
14.4.7 Kerr Nonlinearities
The ability to enhance or reduce the effective Kerr nonlinearity, and at the same
time control the magnitude and wavelength dependence of the GVD, makes PCF a
versatile vehicle for studies of effects such as four-wave mixing, self-p hase
modulation, modulation instability, soliton formation, and stimulated Raman scat-
tering (SRS). For a composite PCF made from two or more homogeneous materials,
the coefficient of fiber nonlinearity takes the form [52]
= k
X
i
n
i
2
A
i
(14.5)
where n
2
i
is the nonlinear refractive index of material i and A
i
its nonlinear
effective area:
A
i
=
n
m
ÐÐ
2
ðx; yÞdx dy
2
ÐÐ
u
i
ðx; yÞ
4
ðx; yÞdxdy
(14.6)
where u
i