Specialty Optical Fibers Handbook

manner. As described earlier, LMA fibers have cores with low NAs, typically

smaller than single-mode telecom fibers. This reduction in core NA reduces the

amount of fluorescence captured by the core and, thus, the reduction of ampli-

fication of that fluorescence. A second mechanism, nonlinear in nature, is SBS,

which results from an acoustic wave formed from the superposition of the

propagating light wave and the counter-propagating stokes wave generated

from the index modulation in the glass created by the propagating wave. The

threshold power at which SBS occurs in single-mode fibers is given by Eq. (22.2):

110

270

485

810

2000

600

1360

30

95

150

0

800

600