All-optical signal processing technology has been of high technical interest in the field of fiber-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 nonlinear optical properties of optical waveguide media such as optical fibers and semiconductor active devices. The two main forms of nonlinear effect used are Kerr nonlinear effects and inelastic nonlinear scattering effects (i.e. Raman and Brillouin scattering). Kerr nonlinear effects including self-phase modulation, cross-phase modulation, and four-wave mixing are due to the response of the bound electrons in a nonlinear 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 nonlinear optical fiber technologies are reviewed from a perspective of practical implementation of all-optical signal processing devices for fiber optic communication systems. Due to the fact that the ultra-high nonlinearity fiber technologies offer significant advantages in terms of reduced length, reduced power requirements for the realization of a variety of all-optical signal processing devices, the compactness and stability issue of fiber-based optical devices relative to semiconductor-based ones can be significantly improved. This review is focused on two state-of-the-art ultra-high nonlinearity optical fibers such as photonic crystal fiber (PCF) and Bismuth oxide-based step index type nonlinear optical fibers, which are considered to be the most promising fibers among various kinds of nonlinear optical fiber. Also presented are basics on optical fiber nonlinearities to help the readers understand its main contents. In addition, nonlinearity efficiency comparison results for various types of commercially available, state-of-the-art nonlinear fiber are presented in terms of various definitions of Kerr nonlinearity figure-of-merit to provide critical information with regard to optimum optical fiber structure and material for the best Kerr nonlinearity efficiency.