<s>
A	O
long-period	B-Device
fiber	I-Device
grating	I-Device
couples	O
light	O
from	O
a	O
guided	O
mode	O
into	O
forward	O
propagating	O
cladding	O
modes	O
where	O
it	O
is	O
lost	O
due	O
to	O
absorption	O
and	O
scattering	O
.	O
</s>
<s>
It	O
is	O
an	O
optical	B-Architecture
fiber	I-Architecture
structure	O
with	O
the	O
properties	O
periodically	O
varying	O
along	O
the	O
fiber	O
,	O
such	O
that	O
the	O
conditions	O
for	O
the	O
interaction	O
of	O
several	O
copropagating	O
modes	O
are	O
satisfied	O
.	O
</s>
<s>
In	O
contrast	O
to	O
the	O
fiber	B-Device
Bragg	I-Device
gratings	I-Device
,	O
LPFGs	O
couple	O
copropagating	O
modes	O
with	O
close	O
propagation	O
constants	O
;	O
therefore	O
,	O
the	O
period	O
of	O
such	O
a	O
grating	O
can	O
considerably	O
exceed	O
the	O
wavelength	O
of	O
radiation	O
propagating	O
in	O
the	O
fiber	O
.	O
</s>
<s>
Microbend	B-Device
gratings	I-Device
,	O
which	O
are	O
antisymmetric	O
with	O
respect	O
to	O
the	O
fiber	O
axis	O
,	O
create	O
a	O
resonance	O
between	O
the	O
core	O
mode	O
and	O
the	O
asymmetric	O
LP1m	O
modes	O
of	O
the	O
core	O
and	O
the	O
cladding	O
.	O
</s>
