Photonics is the technology which is based on the particles that make up light, the photons. This is analogous to the term "electronics", the technology relying on the electron.
The term photonics was coined in order to emphasize the growing importance of optical technologies. Today, laser light is already being used in areas ranging from materials processing to communications and medicine. Until recently, many of these functions had to be performed less accurate or less efficient by mechanical or electronic means. More powerful lasers and new or improved photonic systems will significantly broaden the spectrum of applications for light in the years to come.
*Photonics: The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The range of applications of photonics extends from energy generation to detection to communications and information processing. (Photonics Spectra)