<s>
In	O
optics	B-Algorithm
,	O
an	O
index-matching	B-Device
material	I-Device
is	O
a	O
substance	O
,	O
usually	O
a	O
liquid	O
,	O
cement	O
(	O
adhesive	O
)	O
,	O
or	O
gel	O
,	O
which	O
has	O
an	O
index	O
of	O
refraction	O
that	O
closely	O
approximates	O
that	O
of	O
another	O
object	O
(	O
such	O
as	O
a	O
lens	O
,	O
material	O
,	O
fiber-optic	O
,	O
etc	O
.	O
</s>
<s>
Immersion	O
oils	O
are	O
transparent	O
oils	O
that	O
have	O
specific	O
optical	O
and	O
viscosity	B-Application
characteristics	O
necessary	O
for	O
use	O
in	O
microscopy	O
.	O
</s>
<s>
Some	O
microscopes	O
also	O
use	O
other	O
index-matching	B-Device
materials	I-Device
besides	O
oil	O
;	O
see	O
water	O
immersion	O
objective	O
and	O
solid	O
immersion	O
lens	O
.	O
</s>
<s>
In	O
fiber	O
optics	B-Algorithm
and	O
telecommunications	O
,	O
an	O
index-matching	B-Device
material	I-Device
may	O
be	O
used	O
in	O
conjunction	O
with	O
pairs	O
of	O
mated	O
connectors	O
or	O
with	O
mechanical	O
splices	O
to	O
reduce	O
signal	O
reflected	O
in	O
the	O
guided	O
mode	O
(	O
known	O
as	O
return	O
loss	O
)	O
(	O
see	O
Optical	B-Device
fiber	I-Device
connector	I-Device
)	O
.	O
</s>
<s>
Without	O
the	O
use	O
of	O
an	O
index-matching	B-Device
material	I-Device
,	O
Fresnel	O
reflections	O
will	O
occur	O
at	O
the	O
smooth	O
end	O
faces	O
of	O
a	O
fiber	O
unless	O
there	O
is	O
no	O
fiber-air	O
interface	O
or	O
other	O
significant	O
mismatch	O
in	O
refractive	O
index	O
.	O
</s>
<s>
The	O
twice-reflected	O
,	O
delayed	O
signal	O
superimposed	O
on	O
the	O
direct	O
signal	O
may	O
noticeably	O
degrade	O
an	O
analog	O
baseband	B-Algorithm
intensity-modulated	O
video	O
signal	O
.	O
</s>
