Photonic Crystals - Introduction, Theory and Applications

Photonics, the science and technology of generating, controlling, and detecting photons, has brought mankind laser surgery and manufacturing, global fiber telecommunication, and more recently, optical sensing, measuring, controlling, and the beginning of optical computing. The 21st century could well become the age of photonics and metamaterials, like the 20th century was the age of electronics and semiconductors. The United Nations declared 2015 the “International Year of Light and Light-based Technologies”. Photonic crystals are periodic optical structures (in one, two or three dimensions) that can control the flow of light in the same way that the periodic potential in a semiconductor crystal affects the flow of electrons. Since Eli Yablonovitch and Sajeev John have proposed both the term “photonic crystal” and the light-photon analogy in 1987, scientists have used band theory to describe many properties of photonic crystals. A simple and important example is the analogous use of allowed and forbidden energy bands: if light is forbidden to propagate inside a lattice, i.e. its frequency falls within the photonic bandgap, the lattice acts like a mirror throughout, which can be used to create effective waveguides that are already used commercially. These waveguides use interference instead of the more conventional internal reflection. Photonic crystal devices can also do many other interesting things such as guiding light around sharp bends or even trap it entirely. Other conventional concepts like reciprocal space, Brillouin zones, Bloch wave functions, and dispersion relations are also used to describe optical waves. The first part of this book reviews basic concepts of photonic crystals in the context of sensor applications. This is followed by a discussion how absorption in photonic crystals can be tuned or created through an artificial molding process or naturally, through emotionally triggered skin modifications like those performed by chameleons. Effectively enhanced broadband absorption is then discussed, followed by an efficient method to calculate macroscopic optical responses of periodic composite systems. The latter marks the beginning of the more theoretical part of the book: light guiding beyond photonic bandgaps, a breakdown of the Bose-Einstein distribution, a phase diagram to distinguish photonic crystals form dielectric metamaterials, dynamically controlled emission of single excitons in photonic crystal cavities, topological phases of sound and light, and trapped atoms in one-dimensional photonic crystals. The last part of this collection aims to provide insight into the extraordinary wide range of powerful applications of photonic crystals such as optimized solar cells, “smart” supercapacitors, a torque sensor, photonic tweezers, pressure-responsive shape memory, and controlled NOT gates for the use in future quantum computers.