
221
6
Advanced Modulation Format Optical Transmitters
Following the presentation of optical modulation in the direct and external modulation in
C
hapter
5
,
t
his
c
hapter
p
resents
a
dvanced
m
odulation
f
ormats
o
f
l
ight
w
ave
s
ources
v
ia
ex
ternal
m
odulators.
T
his
i
s
a
n
ex
tension
o
f
t
he
m
odulation
e
mploying
o
ptical
m
odula-
tors
c
onnected
a
t
t
he
o
utput
o
f
a
c
ontinuous-wave
(
CW)
l
aser
s
ource.
T
he
l
aser
i
s
t
hus
t
urned
o
n
a
t
a
ll
t
imes
a
nd
t
he
g
enerated
o
ptical
C
Ws
a
re
t
hen
m
odulated
i
n
t
erms
o
f
f
re-
quency,
phase, and/or amplitude through an external optical modulator. Hence, the pulse
s
equence
t
hat
e
nvelops
t
he
c
arrier
p
hase
o
r
f
requency
u
nderneath
c
an
b
e ...