<s>
An	O
optical	B-Device
interleaver	I-Device
is	O
a	O
3-port	O
passive	O
fiber-optic	B-Architecture
device	O
that	O
is	O
used	O
to	O
combine	O
(	O
Mux	O
)	O
two	O
sets	O
of	O
dense	O
wavelength-division	O
multiplexing	O
(	O
DWDM	O
)	O
channels	O
(	O
odd	O
and	O
even	O
channels	O
)	O
into	O
a	O
composite	O
signal	O
stream	O
in	O
an	O
interleaving	O
way	O
.	O
</s>
<s>
For	O
example	O
,	O
optical	B-Device
interleaver	I-Device
takes	O
two	O
multiplexed	O
signals	O
with	O
100GHz	O
spacing	O
and	O
interleaves	O
them	O
,	O
creating	O
a	O
denser	O
DWDM	O
signal	O
with	O
channels	O
spaced	O
50GHz	O
apart	O
.	O
</s>
<s>
Thus	O
,	O
optical	B-Device
interleaver	I-Device
can	O
expand	O
the	O
number	O
of	O
channels	O
per	O
fiber	O
,	O
and	O
devices	O
and/or	O
networks	O
can	O
be	O
upgraded	O
without	O
requiring	O
that	O
all	O
devices	O
be	O
upgraded	O
.	O
</s>
<s>
Optical	B-Device
interleaver	I-Device
is	O
based	O
on	O
multiple-beam	O
interference	O
.	O
</s>
<s>
Currently	O
,	O
there	O
are	O
two	O
approaches	O
to	O
building	O
optical	B-Device
interleaver	I-Device
:	O
1	O
)	O
Step-phase	O
Michelson	O
interferometer	O
,	O
and	O
2	O
)	O
Birefringent	O
crystal	O
networks	O
.	O
</s>
