This book deals with the study of electromagnetic wave propagation through some new smart structures and refractive index profiles. The objective of the present book is to describe the modal propagation characteristics of some unusual optical waveguides having new geometrical cross-sections with different types of claddings, including dielectric, metallic, and helical. It provides the discussion of the tolerance study of a square waveguide into concave lens shapes, and the concept of negative refraction and photonic band gap in the case of helical waveguide. The book also illustrates the reflection properties of one-dimensional (1D) photonic crystals. Different theoretical approaches have been employed to analyze the suggested unconventional optical waveguides and 1D photonic band gap materials. Although the authors have considered some approximations in their study in view of simplicity, the book introduces some new concepts and insights in the field of optical engineering that can be utilized in fabrication of similar photonic devices. This book will be useful for the researchers working in the area of unconventional waveguides and photonic crystals.