ABSTRACT
Rare earth doped optical fibers are now a well-established class of gain media with many diverse applications that extend far from the original conceived application; namely, inline amplifiers [1]. Erbium-doped silica fiber lasers have been used, for example, for distributed sensing applications [2], remote sensing of magnetic fields [3], and as sources of optical solitons for all-optical fiber-based communications networks [4]. Many of these applications have evolved because of the advantages accrued from placing the rare earth ion in the optical fiber host lattice. As described in Chapter 2, the interaction between the rare earth ion and the intrinsic electric field associated with the host results in a broadening of the absorption and emission lineshapes associated with the rare earth ion. It is fortuitous that the absorption bands associated with many of the rare earth ions occur at wavelengths that are common to well-established laser diodes. The broadening of the absorption bands removes some of the wavelength-tailoring problems encountered with rare earth doped crystalline materials [5]. In fact, the ability to convert the output radiation from low-cost laser diodes, which generally occurs in a low-quality output mode with a poor frequency definition, into a high-brightness coherent source, is beneficial to applications, such as remote sensing and fiber-based communications systems, because it results in compact systems with low power requirements. The broadband emission of trivalent rare earth ions allows the development of sources emitting either broad continuous-wave (CW) spectra (see Chap. 6) or ultrashort pulses (see Chap. 8), as well as widely tunable narrow-linewidth operation, as described in this chapter.
