Photonics, in the same way that electronics deals with electrons, is the science of getting photons and light in general to do useful things. "Useful things" here really means packing data links with as much bits as possible. "Photonics" is a buzzword that entered telecom hype language in the 90's to represent the fact that guided optics is undergoing a rapid development similar to electronics in the 60's. Photonics habitually pertains to fiber optics, dielectric waveguides, integrated optics, optical cross-connects, optical switches, optical multiplexing and demultiplexing, light detection and amplification, Bragg gratings, etc. The analogy with electronics is quite good since, for instance, optical fibers bandwidth and optical switching capacity is growing exponentially, just as in Moore's law. However, the photonics Moore's law is much faster, with a time constant of about 9 months for doubling capacity.