ABSTRACT
Rare earth doped glass and crystal fiber lasers were first investigated experimentally as early as the 1960s [1-3], then in the 1970s [4,5] and early 1980s [6]. Since their more recent emergence in 1985 [7,8], they have received considerable attention for numerous potential applications in optical communication, sensing, medicine, material processing, imaging, data storage, and laser ranging. The optical confinement provided by the fiber, combined with the excellent laser properties of trivalent rare earth ions, make this type of laser extremely efficient. They can operate with exceedingly low thresholds, as low as 100 µW, and yet can be pumped extremely hard to produce output powers in excess of 100 W, with optical conversion efficiencies greater than 50%. Furthermore, the numerous laser transitions available from trivalent rare earth ions lend them the ability to generate light over a wide selection of wavelengths, from the ultraviolet (UV) to the midinfrared (mid-IR), with broad tuning ranges. Pumped with a laser diode, they retain the advantage of compactness, low cost, and ease of large-scale manufacturing critical for many practical applications. Fiber lasers now compete directly in several domains with semiconductor sources, over which they present the advantage of high brightness, excellent mode quality, highly efficient coupling into a single-mode fiber, and a far superior wavelength stability with temperature.
