Photonic Crystal Multiplexer/Demultiplexer Device for Optical Communications

Abstract

Photonic crystals (PhCs) are periodic dielectric structures. They are called crystals because of their periodicity and photonic because they act on light. They can occur when the period (the separation of the periodic dielectric materials) is less than the wavelength of the light. If the choice of lattice geometries and compositional dielectric materials are suitable, it is possible all those reflection and refractions will cancel not only the light scattered sideways, but the light moving forward as well. Then, because the light has to go somewhere (energy is conversed), it has no choice but to go back, which in this case it is forbidden from entering the photonic crystals. This happens no matter what direction the light is coming from, in a certain range of wavelengths which called photonic band gap. Fundamentally, PhCs are based on a concept of extended from conventional diffraction gratings and have unique analogy to solid state crystals. Thus the solid state physics theory is used for the analysis of PhCs. For example, one can calculate photonic band gaps (PBGs), impurity, defects and surface states, for PhCs structure. This allows the manipulation of light in dielectric mediums. For example, by carving a tunnel through the material, an optical “wire” can be created which no light can be deviate in the “wire”. Also, by making a cavity in the center of the crystals, the beam of light could be caught and held which created an optical “cage”. The abilities to trap and guide light have many potential applications in optical communications and computing, where one would like to make tiny optical “circuits” to help manage the ever-increasing traffic through the world’s optical communications networks. Other devices, too, are made possible by this increased control over light: from more-efficient lasers and LED light sources, to opening new regimes for operating optical fibers, to cellular phones.