Specialty Optical Fibers Handbook

amplifiers (EDFAs) [68]. The RFL gain block consists of a P-doped fiber as the

gain medium; the laser cavity is obtained by FBG inscribed in Ge-doped silica

fibers. The two FBGs are then spliced to the gain medium fiber. The splice losses

could be reduced or even avoided by inscribing the FBGs directly into the

heavily P-doped silica fibers. The number of cavities depends on the Stokes

shift. For a Ge-doped silica fiber, the Stokes shift is limited to 13.2 THz. For

example, five laser cavities are needed to shift the Yb-doped fiber laser pump

emitting at 1060 nm to the pump wavelength of 1480 nm for EDFAs. Using a

heavily P-doped silica fiber, the number of cavities is reduced to only two, thanks

to the Stokes shift of 39.9 THz. This shift is three ...