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| What is the difference between Single
Mode and Multi Mode? How do Fiber Optic
Cables Work? How are Fiber Optic Cables
Made? Read the fiber optic training information
below to learn more about the different
types of Fiber Optic Cables. Or, for pictures
of Fiber Optic Cables, visit our Fiber
Optic Cables page. |
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| The problem with "glass" or optical fiber is determining how to
guide the light through optical fiber
that might be hundreds or even thousands
of miles in length. The key comes from
your school physics lessons. You may remember
shining some light through glass blocks,
for instance prisms, and seeing how it
was bent, or "refracted" when it left
the glass. If you sent the light into
the glass at an angle greater than the
"critical angle," it would be totally
reflected within the block and not exit
where you expected. It all |
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| has to do with
refractive indices and is analytically
explained by a principal called Snell's
Law. Snell's law basically states that
the refractive index of a material determines
how quickly light can travel through it. |
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| Once you have your optical fiber core
of pure silica, you add an extra layer
of glass known as "cladding," which has
a lower refractive index than the core.
This refractive index difference guides
the light in the core allowing as little
as possible to leave through the sides
(according to Snell's Law). On top of
the cladding layer are polymer coatings
that make it easier to handle the fiber
and help prevent damage to the fiber. |
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| The size of the optical fiber core determines
how light travels through it. Each optical
signal can actually generate many different
lightwaves. These lightwaves can all travel
through the fiber at the same time. This
is allowed to happen in appropriately
named 'multimode' fibers, but can cause
problems when each wave arrives at the
end of the fiber slightly out of sync.
Most modern optical networks will use
'singlemode' fiber, which has a much smaller
core than multimode. The core size is
small enough to ensure that only one lightwave
from each optical signal can travel inside
the fiber. This ensures there are no problems
at the receiving end. |
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| To
give you an idea of sizes, a singlemode
fiber's core is usually around 10 micrometers
in diameter (0.000010m) with cladding
over 12 times thicker, or a diameter of
125 micrometers (0.000125m or 0.125mm).
Once the polymer coatings are added, the
whole package may be around 0.25 millimeters
in diameter. Still very small. Even the
very pure glass in optical fiber "attenuates"
light. This means it causes some of the
intensity of the light to be lost within
the fiber. These losses can be due to
several mechanisms: light losing its energy
to atoms in the fiber or absorption (this
is the mostprevalent), |
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| light scattering
because of slight changes in the core's
refractive index, and light scattering
because the core is not always a perfect
cylinder. |
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Now that you know some of the basics
on fiber cables, we'll have a little more
fiber optic training on the two types
of fiber optic cables, singlemode and
multi-mode fiber
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Singlemode fiber
A mode is one of the various lightwaves
transmitted in an optical fiber. Each
optical signal generates many different
modes but, in singlemode fiber, the desire
is to have only one of them transmitted.
This is achieved through having a core
with a very small diameter (usually around
10 micrometers). Singlemode fiber has
a higher bandwidth than Multimode and,
for this reason, it is the ideal transmission
medium for many applications |
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Multimode fiber
Multimode fiber is an optical fiber in
which more than one mode can be transmitted
through the core. A multimode fiber core
is much larger in diameter than a singlemode
fiber core (usually 6-8 times the size).
This larger core size generally has greater
bandwidth and is easier to couple and
interconnect. It allows hundreds of rays
of light to propagate through the same
fiber simultaneously. |
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How Fiber Optic Signals are Transmitted
Light that travels along the fiber is
made up of a binary code that pulses "off"
and "on" and determines what information
a signal contains. The advantage of fiber
is that these on/off pulses can be almost
anything: translated video, computer,
or voice data depending on the type of
transmitter and receiver used. |
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| Advantages of Fiber Optic Cables Over
Copper |
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| Speed: Fiber optic networks can
operate at speeds of up to 2.5 gigabits-per-second,
versus 1.54 megabits per second for copper |
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| Bandwidth: Taken in bulk, it would
take approximately 33 tons of copper cable
to transmit the same amount of information
handled by 1/4 pound of optical fiber. |
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| Resistance: Fiber optic cables
have a greater resistance to electromagnetic
noise such as motors, radios, or other
nearby cables. Because optical fibers
carry beams of light, they are free of
electrical interference and noise. |
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| Types of Fiber Cables |
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Now that you know a little more about
the two types of fiber optic cables, we'll
have a little more fiber optic training
on different forms those two types of
glass can be combined together with cable
jackets and overall jackets. Both Multimode
and Singlemode Fiber Optic Cable can come
in many different forms. Typically, Fiber
Optic Patch Cables will be assembled in
Duplex for Multimode Cables and Simplex
for Singlemode Cables. A Duplex Multimode
cable is one that contains two fiber optic
cables, generally in the form of a zip
cable. This duplex cable is used in networking
applications where there is a transmit
and receive signal. Duplex fiber optic
zip cable is the orange cable pictured
at the bottom of this photograph. Simplex
Singlemode Cables are typically yellow
and have one fiber optic cable. In most
cases the outer coating of singlemode
cables will be yellow, and multimode cables
will be orange. |
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| Trunk Fiber Optic Cables are becoming
more and more prevalent. Several examples
of trunk fiber optic cables are pictured
in the photograph to the left. Cypress
Industries specializes in terminating
trunk fiber optic cables with multiple
strands and multiple connectors. |
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| Plastic Optical Fiber (POF) is a newer
plastic-based fiber cable which promises
performance similar to Single Mode Cable
but at a lower cost. POF in general is
still in the infancy stage although many
companies are noticing its potential. |
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| Thank you for reading our Fiber Optic
Training online information. Should you
have any other questions on products,
or need ordering information, please do
not hesistate to contact us. Our staff
is very helpful and knowledgeable, and
can walk you through the ordering process
to determine what type of fiber optic
cable you may need. |
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