I
r
-,
Vol.
BID,
Supplement
CHINESE
JO
UR
NA
L
OF
LASERS
Impact
of
Crosstalk in an
TFGB-OC-Based
Reconfigurable Optical
Add/Drop
WU
Xiangnong
LU
Chao
April,
2001
(Division
of
Communication E
ng
ineering,
Sc
hool
of
Elec
tr
ica
l
anii
Electronic Engineering,
Nan
ya
ng
Technological University, Nan
yan
g Avenue, Sin
gapor
e
6397
98)
Abstract
Tunabl
e fib
er
Bragg
grating
(
TFBG)
based
wavelength
division
multiplexing
(
WDM
)
reconfigura
bl
e optical add/ drop
multiplexer
(OADM)
will play an
important
role in
WDM
optical
n
etwo
rks.
One
possible implementation
of
the
OADM
is to use
two
optical
circulators
(OCs)
, a set
of
tunable
fiber g
rating
s
and
a
WDM
demultiplexer. In this
paper,
we
theoretically
studied the
impact
of
crosstalk on the
performanc
e
of
an
m-
channel
TFBG-OC-based
OADM
with
m.
add/
drop
channels
and m,
pass
throu
gh
chann
els.
The
infl
uence
of
cro
sstalk induced by
imperfect
performances
of
fiber gr
at
in
gs
,
optical circulators and the
demultiplexer
on the perfo
rmance
of
this OA
DM
is
inv
estigated in detail.
Anal
yt
ic
al
equations
are
derived
taking
into c
on
sideration
of
system
ins
ertion
loss.
The
sys
tem sign
al
to
noise ratio
(SNR)
performanc
e
change
s
greatly
with the increase
of
the reflectivities
of
fiber
grat
ings.
There
ex
ists a sa
turation
value
where the
cro
sstalk
of
the
circulators
and
demultiplexer
will no longer be
the
dominating
factors
affecting
the
performance
of
th
e
OADM
system.
This suggests
that
we
can
relax
the
requirement
on the
circulators
and
the
demultipl
exer used for the
implementation
of
th
e
OADM.
1 Introduction
The
recent
progress in the
area
of
dense
wavelength
division
multiplexing
(DWDM)
technology
has
created
much
interest
in
the
study
of
optical
add
/
drop
multiplexers
(OADM
s)
and
the optical cross
connects
(OXCs)
.
The
study
of
crosstalk
characteristics
of
these devices
has
always
been
an
important
area
of
focus.
The
re
sults presented so
far
are
generally
focused
on
multiplexer
/
dem
ultipl
exe
r- based
reconfigurable
OADM
/
OXC
[I- 4].
For
fiber
Bragg
grating
(FBG)
- based
device
s,
mo
st studies
only
considered
the
crosstalk
induc
ed
by
the
imperfect
reflection
of
the
fiber
grating
[5].
The
impact
of
the
crosstalk
of
other
components
of
the
sys
tem
and
the
total
contribution
to
the
performanc
e
of
the
device
are
still
not
fully
evaluated.
It
was
found
that
crosstalk
due
to
small
compon
e
nt
imp
e
rf
ect
ion
s in
transparent
lightwave
network
s
would
tend
to
gen
e
rate
large
performance
degradation
[6]. In this
paper,
we
theoretically
study
th
e
impact
of
crosstalk on
the
performance
of
a
reconfigurable
OADM
cons
tructed
using
two
optical
circulators
(OCs),
a set
of
tunable
FBGs
(TFBG
s )
and
a
WDM
dem ultiplexer. An
analytical
model
considering
all
crosstalk
contributions
to
thi
s
OADM
is established
and the
ex
pressions
for
th
e
electrical
sig
nal-to
-noise
-ratio
(SN
R)
are
deri
ve
d taking
into
consideration
of
system
ins
ert
ion loss.
Th
e
effects
of
variou
s
components
and
ne
twork
par
amete
rs
on
th
e
SNR
performance
of
the
OADM
are
investigated
in detail.
2
OADM
perforance due to crosstalk
Conside
ring
a
reconfigurable
TFBG-OC-
based
OADM
shown
in
Fig.
1,
two
OCs
int
ercon
nected
by a
set
of
TFBG
s
and
a
WDM
demultiple
xe
r
are
used to
construct
a
dynamic
OADM
with
m
WDM
channels.
Th
e
ith
TFBG
is
related
to
the
Bragg
wavelength
at
A;
or
channel
i
(1
~
i
~
m).
Depending