This book provides leading research on Photonics which is the science of generating, controlling, and detecting photons, particularly in the visible and near infra-red spectrum, but also extending to the ultraviolet (0.2 - 0.35 µm wavelength), long-wave infrared (8-12 µm wavelength), and far-infrared/THz portion of the spectrum (e.g., 2-4 THz corresponding to 75-150 µm wavelength) where today quantum cascade lasers are being actively developed. Just as applications of electronics have expanded dramatically since the first transistor was invented in 1948, the unique applications of photonics continue to emerge. Those which are established as economically important applications for semiconductor photonic devices include optical data recording, fibre optic Telecommunications, laser printing (based on xerography), displays, and optical pumping of high-power lasers. The potential applications of photonics are virtually unlimited and include chemical synthesis, medical diagnostics, on-chip data communication, laser defence, and fusion energy to name several interesting additional examples.