<s>
When	O
optical	B-Architecture
fibers	I-Architecture
are	O
exposed	O
to	O
ionizing	O
radiation	O
such	O
as	O
energetic	O
electrons	O
,	O
protons	B-Application
,	O
neutrons	O
,	O
X-rays	B-Library
,	O
Ƴ-radiation	O
,	O
etc.	O
,	O
they	O
undergo	O
'	O
damage	O
 '	O
.	O
</s>
<s>
The	O
loss	O
of	O
power	O
or	O
'	O
darkening	O
 '	O
occurs	O
because	O
the	O
chemical	O
bonds	O
forming	O
the	O
optical	B-Device
fiber	I-Device
core	I-Device
are	O
disrupted	O
by	O
the	O
impinging	O
high	O
energy	O
resulting	O
in	O
the	O
appearance	O
of	O
new	O
electronic	O
transition	O
states	O
giving	O
rise	O
to	O
additional	O
absorption	O
in	O
the	O
wavelength	O
regions	O
of	O
interest	O
.	O
</s>
<s>
Understanding	O
these	O
radiation	O
induced	O
effects	O
is	O
important	O
particularly	O
for	O
space	O
based	O
applications	O
where	O
optical	B-Architecture
fibers	I-Architecture
are	O
being	O
considered	O
for	O
use	O
in	O
increasing	O
number	O
of	O
applications	O
.	O
</s>
<s>
Minimization	O
of	O
defects	O
is	O
achieved	O
not	O
only	O
by	O
reducing	O
the	O
incorporation	O
of	O
impurities	O
in	O
glass	O
but	O
also	O
by	O
controlling	O
the	O
input	O
gas	O
composition	O
,	O
optimizing	O
the	O
thermal	O
history	O
of	O
glass	O
at	O
all	O
stages	O
of	O
fiber	O
manufacturing	O
and	O
optimizing	O
the	O
stress	O
in	O
the	O
fiber	B-Device
core	I-Device
.	O
</s>
<s>
All	O
optical	B-Architecture
fibers	I-Architecture
undergo	O
some	O
darkening	O
depending	O
on	O
a	O
number	O
of	O
factors	O
that	O
include	O
:	O
ionization	O
type	O
,	O
optical	B-Device
fiber	I-Device
core	I-Device
glass	O
composition	O
,	O
operating	O
wavelength	O
,	O
dose	O
rate	O
,	O
total	O
accumulated	O
dose	O
,	O
temperature	O
and	O
power	O
propagating	O
through	O
the	O
core	O
.	O
</s>
<s>
compromises	O
the	O
radiation	O
hardness	O
of	O
optical	B-Architecture
fibers	I-Architecture
.	O
</s>
