Optoelectronics is the study of semiconductor devices that either detect or emit light. The field of optoelectronics has been developed mainly because of the need for emitters and detectors in optical communication systems. One well-regarded author, Clifford Pollock, uses the term optoelectronics to refer to not only optical detectors and emitters, but also optical transmission through waveguides.
Semiconductors have energy bandgaps on the order of 1eV. The energies of photons at visible light frequencies are also on the order of 1eV. When an electron drops from a semiconductor's conduction band to its lower-energy valence band, a photon can be emitted, satisfying conservation of energy. Similarly, a photon incident on a semiconductor can be absorbed, allowing an electron to jump from the valence band to the conduction band. These concepts are the foundations of optoelectronics. For more information on sensors, see optical detector. Additional information on optoelectronic emitters can be found at LED and laser diode.