
261Advanced Modulation Format Optical Transmitters
6.8 Remarks
Since the advent of the optical circular waveguide and the proposed dielectric waveguide
n
ow,
t
he
e
mployment
o
f
m
odulation
t
echniques
i
s
e
xtensively
e
xploited
b
ecause
o
f
t
he
a
vailability
o
f
o
ptical
a
mpliers.
T
he
m
odulation
f
ormats
a
llow
t
ransmission
e
fciency,
a
nd
u
ltra-high
c
apacity
i
nformation
t
elecommunications
h
as
b
ecome
m
ore
e
conomical.
O
ptical
c
ommunications
h
ave
e
volved
s
ignicantly
t
hrough
s
everal
p
hases
f
rom
s
ingle-mode
s
ys-
tems
to coherent detection and modulation, developed with the main aim of improving
o
ptical
p
ower.
T
he
o
ptical
a
mpliers
d
efeated
t
he
m
ai ...