
75Optical Fibers: Signal Attenuation and Dispersion
FWM
become
negligible.
In
terms
of
XPM,
its
effects
can
be
considered
to
be
negligible
in
a
DWDM
system
in
the
following
scenarios:
(1)
highly
locally
dispersive
system
and
(2)large
channel
spacing.
However,
XPM
should
be
taken
into
account
for
optical
transmission
systems
deploying
NZ-DSF
ber
where
local
dispersion
values
are
small.
Thus,
SPM
is
usually
the
dominant
nonlinear
effect
for
systems
employing
transmission
ber
with
high
local
dispersions,
for
example
SSMF
and
DCF.
The
effect
of
SPM
is
normally
coupled
with
the
n
onlinear
p
hase
s
hift
ϕ
NL
dened as:
φ γ γ
γ
ω
α
α
NL eff
L
c
eff
eff
L
P z