Photonics is an area of study that involves the use of radiant energy (such as light), whose fundamental element is the photon.
Photonic applications use the photon in the same way that electronic applications use the electron. Devices that run on light have a number of advantages over those that use electricity. Light travels at about 10 times the speed that electricity does, which means (among other things) that data transmitted photonically can travel long distances in a fraction of the time. Furthermore, visible-light and infrared (IR) beams, unlike electric currents, pass through each other without interacting, so they don't cause interference. A single optical fibre has the capacity to carry three million telephone calls simultaneously.
See an introductory tutorial on photonics: