Laser diode

A semiconductor device that emits coherent light when electrical current drives stimulated emission in an active region. Its compact, electrically powered design makes it a common source of laser light.

Stimulated emission: The process by which an excited atom or molecule emits a photon matching an incoming photon. It produces the matching photons that amplify light inside the diode.
Band gap: The energy range in a solid between its valence-band and conduction-band states where no electron states occur. The active material’s band gap largely determines the emitted photon energy and wavelength.
Fiber-optic communication: The transmission of information as light through optical fibers. Laser diodes provide modulated optical signals for many fiber links.
Light-emitting diode: A semiconductor device that emits light primarily through spontaneous electron–hole recombination. Unlike a laser diode, an ordinary LED does not rely on a resonant cavity for coherent emission.
Robert N. Hall: An American physicist who led the team that demonstrated the first semiconductor laser in 1962. His group produced an early gallium arsenide diode laser operating at cryogenic temperature.
Semiconductor p–n junction: A boundary between p-type and n-type semiconductor regions, where charge carriers recombine under forward bias. Forward bias injects electrons and holes into the diode’s active region.
Direct and indirect band gaps: Two semiconductor band structures distinguished by whether conduction-band and valence-band extrema share the same crystal momentum. Direct-gap materials emit light efficiently; indirect-gap materials generally lose more energy to phonons.
Optical disc drive: A device that reads or writes data on optical discs using focused laser light. Different laser-diode wavelengths read or record CDs, DVDs, and Blu-ray discs.
Vertical-cavity surface-emitting laser: A semiconductor laser that emits perpendicular to the wafer surface from a vertical resonant cavity. It is a laser-diode architecture suited to arrays and wafer-level testing.
Nick Holonyak Jr.: An American engineer who developed the first practical visible-spectrum LED and worked on semiconductor lasers. His 1962 gallium arsenide phosphide laser emitted visible red light.

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