
7.5 FIBER NONLINEARITIES MONITORING
7.5.1 Fiber Nonlinearities
The index of refraction of optical fiber is slightly dependent on optical power,
according to the relationship [17]:
e
nð!; PÞ= n
0
ð!Þþn
2
I = n
0
ð!Þþn
2
P
A
eff
; (7.6)
where n
0
(!) is the linear refractive index of silica, n
2
is the intensity-dependent
refractive index coefficient, and I = P/A
eff
is the effective intensity in the medium.
The typical value of n
2
is 2.6 10
20
m
2
/W. This number takes into account the
averaging of the polarization states of the light as it travels in the fiber.
The intensity dependence of the refracti ve index gives rise to three major
effects which tend to degrade the