Internati
o
nal
Journal of Ele
c
trical
and Computer
Engineering
(IJE
CE)
Vol
.
4
,
No
. 5, Oct
o
ber
2
0
1
4
,
pp
. 76
7~
78
1
I
S
SN
: 208
8-8
7
0
8
7
67
Jo
urn
a
l
h
o
me
pa
ge
: h
ttp
://iaesjo
u
r
na
l.com/
o
n
lin
e/ind
e
x.ph
p
/
IJECE
Implementation of Opti
cal
OFDM Bas
e
d Syst
em f
o
r Optical
Network
s
BU Rin
dhe
*,
Jyothi
Di
gge**, SK Narayankhed
k
ar
***
*Sant Gadge Baba Amravati Univ
ersity
, Amravati and
Smt Indira
Gandhi
College of
Engin
eerin
g
**Sant Gadge B
a
ba Amarav
ti U
n
iversity
***Sant
Gadge Baba
Amravati University
and MGM
CET
Article Info
A
B
STRAC
T
Article histo
r
y:
Received Dec 1, 2013
Rev
i
sed
Au
g
10
, 20
14
Accepted Aug 25, 2014
Orthogonal fr
eq
uency
d
i
vision
m
u
ltiplexi
ng
(O
FDM), a frequ
ency
div
i
sion
m
u
ltiplexing sch
e
m
e
utili
zed
as a digit
a
l m
u
lti-
carrier m
odulatio
n techniqu
e,
implemented us
ing optical
fi
ber link
for practical
appli
cat
ion
s
there
b
y
develop
i
ng optical OFDM using OptS
im
simulation
.
OFDM has m
a
n
y
advantages over
other
modul
ation techniques s
u
ch as
a high
r
e
sistance to
inter-s
y
m
bol in
terferen
c
e (ISI)
and it
is robust against fad
i
ng
caused
b
y
m
u
ltipath propa
gation
.
Optica
l
fi
ber cable (OF
C
) as
a trans
m
iss
i
on m
e
dia is
used for distortion less transmission of
data at
a
ver
y
h
i
gher data
speed. OFC
cable has a lo
t o
f
advantages over ot
her media. And OFDM over
OFC cable
will provide dat
a
speeds at a ver
y
high
speed a
nd with ver
y
les
s
losses. In
this work optica
l
transm
itter
and
rece
iver for OFDM based optic
al network
has designed
fo
r high speed d
a
ta transmission over op
tical
fi
ber
.
While
modeling the
s
y
stem we have also
used post, pre and
sy
mmetric
compensation technique to
reco
nfigure th
e ban
d
width along with add drop
m
u
ltiplexe
r,
tu
nable
fil
t
ers
a
nd opti
cal
am
plifie
rs to
ach
ieve
high
performance with minimum distortion
and low
b
it
error r
a
te (BER).
Keyword:
Bit erro
r
rate
Inter
-
sy
m
bol interfe
re
nce
Optical
fi
ber
c
a
bl
e
Optical O
F
DM
Su
b ca
rri
er
m
odul
at
i
o
n
Copyright ©
201
4 Institut
e
o
f
Ad
vanced
Engin
eer
ing and S
c
i
e
nce.
All rights re
se
rve
d
.
Co
rresp
ond
i
ng
Autho
r
:
BU Rind
h
e
Sant
Ga
dge
B
a
ba
Am
ravat
i
Uni
v
ersi
t
y
, Ta
po
va
n R
o
ad
C
a
m
p
, Am
ravat
i
4
4
4
6
0
2
,
I
n
di
a an
d
Sm
t
In
di
ra Ga
nd
hi
C
o
l
l
e
ge o
f
E
ngi
neeri
n
g
,
Pl
ot
N
o
.
1
7
& 18
,
Sec
-
16
, Ko
par
k
hai
r
ane
,
N
a
vi
M
u
m
b
ai
4
007
09
, Ind
i
a.
Em
a
il: b
u
r
indhe@yaho
o
.co
m
1.
INTRODUCTION
In
or
der t
o
e
x
p
l
oi
t
opt
i
cal
ban
d
wi
dt
h wi
t
h
m
o
re e
ffi
ciently, recently optical OFDM as a special case
of
o
p
t
i
cal
su
b
carri
e
r
m
odul
at
i
on
(SC
M
)
was i
n
t
r
o
d
u
ce
d i
n
t
h
e
opt
i
c
al
dom
ai
n, an
d a
n
a
dva
nce
d
o
p
t
i
cal
OFDM (OOFDM) m
o
du
latio
n techn
i
qu
e
was
p
r
op
o
s
ed
[1
],
[2
].
On
e
of th
e m
a
in
reaso
n
s for su
itabilit
y o
f
OFDM in
op
tical co
mm
u
n
i
c
a
tio
n
s
is its ab
ilit
y to
d
eal with
larg
e pu
lse
sp
read
s
d
u
e
to ch
ro
m
a
t
i
c d
i
sp
ersi
o
n
(C
D)
by
di
vi
di
ng t
h
e b
r
oa
d o
p
t
i
cal
chan
nel
spect
r
u
m
(for
whi
c
h t
h
e di
s
p
ersi
o
n
e
ff
ect is large) int
o
a num
b
er
of s
u
b-cha
n
nel
s
each with a narrow s
p
ectrum which decre
a
ses the dispe
r
sion e
ff
ect for each sub-c
h
a
n
nel [3],
[4
]. A m
a
in
mo
tiv
atio
n
for in
tro
d
u
c
ing
OFDM in
th
e
o
p
t
ical d
o
m
a
i
n
is
th
e p
o
ssib
ility fo
r h
i
g
h
-sp
e
ed
d
a
ta
transm
ission over dis
p
ersi
ve
fi
be
r wit
h
out t
h
e
need for cos
tly optical
di
sp
ersi
o
n
c
o
m
p
ensat
i
on t
e
c
hni
qu
es [
5
]
.
The
basi
c c
o
n
cept
be
hi
n
d
O
F
DM
i
s
t
h
e
di
vi
si
o
n
of a
hi
g
h
bi
t
rat
e
dat
a
st
ream
i
n
t
o
several
l
o
w
bi
t
rat
e
st
ream
s, w
h
i
c
h a
r
e si
m
u
l
t
a
neo
u
sl
y
m
odu
l
a
t
e
d o
n
t
o
o
r
t
h
og
o
n
al
s
ubca
r
r
i
ers as s
h
ow
n
bel
o
w i
n
Fi
g
u
r
e 1.
I
n
gene
ral
,
t
h
e
su
b-ca
rri
er
s are
gene
rat
e
d i
n
t
h
e di
gi
t
a
l
d
o
m
a
in and t
h
ere
f
ore these sy
stems typ
i
cally co
nsist o
f
many subca
rri
ers (typically m
o
re than 50). In t
h
ese sy
stem
s, ch
an
n
e
l esti
m
a
tio
n
is realized
b
y
p
e
riod
ically
i
n
sert
i
n
g t
r
ai
ni
ng
sy
m
bol
s. I
n
fi
be
r-optic transm
ission syste
m
s, the OF
DM syste
m
s where the
subcarriers are
gene
rat
e
d i
n
t
h
e o
p
t
i
cal
do
m
a
i
n
are al
so pr
o
pose
d
. T
h
e
s
e syste
m
s are som
e
tim
es re
ferred to as c
ohe
re
nt
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
I
J
ECE Vo
l. 4
,
N
o
. 5
,
O
c
tob
e
r
20
14
:
767
–
7
81
76
8
wav
e
len
g
t
h
d
i
v
i
sion
m
u
ltip
l
e
xin
g
(C
O-WDM) system
s.
Co
h
e
ren
t
WDM syste
m
s typ
i
cally h
a
v
e
few
sub
car
ri
ers a
n
d
d
o
not
use
t
r
ai
ni
n
g
sy
m
bol
s,
but
rel
y
o
n
bl
i
n
d c
h
an
nel
est
i
m
a
t
i
on i
n
st
ead
[6]
,
[
7
]
,
[
8
]
,
[9
]
.
Fi
gu
re
1.
S
p
ect
rum
of
FDM
&
OF
DM
si
gnal
1.
1
Ma
them
a
t
i
c
al
Form
ul
a
t
i
o
n
of
an
OF
D
M
Si
gn
al
OFDM is a special class of m
u
lti carrier
modula
t
i
on
(M
C
M
) [1
0]
, [
1
1]
, [1
2]
. The M
C
M
t
r
ansm
it
t
e
d
si
gnal
s
(
t
)
i
s
re
prese
n
t
e
d
as
gi
ven
i
n
e
q
uat
i
o
ns
1,
2
an
d
3.
(1
)
(2
)
1,
0
T
0
,
0
,
(3
)
Where
C
ki
is th
e in
fo
rmatio
n
sy
m
b
o
l
at th
e k
th
su
bc
arrier
, S
k
is the
wave
fo
rm
for
the k
th
s
u
bcarrier, N
sc
i
s
t
h
e num
ber of s
ubca
rri
er
, f
k
is
the freque
n
cy of the subca
rrier and T
s
i
s
the sym
bol
peri
od
,
∏
(t) is the pulse
sh
ap
ing
fun
c
tio
n.
1.
2
Spectra
l Effciency
fo
r Optica
l OFDM
In di
rect
det
e
c
t
i
on opt
i
cal
O
F
DM
(D
DO
-
O
F
D
M
)
system
s, th
e o
p
tical sp
ectru
m
is
u
s
ually n
o
t
a
l
i
n
ear repl
i
ca o
f
t
h
e radi
o fre
que
ncy
(R
F) s
p
ec
trum
therefore;
th
e optical spectral e
ffi
ciency is dependent on
th
e d
e
tailed
i
m
p
l
em
en
tatio
n
.
Th
ese wo
rk
s
c
once
n
trate on the optical spectral e
ffi
ciency for cohere
nt optical-
OF
DM
(C
O-
O
F
DM
)
sy
stem
s [1
3]
,
[1
4]
, [
1
5
]
, [1
6]
. I
n
C
O
-OF
D
M
sy
stem
s, N
sc
s
u
bcarrie
r
s are
transm
itted in
every
OF
DM
s
y
m
bol
peri
od
o
f
T
s
. T
h
us, t
h
e
t
o
t
a
l
sym
bol
ra
t
e
R
for C
O
-
O
FDM
sy
st
em
s is gi
ve
n
by
eq
u
a
t
i
on
4.
(4
)
The bel
o
w Fi
g
u
re 2
(a) s
h
o
w
s t
h
e spect
rum
of wa
vel
e
n
g
t
h
-di
v
i
s
i
on m
u
l
t
i
pl
exe
d
(
W
DM
) cha
nnel
s
,
each with CO-OFDM m
odulation, a
nd
Figure
2 (b
) s
h
ows t
h
e z
o
omed-in
optical spectrum
for eac
h
wavel
e
ngt
h ch
annel
.
It
uses
t
h
e ba
nd
wi
dt
h
of t
h
e
fi
rst
n
u
l
l
t
o
den
o
t
e
t
h
e b
o
u
n
d
ary
of eac
h wa
vel
e
ngt
h
chan
nel
.
The
F
i
gu
re 2
(
b
)
s
h
o
w
s OF
DM
ban
d
wi
dt
h,
B
OFDM
, i
s
t
h
us
gi
ve
n
b
y
equat
i
o
n
5.
2
1
(5
)
Evaluation Warning : The document was created with Spire.PDF for Python.
IJECE
ISS
N
:
2088-8708
Im
pl
eme
n
t
a
t
i
o
n of
O
p
t
i
c
al
O
F
DM Base
d Sy
st
em
f
o
r
O
p
t
i
c
al
N
e
t
w
orks
(
B
U Ri
nd
he)
76
9
Fi
gu
re
2.
O
p
t
i
cal
Spect
r
u
m
fo
r (a
)
N-
wa
vel
e
ngt
h
di
vi
si
o
n
m
u
lt
i
p
l
e
xed C
O
-
O
F
D
M
c
h
an
nel
s
,
(b
)
Zo
om
ed-i
n O
F
DM
si
g
n
al
fo
r
one
wa
vel
e
n
g
t
h
Whe
r
e t
s
i
s
the o
b
ser
v
at
i
o
n pe
ri
o
d
as s
h
o
w
n i
n
Fi
g
u
r
e 3.
Ass
u
m
i
ng t
h
at
a l
a
rg
e num
ber o
f
subcarriers a
r
e
use
d
, t
h
e
bandwidth e
ffi
ci
enc
y
of
OF
DM
i
s
fo
u
n
d
t
o
be gi
v
e
n by
eq
uat
i
o
n 6.
2
2
,
(6
)
Fi
gu
re
3.
Ti
m
e
d
o
m
a
i
n
OFD
M
si
gnal
f
o
r
o
n
e c
o
m
p
l
e
t
e
OFDM
sy
m
bol
The fact
or
of 2 accounts fo
r two
polarizations in t
h
e
fi
ber.
Usi
n
g a t
y
pi
cal
val
u
e
of
8/
9
,
t
o
o
b
t
a
i
n
t
h
e
optical spectral
e
ffi
ci
ency
fact
or of 1.
8
dB
/
H
z. The optical spectral e
ffi
cien
cy g
i
v
e
s
3
.
6
bit/s/Hz if q
u
a
tern
ary
pha
se-s
hift ke
ying (QPS
K)
m
odulation is use
d
for each
subcarrier. T
h
e spectral e
ffi
c
i
ency can be furt
her
im
pro
v
ed
by
u
s
i
ng
hi
g
h
er
or
der
QAM
m
o
d
u
l
a
t
i
on t
o
pr
ac
t
i
cal
l
y
im
pl
ement
C
O
-
O
F
D
M
sy
st
em
s, t
h
e opt
i
cal
spectral e
ffi
cien
cy will b
e
red
u
c
ed
d
u
e
t
o
th
e n
e
ed
for a su
ffi
ci
ent
g
u
a
r
d ba
nd bet
w
e
e
n WDM
c
h
a
nnel
s
,
t
a
ki
ng
acc
ou
nt
o
f
l
a
ser
f
r
eq
u
e
ncy
d
r
i
f
t
of
a
p
p
r
oxi
m
a
t
e
ly
2
GHz
. T
h
i
s
g
u
ar
d
ba
nd
can
be a
v
oi
de
d
b
y
usi
n
g
o
r
t
h
ogo
n
a
lity acro
s
s th
e
WDM ch
an
n
e
ls.
1.
3
Optic
a
l OF
DM B
a
sics
1.
3.
1
Cros
s-ch
an
nel
OF
DM
: m
u
l
t
i
p
l
e
xi
ng w
i
t
h
o
u
t
gu
ard
ba
nd
Th
e laser fr
equen
c
y dr
if
t of
W
D
M ch
an
n
e
l
s
can
b
e
reso
l
v
ed
b
y
lo
ck
i
n
g
all th
e lasers to th
e co
mm
o
n
optical standa
rd s
u
c
h
as
an
optical
com
b
an
d
di
rect
l
y
usi
n
g t
h
e f
r
e
que
nc
y
t
ones
f
r
om
an
opt
i
cal
c
o
m
b
. Al
l
t
h
e
subcarriers tha
t
cross t
h
e
WDM ch
ann
e
ls
can
be ortho
gon
al; th
at is, the o
r
t
h
ogo
n
a
l
i
t
y
co
nd
itio
n
is
satis
fi
ed
fo
r any
tw
o s
u
bcar
riers, e
v
e
n
fr
om
di
ff
er
en
t
W
D
M ch
annels. A
s
sh
own in
Figu
r
e
4
cr
o
s
s-
ch
ann
e
l
O
F
D
M
(XC-OFDM)
with
ou
t gu
ard
b
a
nd
, the sub
c
arrier in
ch
an
nel 1
is o
r
tho
gon
al to
an
othe
r subcarrier in a di
ff
ere
n
t
channel.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
I
JECE Vo
l. 4
,
N
o
. 5
,
O
c
tob
e
r
20
14
:
767
–
7
81
77
0
Fi
gu
re
4.
O
p
t
i
cal
spect
r
u
m
for
di
vi
si
on
cr
oss
-
chan
nel
OF
D
M
(XC
-
O
F
DM
) wi
t
h
o
u
t
gua
r
d
ban
d
2.
BLOCK D
I
AG
RA
M OF
OPTI
C
A
L
ORT
H
OGO
NAL FREQ
UEN
C
Y
DI
VISI
ON
MULTIPLE
X
ING (O
OF
DM)
Fi
gu
re
5.
O
O
F
D
M
si
m
u
l
a
t
i
on set
u
p
Fi
gu
re 6.
D
u
al
dri
v
e
M
Z
IM
The M
Z
M
us
ed i
n
t
h
e ab
o
v
e bl
oc
k di
a
g
r
a
m
Fi
gure 5 i
s
dual
d
r
i
v
e
M
Z
M
.
A d
u
al
dri
v
e M
ach
-
Zeh
nde
r i
n
fe
r
o
m
e
t
e
r
m
odul
at
or (M
Z
I
M
)
i
s
c
h
i
r
p free m
o
d
u
l
at
or i
s
sh
ow
n
i
n
ab
ove Fi
gu
r
e
6. T
h
e M
Z
I
M
used
in
th
e
Figu
re
6
is Lith
i
u
m
Niob
ate b
a
sed, th
e
p
u
rp
o
s
e of
ch
oo
sing
t
h
is m
a
teria
l
is i) It is electro
op
tic in
n
a
ture ii) Less
lo
ss MZIM
u
s
ed
h
e
re is of “Z” cu
t. It
s esse
ntial that the MZIM has a t
y
pical phase
re
sponse
,
suc
h
that it
will function as
a
m
odulat
or e
ffe
ctively in the a
b
ove
set up.
The Fi
gu
re
6 s
h
o
w
s t
h
e ‘
Y
’
bra
n
c
h
i
n
t
e
n
s
i
t
y
m
odul
at
o
r
. T
h
e
hat
c
he
d re
g
i
on i
s
a
swi
t
c
h
i
ng
part
o
n
whi
c
h t
h
e p
h
a
s
e ret
a
rdat
i
o
n
of t
h
e l
i
g
ht
(a
ct
ual
l
y
refract
i
v
e i
nde
x
of t
h
e wave
-g
ui
de
)
i
s
vari
ed. T
h
e
devi
ce
param
e
t
e
rs are
ang
u
l
a
r
sepa
rat
i
on
bet
w
ee
n t
h
e a
r
m
s
22
0
, I
n
dex
di
f
f
e
rence
o
f
2
.
3
% ga
p
bet
w
een t
h
e
electrodes
is
4
m
l
e
ngt
h
o
f
t
h
e a
r
m
200
0
0
m,
V
= 5 V.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Im
pl
eme
n
t
a
t
i
o
n of
O
p
t
i
c
al
O
F
DM Base
d Sy
st
em
f
o
r
O
p
t
i
c
al
N
e
t
w
orks
(
B
U Ri
nd
he)
77
1
Wh
en
th
e refractiv
e in
d
e
x
o
f
th
e switch
i
ng
reg
i
o
n
is no
t varied
, th
e two
lig
h
t
b
eam
s are co
m
b
in
ed
wi
t
h
sam
e
phase ret
a
rdat
i
on
(I
n p
h
ase
)
at
t
h
e ‘
Y
’ c
o
m
b
i
n
er. T
h
ere
f
o
r
e
alm
o
st
100
% l
i
ght
t
r
ansm
i
ssi
on i
s
achi
e
ve
d i
n
t
h
e out
put
w
a
ve
-g
ui
de
, as sh
o
w
n i
n
t
h
e Fi
g
u
re
7 (a
). T
h
i
s
con
d
i
t
i
on i
s
k
n
o
w
n as co
nst
r
uct
i
v
e
in
terferen
c
e.
Wh
en
th
e
refractiv
e in
d
e
x
of
t
h
e swi
t
c
hi
n
g
r
e
gi
o
n
i
s
va
ri
ed
by
n
,
th
e
relativ
e p
h
a
se retard
ation
betwee
n t
h
e t
w
o arm
s
bec
o
mes (
=
.L) whe
r
e L denotes
the
le
ngth of
th
e switch
i
n
g
reg
i
on
,
i.e. two
p
a
rallel arm
s
. If th
e relativ
e
ph
ase
retard
ation
satisfies equ
a
tio
n
7
.
2
..
LL
ne
ff
(7
)
Th
en
th
e two
lig
h
t
b
eam
s are co
m
b
in
ed
with
an
ou
t o
f
p
h
a
se con
d
ition
at th
e “Y” co
m
b
in
er as
sh
own
in th
e
Fig
u
re
7
(b). This con
d
ition
is
k
nown as
d
e
stru
ctiv
e in
terferen
ce.
Here th
e
n
e
ff
is a
variation
o
f
effect
i
v
e
i
n
dex
.
O
n
ce t
h
e i
n
t
e
nsi
t
y
m
odul
at
i
o
n
i
s
ac
hi
eve
d
OF
DM
si
gnal
s
are
fe
d as
V
1
(t) a
n
d
V
2
(t).
As we
requ
ire ortho
g
o
n
a
l sign
als.
Essen
tially th
ere are t
w
o sim
u
la
tio
n
set up
for OFDM. i) Ph
ase m
o
du
lated
OFDM syste
m
, ii)
Am
plitude m
odulated
OF
DM
system
.
In our study, we
have conside
r
ed phase m
odulated and am
pllitude
OF
DM. Two
sim
u
lation set up
for ph
ase
m
odulated OF
DM system
and
am
plitude
m
o
dulated syste
m
are
depi
ct
ed
i
n
Fi
g
u
re
8
an
d
Fi
g
u
r
e
9.
Fig
u
re
7
.
a) C
o
n
t
ru
ctiv
e in
te
rference
for zero phase s
h
ift,
b)
D
e
stru
ctiv
e in
ter
f
e
r
e
n
c
e fo
r
phase s
h
ift
Fi
gu
re
8.
B
l
oc
k
di
ag
ram
of o
p
t
i
cal
OF
DM
s
y
st
em
usi
ng
p
h
a
se m
odul
at
i
o
n
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
I
J
ECE Vo
l. 4
,
N
o
. 5
,
O
c
tob
e
r
20
14
:
767
–
7
81
77
2
Fi
gu
re
9.
B
l
oc
k
di
ag
ram
of a
n
opt
i
cal
O
F
D
M
sy
st
em
usi
n
g am
pl
i
t
ude m
o
d
u
l
a
t
i
o
n
The Fi
g
u
r
e 8
and Fi
g
u
re
9 s
h
o
w
s a bl
oc
k di
ag
ram
of fi
b
e
r o
p
t
i
c
com
m
uni
cat
i
o
n sy
st
em
based o
n
opt
i
cal
OF
DM
, i
n
w
h
i
c
h t
h
e
FT bl
oc
ks ar
e im
pl
em
ent
e
d in o
p
t
i
cal
dom
ai
n usi
n
g t
h
e
Fo
uri
e
r t
r
a
n
s
f
o
r
m
i
ng
pr
o
p
ert
y
o
f
t
i
m
e
l
e
nses.
In
t
h
e
pr
o
pose
d
s
c
hem
e
, t
h
e com
b
ined signal
dri
v
es the
Ma
ch-Ze
h
nde
r m
o
dulator
(M
ZM
).
I
n
c
o
nt
rast
,
i
n
t
h
e c
a
se o
f
el
ect
ri
c
a
l
OF
DM
, m
e
ssage
si
g
n
al
s
f
r
om
vari
ous
c
h
an
nel
s
m
odul
at
e
t
h
e
sub
-
ca
rri
ers t
h
r
o
u
g
h
IFF
T
. T
h
e out
p
u
t
o
f
t
h
e
fi
ber
-
o
p
t
i
c
l
i
nk passes t
h
r
o
u
gh a FT
. Si
nce
Fou
r
i
e
r t
r
a
n
sf
orm
of
a Fo
urier tran
sform
lead
s to
ti
m
e
rev
e
rsal with
in
a
OFDM
fram
e
, th
e tran
smitted
sig
n
a
l
can
b
e
recov
e
red
b
y
i
n
t
r
o
d
u
ci
n
g
t
i
m
e reversal
us
i
ng
di
gi
t
a
l
si
gn
al
pr
ocessi
ng.
In t
h
e case of
cohe
re
nt optical/electrical O
F
DM,
a
pha
se c
h
i
r
p
i
s
i
n
t
r
od
uce
d
ac
ross
t
h
e
f
r
am
e d
u
e t
o
fi
ber
di
spe
r
si
ve
ef
fe
ct
s w
h
i
c
h ca
n
be
cancel
l
e
d
usi
n
g
equalization al
gorithm
s
. However, in the
cas
e of
direct
detection e
q
ualizer is not
nee
d
ed, since t
h
e
output of
the direct dete
ction receive
r
is propor
tional
to the absol
u
t
e
squa
re of th
e field envel
ope. To investiga
t
e th
e
per
f
o
r
m
a
nce o
f
t
h
e
o
p
t
i
cal
O
F
DM
,
b
o
t
h
c
o
here
nt
an
d
di
rect d
e
tectio
n
sch
e
m
e
s are si
mu
lated
an
d th
e
b
it error
rate (BER) is calculated at the recei
ve
r
as a
function of optical
signal-to
-noise ratio (OSNR). The
OSNR is
cal
cul
a
t
e
d bas
e
d o
n
0
.
1
nm
noi
se
ban
d
w
i
d
t
h
. Fi
be
r n
o
n
l
i
n
eari
t
y
and am
pl
i
f
i
e
d s
p
o
n
t
a
n
e
ou
s em
i
ssi
on
(AS
E
)
noise a
r
e both
taken int
o
account in t
h
e sim
u
lation. T
h
e
num
ber of sub-channels is
2048
and t
h
e cyclic pre
f
ix
of l
e
n
g
t
h
51
2 i
s
adde
d as t
h
e
gua
r
d
i
n
t
e
rv
al
bet
w
ee
n OF
D
M
fram
e
s. Each o
f
t
h
e su
b-c
h
an
nel
s
co
nsi
s
t
s
of a
BPSK si
g
n
a
l at
a b
it rate of 19
.
5
M
b
/s and
the to
tal in
form
a
tio
n
rate is
4
0
Gb
/s. In
th
e case o
f
d
i
rect
d
e
tection
OF
DM
, a cons
t
a
nt
bi
as vol
t
a
ge i
s
adde
d at
the i
n
p
u
t
of M
Z
M
so t
h
at
t
h
e out
p
u
t
of M
Z
M
i
s
an on-
of
f key
i
n
g
(O
OK
) si
gnal
.
The t
r
an
sm
i
s
si
on
fi
be
r i
s
a
s
t
anda
rd
si
n
g
l
e
-
m
ode fi
ber
(
S
SM
F).
The
pa
r
a
m
e
t
e
rs of
t
h
e
fi
be
r
and
ot
he
r sy
st
em
co
m
pone
nt
s are l
i
s
t
e
d. Th
ere i
s
no di
s
p
e
r
si
o
n
com
p
ens
a
t
i
ng m
odul
e (
D
C
M
) pl
ace
d i
n
t
h
e
fib
e
r link
.
Th
e a
m
p
lifier sp
an
is 80
k
m
with
5
sp
an
s, so th
e to
tal tran
smissio
n
d
i
stance is 4
0
0
k
m
. A De
Bruiji
n seque
n
ce of length 211 is us
ed i
n
each of the sub-c
h
annel in th
e
Monte-Ca
rlo si
m
u
la
tion and the total
num
ber o
f
OF
DM
fram
e
s i
s
50
. The acc
um
ul
at
ed di
s
p
ersi
on
β
2
F
in
ti
m
e
-len
s-b
a
sed
Fou
r
ier tran
sformer is
0
.
10
1
9
ns
2, w
h
ere
F
i
s
t
h
e
f
i
ber l
e
ngt
h a
n
d
β
2
is t
h
e
d
i
sp
ersi
o
n
of t
h
e
stan
d
a
rd SMF
u
s
ed
in th
e time len
s
setup.
The two im
portant buildi
ng
blocks
of OOFDM syst
e
m
ar
e transm
itter and
receive
r. T
h
e com
ponent
that constitutes the tra
n
sm
itter
and
receive
r a
r
e prese
n
ted
in Figure 10
a
n
d Figure 11.
Fig
u
re 10
. OFDM
tran
sm
it
te
r
Evaluation Warning : The document was created with Spire.PDF for Python.
I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Im
pl
eme
n
t
a
t
i
o
n of
O
p
t
i
c
al
O
F
DM Base
d Sy
st
em
f
o
r
O
p
t
i
c
al
N
e
t
w
orks
(
B
U Ri
nd
he)
77
3
Thi
s
c
o
m
pou
n
d
c
o
m
pone
nt
si
m
u
l
a
t
e
s an
OF
DM
t
r
a
n
sm
i
t
t
e
r c
o
m
posed
o
f
:
PRBS d
a
ta
source
SEPAR
m
o
d
e
l to
p
e
rform
th
e co
nv
ersion
serial to
p
a
rallel
M
QAM
OD
IQ
m
odel
t
o
ge
ner
a
t
e
t
h
e b
a
seba
n
d
I/
Q c
o
m
pone
nt
s
of
Q
A
M
sy
m
bol
IFFT
OFDM t
o
calculate t
h
e
IFFT
on t
h
e
Q
A
M
sy
m
bol
an
d
obt
ai
n
t
h
e
O
F
DM
sy
m
bol
QU
A
D
M
I
XI
Q
m
odel
t
o
q
u
a
d
r
a
t
u
re m
i
x u
p
t
h
e OF
DM
si
gna
l
fr
om
baseba
n
d
t
o
car
ri
er
fre
que
ncy
Figure 11. OFDM
recei
ver
This c
o
m
pound c
o
m
pone
nt si
m
u
lates an
OF
DM recei
ver c
o
m
posed of:
QU
A
D
M
I
XI
Q
m
odel
t
o
q
u
a
d
r
a
t
u
re m
i
x d
o
w
n
t
h
e
R
F
m
o
d
u
l
at
ed OF
DM
si
gnal
t
o
base
ba
nd
Two
Bessel
filters to filter
ou
t th
e
rep
lica
o
f
th
e si
g
n
a
l cen
t
ered at twice th
e carrier freq
u
e
n
c
y
FFTOFDM
m
o
d
e
l to
calcu
late th
e FFT
on
the OFDM sym
b
o
l
to
reco
v
e
r t
h
e QAM sym
b
o
l
MQADEMIQ
m
o
d
e
l to
retriev
e
th
e p
a
ralle
l
l
ogi
cal
si
g
n
al
f
r
om
t
h
e Q
A
M
sym
bol
PAR
S
E
V
m
odel
t
o
perf
orm
t
h
e con
v
e
r
si
o
n
paral
l
e
l
t
o
seri
al
and rest
or
e t
h
e t
r
ansm
i
tted seri
al
bi
na
r
y
sequence
The o
p
t
i
cal
ph
ase
m
odul
at
or
con
s
i
d
ere
d
f
o
r
si
m
u
l
a
ti
on op
erat
es
at
re
fere
nce wavel
e
ngt
h 15
5
0
nm
wi
t
h
di
spe
r
si
o
n
1
6
ps/
n
m
/
km
. The fi
ber c
onsi
d
ere
d
he
re
has 0.
2 dB
l
o
ss/
km
. The l
e
ngt
h = 3 km
. The Laser
s
o
ur
c
e
u
s
ed
h
e
r
e
a
r
e of
th
r
e
e typ
e
s
.
a sim
p
le
m
o
d
e
l con
s
id
ering
on
ly th
e
p
h
a
se
no
ise (C
W Loren
t
zian
Laser)
a real
i
s
t
i
c
m
odel
base
d
on
rat
e
eq
ua
tio
n in
teg
r
ation
(Rate Eq
u
a
tion
s
Laser)
a realistic
m
o
d
e
l b
a
sed
on
rate equ
a
tio
n
in
teg
r
atio
n
for Sep
a
rate confin
em
en
t h
e
tero
stru
cture m
u
l
t
i
qua
nt
um
wel
l
l
a
sers
(SC
H
-M
Q
W
)
wh
ere
p
h
y
sical
p
a
ram
e
ters o
f
th
e laser can
be o
b
t
ai
n
e
d
with
a fitting
proced
ure
o
v
e
r ex
perim
e
n
t
al
ly
measured curves.
The
detector s
ection c
o
m
p
rises of
PIN and
APD. T
h
e
qua
n
tum
effici
enc
y
, res
p
o
n
sivity
, da
rk
cu
rre
nt
and
3
dB
ba
n
d
w
i
d
t
h
val
u
es a
r
e 0.
7,
0
.
8
7
5
1
,
2.
5
nA
an
d
2
0
GHz
.
The Dispe
r
sion
section defi
nes
the dispe
r
si
on
cha
r
act
erist
i
cs of the
fibe
r. Se
co
nd
, th
ird, fo
ur
th and
fi
ft
h
or
de
r di
s
p
ersi
o
n
co
ef
fi
ci
ent
s
are t
a
ken
i
n
t
o
acc
ou
nt
.
Yo
u m
a
y
di
r
ectly specify the coefficient val
u
es
or
su
pp
ly a d
e
scrip
tio
n
file. In
th
e latter case t
h
e file
m
u
st co
n
t
ain
t
h
e p
r
ofile o
f
d
i
sp
ersion
β
2
as a f
unct
i
on
o
f
fre
que
ncy
o
r
D
as a fu
nct
i
o
n o
f
wa
vel
e
n
g
t
h. Thi
s
feat
ur
e i
s
used t
o
i
n
t
r
o
duce
dat
a
fr
om
a
m
easured set
of
resul
t
s
.
I
n
a
d
d
i
t
i
on, a
ra
nd
o
m
vari
at
i
on
of
t
h
e sec
o
nd
o
r
de
r
di
spe
r
si
o
n
i
s
t
a
ken
i
n
t
o
acc
o
unt
usi
n
g
t
w
o
di
ffe
re
nt
st
at
i
s
t
i
cal
di
st
ri
but
i
o
ns a
n
d
a
defi
n
e
d c
o
r
r
el
at
i
on
l
e
ngt
h
.
T
h
e st
a
t
i
s
t
i
cal
vari
at
i
on
of
fi
be
r
di
sp
ersi
o
n
is em
ulated by a casca
de
of s
h
ort fi
ber spans the c
h
ar
acteristics of
which are
defi
ne
d at
the
begi
nning of a
sim
u
l
a
t
i
on. T
h
ese char
act
eri
s
t
i
c
s do
not
vary
du
ri
n
g
t
h
e si
m
u
l
a
t
i
on. A di
ffe
rent
ran
d
o
m
evol
ut
i
on
o
f
di
spe
r
si
o
n
m
a
y
be
o
b
t
a
i
n
ed
by
re
-si
m
ul
at
ing
t
h
e
p
r
o
j
ect
wi
t
h
a
di
ffe
re
nt
ra
n
dom
seed.
Fu
rt
he
rm
ore w
h
i
l
e
doi
ng t
h
e si
m
u
l
a
t
i
ons
, SPT
beha
vi
o
u
r
i
s
consi
d
ere
d
. Las
e
r so
urces are
consi
d
e
r
e
d
as i
f
t
h
ey
gener
a
t
e
d a
si
ngl
e t
o
ne at
t
h
e n
o
m
i
nal
cent
e
r em
i
ssi
on f
r
e
que
ncy
o
f
t
h
e s
o
ur
c
e
.
Th
er
e
f
o
r
e,
in
th
e
optical spectrum
a single
line is placed. Its level is equal to t
h
e de
fine
d lase
r
output power. Li
ne wi
dth is neglected if the
C
W
Lore
ntzian La
s
e
r is selected.
For the
rate equations
l
a
ser a
nd t
h
e c
u
st
om
m
u
lt
i
quant
um
wel
l
(M
Q
W)
l
a
ser,
t
h
ei
r o
u
t
p
ut
p
o
w
er c
o
ul
d
be f
o
u
n
d
o
n
l
y
usi
n
g t
i
m
e
-dom
ai
n sim
u
l
a
t
i
on. H
e
nce,
fo
r SP
T
sim
u
l
a
t
i
ons, t
h
e use
r
is ex
p
licitly req
u
e
sted
to
supp
ly th
e ou
tpu
t
p
o
wer. If
you
d
on’t kn
ow the av
erag
e
o
u
t
pu
t po
wer
o
f
the laser,
we suggest pe
rform
a virtual battle space (VBS) sim
u
la
ti
on
of t
h
e de
vi
ce only, m
eas
ure the
output powe
r,
an
d th
en
em
p
l
o
y
s th
e m
easu
r
ed
v
a
lu
e as SPT p
a
ram
e
ter for th
e laser.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
I
J
ECE Vo
l. 4
,
N
o
. 5
,
O
c
tob
e
r
20
14
:
767
–
7
81
77
4
3.
BLOCK D
I
AG
RA
M
OF OPTIC
A
L ORTH
OGO
NAL
FREQ
UEN
C
Y
DI
VISI
O
N
MULTIPLE
X
ING
(O
OF
D
M
)
FO
R B
A
N
D
WI
DTH
RE
CO
NFIG
U
R
A
TIIO
N
Figure 12. OFDM
recei
ver
with add
drop multiplexer
In
or
de
r t
o
e
n
h
a
nce t
h
e
pe
rf
or
m
a
nce of
O
O
F
D
M
l
i
n
k
use
d
i
n
ou
r si
m
u
l
a
t
i
on,
we
repl
ace
d
t
h
e si
m
p
l
e
m
u
l
tip
lex
e
r by an
ad
d-d
r
op
m
u
ltip
lex
e
r.
W
e
con
s
id
ered
10
Gb
/s
1
6
-ch
a
nn
els
wav
e
len
g
t
h
d
i
v
i
sion
m
u
l
tip
lex
i
n
g
(W
D
M
)
syste
m
w
ith
a 4
-
ch
ann
e
l s an
d
o
p
tical ad
d
dr
op
m
u
ltip
lex
e
r
(
OADM)
p
u
t
in
th
e
mid
d
l
e
of t
h
e fi
ber l
i
n
k.T
h
e t
r
ansm
i
t
t
e
r consi
s
t
s
o
f
16 l
a
ser s
o
u
r
c
e
s wi
t
h
wavel
e
ngt
h ran
g
i
n
g f
r
om
193.
0
35 T
H
z t
o
19
3.
7
85 T
H
z, t
h
e cha
nnel
sp
a
c
i
ng i
s
set
t
o
50 G
H
z fo
r 2
0
0
km
opt
i
cal
l
i
n
k. I
n
t
h
i
s
l
i
nk s
h
o
w
n i
n
Fi
g 1
2
, w
e
u
s
ed
po
st,
pre and
symmetric co
m
p
en
satio
n techn
i
qu
e
alo
n
g
with
tun
a
b
l
e
filters an
d d
i
fferen
t
op
tical
am
plifiers to e
nha
nce t
h
e
perform
a
nce.W
e
use
d
Fa
bry Pe
rot filter in
our
m
odule which
offers
tuning range
of
30
nm
i
n
1-1
0
m
s
.Whe
n we t
e
st
ed t
h
e l
i
nk wi
t
h
EDF
A
an
d R
a
m
a
n am
pli
f
i
e
r, ED
FA p
r
ove
d t
o
be t
h
e
best
,
offeri
ng wi
de
powe
r s
p
ectrum
with
a received power of
0.27 m
w
for a
n
i/p
of
1 m
w
for
200 km
optical
l
i
nk.
whi
c
h
ca
n be det
ect
ed usi
n
g
si
m
p
l
e
ph
ot
o det
ect
or
.
4.
METHO
D
OL
OGY
We ha
ve use
d
freq
u
e
n
cy
d
o
m
ai
n sim
u
l
a
ti
on m
o
d
e
l u
s
in
g Op
tSim
. Usin
g
Blo
c
k
m
o
d
e
l si
m
u
latio
n
m
ode, we c
o
ul
d e
ffeci
i
v
el
y
c
a
pt
u
r
e t
h
e
dy
n
a
m
i
c and t
r
a
n
s
i
ent
be
havi
or
o
f
t
h
e
o
p
t
i
cal
ne
t
w
o
r
k
.
F
o
r
t
h
e
choi
c
e
o
f
app
r
o
p
riate laser fo
r
o
u
r si
m
u
la
tio
n
,
we
used
“Best fit” Laser too
l
k
its.
W
e
in
terfaced Op
tSim
m
o
d
e
l with
“B
eam
Pro
p
ag
at
i
on m
odel
”
t
o
si
m
u
l
a
t
e
and
st
udy
t
h
e
cha
r
ect
ri
st
i
c
s of
L
i
hi
um
Ni
obt
e
base
d m
odul
at
or t
o
i
n
co
rp
orat
e i
t
i
n
t
h
e
net
w
o
r
k
m
odel
.
W
e
t
o
o
k
i
n
t
o
c
onsi
d
er
at
i
on “
pol
a
r
i
zat
i
on m
ode
di
sp
ersi
o
n
” (
P
M
D
)
effect
p
r
ov
id
ed
in
“Op
tiSi
m
m
o
d
e
l”.
W
e
h
a
v
e
u
s
ed
v
a
riou
s op
tical a
m
p
liers d
e
sig
n
e
d
u
s
i
n
g
b
u
ilt in
facili
ty o
f
th
is
soft
ware
. Fo
r
vari
ous t
y
pes
of
opt
i
cal
am
p
l
i
f
i
e
rs, t
h
e si
m
u
l
a
t
i
on
was ca
rri
ed
o
u
t
.
To c
o
m
b
at
di
spersi
on
, we
use
d
po
st
, pre
and sy
m
m
et
ri
c com
p
enst
i
on t
echni
que a
nd
obs
er
ved t
h
e e
y
e pat
t
e
rn an
d
com
p
ared t
h
e
B
E
R
per
f
o
r
m
a
nce i
n
a
b
ove
m
e
nt
ione
d
t
h
ree
cas
es. B
y
c
o
m
p
arin
g with earlier
find
ing
s
, where th
e PM
D
was
no
t
tak
e
n
i
n
to
co
nsid
eration
,
we p
r
ov
ed th
at op
ical OF
DM
with
PM
D con
s
id
eratio
n offers op
tim
u
m
v
a
lu
e
of
B
E
R
t
hus
val
i
d
at
i
ng
ou
r
res
u
l
t
s
.
5.
RESULTS
A
N
D
DI
SC
US
S
I
ON
In
or
der t
o
ach
i
e
ve a pr
o
p
er
OF
DM spectrum
,
it’s very essential
th
at th
e p
h
a
se sh
ift offered
b
y
th
e
m
odul
at
or i
s
a
ccurat
e
.
T
h
e m
o
d
u
l
a
t
o
r i
s
si
m
u
l
a
t
e
d at
t
h
e c
o
m
pone
nt
l
e
ve
l
.
It
s
resp
o
n
se
i
s
o
b
ser
v
e
d
a
n
d t
h
e
sam
e
param
e
t
e
rs a
r
e c
o
n
s
i
d
er
ed
whi
l
e
si
m
u
l
a
t
i
ng t
h
e
OF
D
M
bl
oc
k
di
ag
ra
m
.
The res
p
o
n
s
e i
s
s
h
o
w
n i
n
Fi
gu
re
13
(a
) a
n
d
(
b
)
.
Evaluation Warning : The document was created with Spire.PDF for Python.
I
J
ECE
I
S
SN
:
208
8-8
7
0
8
Im
pl
eme
n
t
a
t
i
o
n of
O
p
t
i
c
al
O
F
DM Base
d Sy
st
em
f
o
r
O
p
t
i
c
al
N
e
t
w
orks
(
B
U Ri
nd
he)
77
5
(
a
)
(
b
)
Fig
u
r
e
13
. a)
Pr
op
ag
atio
n of
l
i
g
h
t
f
o
r
zer
o
ph
ase sh
if
ts,
b) Prop
ag
ation
o
f
lig
h
t
wh
en
phase
sh
i
f
t
is
in
tro
d
u
c
ed
whe
n
OF
DM
s
i
gnal is
fed
The p
h
ase
res
p
o
n
se
of t
h
e m
odul
at
or i
n
c
l
ude
d i
n
t
h
e
OF
DM
bl
oc
k
di
agram
i
s
present
e
d i
n
F
i
g
u
r
e
13
.
Figure
14
.
Vari
atio
n
o
f
in
tensity with
th
e
applied
vo
ltag
e
T
h
e
m
odul
at
or
use
d
i
n
o
u
r
st
udy
i
s
pr
ot
o
n
e
x
ch
ange
d
Li
Nb
O
3,
wh
ose s
u
rface
i
nde
x c
h
an
ge
(
n
e
) is
lin
ear an
d th
e
v
a
riation
o
f
extraod
i
n
a
ry
refractiv
e ind
e
x ch
ang
e
with app
lied
vo
ltag
e
i
s
op
tim
u
m
to
ex
p
l
o
i
t
the largest elec
tro-
optic coe
ffi
cient r
33
f
o
r t
h
e
TE
pol
a
r
i
zed l
i
ght
.
Thi
s
i
s
sh
ow
n i
n
Fi
gu
re
14
an
d
Fi
g
u
re
15
.
Figure 15. Surface
inde
x cha
n
ge (
∆
n
e
)
verse
s
m
o
le fraction
0
0.
1
0.
2
0.
3
0.
4
0.
5
0.
6
0.
7
0.
8
0.
9
1
01234
56789
1
0
Vo
l
t
a
g
e
Nor
m
a
liz
e
d
In
te
n
s
it
y
0
0.
1
0.
2
0.
3
0.
4
0.
5
0.
6
0.
7
0.
8
0.
9
1
0.
02
0
.
0
4
0.
06
0
.
08
0.
1
0
.
1
2
M
a
x.
r
e
f
r
a
c
t
i
v
e
i
n
d
e
x c
h
a
n
g
e
o
n
t
h
e
su
r
f
a
c
e
H
+
F
r
a
c
ti
o
n
c
o
n
c
e
n
tr
a
t
i
o
n
Evaluation Warning : The document was created with Spire.PDF for Python.
I
S
SN
:
2
088
-87
08
I
J
ECE Vo
l. 4
,
N
o
. 5
,
O
c
tob
e
r
20
14
:
767
–
7
81
77
6
Fig
u
re
16
. Ex
trao
rd
in
ary refractiv
e in
d
e
x
cha
nge
s
verses
ap
pl
i
e
d
vol
t
a
ge
The a
b
o
v
e
res
u
l
t
s
sh
ow
n i
n
Fi
gu
re
14 a
n
d
Fi
gu
re
15
, e
n
sures
t
h
at
m
odul
at
or
use
d
i
n
ou
r
OF
DM
si
m
u
latio
n
b
l
ock
p
r
ov
id
es
op
ti
m
u
m
p
h
a
se sh
ift to
g
e
n
e
rate th
e OFDM
sig
n
a
l in
th
e o
p
tical d
o
m
ain
.
Th
is
sim
u
lation res
u
lts are
used in the
OFDM s
i
m
u
lation wind
ow to eval
uate the tra
n
sm
itted and
receive
d signa
l
p
o
wer sp
ectrum
fo
r qu
ad
rat
u
e am
p
litu
d
e
mo
du
latio
n (QAM) sign
al fo
llowed b
y
t
h
e co
nstellatio
n
d
i
agra
m
.
By co
m
p
aring the transm
itte
d an
d receive
d powe
r spectrum
of th
e OFDM sym
bol
as shown in
Fi
gu
re 1
7
, 1
8
and
19 an
d t
h
e corres
p
on
di
n
g
co
nst
e
l
l
a
t
i
o
n
di
agram
shown i
n
Fi
g
u
r
e 20
. It
sho
w
s t
h
at
t
h
e
transm
itter and receive
r powe
r
spect
ru
m
are nearly ide
n
tical as shown in
Figure 17
a
n
d 18.
Altough
5 spa
n
s
of
fibe
r len
g
th
are c
o
n
s
idere
d
,
we i
n
fe
r f
r
o
m
the resu
lts th
at in
ter-symb
o
l
i
n
te
rfe
re
nc
e (I
SI
) is m
i
nim
u
m
,
m
i
nim
a
l l
o
ss, opt
i
cal
p
o
we
r l
e
vel
i
s
hi
g
h
a
n
d we a
r
e ab
le t
o
m
a
x
i
mize SNR with
fou
r
o
p
tical am
p
lifi
e
rs. In
t
h
e su
per i
m
pose
d
p
o
we
r sp
ect
rum
as shown i
n
Figure
19, the green
spectru
m
is
th
e tran
sm
it
ted
sig
n
a
l
whe
r
eas the
re
d s
p
ectrum
is the recei
ved
signal. T
h
e r
ecei
ver power s
p
ect
rum
is distorte
d due t
o
the
va
rious
fi
be
r l
o
s
s
es a
n
d at
t
e
n
u
at
i
o
n c
a
use
d
by
t
h
e
fi
ber over long distances.
Howe
ver,
w
e
o
b
s
erve th
at delay spread
is
l
e
ss t
h
an
o
n
e
sym
bol
pe
ri
o
d
t
h
us m
i
nim
i
zi
ng t
h
e i
n
t
e
r
-
car
ri
er i
n
t
e
rfe
rence
an
d e
n
h
a
nci
n
g t
h
e
s
p
ect
ral
efficiency. The
plot
obtaine
d
i
s
of
a
16
b
it QA
M sign
al.
Fi
gu
re
1
7
. T
r
a
n
sm
i
t
t
e
d OF
D
M
po
we
r s
p
ect
rum
.
0.
084
5
0.
084
6
0.
084
7
0.
084
8
0.
084
9
0.
08
5
0.
085
1
0.
085
2
012
345
Vo
l
t
a
g
e
(
V
o
l
t
s
)
E
x
t
r
a
o
r
d
i
n
ar
y
re
f
r
ac
t
i
v
e
ind
e
x
c
h
a
n
ge
(
∆
n
e
)
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