256-QAM modulation over 20 km of SSMF is achieved.