All-optical signal processing technology has been of high technical interest in the field of fibre-optic communication systems and networks, since it can provide the most powerful way to overcome the optical-to-electrical domain conversion-induced data traffic bottleneck. A variety of all-optical signal processing devices demonstrated to date are discussed in this book: for example, wavelength converters, optical demultiplexers, noise rejection filters, amplifiers, clock recovery subsystems, and data regenerators. Those devices are mostly based on the non-linear optical properties of optical waveguide media such as optical fibres and semiconductor active devices. The two main forms of non-linear effect used are Kerr non-linear effects and inelastic non-linear scattering effects (i.e. Raman and Brillouin scattering). Kerr non-linear effects including self-phase modulation, cross-phase modulation, and four-wave mixing are due to the response of the bound electrons in a non-linear optical medium to an intense optical field, whereas Raman and Brillouin scattering effects are caused by the presence of vibrational states of atoms in the optical medium. In this book, the ultimate potential of state-of-the-art highly non-linear optical fibre technologies are reviewed from a perspective of practical implementation of all-optical signal processing devices for fibre optic communication systems. Due to the fact that the ultra-high non-linearity fiber technologies offer significant advantages in terms of reduced length, reduced power requirements for the realisation of a variety of all-optical signal processing devices, the compactness and stability issue of fibre-based optical devices relative to semiconductor-based ones can be significantly improved. This review is focused on two state-of-the-art ultra-high non-linearity optical fibres such as photonic crystal fibre (PCF) and Bismuth oxide-based step index type non-linear optical fibres, which are considered to be the most promising fibres among various kinds of non-linear optical fibre. Also presented are basics on optical fibre non-linearities to help the readers understand its main contents. In addition, nonlinearity efficiency comparison results for various types of commercially available, state-of-the-art non-linear fibre are presented in terms of various definitions of Kerr non-linearity figure-of-merit to provide critical information with regard to optimum optical fibre structure and material for the best Kerr nonlinearity efficiency.