<s>
A	O
delay	B-Device
line	I-Device
interferometer	I-Device
(	O
DLI	O
)	O
can	O
be	O
a	O
Mach	O
–	O
Zehnder	O
interferometer	O
or	O
Michelson	O
interferometer	O
based	O
on	O
two-beam	O
interference	O
,	O
in	O
which	O
one	O
beam	O
is	O
time-delayed	O
to	O
the	O
other	O
by	O
a	O
desired	O
interval	O
.	O
</s>
<s>
Delay	B-Device
line	I-Device
interferometers	I-Device
are	O
also	O
known	O
as	O
optical	B-Protocol
DPSK	I-Protocol
demodulators	I-Protocol
.	O
</s>
<s>
In	O
this	O
application	O
,	O
an	O
incoming	O
differential	B-General_Concept
phase-shift	I-General_Concept
keying	I-General_Concept
(	O
DPSK	B-General_Concept
)	O
optical	O
signal	O
is	O
first	O
split	O
into	O
two	O
equal-intensity	O
beams	O
in	O
two	O
arms	O
of	O
a	O
Mach	O
Zehnder	O
or	O
Michelson	O
interferometer	O
,	O
in	O
which	O
one	O
beam	O
is	O
delayed	O
by	O
an	O
optical	O
path	O
difference	O
corresponding	O
to	O
1-bit	O
time	O
delay	O
.	O
</s>
