<s>
An	O
optical	B-Protocol
cross-connect	I-Protocol
(	O
OXC	B-Protocol
)	O
is	O
a	O
device	O
used	O
by	O
telecommunications	O
carriers	O
to	O
switch	O
high-speed	O
optical	O
signals	O
in	O
a	O
fiber	B-Architecture
optic	I-Architecture
network	O
,	O
such	O
as	O
an	O
optical	B-Protocol
mesh	I-Protocol
network	I-Protocol
.	O
</s>
<s>
There	O
are	O
several	O
ways	O
to	O
realize	O
an	O
OXC	B-Protocol
:	O
</s>
<s>
Opaque	O
OXCs	B-Protocol
(	O
electronic	O
switching	O
)	O
-	O
One	O
can	O
implement	O
an	O
OXC	B-Protocol
in	O
the	O
electronic	O
domain	O
:	O
all	O
the	O
input	O
optical	O
signals	O
are	O
converted	O
into	O
electronic	O
signals	O
after	O
they	O
are	O
demultiplexed	B-Architecture
by	O
demultiplexers	O
.	O
</s>
<s>
Finally	O
,	O
the	O
switched	O
electronic	O
signals	O
are	O
converted	O
back	O
into	O
optical	O
signals	O
by	O
using	O
them	O
to	O
modulate	B-Application
lasers	O
and	O
then	O
the	O
resulting	O
optical	O
signals	O
are	O
multiplexed	B-Architecture
by	O
optical	O
multiplexers	B-Protocol
onto	O
outlet	O
optical	B-Architecture
fibers	I-Architecture
.	O
</s>
<s>
Cross-connects	B-Architecture
based	O
on	O
an	O
OEO	O
switching	O
process	O
generally	O
have	O
a	O
key	O
limitation	O
:	O
the	O
electronic	O
circuits	O
limit	O
the	O
maximum	O
bandwidth	O
of	O
the	O
signal	O
.	O
</s>
<s>
Such	O
an	O
architecture	O
prevents	O
an	O
OXC	B-Protocol
from	O
performing	O
with	O
the	O
same	O
speed	O
as	O
an	O
all-optical	O
cross-connect	O
,	O
and	O
is	O
not	O
transparent	O
to	O
the	O
network	O
protocols	O
used	O
.	O
</s>
<s>
An	O
electronic	O
OXC	B-Protocol
is	O
also	O
called	O
an	O
opaque	O
OXC	B-Protocol
.	O
</s>
<s>
Transparent	O
OXCs	B-Protocol
(	O
optical	O
switching	O
)	O
-	O
Switching	O
optical	O
signals	O
in	O
an	O
all-optical	O
device	O
is	O
the	O
second	O
approach	O
to	O
realize	O
an	O
OXC	B-Protocol
.	O
</s>
<s>
Such	O
a	O
switch	O
is	O
often	O
called	O
a	O
transparent	O
OXC	B-Protocol
or	O
photonic	B-Protocol
cross-connect	I-Protocol
(	O
PXC	O
)	O
.	O
</s>
<s>
Specifically	O
,	O
optical	O
signals	O
are	O
demultiplexed	B-Architecture
,	O
then	O
the	O
demultiplexed	B-Architecture
wavelengths	O
are	O
switched	O
by	O
optical	O
switch	O
modules	O
.	O
</s>
<s>
After	O
switching	O
,	O
the	O
optical	O
signals	O
are	O
multiplexed	B-Architecture
onto	O
output	O
fibers	O
by	O
optical	O
multiplexers	B-Protocol
.	O
</s>
<s>
However	O
,	O
because	O
the	O
signals	O
are	O
kept	O
in	O
the	O
optical	O
format	O
,	O
the	O
transparent	O
OXC	B-Protocol
architecture	O
does	O
not	O
allow	O
easy	O
optical	O
signal	O
quality	O
monitoring	O
.	O
</s>
<s>
Translucent	O
OXCs	B-Protocol
(	O
optical	O
and	O
electronic	O
switching	O
)	O
-	O
As	O
a	O
compromise	O
between	O
opaque	O
and	O
transparent	O
OXC	B-Protocol
's	O
,	O
there	O
is	O
a	O
type	O
of	O
OXC	B-Protocol
called	O
a	O
translucent	O
OXC	B-Protocol
.	O
</s>
<s>
Translucent	O
OXC	B-Protocol
nodes	O
provide	O
a	O
compromise	O
of	O
full	O
optical	O
signal	O
transparency	O
and	O
comprehensive	O
optical	O
signal	O
monitoring	O
.	O
</s>
<s>
An	O
optical	B-Protocol
add-drop	I-Protocol
multiplexer	I-Protocol
(	O
OADM	B-Protocol
)	O
can	O
be	O
viewed	O
as	O
a	O
special	O
case	O
of	O
an	O
OXC	B-Protocol
,	O
where	O
to	O
node	O
degree	O
is	O
two	O
.	O
</s>
