<s>
An	O
optical	B-Architecture
fiber	I-Architecture
,	O
or	O
optical	B-Architecture
fibre	I-Architecture
in	O
Commonwealth	O
English	O
,	O
is	O
a	O
flexible	O
,	O
transparent	O
fiber	O
made	O
by	O
drawing	O
glass	O
(	O
silica	O
)	O
or	O
plastic	O
to	O
a	O
diameter	O
slightly	O
thicker	O
than	O
that	O
of	O
a	O
human	O
hair	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
are	O
used	O
most	O
often	O
as	O
a	O
means	O
to	O
transmit	O
light	O
between	O
the	O
two	O
ends	O
of	O
the	O
fiber	O
and	O
find	O
wide	O
usage	O
in	O
fiber-optic	B-Application
communications	I-Application
,	O
where	O
they	O
permit	O
transmission	O
over	O
longer	O
distances	O
and	O
at	O
higher	O
bandwidths	O
(	O
data	O
transfer	O
rates	O
)	O
than	O
electrical	O
cables	O
.	O
</s>
<s>
Fibers	O
are	O
also	O
used	O
for	O
illumination	O
and	O
imaging	B-Algorithm
,	O
and	O
are	O
often	O
wrapped	O
in	O
bundles	O
so	O
they	O
may	O
be	O
used	O
to	O
carry	O
light	O
into	O
,	O
or	O
images	O
out	O
of	O
confined	O
spaces	O
,	O
as	O
in	O
the	O
case	O
of	O
a	O
fiberscope	B-Algorithm
.	O
</s>
<s>
Specially	O
designed	O
fibers	O
are	O
also	O
used	O
for	O
a	O
variety	O
of	O
other	O
applications	O
,	O
some	O
of	O
them	O
being	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
and	O
fiber	B-Device
lasers	I-Device
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
typically	O
include	O
a	O
core	B-Device
surrounded	O
by	O
a	O
transparent	O
cladding	B-Device
material	O
with	O
a	O
lower	O
index	O
of	O
refraction	O
.	O
</s>
<s>
Light	O
is	O
kept	O
in	O
the	O
core	B-Device
by	O
the	O
phenomenon	O
of	O
total	O
internal	O
reflection	O
which	O
causes	O
the	O
fiber	O
to	O
act	O
as	O
a	O
waveguide	O
.	O
</s>
<s>
Fibers	O
that	O
support	O
many	O
propagation	O
paths	O
or	O
transverse	O
modes	O
are	O
called	O
multi-mode	B-Device
fibers	I-Device
,	O
while	O
those	O
that	O
support	O
a	O
single	O
mode	O
are	O
called	O
single-mode	B-Device
fibers	I-Device
(	O
SMF	O
)	O
.	O
</s>
<s>
Multi-mode	B-Device
fibers	I-Device
generally	O
have	O
a	O
wider	O
core	B-Device
diameter	I-Device
and	O
are	O
used	O
for	O
short-distance	O
communication	O
links	O
and	O
for	O
applications	O
where	O
high	O
power	O
must	O
be	O
transmitted	O
.	O
</s>
<s>
Single-mode	B-Device
fibers	I-Device
are	O
used	O
for	O
most	O
communication	O
links	O
longer	O
than	O
.	O
</s>
<s>
Being	O
able	O
to	O
join	O
optical	B-Architecture
fibers	I-Architecture
with	O
low	O
loss	O
is	O
important	O
in	O
fiber	B-Application
optic	I-Application
communication	I-Application
.	O
</s>
<s>
This	O
is	O
more	O
complex	O
than	O
joining	O
electrical	O
wire	O
or	O
cable	O
and	O
involves	O
careful	O
cleaving	B-Device
of	O
the	O
fibers	O
,	O
precise	O
alignment	O
of	O
the	O
fiber	B-Device
cores	I-Device
,	O
and	O
the	O
coupling	B-Application
of	O
these	O
aligned	O
cores	O
.	O
</s>
<s>
Another	O
common	O
technique	O
is	O
a	O
mechanical	B-Device
splice	I-Device
,	O
where	O
the	O
ends	O
of	O
the	O
fibers	O
are	O
held	O
in	O
contact	O
by	O
mechanical	O
force	O
.	O
</s>
<s>
Temporary	O
or	O
semi-permanent	O
connections	O
are	O
made	O
by	O
means	O
of	O
specialized	O
optical	B-Device
fiber	I-Device
connectors	I-Device
.	O
</s>
<s>
The	O
field	O
of	O
applied	O
science	O
and	O
engineering	O
concerned	O
with	O
the	O
design	O
and	O
application	O
of	O
optical	B-Architecture
fibers	I-Architecture
is	O
known	O
as	O
fiber	B-Architecture
optics	I-Architecture
.	O
</s>
<s>
Daniel	O
Colladon	O
and	O
Jacques	O
Babinet	O
first	O
demonstrated	O
the	O
guiding	O
of	O
light	O
by	O
refraction	O
,	O
the	O
principle	O
that	O
makes	O
fiber	B-Architecture
optics	I-Architecture
possible	O
,	O
in	O
Paris	O
in	O
the	O
early	O
1840s	O
.	O
</s>
<s>
In	O
the	O
1930s	O
,	O
Heinrich	O
Lamm	O
showed	O
that	O
one	O
could	O
transmit	O
images	O
through	O
a	O
bundle	O
of	O
unclad	O
optical	B-Architecture
fibers	I-Architecture
and	O
used	O
it	O
for	O
internal	O
medical	O
examinations	O
,	O
but	O
his	O
work	O
was	O
largely	O
forgotten	O
.	O
</s>
<s>
In	O
1953	O
,	O
Dutch	O
scientist	O
first	O
demonstrated	O
image	O
transmission	O
through	O
bundles	O
of	O
optical	B-Architecture
fibers	I-Architecture
with	O
a	O
transparent	O
cladding	B-Device
.	O
</s>
<s>
The	O
first	O
practical	O
fiber	B-Architecture
optic	I-Architecture
semi-flexible	O
gastroscope	B-Application
was	O
patented	O
by	O
Basil	O
Hirschowitz	O
,	O
C	O
.	O
Wilbur	O
Peters	O
,	O
and	O
Lawrence	O
E	O
.	O
Curtiss	O
,	O
researchers	O
at	O
the	O
University	O
of	O
Michigan	O
,	O
in	O
1956	O
.	O
</s>
<s>
In	O
the	O
process	O
of	O
developing	O
the	O
gastroscope	B-Application
,	O
Curtiss	O
produced	O
the	O
first	O
glass-clad	O
fibers	O
;	O
previous	O
optical	B-Architecture
fibers	I-Architecture
had	O
relied	O
on	O
air	O
or	O
impractical	O
oils	O
and	O
waxes	O
as	O
the	O
low-index	O
cladding	B-Device
material	O
.	O
</s>
<s>
Kapany	O
coined	O
the	O
term	O
fiber	B-Architecture
optics	I-Architecture
after	O
writing	O
a	O
1960	O
article	O
in	O
Scientific	O
American	O
that	O
introduced	O
the	O
topic	O
to	O
a	O
wide	O
audience	O
.	O
</s>
<s>
The	O
first	O
working	O
fiber-optic	B-Architecture
data	O
transmission	O
system	O
was	O
demonstrated	O
by	O
German	O
physicist	O
Manfred	O
Börner	O
at	O
Telefunken	O
Research	O
Labs	O
in	O
Ulm	O
in	O
1965	O
,	O
followed	O
by	O
the	O
first	O
patent	O
application	O
for	O
this	O
technology	O
in	O
1966	O
.	O
</s>
<s>
In	O
1968	O
,	O
NASA	O
used	O
fiber	B-Architecture
optics	I-Architecture
in	O
the	O
television	O
cameras	O
that	O
were	O
sent	O
to	O
the	O
moon	O
.	O
</s>
<s>
Charles	O
K	B-Operating_System
.	O
Kao	O
and	O
George	O
A	O
.	O
Hockham	O
of	O
the	O
British	O
company	O
Standard	O
Telephones	O
and	O
Cables	O
(	O
STC	O
)	O
were	O
the	O
first	O
to	O
promote	O
the	O
idea	O
that	O
the	O
attenuation	O
in	O
optical	B-Architecture
fibers	I-Architecture
could	O
be	O
reduced	O
below	O
20	O
decibels	O
per	O
kilometer	O
(	O
dB/km	O
)	O
,	O
making	O
fibers	O
a	O
practical	O
communication	O
medium	O
,	O
in	O
1965	O
.	O
</s>
<s>
They	O
correctly	O
and	O
systematically	O
theorized	O
the	O
light-loss	O
properties	O
for	O
optical	B-Architecture
fiber	I-Architecture
and	O
pointed	O
out	O
the	O
right	O
material	O
to	O
use	O
for	O
such	O
fibers	O
—	O
silica	O
glass	O
with	O
high	O
purity	O
.	O
</s>
<s>
They	O
demonstrated	O
a	O
fiber	O
with	O
17dB/km	O
attenuation	O
by	O
doping	B-Algorithm
silica	O
glass	O
with	O
titanium	O
.	O
</s>
<s>
A	O
few	O
years	O
later	O
they	O
produced	O
a	O
fiber	O
with	O
only	O
4dB/km	O
attenuation	O
using	O
germanium	O
dioxide	O
as	O
the	O
core	B-Device
dopant	O
.	O
</s>
<s>
In	O
1981	O
,	O
General	O
Electric	O
produced	O
fused	O
quartz	B-General_Concept
ingots	O
that	O
could	O
be	O
drawn	O
into	O
strands	O
long	O
.	O
</s>
<s>
Initially	O
,	O
high-quality	O
optical	B-Architecture
fibers	I-Architecture
could	O
only	O
be	O
manufactured	O
at	O
2	O
meters	O
per	O
second	O
.	O
</s>
<s>
Chemical	O
engineer	O
Thomas	O
Mensah	O
joined	O
Corning	O
in	O
1983	O
and	O
increased	O
the	O
speed	O
of	O
manufacture	O
to	O
over	O
50	O
meters	O
per	O
second	O
,	O
making	O
optical	B-Architecture
fiber	I-Architecture
cables	O
cheaper	O
than	O
traditional	O
copper	O
ones	O
.	O
</s>
<s>
These	O
innovations	O
ushered	O
in	O
the	O
era	O
of	O
optical	B-Architecture
fiber	I-Architecture
telecommunication	O
.	O
</s>
<s>
The	O
Italian	O
research	O
center	O
CSELT	O
worked	O
with	O
Corning	O
to	O
develop	O
practical	O
optical	B-Architecture
fiber	I-Architecture
cables	O
,	O
resulting	O
in	O
the	O
first	O
metropolitan	O
fiber	B-Architecture
optic	I-Architecture
cable	O
being	O
deployed	O
in	O
Turin	O
in	O
1977	O
.	O
</s>
<s>
CSELT	O
also	O
developed	O
an	O
early	O
technique	O
for	O
splicing	O
optical	B-Architecture
fibers	I-Architecture
,	O
called	O
Springroove	O
.	O
</s>
<s>
The	O
emerging	O
field	O
of	O
photonic	O
crystals	O
led	O
to	O
the	O
development	O
in	O
1991	O
of	O
photonic-crystal	B-Device
fiber	I-Device
,	O
which	O
guides	O
light	O
by	O
diffraction	O
from	O
a	O
periodic	O
structure	O
,	O
rather	O
than	O
by	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
The	O
first	O
photonic	B-Device
crystal	I-Device
fibers	I-Device
became	O
commercially	O
available	O
in	O
2000	O
.	O
</s>
<s>
Photonic	B-Device
crystal	I-Device
fibers	I-Device
can	O
carry	O
higher	O
power	O
than	O
conventional	O
fibers	O
and	O
their	O
wavelength-dependent	O
properties	O
can	O
be	O
manipulated	O
to	O
improve	O
performance	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
is	O
used	O
as	O
a	O
medium	O
for	O
telecommunication	O
and	O
computer	B-Architecture
networking	I-Architecture
because	O
it	O
is	O
flexible	O
and	O
can	O
be	O
bundled	O
as	O
cables	O
.	O
</s>
<s>
Through	O
the	O
use	O
of	O
wavelength-division	B-Architecture
multiplexing	I-Architecture
(	O
WDM	O
)	O
,	O
each	O
fiber	O
can	O
carry	O
many	O
independent	O
channels	O
,	O
each	O
using	O
a	O
different	O
wavelength	O
of	O
light	O
.	O
</s>
<s>
The	O
net	O
data	O
rate	O
(	O
data	O
rate	O
without	O
overhead	O
bytes	O
)	O
per	O
fiber	O
is	O
the	O
per-channel	O
data	O
rate	O
reduced	O
by	O
the	O
forward	B-Error_Name
error	I-Error_Name
correction	I-Error_Name
(	O
FEC	O
)	O
overhead	O
,	O
multiplied	O
by	O
the	O
number	O
of	O
channels	O
(	O
usually	O
up	O
to	O
80	O
in	O
commercial	O
dense	O
WDM	O
systems	O
)	O
.	O
</s>
<s>
+	O
Transmission	O
speed	O
milestones	O
Date	O
Milestone	O
2006	O
111	O
Gbit/s	O
by	O
NTT.2009100	O
Pbit/s	O
·km	O
(	O
15.5	O
Tbit/s	O
over	O
a	O
single	O
7000	O
km	O
fiber	O
)	O
by	O
Bell	O
Labs.2011101	O
Tbit/s	O
(	O
370	O
channels	O
at	O
273	O
Gbit/s	O
each	O
)	O
on	O
a	O
single	O
core.January	O
20131.05	O
Pbit/s	O
transmission	O
through	O
a	O
multi-core	O
(	O
lightpath	B-Protocol
)	O
fiber	O
cable	O
.	O
</s>
<s>
For	O
short-distance	O
applications	O
,	O
such	O
as	O
a	O
network	O
in	O
an	O
office	O
building	O
(	O
see	O
fiber	B-Architecture
to	I-Architecture
the	I-Architecture
office	I-Architecture
)	O
,	O
fiber-optic	B-Architecture
cabling	O
can	O
save	O
space	O
in	O
cable	O
ducts	O
.	O
</s>
<s>
This	O
is	O
because	O
a	O
single	O
fiber	O
can	O
carry	O
much	O
more	O
data	O
than	O
electrical	O
cables	O
such	O
as	O
standard	O
category	B-Protocol
5	I-Protocol
cable	I-Protocol
,	O
which	O
typically	O
runs	O
at	O
100Mbit/s	O
or	O
1Gbit/s	O
speeds	O
.	O
</s>
<s>
For	O
example	O
,	O
most	O
high-definition	B-Device
televisions	I-Device
offer	O
a	O
digital	O
audio	O
optical	O
connection	O
.	O
</s>
<s>
This	O
allows	O
the	O
streaming	O
of	O
audio	O
over	O
light	O
,	O
using	O
the	O
S/PDIF	O
protocol	O
over	O
an	O
optical	O
TOSLINK	B-Protocol
connection	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
can	O
be	O
used	O
as	O
sensors	O
to	O
measure	O
strain	O
,	O
temperature	O
,	O
pressure	O
,	O
and	O
other	O
quantities	O
by	O
modifying	O
a	O
fiber	O
so	O
that	O
the	O
property	O
being	O
measured	O
modulates	O
the	O
intensity	O
,	O
phase	O
,	O
polarization	O
,	O
wavelength	O
,	O
or	O
transit	O
time	O
of	O
light	O
in	O
the	O
fiber	O
.	O
</s>
<s>
A	O
particularly	O
useful	O
feature	O
of	O
such	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
is	O
that	O
they	O
can	O
,	O
if	O
required	O
,	O
provide	O
distributed	O
sensing	O
over	O
distances	O
of	O
up	O
to	O
one	O
meter	O
.	O
</s>
<s>
Distributed	B-Algorithm
acoustic	I-Algorithm
sensing	I-Algorithm
is	O
one	O
example	O
of	O
this	O
.	O
</s>
<s>
These	O
can	O
be	O
implemented	O
by	O
various	O
micro	O
-	O
and	O
nanofabrication	B-Algorithm
technologies	O
,	O
such	O
that	O
they	O
do	O
not	O
exceed	O
the	O
microscopic	O
boundary	O
of	O
the	O
fiber	O
tip	O
,	O
allowing	O
for	O
such	O
applications	O
as	O
insertion	O
into	O
blood	O
vessels	O
via	O
hypodermic	O
needle	O
.	O
</s>
<s>
Extrinsic	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
use	O
an	O
optical	B-Architecture
fiber	I-Architecture
cable	O
,	O
normally	O
a	O
multi-mode	O
one	O
,	O
to	O
transmit	O
modulated	B-Application
light	O
from	O
either	O
a	O
non-fiber	O
optical	O
sensor	O
—	O
or	O
an	O
electronic	O
sensor	O
connected	O
to	O
an	O
optical	O
transmitter	O
.	O
</s>
<s>
The	O
fiber	B-Device
optic	I-Device
gyroscope	I-Device
(	O
FOG	O
)	O
has	O
no	O
moving	O
parts	O
and	O
exploits	O
the	O
Sagnac	O
effect	O
to	O
detect	O
mechanical	O
rotation	O
.	O
</s>
<s>
Common	O
uses	O
for	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
include	O
advanced	O
intrusion	O
detection	O
security	O
systems	O
.	O
</s>
<s>
The	O
light	O
is	O
transmitted	O
along	O
a	O
fiber	B-Algorithm
optic	I-Algorithm
sensor	I-Algorithm
cable	O
placed	O
on	O
a	O
fence	O
,	O
pipeline	O
,	O
or	O
communication	O
cabling	O
,	O
and	O
the	O
returned	O
signal	O
is	O
monitored	O
and	O
analyzed	O
for	O
disturbances	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
are	O
widely	O
used	O
as	O
components	O
of	O
optical	O
chemical	O
sensors	O
and	O
optical	O
biosensors	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
can	O
be	O
used	O
to	O
transmit	O
power	O
using	O
a	O
photovoltaic	O
cell	O
to	O
convert	O
the	O
light	O
into	O
electricity	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
are	O
used	O
as	O
light	O
guides	O
in	O
medical	O
and	O
other	O
applications	O
where	O
bright	O
light	O
needs	O
to	O
be	O
shone	O
on	O
a	O
target	O
without	O
a	O
clear	O
line-of-sight	O
path	O
.	O
</s>
<s>
Many	O
microscopes	O
use	O
fiber-optic	B-Architecture
light	O
sources	O
to	O
provide	O
intense	O
illumination	O
of	O
samples	O
being	O
studied	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
is	O
also	O
used	O
in	O
imaging	B-Algorithm
optics	O
.	O
</s>
<s>
A	O
coherent	O
bundle	O
of	O
fibers	O
is	O
used	O
,	O
sometimes	O
along	O
with	O
lenses	O
,	O
for	O
a	O
long	O
,	O
thin	O
imaging	B-Algorithm
device	O
called	O
an	O
endoscope	O
,	O
which	O
is	O
used	O
to	O
view	O
objects	O
through	O
a	O
small	O
hole	O
.	O
</s>
<s>
Industrial	O
endoscopes	O
(	O
see	O
fiberscope	B-Algorithm
or	O
borescope	O
)	O
are	O
used	O
for	O
inspecting	O
anything	O
hard	O
to	O
reach	O
,	O
such	O
as	O
jet	O
engine	O
interiors	O
.	O
</s>
<s>
In	O
some	O
buildings	O
,	O
optical	B-Architecture
fibers	I-Architecture
route	O
sunlight	O
from	O
the	O
roof	O
to	O
other	O
parts	O
of	O
the	O
building	O
(	O
see	O
nonimaging	O
optics	O
)	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
is	O
an	O
intrinsic	O
part	O
of	O
the	O
light-transmitting	O
concrete	O
building	O
product	O
LiTraCon	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
can	O
also	O
be	O
used	O
in	O
structural	O
health	O
monitoring	O
.	O
</s>
<s>
In	O
spectroscopy	O
,	O
optical	B-Architecture
fiber	I-Architecture
bundles	O
transmit	O
light	O
from	O
a	O
spectrometer	O
to	O
a	O
substance	O
that	O
cannot	O
be	O
placed	O
inside	O
the	O
spectrometer	O
itself	O
,	O
in	O
order	O
to	O
analyze	O
its	O
composition	O
.	O
</s>
<s>
An	O
optical	B-Architecture
fiber	I-Architecture
doped	O
with	O
certain	O
rare-earth	O
elements	O
such	O
as	O
erbium	O
can	O
be	O
used	O
as	O
the	O
gain	O
medium	O
of	O
a	O
fiber	B-Device
laser	I-Device
or	O
optical	O
amplifier	O
.	O
</s>
<s>
Rare-earth-doped	O
optical	B-Architecture
fibers	I-Architecture
can	O
be	O
used	O
to	O
provide	O
signal	O
amplification	O
by	O
splicing	O
a	O
short	O
section	O
of	O
doped	O
fiber	O
into	O
a	O
regular	O
(	O
undoped	O
)	O
optical	B-Architecture
fiber	I-Architecture
line	O
.	O
</s>
<s>
Optical	B-Architecture
fiber	I-Architecture
is	O
also	O
widely	O
exploited	O
as	O
a	O
nonlinear	O
medium	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
doped	O
with	O
a	O
wavelength	O
shifter	O
collect	O
scintillation	O
light	O
in	O
physics	O
experiments	O
.	O
</s>
<s>
Fiber-optic	B-Architecture
sights	O
for	O
handguns	O
,	O
rifles	O
,	O
and	O
shotguns	O
use	O
pieces	O
of	O
optical	B-Architecture
fiber	I-Architecture
to	O
improve	O
the	O
visibility	O
of	O
markings	O
on	O
the	O
sight	O
.	O
</s>
<s>
An	O
optical	B-Architecture
fiber	I-Architecture
is	O
a	O
cylindrical	O
dielectric	O
waveguide	O
(	O
nonconducting	O
waveguide	O
)	O
that	O
transmits	O
light	O
along	O
its	O
axis	O
through	O
the	O
process	O
of	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
The	O
fiber	O
consists	O
of	O
a	O
core	B-Device
surrounded	O
by	O
a	O
cladding	B-Device
layer	O
,	O
both	O
of	O
which	O
are	O
made	O
of	O
dielectric	O
materials	O
.	O
</s>
<s>
To	O
confine	O
the	O
optical	O
signal	O
in	O
the	O
core	B-Device
,	O
the	O
refractive	O
index	O
of	O
the	O
core	B-Device
must	O
be	O
greater	O
than	O
that	O
of	O
the	O
cladding	B-Device
.	O
</s>
<s>
The	O
boundary	O
between	O
the	O
core	B-Device
and	O
cladding	B-Device
may	O
either	O
be	O
abrupt	O
,	O
in	O
step-index	B-Device
fiber	I-Device
,	O
or	O
gradual	O
,	O
in	O
graded-index	B-Device
fiber	I-Device
.	O
</s>
<s>
Light	O
can	O
be	O
fed	O
into	O
optical	B-Architecture
fibers	I-Architecture
using	O
lasers	O
or	O
LEDs	O
.	O
</s>
<s>
Information	O
traveling	O
inside	O
the	O
optical	B-Architecture
fiber	I-Architecture
is	O
even	O
immune	O
to	O
electromagnetic	O
pulses	O
generated	O
by	O
nuclear	O
devices	O
.	O
</s>
<s>
Fiber	O
cables	O
do	O
not	O
conduct	O
electricity	O
,	O
which	O
makes	O
fiber	O
useful	O
for	O
protecting	O
communications	O
equipment	O
in	O
high	O
voltage	O
environments	O
such	O
as	O
power	O
generation	O
facilities	O
or	O
applications	O
prone	O
to	O
lightning	B-Architecture
strikes	O
.	O
</s>
<s>
Light	O
travels	O
fastest	O
in	O
a	O
vacuum	B-General_Concept
,	O
such	O
as	O
in	O
outer	O
space	O
.	O
</s>
<s>
The	O
speed	O
of	O
light	O
in	O
a	O
vacuum	B-General_Concept
is	O
about	O
300,000	O
kilometers	O
(	O
186,000	O
miles	O
)	O
per	O
second	O
.	O
</s>
<s>
The	O
refractive	O
index	O
of	O
a	O
medium	O
is	O
calculated	O
by	O
dividing	O
the	O
speed	O
of	O
light	O
in	O
a	O
vacuum	B-General_Concept
by	O
the	O
speed	O
of	O
light	O
in	O
that	O
medium	O
.	O
</s>
<s>
The	O
refractive	O
index	O
of	O
a	O
vacuum	B-General_Concept
is	O
therefore	O
1	O
,	O
by	O
definition	O
.	O
</s>
<s>
A	O
typical	O
single-mode	B-Device
fiber	I-Device
used	O
for	O
telecommunications	O
has	O
a	O
cladding	B-Device
made	O
of	O
pure	O
silica	O
,	O
with	O
an	O
index	O
of	O
1.444	O
at	O
1500nm	O
,	O
and	O
a	O
core	B-Device
of	O
doped	O
silica	O
with	O
an	O
index	O
around	O
1.4475	O
.	O
</s>
<s>
From	O
this	O
information	O
,	O
a	O
simple	O
rule	O
of	O
thumb	O
is	O
that	O
a	O
signal	O
using	O
optical	B-Architecture
fiber	I-Architecture
for	O
communication	O
will	O
travel	O
at	O
around	O
200,000	O
kilometers	O
per	O
second	O
.	O
</s>
<s>
This	O
effect	O
is	O
used	O
in	O
optical	B-Architecture
fibers	I-Architecture
to	O
confine	O
light	O
in	O
the	O
core	B-Device
.	O
</s>
<s>
Most	O
modern	O
optical	B-Architecture
fiber	I-Architecture
is	O
weakly	O
guiding	O
,	O
meaning	O
that	O
the	O
difference	O
in	O
refractive	O
index	O
between	O
the	O
core	B-Device
and	O
the	O
cladding	B-Device
is	O
very	O
small	O
(	O
typically	O
less	O
than	O
1%	O
)	O
.	O
</s>
<s>
Light	O
travels	O
through	O
the	O
fiber	B-Device
core	I-Device
,	O
bouncing	O
back	O
and	O
forth	O
off	O
the	O
boundary	O
between	O
the	O
core	B-Device
and	O
cladding	B-Device
.	O
</s>
<s>
This	O
range	O
of	O
angles	O
is	O
called	O
the	O
acceptance	B-Device
cone	I-Device
of	O
the	O
fiber	O
.	O
</s>
<s>
There	O
is	O
a	O
maximum	O
angle	O
from	O
the	O
fiber	O
axis	O
at	O
which	O
light	O
may	O
enter	O
the	O
fiber	O
so	O
that	O
it	O
will	O
propagate	O
,	O
or	O
travel	O
,	O
in	O
the	O
core	B-Device
of	O
the	O
fiber	O
.	O
</s>
<s>
The	O
size	O
of	O
this	O
acceptance	B-Device
cone	I-Device
is	O
a	O
function	O
of	O
the	O
refractive	O
index	O
difference	O
between	O
the	O
fiber	O
's	O
core	B-Device
and	O
cladding	B-Device
.	O
</s>
<s>
Single-mode	B-Device
fiber	I-Device
has	O
a	O
small	O
NA	O
.	O
</s>
<s>
Fiber	O
with	O
large	O
core	B-Device
diameter	I-Device
(	O
greater	O
than	O
10micrometers	O
)	O
may	O
be	O
analyzed	O
by	O
geometrical	O
optics	O
.	O
</s>
<s>
Such	O
fiber	O
is	O
called	O
multi-mode	B-Device
fiber	I-Device
,	O
from	O
the	O
electromagnetic	O
analysis	O
(	O
see	O
below	O
)	O
.	O
</s>
<s>
In	O
a	O
step-index	O
multi-mode	B-Device
fiber	I-Device
,	O
rays	B-Device
of	O
light	O
are	O
guided	O
along	O
the	O
fiber	B-Device
core	I-Device
by	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
Rays	B-Device
that	O
meet	O
the	O
core-cladding	O
boundary	O
at	O
an	O
angle	O
(	O
measured	O
relative	O
to	O
a	O
line	O
normal	O
to	O
the	O
boundary	O
)	O
greater	O
than	O
the	O
critical	O
angle	O
for	O
this	O
boundary	O
,	O
are	O
completely	O
reflected	O
.	O
</s>
<s>
The	O
critical	O
angle	O
is	O
determined	O
by	O
the	O
difference	O
in	O
the	O
index	O
of	O
refraction	O
between	O
the	O
core	B-Device
and	O
cladding	B-Device
materials	O
.	O
</s>
<s>
Rays	B-Device
that	O
meet	O
the	O
boundary	O
at	O
a	O
low	O
angle	O
are	O
refracted	O
from	O
the	O
core	B-Device
into	O
the	O
cladding	B-Device
where	O
they	O
terminate	O
.	O
</s>
<s>
The	O
critical	O
angle	O
determines	O
the	O
acceptance	B-Device
angle	I-Device
of	O
the	O
fiber	O
,	O
often	O
reported	O
as	O
a	O
numerical	O
aperture	O
.	O
</s>
<s>
A	O
high	O
numerical	O
aperture	O
allows	O
light	O
to	O
propagate	O
down	O
the	O
fiber	O
in	O
rays	B-Device
both	O
close	O
to	O
the	O
axis	O
and	O
at	O
various	O
angles	O
,	O
allowing	O
efficient	O
coupling	B-Application
of	O
light	O
into	O
the	O
fiber	O
.	O
</s>
<s>
However	O
,	O
this	O
high	O
numerical	O
aperture	O
increases	O
the	O
amount	O
of	O
dispersion	O
as	O
rays	B-Device
at	O
different	O
angles	O
have	O
different	O
path	O
lengths	O
and	O
therefore	O
take	O
different	O
amounts	O
of	O
time	O
to	O
traverse	O
the	O
fiber	O
.	O
</s>
<s>
In	O
graded-index	B-Device
fiber	I-Device
,	O
the	O
index	O
of	O
refraction	O
in	O
the	O
core	B-Device
decreases	O
continuously	O
between	O
the	O
axis	O
and	O
the	O
cladding	B-Device
.	O
</s>
<s>
This	O
causes	O
light	B-Device
rays	I-Device
to	O
bend	O
smoothly	O
as	O
they	O
approach	O
the	O
cladding	B-Device
,	O
rather	O
than	O
reflecting	O
abruptly	O
from	O
the	O
core-cladding	O
boundary	O
.	O
</s>
<s>
The	O
resulting	O
curved	O
paths	O
reduce	O
multi-path	O
dispersion	O
because	O
high-angle	O
rays	B-Device
pass	O
more	O
through	O
the	O
lower-index	O
periphery	O
of	O
the	O
core	B-Device
,	O
rather	O
than	O
the	O
high-index	O
center	O
.	O
</s>
<s>
The	O
index	O
profile	O
is	O
chosen	O
to	O
minimize	O
the	O
difference	O
in	O
axial	O
propagation	O
speeds	O
of	O
the	O
various	O
rays	B-Device
in	O
the	O
fiber	O
.	O
</s>
<s>
Fiber	O
with	O
a	O
core	B-Device
diameter	I-Device
less	O
than	O
about	O
ten	O
times	O
the	O
wavelength	O
of	O
the	O
propagating	O
light	O
cannot	O
be	O
modeled	O
using	O
geometric	O
optics	O
.	O
</s>
<s>
The	O
waveguide	O
analysis	O
shows	O
that	O
the	O
light	O
energy	O
in	O
the	O
fiber	O
is	O
not	O
completely	O
confined	O
in	O
the	O
core	B-Device
.	O
</s>
<s>
Instead	O
,	O
especially	O
in	O
single-mode	B-Device
fibers	I-Device
,	O
a	O
significant	O
fraction	O
of	O
the	O
energy	O
in	O
the	O
bound	O
mode	O
travels	O
in	O
the	O
cladding	B-Device
as	O
an	O
evanescent	O
wave	O
.	O
</s>
<s>
The	O
most	O
common	O
type	O
of	O
single-mode	B-Device
fiber	I-Device
has	O
a	O
core	B-Device
diameter	I-Device
of	O
8	O
–	O
10	O
micrometers	O
and	O
is	O
designed	O
for	O
use	O
in	O
the	O
near	O
infrared	O
.	O
</s>
<s>
Multi-mode	B-Device
fiber	I-Device
,	O
by	O
comparison	O
,	O
is	O
manufactured	O
with	O
core	B-Device
diameters	I-Device
as	O
small	O
as	O
50	O
micrometers	O
and	O
as	O
large	O
as	O
hundreds	O
of	O
micrometers	O
.	O
</s>
<s>
Some	O
special-purpose	O
optical	B-Architecture
fiber	I-Architecture
is	O
constructed	O
with	O
a	O
non-cylindrical	O
core	B-Device
or	O
cladding	B-Device
layer	O
,	O
usually	O
with	O
an	O
elliptical	O
or	O
rectangular	O
cross-section	O
.	O
</s>
<s>
These	O
include	O
polarization-maintaining	B-Device
fiber	I-Device
used	O
in	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
and	O
fiber	O
designed	O
to	O
suppress	O
whispering	O
gallery	O
mode	O
propagation	O
.	O
</s>
<s>
Photonic-crystal	B-Device
fiber	I-Device
is	O
made	O
with	O
a	O
regular	O
pattern	O
of	O
index	O
variation	O
(	O
often	O
in	O
the	O
form	O
of	O
cylindrical	O
holes	O
that	O
run	O
along	O
the	O
length	O
of	O
the	O
fiber	O
)	O
.	O
</s>
<s>
Such	O
fiber	O
uses	O
diffraction	O
effects	O
instead	O
of	O
or	O
in	O
addition	O
to	O
total	O
internal	O
reflection	O
,	O
to	O
confine	O
light	O
to	O
the	O
fiber	O
's	O
core	B-Device
.	O
</s>
<s>
Attenuation	O
in	O
fiber	B-Architecture
optics	I-Architecture
,	O
also	O
known	O
as	O
transmission	O
loss	O
,	O
is	O
the	O
reduction	O
in	O
the	O
intensity	O
of	O
the	O
light	O
signal	O
as	O
it	O
travels	O
through	O
the	O
transmission	O
medium	O
.	O
</s>
<s>
Attenuation	O
coefficients	O
in	O
fiber	B-Architecture
optics	I-Architecture
are	O
usually	O
expressed	O
in	O
units	O
of	O
dB/km	O
.	O
</s>
<s>
The	O
four	O
orders	O
of	O
magnitude	O
reduction	O
in	O
the	O
attenuation	O
of	O
silica	O
optical	B-Architecture
fibers	I-Architecture
over	O
four	O
decades	O
was	O
the	O
result	O
of	O
constant	O
improvement	O
of	O
manufacturing	O
processes	O
,	O
raw	O
material	O
purity	O
,	O
preform	O
,	O
and	O
fiber	O
designs	O
,	O
which	O
allowed	O
for	O
these	O
fibers	O
to	O
approach	O
the	O
theoretical	O
lower	O
limit	O
of	O
attenuation	O
.	O
</s>
<s>
Single-mode	B-Device
optical	I-Device
fibers	I-Device
can	O
be	O
made	O
with	O
extremely	O
low	O
loss	O
.	O
</s>
<s>
Corning	O
's	O
SMF-28	O
fiber	O
,	O
a	O
standard	O
single-mode	B-Device
fiber	I-Device
for	O
telecommunications	O
wavelengths	O
,	O
has	O
a	O
loss	O
of	O
0.17dB/km	O
at	O
1550nm	O
.	O
</s>
<s>
Empirical	O
research	O
has	O
shown	O
that	O
attenuation	O
in	O
optical	B-Architecture
fiber	I-Architecture
is	O
caused	O
primarily	O
by	O
both	O
scattering	O
and	O
absorption	O
.	O
</s>
<s>
The	O
propagation	O
of	O
light	O
through	O
the	O
core	B-Device
of	O
an	O
optical	B-Architecture
fiber	I-Architecture
is	O
based	O
on	O
the	O
total	O
internal	O
reflection	O
of	O
the	O
lightwave	O
.	O
</s>
<s>
Rough	O
and	O
irregular	O
surfaces	O
,	O
even	O
at	O
the	O
molecular	O
level	O
,	O
can	O
cause	O
light	B-Device
rays	I-Device
to	O
be	O
reflected	O
in	O
random	O
directions	O
.	O
</s>
<s>
At	O
the	O
electronic	O
level	O
,	O
it	O
depends	O
on	O
whether	O
the	O
electron	O
orbitals	O
are	O
spaced	O
(	O
or	O
"	O
quantized	O
"	O
)	O
such	O
that	O
they	O
can	O
absorb	O
a	O
quantum	O
of	O
light	O
(	O
or	O
photon	O
)	O
of	O
a	O
specific	O
wavelength	O
or	O
frequency	O
in	O
the	O
ultraviolet	B-Application
(	O
UV	O
)	O
or	O
visible	O
ranges	O
.	O
</s>
<s>
They	O
are	O
the	O
result	O
of	O
the	O
interactive	O
coupling	B-Application
between	O
the	O
motions	O
of	O
thermally	O
induced	O
vibrations	O
of	O
the	O
constituent	O
atoms	O
and	O
molecules	O
of	O
the	O
solid	O
lattice	O
and	O
the	O
incident	O
light	O
wave	O
radiation	O
.	O
</s>
<s>
dB	O
loss	O
due	O
to	O
the	O
type	O
and	O
length	O
of	O
fiber	B-Architecture
optic	I-Architecture
cable	O
,	O
</s>
<s>
For	O
example	O
,	O
a	O
typical	O
1550nm	O
single-mode	B-Device
fiber	I-Device
has	O
a	O
loss	O
of	O
0.3dB	O
per	O
kilometer	O
.	O
</s>
<s>
Glass	O
optical	B-Architecture
fibers	I-Architecture
are	O
almost	O
always	O
made	O
from	O
silica	O
,	O
but	O
some	O
other	O
materials	O
,	O
such	O
as	O
fluorozirconate	O
,	O
fluoroaluminate	O
,	O
and	O
chalcogenide	O
glasses	O
as	O
well	O
as	O
crystalline	O
materials	O
like	O
sapphire	B-Application
,	O
are	O
used	O
for	O
longer-wavelength	O
infrared	O
or	O
other	O
specialized	O
applications	O
.	O
</s>
<s>
Typically	O
the	O
index	O
difference	O
between	O
core	B-Device
and	O
cladding	B-Device
is	O
less	O
than	O
one	O
percent	O
.	O
</s>
<s>
Plastic	B-Application
optical	I-Application
fibers	I-Application
(	O
POF	O
)	O
are	O
commonly	O
step-index	O
multi-mode	B-Device
fibers	I-Device
with	O
a	O
core	B-Device
diameter	I-Device
of	O
0.5	O
millimeters	O
or	O
larger	O
.	O
</s>
<s>
Alternatively	O
,	O
a	O
high	O
OH	O
concentration	O
is	O
better	O
for	O
transmission	O
in	O
the	O
ultraviolet	B-Application
(	O
UV	O
)	O
region	O
.	O
</s>
<s>
One	O
other	O
advantage	O
is	O
that	O
fusion	O
splicing	O
and	O
cleaving	B-Device
of	O
silica	O
fibers	O
is	O
relatively	O
effective	O
.	O
</s>
<s>
Even	O
simple	O
cleaving	B-Device
of	O
the	O
ends	O
of	O
the	O
fiber	O
can	O
provide	O
nicely	O
flat	O
surfaces	O
with	O
acceptable	O
optical	O
quality	O
.	O
</s>
<s>
One	O
purpose	O
of	O
doping	B-Algorithm
is	O
to	O
raise	O
the	O
refractive	O
index	O
(	O
e.g.	O
</s>
<s>
Doping	B-Algorithm
is	O
also	O
possible	O
with	O
laser-active	O
ions	O
(	O
for	O
example	O
,	O
rare-earth-doped	O
fibers	O
)	O
in	O
order	O
to	O
obtain	O
active	O
fibers	O
to	O
be	O
used	O
,	O
for	O
example	O
,	O
in	O
fiber	O
amplifiers	O
or	O
laser	O
applications	O
.	O
</s>
<s>
Both	O
the	O
fiber	B-Device
core	I-Device
and	O
cladding	B-Device
are	O
typically	O
doped	O
,	O
so	O
that	O
the	O
entire	O
assembly	O
(	O
core	B-Device
and	O
cladding	B-Device
)	O
is	O
effectively	O
the	O
same	O
compound	O
(	O
e.g.	O
</s>
<s>
Because	O
of	O
these	O
properties	O
,	O
silica	O
fibers	O
are	O
the	O
material	O
of	O
choice	O
in	O
many	O
optical	O
applications	O
,	O
such	O
as	O
communications	O
(	O
except	O
for	O
very	O
short	O
distances	O
with	O
plastic	B-Application
optical	I-Application
fiber	I-Application
)	O
,	O
fiber	B-Device
lasers	I-Device
,	O
fiber	O
amplifiers	O
,	O
and	O
fiber-optic	B-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
Because	O
of	O
the	O
low	O
viscosity	B-Application
of	O
these	O
glasses	O
,	O
it	O
is	O
very	O
difficult	O
to	O
completely	O
avoid	O
crystallization	O
while	O
processing	O
it	O
through	O
the	O
glass	O
transition	O
(	O
or	O
drawing	O
the	O
fiber	O
from	O
the	O
melt	O
)	O
.	O
</s>
<s>
Fluoride	O
fibers	O
are	O
used	O
in	O
mid-IR	O
spectroscopy	O
,	O
fiber	B-Algorithm
optic	I-Algorithm
sensors	I-Algorithm
,	O
thermometry	O
,	O
and	O
imaging	B-Algorithm
.	O
</s>
<s>
Phosphate	O
glasses	O
can	O
be	O
advantageous	O
over	O
silica	O
glasses	O
for	O
optical	B-Architecture
fibers	I-Architecture
with	O
a	O
high	O
concentration	O
of	O
doping	B-Algorithm
rare-earth	O
ions	O
.	O
</s>
<s>
The	O
chalcogens	O
—	O
the	O
elements	O
in	O
group	O
16	O
of	O
the	O
periodic	O
table	O
—	O
particularly	O
sulfur	O
(	O
S	O
)	O
,	O
selenium	B-Library
(	O
Se	O
)	O
and	O
tellurium	O
(	O
Te	O
)	O
—	O
react	O
with	O
more	O
electropositive	O
elements	O
,	O
such	O
as	O
silver	O
,	O
to	O
form	O
chalcogenides	O
.	O
</s>
<s>
Standard	O
optical	B-Architecture
fibers	I-Architecture
are	O
made	O
by	O
first	O
constructing	O
a	O
large-diameter	O
"	O
preform	O
"	O
with	O
a	O
carefully	O
controlled	O
refractive	O
index	O
profile	O
,	O
and	O
then	O
"	O
pulling	O
"	O
the	O
preform	O
to	O
form	O
the	O
long	O
,	O
thin	O
optical	B-Architecture
fiber	I-Architecture
.	O
</s>
<s>
The	O
preform	O
is	O
commonly	O
made	O
by	O
three	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
methods	O
:	O
inside	O
vapor	O
deposition	O
,	O
outside	O
vapor	O
deposition	O
,	O
and	O
vapor	O
axial	O
deposition	O
.	O
</s>
<s>
With	O
inside	O
vapor	O
deposition	O
,	O
the	O
preform	O
starts	O
as	O
a	O
hollow	O
glass	O
tube	O
approximately	O
long	O
,	O
which	O
is	O
placed	O
horizontally	O
and	O
rotated	O
slowly	O
on	O
a	O
lathe	B-Algorithm
.	O
</s>
<s>
When	O
the	O
reaction	O
conditions	O
are	O
chosen	O
to	O
allow	O
this	O
reaction	O
to	O
occur	O
in	O
the	O
gas	O
phase	O
throughout	O
the	O
tube	O
volume	O
,	O
in	O
contrast	O
to	O
earlier	O
techniques	O
where	O
the	O
reaction	O
occurred	O
only	O
on	O
the	O
glass	O
surface	O
,	O
this	O
technique	O
is	O
called	O
modified	O
chemical	B-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
(	O
MCVD	O
)	O
.	O
</s>
<s>
The	O
deposition	O
is	O
due	O
to	O
the	O
large	O
difference	O
in	O
temperature	O
between	O
the	O
gas	O
core	B-Device
and	O
the	O
wall	O
causing	O
the	O
gas	O
to	O
push	O
the	O
particles	O
outward	O
(	O
this	O
is	O
known	O
as	O
thermophoresis	O
)	O
.	O
</s>
<s>
For	O
some	O
applications	O
such	O
as	O
double-clad	B-Device
fibers	I-Device
another	O
form	O
is	O
preferred	O
.	O
</s>
<s>
In	O
fiber	B-Device
lasers	I-Device
based	O
on	O
double-clad	B-Device
fiber	I-Device
,	O
an	O
asymmetric	O
shape	O
improves	O
the	O
filling	B-Device
factor	I-Device
for	O
laser	O
pumping	O
.	O
</s>
<s>
The	O
preform	O
,	O
regardless	O
of	O
construction	O
,	O
is	O
placed	O
in	O
a	O
device	O
known	O
as	O
a	O
drawing	O
tower	O
,	O
where	O
the	O
preform	O
tip	O
is	O
heated	O
and	O
the	O
optical	B-Architecture
fiber	I-Architecture
is	O
pulled	O
out	O
as	O
a	O
string	O
.	O
</s>
<s>
The	O
light	O
is	O
guided	O
down	O
the	O
core	B-Device
of	O
the	O
fiber	O
by	O
an	O
optical	O
cladding	B-Device
with	O
a	O
lower	O
refractive	O
index	O
that	O
traps	O
light	O
in	O
the	O
core	B-Device
through	O
total	O
internal	O
reflection	O
.	O
</s>
<s>
The	O
cladding	B-Device
is	O
coated	O
by	O
a	O
buffer	B-Device
that	O
protects	O
it	O
from	O
moisture	O
and	O
physical	O
damage	O
.	O
</s>
<s>
The	O
buffer	B-Device
coating	O
is	O
what	O
gets	O
stripped	O
off	O
the	O
fiber	O
for	O
termination	O
or	O
splicing	O
.	O
</s>
<s>
Today	O
’s	O
glass	O
optical	B-Architecture
fiber	I-Architecture
draw	O
processes	O
employ	O
a	O
dual-layer	O
coating	O
approach	O
.	O
</s>
<s>
These	O
fiber	B-Architecture
optic	I-Architecture
coating	O
layers	O
are	O
applied	O
during	O
the	O
fiber	O
draw	O
,	O
at	O
speeds	O
approaching	O
.	O
</s>
<s>
Fiber	B-Architecture
optic	I-Architecture
coatings	O
are	O
applied	O
using	O
one	O
of	O
two	O
methods	O
:	O
wet-on-dry	O
and	O
wet-on-wet	O
.	O
</s>
<s>
Fiber	B-Architecture
optic	I-Architecture
coatings	O
are	O
applied	O
in	O
concentric	O
layers	O
to	O
prevent	O
damage	O
to	O
the	O
fiber	O
during	O
the	O
drawing	O
application	O
and	O
to	O
maximize	O
fiber	O
strength	O
and	O
microbend	O
resistance	O
.	O
</s>
<s>
where	O
is	O
the	O
fiber	O
’s	O
Young	O
’s	O
modulus	O
,	O
is	O
the	O
diameter	O
of	O
the	O
mandrel	O
,	O
is	O
the	O
diameter	O
of	O
the	O
cladding	B-Device
and	O
is	O
the	O
diameter	O
of	O
the	O
coating	O
.	O
</s>
<s>
Fiber	B-Architecture
optic	I-Architecture
coatings	O
protect	O
the	O
glass	O
fibers	O
from	O
scratches	O
that	O
could	O
lead	O
to	O
strength	O
degradation	O
.	O
</s>
<s>
Three	O
key	O
characteristics	O
of	O
fiber	B-Architecture
optic	I-Architecture
waveguides	O
can	O
be	O
affected	O
by	O
environmental	O
conditions	O
:	O
strength	O
,	O
attenuation	O
,	O
and	O
resistance	O
to	O
losses	O
caused	O
by	O
microbending	O
.	O
</s>
<s>
External	O
optical	B-Architecture
fiber	I-Architecture
cable	O
jackets	O
and	O
buffer	B-Device
tubes	O
protect	O
glass	O
optical	B-Architecture
fiber	I-Architecture
from	O
environmental	O
conditions	O
that	O
can	O
affect	O
the	O
fiber	O
’s	O
performance	O
and	O
long-term	O
durability	O
.	O
</s>
<s>
In	O
practical	O
fibers	O
,	O
the	O
cladding	B-Device
is	O
usually	O
coated	O
with	O
a	O
tough	O
resin	B-Language
coating	O
and	O
an	O
additional	O
buffer	B-Device
layer	O
,	O
which	O
may	O
be	O
further	O
surrounded	O
by	O
a	O
jacket	O
layer	O
,	O
usually	O
plastic	O
.	O
</s>
<s>
This	O
reduces	O
crosstalk	O
between	O
the	O
fibers	O
,	O
or	O
reduces	O
flare	O
in	O
fiber	O
bundle	O
imaging	B-Algorithm
applications	O
.	O
</s>
<s>
Multi-fiber	O
cable	O
usually	O
uses	O
colored	O
coatings	O
and/or	O
buffers	B-Device
to	O
identify	O
each	O
strand	O
.	O
</s>
<s>
The	O
cost	O
of	O
small	O
fiber-count	O
pole-mounted	O
cables	O
has	O
greatly	O
decreased	O
due	O
to	O
the	O
high	O
demand	O
for	O
fiber	B-Architecture
to	I-Architecture
the	I-Architecture
home	I-Architecture
(	O
FTTH	B-Architecture
)	O
installations	O
in	O
Japan	O
and	O
South	O
Korea	O
.	O
</s>
<s>
Some	O
fiber	B-Architecture
optic	I-Architecture
cable	O
versions	O
are	O
reinforced	O
with	O
aramid	O
yarns	O
or	O
glass	O
yarns	O
as	O
an	O
intermediary	O
strength	O
member	O
.	O
</s>
<s>
Glass	O
yarns	O
also	O
protect	O
the	O
cable	O
core	B-Device
against	O
rodents	O
and	O
termites	O
.	O
</s>
<s>
This	O
creates	O
a	O
problem	O
when	O
the	O
cable	O
is	O
bent	O
around	O
corners	O
or	O
wound	O
around	O
a	O
spool	O
,	O
making	O
FTTX	B-Architecture
installations	O
more	O
complicated	O
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
are	O
connected	O
to	O
terminal	O
equipment	O
by	O
optical	B-Device
fiber	I-Device
connectors	I-Device
.	O
</s>
<s>
Optical	B-Architecture
fibers	I-Architecture
may	O
be	O
connected	O
by	O
connectors	O
,	O
or	O
permanently	O
by	O
splicing	O
,	O
that	O
is	O
,	O
joining	O
two	O
fibers	O
together	O
to	O
form	O
a	O
continuous	O
optical	O
waveguide	O
.	O
</s>
<s>
For	O
quicker	O
fastening	O
jobs	O
,	O
a	O
“	O
mechanical	B-Device
splice	I-Device
”	O
is	O
used	O
.	O
</s>
<s>
The	O
splice	O
is	O
usually	O
inspected	O
via	O
a	O
magnified	O
viewing	O
screen	O
to	O
check	O
the	O
cleaves	B-Device
before	O
and	O
after	O
the	O
splice	O
.	O
</s>
<s>
The	O
location	O
and	O
energy	O
of	O
the	O
spark	O
is	O
carefully	O
controlled	O
so	O
that	O
the	O
molten	O
core	B-Device
and	O
cladding	B-Device
do	O
not	O
mix	O
,	O
and	O
this	O
minimizes	O
optical	O
loss	O
.	O
</s>
<s>
A	O
splice	O
loss	O
estimate	O
is	O
measured	O
by	O
the	O
splicer	O
,	O
by	O
directing	O
light	O
through	O
the	O
cladding	B-Device
on	O
one	O
side	O
and	O
measuring	O
the	O
light	O
leaking	O
from	O
the	O
cladding	B-Device
on	O
the	O
other	O
side	O
.	O
</s>
<s>
Mechanical	O
fiber	O
splices	O
are	O
designed	O
to	O
be	O
quicker	O
and	O
easier	O
to	O
install	O
,	O
but	O
there	O
is	O
still	O
the	O
need	O
for	O
stripping	O
,	O
careful	O
cleaning	O
,	O
and	O
precision	O
cleaving	B-Device
.	O
</s>
<s>
The	O
fiber	O
ends	O
are	O
aligned	O
and	O
held	O
together	O
by	O
a	O
precision-made	O
sleeve	O
,	O
often	O
using	O
a	O
clear	O
index-matching	B-Device
gel	I-Device
that	O
enhances	O
the	O
transmission	O
of	O
light	O
across	O
the	O
joint	O
.	O
</s>
<s>
A	O
fiber-optic	B-Device
connector	I-Device
is	O
a	O
rigid	O
cylindrical	O
barrel	O
surrounded	O
by	O
a	O
sleeve	O
that	O
holds	O
the	O
barrel	O
in	O
its	O
mating	O
socket	O
.	O
</s>
<s>
For	O
single-mode	B-Device
fiber	I-Device
,	O
fiber	O
ends	O
are	O
typically	O
polished	O
with	O
a	O
slight	O
curvature	O
that	O
makes	O
the	O
mated	O
connectors	O
touch	O
only	O
at	O
their	O
cores	O
.	O
</s>
<s>
Such	O
connections	O
have	O
higher	O
loss	O
than	O
PC	O
connections	O
but	O
greatly	O
reduced	O
back	O
reflection	O
,	O
because	O
light	O
that	O
reflects	O
from	O
the	O
angled	O
surface	O
leaks	O
out	O
of	O
the	O
fiber	B-Device
core	I-Device
.	O
</s>
<s>
The	O
resulting	O
signal	O
strength	O
loss	O
is	O
called	O
gap	B-Device
loss	I-Device
.	O
</s>
<s>
In	O
the	O
1990s	O
,	O
terminating	O
fiber	B-Architecture
optic	I-Architecture
cables	O
was	O
labor-intensive	O
.	O
</s>
<s>
The	O
number	O
of	O
parts	O
per	O
connector	O
,	O
polishing	O
of	O
the	O
fibers	O
,	O
and	O
the	O
need	O
to	O
oven-bake	O
the	O
epoxy	O
in	O
each	O
connector	O
made	O
terminating	O
fiber	B-Architecture
optic	I-Architecture
cables	O
difficult	O
.	O
</s>
<s>
A	O
cleave	B-Device
is	O
made	O
at	O
a	O
required	O
length	O
,	O
to	O
get	O
as	O
close	O
to	O
the	O
polished	O
piece	O
already	O
inside	O
the	O
connector	O
.	O
</s>
<s>
It	O
is	O
often	O
necessary	O
to	O
align	O
an	O
optical	B-Architecture
fiber	I-Architecture
with	O
another	O
optical	B-Architecture
fiber	I-Architecture
or	O
with	O
an	O
optoelectronic	O
device	O
such	O
as	O
a	O
light-emitting	O
diode	O
,	O
a	O
laser	O
diode	O
,	O
or	O
a	O
modulator	B-Application
.	O
</s>
<s>
This	O
can	O
involve	O
either	O
carefully	O
aligning	O
the	O
fiber	O
and	O
placing	O
it	O
in	O
contact	O
with	O
the	O
device	O
,	O
or	O
can	O
use	O
a	O
lens	O
to	O
allow	O
coupling	B-Application
over	O
an	O
air	O
gap	O
.	O
</s>
<s>
A	O
precision	O
translation	O
stage	O
(	O
micro-positioning	O
table	O
)	O
is	O
used	O
to	O
move	O
the	O
lens	O
,	O
fiber	O
,	O
or	O
device	O
to	O
allow	O
the	O
coupling	B-Application
efficiency	O
to	O
be	O
optimized	O
.	O
</s>
<s>
Fibers	O
with	O
a	O
connector	O
on	O
the	O
end	O
make	O
this	O
process	O
much	O
simpler	O
:	O
the	O
connector	O
is	O
simply	O
plugged	O
into	O
a	O
pre-aligned	O
fiber-optic	B-Architecture
collimator	O
,	O
which	O
contains	O
a	O
lens	O
that	O
is	O
either	O
accurately	O
positioned	O
to	O
the	O
fiber	O
or	O
is	O
adjustable	O
.	O
</s>
<s>
To	O
achieve	O
the	O
best	O
injection	O
efficiency	O
into	O
a	O
single-mode	B-Device
fiber	I-Device
,	O
the	O
direction	O
,	O
position	O
,	O
size	O
,	O
and	O
divergence	O
of	O
the	O
beam	O
must	O
all	O
be	O
optimized	O
.	O
</s>
<s>
With	O
good	O
beams	O
,	O
70	O
to	O
90%	O
coupling	B-Application
efficiency	O
can	O
be	O
achieved	O
.	O
</s>
<s>
With	O
properly	O
polished	O
single-mode	B-Device
fibers	I-Device
,	O
the	O
emitted	O
beam	O
has	O
an	O
almost	O
perfect	O
Gaussian	O
shape	O
—	O
even	O
in	O
the	O
far	O
field	O
—	O
if	O
a	O
good	O
lens	O
is	O
used	O
.	O
</s>
<s>
The	O
open	B-Device
fiber	I-Device
control	I-Device
system	O
,	O
which	O
ensures	O
laser	O
eye	O
safety	O
in	O
the	O
event	O
of	O
a	O
broken	O
fiber	O
,	O
can	O
also	O
effectively	O
halt	O
propagation	O
of	O
the	O
fiber	O
fuse	O
.	O
</s>
<s>
In	O
situations	O
,	O
such	O
as	O
undersea	O
cables	O
,	O
where	O
high	O
power	O
levels	O
might	O
be	O
used	O
without	O
the	O
need	O
for	O
open	B-Device
fiber	I-Device
control	I-Device
,	O
a	O
"	O
fiber	O
fuse	O
"	O
protection	O
device	O
at	O
the	O
transmitter	O
can	O
break	O
the	O
circuit	O
to	O
keep	O
damage	O
to	O
a	O
minimum	O
.	O
</s>
<s>
Modulation	B-Application
of	O
the	O
light	O
source	O
to	O
transmit	O
a	O
signal	O
also	O
slightly	O
widens	O
the	O
frequency	O
band	O
of	O
the	O
transmitted	O
light	O
.	O
</s>
<s>
This	O
has	O
the	O
effect	O
that	O
,	O
over	O
long	O
distances	O
and	O
at	O
high	O
modulation	B-Application
speeds	O
,	O
the	O
different	O
frequencies	O
of	O
light	O
can	O
take	O
different	O
times	O
to	O
arrive	O
at	O
the	O
receiver	O
,	O
ultimately	O
making	O
the	O
signal	O
impossible	O
to	O
discern	O
,	O
and	O
requiring	O
extra	O
repeaters	O
.	O
</s>
