Specialty Optical Fibers Handbook

ground state is either radiatively by emission of photon or nonradiatively by

coupling energy into the vibrational modes of the glass network. However, since

the average phonon energy of silica is about 1100 cm

1

, bridging the energy gap

requires five phonons. Because the probability of decay decreases exponentially

with the number of phonons, the nonradiative lifetime is very long. As a

consequence, Er is an excellent energy storage medium and optical conversion

efficiencies very close to theoretical maximum are readily achieved [55].

The optical gain experienced by the signal can be represented as

G ¼ 4:343GLN

0

[s

e

(l)  (s

a

(l)n

2

 s

a

(l))], (7:1)

where gain is expressed in decibels, G is the spatial overlap between optical field

and dopant distribution, ...