Glossary term
Laser Diode
A semiconductor light source that produces coherent optical emission by stimulated recombination in a p-n junction structure.
Definition
deviceA laser diode is a semiconductor diode that emits coherent light when carrier recombination is amplified by optical feedback and stimulated emission.
A laser diode uses a forward-biased semiconductor junction or quantum-well structure to inject electrons and holes into an active region. Above threshold current, stimulated emission dominates and an optical cavity provides feedback, producing narrow-spectrum, directional light. Laser diodes are used in optical communications, barcode scanners, LiDAR, sensors, laser printers, optical storage, medical devices, and precision instrumentation.
A laser diode is a semiconductor light source that produces coherent optical emission. Like an ordinary diode, it is based on a p-n junction or related semiconductor heterostructure. Unlike an LED, it includes an optical cavity and is operated so stimulated emission dominates above a threshold current.
Below threshold, a laser diode behaves more like a weak spontaneous emitter. Above threshold, optical gain exceeds losses, and output power rises strongly with current. The threshold current I_{th}, slope efficiency, wavelength, beam divergence, linewidth, and maximum optical power are key design parameters.
Structure and operation
Most laser diodes use compound semiconductors and quantum wells to confine carriers and optical fields. Cleaved facets, distributed feedback gratings, distributed Bragg reflectors, or vertical cavities provide optical feedback. The wavelength depends on material bandgap and cavity design, while temperature shifts both threshold and wavelength.
Laser diodes can be directly modulated by changing drive current, which is why they are important in optical communication. High-speed modulation depends on carrier dynamics, parasitic capacitance, package design, thermal behaviour, and optical feedback control.
Engineering constraints
Laser diodes are sensitive to overcurrent, electrostatic discharge, reverse voltage, excessive junction temperature, optical feedback, and poor heat sinking. Many drivers include current regulation, soft start, temperature control, monitor photodiode feedback, and fault shutdown. For precision systems, temperature stabilization is used because wavelength and power vary with temperature.
Common mistakes
A common mistake is driving a laser diode like an ordinary indicator LED. Laser diodes can fail from short current spikes, electrostatic discharge, or optical facet damage. Another mistake is specifying optical power without beam quality, wavelength tolerance, modulation bandwidth, thermal path, lifetime, and eye-safety classification. Good integration treats the laser diode, driver, optics, heat sink, monitor photodiode, and safety controls as one system.