Laserdiodes

A laser diode is a semiconductor device that emits coherent light through stimulated emission from a p-n junction embedded in an optical cavity. It directly converts electrical power into optical power, producing a narrow, highly directional beam in a compact package.

Most diode lasers use a heterostructure grown by epitaxy to create an active region inside a waveguide. Emission is typically confined by cleaved end facets, or by mirrors such as distributed Bragg reflectors (DBR) or external cavities. Common material systems include GaAs/AlGaAs and InP-based compounds, enabling near-infrared wavelengths; GaN-based devices provide blue–violet light.

Operation involves a threshold current; above threshold, light output increases with current (slope efficiency). Diode lasers are sensitive to temperature, so practical devices use thermoelectric coolers or temperature control. They can be directly modulated at high speeds and in some designs are integrated in single-mode or multimode configurations for different beam qualities.

Applications span telecommunications (fiber optic transmitters at 1310 and 1550 nm in InP devices), data storage and multimedia drives, barcode scanners, laser pointers, and projection. Types include edge-emitting diode lasers and vertical-cavity surface-emitting lasers (VCSELs). Wavelengths range from blue (approximately 405 nm) with GaN devices to near-infrared and infrared.

Manufacture involves epitaxial growth, facet coating, and precision packaging with heat sinking. Reliability is generally high but lifetime and performance degrade with temperature and current; failures often originate at facets or contact degradation.

The first practical laser diode was demonstrated in 1962, paving the way for widespread use in communications and consumer electronics.