Semiconductor lasers - Devices and applications

Since their invention in the 1960s, lasers have revolutionized numerous scientific and technological fields, becoming indispensable tools in modern photonics. Among the wide variety of laser sources available today (gas lasers, solid-state lasers, fiber lasers, etc.), laser diodes are a preferred solution that has become established in a growing number of applications. The operating principle of laser diodes is based on the stimulated emission of photons within a P-N junction of semiconductor materials. This relatively simple architecture gives rise to a set of remarkable characteristics that distinguish these components from other laser technologies.

First and foremost, laser diodes feature an extremely compact size (typically a few cubic millimeters) combined with exceptional external quantum efficiency, which regularly exceeds 50% and can even reach 70% for the most advanced devices. This efficiency in converting electrical energy into coherent radiation is difficult for other types of lasers to match. One of their major advantages lies in their spectral versatility. Thanks to a judicious choice of semiconductor materials (GaN, GaAs, InP, GaSb, etc.) and controlled structural engineering at the atomic-layer scale (quantum wells, quantum dots), it is possible to cover a wavelength range extending from the near-ultraviolet to the far-infrared, with the potential to open up new spectral windows through the development of new materials. In terms of power performance, the technological maturity of certain material systems (notably InGaAs around 1 µm) now makes it possible to achieve optical powers ranging from the watt level for single-mode devices to the kilowatt level for diode array systems. Furthermore, semiconductor substrate fabrication processes, inherited from microelectronics, offer the possibility of mass-producing these components, which significantly contributes to reducing production costs and explains their growing affordability.

This unique combination of advantages— –, compactness, efficiency, spectral tunability, scalability, and low cost—explains the– widespread use of laser diodes across numerous application sectors. They are widely used in optical telecommunications, industrial applications (cutting, welding, marking, surface treatment), detection and telemetry systems (lidar sensors for autonomous vehicles, 3D mapping), and the medical field (ophthalmic surgery, dermatology, diagnostics).

Beyond these well-established commercial products, research activity remains particularly dynamic. Numerous academic and industrial teams are actively working to continuously improve the performance of these components: increasing power, expanding the spectral range (particularly toward the deep ultraviolet and far infrared), and reducing...