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This
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article
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was
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written
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by
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Joni
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Nurmi
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,Zhen
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Shi
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and
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Sun
...
Hai
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!history-of-fiber-optic.jpg|width=300!
|
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\[1\] Source of the figure: [http://fiberoptic101.blogspot.fi/2010/11/history-of-fiber-optic.html] |
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Principle
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of
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operation
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Fiber
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optical
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cables
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are
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highly
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transparent,
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cylindrical
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conduits
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for
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light.
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These
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cables
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are
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formed
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of
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two
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materials
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with
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different
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refractive
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indices.
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This
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creates
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a
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optimal
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waveguide
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for
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transmitting
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light.
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When
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light
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enters
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the
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fiber
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made
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of
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material
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with
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higher
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refractive
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index
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than
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the
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cladding
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surrounding
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it,
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it
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stays
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inside
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the
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material
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due
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to
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total
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internal
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reflection
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and
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is
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thus
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transmitted
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forward.
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Index
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of
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refraction
...
Index
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of
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refraction
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is
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a
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measurement
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of
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speed
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of
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light
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in
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material.
...
By
...
definition,
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vacuum
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has
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refractive
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index
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of
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1(c
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in
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vacuum
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=
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1).
...
The
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higher
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the
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index,
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the
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slower
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the
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light
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will
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travel
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in
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the
...
material.
...
Typical
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value
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for
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fiber
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core
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is
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1,62
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and
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for
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the
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cladding
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1,52.
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Total
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internal
...
refraction:
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When
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light
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travelling
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inside
...
material
...
hits
...
a
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boundary,
...
it
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is
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partially
...
refracted
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and
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partially
...
reflected.
...
However
...
if
...
the
...
angle
...
is
...
greater
...
than
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the
...
critical
...
angle
...
of
...
the
...
materials
...
them
...
it
...
is
...
reflected
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back
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in
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its
...
entirety.
...
For
...
this
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to
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occur
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the
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material
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in
...
which
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the
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light
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is
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travelling
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in
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must
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have
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higher
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refractive
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index
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than
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the
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material
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outside.
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Multi-mode
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fiber
In optical fiber technology, multimode fiber is optical fiber that is designed to carry multiple light rays or modes concurrently, each at a slightly different reflection angle within the optical fiber core. Multimode fiber transmission is used for relatively short distances because the modes tend to disperse over longer lengths.
Multi-Mode cable has a little bit bigger diameter, with a common diameters in the 50-to-100 micron range for the light carry component (in the US the most common size is 62.5um). Most applications in which Multi-mode fiber is used, 2 fibers are used (WDM is not normally used on multi-mode fiber). POF is a newer plastic-based cable which promises performance similar to glass cable on very short runs, but at a lower cost.
Multimode fiber gives you high bandwidth at high speeds (10 to 100MBS - Gigabit to 275m to 2km) over medium distances. Light waves are dispersed into numerous paths, or modes, as they travel through the cable's core typically 850 or 1300nm. Typical multimode fiber core diameters are 50, 62.5, and 100 micrometers. However, in long cable runs (greater than 3000 feet 914.4 meters), multiple paths of light can cause signal distortion at the receiving end, resulting in an unclear and incomplete data transmission so designers now call for single mode fiber in new applications using Gigabit and beyond.
Single-mode fiber
In [optical fiber|http://searchtelecom.techtarget.com/definition/optical-fiber]
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technology,
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single
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mode
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fiber
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is
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optical
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fiber
...
that
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is
...
designed
...
for
...
the
...
transmission
...
of
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a
...
single
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ray
...
or
...
mode
...
of
...
light
...
as
...
a
...
carrier
...
and
...
is
...
used
...
for
...
long-distance
...
signal
...
transmission.
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Single
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Mode cable is a single stand (most applications use 2 fibers) of glass fiber with a diameter of 8.3 to 10 microns that has one mode of transmission. Single Mode Fiber with a relatively narrow diameter, through which only one mode will propagate typically 1310 or 1550nm. Carries higher bandwidth than multimode fiber, but requires a light source with a narrow spectral width.
Single Modem fiber is used in many applications where data is sent at multi-frequency (WDM Wave-Division-Multiplexing)
...
so
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only
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one
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cable
...
is
...
needed
...
-
...
(single-mode
...
on
...
one
...
single
...
fiber)
...
Single-mode
...
fiber
...
gives
...
you
...
a
...
higher
...
transmission
...
rate
...
and
...
up
...
to
...
50
...
times
...
more
...
distance
...
than
...
multimode,
...
but
...
it
...
also
...
costs
...
more.
...
Single-mode
...
fiber
...
has
...
a
...
much
...
smaller
...
core
...
than
...
multimode.
...
The
...
small
...
core
...
and
...
single
...
light-wave
...
virtually
...
eliminate
...
any
...
distortion
...
that
...
could
...
result
...
from
...
overlapping
...
light
...
pulses,
...
providing
...
the
...
least
...
signal
...
attenuation
...
and
...
the
...
highest
...
transmission
...
speeds
...
of
...
any
...
fiber
...
cable
...
type.
...
Single-mode
...
optical
...
fiber
...
is
...
an
...
optical
...
fiber
...
in
...
which
...
only
...
the
...
lowest
...
order
...
bound
...
mode
...
can
...
propagate
...
at
...
the
...
wavelength
...
of
...
interest
...
typically
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1300
...
to
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1320nm.
...
Comparison
...
of
...
single-mode
...
fiber
...
and
...
muti-mode
...
fiber
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Constructions
...
are different
| Wiki Markup |
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\[2\] Source of the figure: [http://www.rp-photonics.com/multimode_fibers.html] |
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Transmissions
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are
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different
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!Fiber single mode.GIF!
!fiber multimode fiber.GIF!
|
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\[3\] Source of the figure: [http://www.arcelect.com/fibercable.htm] |
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Special-purpose fiber: Polarization - maintaining fibers
What is polarization-maintaining
...
fibers?
...
Polarization-maintaining
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fibers
...
is
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a
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special
...
purpose
...
single
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mode
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fiber,
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it
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preserves
...
and
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transmits
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the
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polarization
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state
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of
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light
...
that
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is
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launched
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into
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it.
...
Why do we need the polarization-maintaining
...
fibers?
...
The
...
reason
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why
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we
...
need
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to
...
have
...
polarization-maintaining
...
fibers
...
is
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that
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regular
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single
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mode
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fiber
...
cannot
...
maintain
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the
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polarization
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state
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of
...
input
...
laser
...
beam.
...
Because
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in
...
a
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regular
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single
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mode
...
fiber,
...
the
...
input
...
polarized
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laser
...
beam
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(consist
...
of
...
two
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perpendicular
...
polarized
...
modes
...
-
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horizontal
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and
...
vertical)
...
have
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the
...
same
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propagation
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constant
...
(propagation
...
constant
...
is
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a
...
measure
...
of
...
the
...
change
...
undergone
...
by
...
the
...
amplitude
...
of
...
the
...
wave
...
as
...
it
...
propagates
...
in
...
a
...
given
...
direction),
...
in
...
other
...
words
...
they
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both
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travel
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at
...
the
...
same
...
velocity
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(not
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good).
...
It
...
would
...
cause
...
optical
...
energy
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from
...
one
...
of
...
these
...
modes
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(horizontal
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or
...
vertical
...
mode)
...
to
...
transfer
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the
...
other
...
or
...
“cross-couple”.
...
That
...
is
...
the
...
reason
...
why
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single
...
mode
...
fiber
...
cannot
...
maintain
...
the
...
polarization
...
state
...
of
...
input
...
laser
...
beam.
...
How does polarization-maintaining
...
fibers
...
work?
...
Then
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the
...
polarization-maintaining
...
fibers
...
was
...
invented
...
to
...
overcome
...
this
...
problem.
...
The
...
polarization-maintaining
...
fibers
...
are
...
designed
...
in
...
such
...
a
...
way
...
that
...
two
...
perpendicular
...
polarized
...
modes
...
are
...
forced
...
to
...
travel
...
at
...
different
...
propagation
...
constants,
...
which
...
means
...
they
...
travel
...
at
...
different
...
velocity.
...
This
...
difference
...
in
...
velocities
...
makes
...
it
...
very
...
hard
...
for
...
optical
...
energy
...
to
...
transfer
...
between
...
each
...
other.
...
As
...
the
...
result
...
that
...
polarization
...
state
...
of
...
input
...
laser
...
beam
...
is
...
preserved.
...
This
...
special
...
purpose
...
fiber
...
is
...
commonly
...
used
...
in
...
fiber
...
optic
...
sensing,
...
interferometry
...
and
...
slab dielectric waveguides.
Cross Section of Polarization Maintaining Fibers
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Figure. 4. Cross Section of Polarization Maintaining Fibers |
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\[4\] |
The above three pictures illustrated the three different types of polarization maintaining fibers, which are Panda, Elliptical-clad, Bow-tie. There fibers contain a unique feature; they have stress rods in fibers (a feature not seen in other fiber types). The stress rods are two circles in the Panda PM fiber, a elliptical clad in elliptical-clad PM fiber and two bow-ties in the Bow-Tie type PM fiber. The most important property of stress rods is that it creates stress in the core of the fiber such that the transmission of only one polarization plane of light is favored.
YouTube video - A Brief Introduction of the Polarization-maintaining Fibers
| Widget Connector | ||
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Video.1. A Brief Introduction of the Polarization-maintaining Fibers \[5\] |
References:
Principle of operation - Special purpose fiber - http://en.wikipedia.org/wiki/Optical_fiber
| Wiki Markup |
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\[2\]Multimode fibers - [http://www.rp-photonics.com/multimode_fibers.html |
...
] |
| Wiki Markup |
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\[3\]The basic of fiber optic cable (single mode and multi mode) - [http://www.arcelect.com/fibercable.htm] |
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/ |
| Wiki Markup |
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\[4\] What Are Polarization Maintaining Fibers? - [http://www.fiberoptics4sale.com/wordpress/what-are-polarization-maintaining-fibers/|http://www.fiberoptics4sale.com/wordpress/what-are-polarization-maintaining-fibers/] |
| Wiki Markup |
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\[5\] What is Polarization Maintaining Fiber? \- [http://www. |
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youtube.com/ |
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watch?v=7rrb-_Iin-g|http://www.youtube.com/watch?v=7rrb-_Iin-g] |