<s>
In	O
fiber	B-Architecture
optics	I-Architecture
,	O
the	O
mode	B-Device
field	I-Device
diameter	I-Device
(	O
MFD	O
)	O
is	O
a	O
measure	O
of	O
the	O
width	O
of	O
an	O
irradiance	O
distribution	O
,	O
i.e.	O
,	O
the	O
optical	O
power	O
per	O
unit	O
area	O
,	O
across	O
the	O
end	O
face	O
of	O
a	O
single-mode	B-Device
fiber	I-Device
.	O
</s>
<s>
The	O
mode	B-Device
field	I-Device
diameter	I-Device
is	O
defined	O
as	O
twice	O
the	O
mode	O
field	O
radius	O
,	O
and	O
the	O
mode	O
field	O
radius	O
is	O
equal	O
to	O
the	O
distance	O
from	O
the	O
center	O
at	O
which	O
the	O
electric	O
and	O
magnetic	O
field	O
strengths	O
are	O
reduced	O
to	O
of	O
their	O
maximum	O
values	O
.	O
</s>
<s>
For	O
a	O
Gaussian-shaped	O
mode	O
,	O
the	O
mode	B-Device
field	I-Device
diameter	I-Device
is	O
twice	O
the	O
beam	O
waist	O
.	O
</s>
<s>
The	O
MFD	O
is	O
typically	O
slightly	O
larger	O
than	O
the	O
core	B-Device
of	O
an	O
optical	B-Architecture
fiber	I-Architecture
extending	O
slightly	O
into	O
the	O
cladding	B-Device
.	O
</s>
