
328 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
phase
signal
is
perfectly
modulated
such
that
it
acts
in
phase
or
in
counterphase
with
the
LO,
t
he
h
omodyne
d
etection
w
ould
g
ive
a n
ormalized
s
ignal
c
urrent
o
f
i
T
n n t T
sC p LO
= +
≤ ≤
1
2
2 2 0
2
∓ for (8.34)
Assuming
further
that
n
p
= n
LO
, the number of photons for the LO for generation of
detected
signals,
then
the
current
can
be
replaced
with
4n
p
for the detection of a “1” and
nothing
f
or
a “
0”
s
ymbol.
8.3.2.3 Linewidth
I
nuences
8.3.2.3.1 Heterodyne Phase Detection
When
the
linewidth
of
the
light
sources
is
signicant,
the
IF
deviates
due
to
a
phase
uc-
tuation
and