
6 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
These
f
our
d
igital
m
odulation
f
ormats
f
orm
t
he
b
asis
o
f
m
odulation
f
ormats
i
n
a
dvanced
o
ptical
ber
c
ommunication
s
ystems.
B
esides
t
hese
f
ormats,
p
ulse
s
haping
a
lso
p
lays
a
n
i
mportant
p
art
i
n
t
hese
a
dvanced
s
ystems.
T
hey
i
nclude
N
on-Return-to-
Rero
(
NRZ),
r
eturn
t
o-zero
(
RZ),
a
nd
d
uobinary
(
DuoB).
R
Z
a
nd
N
RZ
a
re
b
inary
f
ormats
t
aking
t
wo
l
evels
“
0
a
nd
1
”
w
hile
D
uoB
i
s
a t
ri-level
s
haping
t
aking
t
he
v
alues
o
f
“
−1,
0
,1”.
T
he
−
1
i
n
o
ptical
w
aves
i
s
t
aken
c
are
o
f
b
y
a
n
a
mplitude
o
f
“
1”
a
nd
a p
hase
s
hift
o
f
π w
ith
r
espect
t
o
t
he
“
+1”,
w
hich
i
mplies
t
hat
a ...