<s>
Microstructured	B-Device
optical	I-Device
fibers	I-Device
(	O
MOF	O
)	O
are	O
optical	B-Architecture
fiber	I-Architecture
waveguides	I-Architecture
where	O
guiding	O
is	O
obtained	O
through	O
manipulation	O
of	O
waveguide	O
structure	O
rather	O
than	O
its	O
index	O
of	O
refraction	O
.	O
</s>
<s>
In	O
conventional	O
optical	B-Architecture
fibers	I-Architecture
,	O
light	O
is	O
guided	O
through	O
the	O
effect	O
of	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
The	O
guiding	O
occurs	O
within	O
a	O
core	O
of	O
refractive	O
index	O
higher	O
than	O
refractive	O
index	O
of	O
the	O
surrounding	O
material	O
(	O
cladding	B-Device
)	O
.	O
</s>
<s>
The	O
index	O
change	O
is	O
obtained	O
through	O
different	O
doping	O
of	O
the	O
core	O
and	O
the	O
cladding	B-Device
or	O
through	O
the	O
use	O
of	O
different	O
materials	O
.	O
</s>
<s>
In	O
microstructured	B-Device
fibers	I-Device
,	O
a	O
completely	O
different	O
approach	O
is	O
applied	O
.	O
</s>
<s>
While	O
periodic	O
arrangement	O
of	O
the	O
holes	O
would	O
justify	O
the	O
use	O
of	O
term	O
"	O
photonic	B-Device
crystal	I-Device
fiber	I-Device
"	O
,	O
the	O
term	O
is	O
reserved	O
for	O
those	O
fibers	O
where	O
propagation	O
occurs	O
within	O
a	O
photonic	O
defect	O
or	O
due	O
to	O
photonic	O
bandgap	O
effect	O
.	O
</s>
<s>
As	O
such	O
,	O
photonic	B-Device
crystal	I-Device
fibers	I-Device
may	O
be	O
considered	O
a	O
subgroup	O
of	O
microstructured	B-Device
optical	I-Device
fibers	I-Device
.	O
</s>
<s>
Structured	O
optical	B-Architecture
fibers	I-Architecture
,	O
those	O
based	O
on	O
channels	O
running	O
along	O
their	O
entire	O
length	O
go	O
back	O
to	O
Kaiser	O
and	O
Co	O
in	O
1974	O
.	O
</s>
<s>
These	O
include	O
air-clad	O
optical	B-Architecture
fibers	I-Architecture
,	O
microstructured	B-Device
optical	I-Device
fibers	I-Device
sometimes	O
called	O
photonic	B-Device
crystal	I-Device
fiber	I-Device
when	O
the	O
arrays	O
of	O
holes	O
are	O
periodic	O
and	O
look	O
like	O
a	O
crystal	O
,	O
and	O
many	O
other	O
subclasses	O
.	O
</s>
<s>
These	O
too	O
can	O
be	O
made	O
by	O
using	O
air	O
channels	O
appropriately	O
positioned	O
on	O
the	O
virtual	O
zones	O
of	O
the	O
optical	B-Architecture
fiber	I-Architecture
.	O
</s>
<s>
Photonic	B-Device
crystal	I-Device
fibers	I-Device
are	O
a	O
variant	O
of	O
the	O
microstructured	B-Device
fibers	I-Device
reported	O
by	O
Kaiser	O
et	O
al	O
.	O
</s>
<s>
The	O
first	O
such	O
fibers	O
did	O
not	O
propagate	O
by	O
such	O
a	O
bandgap	O
but	O
rather	O
by	O
an	O
effective	O
step	O
index	O
–	O
however	O
,	O
the	O
name	O
has	O
,	O
for	O
historical	O
reasons	O
,	O
remained	O
unchanged	O
although	O
some	O
researchers	O
prefer	O
to	O
call	O
these	O
fibers	O
"	O
holey	O
"	O
fibers	O
or	O
"	O
microstructured	O
"	O
optical	B-Architecture
fibers	I-Architecture
in	O
reference	O
to	O
the	O
pre-existing	O
work	O
from	O
Bell	O
Labs	O
.	O
</s>
<s>
Many	O
other	O
practical	O
design	O
benefits	O
include	O
broader	O
photonic	O
bandgaps	O
in	O
diffraction	O
based	O
propagating	O
waveguides	O
and	O
reduced	O
bend	O
losses	O
,	O
important	O
for	O
achieving	O
structured	O
optical	B-Architecture
fibers	I-Architecture
with	O
propagation	O
losses	O
below	O
that	O
of	O
step-index	O
fibers	O
.	O
</s>
