<s>
In	O
optical	B-Architecture
fiber	I-Architecture
technology	O
,	O
the	O
substitution	B-Device
method	I-Device
is	O
a	O
method	O
of	O
measuring	O
the	O
transmission	O
loss	O
of	O
a	O
fiber	O
.	O
</s>
<s>
using	O
a	O
stable	O
optical	O
source	O
,	O
at	O
the	O
wavelength	O
of	O
interest	O
,	O
to	O
drive	O
a	O
mode	B-Device
scrambler	I-Device
,	O
the	O
output	O
of	O
which	O
overfills	O
(	O
drives	O
)	O
a	O
1	O
to	O
2meter	O
long	O
reference	O
fiber	O
having	O
physical	O
and	O
optical	O
characteristics	O
matching	O
those	O
of	O
the	O
fiber	O
under	O
test	O
,	O
</s>
<s>
The	O
substitution	B-Device
method	I-Device
has	O
certain	O
shortcomings	O
with	O
regard	O
to	O
its	O
accuracy	O
,	O
but	O
its	O
simplicity	O
makes	O
it	O
a	O
popular	O
field	O
test	O
method	O
.	O
</s>
