This book addresses quantum communications in the light of new technological developments on photonic crystals and their potential applications in systems. We begin with a state of the art on extensive quantum communications. The quantum gates such as Deutsch gates, Toffoli gates, Dedekind gates are reviewed and exposed. We examine their feasibility as electronic circuits and their implementation in systems, a comparison is performed in parallel with conventional circuits such as FPGAs and DSPs. the specificities of quantum communication are also exposed through the entanglement and Bell states. Mathematical and physical aspects of quantum optical fibers and photonic crystals are considered in order to optimize the quantum transmissions. Two fundamentals elements are treated, reconfigurable optical add-drop multiplexer and WDM.