Optical Fibers for High-Power Lasers

Lasers with high output powers are demanded for a wide variety of applications, ranging from material processing, remote sensing, medical surgery, to fundamental science. Across all these application scenarios, there are two main challenges: the scaling of output power and the quality of the laser beam. In the past decade, there have been tremendous research efforts to tackle these two issues in both continuous wave (CW) and pulsed lasers, to improve the power level, wavelength tunability, coherence, line width, etc. Among them, fiber technology has enabled the flexible delivery of high-power laser beams with precision beam quality (Jauregui et al., Nat Photonics 7:861–867, 2013). The technology development could be summarized in two approaches: passive fiber technology and active fiber technology. Passive fibers offer the last step manipulation of high-power laser beams from gas laser, semiconductor lasers, or other solid-state lasers. Active fibers are the gain component in the fiber oscillator or amplifier to generate the optical emission. Compared with traditionally step-index fibers, new fiber structure designs open new horizons in laser technology. In this book chapter, the main content has been arranged according to different fiber structure designs. Typical specialty fibers have been chosen, including double-cladding fibers, large mode area photonic crystal fibers, large pitch fibers, leakage channel fibers, chirally coupled core fibers, pixelated Bragg fibers, and hollow-core fibers. The design principle, manufacturability, and future outlook have been discussed in each subsections.