Dense wavelength division multiplexing (DWDM) systems have the potential to meet the demands of emerging needs of information technology. The main objective of this Book is to examine the role of linear and nonlinear optical effects in DWDM optical communication systems with emphasis on pulse propagation characteristics. These effects are important and critically influence the performance of DWDM optical systems. The main contribution has been made to three main aspects of the problem: - Accurate analysis of uniform/non-uniform optical waveguides with arbitrary refractive index profiles - Pulse propagation and distortion in DWDM Raman amplification systems - Use of non-uniform fiber Bragg grating to compensate for pulse distortion This Book contains the analytical and numerical methods to analysis of optical waveguide and devices. The book explain the optical waveguide theory in lucid form.