Fibrelasers

Fibrelasers are lasers in which the gain medium is an optical fiber doped with rare-earth ions. The most common configurations use ytterbium-, erbium-, or thulium-doped fibers, pumped by laser diodes. The laser cavity is formed using fiber components such as fiber Bragg gratings and mirror coatings integrated into the fiber, yielding a compact and robust light source with high beam quality.

Most practical fibrelasers follow a seed-and-amplifier architecture, often a master oscillator power amplifier (MOPA). A low-noise seed laser provides the initial pulse or continuous-wave light, which is then amplified in one or more high-gain fiber amplifiers. Pump light is delivered through cladding-pumped fiber designs that allow the use of high-power diode stacks while keeping the fiber single-mode or nearly single-mode for output.

Wavelengths depend on the dopant: ytterbium-doped fibers typically emit around 1030–1080 nm; erbium-doped fibers around 1550 nm; thulium-doped fibers near 1.9–2.1 µm. Fiber lasers can operate in near-continuous wave, pulsed, or ultrafast regimes, including mode-locked operation for picosecond to femtosecond pulses.

Key advantages of fibrelasers include high electrical-to-optical efficiency, excellent beam quality, and inherent robust alignment due to the fiber geometry. They also enable straightforward power scaling by chaining fiber amplifiers and distributing heat along the length of the fiber. Their compact footprint and air cooling can reduce facility requirements compared with bulk solid-state lasers.

Limitations include nonlinear optical effects such as stimulated Brillouin scattering and Raman scattering at high powers, which can limit performance in narrow-linewidth or high-energy systems. Managing heat, fiber damage at interfaces, splicing losses, and cost for large-diameter, highly doped fibers are ongoing considerations.

Applications span materials processing (cutting, welding, marking), micromachining, medical and dental procedures, telecommunications components, and research instrumentation. Advances focus on higher power, better beam quality, ultrafast pulse generation, and further integration of fiber-based laser systems.