Fiber Lasers and Amplifiers

This chapter talks about fiber lasers, which technically are a type of solid‐state laser, but differ in important ways from the other solid‐state lasers. Simple optical fibers have a circular core of glass with a high refractive index surrounded by a circular cladding with lower refractive index. The selection of doped fibers is crucial in fiber laser design. In most cases, the doped central core has a small diameter for single‐mode operation. The most important rare earths for fiber lasers are ytterbium, erbium, thulium, and holmium. A separate family of fiber lasers (and amplifiers) is based not on rare‐earth doped fibers but on an effect called Raman scattering that occurs when photons lose or gain a bit of extra energy when they bounce off atoms in undoped glass fibers. Fiber Raman amplification is attractive in telecommunication systems because the amplification can take place in the undoped core of the fiber transmitting the signals.