Specialty Optical Fibers Handbook

As available pump power has increased over time, the requirement on reduced

mode-field diameter has relaxed, so D is typically in the range of about 1%,

although communications applications with higher optical output signal power

use fiber with even lower D. These designs do not require confined dopant

distribution to improve efficiency. On the contrary, the distribution of Er may

be reduced at the center of the core or extended into the cladding to manipulate

the interaction between pump and signal intensities to control the population

inversion. As illustrated in Fig. 7.7, since the emission spectrum is highly depen-

dent on the population inversion, such schemes can be used to tailor the emission

spectrum.

7.5.3 Fiber Composition Issues

The amazing ...