<s>
Coherent	B-Protocol
optical	I-Protocol
module	I-Protocol
refers	O
to	O
a	O
typically	O
hot-pluggable	O
coherent	O
optical	O
transceiver	O
that	O
uses	O
coherent	O
modulation	O
(	O
BPSK/QPSK/QAM	O
)	O
rather	O
than	O
amplitude	O
modulation	O
(	O
RZ/NRZ/PAM4	O
)	O
and	O
is	O
typically	O
used	O
in	O
high-bandwidth	O
data	O
communications	O
applications	O
.	O
</s>
<s>
Optical	B-Protocol
modules	I-Protocol
typically	O
have	O
an	O
electrical	O
interface	O
on	O
the	O
side	O
that	O
connects	O
to	O
the	O
inside	O
of	O
the	O
system	O
and	O
an	O
optical	O
interface	O
on	O
the	O
side	O
that	O
connects	O
to	O
the	O
outside	O
world	O
through	O
a	O
fiber	O
optic	O
cable	O
.	O
</s>
<s>
The	O
technical	O
details	O
of	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
were	O
proprietary	O
for	O
many	O
years	O
,	O
but	O
have	O
recently	O
attracted	O
efforts	O
by	O
multi-source	O
agreement	O
(	O
MSA	O
)	O
groups	O
and	O
a	O
standards	O
development	O
organizations	O
such	O
as	O
the	O
Optical	O
Internetworking	O
Forum	O
.	O
</s>
<s>
Coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
can	O
either	O
plug	O
into	O
a	O
front	O
panel	O
socket	O
or	O
an	O
on-board	O
socket	O
.	O
</s>
<s>
Coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
form	O
a	O
smaller	O
piece	O
of	O
a	O
much	O
larger	O
optical	B-Protocol
module	I-Protocol
industry	O
.	O
</s>
<s>
There	O
are	O
multiple	O
variants	O
of	O
the	O
electrical	O
interface	O
of	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
use	O
.	O
</s>
<s>
This	O
IA	O
supports	O
a	O
configuration	O
where	O
the	O
digital	B-Architecture
signal	I-Architecture
processor	I-Architecture
(	O
DSP	O
)	O
is	O
on	O
the	O
main	O
board	O
and	O
analog	O
optical	O
components	O
are	O
on	O
the	O
module	O
.	O
</s>
<s>
The	O
ACO	O
interface	O
can	O
be	O
used	O
in	O
coherent	O
optics	O
applications	O
when	O
the	O
link	O
delivers	O
a	O
flexible	O
amount	O
of	O
bandwidth	O
to	O
the	O
system	O
,	O
for	O
example	O
when	O
combined	O
with	O
FlexE	B-Protocol
.	O
</s>
<s>
The	O
typical	O
optical	O
modulations	O
that	O
are	O
used	O
include	O
Dual	B-General_Concept
Polarization	I-General_Concept
Quadrature	I-General_Concept
Phase	I-General_Concept
Shift	I-General_Concept
Keying	I-General_Concept
(	O
DP-QPSK	O
)	O
and	O
Quadrature	B-Device
Amplitude	I-Device
Modulation	I-Device
QAM-16	B-Device
.	O
</s>
<s>
Many	O
different	O
forms	O
of	O
optical	O
modulation	O
and	O
multiplexing	O
have	O
been	O
employed	O
in	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
.	O
</s>
<s>
Some	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
can	O
fall	O
back	O
to	O
older	O
,	O
simpler	O
modulation	O
techniques	O
such	O
as	O
on-off	B-Device
keying	I-Device
(	O
NRZ	B-Protocol
)	O
and/or	O
Pulse-amplitude	B-Device
modulation	I-Device
with	O
4	O
levels	O
(	O
PAM-4	O
)	O
when	O
appropriate	O
.	O
</s>
<s>
Techniques	O
include	O
Dual	B-General_Concept
Polarization	I-General_Concept
Quadrature	I-General_Concept
Phase	I-General_Concept
Shift	I-General_Concept
Keying	I-General_Concept
(	O
DP-QPSK	O
)	O
and	O
QAM-16	B-Device
.	O
</s>
<s>
Tunable	O
lasers	O
are	O
sometimes	O
used	O
in	O
combination	O
with	O
coherent	O
modulation	O
to	O
allow	O
a	O
module	O
to	O
support	O
various	O
forms	O
of	O
network-based	O
optical	O
switching	O
such	O
as	O
needed	O
in	O
certain	O
cases	O
by	O
an	O
optical	B-Protocol
mesh	I-Protocol
networks	I-Protocol
or	O
a	O
Reconfigurable	O
optical	O
add-drop	O
multiplexer	O
(	O
ROADM	O
)	O
.	O
</s>
<s>
Different	O
optical	O
wavelengths	O
,	O
also	O
referred	O
to	O
as	O
lambdas	O
,	O
of	O
light	O
are	O
multiplexed	O
within	O
some	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
using	O
wavelength-division	B-Architecture
multiplexing	I-Architecture
(	O
WDM	O
)	O
.	O
</s>
<s>
Variants	O
include	O
Coarse	B-Architecture
WDM	I-Architecture
(	O
CWDM	O
)	O
,	O
Dense	O
WDM	O
(	O
DWDM	O
)	O
.	O
</s>
<s>
Coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
have	O
a	O
series	O
of	O
components	O
inside	O
,	O
some	O
of	O
which	O
have	O
received	O
attention	O
from	O
standards	O
development	O
organizations	O
.	O
</s>
<s>
Because	O
coherent	O
modules	O
typically	O
have	O
Digital	B-Architecture
Signal	I-Architecture
Processors	I-Architecture
,	O
these	O
gearbox	O
functions	O
sometimes	O
are	O
implemented	O
in	O
firmware	O
.	O
</s>
<s>
Particularly	O
in	O
the	O
long-reach	O
module	O
market	O
,	O
in-module	O
Forward	B-Error_Name
Error	I-Error_Name
Correction	I-Error_Name
(	O
FEC	O
)	O
has	O
been	O
included	O
.	O
</s>
<s>
The	O
OIF	O
has	O
created	O
interoperability	O
agreements	O
to	O
create	O
multi-vendor	O
interoperability	O
for	O
the	O
tunable	O
lasers	O
that	O
are	O
sometimes	O
used	O
in	O
optical	B-Protocol
modules	I-Protocol
.	O
</s>
<s>
Several	O
Multi-source	O
agreements	O
(	O
MSAs	O
)	O
have	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
.	O
</s>
<s>
Long-haul	O
Optical	B-Protocol
Transport	I-Protocol
Network	I-Protocol
(	O
OTN	O
)	O
networks	O
were	O
the	O
traditional	O
users	O
of	O
coherent	O
modulation	O
.	O
</s>
<s>
Cloud	O
scale	O
data	O
centers	O
have	O
become	O
an	O
important	O
consumer	O
of	O
coherent	B-Protocol
optical	I-Protocol
modules	I-Protocol
,	O
particularly	O
in	O
the	O
Ethernet	O
connectivity	O
space	O
for	O
reaches	O
greater	O
than	O
10km	O
where	O
the	O
advantages	O
of	O
coherent	O
modulation	O
can	O
outweigh	O
the	O
increased	O
cost	O
.	O
</s>
<s>
The	O
main	O
trade	O
show	O
for	O
the	O
coherent	B-Protocol
optical	I-Protocol
module	I-Protocol
industry	O
is	O
the	O
Optical	O
Fiber	O
Conference	O
(	O
OFC	O
)	O
,	O
that	O
is	O
held	O
annually	O
in	O
southern	O
California	O
.	O
</s>
