
118 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
Equation
4
.29
c
an
n
ow
b
e
m
odied
a
s:
A z z T
z
D N z dz
z
D
z
z z
( , ) exp exp ( ) exp+ ≈
′ ′
+
∫
δ
δ δ
δ
2 2
ˆ ˆ ˆ
A z T( , )
(4.30)
This
method
is
accurate
to
the
third
order
of
the
step
size
δz.
In
symmetric
SSFM,
the
optical
pulse
propagates
along
a
ber
segment
δz
in
two
stages.
First,
the
optical
pulse
propagates
through
the
linear
operator
that
has
a
step
size
of
δz/2
that
takes
into
account
ber
attenuation
and
dispersion
effects.
Then,
the
ber
nonlinearity
is
calculated
in
the
middle
of
the
segment.
After
that,
the
pulse
propagates
through
the
second
hal ...