
318 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
the
o
ptical
eld
i
s
a
vailable
i
n
t
he
e
lectrical
d
omain.
T
hat
w
ay,
c
omplex
o
ptical
d
emodulation
w
ith
i
nterferometric
d
etection—which
h
as
t
o
b
e
u
sed
i
n
d
irect
d
etection
s
ystems—can
b
e
a
voided,
a
nd
t
he
c
omplexity
t
ransferred
f
rom
t
he
o
ptical
t
o
t
he
e
lectrical
d
omain.
S
everal
d
ifferent
m
odulation
f
ormats
b
ased
o
n
t
he
m
odulation
o
f
a
ll
f
our
q
uadratures
o
f
t
he
o
pti-
cal
eld
w
ere
p
roposed
i
n
t
he
e
arly
1
990s,
d
escribing
t
he
p
ossible
t
ransmitter
a
nd
r
eceiver
s
tructures
a
nd
c
alculating
t
he
t
heoretical
b
it
e
rror
r
ate
(
BER)
p
erformance.
H
owever,
a m
ore
d
etailed
a
nd
p
ractical
i
nv